Biology: Zoology: UPSC Previous Year Questions (Science and Technology)

Explanation

Assertion (A) is false: Glycine, serine, and tyrosine are non-essential amino acids which means they can be synthesized by the human body and do not need to be obtained through diet. Glycine and serine are produced from intermediate metabolites such as glucose and tyrosine is derived from phenylalanine, an essential amino acid. Hence, their dietary intake is not compulsory. Reason (R) is true: Essential amino acids are those that the human body cannot synthesize on its own and must be obtained from the diet. There are nine essential amino acids: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. These amino acids are vital for protein synthesis and other metabolic functions.

Explanation

Speciation is the process by which new and distinct species evolve from a common ancestor. Hugo deVries believed that mutation caused speciation and hence called it saltation (single step large mutation). Mutations are permanent changes in the DNA sequence, which can lead to new traits in a population. Some mutations provide adaptive advantages, increasing survival and reproduction. Over time, accumulation of mutations can result in significant genetic divergence, leading to speciation.

Explanation

Ticks and mites belong to the class Arachnida making them closely related to spiders and scorpions. They possess eight legs (in their adult stage), two body segments (cephalothorax and abdomen), and lack antennae, distinguishing them from insects. Ticks are primarily ectoparasites, feeding on the blood of vertebrates, while mites can be parasitic, free-living, or plant-feeding. Examples include the Deer Tick (Ixodes scapularis), which spreads Lyme disease, and the Scabies Mite (Sarcoptes scabiei), responsible for scabies.

Explanation

Platelets are more numerous than white blood cells in the bloodstream. The concentration of platelets ranges from 150,000 to 450,000 per microliter of blood whereas white blood cells are present at concentrations of about 4,000 to 11,000 per microliter. Platelets are essential for blood clotting, while WBCs are part of the immune system and are less numerous.

Option (a), (b) and (c) are incorrect:

Veins are more numerous than arteries and hold a significantly larger portion of the body’s blood at any given time. Approximately 70% of the body’s blood volume is found in the venous system at rest, as veins act as capacitance vessels that can expand to store blood. Arteries, on the other hand, carry oxygenated blood away from the heart and are under higher pressure, but they hold a smaller volume of blood compared to veins. Blood is composed of two main components: plasma (the liquid portion) and blood cells (red blood cells, white blood cells, and platelets). Blood cells make up approximately 45% of the total blood volume, a measure known as the hematocrit. The remaining 55% is plasma, which consists of water, proteins, electrolytes, and other dissolved substances. White blood cells (WBCs) are produced primarily in the bone marrow, not exclusively in lymph nodes. Lymph nodes play a role in the maturation and activation of certain types of WBCs, such as lymphocytes, but they are not the primary site of WBC production. Other organs, such as the spleen and thymus, also contribute to the development and function of WBCs.