AP Bio Unit 3 Study Guide

9. Why is ATP the common energy source for organisms?

Because the bonds between the phosphates are very high energy and so breaking them releases a lot of energy and its energy can be easily transferred to do cellular work. ATP can also be easily broken down.

19. Oxygen is a byproduct of the light dependent reaction in photosynthesis. What compound is oxidized, releasing oxygen?

Water is oxidized in photosynthesis which releases oxygen (see number 17).

1. Define chemiosmosis and describe where and when it happens in photosynthesis and cell respiration.

1. Define chemiosmosis and describe where and when it happens in photosynthesis and cell respiration. Chemiosmosis is the movement of ions by diffusion across a semipermeable membrane. In photosynthesis, chemiosmosis occurs in the light-dependent reactions. The hydrogen ions in the thylakoid space form an electrochemical gradient and are moved down their electrochemical gradient through ATP synthase in the chloroplasts, which creates the energy needed to create ATP through photophosphorylation. In cellular respiration, chemiosmosis is used in the mitochondria. During chemiosmosis, the free energy from the reactions that make up the electron transport chain is used to pump hydrogen ions across the membrane (establishing an electrochemical gradient). The hydrogen ions are pumped through ATP synthase, and as they move through ATP synthase ADp is turned into ATP, known as oxidative phosphorylation.

21. What process do aerobic and anaerobic respiration have in common?

Aerobic and anaerobic respiration have glycolysis in common. Glycolysis can occur without oxygen but takes place in both aerobic and anaerobic respiration. After glycolysis, aerobic respiration occurs in the mitochondria of eukaryotes and cytoplasm of prokaryotes, while anaerobic respiration only occurs in the cytoplasm of a cell.

20. What is the difference between aerobic and anaerobic respiration?

Aerobic respiration takes place with oxygen and anaerobic respiration takes place without oxygen. In aerobic respiration, the final electron acceptor on the electron transport chain is oxygen, and in anaerobic respiration the final electron acceptor on the electron transport chain is an inorganic molecule other than oxygen. This makes aerobic reception more effective because the double bond in oxygen has higher energy than other bonds which helps to produce ATPs more quickly. Aerobic respiration equation: C6H12O6 + 602 -> 6CO2 +6H2O + energy Anaerobic respiration equation: C6H12O6 -> C2H5OH + CO2 + energy

6. What are the products of photosynthesis?

C6H12O6+O2+H2O

5. What are the reactants required to start photosynthesis?

CO2+H2O

11. What three characteristics of enzymes make them efficient?

Enzymes have a tertiary structure, which allows them to stabilize a temporary association between substrates. Because the enzyme itself is not changed or consumed in the reaction, only a small amount is needed and they can be reused. Activators, higher temperatures, more enzyme/more substrate concentration, and the right pH can all make enzymes more efficient.

8. What electron acceptor transfers electrons from Krebs cycle to the electron transport Chain?

FAD (becomes FADH2) and NADH transfer electrons from the Krebs cycle to the electron transport chain.

18. Describe glycolysis - reactants and products

Glycolysis is a series of reactions that extract energy from glucose by splitting it into two 2-carbon molecules called pyruvates. Glycolysis takes place in the cytosol of a cell and it has two phases- an energy-requiring phase and an energy-releasing phase. The reactant is glucose. In the energy-requiring phase, the starting molecule of glucose gets rearranged and two phosphate groups are attached it, which make the modified sugar unstable and make it split in half, forming two phosphate-bearing 3-carbon sugars. This uses up 2 ATP molecules as well. In the energy-releasing phase, each 3-carbon sugar is converted into another 3-carbon molecule, pyruvate, in a series of reactions that produce 2 ATP molecules and one NADH molecule. This phase takes place twice, so it makes 4 TP and 2 NADH overall. Overall, glycolysis converts one six-carbon molecule of glucose into two 3-carbon molecules of pyruvate. The net products are 2 molecules of ATP (4 produced-2 ATP used up) and 2 molecules of NADH.

7. What electron acceptor occurs in both glycolysis and Krebs cycle?

NAD+. NAD+ accepts a hydrogen ion (H+) , adds two electrons (2e-) and becomes reduced to NADH + H+. The NADH moves to the electron transport train and donates a pair of electrons (becomes oxidized) to the first compound of the chain.

14. What step of cellular respiration uses oxygen?

Oxidative phosphorylation (the 4th step). Oxygen is at the end of the electron transport chain and accepts electrons and protons to form water. If the oxygen wasn't there to accep the electrons, the electron transport chain would stop running and ATP would no longer be produced by chemiosmosis.

