Test: Photosynthesis in Higher Plants - 2 - NEET MCQ

Chlorophyll a, shows higher rate of photosynthesis. Hence, it is conclude that chlorophyll a is the chief pigment associated with photosynthesis.

The key features of plant photosynthesis were known, namely, that plants could use light energy to make carbohydrates C₆H₁₂O₆ from CO₂ and water,  Where C₆H₁₂O₆ represents glucose.

Each photosystem has all the pigments (except one molecule of chlorophyll a) forming a light harvesting system also called antennae. These pigments help to make photosynthesis more efficient by absorbing different wavelengths of light.

Phytochrome absorbs red of wavelength 660nm and far red of wavelength 730nm.

The C₄ plants respond to higher temperatures and show higher rate of photosynthesis while C₃ plants have a much lower temperature optimum.

Joseph Priestley (1733-1804) in 1770 performed a series of experiments that revealed the essential role of air in the growth of green plants. Priestley, you may recall, discovered oxygen in1774.

The central element of chlorophyll contain Magnesium element.

This option is correct. Cyt b₆-f complexes are evenly distributed in the stroma and granal thylakoids.

Photolysis of water is mainly carried out to compensate the electrons that are transferred to photosystem I by photosystem II during the non-cyclic photophosphorylation that reduce NADP⁺ into NADPH.

Most of the plants that are adapted to dry tropical regions have the C₄ pathway. e.g. Sugarcane, Maize, Sorghum,etc. These plants are known as C₄ plants. For the formation of sugars, C₄ plants undergo C₄ cycle as well as C₃ cycle or Calvin cycle. In these plants double fixation of carbon dioxide occurs.

ATP consumed in C₄ plants:

C₄ cycle - 2 ATP per CO₂ fixed

C₃ cycle - 3 ATP per CO₂ fixed 

Total - 5 ATP per CO₂ fixed

Thus, to form one molecule of glucose or to fix 6 CO₂, 6 X 5 = 30 ATP are consumed.

In chloroplast there is the membranous system consisting of grana, the stroma lamellae, and the fluid stroma. There is a clear division of labour within the chloroplast. The granum is responsible for trapping the light energy.

• In pure state, chlorophyll b is olive-green. In pure state, chlorophyll a is blue-green.
• Chlorophyll b is an accessory photosynthetic pigment.
• Chlorophyll a is a primary photosynthetic pigment.
• Chlorophyll b absorbs more violet-blue wavelength than red wavelength of light.
• Chlorophyll a absorbs more red wavelength than violet-blue wavelength of light.
• Chlorophyll b is soluble in 92% methyl alcohol.

Excitation of electrons, transfer to another accepter, and finally down-hill to NADP⁺ causing it to be reduced to NADPH⁺ H⁺ is called the Z scheme.

Fixing of one molecule of carbon dioxide in Calvin cycle require 3 ATP and 2 NADPH₂ as the source of energy. One NADPH₂ molecule produces 3 molecules of ATP.

RuBisCO that is the most abundant enzyme in the world and is characterised by the fact that its active site can bind to both CO₂ and O₂ hence the name.

Photosynthesis takes place only in the green parts of the plants, mainly the leaves.

Living organisms have the capability of extracting energy from oxidisable substances and store this in the form of bond energy. Special substances like ATP, carry this energy in their chemical bonds.

While PS II has a P680 reaction centre that absorbs red light at 680 nm.

ATP is formed in the first part of photosynthesis, (light reaction). In the second part of the cycle, known as dark reactions (or Calvin Cycle), which happens in the stroma of the plant, ATP (and NADPH) combine with CO2 and H2O to make glucose. The energy required in the dark reaction comes from ATP (and NADPH)

• C₄ plant species have a higher temperature optimum for photosynthesis than C₃ plants due to the operation of a CO₂ concentrating system that inhibits RuBisCO oxygenase activity.
• In C₃ plants, photosynthesis is decreased at higher temperature due to increased photorespiration.

There is maximum absorption by chlorophyll a, in the red region and so there is higher rate of photosynthesis.

The dark reactions of photosynthesis is purely enzymatic and slower than the primary photochemical reaction. It takes place in stroma portion of the chloroplast and is independent of light i.e., it can occur either in presence or in absence of light provided that assimilatory power is available.

• In the photosystem II (PSII) reaction center, energy from sunlight is used to extract electrons from water.
• The electrons travel through the chloroplast electron transport chain to photosystem I (PSI), which reduces NADP⁺ to NADPH.
• The electron transport chain moves protons across the thylakoid membrane into the lumen.

Quantum yield is the number of Oxygen molecules released per photon or quantum of light. During light reaction of photosynthesis oxygen molecules are release during photolysis.

• C₄ plants show Kranz anatomy in which bundle sheath cells surrounds the vascular bundles.
• They lack photorespiration and show presence of bundle sheaths.
• However, chloroplasts are present in both types of plants.