Answers to Reviewing the Concepts Questions - Appendices - Biology of Humans

Biology of Humans


Appendix 1. Answers to Reviewing the Concepts Questions

Chapter 1

1. Seven features that characterize life:

a. Living things contain molecules of nucleic acids, proteins, carbohydrates, and lipids.

b. Living things are composed of cells (smallest unit of life).

c. Living things grow and reproduce.

d. Living things use energy and raw materials for metabolism.

e. Living things respond to their environment.

f. Living things maintain homeostasis.

g. Populations of living organisms evolve and have traits.

2. Mammals are unique in that they have hair and that they feed their young milk produced by mammary glands. In addition to mammalian traits, primates also have forward-looking eyes, a well-developed brain, and opposable thumbs.

3. A population is a group of organisms of the same species that live and reproduce in the same area. A community is all the living species that interact in a particular geographic area. An ecosystem includes all the living organisms in a community along with their physical environment. The biosphere is where life is found on Earth (land, air, and sea).

4. A hypothesis is a tentative explanation for an observation or phenomenon that can be tested by experimentation. A theory is different from a hypothesis in that it is a broad-ranging explanation for a phenomenon with much evidence to support the explanation from both experimentation and discovery.

5. A controlled experiment is an experiment that has two groups. One group is the control group, and the other group is the experimental group. Each group is treated in the same manner, except for the variable manipulated in the experiment. The control group is not treated/manipulated, and the experimental group is treated/manipulated.

6. Inductive reasoning uses accumulated facts to draw a logical conclusion. Deductive reasoning uses general statements to deduce other conclusions. Deductive reasoning is usually described as an "if-then" series of associations.

7. A placebo is generally used in human drug testing experiments to evaluate the effectiveness of a drug. The placebo is not the real drug being tested; it is usually a sugar pill that looks like the real drug and is given to the control group to see if the effects of the drug are real or imagined.

8. In a double-blind experiment neither the participants nor the researcher evaluating the results knows who received the placebo until after the experiment is completed.

9. In an epidemiological study, the researcher studies patterns occurring in a population. An epidemiologist might hypothesize that exposure to a certain chemical pollutant causes a rare cancer. The study would consist of correlating the rare cancer "hot spots" (areas where incidence of a rare cancer are high) and the known chemical pollution in the area.

10. c

11. homeostasis

12. hypothesis

13. adaptive

Chapter 2

1. An atom is the smallest unit of matter that cannot be broken down by simple chemical means. Atoms consist of three subatomic particles; the neutrons and protons form the nucleus, and the electrons surround the nucleus.

2. Protons are positively charged, are located in the nucleus, and have a mass of one atomic mass unit (AMU). Neutrons have no charge, are located in the nucleus, and have a mass of one AMU. Electrons are negatively charged, found outside the nucleus, and have essentially no mass.

3. An isotope is an atom with a different number of neutrons than the most common form, resulting in a different mass. Carbon is usually found as Carbon 12. Carbon isotopes such as Carbon 13 and Carbon 14 have more mass with extra neutrons.

4. Medical x-rays are used to diagnose illness. Radiation therapy is used directly at tumor sites to kill cancer cells.

5. Ionic bonds form between oppositely charged ions, such as the bonds that form NaCl (table salt). The sodium loses an electron to become positively charged and the chlorine gains an electron to become negatively charged, and the two ions are attracted to one another. A covalent bond forms between atoms when the atoms share electrons. Carbon dioxide (CO2) is bonded by two double covalent bonds where the carbon atom shares its electrons with two oxygen atoms. Hydrogen bonds are the weakest bonds of the three types. They form between molecules that are partially charged (due to sharing of electrons). Water molecules are bonded to other water molecules by hydrogen bonds. The helix structure of DNA is due to hydrogen bonds.

6. Water is a polar molecule so it makes a perfect solvent and medium for moving substances to and from cells in the body. Water has a high heat capacity, which allows for better temperature regulation of the body. Water has a high heat of vaporization, so when our sweat evaporates it removes heat from the body.

7. An acid dissociates in water and contributes hydrogen ions (H+). A base dissociates in water and contributes hydroxide ions (OH-).

8. Polymers are chains of repeating molecules (monomers) formed by dehydration synthesis (loss of H2O) and broken by hydrolysis (addition of H2O). DNA is a polymer of nucleotides. Starch is a polymer of glucose. Proteins are polymers of amino acids.

9. Energy-storage polysaccharides are starch in plants and glycogen in humans and other animals. A structural polysaccharide is cellulose for plants.

10. A phospholipid is composed of a molecule of glycerol, two fatty acids, and a phosphate group. The end with the phosphate group is negatively charged and hydrophilic. The fatty acid tails are nonpolar and hydrophobic. Cell membranes consist of phospholipids in a bilayer: the hydrophobic fatty acid tails are on the inside of the membrane and the hydrophilic heads are on the outsides of the membrane.

11. The primary structure of proteins is the sequence of amino acids. The secondary structure refers to the bends, folds, or spirals caused by hydrogen bonding in the chain. The tertiary structure refers to the 3-D shape that results when bonds form between side chains. Some proteins have a quaternary structure, which consists of the assembled subunits (polypeptide chains).

12. DNA and RNA are both nucleic acids composed of chains of nucleotides. DNA consists of two strands twisted to form a double helix; it contains the sugar deoxyribose and four nitrogen- containing bases (adenine, guanine, cytosine, and thymine). RNA is single stranded and contains the sugar ribose and four nitrogen-containing bases (adenine, guanine, cytosine, and uracil).

13. ATP is the nucleotide adenosine triphosphate formed from ribose, the nitrogen-containing base adenine, and three phosphate groups. ATP is a high-energy molecule used in the human body to provide energy by the breaking of a phosphate bond.

14. Genes are made of DNA. RNA, in various forms, converts the genetic information in DNA into proteins. Proteins have a variety of functions within the cell such as acting as enzymes, transporting molecules, and providing structure.

15. d

16. b

17. b

18. a

19. d

20. denaturation

21. nucleotides

22. primary

23. Phospholipids

24. starch; glycogen

25. pH

Chapter 3

1. Prokaryotic cells, which include bacteria and archaea, do not have membrane-bound organelles and are typically smaller than eukaryotic cells. Their DNA is circular and found in the cytoplasm. Eukaryotic cells, such as those found in plants and animals, are larger and more complex, have membrane-bound organelles, and their DNA occurs in coiled linear strands in the nucleus.

2. The plasma membrane is a selectively permeable membrane composed of a phospholipid bilayer embedded with proteins that can span the bilayer and carbohydrates that are found on the outer surface. The structure of the plasma membrane is often described as a fluid mosaic.

3. The plasma membrane maintains structural integrity of the cell, regulates movement of substances into and out of a cell, allows cell-cell recognition by glycoproteins, provides cell-to-cell communication, and sticks cells together to form tissues and organs.

4. Simple diffusion is the random movement of substances from a region of high concentration to a region of lower concentration. Oxygen crosses the cell membrane by simple diffusion. Molecules of glucose require facilitated diffusion where the movement of the molecule is from a region of high concentration to a region of lower concentration with the aid of membrane carrier proteins.

5. Endocytosis uses a portion of the cell membrane to encircle large molecules or bacteria and bring them into the cell. Exocytosis is the process by which large molecules packaged in membrane- bound vesicles leave a cell.

6. The nucleus contains almost all the genetic information of a eukaryotic cell.

7. Lysosomes break down bacteria and macromolecules that a cell takes in by phagocytosis. They also rid the cell of old organelles.

8. Lysosomal storage diseases occur when lysosomal enzymes are absent and the cell cannot rid itself of certain molecules. The lysosomes fill up with these molecules, which then interfere with normal cellular functions.

9. The three types of fibers that make up the cytoskeleton are: microtubules (hollow rods of tubulin that function in cell support and shape, movement of organelles, and form cilia and flagella); microfilaments (solid rods of actin that function in muscle contraction and pinching cells in two during cell division); and intermediate filaments (ropelike fibers composed of different proteins that function in cell shape and anchoring organelles in place).

10. Cellular respiration provides energy to a cell by the breakdown of glucose through a series of chemical reactions that take place either in the cytoplasm or mitochondria of the cell.

11. Cellular respiration requires oxygen in order to proceed and yields 36 ATP per molecule of glucose. Lactic acid fermentation does not require oxygen and yields 2 ATP per molecule of glucose.

12. c

13. a

14. d

15. c

16. b

17. a

18. a

19. c

20. Cytoplasm

21. Pinocytosis

22. nucleolus

23. Oxygen

24. lactic acid fermentation

Chapter 4

1. The four types of human tissue are epithelial, connective, muscular, and nervous.

2. Epithelial tissue is formed from cells that are packed close together forming layers of cells of varying thickness. This type of organization makes it good for coverings such as the skin and for lining organs or body cavities. Connective tissue cells secrete a matrix that is found between the cells. The type of matrix dictates the function of the connective tissue. For example, the protein fibers in the gelatinous matrix of cartilage make it resilient and strong, which is ideal for strong, flexible support. The hard matrix of bone makes it a good support material. The liquid matrix of blood (plasma) allows for the tissue to flow.

3. Bone is well supplied by blood vessels whereas cartilage is not, so bone receives nutrients for growth and repair more rapidly than cartilage, which depends on diffusion for nutrients.

4. Blood is a connective tissue with a liquid matrix (plasma).

5. a. Skeletal muscle is composed of long cylinder shaped cells with many nuclei and mitochondria (for energy). It is called striated muscle because of the visible striations of actin and myosin filaments. Skeletal muscle tissue is usually attached to bone and has the ability to contract voluntarily.

b. Cardiac muscle is composed of cells with only one nucleus that have striations and branch. They are found only in the heart and contract involuntarily continuously.

c. Smooth muscle is composed of tapered cells with only one nucleus and lacks striations. Smooth muscle is found in blood vessels and airways or organs such as the stomach, and contracts involuntarily when needed.

6. Nerve tissue is composed of neurons that conduct and transmit nerve impulses (via dendrites and axons), and of neuroglia cells that protect, support, and insulate the neurons.

7. Protection, temperature regulation, prevention of water loss, conversion of cholesterol to vitamin D, contains receptors that receive stimuli

8. Cells called melanocytes produce the pigment melanin. The color of melanin is variable (red to yellow, or brown to black) and the amount produced by the melanocytes is also variable, which influences the amount of and type of skin color. Blood flow can influence the color of skin. More blood flow increases the red coloration of the skin.

