Tag: photosynthesis in higher plants

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Questions Related to photosynthesis in higher plants

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

Which statement regarding cycling flow of electrons during light reactions is false

  1. PS II is not involved in the process.

  2. ATP synthesis takes place
  3. $NADP + H^+$ is synthesised

  4. Takes place only when light of wavelength beyond 680 nm is available for excitation
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Cycling flow of electrons during light reactions is known as cyclic photophosphorylation. It is performed by photosystem I independently. PS II is not involved in the process. In PS I, the reaction centre chlorophyll a has an absorption peak at 700 nm, hence is called $P _{700}$, while in PS II, reaction centre has an absorption maxima at 680 nm and is called $P _{680}$. As cyclic photophosphorylation requires only PS I, so it takes place only when light of wavelength beyond 700 nm is available for excitation. This process takes place in stroma lamellae membrane. An external source of electrons is not required. There is no evolution of oxygen takes place because it is not connected with photolysis of water. Cyclic photophosphorylation produces ATP only. It operates under low light intensity, anaerobic conditions or when $CO _{2}$ availability is low. When only PS I is functional, the electron is circulated within the photosystem and the phosphorylation occurs, due to cyclic flow of electrons. The membrane and lamella of the grana have both PS I and PS II, the stroma lamella membrane lack PS II as well as NADP reductase enzyme. The excited electron does not pass on to $NADP^{+}$ and is cycled back to the PS I complex through the electron transport chain.

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

Splitting of water is associated with 

  1. Photosystem I

  2. Lumen of thylakoid

  3. Both photosystem I and II

  4. Inner surface of thylakoid membrane
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Splitting up of water or photolysis is associated with Photosystem 2 and this photosystem 2 is present only in the membrane of thylakoids. 

So,  the right answer is 'inner surface of thylakoid membrane'.

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

Manganese is required in

  1. Nucleic acid synthesis

  2. Plant cell wall formation

  3. Photolysis of water during photosynthesis

  4. Chlorophyll synthesis
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
Manganese is required in the photolysis of water during photosynthesis. During photosynthesis after the water get split after assimilation of carbon dioxide manganese activates fat forming enzymes which function in the formation of riboflavin, ascorbic acid, and carotene which works as electron transport during photosynthesis.

So, the correct answer is 'Photolysis of water during photosynthesis'.
Multiple choice botany photosynthesis modern concept of photosynthesis photosystems photosynthesis in higher plants

Light energy is mainly used in photosynthesis for :-

  1. Spliting of $H _2 O $
  2. For $CO _2$ reduction
  3. Activation of reaction centre to emerge $e^-$

  4. NADPH formation
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
The photolysis of water (H2O) in the light reactions of photosynthesis occurs in the water-splitting complex of photosystem II embedded in thylakoid membranes of chloroplasts where light is used to split water molecules as represented by the following equation:

2H2O → 4H+ + 4e- + O2

Oxygen (O2) is liberated to the atmosphere as a waste product in this process. In this way, electrons (e-) are gained to replace those lost through photoexcitation from chlorophyll a in the reaction center of photosystem II which begins noncyclic photophosphorylation.

In the light reactions, electrons lost by chlorophyll are used to generate ATP for energy, and to reduce NADP to use as a reducing agent in the Calvin cycle where monosaccharides are fixed from atmospheric carbon dioxide (CO2) and used by the plant for structure and energy.

So the correct option is 'Spliting of H2O'.
Multiple choice botany photosynthesis modern concept of photosynthesis photosystems photosynthesis in higher plants

How many water molecule splite during light reaction for evolution of $4$ oxygen molecule?

  1. $2$
  2. $4$
  3. $6$
  4. $8$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In order to split water, four photochemical reactions are needed to take out four electrons and four protons from two water molecules. This leads to the formation of one oxygen molecule. Protons form water are released into the lumen (donor side of PSII) and electrons are moved to the plastoquinone (QB) binding site. So, the correct option is "A" (2).

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

Which one of the following ion is essential for photolysis of water?

  1. Calcium

  2. Boron

  3. Manganese

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

The light reaction, convert energy from the sun into chemical energy in the form of NADPH and ATP. These reactions must take place in the light and in chloroplasts of plants. Chlorophyll, which is a light-absorbing organelle in plant cells, is a very complex molecule that works in conjunction with the metal magnesium. There are primarily two types of chlorophyll: chlorophyll a and chlorophyll b. These chlorophyll molecules absorb light in the red and blue wavelengths, making the plants in which they are stored look green. Thus, the correct answer is option C.

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.