Cracking the AP Biology Exam


Answers and Explanations to the Chapter Quizzes


1. A Hydrogen bonds are weak-bond attractions between the positively polar hydrogen of one molecule and the negatively polar oxygen of another molecule.

2. C Two monosaccharides (or simple sugars) are linked together by a glycosidic bond.

3. B Two amino acids are held together by a peptide bond (CO–NH bond).

4. D Fats are composed of three fatty acids and one glycerol molecule. The bond that holds together one of the fatty acids to the glycerol molecules is called an ester bond.

5. E The amino group is a basic functional group (–NH2).

6. D There are only two major storage forms of carbohydrates, starch and glycogen. Starch is the storage form of sugars in plants. (E), Glycogen is the storage form of sugar in animals. (A), Cellulose is a structural component of the cell wall. (B) and (C), Maltose and fructose are monosaccharides.

7. D A change of one pH equals a tenfold change in hydrogen ion concentration. Therefore, if the pH changes from 8 to 10 (a pH change of 2), the resulting solution is 10 × 10, or 100 times more basic.

8. D In order for lactose to be hydrolyzed to glucose and galactose, a water molecule must be added. The other species—O2, H2, ATP, and NADH—will not hydrolyze lactose.

9. D Glycine is a simple amino acid, not a polymer. (A), (B), and (E), Starch, cellulose, and glycogen are all polymers of carbohydrates. (C), A polypeptide is a polymer of amino acids.

10. E A triglyceride (a fat) does not have a hydroxyl functional group. That’s because the hydroxyl groups from the glycerol molecule are involved in forming the bond that makes the triglyceride. (A), (B), (C), and (D), All of these organic compounds have a hydroxyl group.

11. D A polypeptide that consists of 90 amino acids has 89 peptide bonds. How do we know that? There is one peptide bond that holds one amino acid to another. If a molecule has three amino acids linked together then it has two peptide bonds. When you add water it will release two molecules of water. If a molecule has four amino acids linked together, it will release three molecules of water. See the trend? Now, if a polypeptide has 90 amino acids linked together, it will release 89 molecules of water, one per bond.

12. E Water has a high heat capacity, not a low one. (A), (B), (C), (D), Capillary action is the means by which water is pulled up from the roots to leaves. This process involves hydrogen bonding (which links polar molecules), cohesion, and adhesion.


1. E Protein synthesis involves the production of proteins. It begins in the nucleus where transcription occurs (the making of mRNA) and ends in the cytoplasm where the final protein is made. This is called translation. Translation requires a ribosome, which sometimes sits on the rough endoplasmic reticulum. When the appropriate amino acids are brought to the ribosome a polypeptide is formed. The Golgi bodies help to sort secreted proteins. The smooth endoplasmic reticulum is the site of lipid, not protein synthesis.

2. C Bacterial cells have a cell wall made up of peptidoglycan while animal cells don’t. (A) and (B), Both bacterial cells and animal cells have ribosomes and plasma membranes made of phospholipids. (D) and (E), Bacterial cells do not have nuclear membranes and vacuoles.

3. D Active transport requires ATP because it involves movement of materials against a concentration gradient. Materials can be transported across a plasma membrane in a variety of ways. For passive transport (diffusion), osmosis, and facilitated transport, materials move down a concentration gradient.

4. B Lysosomes contain digestive enzymes that destroy worn-out organelles.

5. A The smooth ER is a channel inside the cytoplasm that is the site of lipid synthesis. Lipids are nonprotein substances.

6. D Microtubules are polymers, made up of the protein tubulin, which participate in cellular division and movement and are found in cilia, flagella, and spindle fibers.

7. E The nucleolus is the site at which rRNA is formed.


1. B NADH is not reduced during lactic acid fermentation. NAD+ is a product of lactic acid fermentation. (A), (C), (D), and (E), During lactic acid fermentation, your body does not get enough oxygen, lactate and ATP are produced, and NAD+ is recycled.

