AP Biology Practice Test: Unit 3 — Cellular Energetics - High School Test Prep (2024)

Question 1

Question 1 Explanation:

The correct answer is (B). Typically, the rate of enzymatic reactions increases with temperature (up to a point), this is because increased temperature means increased energy means increased motion which makes for more frequent collisions of substrates with active sites. pH can have an impact on the functioning of an enzyme. For example, the stomach enzyme pepsin works best at a pH of about 1.5 and the enzyme trypsin, which acts in the small intestine, works best at a pH of about 8. Because enzymes are sensitive to their environment, certain chemicals can denature the protein, rendering it unable to perform its function. The amount of free energy in the cell does not affect the function of the enzyme.

Question 2

Question 2 Explanation:

The correct answer is (C). The binding of an effector to the allosteric site will change the shape of the active site (the site to which the substrate binds) allowing (or preventing) the substrate to attach.

Question 3

Question 3 Explanation:

The correct answer is (C). Enzymes work exclusively on specific substrates, based on their shape.

Question 4

Question 4 Explanation:

The correct answer is (D). Enzymes have a specialized area on the molecules called the active site, which bring substrates together for a chemical reaction to take place.

Question 5

Question 5 Explanation:

The correct answer is (D). Answers (A), (B) & (C) are catabolic because they result in the net release of energy with the end products being simpler than the input. Photosynthesis is an anabolic pathway since it results in the net gain of energy with the end products of the reaction being more complex than the input.

Question 6

Question 6 Explanation:

The correct answer is (C). Chemical energy is energy that is stored in chemicals. In the case of the battery, when the positive and negative terminals are connected so that electricity can flow between them, chemical reactions occur at the electrodes. The reactions release excess electrons at the anode which flow to the cathode.

Question 7

Question 7 Explanation:

The correct answer is (A). If chemical reactions occurred in a test tube, they would eventually reach chemical equilibrium. Systems with chemical equilibrium have a minimum amount of free energy, and therefore they cannot do any work, and will eventually die. This is a very important aspect of life: that metabolism as a whole is never at equilibrium.

Question 8

Questions 8–9

During the above reaction in glycolysis, which molecule acts as the oxidizing agent?

Question 8 Explanation:

The correct answer is (A). NAD⁺ is the oxidizing agent because it accepts electrons from glyceraldehyde-3-phosphate.

Question 9

In the same reaction above in glycolysis, which molecule acts as the reducing agent?

Question 9 Explanation:

The correct answer is (C). Glyceraldehyde-3-phosphate is the reducing agent because it donates electrons to NAD⁺.

Question 10

Question 10 Explanation:

The correct answer is (A). The Calvin Cycle can be broken down into 3 steps: (1) Carbon fixation, which incorporates each CO₂ molecule by attaching it to a 5-carbon sugar (ribulose-1,5-bisphosphate), (2) Reduction, where each molecule of 3-phosphoglycerate receives an additional phosphate group from ATP and hydrogen from NADPH forming glyceraldehyde-3-phosphate, and (3) Regeneration of the CO₂ acceptor (ribulose-1,5-bisphosphate). This all takes place in the stroma.

Question 11

Question 11 Explanation:

The correct answer is (D). The summary equation of photosynthesis is the reverse of that of cellular respiration. Carbon dioxide, plus water, plus energy in the form of light are converted to glucose and oxygen inside a chloroplast.

Question 12

Question 12 Explanation:

The correct answer is (C). Most plants appear to be green. This is because green light is reflected and not available to provide energy for photosynthesis.

Question 13

Question 13 Explanation:

The correct answer is (A). C₄ plants are given such a name because they preface the Calvin Cycle with an alternate mode of carbon fixation that forms a 4-carbon compound as its first product.

Question 14

Question 14 Explanation:

The correct answer is (D). The Calvin Cycle is a the process by which ATP and NADPH convert CO₂ to sugar in photosynthesis.

Question 15

Question 15 Explanation:

The correct answer is (B). Oxidative phosphorylation uses energy released by the electron transport chain to power ATP synthesis.

Question 16

Question 16 Explanation:

The correct answer is (A). Fermentation consists of glycolysis plus reactions that regenerate NAD⁺.

Question 17

Question 17 Explanation:

The correct answer is (B). Negative feedback is the most common type of regulation in which the accumulation of the end product slows the process of producing more.

Question 18

Question 18 Explanation:

The correct answer is (C). One way in which an animal adjusts to changes in their external environment within the normal range of homeostasis is known as acclimatization. Acclimatization is a temporary change.

Question 19

Question 19 Explanation:

The correct answer is (D). Conduction takes place when heat moves between two objects that are touching each other, such as a snake basking on a rock.

Question 20

Question 20 Explanation:

The correct answer is (D). Countercurrent exchange reduces heat loss when arteries carrying warm blood down the legs of waterfowl are in close contact with veins returning cold blood from cold lakes or ponds. This allows the heat from the blood in the arteries to warm the cold blood returning in the veins. When the blood from the veins reaches the body core, it is almost as warm as the body.

Question 21

Question 21 Explanation:

The correct answer is (A). The osmolarity of the body fluids of sea stars (starfish) conforms to that of marine waters in which they are found.

Question 22

Question 22 Explanation:

The correct answer is (C). When there is physical or emotional stress, nervous and hormonal responses trigger smooth muscles in arteriole walls to contract. This causes the arterioles to narrow, increasing blood pressure in the upstream arteries.

Question 23

Question 23 Explanation:

The correct answer is (C). Gravity provides the environmental cue signaling for the roots display positive gravitropism (growing downward) and the shoots to display negative gravitropism (growing upward). Photomorphogenesis describes the effects of sunlight on plant growth. Photoperiodism is the physiological response to a photoperiod (relative lengths of day and night), such as long-day and short-day plants. Thigmotropism is directional growth in response to touch, such as a vine wrapping its tendrils around another plant’s stem.