AP Biology Study Guide
Unit 3
Metabolism
1. Explain the role of catabolic and anabolic pathways in cellular metabolism.
● Catabolic pathways break down macromolecules into forms to be used in our body by breaking the bonds
between the monomers of those macromolecules, releasing energy.
● Anabolic pathways use those broken down molecules produced by catabolism to rearrange them into
usable forms for the body by using kinetic energy to form new chemical bonds between the monomers.
2. Explain the first and second laws of thermodynamics in your own words.
● 1st law - energy cannot be created nor destroyed, only transformed
● 2nd law - energy transformation increases the entropy of universe
3. Explain why highly ordered living organisms do not violate the second law of thermodynamics.
● Even though cells create organized structures by taking in less organized starting materials, the organisms
eat, so the catabolic reactions turn complex molecules into simpler ones. As they use that energy, they
release by products such as CO2 and H2O, which in turn increases energy.
4. Describe the function of enzymes in biological systems.
● Enzymes decrease the activation energy for a chemical reaction to occur, allowing chemical reactions to
occur more quickly in biological systems.
5. Explain how enzyme structure determines enzyme specificity.
● Enzymes are proteins. The folding and arrangement of protein R groups determine the structure and
function of proteins, therefore influencing the structure and function of enzyme specificity.
6. Explain the induced-fit model of enzyme function.
● Active site - where the substrate binds to the enzyme
● Induced fit allows enzymes to change the shape of their active site to allow the substrate to bind better by
bringing chemical groups of the active site into positions that enhance their ability to catalyze the
chemical reaction.
7. Describe the mechanisms by which enzymes lower activation energy.
● Enzymes catalyze reactions by lowering the activation energy to allow reactants to absorb enough energy
to reach the transition state at normal conditions
8. Explain how substrate concentration affects the rate of an enzyme-catalyzed reaction.
● With a higher substrate concentration, more products are formed through enzyme-catalyzed reactions.
9. Explain how temperature, pH, cofactors, and enzyme inhibitors can affect enzyme activity.
● Enzyme activity typically increases with the temperature until it reaches optimal temperature. After it
reaches optimal temperature, it begins to denature.
● Same with pH - the optimal pH increases enzyme activity, but a pH that is too low or too high will cause
the enzyme to denature.
● Competitive inhibitors reduce enzyme activity by blocking the active site
●
●
Noncompetitive inhibitors bind to the allosteric site, changing the shape of the active site, preventing
substrates from binding
Allosteric inhibitors allow the substrate to bind to the allosteric site to stabilize the enzyme shape so that
the active sites are closed (inactive form)
Photosynthesis
1. Describe the structure of a chloroplast, listing all membranes and compartments.
● Stroma- aqueous fluid within the double membrane
○ Thylakoids - membrane system houses the chlorophyll
○ Grana (stacks of thylakoids)
○ Chlorophyll (pigment used in photosynthesis - inside the thylakoid membranes)
2. Describe the two main stages of photosynthesis in general terms.
● Light reactions - electrons become excited in PS II, move through an electron transport chain (linear
electron flow) through photosystem II, and supplying electrons to the Calvin cycle, producing oxygen,
ATP, and NADPH in the process.
● Calvin cycle - occurs in three phases (carbon fixation, reduction, and regeneration) uses ATP and NADH to
reduce carbon dioxide to glucose. This is cyclic electron flow - Calvin cycle recycles 5 PGAL molecules to
regenerate 3 RuBP to accept more carbon dioxide to start the process over. Also produces more electron
carriers to use in the light reactions (ADP + NADH+)
3. Explain how carotenoids protect the cell from damage by light.
● Carotenoids are accessory pigments that broaden the spectrum of colors that drive photosynthesis.
● Photoprotection - they can absorb and dissipate excessive light that could damage chlorophyll or interact
with oxygen to form reactive oxidative molecules to damage the cell.
4. List the wavelengths of light that are most effective for photosynthesis.
● 380 nm - 750 nm
● Violet blue + red light
5. List the components of a photosystem and explain the function of each component.
● Reaction center - complex of proteins holding a pair of chlorophyll a molecules and an electron acceptor
● Light capturing complexes - pigments (Chlorophyll a, b and carotenoids) associated with proteins, which
serve as the antennas for the reaction centers
● There are 2 photosystems
○ Photosystem II absorbs light at 680 nm + produces ATP
○ Photosystem I absorbs light at 700 nm + produces NADPH
6. State the function of each of the three phases of the Calvin cycle (carbon fixation, reduction, regeneration of
RuBP)
● Carbon fixation - altering carbon in a way that is useful for the cycle
● Reduction ● Regeneration of RuBP 7. Describe the role of ATP and NADPH in the Calvin cycle.
● ATP -
●
NADPH -
8. Trace the movement of electrons in linear electron flow. Trace the movement of electrons in cyclic electron
flow.
9. Describe what happens to rubisco when O2 concentration is much higher than CO2
concentration.
10. Describe the major consequences of photorespiration.
11. Describe two important photosynthetic adaptations that minimize photorespiration.
12. Compare and contrast the light reactions and the calvin cycle.
Cellular Respiration
1. In general terms, distinguish between fermentation and cellular respiration.
2. Define oxidation and reduction.
3. Explain in general terms how redox reactions are involved in energy exchanges.
4. Describe the role of NAD+ in cellular respiration.
5. In general terms, explain the role of the electron transport chain in cellular respiration. 6. Name the three stages
of cellular respiration and state the region of the eukaryotic cell where each stage occurs.
7. Describe how the carbon skeleton of glucose changes as it proceeds through glycolysis.
8. Explain why ATP is required for the preparatory steps of glycolysis.
9. Describe where pyruvate is oxidized to acetyl CoA, what molecules are produced, and how this process links
glycolysis to the citric acid cycle.
10. List the products of the citric acid cycle. Explain why it is called a cycle.
11. Describe the point at which glucose is completely oxidized during cellular respiration
12. Summarize the net ATP yield from the oxidation of a glucose molecule.
13. Compare the processes of fermentation and cellular respiration.
14. Distinguish between obligate and facultative anaerobes.