2. C (E), Spontaneous reactions are those that occur without the input of energy. However, that doesn’t mean that they happen instantaneously. A spontaneous reaction could take days, or even years. (B) and (D), When a spontaneous reaction does occur, it releases energy, which can be used to do work. (A), That’s why the products contain less energy than the reactants.

3. D Enzymes operate under a narrow pH range. (A), Enzymes often work with coenzymes but these substances are not always needed. (B), Enzymes do not become hydrolyzed, that is, broken down in the presence of water during a chemical reaction. (C), They are not consumed in a reaction. (E), Enzymes are proteins. This means they are polymers of amino acids not carbohydrates.

4. C Don’t forget that oxygen is the final acceptor of electrons as they are passed down the electron chain. These electrons then combine with oxygen to produce water. (A), (D), and (E), Electrons are brought to the electron transport chain by carriers such as FADH2 and NADH. (B), Water is a by-product of the acceptance of electrons by free oxygen.

5. E The activity of an enzyme is influenced by a number of factors, pH, temperature, and concentration of substrates and enzymes. Water concentration has no effect on the enzyme since water is chemically neutral.

6. A Let’s use Process of Elimination. The starting materials in the reaction are glucose, oxygen, and water. This reaction represents the complete oxidation of glucose. That is, aerobic respiration. This means you can eliminate photosynthesis (it produces glucose) and anaerobic respiration (it doesn’t use oxygen). (C), Glycolysis is only part of aerobic respiration. It produces pyruvic acid. (D), Finally, fermentation produces lactic acid or ethanol, neither of which is represented in the equation.

7. C Glycolysis is not considered an aerobic process because it does not require oxygen. Glycolysis is therefore an anaerobic process. The Krebs cycle, formation of acetyl CoA, the electron transport chain, and oxidative phosphorylation are all stages within aerobic respiration that require oxygen.

8. C Since CO2, H2O, and ATP are produced, the muscle cell undergoes aerobic respiration. Aerobic respiration occurs first in the cytoplasm, then in the mitochondrion.

9. C Prokaryotes carry out oxidative phosphorylation in their plasma membranes. (A) and (E), They do not contain membrane-bound organelles or a nuclear membrane. (B), The cell wall is not involved in oxidative phosphorylation. (D), Ribosomes are the sites of protein synthesis.

10. C FAD+ is both an electron and hydrogen carrier in the Krebs cycle. It shuttles electrons (along with some hydrogens) to the electron transport chain. When it is oxidized it becomes FAD+.

11. B There are two types of fermentation, alcoholic and lactic acid fermentation.

12. A During glycolysis, the final product is pyruvic acid, which is also known as pyruvate.

13. D During oxidative phosphorylation, ATP is produced when hydrogen ions cross a special protein channel called ATP synthase (also known as ATP synthetase).

14. E Cofactors as well as coenzymes can assist enzymes during chemical reactions.


1. E Carbon dioxide is used to make glucose in the dark reaction. All of the other statements are true concerning the light reaction. (A), All pigments, including the antennae pigments, are capable of capturing sunlight. (B) and (D), These pigments send energy to the reaction center (which in photosystem II is P680), where electrons are activated and eventually passed down an electron transport chain. (C), During photosynthesis, sunlight energy is converted to chemical energy.

2. A As electrons are passed down the electron transport chain, they eventually combine with an electron carrier to form NADPH. (B), ATP is produced in photosystem II. (C), Cytochromes are carriers that are involved in passing electrons down a chain. (D), Water is not produced during the electron transport chain. (E), Glucose is the final product of photosynthesis. It is not produced during the light reaction.

3. C During noncyclic phosphorylation, both ATP and NADPH are produced, whereas in cyclic phosphorylation, only ATP is produced. (A) and (D), Light is absorbed and electrons are passed along the electron transport chain in both reactions.

4. B Use Process of Elimination. Since sunlight is part of the reaction, we can eliminate the electron transport system (E), Calvin cycle (D), and glycolysis (C). (A), In photosystem I, only sunlight and ADP are required. Photosystem II requires water, since water is split during this reaction.

