Biology

Photosynthesis in Plants

1,492 Questions

Photosynthesis is the biological process by which plants convert light energy into chemical energy. This page contains practice questions covering essential topics like chlorophyll, light reactions, and the pathways specific to plants. This material is crucial for medical entrance exams and academic assessments.

Chlorophyll and pigmentsLight reactionsCalvin cycleCAM plantsElectron transportPhotosynthesis factors

Photosynthesis in Plants Questions

Multiple choice botany metabolism, cell respiration, and photosynthesis light dependent or hill reaction phases of photosynthesis emerson's experiments & hill's reaction

Choose the correct answer from the alternatives given.
In a plant cell, which of the following pigments participates directly in the light reaction of photosynthesis

  1. chlorophyll a

  2. chlorophyll b

  3. carotenes

  4. xanthophylls
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Green pigments are located within the chloroplasts of plant. Chlorophyll a can participate directly in light reaction which convert solar energy to chemical energy.

Thus, the correct answer is 'Chlorophyll a.'

Multiple choice botany metabolism, cell respiration, and photosynthesis light dependent or hill reaction phases of photosynthesis emerson's experiments & hill's reaction

In the light-dependent reactions

  1. carbon dioxide is fixed
  2. $CO _2$ accepts electrons

  3. ATP and NADPH are formed

  4. sugar phosphates are formed
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The ATP and NADPH from the light-dependent reactions are used to make sugars in the next stage of photosynthesis. The net result of this reaction is the production of 2 ATP and 9 NADPH and the photolysis of water. Light is absorbed and the energy is used to drive electrons from water to generate NADPH and to drive protons across a membrane. These protons return through ATP synthase to make ATP.

So, the correct option is ' ATP and NADPH are formed'.

Multiple choice botany metabolism, cell respiration, and photosynthesis light dependent or hill reaction phases of photosynthesis emerson's experiments & hill's reaction

When a photosystem absorbs light

  1. sugar phosphates are produced

  2. electrons are transferred to ATP

  3. RuBP accepts electrons

  4. light-dependent reactions begin
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

When photosystem II absorbs light, electrons in the reaction-centre chlorophyll are excited to a higher energy level and are trapped by the primary electron acceptors. Photoexcited electrons travel through the cytochrome b6f complex to photosystem I via an electron transport chain set in the thylakoid membrane. The light-dependent reactions use light energy to make two molecules needed for the next stage of photosynthesis: the energy storage molecule ATP and the reduced electron carrier NADPH. In plants, the light reactions take place in the thylakoid membranes of organelles called chloroplasts.

So, the correct option is, 'light-dependent reactions begin'.

Multiple choice botany metabolism, cell respiration, and photosynthesis light dependent or hill reaction phases of photosynthesis emerson's experiments & hill's reaction

Assume a thylakoid which is somehow punctured so that the interior of the thylakoid is no longer separated from the stroma. This damage will have the most direct effect on which of the following processes?

  1. Splitting of water

  2. Absorption of light energy by chlorophyll

  3. Flow of electrons from photosystem II to photosystem I

  4. Synthesis of ATP
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The thylakoid membranes have pigment system, electron transport proteins as well as the ATP synthases. When the transfer of electron down the transport proteins occurs, many H$^{+}$ are transported into the thylakoid lumen from the stroma. This high concentration of H$^{+}$ is then used by the ATP synthases to make ATP by transferring these H$^{+}$ out of the thylakoid lumen in the stroma. The punctured thylakoid will not have an intact thylakoid lumen, so the concentration of the H$^{+}$ ins will not be developed. As a result, ATP synthase will not function and so ATP will not be synthesized. 

Hence, the correct answer is 'Synthesis of ATP' 

Multiple choice botany metabolism, cell respiration, and photosynthesis light dependent or hill reaction phases of photosynthesis emerson's experiments & hill's reaction

The function of light in photosynthesis is

  1. photolysis of water

  2. assimilation of carbon dioxide

  3. production of organic food

  4. activation of enzymes
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
The process of photosynthesis occurs when green plants use the energy of light to convert carbon dioxide (CO2) and water (H2O) into carbohydrates. Light energy is absorbed by chlorophyll, a photosynthetic pigment of the plant. This process is to change the energy in sunlight into the energy in sugar, the end product of photosynthesis. Photosynthesis of water resulting H+ion for the reduction of NADPH2.
So, the correct option is, 'photolysis of water'.
Multiple choice botany metabolism, cell respiration, and photosynthesis light dependent or hill reaction phases of photosynthesis emerson's experiments & hill's reaction

Synthesis of an assimilatory power takes place in _____________ phase of photosynthesis.

