Ecology – Organisms and its Environment: NEET MCQs with Answers

Explanation: Population B increases exactly as population A declines, which is the pattern expected when two herbivores compete for the same limited food and the superior competitor (B) gradually displaces the other.

Explanation: Herbivores grazing on plants is regarded as predation, since the herbivore is the predator and the plant is the prey (A-iii). Mycorrhiza — fungus and plant root — benefits both partners, hence mutualism (B-ii). Sheep and cattle in the same pasture compete for the same food, i.e. grass (C-iv). An orchid growing as an epiphyte on a tree gets a place to grow and access to light, while the tree is neither harmed nor benefitted — commensalism (D-i).

Explanation: Leopard and lion sharing the same forest are both large carnivores occupying similar niches, hence competition (A-I). The cuckoo laying eggs in a crow's nest so that the host raises its chicks is brood parasitism (B-II). Mycorrhiza — fungal hyphae with roots of higher plants — benefits both partners, hence mutualism (C-III). The cattle egret gains insects flushed out by grazing cattle while the cattle are unaffected, hence commensalism (D-IV).

Explanation: In mutualism both partners benefit, i.e. +/+ (A-IV). In commensalism one species benefits while the other is unaffected, i.e. +/0 (B-I). In amensalism one species is harmed while the other is unaffected, i.e. −/0 (C-II). In parasitism the parasite benefits at the expense of the host, i.e. +/− (D-III).

Explanation: These chemicals make the plant unpalatable or toxic to herbivores, thereby serving as chemical defences against grazing and browsing.

Explanation: The Yucca plant is pollinated only by its partner moth, and the moth's larvae feed only on the developing Yucca seeds — an obligate mutualism in which the life cycles are tightly linked.

Explanation: Antibiotic production is an example of amensalism: the microbe secreting the antibiotic inhibits or kills other microbes while itself gaining no benefit from the interaction.

Explanation: Mycorrhiza is formed by fungi such as Glomus, not by the bacterium Rhodospirillum. Anabaena fixes nitrogen, Rhizobium nodulates alfalfa and Frankia nodulates Alnus.

Explanation: In mycorrhiza the fungus absorbs phosphorus and other nutrients from the soil for the plant, and the plant supplies energy-yielding carbohydrates to the fungus — both partners benefit.

Explanation: Two species competing for the same limiting resource cannot coexist indefinitely; the competitively inferior one is eventually eliminated unless the species partition the resource.

Explanation: Competition is a (–, –) interaction. In predation and parasitism one partner benefits while the other is harmed, and in mutualism both gain.

Explanation: A species is a group of organisms similar in structure, function and behaviour that interbreed freely to produce fertile offspring. All individuals of the same kind therefore belong to one species. A community consists of populations of many different species living together.

Explanation: Ecology (also called environmental biology) is the study of interactions among organisms and between organisms and their physical environment, at the levels of organism, population, community, ecosystem and biome. Ethology is the study of animal behaviour and phytogeography deals with the geographical distribution of plants.

Explanation: Xeric (dry) conditions are essentially defined by low atmospheric humidity together with scanty precipitation. Such conditions occur in arid deserts, in extremely cold habitats (physiological drought) and in salt marshes. Plants growing there are xerophytes with sunken stomata, thick cuticle and succulent tissues.

Explanation: Tropical rainforests need high temperature and heavy rainfall throughout the year; in India they occur in the Western Ghats (Kerala, Karnataka) and in north-eastern India including Assam. Jammu and Kashmir is temperate to alpine and Rajasthan is arid.