Test: Biology Assertion and Reasoning Type Questions (March 29) - NEET MCQ

Chloroplasts function as the site of photosynthesis in eukaryotic photoautotrophs. Inside the leaves, the chloroplasts occur mostly in the mesophyll cells along their walls for easy diffusion of gases and receiving optimum quantity of incident light. Within the chloroplast there is the membranous system consisting of grana, the stroma lamellae, and the fluid stroma. The membrane system is responsible for trapping the light energy and also for the synthesis of ATP and NADPH.

Chlorophyll a is found in all photosynthetic plants except bacteria. Hence, it is called as universal photosynthetic pigment. It is also called primary photosynthetic pigment because it performs primary reaction of photosynthesis which involves conversion of light into chemical energy. Other photosynthetic pigments like chlorophyll b, carotenes and xanthophylls are called accessory pigments.

Although the efficiency of photosynthesis is uniform over most of the spectrum, it declines significantly in the red, i.e., at wavelength of 680 nm and above. This phenomenon is called red drop. However, it was shown by Emerson that if light at 680 nm is supplemented with light of a shorter wavelength (< 600 nm), the quantum efficiency of photosynthesis in the red can
be restored to normal

Cyclic pathway of photosynthesis appeared first in some eubacterial species. It is supposed to be the first evidence of production of ATP in the presence of light. During non-cyclic photophosphorylation photolysis of water takes place. Under the influence of light energy and the catalytic action of chlorophyll, water a substance of low energy value, is split up into oxygen and hydrogen. Oxygen is used in the chloroplast. Non-cyclic photophosphorylation is the only natural process which adds molecular oxygen to the atmosphere.

The grana stacks of membranes are enriched in PS II and LHC (Light harvesting centre), while there is little ATP synthetase. On the other hand, a fraction of stroma thylakoids is rich in PS I and ATPase and poor in PS II and LHC

Stomata are absent since gaseous exchange takes place through diffusion in submerged plants.

Glycolysis is the process of breakdown of glucose or similar hexose sugar into two molecules of pyruvic acid through a series of enzyme mediated reactions, releasing energy (ATP) and reducing power (NADH₂). It is the first step of respiration, which occurs inside the cytoplasm and is independent of O₂. In glycolysis, two molecules of ATP are consumed during double phosphorylation of glucose to form fructose 1, 6 diphosphate. Four molecules of ATP are produced in the conversion of 1, 3-diphosphoglycerate to 3-phospho- glycerate and phosphenol pyruvate to pyruvate whereas, two molecules of NADH, are formed during oxidation of glyceraldehyde 3-phosphate to 1,3-diphosphoglycerate. Since, each NADH is equivalent to 3 ATP, so net gain in glycolysis is 8 ATP.

Glycolysis occurs in cytoplasm as all necessary enzymes are found in it. This process is common in aerobic/anaerobic respiration. In this process, one glucose molecule is converted into 2 moles of pyruvic acid.

One of the two phosphate of diphosphoglycerate is linked by high energy bond. It can synthesize ATP and form 3- phosphoglycerate. The enzyme is phosphoglycerate kinase. The direct synthesis of ATP from metabolites is called substrate level phosphorylation. During formation of phosphoenol pyruvate the phosphate radical pick up energy. It helps in the production of ATP by substrate level phosphorylation.

In the presence of enzyme aldolase, fructose 1, 6-diphosphate is converted into a glyceraldehyde-3-phosphate and a dihydroxy acetone-3-phosphate molecules.

The shoot tip tissues in plants are meristematic.

Nutrients are raw materials required for synthesis of protoplasm as well as source of energy. It should be rich in nitrogenous components to increase the synthesis of protoplasm and carbohydrates for energy and cell wall synthesis. All types of micronutrients and macronutrients should be available for proper growth. Water is required for cell elongation, maintenance of turgidity of growing cells and for providing medium for enzyme action. Even slight deficiency of water reduces growth. It may, however, promote differentiation. Water stress completely stops growth.

The root apex, shoot apex and many other regions consists meristematic tissue. By mitotic divisions of the meristematic cells new cells are produced. These cells have cellulosic cells walls, contains large nucleus and rich in protoplasm. It is called the phase of cell formation or cell division.

Growth is unique in plants because plants retain the capacity for unlimited growth throughout their life. These ability of the plants is due to the presence of meristem at certain locations in their body. The cells of such meristems have the ability to divide and self-perpetuate. The root apical meristem and shoot apical meristem are indeterminate meristems, because these meristem continue their activity throughout life of the plant. Root apical meristem and shoot apical meristem cause primary growth of plants and also causes the elongation of the plants along their axis.

An S-shaped or sigmoid curve is obtained, if total growth is plotted against time. It consists of four parts-lag phase, log phase, phase of diminishing growth and stationary phase. Growth is slow in the lag phase, rapid during log or exponential phase, slow again during the phase of diminishing growth. During the stationary phase growth stops completely. Log phase is also called as grand phase of growth due to fast growth in this phase. 6. (b) During different phases of growth as well as in response to environment different structures are developed. To cope up with the changes in environment. The plant

In the life of a plant, growth, differentiation and development are closely related events. Development is sum of growth and differentiation. Development in plants is under control of both intrinsic and extrinsic factors. Intrinsic factors include intracellular genetic factors and intercellular factors growth regulators. Extrinsic factors are light, temperature, water, oxygen and nutrition, etc.