  1. Light phase

  2. Dark phase

  3. Glycolysis

  4. All the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Photochemical phase is also called as the light phase or hill reaction and it occurs inside the thylakoids. This photochemical phase is mainly dependent on light and it functions to produce assimilatory power, which consists of reduced coenzyme NADPH and energy rich ATP molecules.
So the correct option is 'Light phase'
Multiple choice botany metabolism, cell respiration, and photosynthesis light dependent or hill reaction phases of photosynthesis emerson's experiments & hill's reaction

Which statement are not true for photosynthesis?

  1. $CO _2$ reduction occur in dark reaction
  2. $H _2O$ oxidation occur in light reaction

  3. Light reaction is an enzymatic phase of photosynthesis

  4. Dark reaction may occur in dark if light reaction products are available there
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The overall function of light-dependent reactions is to capture the energy from the light for the generation of ATP and NADPH molecules. The dark reactions of the C$ _{3}$ cycle utilize the energy from short-lived electronically excited carriers to convert CO$ _{2}$ & H$ _{2}$O into glucose catalyzed by the enzyme RuBisCo, and this constitutes carbon fixation and makes it the enzymatic phase.

So the correct  option is 'Light reaction is an enzymatic phase of photosynthesis'.

Multiple choice botany metabolism, cell respiration, and photosynthesis light dependent or hill reaction phases of photosynthesis emerson's experiments & hill's reaction

Which one is not included in photochemical phase?

  1. Light absorption

  2. Photosphorylation
  3. ${ H } _{ 2 }O$ splitting
  4. ${ CO } _{ 2 }$ reduction
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
  • The photochemical step is dependent upon light, therefore it is also called as Light or Hill reaction. It involves the following reactions:
  • Photolysis of water: It is the phenomenon of breaking up of water into hydrogen and oxygen in the illuminated chloroplasts 
  • Production of assimilatory power: While passing over cytochrome complex, the electron loses sufficient energy for the creation of proton gradient and synthesis of ATP from ADP and inorganic phosphate. The process is called photophosphorylation
  • So, the correct option is 'CO2 reduction'.
Multiple choice botany metabolism, cell respiration, and photosynthesis light dependent or hill reaction phases of photosynthesis emerson's experiments & hill's reaction

Chlorophylls absorb visible light of wavelengths

  1. 400-500 nm only

  2. 300-400 nm only

  3. 600-800 nm only

  4. 400-500 nm and 600-700 nm.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Chlorophyll present in the plants can absorb the the wavelength of both blue and red regions of VIBGYOR which ranges from 400-500 nm and 600-700 nm respectively. It reflects the green light range of 500-600 nm hence the leaves appear green. 

Therefore the correct option is D

Multiple choice botany metabolism, cell respiration, and photosynthesis light dependent or hill reaction phases of photosynthesis emerson's experiments & hill's reaction

Which one directly transfers electrons to $NADP^+$ during light reaction?

  1. PS I

  2. PS II

  3. Cytochromes

  4. Plastocyanin.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The light-dependent reactions start in photosystem II (PSII). When the pigment in the reaction centre of PS II i.e, P$ _{680}$ absorbs a photon, an electron in this molecule gets excited and transferred to a primary electron acceptor, Pheophytin and then go through molecules in a series of redox. The electron flow goes from PSII to cytochrome b6f complex than to PSI. In PSI, the electron is finally accepted by NADP. Thus photosystem I in light-dependent reaction directly transfers electrons to NADP.

Multiple choice botany metabolism, cell respiration, and photosynthesis light dependent or hill reaction phases of photosynthesis emerson's experiments & hill's reaction

In the light reactions of photosynthesis,

  1. PS I produces strong oxidant while PS II a strong reductant.
  2. PS I produces strong reductant $NADPH$ while PS II a strong oxidant.

