CBSE Questions for Class 11 Medical Biology Photosynthesis In Higher Plants Quiz 9 - MCQExams.com

Plants such as sugarcane and sorghum fix atmospheric carbon dioxide with the carboxylation of phosphoenol pyruvic acid to produce oxaloacetic acid (a C$$_4$$ acid) in the presence of phosphoenolpyruvate carboxylase (PEP carboxylase). Such plants are called C$$_4$$ plants.

C$$_4$$ plants have Kranz leaf anatomy. The vascular bundles, in these leaves, are surrounded by a layer of bundle sheath cells that contain a large number of chloroplasts.

Malic acid (Product of C$$_4$$ cycle) transport from mesophyll cell to bundle sheath where C$$_3$$ cycle starts which require RuBisco enzyme.

So, the correct answer is 'All a,b, and c'.

C$$_4$$ plants have Kranz anatomy of a leaf. The vascular bundles in these leaves are surrounded by a layer of bundle sheath cells that contain a large number of chloroplasts.

The chloroplasts in these leaves are dimorphic:

Bundle sheath- Chloroplast larger in size and arranged centripetally. It has unstacked thylakoids called agranal chloroplast. The cells perform C$$_3$$ cycle.

Mesophyll cells- Normal type of chloroplast. It has stacked thylakoids called granal chloroplast. The cells perform C$$_4$$ cycle.

Hence, the correct answer is 'Agranal bundle sheath chloroplasts and granal mesophyll chloroplasts'.

• According to the chemiosmotic hypothesis of ATP synthesis, the ATP synthase enzyme synthesizes ATP by chemiosmosis. 
• As electrons travel through the photosystems during cyclic photophosphorylation of light reaction, protons are transferred through the thylakoid membrane i.e. from stroma to thylakoid lumen.
  
• Thus, within the chloroplast, the number of protons in the stroma decreases, while the number of protons increases in the lumen.
  
• This generates a proton gradient. This free energy difference is used to phosphorylate ADP to make ATP by ATP synthase by transferring H$$^+$$ from lumen to stroma as shown in the given diagram.

A. Aerobic respiration is the oxidative breakdown of respiratory substrates with the help of atmospheric O$$_2$ $. 

B. Anaerobic respiration is the oxidative breakdown of respiratory substrates in absence of O$$_2$$.

C. Fermentation -The chemical breakdown of a substance by bacteria, yeasts, or other microorganisms, typically involving effervescence and the giving off of heat.

D. Photorespiration: It is inhibition of photosynthesis by high O$$_2$$ level. It was termed as Warburg effect. However, the inhibition was observed mostly in C$$_3$$ plants. The C$$_4$$ plants were hardly affected by varying O$$_2$$ concentrations. The process occurs in chloroplast, peroxisome and mitochondria.

Hence, the correct answer is 'Photorespiration'.

Mitochondria and chloroplast both have:

• A double membrane surrounding the organelles.
• Purportedly prokaryotic origins according to the endosymbiotic theory which suggests that mitochondria and chloroplast were once prokaryotic bacteria engulfed by endocytosis in early eukaryotes.
• Their own circular DNA which codes for certain enzymes required for the chemical reactions that take place in these organelles.
• Their own 70S ribosomes made up of 50S and 30S subunits to translate proteins
• The enzyme ATP synthase which utilizes the energy released from the movement of protons across it (proton-motive force) to phosphorylate ADP to ATP. (Thus, another similarity would be that they both produce ATP)
• Electron transport chains, which are embedded in the inner mitochondrial membrane and thylakoid membrane in mitochondria and chloroplasts respectively.

A. Chlorophyll a occurs with peak absorption at 700 nm in PS I and 680 nm in PS II.

B. Mn and Cl$$^-$$ are associated with photolysis of water.

C. No O$$_2$$ is evolved during cyclic photophosphorylation

D. In non electron transport process the excited electron from PS II  is accepted by primary acceptor quinone, which sends them to an electron transport system consisting of plastoquinone, cytochrome complex and plastocyanin.The excited electron absorbed by PS I reaction center, then transfer to the ferredoxin(Fe), then the reduced Ferredoxin donates the electron to NADP$$^+$$.

So, the correct answer is 'PS I and PS II are both involved in non- cyclic photophosphorylation'.

C$$_4$$ plants can absorb CO$$_2$$ even in a much low CO$$_2$$ concentration while the C$$_3$$ plants fail to avail it. C$$_4$$ cycle is much more efficient photosynthetically. Primary Carboxylation of phosphoenolpyruvate acid (PEP) to form oxaloacetic acid (a 4- carbon compound) in presence of enzyme phosphoenolpyruvate carboxylase (PEP carboxylase) is an additional step in the C$$_4$$ plants that allow an efficient CO$$_2$$ utilization. Secondary carboxylation to synthesize carbohydrates occurs in bundle sheath.

Hence, the correct answer is 'Primary fixation of CO$$_2$$ is mediated via PEP carboxylase'.

In photorespiration, the glycine is transported out of peroxisomes into mitochondria, where two molecules of glycine interact to form one molecule each of serine, CO$$_2$$, NH$$_3$$.

2 Glycine + H$$_2$$O + NAD$$^+\rightarrow$$ Serine + CO$$_2$$+ NH$$_3$$ + NADH

When glyceric acid finally enters the chloroplast where it is phosphorylated to 3 PGA which enters in C$$_3$$ cycle, where during the reduction process, NAD$$^+$$ is reduced.

Hence, the correct answer is 'Mitochondria and chloroplasts'.

The photosystem II complex replaced its lost electrons from an external source; however, the two other electrons are not returned to photosystem II as they would in the analogous cyclic pathway. Instead, the still-excited electrons are transferred to a photosystem I complex, which boosts their energy level to a higher level using a second solar photon. The highly excited electrons are transferred to the acceptor molecule, but this time is passed on to an enzyme called Ferredoxin-NADP^+ reductase which uses them to catalyse the reaction (as shown):

NADP⁺ + 2H⁺ + 2e⁻ → NADPH + H⁺

This consumes the H⁺ ions produced by the splitting of water, leading to a net production of 1/2O₂, ATP, and NADPH+H⁺ with the consumption of solar photons and water.

So, the correct option is 'Option A'.

Photorespiration: It is inhibition of photosynthesis by high O$$_2$$ level. It was termed as Warburg effect. The process occurs in chloroplast, peroxisome and mitochondria. However, the inhibition was observed mostly in C$$_3$$ plants. The C$$_4$$ plants were hardly affected by varying O$$_2$$ concentrations.’ This is because of the spatial separation of initial carbon dioxide fixation by the phosphoenolpyruvate carboxylase in the mesophyll cells and then the proceeding of the C$$_3$$ cycle in the bundle sheath cells with the involvement of the RuBiSCo enzyme. In this way, the RuBiSCo does not get to interact with the atmospheric oxygen.

Hence, the correct answer is 'C$$_4$$ plants'.