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

During photosynthesis, oxygen is evolved from

  1. $H _{2}S$.
  2. $H _{2}O$.
  3. $CO _{2}$.
  4. $HCO _{3}$.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Photosynthesis is a redox reaction in which carbon dioxide is reduced to sugars and water is oxidised to release oxygen.

Photolysis refers to light dependent split of water molecule, which occurs during photosynthesis. The process of photolysis provides electrons for non cyclic electron flow during non cyclic photophosphorylation. Mineral ions required for the process of photolysis are manganese, calcium and chlorine.

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

In the process of photosynthesis, the water molecule is broken down in

  1. Red drop.

  2. Photolysis.

  3. Phoshorylation.

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

Photosynthesis is chemically a redox reaction in which carbon dioxide is reduced and water is oxidised. During light reaction phase of photosynthesis, the electron that has been donated to the electron transport chain is replaced through photolysis (light dependent splitting) of water, a process that not only yields electrons but also is the source of almost all the oxygen in Earths atmosphere. 

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

Photolysis of water releases ........... gas.

  1. ${ CO } _{ 2 }$
  2. ${ O } _{ 2 }$
  3. ${ NH } _{ 3 }$
  4. ${ CH } _{ 3 }$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Photolysis, the chemical process by which molecules are broken down into smaller units through the absorption of light.

Photolysis of water is the process by which water is split into H+, oxygen, and electrons in the presence of light.
So the answer is 'O2'. 

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

Splitting of water is associated with 

  1. Photosystem I

  2. Lumpen 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

Light reaction occur inside the thylakoids, especially those of grana region. It involves two types of reaction photosynthesis of water and production of assimilation power.  The phenomenon of breaking up of water into hydrogen and oxygen in the illuminated chloroplasts is called photolysis or photocatalytic , splitting of water, Water splitting complex is associated with the PSII, which itself is physically located on the inner surface of thylakoid  membrane. 
$4H _{2} O \rightleftharpoons 4H^{+} + 4OH^-$
$ 4OH^- \xrightarrow[Mn^{2+}, Ca^{2+}, Cl^-]{Oxygen \,\,evolving\,\, complex} 2H _{2} + O _{2}\uparrow + 4e^- $ , So, the correct answer is 'inner surface of thylakoid membrane.'.

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).