5. D C4 is an alternate pathway to produce glucose. It is common among tropical plants and results in a higher rate of photosynthesis than in C3 plants. (A), There are no special pigments involved in the dark reaction in photosynthesis. (B), C4 plants do not use oxygen instead of carbon to make glucose. (C), C3 plants fix carbon days and nights. (E), This statement is incorrect because C4 plants are better adapted to intense sunlight.

6. A The dark reaction and its enzymes are found in the stroma of the leaf.

7. B The thylakoids are the site of photophosphorylation.

8. E Ribulose bisphosphate is a 5-carbon molecule that combines with carbon dioxide in the Calvin cycle.

9. E Ribulose bisphosphate is the molecule that accepts carbon dioxide during the Calvin cycle. Don’t forget you can use an answer choice more than once.


1. B Transcription involves the production of mRNA. This occurs in the nucleus. (A) and (E) are both incorrect because the mitochondria and lysosomes are organelles that have nothing to do with translation. (C) and (D), Ribosomes and the Golgi apparatus are both involved in translation—the production of proteins.

2. B Use Process of Elimination. A phenotypic expression refers to traits. The sequence must therefore end with trait. That means we can eliminate (D) and (E). The question begins with genes, which are segments of a chromosome. The sequence must therefore begin with DNA.

3. E Both DNA and RNA contain a phosphate group, a nitrogenous base, and a five-carbon sugar. However, the sugar in RNA (ribonucleic acid) is ribose, whereas the sugar in DNA (deoxyribonucleic acid) is deoxyribose. The nitrogenous bases adenine, guanine, and cytosine are found in both DNA and RNA; thymine is found only in DNA, and uracil is found only in RNA.

4. C If an mRNA codon is UAC, the complementary segment on a tRNA anticodon is AUG.

5. D During posttranslational modification, the polypeptide undergoes a conformational change (secondary, tertiary, or quaternary structure). (A) and (B) are incorrect because they refer to posttranscriptional modification—changes that occur once the mRNA molecule is formed. (C) is incorrect because formation of peptide bonds occurs during translation. (E) is incorrect because amino acids are not made during translation.

6. C RNA polymerase does not participate in DNA replication. It is used during RNA synthesis to bring RNA nucleotides to the sense strand in DNA. (A), DNA helicase is used to unwind the double helix during DNA replication. (B), DNA polymerase is the enzyme that brings DNA nucleotides to each DNA strand. (D), RNA primase is the enzyme that initiates the process of DNA replication. (E), DNA ligase links the Okazaki fragments during DNA replication.

7. B Since three nucleotides make up one amino acid, seven amino acids would be incorporated into the polypeptide.

8. B Transposons are DNA segments that move around.

9. C The lagging strand is assembled in discrete nucleotide segments known as Okazaki fragments. This strand is made discontinuously.

10. C Notice how the same answer can be used twice, two slightly different questions refer to the same choice, the lagging strand.

11. E hnRNA is the precursor of mRNA. The discontinuous stretches of DNA are the Okazaki fragments.


1. B A diploid cell contains twice the number of chromosomes as a haploid cell. If the diploid number is 24 then the haploid number is 12.

2. B During the first half of meiosis I, the homologous chromosomes lie adjacent to each other. This is called synapsis. (A), Crossing-over refers to the exchange of segments of DNA. (C), A tetrad refers to two homologous chromosomes that are attached to each other. (D), Cytokinesis refers to the distribution of cytoplasm to the two daughter cells. (E), Interphase is the stage during which chromosomes replicate.

3. E During meiosis, there are two rounds of all the same stages as mitosis except interphase. Why? Because the chromosomes do not replicate again.

4. B Sister chromatids disjoin (separate) during meiosis II. All other events occur during meiosis I.

5. B The genetic material is called chromatin during interphase. It is not visible.

6. E Chromosomes are replicated during the S phase of the cell cycle.

7. C The centromere is the structure that holds the chromatids together.

8. D Centrioles are contained within microtubule organizing centers.

9. A During G2 more proteins are made.


1. C Hybrids are organisms that have one of each allele, Ss. When two hybrids cross the offspring are SS, Ss, Ss, and ss. Therefore the percent of the offspring that will possess the same genotype as their parents is 50 percent.