9. Goose bumps occur when the arrector pili muscles in the skin contract to adjust the positioning of hairs and hair follicles.

10. Oil glands are specialized structures present in the skin that produce sebum (fats, cholesterol, proteins, and salts). Acne occurs when oil glands clog and bacteria build up causing an infection in the gland and hair follicle.

11. The function of sweat glands is to regulate body temperature by producing sweat, which cools the body when it evaporates.

12. Homeostasis is the ability of the body to maintain a relatively stable internal environment in spite of changes in the surroundings.

13. Body temperature regulation is a negative feedback system. When body temperature rises above the set point, receptors in the skin send a message to the hypothalamus in the brain. The hypothalamus then sends a message to the sweat glands to produce sweat and cool the body. When body temperature drops below the set point, receptors in the skin send a message to the hypothalamus. The hypothalamus then sends a message to blood vessels to constrict so blood flow to the arms and legs is reduced, which conserves heat. In addition, metabolism is increased to produce more heat.

14. b

15. a

16. d

17. calcium

18. homeostasis

Chapter 5

1. Six functions of the skeleton:

a. Support

b. Movement

c. Protection

d. Storage of minerals

e. Fat storage

f. Blood cell production

2. Compact bone is dense bone with very few spaces and is covered by a nourishing membrane called the periosteum. Spongy bone is identified by its many spaces that are filled with red bone marrow, which produces red blood cells.

3. A long bone in the human body contains both compact bone and spongy bone. The compact bone is found on the outer surface of the bone and composes the shaft. The spongy bone is found at the ends of the long bone. Yellow bone marrow is found in the central shaft of the long bone surrounded by the compact bone. Red bone marrow is found in spaces of the spongy bone.

4. The osteon consists of a central canal surrounded by concentric rings of osteocytes (mature bone cells) in a rigid matrix. Osteocytes are located within a lacuna in the matrix. Canals connect the lacunae to each other and to the central canal. This allows for the transport of items between the cells and the blood vessels in the central canal.

5. During fetal development, most of the skeleton is first formed of cartilage. Cartilage cells actively divide, allowing the skeleton to grow as the fetus does. Beginning around the third month of development, osteoblasts (bone-forming cells) form a ring of bone around the cartilage and create the shaft of the bone; the cartilage cells degenerate forming the center cavity of the bone. Osteoblasts then fill the cavity with spongy bone. After birth, bones grow longer as the cartilage cells in the growth plates at the ends of the bone divide. Bone replaces the newly formed cartilage. At puberty, hormones usually cause an increase in the rate of growth that lasts until the end of teenage years (usually ~ 18 years old) when cartilage cells slow their rate of division.

6. After a fracture, a blood clot is formed at the site of the fracture. Next, fibroblasts secrete collagen fibers, which form a fibrocartilaginous callus that is replaced by a bony callus. Over time, bone remodeling restores the bone to the original shape.

7. Bone remodeling is the continuous reshaping and replacing of bone during one's lifetime. Osteoblasts continuously form bone while osteoclasts continuously break down bone. Bone is built along the lines of stress on a bone, providing strength where it is needed the most.

8. The axial skeleton includes the bones of the skull, vertebral column, ribcage, and sternum. The appendicular skeleton includes the bones of the pectoral girdle and arms, and the bones of the pelvic girdle and legs.

9. A synovial joint is a freely moveable joint, such as the knee joint. A thin layer of cartilage reduces friction on the surfaces of the bones that slide over one another. A synovial joint is surrounded by a two-layered joint capsule. The synovial membrane, which forms the inner layer of the capsule, secretes synovial fluid to lubricate the joint. Ligaments hold the joint together, support the joint, and determine the direction of movement at the joint.

10. c

11. c

12. axial

13. calcium, phosphorus

14. osteoblasts

15. sprain

Chapter 6

1. Most muscles in the human body are arranged in antagonistic pairs so that the contraction of one muscle moves a bone in one direction and the contraction of another muscle moves the bone back. A good example of an antagonistic pair (Figure 6.1) is the biceps that pulls the forearm up to bend the arm at the elbow and the triceps that pulls the forearm down to extend the arm.

2. Skeletal muscles are attached to bone and are made up of fascicles, smaller bundles of muscle cells. Muscle cells (also called muscle fibers) contain specialized bundles of proteins called myofibrils. The orderly arrangement of myofibrils creates the striated (striped) appearance of muscle cells. The myofibrils in turn are made up of two types of myofilaments: actin and myosin filaments. Each myofibril is divided by bands of proteins, called Z-lines, to form many sarcomeres, which are the contractile units of the muscle. The actin myofilaments are attached to the Z-lines. The myosin filaments are positioned in the middle of the sarcomere, between the actin filaments.

3. The sliding filament model of muscle contraction proposes that muscles shorten when the thin actin filaments slide past the thick myosin filaments, increasing the degree of overlap between them.

4. The actin filaments are pulled across the myosin filaments by movements of the heads of myosin filaments. The head of a myosin filament, located at its end, has two important characteristics: It can bend, and it can bind and split ATP. The myosin head binds to the actin filament. The myosin head then bends pulling the actin filament to the center of the sarcomere. ATP provides energy to move the myosin head and the actin. ATP is also needed for the myosin head to release the actin.

5. Tropomyosin and troponin are proteins that cover the myosin-binding sites on actin during muscle relaxation. Calcium ions enter the sarcomere, bind to the tropomyosin-troponin complex, which changes shape and exposes the myosin-binding sites on the actin. The actin is then free to bind with the myosin again and cause contraction.

6. When a nerve impulse reaches the neuromuscular junction acetylcholine is released, which creates an electrochemical message sent to the sarcoplasmic reticulum that releases calcium ions. Calcium ions enter the sarcomere, bind to the tropomyosin-troponin complex, which then changes shape and exposes the myosin-binding sites on the actin. The actin is then free to bind with the myosin again and cause contraction.

7. A motor unit is a motor neuron and all the muscle cells it stimulates. In general, the finer the movement the fewer muscle cells per motor unit.

8. A muscle twitch (contraction) is a brief contraction of a muscle in response to a single stimulus. Wave summation of muscle contraction occurs when the muscle is stimulated again before the muscle can completely relax from the previous stimulus. Tetanus is a smooth, sustained contraction that occurs when stimuli arrive in such rapid succession that there is no time for muscle relaxation.

9. Sources of ATP for muscle contraction are

a. muscle cells—the first source of ATP which is replenished during relaxation.

b. creatine phosphate—used after the first 6 seconds of exercise, supplies energy to convert ADP to ATP.

c. anaerobic respiration—occurs after about 10 minutes of exercise, does not need oxygen; glucose source is glycogen.

d. aerobic respiration—occurs when the heart begins to beat faster to deliver the oxygen needed.

10. Slow-twitch muscle cells contract slowly, but have more endurance than the fast-twitch muscle cells that contract powerfully and quickly.

11. Resistance exercise builds the size of muscles when the muscle exerts more than 75% of its maximum force during the exercise.

12. c

13. a

14. actin, myosin

15. sarcomere

Chapter 7

1. There are several types of glial cells, which support, protect, insulate, and nurture neurons.

2. Motor neurons conduct information away from the brain to muscles or glands.

Sensory neurons conduct information toward the brain.

Interneurons (association neurons) are found in the brain or spinal cord. They function in integrating information between motor and sensory neurons and are the most numerous.

3. Draw a typical neuron and label the following: cell body, nucleus, dendrites, and axon. Refer to Figure 7.2, p. 118.

4. Schwann cells form the myelin sheath in the peripheral nervous system. A Schwann cell wraps around the axon many times, forming a spiral of membrane. The myelin sheath serves as an insulator for individual axons, allows the signals to move faster along the axon, and helps in the repair of a damaged axon.

5. In a resting neuron, sodium and potassium ions are unequally distributed across the plasma membrane. There are more sodium ions outside the membrane and more potassium ions on the inside of the membrane. There is a -70mv difference between the inside and outside of the membrane during the resting potential. During an action potential the sodium ions enter the cell, causing the loss of charge difference across the membrane and eventually creating a positive charge on the inside of the membrane.

6. When a neuron is resting (not conducting an impulse), energy is used to maintain the difference in the distribution of sodium ions and potassium ions across the membrane that causes the resting potential. When the neuron is stimulated, the potential difference across the membrane allows the neuron to respond quickly.

7. Sodium ions (with their positive charge) enter the cell when the sodium gates open. This movement causes the inside of the membrane to become less negative and eventually to become positive.

8. Potassium ions (with their positive charge) leave the cell, which returns the cell to its resting potential.

9. The sodium-potassium pump restores the initial ion distribution by using energy in ATP to pump sodium ions out of the cell and potassium ions back into the cell.

10. The refractory period is time following an action potential during which a neuron cannot be stimulated to generate another action potential. 11

11. Draw a synapse between two neurons. Label the following: presynaptic neuron, postsynaptic neuron, synaptic cleft, synaptic vesicles, neurotransmitter molecules, and receptors. Refer to Figure 7.6 on page 122.

12. When the neurotransmitter of an excitatory synapse binds to receptors, the sodium channels open, allowing sodium ions to enter the cell. This movement of sodium ions reduces the charge difference across the membrane, increasing the likelihood that an action potential will be generated. In an inhibitory synapse, the neurotransmitter binds to receptors that open other ion channels, often chloride channels. As a result of ion movements, the inside of the membrane becomes more negative, decreasing the likelihood that an action potential will be generated.

13. The neurotransmitter must be removed from the synapse to stop its action on the postsynaptic neuron. In some synapses, enzymes break down the neurotransmitter. In other synapses, the neurotransmitter is actively pumped back into the axon tip.

14. a

15. c

16. b

17. b

18. b

19. myelin sheath

20. sodium-potassium pump

Chapter 8

1. Parts of the nervous system:

The central nervous system (CNS) consists of the brain and spinal cord.

The peripheral nervous system (PNS) consists of the nerves and ganglia outside of the CNS. The PNS is subdivided into the autonomic and somatic nervous systems.

2. Protection of the CNS:

a. Meninges—protective outer coverings of the brain and spinal cord

b. Cerebrospinal fluid—fills internal cavities in the brain for protection and cushioning

c. Blood-brain barrier—selectively permeable barrier between the circulatory system and the cerebrospinal fluid

3. The functions of the cerebrospinal fluid are shock absorption, support, and nourishment.

4. The gray matter is the thin cerebral cortex of each hemisphere of the cerebrum. It is composed of interneurons, which integrate information. The white matter consists of myelinated axons that lie below the cerebral cortex. Bands of white matter allow communication between different regions of the brain. The corpus callosum is a band of white matter that connects the two hemispheres.

