Tag: botany

Questions Related to botany

Which one is not included in photochemical phase?

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

  1. Light absorption

  2. Photosphorylation

  3. ${ H } _{ 2 }O$ splitting

  4. ${ CO } _{ 2 }$ reduction

Show answer
Correct Option: D
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'.

Chlorophylls absorb visible light of wavelengths

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

  1. 400-500 nm only

  2. 300-400 nm only

  3. 600-800 nm only

  4. 400-500 nm and 600-700 nm.

Show answer
Correct Option: D
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

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

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

  1. PS I

  2. PS II

  3. Cytochromes

  4. Plastocyanin.

Show answer
Correct Option: A
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.

Light energy is converted into chemical energy through the formation of

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

  1. $NADPH _2$

  2. $ATP$

  3. $ATP$ and $NADPH _2$

  4. None of the above.

Show answer
Correct Option: C
Explanation:
In light-dependent reactions, the energy from sunlight is absorbed by chlorophyll and converted into chemical energy in the form of electron carrier molecules like ATP and NADPH.
Light energy is harnessed in Photosystems I and II, both of which are present in the thylakoid membranes of chloroplasts.
Just as the name implies, light-dependent reactions require sunlight. In the light-dependent reactions, energy from sunlight is absorbed by chlorophyll and converted into stored chemical energy, in the form of the electron carrier molecule NADPH (nicotinamide adenine dinucleotide phosphate) and the energy currency molecule ATP (adenosine triphosphate). The light-dependent reactions take place in the thylakoid membranes in the granum (stack of thylakoids), within the chloroplast.

In the light reactions of photosynthesis,

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

  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.

Show answer
Correct Option: B
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'.

Photosynthesis is considered as an oxidation reaction, because

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

  1. $CO _2$ is oxidised

  2. $H _2O$ is oxidised

  3. $O _2$ is released

  4. $(CH _2O)$ is oxidised.

Show answer
Correct Option: B
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'.

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

  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

Show answer
Correct Option: D
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'.

Hill used a dye for his famous hill reaction is

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

  1. Sulphur green

  2. Eosine

  3. Methylene blue

  4. Dichlorophenol indophenol

Show answer
Correct Option: D
Explanation:

In the year 1937 and 1939, Robert hill studied the light dependent reaction and revealed that oxygen evolved during photosynthesis came from water. In his experiment, he used Dichlorophenolindophenol (DCPIP) as a redox dye to measure the rate of photosynthesis. The dye is blue in oxidized state with a maximal absorption at 600 nm whereas in reduced, DCPIP is colourless.

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

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

  1. cause rubisco to fix $CO _2$

  2. cause electrons to move along their pathways

  3. reform the photosystems

  4. convert PGA to PGAL

Show answer
Correct Option: D
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'

Which one is directly involved in light reaction of photosynthesis

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

  1. Chlorophyll a

  2. Chlorophyll b

  3. Carotenoids

  4. All the above.

Show answer
Correct Option: A
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.