NEET Biology Solved Question Paper 2013

Secondary metabolites are derivatives of primary metabolites which have no direct function in growth and development of plants. These compounds arc accessory rather than central to the functioning, e.g., arbrin, cellulose, gums, diterpenes, carotenoids, curcumin, rubber etc. Arginine, tyrosine, glycine, serine and phenylalanine are amino acids, which are primary metabolites.

Non-native or alien species are often introduced accidently for their economic and other uses. They often become invasive ' and drive away the local species. Therefore, these species are second major cause of extinction.

Lantana camara has replaced many species in forests of Central India.

Parthenium hystero- phorus has pushed out various shrubs and herbs from open places in the plains. 

Water hyacinth Eicchornia crassipes is used in India to reduce pollution.

External fertilization is the fertilization that occurs outside the body of the organism. It requires an external medium such as water for its fertilization.Thus, in most aquatic organisms such as a majority of algae, fishes and amphibians, this type of fertilization occurs.

Stinging cells are used for offence and defence. They have nematocysts, composed of capsule, shaft and thread tube. The thread tube coils around the prey or attaches to it and injects a toxin called hypnotoxin which paralyzes the victim. They are found in cnidarians- sea pen (Pennatula), sea fan (Gorgonia) etc.

Endosperm nourishes embryo in seed plants. In gymnosperms, it represents the female gametophyte and is haploid (n). In angiosperms, it is a special tissue which is formed as a result of fusion of a male gamete with diploid secondary nucleus of the central cell. The fusion product is primary endosperm cell having a triploid (3n) endosperm nucleus.

S- phase or Synthesis phase is the phase where DNA replication takes place. It takes place on the template of the existing DNA and thus, the amount of DNA per cell doubles. If the initial amount of DNA is denoted as 2C, then it increases to 4C.

The total number of species estimated is about 1.74 million. Out of these , species in India is roughly 8.1%. India with about 45000 species of plants and twice as many species of animals is one of the 12 megadiversity countries of the world.

Cardiac muscle fibres are found in the wall of heart. They have dark intercalated discs at intervals. These are the specialized regions of cell membranes of two adjacent fibres. They permit the wave of muscle contraction to be transmitted from one cardiac fibre to another.

Presence of photorespiration is a wasteful and energy consuming process in crop plants which ultimately leads to reduction in final yield of crops.  During C₃ photosynthesis, upto 50% of the CO₂ fixed may have to pass through photorespiratory process, thereby resulting in considerable decrease in photosynthetic productivity. In C₃ plants, there is little loss of photosynthetic activity on account of photorespiration which is absent in C₄ plants and hence they have better productivity.

Oxytocin is released by posterior pituitary.

Vasopressin decreases the amount of urine by increasing reabsorption of water from DCT and collecting tubules.It stimulates the contraction of walls of blood vessels.

Glucagon  stimulates liver to convert stored glycogen into glucose and thus raises the blood sugar level.

Thymus releases thymosin which aids in proliferation of T- lymphocytes.