13. Why are pigments important to the process of photosynthesis? Do all pigments absorb the same wavelengths? Explain

Pigments are important to photosynthesis because pigments absorb light energy which is what powers photosynthesis. All pigments don't absorb the same wavelengths. For example, chlorophyll absorbs wavelengths of all colors except green. Other pigments help chlorophyll trap light in other wavelengths, like xanthophylls which are yellow pigments and carotenes which are orange pigments.

16. What steps of cellular respiration release carbon dioxide into the atmosphere?

Pyruvate oxidation and the Krebs cycle release carbon dioxide into the atmosphere. In pyruvate oxidation, each pyruvate glycolysis goes into the mitochondrial matrix where it's converted into a two-carbon molecule acetyl CoA and carbon dioxide is released. In the Krebs cycle, the acetyl CoA combines with a four-carbon molecule and goes through a cycle of reactions and ultimately regenerates the starting molecule, and carbon dioxide is released.

4. What characteristics allow enzymes to speed up chemical reactions?

Temperature increases the rate of an enzyme-catalyzed reaction but only up to an optimum temperature. There are also pH levels that are the most optimum for enzyme activity. An increase in substrate concentration will also cause an increase in reaction rate because there are more enzyme substrate collision opportunities but a peak can be reached in which substrate concentration no longer affects reaction rate. An increase in enzyme concentration also allows enzymes to speed up chemical reactions.

15. What molecules/reactants are required to start the Calvin cycle? Where do those molecules/reactants come from?

The Calvin Cycle requires CO2 from the atmosphere and the ATP and NADPH produced by the light reactions. In fixation, the first stage, light-independent reactions occur and CO2 is fixed from an inorganic to an organic molecule. In the second stage ATP and NADPH are used to reduce 3-PGA into G#- and then ATP and NADPH are converted to ADP and NADP+. In the last stage of the Calvin Cycle RuBP is regenerated. The products of the calvin cycle are ATP, NADP+ + H+, and 1 molecule GA3P which becomes ½ molecule glucose (C6H12O6).

10. During respiration most ATP is formed by ATP synthase. What powers ATP synthase?

The electron transport chain powers ATP synthase. The molecules NADH and FADH2 pass electrons down the electron transport chain, which releases energy. This energy allows hydrogen ions to travel down a proton gradient through chemiosmosis, which provides the energy for ATP synthase to make ADP.

17. Which step of photosynthesis releases oxygen into the atmosphere?

The light dependent reaction releases oxygen into the atmosphere. Inside the grana of the chloroplast, photon energy boosts electrons in the chlorophyll to higher energy levels. The energized electrons then move through an electron transport chain of molecules. The energy and electrons released from the electron transport chain are used to form ATP molecules and split a water molecule (photolysis) from 2H20 to 2H2 + O2, releasing oxygen into the air.

23. If the ΔG is -586 kcal/mol, what could you conclude about the reaction? Is it endergonic or exergonic? anabolic or catabolic?

There is a negative change of energy which means it's an exergonic/catabolic reaction.

2. Energy is required to move protons across a membrane against the concentration gradient. Where does this energy come from?

This energy comes from the electron transport chain. In cellular respiration, electron transport uses energy to pump hydrogen ions across the mitochondrial inner membrane from the matrix into the intermembrane space. The chemiosmotic gradient then causes hydrogen ions to flow back across the mitochondrial membrane into the matrix through ATP synthase which produces ATP. The energy in the H+ ions is harnessed by ATP synthase to add a phosphate and produce ATP. The free energy from the electron transport chain is used to pump the ions in chemiosmosis.

22. During a workout or strenuous activity our muscle cells run out of oxygen and can no longer perform cellular respiration. Instead of producing ATP our cells are now producing what?

When our muscle cells run out of oxygen, they use fermentation where electrons that result from the glycolytic breakdown of glucose are donated to an organic molecule. It regenerates NAD+ from NADH, which produces lactic acid and causes muscle soreness.

24. If a reaction produces a ΔG of -686 kcal/mol, and then right after is coupled with another reaction that produces a ΔG of +484 kcal/mol,what can you tell me about the reaction?

a. Is the reaction overall, + or - (exo or endo) ? The reaction overall is negative, meaning that it's exergonic. b. What is that value? The value is ΔG of -202 kcal/mol. c. Is the reaction anabolic or catabolic? The reaction is catabolic because energy is being released.

12. If pH levels are too high or too low enzymes can not function properly. Each enzyme has an optimal pH at which they function most efficient. What pH range is for basic solutions? What pH range is for acidic solutions?

pHs less than 7 are acidic and pHs greater than 7 are basic. 7 is a neutral pH.