2. B This question is a bit tricky. In the chapter we discussed two independently assorting traits, such as AB or ab. This question is asking about three independently assorting traits. The first thing to do is to write out the gametes that are possible. They are, ABC, ABc, AbC, Abc, aBC, aBc, abC, and abc. Notice that only one out of the eight gametes is recessive. Another way to do this problem is to use this equation, x = 2n, where n represents the number of independently assorting traits. In our example, for three traits, there are 23 = 8 gametes produced. For four independently assorting traits, there are 24 =16 gametes. In all of these examples, the number of gametes that are recessive is always 1. Therefore, for three independently assorting traits, 1 out of 8 is recessive.

3. E Sex-linked traits are traits that almost always exist on the X chromosome. They are therefore often passed from mother to son since sons must receive the X chromosome from their mothers. (A), Many traits can skip a generation. (B), Some diseases that have carriers are not sex-linked. (C), Just because a trait appears in all the offspring, it doesn’t necessarily mean that the trait is sex-linked. (D), Sex-linked traits do not necessarily have to be passed from mothers to daughters. Daughters can inherit a good X from their fathers.

4. C The total number of offspring produced is 400. The number of offspring that exhibit the recessive trait is 81. This means that roughly 25 percent of the offspring show the recessive trait. Do a Punnett square to determine the genotype of the parents, Bb × Bb = BB, Bb, Bb, and bb. This would yield phenotypes in approximately the proportions described above (3,1).

5. A Use the product rule to solve this problem, (1/2)(1/2)(1/2) = 1/8.

6. C When two different alleles are present in regard to a trait, the organism is a heterozygote.

7. A The physical appearance of an organism is called the phenotype. In contrast, the genetic makeup is called the genotype.

8. B When two different alleles are both expressed, this is an example of codominance.

9. D A dihybrid cross is a cross that involves two traits that are independently assorting, such as tall, green pea plants versus short, yellow pea plants.


1. A Use Process of Elimination. This organism has a nucleus, so we can eliminate bacteria (E). It has a cell wall, so we can eliminate animals (D). It is photosynthetic, so we can eliminate fungi (B). It is unicellular. Therefore, we can eliminate plants (C).

2. D Arthropods have the following characteristics, They have segmented bodies, a chitinous exoskeleton, jointed appendages, and an open circulatory system. (A) and (B), Only insects have wings.

3. A Once again, use Process of Elimination to arrive at your answer. The organism is unicellular, so we can eliminate animals and plants, (D) and (E). The organism is a eukaryote, so we can eliminate Monera, (B). It has threadlike branches and a chitinous cell wall—it’s a fungus.

4. D Review the excretory systems of animals. Earthworms excrete nitrogenous waste via nephridia. Insects use special structures call Malpighian tubules. Fish and amphibians have kidneys. Flatworms have flame cells. Notice we didn’t mention flame cells in this chapter, but you could still arrive at the right answer using Process of Elimination.

5. B Review the characteristics of vertebrates. Vertebrates include the following organisms, fish, amphibians, reptiles, birds, and mammals. Arthropods are invertebrates.

6. C Fungi are not photosynthetic. Think about your average mushroom. They live off dead organisms. Fungi are eukaryotes that reproduce sexually (the fusion of gametes) and asexually (via spores). They require oxygen and have cell walls.

7. A This is an example of a mutualistic relationship. Both organisms benefit. (C), Commensalism means that one organism benefits and one is unaffected. (B), Parasitism means that one organism benefits and the other is harmed. (E), Tropism is a type of behavior in plants, such as phototropism. (D), Competition occurs when two individuals or species compete for the same resources.

8. C Viruses are microorganisms that contain nucleic acid (either DNA or RNA) and a protein coat. They do not contain a nuclear membrane, a cell wall, or organelles.