5. Three types of functional areas of the cerebral cortex are

a. sensory—senses, including vision, hearing, olfaction.

b. motor—movement.

c. association—interpretation of sensations, language, thinking, decision making, memories, creativity.

6. The general arrangement of the primary somatosensory area and the primary motor area is similar, but more of the sensory cortex is devoted to areas of greater sensitivity. The motor cortex has larger areas devoted to body parts with finer motor control.

7. The hypothalamus influences or regulates

a. blood pressure and heart rate.

b. digestive activity.

c. breathing rate.

d. body temperature.

e. coordination of endocrine system.

8. The cerebellum is the part of the brain responsible for sensory-motor coordination.

9. The limbic system is the functional system of the brain responsible for emotions.

10. The reticular activating system

a. filters sensory input.

b. activates the cerebral cortex to keep us awake.

11. The spinal cord

a. transmits messages to and from the brain. Tracts of white matter on the periphery of the cord carry information up to the brain or down from the brain. Spinal nerves connect the spinal cord with regions of the body.

b. serves as a reflex center for quick action when needed. Reflex arcs are located in the inner, butterfly-shaped gray matter.

12. In a spinal reflex arc, a response to a stimulus can result from the activity of only three neurons. Sensory information enters the spinal cord over a sensory neuron. An interneuron receives the sensory information and communicates it to a motor neuron, which causes muscles to contract and remove the hand from the burner. The perception of pain occurs in the brain, which requires more neurons and synapses.

13. Two divisions of the peripheral nervous system:

a. Somatic—controls the conscious, voluntary functions

b. Autonomic—controls the internal organs and maintains homeostasis

14. The sympathetic nervous system prepares the body for stressful situations, such as fear or rage. The parasympathetic nervous system adjusts the functioning of the organism to conserve energy during nonstressful times. Both systems innervate the internal organs but have usually opposite actions on an organ.

15. Some effects of sympathetic stimulation and how these prepare the body for an emergency:

a. Increases breathing, heart rate, and blood pressure

b. Increases the amount of glucose and oxygen in the blood

c. Stimulates the adrenal glands to release epinephrine and norepinephrine into the blood stream to prolong the effects mentioned above

16. a

17. a

18. d

19. hypothalamus

20. medulla

21. sympathetic nervous system

22. cerebrum

Chapter 9

1. Sensory adaptation is the process by which sensory receptors stop responding when they are continuously stimulated. Olfactory receptors adapt quickly. When we enter a room with an odor, we generally smell it at first, then after a while the odor becomes less noticeable.

2. Five classes of receptors:

a. Mechanoreceptors—general senses and special senses

b. Chemoreceptors—special senses (taste and smell) and internal conditions

c. Photoreceptors—special senses

d. Thermoreceptors—general senses

e. Pain receptors—general senses

3. Merkel disks are receptors for light touch on the skin.

4. The sclera protects and shapes the eye. The cornea provides a window for light to enter the eye and refracts light to the retina.

5. The cornea refracts (bends) light toward the retina. The lens changes shape to bend light in the appropriate direction to focus on close or far objects.

6. Light causes a photopigment within the receptor to split into its component parts, which causes a series of reactions that create a neural message.

7. Sound waves are pressure waves in air or water produced by vibrating objects. The amplitude (height) of the waves determines the loudness, and the frequency (cycles per second) determines the pitch of the sound.

8. The function of the tympanic membrane (eardrum) is to transfer vibrations caused by sound waves to the bones of the middle ear. The tympanic membrane forms the outer boundary of the middle ear and vibrates in response to sound waves. Vibrations of the tympanic membrane are transferred through the middle ear by three small bones (malleus, incus, and stapes; also known as the hammer, anvil, and stirrup) to the inner ear, where hearing occurs when neural messages are generated in response to the pressure waves caused by the vibrations.

9. The amplification of the force of vibration in the middle ear is necessary to transfer the vibrations to the fluid of the inner ear. Amplification occurs because of the arrangement of the middle ear bones and the difference in size of the larger eardrum and the oval window.

10. Unequal pressure on either side of the eardrum causes pain and difficulty hearing. The auditory tube that connects the middle ear to the throat can be opened by yawning or swallowing, which allows equalization of pressure between the middle ear and the atmosphere and alleviates the pain.

11. The basilar membrane vibrates in different areas along its length according to pitch. The auditory nerve sends messages to the brain, which interprets the movement of the different areas of the membrane as differences in pitch.

12. Two types of hearing loss:

a. Conductive hearing loss—sounds are not conducted through the auditory canal.

b. Sensorineural hearing loss—is caused by damage to the hair cells of the inner ear.

13. Two structures for equilibrium:

a. Semicircular canals are fluid-filled canals that are oriented at right angles to one another. At the base of each canal is an enlarged area called the ampulla, which contains a tuft of hair cells. The hair cells are embedded in a gelatinous material called the cupula. Movements of the body or head cause movements of the fluid in the semicircular canals. This movement of fluid causes the cupula to bend the hair cells, thereby stimulating them. Thus, the semicircular canals help us stay balanced as we move.

b. The vestibule consists of two fluid-filled chambers—the utricle and the saccule. These chambers contain hair cells embedded in a gelatinous mass containing small granules of calcium carbonate called otoliths. When the position of the head changes, the otoliths cause the gelatinous mass to move and bend the hair cells. The brain interprets the pattern of stimulation from the hair cells to determine the position of the head relative to gravity.

14. Motion sickness is caused by mismatched sensory input from the eyes and the inner ear. Drugs designed for relieving motion sickness are effective, and they work by inhibiting messages from the vestibular apparatus. Some people say that staring at the horizon while moving can help.

15. Olfactory receptors are located at the roof of the nasal cavity. The receptors have long olfactory hairs that project into a coat of mucus that traps odor molecules. The odor molecules can then stimulate the olfactory receptors.

16. Taste buds are responsible for taste and are located on the tongue; a few are in the cheeks, the roof of the mouth, or the throat. Most taste buds are located in papillae on the tongue.

17. The five primary tastes are sweet, sour, bitter, salty, and umami (savory).

18. Taste buds are located on the papilla of the tongue and cheek. They are lemon-shaped. Each taste bud has taste hairs projecting out at the tip that have receptors for chemicals dissolved in

19. a

20. b

21. d

22. a

23. b

24. cones

25. lens

26. cochlea

27. maintain balance while we are moving

Chapter 10

1. Cells that are affected by a particular hormone are called target cells. Target cells have receptors for the hormone that is released. Other cells do not have the receptor and cannot be affected by the hormone.

2. Lipid-soluble (steroid) hormones can move through the lipid bilayer into a cell where the receptors reside. Steroid hormones combine with a receptor inside the cell, and then the hormone- receptor complex moves to the DNA where it activates genes that direct the synthesis of specific proteins. Water-soluble hormones are composed of amino acids and cannot pass through the lipid bilayer. In this case, the hormone, considered the first messenger, attaches to a receptor on the surface of the cell, and this binding activates a molecule in the cytoplasm. This molecule inside the cell, considered the second messenger, sets off an enzyme cascade that affects cell activity.

3. In negative feedback systems, the outcome of a process feeds back on the system, shutting down the process. For example, the pancreas secretes the hormone insulin when blood glucose is high to stimulate glucose uptake and storage. When the blood glucose becomes low, the pancreas stops secreting insulin. In positive feedback systems, the outcome of a process feeds back to the system and stimulates the process to continue. For example, during childbirth the posterior pituitary secretes the hormone oxytocin. Oxytocin stimulates uterine contractions, which in turn stimulate the production of more oxytocin, and this increases the frequency and intensity of uterine contractions.

4. The anterior pituitary is larger than the posterior pituitary and is directly connected to the hypothalamus by a circulatory connection. The much smaller posterior pituitary is connected to the hypothalamus by neurosecretory cells.

5. The anterior pituitary gland secretes growth hormone (stimulates growth of bones and muscles), thyroid stimulating hormone (stimulates thyroid gland to produce hormones), adrenocorticotropic hormone (stimulates the adrenal cortex to produce hormones), prolactin (stimulates the mammary glands to produce milk), follicle-stimulating hormone (promotes development of egg cells and the secretion of estrogen from the ovaries), and luteinizing hormone (in females, causes ovulation and stimulates the ovaries to secrete hormones; in males, promotes the maturation of sperm and stimulates testes to produce hormones).

6. The posterior pituitary secretes antidiuretic hormone (prompts kidneys to conserve water by decreasing urine output) and oxytocin (stimulates uterine contractions of childbirth and causes milk letdown).

7. Thyroid hormone affects most cells of the body; it increases metabolism and heat production.

8. In response to high levels of calcium in the blood, the thyroid secretes calcitonin, which promotes calcium storage by bones. When levels of calcium become too low, the parathyroid glands release parathyroid hormone, which increases calcium levels in the blood by stimulating bone- destroying cells (osteoclasts), reabsorption of calcium by the kidneys, and absorption into the bloodstream by the GI tract.

9. Glucocorticoids affect glucose homeostasis. Mineralocorticoids affect mineral homeostasis and water balance. The gonadocorticoids (sex hormones) probably have minimal effects, especially in normal adult males, because secretion by the testes far surpasses that by the adrenal cortex. In females, sex hormones from the adrenal cortex may somewhat alleviate menopausal symptoms brought on by the cessation of sex hormone production by the ovaries.

10. Hormones released by the adrenal medulla (epinephrine and norepinephrine) are responsible for the fight-or-flight response, which is prompted by stress or danger. The response includes increases in heart rate, respiratory rate, and blood glucose, as well as vasoconstriction (in areas that are not of immediate importance, such as the digestive tract) and dilation (in areas that are of immediate importance, such as skeletal and cardiac muscle).

11. The main hormones secreted by the pancreas are glucagon and insulin. Glucagon increases blood glucose by stimulating the liver to convert glycogen to glucose and forming glucose from lactic acid and amino acids. Insulin decreases glucose in the blood by increasing transport of glucose into cells, inhibiting the breakdown of glycogen to glucose, and preventing conversion of amino acids to glucose.

