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.

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Photosynthesis in Plants Questions

Multiple choice botany photosynthesis modern concept of photosynthesis photosystems photosynthesis in higher plants

Hill reaction takes place

  1. In the absence of ${CO _2}$

  2. In the presence of carbon dioxide

  3. In the absence of a suitable electron acceptor

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

Robin Hill in the year 1939 showed that all chloroplasts extracted from leaves of Stellaria media and Lamium album are suspended in a test tube containing suitable electron acceptor, e.g., potassium ferrioxalate and potassium ferricyanide, oxygen is released due to the photochemical splitting of water. Under these conditions, no CO$ _2$ is consumed and no carbohydrate is produced.

So the correct option is 'None of the above'.

Multiple choice botany photosynthesis modern concept of photosynthesis photosystems photosynthesis in higher plants

The important role of PS-II in photosynthesis is

  1. To cause photolysis of water

  2. To release energy
  3. To trap and assimilate $CO _2$
  4. To reduce NAD to NAD$H _2$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The photolysis of water occurs during light reaction. The site for occurrence of photolysis is thylakoid lumen. The photolysis of water releases protons which accumulate in the lumen and contribute to the electrochemical gradient of protons. The electrons released are used up to fill the electron hole in the reaction centre of PSII and oxygen molecule is released as by product of photosynthesis. The electrons released during photolysis of water are ultimately used to synthesize the reducing power for reducing carbon dioxide later on. The mineral ions required for photolysis of water are calcium, manganese and chlorine. 

Multiple choice botany photosynthesis modern concept of photosynthesis photosystems photosynthesis in higher plants

What occurs during the light reaction of photosynthesis?

  1. Chlorophyll is produced
  2. Water splits to form $2H^+$ and $O _{2}$
  3. $CO _{2}$ is given off as a waste
  4. Sugar is formed from $CO _{2}$ and water
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The photolysis of water occurs during light reaction. The site for occurrence of photolysis is thylakoid lumen. The photolysis of water releases protons, which accumulate in the lumen and contribute to the electrochemical gradient of protons. The electrons released are used up to fill the electron hole in the reaction centre of PSII and oxygen molecule is released as by product of photosynthesis. The electrons released during photolysis of water are ultimately used to synthesize the reducing power for reducing carbon dioxide later on. The mineral ions required for photolysis of water are calcium, manganese and chlorine. 

Multiple choice botany photosynthesis modern concept of photosynthesis photosystems photosynthesis in higher plants

In plants, hill reaction occurs

  1. All the time

  2. Only in day time

  3. Only when the plants are grown in cold climate of hills

  4. When the plant carries out up hill task of slat absorption and food translocation
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Experiments with isolates chloroplasts, in presence of oxidants like ferricyanides and benzoquinone (Hill reagents) were conducted by Hill in 1937 and 1939. By placing the isolated chloroplasts in sunlight, he notices evolution of oxygen from water. Hill concluded that if there was suitable hydrogen acceptor in the medium it would have been reduced. In absence of light Hill reaction can not be possible. So, it can say it occurs only in day time.

Multiple choice botany photosynthesis modern concept of photosynthesis photosystems photosynthesis in higher plants

Photolysis is related to 

  1. Calvin cycle

  2. H.S.K. cycle

  3. Cyclic photophosphorylation

  4. Non cyclic flow of electrons
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Photolysis means splitting of water in presence of sunlight. During photosynthesis, light reaction occurs in chloroplasts. In light reaction the water is oxidised and the electrons from water are passed on through a series of electron acceptors and ultimately used to reduce NADP. Since electrons from water molecule are never returned or cycled back, this process is called as non cyclic flow of electrons. It involves PS-II and PS-I both.

Multiple choice botany photosynthesis modern concept of photosynthesis photosystems photosynthesis in higher plants

Photochemical reaction taking place in the chloroplasts is directly involved in the 

  1. Fixation of carbon dioxide.

  2. Synthesis of glucose and starch.

  3. Formation of phosphoglyceric acid.

  4. Photolysis of water and phoshorylation of ADP to ATP.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Chloroplasts contain light trapping chlorophyll molecules. The chlorophyll molecules are an essential requirement for light reaction. The light energy is trapped by chlorophyll molecules for carrying out photolysis of water i.e., light dependent split of water molecules and photophosphorylation i.e., light dependent synthesis of adenosine triphosphate (ATP) by phosphorylation of adenosine diphosphate (ADP).

Multiple choice botany photosynthesis modern concept of photosynthesis photosystems photosynthesis in higher plants

The product of hill reaction are

  1. ATP and $NADPH _{2}$ in chloroplast
  2. ATP and $NADPH _{2}$ in mitochondria

  3. Only oxygen
  4. $NADPH _{2}$, ATP and $O _{2}$ in chloroplast
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Experiments with isolated chloroplasts, in presence of oxidants like ferricyanides and benzoquinone (Hill reagents) were conducted by Hill in 1937 and 1939. By placing the isolated chloroplasts in sunlight, he noticed evolution of oxygen from water. Hill concluded that if there was suitable hydrogen acceptor in the medium it would have been reduced. Arnon 1951 and 1954 repeated the experiment of isolated chloroplast and concluded that, the hydrogen acceptor present in plants is NADP (Nicotinamide adenine dinucleotide phosphate). It is reduced to $NADPH _2$ and an ADP molecule is converted to ATP in light by utilizing inorganic phosphate. This phenomenon is called as photophosphorylation.

