NEET Practice Questions (MCQs) with Answers & Solutions

Electrons from excited chlorphyll molecule of photosystem II are accepted first by Quinone. Photosystem II is a photosynthetic pigment system along with some electron carriers that is located in the appressed part of the grana thylakoids. Photosystem II has chlorophyll a, b and carotenoids. Other components of PS II are phaeophytin, plastoquinone (PQ), cytochrome complex and blue coloured copper containing plastocyanin.

C₄ -plants show Kranz anatomy. In the leaves of C₄ -plants the vascular bundles are surrounded by bundle sheath of parenchymatous cells, which in turn are surrounded by mesophyll cells. In C₄ -plants the Hatch and Slack pathway involves two carboxylation reaction one taking place in chloroplast of mesophyll cells and other in chloroplast of bundle sheath cells. The initial CO₂ fixation occurs in mesophyll cells where primary CO₂ acceptor is phosphoenol pyruvate and formed oxaloacetate. The oxaloacetate is reduced to malic acid. From chloroplasts of mesophyll cells the malic acid is transferred to chloroplast of bundle sheath cells and decarboxylated to form CO₂ and pyruvic acid. The CO₂ is again fixed by C₃ cycle. 

In plants, stoma is surrounded by two small specialized, green epidermal cells called guard cells. The guard cells are small in size and therefore, rapidly influenced by turgor changes.

Starch is a high molecular weight polymer of D-glucose in α 1 → 4 linkage. It is synthesized in chloroplasts as it is one of the stable end product of photosynthesis. It is most abundant and common storage polysaccharide in plants hence, most staple food for man and herbivores.

Carbohydrates are commonly found as starch in plant storage organs. It is chemically non-reactive and osmotically inactive polysaccharides of much greater molecules weight. Carbohydrates performs a vital role in living organisms. Starch and other polysaccharides serve as energy storage in plants, particularly in seeds, tubers, etc. which provide a major energy source for animals, including humans.

When P_r absorbs red light (660-665 nm) it is converted into P_fr form and when P_fr absorbs far red light (730-735 nm) it is converted into P_r form.

The first reaction of photorespiration occur in stroma of chloroplast. In this reaction the RuBP (Ribulose 1-5 biphosphate) consume one oxygen molecule in presence of Rubisco. 

In peroxisome the glycolate transfered from chloroplast takes up O₂ and formed the glyoxylate whereas the H₂O₂ release as byproduct.

Photorespiration is a type of respiration which occurs in small organelles called peroxisomes, and because it occurs only in light, it is called photorespiration. In contrast to 'normal respiration' or 'dark respiration' which occurs in the mitochondria, no ATP or reduced NAD is produced by photorespiration. The energy released being lost as heat. Under conditions of low carbon dioxide and high oxygen concentration which are normal atmospheric conditions, as much as 30-50 percent of the photosynthetically fixed carbon may be lost as carbon dioxide by photorespiration and the energy that was expanded to fix it is wasted to the plant. 

In photosystem II there is a complex of proteins with Mn²⁺, known as the water splitting centre, which extracts the electrons from water with the release of oxygen and protons and passes then to P₆₈₀ molecules restoring them to ground state. In this process manganese ions have a special role to play but chloride and calcium ions are also helpful.

In photorespiration uptake of oxygen and evolution of carbon dioxide are light dependent. RuBP carboxylase acts as RuBP oxygenase. Photorespiration occurs in chloroplast and requries the help of peroxisomes and mitochondria.

 Photosynthetic bacteria do not contain quantasome. Photosynthetic bacteria are of two types oxygenic (cyanobacteria) and anoxygenic (H2S donor like purple sulphur and green sulfur bacteria and organic donor like purple non-sulfur and green non-sulfur bacteria). Bacteria only have one photosystem i.e. type I reaction centre (PS I - 700) in green sulphur bacteria and type II reaction center (PS II - 680) in non sulphur bacteria.

Photorespiration in C3 plants starts with the formation of phosphoglycolate from ribulose-1,5-bisphosphate (RuBP) when oxygen instead of carbon dioxide binds to the enzyme RuBP carboxylase/oxygenase (RuBisCO). This phosphoglycolate is then dephosphorylated to glycolate, initiating the photorespiratory pathway.