12. Diabetes mellitus is a group of diseases characterized by problems with insulin production or insulin function. Diabetes insipidus results from a deficiency in antidiuretic hormone (ADH).

13. The thymus gland produces hormones that are involved in the maturation of the white blood cells known as T-lymphocytes.

14. Melatonin reduces jet lag and promotes sleep.

15. Local signaling molecules act at or near the site of their release within seconds or milliseconds. In contrast, true hormones travel in the blood to relatively distant sites in the body, so their effects take longer to materialize.

16. a

17. d

18. c

19. c

20. a

21. lipid-soluble; water-soluble

22. gigantism; acromegaly

23. calcitonin; parathyroid hormone

24. adrenal cortex

25. insulin; glucagon

Chapter 11

1. Plasma is the liquid matrix portion of blood. Plasma functions to transport dissolved substances such as nutrients, ions, dissolved gasses, plasma proteins (for water balance) and hormones. Plasma functions in transporting cellular wastes from the cells to the kidneys.

2. The three categories of plasma proteins are albumins, globulins, and clotting proteins.

3. Three types of formed elements and their functions:

a. Platelets are cell fragments that function in clotting.

b. Red blood cells (erythrocytes) function in transporting oxygen to other cells in the body for cellular respiration and transporting a portion of the carbon dioxide waste from cells.

c. White blood cells (leukocytes) function in defense against disease.

4. Erythrocytes compared with leukocytes:

a. Erythrocytes are small, biconcave disk-shaped cells that lack a nucleus and are packed with hemoglobin. They account for about 45% of the blood volume.

b. Leukocytes are larger than the erythrocytes, have a large nucleus, and account for less than 1% of the total blood volume.

5. Five types of white blood cells and the role each plays in body defense:

a. Neutrophils phagocytize bacteria and other microbes.

b. Eosinophils attack parasitic worms and phagocytize antibody-antigen complexes.

c. Basophils release histamine, which attracts other white blood cells to the site of injury, and causes blood vessels to dilate.

d. Monocytes develop into macrophages.

e. Lymphocytes—B-lymphocytes give rise to plasma cells that produce antibodies, and T-lymphocytes perform various functions of the immune response.

6. Each red blood cell is a biconcave disk, a shape that creates a large surface area for such a small cell. Red blood cells are packed with the protein hemoglobin, which has the ability to pick up oxygen in the lungs and release it in the tissues. Red blood cells lack a nucleus and mitochondria, so most of the room is taken up by the hemoglobin molecules.

7. The function of hemoglobin is to bind to oxygen in the lungs and release it in the tissues. Hemoglobin is a globular-shaped protein consisting of four polypeptide chains. Each chain contains a heme group (with an iron atom) that can bind to an oxygen molecule.

8. Red blood cells are produced in the red bone marrow. When the oxygen-carrying capacity of the blood is low, the kidneys release the hormone erythropoietin. This stimulates the red bone marrow to produce more red blood cells. The kidneys reduce erythropoietin production when the oxygen-carrying capacity of the blood increases.

9. The liver and spleen destroy worn out red blood cells. The red blood cells get stuck in the tiny circulatory channels of these organs where macrophages destroy them. The hemoglobin is broken down into its component amino acids and bilirubin.

10. People with pernicious anemia cannot absorb Vitamin B12 from the digestive system so they need injections of this vitamin.

11. Antigens on the surface of red blood cells determine blood type. Type A blood has A antigens. Type B blood has B antigens. Type AB blood has both A and B antigens. Type O blood lacks these antigens on the red blood cell surfaces.

12. If a person is given an incompatible blood type, agglutination occurs because recipient's antibodies react to the antigens on the donor's red blood cells, causing the cells to clump and get stuck in blood vessels and block blood flow. The clumped cells may also break open and release hemoglobin, which can clog the filtering system of the kidneys and lead to death.

13. A person with type B blood can receive type B and type O blood. Type B blood is compatible because it has the same antigen as the recipient, and type O blood does not have any antigens so it will not cause agglutination.

14. Hemolytic disease of the newborn occurs when anti-Rh antibodies from the mother cross the placenta and cause clumping of an Rh-positive fetus's blood cells. An Rh-negative mother may have formed anti-Rh antibodies if she previously gave birth to an Rh-positive baby and fetal blood entered the mother's body during the delivery. In subsequent pregnancies with an Rh-positive fetus, the Rh-negative antibodies enter the fetus's circulatory system and cause red blood cells to clump.

15. When a blood vessel is cut, it contracts and reduces blood flow. Next, platelets stick to the collagen fibers on the damaged blood vessel's wall to form a "plug." The platelets then produce thromboxane, which makes them stick together and attracts other platelets to the wound. Injured cells in the blood vessel release blood clotting factors and a clot forms.

16. The steps involved in blood clotting:

a. Clot formation begins when clotting factors are released from injured cells of the damaged blood vessel.

b. The clotting factors convert an inactive blood protein to prothrombin activator, which converts prothrombin to an active form, thrombin.

c. Thrombin then causes a change in fibrinogen from the liver. The altered fibrinogen forms long strands of fibrin, which form a web that traps blood cells and forms the clot.

17. Blood clotting after an injury occurs when blood cells get trapped in a web of fibrin at the site of injury. Agglutination following a mismatched blood transfusion occurs because antibodies in the recipient's blood cause the donor's red blood cells to clump.

18. a

19. c

20. b

21. transport oxygen

22. hemoglobin

23. fibrin

Chapter 12

1. The path of blood flow from the heart and back to the heart is: heart : artery : arterioles : capillaries : venules : veins : heart.

2. A pulse is a pressure wave in the arteries created by the contraction of the ventricles of the heart.

3. An aneurysm is a weakened area in an artery. If the aneurysm ruptures, a hemorrhage occurs, which may cause a stroke or death from blood loss.

4. Two important functions of arterioles:

a. Control blood pressure

b. Regulate the amount of blood going into a capillary bed

5. Blood flow into a capillary bed is controlled by a ring of smooth muscle called a precapillary sphincter that surrounds a capillary before it branches to form the capillary bed. When the sphincter contracts, blood is channeled through the capillary bed without filling it. The capillary bed opens when the sphincter relaxes. Input from hormones, the nervous system, and local conditions of the arterioles regulate the opening or closing of any particular capillary bed.

6. All blood vessels have a lumen, the hollow interior through which blood flows, and a smooth lining called the endothelium. In addition to these characteristics, an artery has a middle layer containing elastic fibers that allow the artery to expand as blood is pumped into it and recoil to its original size. The middle layer also contains circular smooth muscle, which allows the artery to contract. The outer, supporting layer of an artery is connective tissue containing elastic fibers and collagen. The smallest arteries—the arterioles—have the same three layers, but the middle layer is primarily smooth muscle. The smooth muscle allows arterioles to regulate blood pressure by constricting or dilating. Capillaries have only one cell layer; this facilitates exchange of materials between the blood and cells. Veins have the same three layers that arteries have, but the walls are thinner and have less smooth muscle. Thus, veins can expand and serve as blood reservoirs. Many veins have one way valves that keep blood from "backing up."

7. Three mechanisms allow blood to return to the heart from the lower torso against the force of gravity. First, veins have valves that prevent the backflow of blood. Second, veins are surrounded by skeletal muscle. When the skeletal muscle contracts, it squeezes the vein pushing blood along. The valves ensure that blood flows one way—back to the heart. Third, pressure changes in the thoracic cavity that occur during breathing pull blood back toward the heart.

8. Each atrioventricular (AV) valve has flaps of connective tissue located between the atria and the ventricles. The AV valve on the right side of the heart has three cusps; the AV valve on the left side has two cusps. They are attached to the wall of the ventricle by connective tissue called chordae tendineae, which prevent them from flapping back into the atria. The semilunar valves are located between the ventricles and their arteries. These valves are small pockets of tissue attached to their arteries, which fill with blood to prevent backflow from the artery to the ventricle.

9. The human heart has four chambers—two atria and two muscular ventricles. Between each atrium and ventricle are the AV valves, which allow blood to move from the atrium to the ventricle. One-way valves exist between the ventricles and their arteries. The heart serves as two pumps. The right side of the heart pumps blood to the lungs through the pulmonary artery (pulmonary circuit). Blood is oxygenated in the lungs. The left atrium receives oxygenated blood from the pulmonary veins. The left side of the heart pumps oxygenated blood to the body cells (systemic circuit).

10. The path of blood from the left ventricle to the left atrium is: left ventricle : aortic semilunar valve : aorta : body tissues : superior and inferior vena cava : right atrium : right atrioventricular valve : right ventricle : pulmonary semilunar valve : pulmonary arteries : lungs : pulmonary veins : left atrium : left atrioventricular valve.

11. Each heartbeat (cardiac cycle) involves contraction (systole) and a relaxation (diastole).

First, all the chambers relax and blood passes through the atria and enters the ventricles. Then, the atria contract and push the remaining blood into the ventricles. Next, the atria relax and the ventricles contract.

12. The sinoatrial (SA) node, located in the right atrium, consists of specialized cardiac muscle cells that initiate each heartbeat. The SA node generates an electrical impulse that travels through the wall of the right atrium. The signal reaches another cluster of specialized muscle cells called the atrioventricular (AV) node, located in the partition between the two atria. The AV node relays the stimulus by a bundle of specialized muscle fibers, called the atrioventricular bundle, located along the wall between the ventricles. The electrical signal is conducted to the ventricles through the atrioventricular bundle and quickly fans out through the ventricle walls through the Purkinje fibers. The rapid spread of the impulse through the ventricles ensures that they contract smoothly.

13. Three important functions of the lymphatic system are

a. return of excess interstitial fluid to the bloodstream.

b. transport of products of fat digestion from the small intestine to the bloodstream.

c. help defend against disease-causing organisms.

14. The lymphatic capillaries differ from circulatory capillaries in that they end blindly and are much more permeable. The endothelial cells of the wall of lymph capillaries overlap one another.

Each is anchored to surrounding tissue by fine filaments. The endothelial cells function as one-way valves that respond to the pressure of accumulating interstitial fluid.

15. The lymph nodes are small nodular organs found along lymph vessels that filter lymph. The lymph nodes contain macrophages and lymphocytes, cells that play an essential role in the body's defense system.

16. a

17. b

18. b

19. b

20. sinoatrial node

21. an aneurysm

22. capillaries

Chapter 13

1. Nonspecific innate defenses are those you are born with. Nonspecific defenses target any foreign invaders; they are physical and chemical barriers. Specific defenses are our immune responses that target specific invaders of the body that manage to get by the nonspecific defenses. Specific defenses are adaptive, meaning that you acquire them to defend against specific invaders that you have experienced.