  3. PS I emits electrons for PS II.

  4. PS I produces ATP which is not formed by PS II.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

PS I: This system produces a strong reductant which reduces ${NADP}^+$ to $NADPH$.

This system does not directly involve with the photooxidation of water and evolution of molecular oxygen.
PS II: This system is directly involved with the photooxidation of water and evolution of molecular oxygen.
It donates electrons to PS I when ${NADP}^+$ is reduced.
Hence, the correct answer is 'PS I produces strong reductant $NADPH$ while PS II a strong oxidant'.

Multiple choice botany metabolism, cell respiration, and photosynthesis light dependent or hill reaction phases of photosynthesis emerson's experiments & hill's reaction

Photosynthesis is considered as an oxidation reaction, because

  1. $CO _2$ is oxidised
  2. $H _2O$ is oxidised
  3. $O _2$ is released
  4. $(CH _2O)$ is oxidised.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A) Carbon dioxide is reduced, not oxidised. 
B) Water is oxidised to form protons and release oxygen. ${ H } _{ 2 }O\longrightarrow { O } _{ 2 }+{ 2H }^{ + }$

C) Oxygen is released after water undergoes oxidation.
D) ${ CH } _{ 2 }O$ does not undergo oxidation.
So the correct answer is '${ H } _{ 2 }O$ is oxidised'.

Multiple choice botany metabolism, cell respiration, and photosynthesis light dependent or hill reaction phases of photosynthesis emerson's experiments & hill's reaction
The absorption spectrum of chlorophyll

  1. approximates the action spectrum of photosynthesis

  2. shows that some colours of light are absorbed more than others

  3. explains why chlorophyll is a green pigment

  4. all of the above are correct
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Green plants are green because they contain a pigment called chlorophyll as in the absorption spectra, chlorophyll absorbs light in the red (long wavelength) and the blue (short wavelength) regions of the visible light spectrum. The green light is not absorbed but reflected, making the plant appear green. An absorption spectrum shows all the light typically absorbed by a leaf. An action spectrum, meanwhile, shows all the light that is actually used for photosynthesis. The similarity of the action spectrum of photosynthesis and the absorption spectrum of chlorophyll tells us that chlorophyll is the most important pigments in the process. The spectra are not identical, though, because carotenoid, which absorbs strongly in the blue, play a role as well.

So, the correct option is, 'all of the above are correct'.

Multiple choice botany metabolism, cell respiration, and photosynthesis light dependent or hill reaction phases of photosynthesis emerson's experiments & hill's reaction

Choose the correct answer from the alternatives given.
NADPH and ATP from the light-dependent reactions are used to

  1. cause rubisco to fix $CO _2$

  2. cause electrons to move along their pathways

  3. reform the photosystems

  4. convert PGA to PGAL
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
Light-dependent reactions provide NADPH (electrons) and ATP (energy) to reduce PGA to PGAL. PGAL, the product of the Calvin Cycle can be converted into all sorts of other molecules. 2. Glucose phosphate is one result of PGAL metabolism; it is a common energy molecule
So, the correct answer is 'convert PGA to PGAL'

Multiple choice botany metabolism, cell respiration, and photosynthesis light dependent or hill reaction phases of photosynthesis emerson's experiments & hill's reaction

Which one is directly involved in light reaction of photosynthesis

  1. Chlorophyll a

  2. Chlorophyll b

  3. Carotenoids

  4. All the above.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Photosynthesis takes place in the green leaves of plants and other green part of plants like stem etc. The most active photosynthetic tissue in higher plants is the mesophyll of leaves. Mesophyll cells have many chloroplasts, which contain the specialised light absorbing green pigments, the chlorophylls. When chlorophyll absorbs light, it gets excited and emits electrons. Chlorophyll a is the primary photosynthetic pigment. It shows bright or blue green colour in chromatogram. Chlorophyll a is directly involved in light reaction of photosynthesis. It is present in the reaction centres of Photosystem I and Photosystem II which absorbs light energy of longer wavelength. These centres can release electron upon absorption of energy.