9. A Conjugation is the exchange of genetic material via a pilus.

10. B When a virus transfers DNA from one bacterium to another, it is called transduction.

11. D A plasmid is a small circular DNA that carries genes separate from the main bacterial DNA.

12. C Transformation involves the incorporation of naked DNA segments.


1. D Use Process of Elimination. Dicots are angiosperms that have two cotyledons, netted veins, and flower parts in multiples of four and five. We can therefore eliminate (B) and (C). Since dicots are flowering plants, they have vascular tissue. We can therefore eliminate (A). The cotyledon provides nutrition for the plant, so we can eliminate (E).

2. D Conifers, which are gymnosperms, and flowering plants, which are angiosperms, both contain seeds. The other characteristics listed are only true for gymnosperms. Gymnosperms are perennials (live year after year), contain xylem that is dead (the rings of trees), and are deciduous (they have leaves that shed). Only some angiosperms are woody plants.

3. D The anther is the male part of the flower. The pistil is the female part of flowering plants. It consists of the ovule, style, ovary (which contains the female gametes), and the stigma (the sticky portion that traps pollen grains).

4. D The plant tissue that gives girth to a plant is called the lateral meristem. It is subdivided into the vascular cambium and the cork cambium.

5. C Carnivorous plants are capable of obtaining proteins by trapping flying insects. They therefore would thrive in nitrogen-poor environments.

6. B Tracheophytes are vascular plants. This means they include trees, grass, corn, and beans. Mosses are bryophytes; they lack true stems and roots.

7. D Ethylene is the hormone responsible for ripening fruits. (A), Auxins promote growth in plants and cause them to bend toward light. (C), Gibberellins cause dwarf plants to grow. (E), Abscisic acids inhibit leaves from falling and promote bud and seed dormancy. (B), Cytokinins promote cell division and differentiation.

8. B The bending of plants toward light is called phototropism.

9. D When a Venus flytrap responds to touch, it exhibits thigmotropism.

10. A The pigment phytochrome is involved in regulating sexual reproduction in plants.

11. E Gravitropism refers to growth in plants in response to gravity.

12. C Photoperiodism is the process by which flowering plants are affected by day length.



1. B Within the small intestine there are lacteals, the job of which is to absorb digested fats. (A), The nephrons are the excretory units in the kidneys. (C), Lacteals are found within villi. (D), Root hairs are tiny structures that absorb water and minerals in plants. They also increase the surface area for absorption. (E), Hormones are substances that travel in the blood.

2. B The enzyme that initially breaks down protein in the stomach is pepsin. (A), Bile is not an enzyme; it emulsifies fats. (C), Trypsin breaks down proteins later on; it is active in the small intestine. (D) and (E), Salivary amylase and pancreatic amylase break down carbohydrates.

3. B Enzymes that digest fats are called lipase. (A, Bile isn’t an enzyme; it emulsifies fats. (C) and (E), Trypsin digests proteins in the small intestine, and amylase digests carbohydrates. Now you’re down to two answer choices. You may not know what proteases are, but you should know that lipase digests fats. By the way, proteases are enzymes that digest proteins. Again, you didn’t necessarily have to know that for this question.

4. D The pancreatic duct carries trypsin and chymotrypsin, among other enzymes, to the small intestine.

5. C Bile is made in the liver and stored in the gall bladder.

6. B Complete digestion of food occurs in the small intestine.

7. E The function of the large intestine is to reabsorb water.


1. E All of the following cause oxygen and carbon dioxide to undergo exchange between the lungs and bloodstream EXCEPT the higher PO2 of blood entering the lungs. Blood entering the lungs is oxygen-poor therefore it has a lower PO2. (A), Differences in partial pressure gradients of alveolus wall and wall of surrounding capillaries allow for gas exchange. (B), The spongy, moist epithelium of the lungs allow for gas exchange. (C), the capillaries surrounding the alveoli allow for gas exchange. (D), The thin, epithelia of the alveoli allow for gas exchange.