2. Seven innate, nonspecific defense mechanisms are

a. physical and chemical barriers prevent foreign cells from entering the body.

b. phagocytes engulf foreign cells.

c. inflammatory response of redness, warmth, swelling, and pain destroys the invader and helps repair damaged tissue.

d. natural killer cells kill abnormal cells that are not recognized as belonging in the body.

e. the complement system is a group of plasma proteins that assist other defense mechanisms.

f. interferons interfere with viral replication.

g. fever raises the body's temperature to become less hospitable to invaders.

3. Natural killer cells kill their target cells by releasing chemicals that form pores in the membranes of infected cells or tumor cells.

4. Interferons are proteins that are secreted by cells that are infected with a virus. They help protect healthy cells from becoming infected with a virus in two ways. First, they secrete chemicals that attract phagocytes and natural killer cells to kill infected cells. Second, interferons stimulate healthy cells to produce proteins that interfere with viral replication.

5. The complement system consists of plasma proteins that help the body's defense mechanisms. They are activated by an infection, which begins a series of different possible reactions. These include formation of protein complexes that create holes in bacterial cell walls, marking bacteria for destruction, and stimulating cells to release histamine or serve as chemical attractors for phagocytes.

6. The inflammatory response begins when injured tissues release chemicals that stimulate mast cells to release histamine. Histamine causes blood vessels to dilate, which brings more blood into the area, causing redness and heat. Increased blood flow brings in defensive cells and chemicals. The heat increases the metabolic rate of cells, which speeds healing. Histamine also causes capillaries to become more permeable. As a result, fluid seeps into the injured area carrying defensive cells and chemicals and causing swelling. Pain hampers movement, which allows the injured area to heal.

7. An antigen-presenting cell engulfs invaders, digests them, and presents fragments of the antigen on its surface attached to a self-marker (MHC marker). Macrophages, activated B-cells, and dendritic cells are antigen-presenting cells. They are recognized by an antigen-MHC complex on their surface that allows them to have self-markers along with the antigen fragments.

8. The antibody-mediated response is brought about by B-lymphocytes, which transform to form plasma cells that secrete antibodies. The targets of the antibody-mediated response are antigens in the blood or lymph. These targets include viruses, bacteria, and foreign molecules.

9. An antibody is a Y-shaped protein with antigenbinding variable regions at the tips of the Y that are specific to a particular antigen. The antigen- antibody complex marks a cell for destruction by activating the complement system, attracting phagocytes, neutralizing the target, or agglutinating the target.

10. Cytotoxic T cells are responsible for cell- mediated responses. Their targets are cellular—bacteria, infected cells, and cancerous cells. They kill their targets by releasing proteins that form holes in the target cell.

11. Natural killer cells are nonspecific defenders, whereas cytotoxic T-cells are programmed to kill specific abnormal cells.

12. The primary immune response involves recognition of the antigen and production of B- and T-cells. The secondary response uses memory cells that remain in the system and can be activated as soon as a recognized antigen enters the body.

13. Active immunity involves vaccinating with an antigen-containing preparation. Passive immunity involves injecting prepared antibodies for a specific pathogen.

14. Monoclonal antibodies are antibodies produced in the laboratory from a single hybrid B-cell. Some uses for these antibodies include home pregnancy tests; screening for prostate cancer; and diagnostic testing for hepatitis, AIDS, and influenza.

15. An autoimmune disorder is an immune response misdirected against the body's own tissues. In lupus erythematosus connective tissue is attacked, and in rheumatoid arthritis synovial joints are attacked. There are no cures, but therapy to suppress the immune system can relieve some of the symptoms.

16. An allergy is an inappropriate immune response to an allergen that is not harmful. The symptoms are caused by release of histamine from activated mast cells and an inflammatory response.

17. a

18. d

19. b

20. a

21. c

22. natural killer cell

23. histamine

24. plasma cells

25. macrophages (or activated B cells or dendritic cells)

Chapter 14

1. We must breathe oxygen to obtain the maximal amount of ATP during cellular respiration.

2. The path of air from the nose to the cells that use the oxygen is: nose : pharynx : larynx : trachea : bronchus : bronchioles : alveoli : capillary bed : blood stream : capillary bed : cells that need oxygen.

3. Mucus in the respiratory tract traps debris and pathogens. Cilia in the respiratory tract constantly beat in an upward motion to force debris toward the pharynx. The debris can then be swallowed or spit out.

4. When we swallow, the larynx moves up and under the epiglottis, covering the opening to the larynx. This movement prevents food or drink from entering the trachea.

5. The sound of the voice is created when air passes through the larynx and causes the vocal cords to vibrate. The pitch can be altered by adjusting the tension on the vocal cords. The tone can be changed by changing the shape of the resonating chamber created by the mouth. Loudness is determined by the volume of air passing through the cords.

6. The cartilage rings in the trachea keep the trachea open at all times. As we breathe, the air passing through the trachea creates a negative pressure that pulls in on the wall of the trachea. The negative pressure would cause the trachea to collapse if it were not supported open.

7. The bronchial tree is the system of bronchi that splits at each lung to form treelike structures of bronchioles ending in alveoli sacs.

8. The pressure changes within the thoracic cavity that cause inhalation and exhalation are created by the diaphragm and muscles between the ribs. When the muscles of the rib cage contract, the ribs are lifted upward and outward, which increases the size of the thoracic cavity from front to back. The diaphragm flattens when it contracts, which increases the size of the thoracic cavity from top to bottom. The increase in size of the thoracic cavity causes the pressure within it to drop, which draws air into the lungs (inhalation). When these muscles relax, the size of the thoracic cavity decreases and air moves outward (exhalation).

9. The vital capacity is larger than the tidal volume. Tidal volume is the volume we take in breathing normally (~500 ml). Vital capacity is the maximum amount of air we can exhale after a maximum inhalation (~4800 ml).

10. Most oxygen is transported in the blood stream to the body cells by binding to hemoglobin in red blood cells.

11. Most carbon dioxide transported from the cells to the lungs is dissolved in the plasma and transported by the blood stream.

12. The medulla oblongata of the brain contains the respiratory center that regulates breathing.

13. The medulla oblongata detects increased CO2 levels in the blood by responding to increases in H+ concentrations that result from carbonic acid that forms when CO2 dissolves in plasma.

Increases in H+ result in an increased breathing rate, which lowers CO2 levels in the blood.

14. Emphysema is the destruction of the alveolar walls. People with emphysema experience shortness of breath because they cannot get enough oxygen due to the loss of alveolar surface area.

15. a

16. b

17. b

18. a

19. a

20. epiglottis

21. carbonic anhydrase

Chapter 15

1. The structures of the gastrointestinal tract in the order that food passes through them are: mouth : esophagus : stomach : small intestine : large intestine : colon : rectum.

2. The processing of food begins in the mouth, where food is mechanically broken down by the teeth. Saliva contains the enzyme salivary amylase, which begins the chemical breakdown of starch. The tongue functions in keeping the food in the mouth and then swallowing the food.

3. The tooth is a hard structure covered by enamel. The inner portion is called dentin and surrounds the pulp. In the center there is a pulp cavity that houses blood vessels and nerves—structures that keep the tooth alive. Tooth decay is the destruction of the enamel coating of the tooth by acids produced by bacteria in the mouth. The result is a cavity.

4. The functions of the stomach are food storage, mechanical digestion, and chemical digestion. Gastric juice contains hydrochloric acid and pepsin, which begin the digestion of proteins.

5. Very few foods are absorbed from the stomach because food is not digested sufficiently.

6. Bile assists in the digestion of fats by coating small fat droplets created by mechanical digestion in the small intestine. This bile coating keeps the fat in small droplets (emulsifies it), which creates a larger surface area for lipase, a water-soluble enzyme, to chemically digest the fat into glycerol and fatty acids. Bile salts then combine with the glycerol and fatty acids to form micelles, which can be absorbed.

7. The primary site for digestion of carbohydrates, proteins, and fats is the small intestine. Carbohydrate digestion begins in the mouth, and protein digestion begins in the stomach.

8. The small intestine has many structures that increase the surface area for absorption. It has accordion-like folds (circular folds). The surface of the lining of the small intestine also has many fingerlike projections called villi. Each villus is covered with microvilli. The combined effect greatly increases the surface area for absorption.

9. The small intestine and pancreas produce enzymes that act in the small intestine.

10. The functions of the large intestine are to absorb water and store feces for removal from the body.

11. The sight, thought, or smell of food cause neural reflexes that stimulate the salivary glands to secrete salivary amylase. Chewing causes a neural influence that causes the stomach to produce gastric juice. The distention of the stomach by food and the partial digestion of protein cause the stomach to release the hormone gastrin, which circulates in the bloodstream and stimulates the stomach to produce gastric juices. Acidic chyme entering the small intestine triggers the release of the hormone secretin from the small intestine that causes the pancreas to release bicarbonate. Acidic chyme also causes the small intestine to release cholecystokinin, which causes the gallbladder to release bile and the pancreas to release digestive enzymes.

12. a

13. b

14. d

15. d

16. chyme

17. liver

18. starch

19. cholecystokinin

Chapter 16

1. Ammonia is formed in the liver when amino acids are broken down. It is converted to urea before leaving the liver. Urea is excreted by the kidneys and skin. Uric acid is formed from the recycling of nucleotides and is excreted by the kidneys and skin. Creatinine is produced in muscle cells as they use creatine phosphate as an alternate energy source; it is excreted by the kidneys.

2. The urinary system consists of the kidneys (filter blood and form urine), ureters (transport urine from kidneys to the bladder), urinary bladder (stores urine), and urethra (carries urine away from the body).

3. Kidneys remove nitrogenous wastes, excess ions, and unneeded substances from the blood. They also maintain water balance and the volume, pH, and pressure of the blood.

4. Glomerular filtration is movement of a protein- free solution of fluid and solutes from the glomerulus into the filtrate within the glomerular capsule; it occurs at the renal corpuscle. Tubular reabsorption occurs in the proximal convoluted tubule and returns most of the fluid and solutes from the filtrate to the blood. Tubular secretion removes additional wastes and excess ions from the blood and adds them to the filtrate; this occurs along the convoluted tubules and collecting ducts.

