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KCSE Photosynthesis — practice questions — page 2

Explore 56 free Photosynthesis questions in KCSE Biology. Open each question or exercise to read its content, reference answers and available explanation.

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Photosynthesis questions and exercises with answers

Showing questions 31–56 of 56.

P680 is the name given to which structure?Read the answer and worked solution →Where does photosystem II obtain the electron that replaces the one it has given up?Read the answer and worked solution →What proportion of the oxygen produced by a leaf is used by its own mitochondria?Read the answer and worked solution →Why must a second photon be absorbed at photosystem I?Read the answer and worked solution →Which product does photosystem I capture the energy to make?Read the answer and worked solution →Which statement correctly describes photosystem II?Read the answer and worked solution →In which direction do hydrogen ions diffuse when adenosine triphosphate is made in the chloroplast?Read the answer and worked solution →What is the name of the flow of hydrogen ions through the protein channel of the thylakoid membrane?Read the answer and worked solution →Which pigment sits in the reaction centre that a photon reaches after striking the antenna pigments of photosystem II?Read the answer and worked solution →How do the lifespans of the light-dependent products compare with those of the light-independent products?Read the answer and worked solution →Where in the plant cell do the light-independent reactions take place?Read the answer and worked solution →Why is the term dark reactions considered misleading?Read the answer and worked solution →Into which three basic stages are the light-independent reactions organised?Read the answer and worked solution →Which enzyme catalyses the reaction between carbon dioxide and the five-carbon acceptor in the stroma?Read the answer and worked solution →How is the molecule ribulose bisphosphate built?Read the answer and worked solution →What is carbon fixation?Read the answer and worked solution →In the reduction stage, six molecules of 3-PGA are converted into six molecules of which compound?Read the answer and worked solution →What is meant by a reduction reaction?Read the answer and worked solution →How many molecules of adenosine triphosphate and NADPH are used in the reduction stage?Read the answer and worked solution →Of the six molecules made after three turns of the cycle, how many leave and how many stay?Read the answer and worked solution →How many extra molecules of adenosine triphosphate are used in the regeneration reactions?Read the answer and worked solution →How many turns of the cycle are needed before a three-carbon molecule can leave to join a carbohydrate?Read the answer and worked solution →How does modern oxygenic photosynthesis differ from the older bacterial type?Read the answer and worked solution →Why does a plant lose water during active photosynthesis?Read the answer and worked solution →Match each leaf part to its jobRead the answer and worked solution →Knock out the false leaf claimsRead the answer and worked solution →

Worked practice questions

P680 is the name given to which structure?

  1. The primary electron acceptor molecule
  2. The cytochrome complex of the chain
  3. The reaction centre of photosystem II
  4. The reaction centre of photosystem I
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Correct answer: C. The reaction centre of photosystem II

1. P680 is the reaction centre of photosystem II. 2. It delivers its high-energy electrons one at a time to the primary electron acceptor. 3. From there they travel through the chain to photosystem I. 4. P700 is the reaction centre of photosystem I, so the two numbers must be kept apart. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 8 "Photosynthesis", section 8.2 The Light-Dependent Reactions of Photosynthesis_

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Where does photosystem II obtain the electron that replaces the one it has given up?

  1. From a molecule of NADPH
  2. From a molecule of oxygen
  3. From a molecule of glucose
  4. From a molecule of water
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Correct answer: D. From a molecule of water

1. The reaction centre of photosystem II loses an electron at every photoact. 2. Its missing electron is replaced by extracting a low-energy electron from water. 3. Water is therefore split and photosystem II is re-reduced after every photoact. 4. Oxygen is released as the waste product of that splitting, so it is an output rather than a source. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 8 "Photosynthesis", section 8.2 The Light-Dependent Reactions of Photosynthesis_

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What proportion of the oxygen produced by a leaf is used by its own mitochondria?

  1. About 10 percent of it
  2. About 30 percent of it
  3. About 50 percent of it
  4. About 90 percent of it
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Correct answer: A. About 10 percent of it

1. Splitting water at photosystem II releases oxygen as a waste product. 2. About 10 percent of that oxygen is used by mitochondria in the leaf. 3. It supports oxidative phosphorylation there, since plants respire as well as photosynthesise. 4. The remainder escapes to the atmosphere where aerobic organisms use it to support respiration. 5. The word about again marks an approximate share rather than a fixed proportion. 6. A figure of 90 percent inverts the split between what is kept and what is released. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 8 "Photosynthesis", section 8.2 The Light-Dependent Reactions of Photosynthesis_

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