If chlorophyll a is blocked from absorbing light, what would be the effect on the ability of the plant to do photosynthesis?

Question

A.  The plant will have an enhanced ability to carry out light-dependent reactions
B.  The plant will have an enhanced ability to carry out light-independent reactions
C.  The plant will have a decreased ability to carry out light-dependent reactions
D.  The plant's ability to carry out photosynthesis will be unchanged, as one of the accessory pigments can fill in for chlorophyll a

Clarify Question
What is the key concept addressed by the question?
What type of thinking is required?

  Gather Content
What do you already know about the role of pigments during photosynthesis? What other information is related to the question?

  Choose Answer
Do you have all the information needed to determine what would happen?

  Reflect on Process
Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

C.  The plant will have a decreased ability to carry out light-dependent reactions

Clarify Question
What is the key concept addressed by the question?
        · The question asks you to determine what would happen to photosynthesis if chlorophyll a was blocked from absorbing light.
What type of thinking is required?
        · You are being asked to use what you know about photosynthetic pigments and use, or apply, this knowledge to determine what would happen to a plant when chlorophyll a was blocked from absorbing light.

  Gather Content
What do you already know about the role of pigments during photosynthesis? What other information is related to the question?
        · Photosynthesis is comprised of the light reactions, which produces ATP, NADPH, and oxygen and the Calvin cycle, which produces organic molecules from inorganic carbon dioxide. The first phase of photosynthesis includes the light reactions, where energy from the sun is captured using concentrated chlorophyll clusters organized in photosystems to remove electrons from water, excite them to a higher energy level, and to use redox reactions in order to eventually produce ATP and NADPH.
        · Each of the two photosystems in plants is comprised of multiple chlorophyll molecules, one of which is chlorophyll a. If you blocked chlorophyll a, what you think would happen to the plants ability to photosynthesize?

  Choose Answer
Do you have all the information needed to determine what would happen?
        · Let’s see if we can eliminate some possible answers. First, we know that blocking one of the main light harvesting molecules will have an impact on photosynthesis, so the plants ability to photosynthesize will certainly be changed. Second, light independent reactions like the Calvin cycle don’t depend on light directly, so all other things being equal that would also not be a correct choice. The question then becomes about whether blocking chlorophyll a will enhance or decrease light dependent reactions.
        · Let’s consider now what makes up a photosystem. Chlorophyll a molecules arranged in a cluster absorb photons from the sun and elevate the potential energy of an electron stripped from a water molecule. During this process the high-energy electron is passed to the photosystem reaction center and eventually on to an electron acceptor that begins the downstream process of electron transport, establishment of a proton gradient, and ATP production. Therefore, if you block chlorophyll a from absorbing light, fewer of those processes will take place, and the plants ability to photosynthesize will suffer.

  Reflect on Process
Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        · Answering this question correctly depended on your ability to apply what you know about chlorophyll a and its role in photosynthesis.
        · If you got a correct answer, good job! If you got an incorrect answer, did you recall that a plant’s ability to photosynthesize relies on pigments like chlorophyll a? Did you remember that chlorophyll a molecules are a key component of photo systems, and that photo systems are core to the light reactions ability to function? Were you able to infer that blocking chlorophyll a would then decrease photosynthesis?