5. Nephrons contribute to the regulation of blood pH by secreting hydrogen ions into the filtrate (which will become urine) and by reabsorbing bicarbonate, which is critical to the carbonic acid buffer system in the blood.

6. Kidneys promote water conservation by producing concentrated urine; this is performed by the 20% of nephrons with long loops that dip into the renal medulla. Water conservation maintains blood volume and blood pressure.

7. Antidiuretic hormone (ADH) increases the permeability of the collecting duct to water so more water is reabsorbed, increasing blood volume and pressure and resulting in the production of concentrated urine. Aldosterone increases reabsorption of sodium by the distal tubule and collecting duct, increasing blood volume and pressure (because water follows sodium) and resulting in the production of concentrated urine. Atrial natriuretic peptide (ANP) decreases the reabsorption of sodium, and this decreases blood volume and pressure and results in the production of dilute urine.

8. The solute concentration in the interstitial fluid of the kidney increases from the cortex to the medulla. The increasing concentration of salt allows for the reabsorption of more water in the loop of Henle and production of concentrated urine.

9. The bladder is prevented from emptying by internal and external urethral sphincters. The internal sphincter is made of smooth muscle and is involuntary while the external sphincter is skeletal muscle and voluntary. When these sphincters relax, urine flows down the urethra to the external environment.

10. Males have a long urethra (~8") and females have a short urethra (~1.5"). Females are more prone to urinary tract infections due to their short urethra.

11. a

12. c

13. a

14. c

15. b

16. The juxtaglomerular apparatus

17. Hemodialysis

18. internal; smooth; external; skeletal

Chapter 17

1. The male gonads are testes, and the female gonads are the ovaries. They both function to produce gametes (eggs and sperm) and sex hormones. The ovaries produce eggs and the hormones estrogen and progesterone. The testes produce sperm and the hormone testosterone.

2. Temperature regulation in the testes depends on a muscle that contracts to bring the testes closer to the body for warmth when scrotal temperature is low or relaxes when the scrotal temperature is high, so the testes are farther away from the body. Sperm develop better in the testes at a few degrees lower than body temperature.

3. The path of sperm from their site of production to their release from the body is: seminiferous tubules : epididymis : vas deferens : urethra.

4. The male accessory glands and their functions are

a. seminal vesicles—secrete most of the seminal fluids.

b. prostate gland—secretes watery alkaline fluid, which activates sperm and raises the vaginal pH.

c. bulbourethral glands—secrete lubricating mucus.

5. The function of the penis is to deliver sperm to the vagina. The penis becomes erect when neural activity dilates arterioles in the penis, allowing blood to enter the spongy tissue and causing the veins to drain less blood. The change in blood distribution allows blood to accumulate in the spongy tissue and cause an erection.

6. The three regions of a sperm cell are

a. head—contains the DNA and is covered by the acrosome, an enzyme-rich cap that helps egg penetration.

b. mid-piece—contains mitochondria to power the tail for locomotion.

c. tail—locomotion to the egg.

7. Hormones from the hypothalamus, the anterior pituitary gland, and the testes that are important in the control of sperm production are

a. testosterone—produced in the testes. Testosterone is necessary for the maturation of sperm. When testosterone levels in the blood fall, the hypothalamus is stimulated to release GnRH.

b. GnRH—produced in the hypothalamus, stimulates the anterior pituitary to release LH and FSH.

c. LH—produced in the anterior pituitary; stimulates the testes to produce testosterone.

d. FSH—produced in the anterior pituitary; stimulates sperm production (with testosterone).

8. The uterus has two layers. The inner layer is the endometrium, which is the lining that builds up each month in preparation for pregnancy. These preparations include cell division to thicken the endometrium, which is stimulated by estrogen, and an increase in glandular activity to nourish the embryo, which is stimulated by progesterone. The outer layer is the myometrium, which consists of smooth muscle. The myometrium allows the uterus to get larger as the fetus grows and provides the force to push the baby out during delivery.

9. The major structures of the female reproductive system are

a. ovaries—produce the eggs.

b. oviducts—path for egg/early embryo to travel to uterus.

c. uterus—site for implantation of the embryo and development of the fetus.

d. vagina—birth canal.

10. An ectopic pregnancy occurs if the embryo implants in a place other than the uterus. The most common type of ectopic pregnancy is a tubal pregnancy in which the embryo implants in the oviduct. Because the oviduct cannot expand as the uterus does to accommodate embryonic growth, the oviduct may rupture, causing the mother to hemorrhage, which can be fatal.

11. The breasts contain milk glands that produce milk for offspring. The milk glands are connected to ducts that lead to the outside environment at the nipple. Most of the breast consists of fatty tissue.

12. The ovarian cycle starts with a primary follicle, which is a primary oocyte surrounded by a layer of follicle cells. As the primary follicle matures, the follicle cells divide and produce estrogen, which enters the bloodstream and accumulates in a fluid within the follicle. The accumulation of fluid causes the layer of follicle cells to split, and the fluid continues to accumulate in the newly formed cavity. The estrogen in the fluid causes the first meiotic division in the primary oocyte, forming a secondary oocyte. Estrogen-containing fluid continues to accumulate as the follicle grows. Eventually, the mature Graafian follicle forms. The Graafian follicle contains a secondary oocyte that is located at the edge and surrounded by follicle cells and a large fluid- filled cavity. At ovulation, the mature follicle pops, releasing the egg. The follicle cells remaining in the ovary are transformed into an endocrine structure called the corpus luteum, which secretes estrogen and progesterone. If pregnancy does not occur the corpus luteum will degenerate within about 2 weeks.

13. Day 1 of the menstrual cycle is considered the first day of menstrual flow. At this point in the cycle, estrogen and progesterone levels are low, and a new follicle is beginning to develop. FSH from the anterior pituitary stimulates estrogen production by the developing follicle. As the follicle develops, estrogen levels rise and cause cell division in the endometrium, which thickens the endometrium for implantation of an embryo. As the follicle approaches maturity, the rapidly rising level of estrogen stimulates LH release from the anterior pituitary, which triggers ovulation. The follicle cells remaining in the ovary after ovulation are transformed into an endocrine structure, called the corpus luteum, that produces estrogen and progesterone. The estrogen continues to stimulate cell division in the endometrium, and progesterone causes the development of mucous glands that will nourish the embryo if one forms. Progesterone is also needed to maintain the endometrium. If pregnancy does not occur, the corpus luteum degenerates, and the level of estrogen and progesterone decrease. Without progesterone to maintain the endometrium, it decreases and the endometrium is no longer maintained. The endometrium breaks down and is lost as menstrual fluid.

14. Menopause is the cessation of the menstrual cycle and ovulation, because follicles are no longer developing. From the moment of birth, the number of primary follicles in a woman's ovaries begins to decrease. By the time she is about 45 to 55 years old, follicles remaining in the ovaries no longer respond to FSH and develop. Without egg development, ovulation cannot occur. Without the cycling of hormones, the menstrual cycle does not occur.

15. The stages of the human sexual response are excitement, plateau, orgasm, and resolution.

16. A vasectomy includes making incisions in the scrotum and sealing off each vas deferens so that sperm cannot enter the urethra. A tubal ligation includes cutting and sealing each oviduct so that the egg cannot reach the uterus and the sperm cannot reach the egg.

17. Birth control pills contain the hormones estrogen and progesterone, which inhibit the production of FSH and LH. This prevents the follicles from maturing, as well as preventing ovulation if a follicle should develop.

18. Side effects of using the birth control pill may include acne and headaches. More serious side effects include high blood pressure and blood clots, which could lead to heart attack, stroke, or pulmonary embolism.

19. Use of progesterone-only means of contraception does not prepare the endometrium for embryo implantation and may prevent ovulation.

20. An IUD is an intrauterine device that can remain in the uterus for several years. It prevents pregnancy by interfering with fertilization and implantation.

21. The diaphragm, male condom, and female condom are barrier methods for birth control.

They prevent pregnancy by preventing the sperm from reaching the egg.

22. c

23. b

24. a

25. b

26. c

27. epididymis

28. oviduct

Chapter 18

1. The prenatal period is divided into the preembryonic period, embryonic period, and fetal period. The pre-embryonic period runs from fertilization through the second week and is characterized by formation and implantation of the blastocyst. The extraembryonic membranes and placenta also begin to form at this time. The embryonic period extends from week 3 through week 8 and is characterized by gastrulation and the formation of organs and organ systems. The fetal period runs from the ninth week until birth and is a period of intense growth.

2. Secretions from the female reproductive tract alter the surface of the acrosome to destabilize the plasma membrane of the sperm.

3. Polyspermy is the abnormal condition when more than one sperm fertilizes the egg. During fertilization, fusion of the plasma membranes of the sperm and egg triggers granules near the plasma membrane of the oocyte to release enzymes. These enzymes cause the zona pellucida to quickly harden and thereby prevent passage of other sperm.

4. Implantation is the process by which the blastocyst becomes imbedded in the endometrium. Implantation normally occurs high up on the back wall of the uterus. A blastocyst that implants outside the uterus may result in an ectopic pregnancy. Most implantations outside the uterus occur in the oviducts.

5. The four extraembryonic membranes are the amnion (which protects the embryo by enclosing it in a fluid-filled sac), yolk sac (which serves as a site of early blood cell formation and contains primordial germ cells that migrate to the gonads), allantois (which becomes part of the umbilical cord), and chorion (which becomes the embryo's major contribution to the placenta).

6. The placenta provides oxygen and nutrients to the fetus and removes wastes (such as carbon dioxide and urea). It is formed from the chorion of the embryo and the endometrium of the mother where implantation occurred. During implantation, cells of the outer layer of the trophoblast rapidly divide and invade the endometrium. Then, one layer of the trophoblast forms fingerlike processes called chorionic villi that grow into the endometrium. Chorionic villi contain blood vessels connected to the developing embryo that provide exchange surfaces for diffusion of nutrients, oxygen, and wastes.

7. Gastrulation is the process early in prenatal development that forms the three germ layers— ectoderm, mesoderm, and endoderm. Ectoderm forms the nervous system and the outer layer of skin (including hair and nails). Mesoderm forms connective tissues and muscle, as well as organs such as the heart, kidneys, ovaries, and testes. Endoderm forms the linings of the urinary, respiratory, and digestive tracts. The pancreas, liver, thyroid, and parathyroid glands also form from endoderm.

