Biology

Photosynthesis in Plants

1,508 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

Which equation represents photosynthesis?

  1. CO2 + H20 + sunlight + chlorophyll → glucose + oxygen

  2. CO2 + sunlight + chlorophyll → glucose + oxygen

  3. CO2 + H20 + sunlight + chlorophyll → glucose

  4. CO2 + H20 + chlorophyll → glucose + oxygen
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Photosynthesis uses carbon dioxide and water in the presence of sunlight and chlorophyll to produce glucose and oxygen. Option A correctly lists all necessary reactants and products.

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

The product of the light reaction of photosynthesis which is not common between cyclic and non-cyclic photophosphorylation and is not utilised in the Calvin cycle is 

  1. O$ _2$

  2. ATP
  3. $NADPH _2$
  4. O$ _2$ and ATP
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In cyclic phosphorylation, oxygen is not evolved as the by-product where as, oxygen is evolved as a by-product during non-cyclic phosphorylation. Calvin cycle is the second stage of photosynthesis in which carbon atoms from carbon dioxide are combined, using the energy in ATP and NADPH, to make glucose.

So, the correct option is 'O$ _{2}$'.

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

How many quanta of lights are required to evolve one oxygen molecule in photosythesis?

  1. Three

  2. Eight

  3. Four

  4. Two
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
 The quantum of light required in photosynthesis is 8 photons for one molecule of oxygen to be evolved. In this, 4 photons are required by photosystem II and 4 by photosystem I. The equation for the same is, 
2 x 2H$ _2$O --> 4H$^+$ + O$ _2$ + 4 electrons. 
Thus, the correct answer is 'Eight.'
Multiple choice botany metabolism, cell respiration, and photosynthesis light dependent or hill reaction phases of photosynthesis emerson's experiments & hill's reaction

During the light phase of photosynthesis .......... is oxidized and .......... is reduced.

  1. $CO _2$ and Water
  2. Water and $CO _2$
  3. Water and $NADP$
  4. $NADPH _2$ and $CO _2$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The light reaction takes place in thylakoid discs. There, water is oxidized and oxygen is released. The hydrogen is accepted by $NADP$ and hence get reduced to $NADPH _2$. 

So the correct answer is 'water and $NADP$' respectively.

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

Which of the following process is supported by photolysis?

  1. Oxidation

  2. Reduction

  3. Electroporation

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

Photolysis is the process of breakdown of water molecule in the presence of sunlight. It results in the release of oxygen and hydrogen. It is also called as photodecomposition. It occurs during photosynthesis in a series of light-driven oxidation events. In this, water absorbs photons and the energy released during this process drives oxidation processes induced by light. 

Thus, the correct answer is 'Oxidation.'

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 include in photochemical phase

  1. Light absorption

  2. Photophosphorylation
  3. $H _2O$ spliting
  4. $CO _2$ reduction
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
The photochemical phase of photosynthesis, also known as light reaction includes absorption of light by chlorophyll molecules, splitting of water to generate electrons along with release of oxygen and photophosphorylation to generate ATP.

So, the correct answer 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

Which statement is correct for given reaction for photosynthesis?


$ 2 H _2 A + CO _2 \xrightarrow []{light} 2A + CH _2 O + H _2 O $

  1. $H$ donor is oxidisable substrate
  2. $O _2 $ evolve from $H _2 O $ if reducible compound is $H _2 O $
  3. Glucose gain its oxygen from $H _2 O $

  4. Both A and C
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The light reaction of the photosynthesis starts when the chlorophyll loses its electron after absorbing the light. In order to maintain the continuity of the reaction, there is a requirement of an oxidizable substance that can donate its electron to the chlorophyll. Water acts as the electron donor through a process called photolysis of water. In this process, the oxygen is also released as a by-product.

A. In the given equation H donor is an oxidizable substrate that happens to be water.
B. O$ _{2}$ is evolved from water but it is not reducible compound.
C. Glucose in oxygen comes from the carbon dioxide and not water. The oxygen from water is released as a by-product of the reaction.
Hence, the correct answer is 'H donor is oxidizable substrate'.

