491: Assertion (A): Amoeba reproduces by fission.
Reason (R): All unicellular organisms reproduce by asexual methods.
(a) Both A and R are individually true and R is the correct explanation of A.
(b) Both A and R are individually true but R is not the correct explanation of A
(c) A is true but R is false.
(d) A is false but R is true.
492: Which one of the following terms describes not only the physical space occupied by an organism, but also its functional role in the community of organisms?
(a) Ecotone
(b) Ecological niche
(c) Habitat
(d) Home range
Explanation:
In ecology, a niche is a term describing the way of life of a species. Each species is thought to have a separate, unique niche. The ecological niche describes now an organism or population responds to the distribution of resources and competitors (e.g., by growing when resources are abundant, and when predators, parasites and pathogens are scarce) and how it in turn alters those same factors (e.g., limiting access to resources by other organisms, acting as a food source for predators and a consumer of prey). The majority of species exist in a standard ecological niche.
493: Which of the following statements is/are correct?
Viruses can infect
1. bacteria
2. fungi
3. plants
Select the correct answer using the code given below.
(a) 1 and 2 only
(b) 3 only
(c) 1 and 3 only
(d) 1, 2 and 3
494: Production of which one of the following is a function of the liver?
(a) Lipase
(b) Mucus
(c) Hydrochloric acid
(d) Urea
Explanation:
The liver regulates most chemical levels in the blood and excretes a product called 'bile' which helps carry away waste products from the liver. It involves in conversion of poisonous ammonia to urea. (Urea is oneof the end products of protein metabolism that is excreted in the urine).
495: With reference to the human body consider the following statements:
1. The production of somatotropin goes up when a person exercises
2. Men's testes produce progesterone
3. Women's adrenal glands secrete testosterone
4. Stress causes the adrenals to release very less amount of cortisol than usual
Which of these statements are correct?
(a) 1 2 3 4
(b) 1 2 3
(c) 2 3 4
(d) 1 and 4
Explanation:
'Somatotropin' is a growth hormone, the production of this hormone goes up when a person exercises. It helps in shaping of muscles and growth.
Men's testes produce Testosterone while female's ovary produces Estrogen and Progesterone.
Women's adrenal glands secretes steroids, mineralocorticoids and glucocorticoids.
During physical and mental (emotional) stress sympathetic nerves and adrenal medulla produces less amount of cortisols than usual.