2. E Underwater swimmers hyperventilate before going under water and take deep rapid breathes in order to (D), blow off carbon dioxide, which (A), increases the oxygen content of the blood, which (B), decreases the urge to breathe, and (C), decreases the pH of the blood. (E), Hyperventilating decreases not increases the carbon dioxide content of alveoli air.

3. A The diaphragm is the skeletal muscle that forms the bottom wall of the chest cavity.

4. C Alveoli are dead-end sacs that allow for gas exchange.

5. D The bronchioles are air ducts covered by cilia and mucus.

6. E The trachea is surrounded by C-shaped rings of cartilage.


1. C The blood component responsible for blood coagulation is platelets. (A), Erythrocytes are red blood cells that carry oxygen. (B), Leukocytes are white blood cells that fight infection. (D), Lymphocytes are immune cells that include T and B cells. (E), Plasma is the liquid portion of blood.

2. C There are four blood types, A, B, AB, and O. Blood type O is the universal donor, and AB is the universal recipient. Individuals with blood type AB can receive blood from all of the other blood groups without any blood clotting.

3. E Carbon dioxide can travel in the bloodstream in many forms. It can mix with water and form carbonic acid. It can also attach to hemoglobin in red blood cells. (E), Platelets, on the other hand, are cell fragments that are involved in blood clotting.

4. C Blood leaves the right ventricle and enters the lungs via the pulmonary arteries.

5. A When blood returns from the body, it enters the right atrium via the vena cava.

6. E The vena cava is the vessel that sends blood to the right atrium.


1. D All of the following statements about lymph are true except that it found within the capillaries of the lymphatic system not cardiovascular system. (A), Lymph is fluid that is returned to the blood. (B), Lymph is derived from interstitial fluid. (C), Lymph does diffuse into tiny lymph capillaries from capillaries in the cardiovascular system. (E), Lymph contains phagocytes which kill harmful materials in the lymph.

2. B B lymphocytes responding to the HIV surface antigens will release antibodies. (A), Proteolytic enzymes are produced by the pancreas and small intestine. (C), T lymphocytes, include helper T cells and cytotoxic T cells, are responsible for cell-mediated response. (D), Macrophages are antigen-presenting cells that are capable of ingesting and digesting bacteria. (E), B lymphocytes do not destroy body cells infected by the HIV virus.

3. E Use Process of Elimination. We know that immune cells are made in the bone marrow, so we can eliminate (B). We also know that immune cells are found in the lymph vessels, so eliminate (C). T-cells mature in the thymus, so we can eliminate (A). If you’re not sure about the spleen, skip it and look at answer choice (E). The kidney has nothing to do with the immune system. Therefore the answer is (E). By the way, the spleen also contains lymphocytes. Notice that you didn’t have to know that to get the question right.

4. E MHC markers are cell surface proteins that distinguish self from nonself.

5. B Complement proteins can be activated against any antigen and are nonspecific.

6. C Inflammatory response is the body’s reaction to pathogen invasion or physical injury.


1. C Compared to the human kidney, the kangaroo rat’s kidney is capable of producing more concentrated urine because its kidney allows the longer loop of Henle to move more water into the interstitial fluid. Based on the diagram there is no information that (A), more filtrate is reabsorbed in the proximal convoluted tubule, (B), the glomerulus filters the blood more rapidly (D), the rat’s kidney produces uric acid instead of urea since all mammals produce urea, or that (E), it contains more nephrons. The difference in the two nephrons is the longer length of the loop of Henle and collecting duct.

2. B The bladder is the structure that expands as it stores urine.

3. C The urethra is the structure through which urine leaves the bladder.

4. A The ureter is the structure that carries the urine from the kidney to bladder.

5. E ADH is the hormone that controls the rate of water reabsorption in the kidney.

6. B The substances that would not filter through the glomerulus into the Bowman’s capsule are proteins. Only small substances such as (A), monosaccharides; (C), water; (D), salts; or (E), ions would pass into the Bowman’s capsule.