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

Compensation point refers to the intensity of light at which 

  1. Rate of respiration = Rate of photosynthesis

  2. Rate of respiration > Rate of photosynthesis

  3. Rate of respiration < Rate of photosynthesis

  4. None of the above is correct
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Rate of photosynthesis in plants is generally higher than respiration but there comes a point of certain light intensity at which uptake of CO2 for photosynthesis is equal to CO2 released from respiration. This point is known as compensation point at which rate of photosynthesis is equal to rate of respiration.
So, the correct answer is 'Rate of respiration = Rate of photosynthesis'.
Multiple choice botany metabolism, cell respiration, and photosynthesis light dependent or hill reaction phases of photosynthesis emerson's experiments & hill's reaction

During photosynthesis

  1. Both ${ CO } _{ 2 }$ and water get oxidised
  2. Both ${ CO } _{ 2 }$ and water get reduced
  3. Water is reduced and ${ CO } _{ 2 }$ is oxidised

  4. Carbon dioxide get reduced and water get oxidised
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
Photosynthesis transfers electrons from water to energy-poor CO$ _{2}$ molecules, forming energy-rich sugar molecules. This electron transfer is an example of an oxidation-reduction process:Water is oxidized in photosynthesis, which means it loses electrons, and carbon dioxide is reduced, meaning it gains electrons.
So, the correct option is 'Carbon dioxide get reduced and water get oxidised'.
Multiple choice botany metabolism, cell respiration, and photosynthesis light dependent or hill reaction phases of photosynthesis emerson's experiments & hill's reaction

Oxidative phosphorylation occurs in respiration and _______ occurs in photosynthesis.

  1. Oxidative phosphorylation

  2. Reductive phosphorylation

  3. Cyclic phosphorylation

  4. None of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Phosphorylation refers to the process of formation of ATP. During respiration, the oxidation of NADH and FADH$ _{2}$ results in ATP formation, hence called oxidative phosphorylation. In photosynthesis, the photosystem II is involved in cyclic photophosphorylation. 

Hence, the correct answer is 'Cyclic Phosphorylation'

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

Suppose the interior of the thylakoids (lumen) of isolated chloroplasts were made acidic and then transferred in dark to a $pH = 8$ solution, what would be likely to happen? 

  1. The isolated chloroplast will make $ATP$

  2. The Calvin cycle will be activated

  3. Cyclic photophosphorylation will occur
  4. The isolated chloroplast will reduce $NADP^+$ to $NADPH + H^+ $
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The acidic lumen of the thylakoids will have a higher concentration of H$^{+}$ ions. When these are transferred to basic pH of 8, the H$^{+}$ will tend to move outside due to their concentration gradient, which is higher in the lumen and lower in the surrounding. The thylakoids bear ATP synthases that will use the proton motive force H$^{+}$ ions and will make the ATP. So, an isolated chloroplast is capable of synthesizing the ATP when the lumen is made acidic and the outer medium is made alkaline.

Hence, the correct answer is 'The isolated chloroplast will make ATP'

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

Light reaction or photochemical phase includes
I. light absorption
II. water splitting
III. oxygen release
IV. ATP and NADPH formation
Choose the correct option.

  1. I, II and IV

  2. I, II and III

  3. I, III and IV

  4. I, II, III and IV
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Light reaction or photochemical phase is called as photophosphorylation or Hill's reaction. It includes non-cyclic phosphorylation and cyclic phosphorylation. During this reaction, the light is absorbed by the chlorophyll and water splits into H$ _2$ and 1/2O$ _2$. Oxygen is released as the byproduct of the reaction along with formation of carbohydrate. Along with oxygen, ATP and NADPH are also formed.

Thus, the correct answer is 'I, II, III and IV.'

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

Which of the following events does not occur during the light reaction of photosynthesis?

(1) Photolysis of H$ _2$O
(2) Reduction of NADPH to NADP+
(3) Evolution of molecular oxygen
(4)Synthesis of assimilatory powers
(5)Conversion of CO$ _2$ to carbohydrates

  1. 1 and 2 only

  2. 2 and 5 only

  3. 2 ,3 and 5 only

  4. 1, 3 and 4 only
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The events occurring in the light reaction of the photosynthesis are:

  1. Absorption of sunlight by the chlorophyll and release of the electron to the carriers.
  2. Photolysis of water to provide the electron to the chlorophyll.
  3. The release of molecular oxygen due to the photolysis of water.
  4. Assimilatory powers are synthesized in the form of ATP and NADPH
  5. Reduction of NADP$^{+}$ occurs to form NADPH
The oxidation of NADPH and conversion of CO$ _{2}$ occurs during the dark reaction.

Hence, the correct answer is '2 and 5'.

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

Which of the following is not correct regarding light compensation point?

  1. This condition occurs usually in evening and morning

  2. Net production is equal to respiration consumption

  3. Gross production is more than Net production

  4. There is no gaseous exchange with environment by plant
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
  • The (light) compensation point is the light intensity on the light curve where the rate of photosynthesis exactly matches the rate of cellular respiration.
  •  When the rate of photosynthesis equals the rate of respiration or photorespiration, the compensation point occurs.
  • The compensation point is reached during early mornings and late evenings.
  • Hence This condition occurs usually in evening and morning is not correct regarding light compensation point.
  • So, the correct answer is 'Option A'.