8. During neurulation the neural plate folds inward to form a groove extending the length of the embryo on its dorsal surface. The raised sides of the groove are called neural folds. These will meet and fuse to form the neural tube, which is a fluid-filled tube that becomes the central nervous system. The embryo during this period is called a neurula. Later, the anterior portion of the neural tube develops into the brain, and the posterior portion forms the spinal cord.

9. Gender is determined at fertilization by the sex chromosome carried by the sperm. If the sperm has an X chromosome, a female will be produced. If the sperm has a Y chromosome, a male will be produced.

10. Fetal circulation is designed to bypass the lungs and liver, which are not fully functional until after birth. There are two shunts that keep most blood away from the lungs. The foramen ovale is a shunt between the right and left atria, and the ductus arteriosis is a shunt between the pulmonary trunk and aorta. The ductus venosus shunts most blood past the liver. After birth these temporary shunts close so more blood can go to the lungs and the liver.

11. The three stages of true labor are the dilation stage, expulsion stage, and placental stage.

12. Environmental agents have the most drastic effects during critical periods, and most critical periods occur during the embryonic period when tissues and organs are forming (from weeks 3-8). For example, limb development is most sensitive to environmental agents during weeks 4-6. Critical periods for the CNS are longer than those for most other organs and organ systems and span from weeks 3-16.

13. Milk production begins after birth when estrogen and progesterone levels decline to a level where prolactin can exert its effects.

14. Possible causes of aging include declines in the functioning of key organ systems, damage to cellular processes by free radicals, changes in proteins caused by glucose, and genetically programmed cessation of cell division. Besides medical advances, a healthy, moderate lifestyle can improve your chances of having a high-quality old age.

15. d

16. c

17. b

18. a

19. b

20. d

21. inner cell mass; trophoblast

22. cleavage

23. chorion; endometrium

24. Gastrulation

25. prolactin; oxytocin

26. Free radicals

Chapter 19

1. A chromosome is composed of tightly coiled DNA and associated proteins, whereas a gene is a segment of the DNA in a chromosome that codes for a particular protein.

2. Mitosis is a type of division of the nucleus occurring in somatic cells in which two identical cells, called daughter cells, are generated from a single cell. The original cell first replicates its genetic material and then distributes a complete set of genetic information to each of its daughter cells. Mitosis is usually divided into prophase, metaphase, anaphase, and telophase. Cytokinesis is the division of the cytoplasm and organelles into two daughter cells during cell division. Cytokinesis usually occurs during telophase.

3. Meiosis is important because it is the type of nuclear division that produces haploid gametes (eggs or sperm) from diploid germ cells. The process is needed so that gametes have only one set of chromosomes. When fertilization occurs the diploid number is restored. Meiosis is also important because it introduces genetic variability through independent assortment and crossing over.

4. In meiosis I, homologous chromosomes pair up at the equatorial plate so that each new cell will receive only one set of chromosomes during division. The orientation of the members of the pair (maternal or paternal) is random with respect to which member is closer to which pole. Each of the 23 pairs of chromosomes orients independently during metaphase I. The orientations of all 23 pairs will determine the assortments of maternal and paternal chromosomes in the daughter cells.

In meiosis II, the chromosomes line up on the equatorial plate in a manner similar to the way they do in mitosis. During anaphase II, the sister chromatids separate so that each gamete receives only one copy of each chromosome.

5. Independent assortment and crossing over create genetic variability in different ways. Crossing over is the breaking and rejoining of nonsister chromatids of homologous pairs of chromosomes during meiosis (specifically at prophase I when homologous chromosomes pair up side by side). Crossing over results in the exchange of corresponding segments of chromatids and increases genetic variability in populations by changing the combination of alleles on a chromosome. Independent assortment is the process by which homologous chromosomes and the alleles they carry segregate randomly during meiosis, creating mixes of maternal and paternal chromosomes in gametes. During meiosis I, exchanges of genetic material between homologous chromosomes produce new combinations of genes. Independent assortment allows homologous chromosomes to assort independently of each other during meiosis I, thereby producing new combinations of genes for each gamete.

6. Nondisjunction is when chromosomes fail to separate properly during anaphase of meiosis I or II.

If a chromosome pair does not separate during meiosis I, one of the daughter cells will receive an extra chromosome and one will lose a chromosome. This can happen in meiosis II with the same result: one gamete with an extra chromosome and one missing a chromosome. This can result in a trisomy (n+1) or in monosomy (n-1) after fertilization.

7. Down syndrome is caused by a trisomy of chromosome 21. The symptoms of Down syndrome include moderate to severe mental retardation, short stature or shortened body parts due to poor skeletal growth, characteristic facial features, and mild to severe heart conditions.

8. b

9. a

10. a

11. crossing over and independent assortment

12. homologous

13. synapsis

14. anaphase

15. anaphase II

Chapter 20

1. In a cross between a homozygous dominant individual and a homozygous recessive one all the offspring will be heterozygous for the trait. Their phenotypes will be the dominant phenotype.

2. A pedigree is a diagram showing all the known phenotypes for a particular trait of individuals in an extended family. It can be helpful in determining whether a person who has the dominant phenotype is homozygous or heterozygous. This information can be useful in determining whether a person is a carrier for a harmful recessive trait.

3. Codominance is the condition in which the effects of both alleles are separately expressed in a heterozygote. The human blood type AB is codominant because both the A and the B allele are expressed.

4. Multiple alleles occur when there are more than two different alleles for a trait. Human blood types (ABO) are an example of multiple alleles.

Polygenic inheritance occurs when more than one gene controls the trait. The effects of polygenic inheritance are a range of phenotypes depending on the number of dominant or recessive alleles inherited. Human height is an example of polygenic inheritance.

5. Linked genes are genes located on the same chromosome. Independent assortment does not apply to linked genes. Crossing over can "unlink" the genes.

6. The pattern of inheritance for recessive X-linked genes in males is different from the pattern for recessive autosomal alleles in females because males inherit only one X chromosome. When a male inherits a recessive allele on the X chromosome, the allele is expressed without the other recessive allele present. In contrast, recessive autosomal alleles are not expressed unless they are homozygous.

7. Chorionic villi sampling and amniocentesis are two forms of prenatal genetic testing. In amniocentesis, a small amount of amniotic fluid is removed for genetic testing of living fetal cells in the fluid. Chorionic villi sampling involves removal of a small piece of a chorionic villus to be genetically tested. The villi have the same genetic makeup as the fetus.

8. b

9. a

10. polygenic

11. phenotype, genotype

12. homozygous heterozygous

13. linked

Chapter 21

1. The structure of DNA is somewhat like a long ladder, twisted about itself like a spiral staircase. The DNA ladder is composed of two long strings of smaller molecules called nucleotides. Each nucleotide chain makes up one side of the ladder and half of each rung. A nucleotide consists of a phosphate, a nitrogen-containing base, and a sugar called deoxyribose. There are only four different nitrogen-containing bases used in DNA: adenine (A), thymine (T), cytosine (C), and guanine (G). Although DNA has only four different nucleotides, a DNA molecule is very long and has thousands of nucleotides. When forming a rung of the ladder, adenine must pair with thymine and cytosine must pair with guanine.

2. During replication the two DNA strands unwind and new nucleotides are added to each side to make two new strands. New nucleotides are added following complementary base pairing rules: Adenine must pair with thymine, and cytosine must pair with guanine. The specificity of these base pairs is important, not only for the accurate production of new DNA molecules, but also for converting the information in the gene into a protein.

3. DNA replication is described as semiconservative because each strand of the original DNA molecule serves as a template for the formation of a new strand. This process is called semiconservative replication because in each of the new double-stranded DNA molecules, one original (parent) strand is saved (conserved) and the other (daughter) strand is new. Complementary base pairing creates two new DNA molecules that are identical to the parent molecule.

4. Transcription of DNA is the process by which a complementary single-stranded messenger RNA (mRNA) molecule is formed from a single-stranded DNA template. As a result, the information in DNA is transferred to RNA. Translation is the process of converting the nucleotide language of messenger RNA into the amino acid language of a protein.

The mRNA template codes for the production of amino acid chains during translation.

5. RNA differs from DNA in three ways: (1) RNA is single-stranded, and DNA is double-stranded; (2) in RNA, the nucleotide sugar is ribose, and in DNA the nucleotide sugar is deoxyribose; and (3), in RNA, uracil replaces thymine found in DNA.

6. Messenger RNA, tRNA, and rRNA play different roles in protein synthesis. Messenger RNA (mRNA) is the type of RNA synthesized from and complementary to a region of DNA. It attaches to ribosomes in the cytoplasm and specifies the amino acid order in the protein. It carries the DNA's instructions for synthesizing a particular protein. Transfer (tRNA) is specialized to bring a specific amino acid to where it can be added to a polypeptide that is under construction. Ribosomal RNA (rRNA) combines with proteins to form ribosomes, which are the structures on which protein synthesis occurs.

7. A three-base sequence on messenger RNA (mRNA) specifies one of the 20 common amino acids or the beginning or end of the protein chain. Codons are read from the mRNA to produce amino acid chains. The order of the codons on mRNA determines the order of amino acids in the protein formed by translation. Codons also signal the start and end of a protein.

8. An anticodon is a three-base sequence on transfer RNA (tRNA) that binds to the complementary base pairs of a codon on the mRNA. Complementary base pairing ensures the correct amino acid is added to the amino acid chain.

9. The events in translation (protein synthesis) are

a. initiation—small ribosomal subunit joins with the mRNA start codon. Complementary tRNA binds to the start codon on mRNA, and the large subunit joins to form a functional ribosome. tRNA continues to pair with the codons to produce a chain.

b. elongation—the amino acid chain continues to get longer.

c. termination—occurs when a stop codon is encountered. The ribosomes separate and the process is terminated.

10. When a deletion occurs, it changes all the codons for the part of the mRNA molecule downstream.

11. Gene activity is regulated by chromosomal coiling and uncoiling, regulatory genes, and chemical signals such as hormones.

12. Genetic engineering is the manipulation of genetic material for human purposes. Restriction enzymes cut out pieces of DNA according to the nucleotide sequence they recognize. The "gene of interest" is identified in the mixture of pieces of DNA and added to a vector. Vectors are biological carriers of recombinant DNA to the new host cell.

13. In farming, genetically engineered crops are increasingly common. These crops are disease resistant, drought resistant, or pest resistant. In medicine, genetic engineering is being used to provide vaccines, therapeutic proteins, and some antibodies.