Although atmospheric air contains far more oxygen content than the water (air contains 21% oxygen and water contains 0.5-0.9% oxygen by volume depending on the temperature), still most fish when out of water die of suffocation due to lack of oxygen. When fish is taken out of water the gills stick together thereby reducing the surface area. Reduced surface area lowers gas exchange and so death occurs.

Gills are the main respiratory organs of aquatic animals. Each gill bears rows of comb-like, soft, thin gill-filament, each gill- filament bears many flat, parallel membrane- like gill-lamellae. Each gill lamella carries many blood capillaries. Water taken through the mouth, is made to flow from the pharynx in a single direction between the gill lamella. This greatly helps in the gaseous exchange across the lamellar membrane between the capillary blood and the flowing water.

Mammalian skin is impermeable so that water loss through it, is minimized. But mammals need far more oxygen to maintain their high metabolic rates than lower animals; so they need a more extensive respiratory surface. Thus a complex respiratory system has evolved in mammals to meet this need. The mammalian respiratory system consists of the nasal cavity, nasopharynx, larynx, trachea, bronchi, bronchioles and lungs

As the integument of insect is thick and impermeable to minimize lose of body water, they can not carry out gas exchange through their body surface. To overcome this difficulty they have developed a complex system of air tubes called trachea to reach the air directly near the tissue cells. Each tracheal communicates with the exterior through openings in the body wall.

Coughing and sneezing should to take place because these reactions serve to keep the air passages free from foreign matter. Coughing is a reflex action under nervous control. The minute receptors found in the wall of trachea, bronchi, bronchioles and alveoli are highly sensitive to foreign matter (smoke, dust etc.) Like coughing, sneezing is also a reflex action triggered because of irritation to nasal passages. In this, sensory impulses travel from nasal passages to the medulla through trigeminal nerves. The reaction involves the same series of events as in cough reflex, but the air explodes out both through nose and mouth, expelling the foreign matter from nasal passages.

In most animals, tissue oxidation are carried out by aerobic respiration. But sometimes in aerobically respiring animals, anaerobic metabolism take place in certain tissues like skeletal muscles which do not immediately get as much oxygen as in necessary for metabolize glucose during vigorous movements.

During wound, germs are removed by the process of phagocytosis by WBC. WBCs accumulate at the site of wound by diapedesis. It is the squeezing of leucocytes out from the endothelium of capillaries to fight against foreign agent.

Mature mammalian RBC lack cell organelles including nucleus, mitochondria, ribosomes, centrioles and endoplasmic reticulum. It increases the surface area of RBCs and enables them to contain more haemoglobin. Thus, almost entire cytoplasm is filled with haemoglobin.

Lymphatic system comprises of lymph, lymphatic capillaries, lymphatic vessels, lymphatic nodes and lymphatic ducts. Lymph is a transparent fluid derived from blood and other tissues, that accumulates in the interstitial spaces as the interstitial fluid. It also contains leukocytes, mainly the lymphocytes. This fluid has a composition similar to that of plasma, except that it is low in proteins.

If a blood transfusion is made between an incompatible donor and recipient, reaction of antigens on the cells and antibodies in the plasma will produce clots that will clog the capillaries. Type O blood group individuals are without A and B antigens on their RBCs, but consists antibodies for both these antigens in their plasma. Hence, these persons can donate blood to anyone. O blood group is the most important blood group for transfusion.

When an injury is caused to a blood vessel, bleeding starts which is stopped by blood clotting. At the site of injury blood platelets release platelet factor - 3 and injured tissues release thromboplastin. The two combine to form prothrombinase enzyme which converts prothrombin to thrombin. The latter stimulates formation of fibrin thread or clot. Blood contains an anticoagulant heparin which prevents blood clotting in uninjured vessels.

A coagulum is mainly formed of a network of threads called fibrins in which dead and damaged formed elements of blood are trapped. Fibrins are produced by the conversion of inactive fibrinogens in the plasma by the enzyme thrombin. Thrombin, in turn are formed from another inactive substance present in the plasma called prothrombin. An enzyme complex, prothrombinase, is required for the above reaction. The clot seals the wound and stops bleeding. After its formation, clot starts contracting and a pale yellow fluid, the serum, oozes out. This serum is blood plasma minus fibrinogen and blood corpuscles.

Uricotelism is defined as the urinary elimination of nitrogen mainly as urea. Aquatic mammals like whales and seals are said to be ureotelic animals because their major nitrogenous waste product is urea. As a matter of fact, ammonia is the basic nitrogenous catabolite of protein but since ammonia is highly toxic to the animals, therefore, its concentration must be kept very low in the blood.

Sharks are ureotelic, they are not ammonotelic animals. Ureotelic animals excrete urea instead of ammonia as the major nitrogenous waste product. These include man and all other mammals, terrestrial and semi-aquatic amphibians such as toads and frogs, cartilaginous fishes (elasmobranchs) such as sharks and sting rays. Sharks need to avoid water loss from body, thus they cannot excrete ammonia, as it requires enough water to be eliminated. In order to retain so much urea in their blood, their blood osmotic pressure approaches that of sea water. This minimizes water loss from their body to adjust to the concentrated saline water of the sea.