1. E Voltage-gated Na+ and K+ channels are concentrated at the nodes of Ranvier because myelin speeds up the action of action potentials. (A), As K+ ions move out of the axon it inactivates Na+ gates of sodium channels during an action potential. (B), It does not release neurotransmitters into the synapse. Neurotransmitters are released by the axon bulb. (C), Myelin does not completely insulate the axon of neurons. The nodes of Ranvier are not covered. (D), It speeds up, not slows down the conduction of nerve impulses.

2. C The medulla oblongata controls many vital functions such as heartbeat, respiration and blood pressure.

3. D The cerebellum integrates simple motor responses as it coordinates movements.

4. B The spinal cord is the reflex center for muscular coordination.

5. A The cerebral cortex is composed of gray matter.

6. A The cerebral cortex is the most complex part of the mammalian brain.


1. C The flow of calcium into cells is essential to skeletal muscle contraction. Calcium ions are released form the sarcoplasmic reticulum. (A), Activation of pepsin is caused by HCl and other enzymes in the stomach. (B), The thyroid hormone is released by the thyroid. (D), Urine concentration is caused by the loop of Henle, ADH and the collecting duct. (E), Depolarization is caused by the influx of sodium ions into the axon.

2. D All of the following substances are involved in bone remodeling EXCEPT thyroxine which increase metabolic rate. (A), Vitamin D provides calcium for bones (B), Parathyroid hormone regulates calcium and phosphate metabolism. (C), Calcitonin lowers calcium levels in the blood. (E), Osteoclasts are bone cells involved in breaking down bones.

3. B Use Process of Elimination again. Smooth muscle cells are slow contracting, so eliminate answer choices (A), (C), and (E). They are under involuntary control, so the answer must be (B).

4. C Ligaments connect bone to bone.

5. B Tendons connect muscle to bone.

6. A Cartilage is the embryonic tissue in the skeletal system.

7. E Bone is made up of collagen (a protein) and calcium (mineral). Calcium is the mineral that hardens the bones.


1. D Increased levels of vasopressin would most likely not be observed because it is secreted by the posterior pituitary. Two of the other hormones (ACTH and Growth hormone) are released by the anterior pituitary while glucocorticoids and thyroxine are released by the adrenal cortex and thyroid respectively.

2. C High levels of hypothalamic and pituitary secretions would be found in people who are under stress. The only individual listed that is not under some form of stress is a resting infant.

3. D Oxytocin is the hormone that causes uterine contractions during labor. (A) and (B), FSH and LH are hormones that are involved in the menstrual cycle. (C), Prolactin promotes the production of milk in mammary glands. (E), Epinephrine is the hormone involved in flight/fight responses.

4. D The hypothalamus is the part of the brain that regulates the pituitary gland and produces neurosecretory hormones. (A) and (B), TSH and LH are hormones secreted by the anterior pituitary. (C), The hypothalamus is not an extension of the pituitary gland. (E), It secretes hormones, not neurotransmitters.

5. B Diabetics have too much sugar in their blood. This means they are not storing the sugar. Some diabetics lack insulin, which is why they take insulin shots. (A), Glucagon is the hormone antagonistic to insulin. (C), Parathyroid hormone regulates calcium in the blood. (D), Calcitonin lowers blood calcium levels. (E), Norepinephrine regulates fight/flight responses.


1. A The process that produces embryonic germ layers is gastrulation. (B), Cleavage is the mitotic division of the zygote after fertilization. (C), Blastulation is the hollow ball of cells produced by cleavage of a fertilized ovum. (D), Organogenesis is the process by which organs develop. (E), Fertilization is the fusion of two gametes.

2. C Cleavage is a series of rapid mitotic not meiotic divisions. (A), The infolding and clustering of cells leading to the formation of the notochord occurs during organogenesis. (B), Induction is the influence of embryonic cells in the differentiation of neighboring cells. (D), Gastrulation is the movement of embryonic cells from the surface of the embryo to an interior location. (E), The development of extraembryonic membranes occurs following gastrulation.