14. Gene therapy is treating a genetic disease by inserting healthy functional genes into the body cells that are affected by the faulty gene. The usual method is to use a virus to deliver the DNA.

15. a

16. c

17. b

18. a

19. tRNA

20. uracil

21. restriction enzymes

Chapter 22

1. The following steps are thought to explain how life evolved from inorganic molecules to complex cells: Inorganic molecules formed organic molecules; small organic molecules joined to form complex organic molecules; genetic material originated; organic molecules and DNA aggregated into droplets which eventually formed prokaryotic cells and then eukaryotic cells.

2. Microevolution refers to changes in allele frequencies in a population. Macroevolution describes large-scale changes in organisms over long periods of time.

3. Four sources of variation within populations are the chance union of a certain egg and sperm at fertilization in sexually reproducing species, mutation, crossing over, and independent assortment.

4. Genetic drift is a random change in allele frequencies so that the allele in question can become fixed or lost in the population.

5. Speciation is the formation of different species from a common ancestor. Disruption in gene flow between populations can cause speciation.

6. Natural selection is the process by which organisms differentially survive and reproduce.

Variation in a population is maintained due to changing environments.

7. The binomial system of naming is a two-part unique scientific name that identifies a species. It is composed of the genus name and the specific epithet. Organisms are classified by a hierarchical system of increasingly broad categories: species, genus, family, order, class, phylum, kingdom, and domain.

8. A phylogenetic tree is a hypothesis of organis- mal (evolutionary) relatedness (it is similar to a family tree).

9. A fossil is a preserved remnant or impression of past organisms. Dead organisms are covered by sediment, and minerals move into the parts that are not destroyed. Uplift or erosion may later expose the fossil. Organisms that have no "hard parts" generally do not fossilize well, so the fossil record is a biased sampling of past life.

10. New distributions of organisms arise when organisms disperse to new areas or when the areas occupied by organisms move or are subdivided.

11. Homologous structures have arisen from a common ancestry. Analogous structures have the same function, but arose through convergent evolution, not shared ancestry.

12. Common embryological origins are evidence of common descent.

13. The molecular clock is the constant rate of divergence of macromolecules from one another due to nucleotide changes in the genome.

14. Rotating shoulder joints, opposable thumbs, nails instead of claws, large brain and complex visual system, extensive parental care, and small litter size set primates apart from other mammals.

15. Humans differ from chimpanzees in having a larger braincase, less pronounced brow ridge, s-shaped (as opposed to bow-shaped) vertebral column, and less sexual dimorphism in canines.

16. Three popular misconceptions about human evolution are humans descended from chimpanzees; humans evolved in an orderly stepwise fashion from primitive to modern; and all human organs and organ systems evolved at the same rate.

17. The oldest hominin remains found to date are those of Ardipithecus ramidus, estimated to be at least 4.4 million years old. The remains suggest facultative bipedalism. Several hominin species in the genera Australopithecus and Paranthropus also have been identified. Some general characteristics of Australopithecines include a relatively small brain given their body size and significant differences in the heights of males and females. Species within Paranthropus were more robust than those within Australopithecus. One species of Australopithecus may have given rise to the Homo genus. About 2.5 million years ago, Homo habilis remains appear in the fossil record; this species appears to have used tools. About 1.9 million years ago, Homo ergaster arose, and Homo erectus diverged from this species 1.6 million years ago. Fossils of H. erectus are not restricted to Africa, indicating that this was the first hominin to disperse from Africa; this species may have used fire. The oldest remains of modern humans, Homo sapiens, are dated at 130,000 years old. Homo neanderthalensis was a cold-adapted species that coexisted with modern humans until about 30,000 years ago. Two major milestones of H. sapiens are the domestication of animals and the cultivation of crops.

18. a

19. d

20. c

21. a

22. c

23. d

24. c

25. a

26. a

27. Natural selection

28. Mosaic evolution

29. multiregional

Chapter 23

1. Ecological succession is the sequence of change of species over time in a community. Primary succession occurs on bare rock. Secondary succession occurs on disturbed land (old abandoned fields) where soil already exists.

2. The source of energy in an ecosystem is the sun. Producers capture the sun energy by photosynthesis and use it to produce sugars for energy. Consumers eat producers for energy. Decomposers get energy from dead consumers and producers, then release inorganic materials that can be reused by producers.

3. Roles in an ecosystem are

a. producers—photosynthetic organisms capable of using light energy to produce sugars.

b. primary consumers—eat the producers.

c. secondary consumers—eat the primary consumers.

d. decomposers eat dead producers and consumers and release inorganic materials that can be reused by producers.

4. A food chain is the successive series of organisms that energy (in the form of food) flows through in an ecosystem. Each organism in the series consumes the preceding one. It begins with the photosynthesizers and flows to herbivores and then to carnivores. The feeding relationships in a community are more realistically portrayed as a food web than as a food chain because an animal may feed at a number of different trophic levels. A food web describes all the interconnections in feeding and accounts for varied diets of animals.

5. One reason for energy loss between trophic levels is that roughly two-thirds of the energy in the food that is digested is used by that animal for cellular respiration. In addition, an animal must first expend energy to obtain its food, usually by grazing or hunting. Furthermore, not all the food available at a given trophic level is captured and consumed. Finally, some of the food eaten cannot be digested and is lost as feces. The energy in the indigestible material is unavailable to the next higher trophic level. However, the remaining energy can be converted to biomass and will be available to the next higher trophic level.

6. An energy pyramid is a graphical representation in which blocks represent the decreasing amount of energy available at each trophic (feeding) level. It is a pyramid shape because energy is lost with each transfer, so less energy is available at each successive level.

7. A pyramid of biomass is a diagram in which blocks represent the amount of biomass (dry body mass of organisms) available at each trophic (feeding) level. The biomass pyramid is similar to the energy pyramid in that the producers contribute the most biomass and the tertiary consumers produce the least.

8. Biological magnification is the tendency of a nondegradable chemical to become increasingly concentrated in the bodies of organisms as it passes along the food chain. Humans are the top carnivore. If there is biological magnification of a harmful substance, the substance will be highly concentrated in the animals we eat on the next lower trophic level.

9. More people could be fed if humans ate at a lower trophic level because only 10% of the energy is transferred from one level to the next. Thus, if humans began to eat one level lower on the food chain, about 10 times more energy would be available to them.

10. Describe the water cycle, the carbon cycle, the nitrogen cycle, and the phosphorus cycle.

a. The water cycle is the pathway of water as it falls as precipitation; collects in ponds, lakes, and seas; and returns to the atmosphere through evaporation.

b. The carbon cycle is the worldwide circulation of carbon from the carbon dioxide in air to the carbon in organic molecules of living organisms and back to the air. Carbon enters living systems when photosynthetic organisms use carbon dioxide (and oxygen) to produce organic materials. Carbon dioxide is formed again when the organic molecules are used by living organisms for cellular respiration.

c. The nitrogen cycle is the worldwide circulation of nitrogen from nonliving to living systems and back again. Atmospheric nitrogen (N2) cannot enter living systems. Nitrogenfixing bacteria living in nodules on the roots of leguminous plants convert N2 to ammonium (NH+), which is converted to nitrites (NO2-) and then to nitrates (NO3-) by nitrifying bacteria. The ammonium and nitrates are then available to plants to use in their proteins and nucleic acids. Next, the nitrogen is transferred to organisms that consume the plants.

Nitrates that are not assimilated into living organisms can be converted to nitrogen gas by denitrifying bacteria.

d. Phosphorus in the form of phosphates is washed from sedimentary rock by rainfall.

The dissolved phosphates are used by producers to produce important biological molecules, including DNA and ATP. When animals eat producers or other animals, phosphates are passed through the food webs. Decomposers release phosphates from dead organisms into the soil or water.

11. Humans are disturbing the water cycle by emptying aquifers, building dams, changing watersheds, and draining wetlands.

12. The human activities that are primarily responsible for the rising level of atmospheric carbon dioxide are burning fossil fuels and cutting down trees without replanting.

13. Biodiversity, the number and variety of living things, is being reduced dramatically, largely because of human activity. Most of the loss is occurring in the tropics and is due to habitat destruction. Two practical reasons for concern over the loss of biodiversity are that the disappearing species could have genes that would someday prove useful or that they could be found to produce chemicals with medicinal qualities.

14. a

15. b

16. niche

17. secondary consumer, carnivore

Chapter 24

1. A population's growth rate is its birth rate minus its death rate per 1000 individuals per year. Thus the growth rate of the world's population, an increase of 12 individuals per 1000, is 1.2%.

2. The age structure of a population is the number of males and females of each age in a population. The ages are often grouped into prereproductive, reproductive, and postreproductive categories. Generally, only individuals of reproductive age add to the size of the population. A population with a very large prereproductive age relative to the other groups will get larger in the future. The population with a large postreproductive group relative to the other groups will decline in size in the future. In a population that will remain stable in size, the categories are roughly equal in size.

3. Density-independent and density-dependent factors regulate population size.

a. Density-dependent factors are dependent on population size. Competition for food is a density-dependent factor.

b. Density-independent factors are not related to population size and include natural disasters such as fire and flood.

4. An ecological footprint is a measure of the impact a person or population makes on the environment. It is expressed as the total amount of biological productive land and water needed to produce and dispose of the products that are consumed. Calculation of an ecological footprint includes everything that is consumed and the corresponding waste removal. Thus, ecological footprints describe the burden placed on Earth's carrying capacity.

5. Overfarming and overgrazing can cause loss of topsoil, which results in desertification.

6. The carrying capacity of the environment is the number of individuals of a given species that a particular environment can support for a prolonged time period. The carrying capacity of the environment is determined by such factors as availability of resources, including food, water, and space; ability to clean away wastes; and predation pressure.

7. Deforestation is the removal of trees without replacement. Deforestation is occurring at an alarming rate in the tropical rain forests. The land is being used for growing crops to feed human populations and for logging.

8. Ozone in the upper atmosphere is helpful because it shields the earth from UV radiation. Ozone at low levels (in smog) can lead to breathing problems, irritated eyes, nose and throat. CFCs released into the atmosphere can destroy beneficial ozone in the stratosphere in a chemical reaction.

9. The greenhouse effect is a process in which greenhouse gases trap heat in the atmosphere. Examples of greenhouse gases include carbon dioxide and methane. The greenhouse effect could lead to a rise in temperatures throughout the world.

10. b

11. d

12. d