Multiple choice botany photosynthesis modern concept of photosynthesis photosystems photosynthesis in higher plants

Hill reaction completes in the

  1. Light.

  2. Dark.

  3. Both A and B.

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

Hill reaction occurs in light or can be called as light reaction. Hill first of all demonstrated that isolated chloroplasts can release oxygen in presence of suitable inorganic electron acceptors. The Hill reaction is the light-driven transfer of electrons from water to Hill reagents (non-physiological oxidants) against a chemical potential gradient. 

Multiple choice botany photosynthesis modern concept of photosynthesis photosystems photosynthesis in higher plants

Which element is essential for photolysis of water?

  1. Nitrogen

  2. Chlorine

  3. Carbon

  4. Oxygen
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Photolysis of water refers to the light dependent split of water, which occurs during the light phase of photosynthesis in the chloroplast. The minerals essential for the process of photolysis are calcium, chlorine and manganese.

Multiple choice botany photosynthesis modern concept of photosynthesis photosystems photosynthesis in higher plants

Oxygen released during photosynthesis comes from

  1. Water

  2. Carbon dioxide

  3. Chloroplast

  4. Chlorophyll
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Photolysis takes place in the light dependent reaction of the photosynthesis. The reaction can be represented as:
H$ _2$O + 2 photons --> 2 e$^-$ + 2H$^+$ + O. 
Here, the electrons released are accepted by the photosystem to fulfill the electron gap. The last electron acceptor is the oxygen and thus, the oxygen is liberated from the water molecule. The experiments conducted by Samuel Ruben and Martin Kamen by using radioactive isotopes helped to prove that the oxygen liberated during photosynthesis came from photolysis the water.
Thus, the correct answer is option A.
Multiple choice botany photosynthesis modern concept of photosynthesis photosystems photosynthesis in higher plants

In photosynthesis, there is an (a)

  1. Reduction of $H _{2}O$.
  2. Oxidation of $H _{2}O$.
  3. Oxidation of $CO _{2}$.
  4. Oxidation of $NO _{2}$.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The process of photosynthesis occurs in two stages light reaction and dark reaction. The light reaction involves oxidation of water (photolysis i.e., light dependent splitting of water), which releases oxygen as a by product. The photolysis of water also releases electrons, which are used to drive electron flow in the thylakoid membrane ultimately this electron flow results in the synthesis of ATP and $NADPH _2$. These products ATP and $NADPH _2$ are used up subsequently in the process of dark reaction.

Multiple choice botany photosynthesis modern concept of photosynthesis photosystems photosynthesis in higher plants

The source of $O _{2}$ liberated in photosynthesis in green plants is

  1. Photosynthetic enzyme

  2. Carbohydrate present in leaf

  3. Water

  4. Carbon dioxide
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

When the chlorophyll molecule is excited by light, the energy level of an electron in its structure is boosted to a higher energy level and this excited chlorophyll moves rapidly the reaction center of the photosystem I where it transfers its extra energy to an electron which is then expelled from the reaction center and is accepted by the first member of a chain of electron carriers and ultimately reaches NADP$^+$, reducing it to NADPH. The reaction center has lost an electron and this electron hole is filled by stripping electrons from water which leaves hydrogen ion (H$^+$) and molecular oxygen (O$ _2$). The pathway of electrons from water to NADP$^+$ has Z shape called as Z scheme. 

Therefore, the correct answer is option C.

Multiple choice botany photosynthesis modern concept of photosynthesis photosystems photosynthesis in higher plants

Photolysis of water involves

  1. Excitement of water

  2. Evolution of oxygen

  3. Breakdown of water by light
  4. Splitting of water into its ions, $H^+$ and $OH$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Photolysis, as the name suggests, is the breakdown of water in the presence of sunlight to form H⁺ and  O₂ and electron. This takes place during the light phase of photosynthesis in the PS-II. This creates the oxygen which is the net product of photolysis.

So, the correct option is 'Breakdown of water by light'

Multiple choice botany photosynthesis modern concept of photosynthesis photosystems photosynthesis in higher plants

Source of protons within the chloroplasts is

  1. Water

  2. Excited chlorophyll

  3. Carbon dioxide

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

Chemiosmotic hypothesis explains how ATP is synthesized in the chloroplast. ATP synthesis is linked to the development of a proton gradient across the membrane of the thylakoid of chloroplast and proton accumulation is towards the inside of the membrane i.e., in the lumen. Source of protons within the chloroplasts is water. The splitting of water molecule takes place on the inner side of the membrane and so the protons (hydrogen ions) are produced, they accumulate within the lumen of the thylakoids. Thus, the correct answer is option A.