3. E The pancreas is derived from the endoderm. (A), The epidermis of skin is derived from the ectoderm. (B), (C), and (D), The muscular system, skeletal system, and stomach are derived from the mesoderm.

4. B The reduction of the cell size is most likely due to decreases in the amount of cytoplasm in each cell since the embryo does not enlarge during this stage. (A), The embryo does not suffer a loss of DNA. (C), Feedback inhibition is not responsible for the reduction in cell size. (D), The cells within the zygote are diploid not haploid. (E), The formation of the blastocyst occurs after cleavage and does not affect cell size.

5. E Sperms are produced in the seminiferous tubules.

6. C The seminal vesicles secrete a fructose-rich fluid that serves as an energy source for sperm.

7. A The interstitial cells produce male sex hormones.

8. C The extraembryonic membrane that stores wastes is the allantois. (A), The chorion is the outermost membrane that surrounds all the other membranes. (B), The amnion forms a sac that protects the embryo. (D) and (E), The yolk sac provides food for the embryo, and the eggshell is the hard covering.

9. E The germ line cells are also called gametes.

10. B The blastocoel in the fluid-filled cavity that forms during blastula.

11. A When a sperm and an egg unite, they form a zygote.

12. C Morula is the first stage after cleavage during morphogenesis.


1. C Genetic variability is usually due to a mutation during meiosis (sexual reproduction). Answer choices (A), (B), (D), and (E) are all examples of asexual reproduction. They create identical offspring.

2. C We mentioned that one way to get genetic variability is by mutations. Mutations are not irreversible. They can revert (or back mutate). (B) and (E), Mutations are not common (there are low rates) in a population. (D), Mutations can influence any gene locus in a population.

3. A When the extremes are eliminated in a population, this is called stabilizing selection.

4. E When the extremes are favored over the intermediates, this is called disruptive selection.

5. A When the intermediates are favored over the extreme phenotypes, this is once again called stabilizing selection.

6. B When one extreme is favored in a population, this is called directional selection.

7. D When organisms are isolated from other members of their species by a geographical barrier, it is called allopatric speciation.

8. A This is an example of use and disuse. The muscle mass increases because of exercise.

9. B When a change occurs in a population that confers a benefit on some members of that population, increasing their likelihood of survival, this is called natural selection.

10. D The study of the geographical distribution of living organisms is called biogeography.

11. E This is the study of life based on fossils and footprints.


1. C Gravitropism refers to a plant’s response to gravity. (A), Hydrotropism refers to a plant’s response to water. (B), Chemotropism refers to a plant’s response to a chemical substance. (D), Thigmotropism refers to a plant’s response to touch. (E), Circadian rhythm refers to a behavioral rhythm with a period of about 24 hours.

2. E The two systems that regulate behavior and how we respond to our environment are the nervous system (that’s our immediate response) and the endocrine system (that’s our slow response). The excretory, reproductive, and digestive systems do not directly regulate any behavioral responses.

3. C Plants are producers and can convert light energy to chemical energy.

4. A The animal with the smallest biomass is at the top of the pyramid. Therefore, birds have the smallest biomass.

5. E A secondary consumer feeds on a primary consumer, which feeds on producers. Based on the food chain, the secondary consumers are mice.

6. B The part of the earth in which life exists is called the biosphere.

7. B Fungi and bacteria both serve as decomposers. They break down organic matter. Viruses invade other organisms, but they’re not decomposers. Protists are unicellular organisms, such as paramecium and euglena. They’re not decomposers either.

8. A A stickleback fish will attack another fish if it has a red belly (or if an object has a similar red mark). This is an act of aggression that is innate.

9. B A blue jay avoids eating a particular type of butterfly because it “remembers” the initial unpleasant taste it had from a previous exposure.

10. E The chimpanzee has figured out on its own how to get those bananas from the ceiling. This is called insight learning.

11. B The biome at the highest latitude is the tundra—the cold, treeless region.

12. A The biome with evergreen trees (conifers) is the taiga.

13. B This biome has little vegetation (mainly grass).

14. D This biome has the most diverse plant life.