Answer: Option B. -> Closely related species growing in the same habitat
:
B
When the species are closely related they tend to require the same resources, the same habitat and food, this leads to high competition between them, whereas two distantly related species in the same habitat, will have different food requirements and different shelter requirements and therefore do not compete for the same resources or atleast will have different modes to acquire these resources, thereby decreasing competition between them. Species occupy different ecological niches to apportion resources between them and to decrease the competition between them. Ecological niche can be defined as the role of an organism in its environment. Therefore closely related species that occupy different niches, do not compete heavily.   

Answer: Option D. -> 0
:
D
In a logistic growth curve, the rate of change in population size dN/dt = rN (1-(N/K)). Here if the value of N approaches K, then the equation will become dN/dt = rN ((K/K) - (K/K)), which is equal to 0. Whereas in the intial phase of growth when N is very small, N/K is negligent and the equation will be dN/dt = rN (1) = rN

Answer: Option A. -> A is more recent and shows slight reduction in the growth rate
:
A

Interpretation (a) is correct.
The Diagram A shows reduction in the number of males and females of the population. As you can see the 0-9 bar shows a total of 15 individuals in the digram B and the 0-9 bar in diagram A shows only 12 individuals. So Figure A shows slight reduction in the growth rate.

Answer: Option D. -> Head louse living on the human scalp as well as laying eggs on human hair
:
D
Head louse living on the human scalp as well as laying eggs on human hair is a parasite in true sense. Female mosquito is not considered a parasite, as it needs human blood only for reproduction. Cuckoo that lays eggs in crow's nest is a brood parasite not a parasite in true sense. 

Answer: Option B. -> Red algae
:
B

The blue-green light have short wavelength and penetrates deep into the water. Red algae are commonly found in the depths of oceans as they contain pigments such as phycobilins that can utilise short wavelength blue light that can penetrate deeper than other wavelengths of light.

Answer: Option C. -> Plants resistant to salt 
:
C

A halophyte is a plant that grows in waters of high salinity, coming into contact with saline water through its roots or by salt spray, such as in saline semi-deserts, mangrove swamps, marshes and sloughs and seashores.Plants divided on the basis of soil in which they are found into the following groups.

(i) Halophytes are plants growing in saline soil i.e., these plants are salt resistant

(ii) Oxalophytes are plants growing in acidic soil

(iii) Lithophytes are plants growing on the surface of rocks
(iv) Xerophytes plants resistant to dry conditions.

 

Answer: Option B. -> Both Assertion and Reason are true but Reason is not the correct explanation of Assertion
:
B

Predation is a complex interspecific interaction with a feeding strategy i.e., one species eats another. The population of the prey is regulated by the number of predators, but if the population of the prey drop heavily, the predator population also drops because they run out of food. Thus predator and their prey maintain fairly stable population through time and one population does not become abundant or scarce, without affecting the other. However, population size of the prey or the predator does not explain the predatory interaction, therefore the two statements are not related, and Reason does not explain Assertion.

 

Answer: Option A. -> An overwhelming majority of animals and nearly all plants maintain a constant internal temperature
:
A
Warm blooded animals like birds and mammals are the only animals that can maintain a constant internal temperature, most of the animals do not regulate their internal temperature.  
The largest purely terrestrial animal found in Antarctica is a flightless midge (a flightless fly) that grows no more than 13mm in length. All other Antarctic animals are either smaller than this or migrate spending some of the year away from the deep south and the extreme cold. They either swim or fly away - and back again.
An orchid growing as an epiphyte on a mango branch is an example of commensalism, because the orchid derives its nourishment from the mango tree, but the mango tree however is not harmed.

Answer: Option C. -> A is correct but R is incorrect
:
C
Stenothermal organisms are those which can thrive only within a limited temperature range. They could be further categorised into two groups- thermophiles and cryophiles. The former refers to those organisms which can thrive only in high temperatures (at least above ${20}^{\circ }C$) while the latter includes organisms which can thrive only in lower temperatures (below ${20}^{\circ }C$). Corals, some insects and a majority of the reptiles are thermophiles. Arctic crustaceans are examples of cryophiles.

Answer: Option D. -> Assertion is false and reason is true
:
D

Open systems are material systems in which mass or energy can be lost to or gained from the environment. Living organisms basically gain energy from the sun or other organisms, that is from a source outside the organism, and they lose energy in the form of heat. Similarly they gain mass through food, from an outside source. Therefore matter and energy enters the system from an external source and is lost from the system eventually. Therefore living organisms are open systems.