The interaction in which one organism is benefitted and the other is neither harmed nor benefitted is called:
- (a)Symbiosis
- (b)Commensalism
- (c)Parasitism
- (d)Exploitation
Correct — B, Commensalism.
The stem sets out a two-part signature: benefit for one organism, no effect either way on the other. Commensalism is the term reserved for exactly that pattern, written (+ / 0) in the sign notation used for interactions between species.
The standard textbook examples fit that signature. An orchid growing as an epiphyte on a mango branch gains a perch in the light, while the mango tree gains and loses nothing. Barnacles attached to a whale gain transport and feeding currents, and the whale is unaffected.
Carry away the sign pair rather than the story: judge the effect on each partner separately, and the label follows from the pair.
- (a)Symbiosis — Symbiosis is a wider label rather than a sign pair. In its broad sense it covers unlike species living together in close, prolonged association, and in common textbook usage it is applied to the association in which both partners gain.
It fits a stem asking for the general term for two different species living together in intimate, long-term association — a lichen, or Rhizobium inside legume root nodules.
Since it leaves open what happens to the second partner, it does not pick out the "neither harmed nor benefitted" half of this stem, which is the part being tested.
- (c)Parasitism — Parasitism is (+ / −). The parasite draws food or shelter from a host, and the host pays for it in reduced growth, survival or reproduction. Here the second organism pays nothing, so the sign pair does not match.
It fits a stem describing one organism living on or in another and benefiting at that host's expense — Cuscuta twining on its host plant, or a tapeworm in the gut.
The stem's phrase "neither harmed" is what rules this option out, and it does so on its own.
- (d)Exploitation — Exploitation names the class of interactions in which one organism gains by using another as a resource. Cost to that other organism is built into the definition, not incidental to it.
It fits a stem asking for the umbrella term covering predation, herbivory and parasitism — the (+ / −) interactions grouped together.
This stem specifies an organism that is neither harmed nor benefitted, and that is the one condition an exploitative interaction is defined so as to exclude.
Two species sharing a habitat affect each other's fitness, and ecology classifies the interaction by the sign of that effect on each partner: '+' for benefit, '−' for harm, '0' for no effect.
That yields a small grid of named relationships. Mutualism is (+ / +), competition (− / −), predation and parasitism (+ / −), commensalism (+ / 0), and amensalism (− / 0).
Commensalism is the case where one partner gains while the other's fitness is left where it was. Amensalism is its mirror image, with harm to one partner in place of gain.
These categories sit in the population-ecology portion of the syllabus, next to population growth and the ecological niche. They supply the vocabulary for describing how species coexist without being independent of one another.
They also carry into applied ground. Biological control rests on predation and parasitism, legume cultivation on the Rhizobium mutualism, and conservation arguments on the point that removing one species alters the species tied to it.
Because the labels are fixed by effects rather than by appearance, the same physical closeness — one organism perched on another — can be commensalism, parasitism or mutualism depending on the fitness outcome.
- Commensalism is written (+ / 0): one species is benefited, the other is neither harmed nor benefited.
- An orchid growing as an epiphyte on a mango branch is the standard example — the orchid gains support and light, the tree is unaffected.
- Barnacles growing on the back of a whale gain a moving substratum and feeding currents, with no effect on the whale.
- The cattle egret feeds on insects flushed out by grazing cattle; the egret gains a meal and the cattle are unaffected.
- NCERT also lists the clownfish sheltering among a sea anemone's stinging tentacles: the fish gains protection, the anemone is unaffected.
- Amensalism is the reverse sign pair, (− / 0) — one species harmed while the other is neither harmed nor benefited.
- Mutualism is (+ / +): Rhizobium in legume root nodules, and the fungus–root association called mycorrhiza.
- Predation and parasitism share the sign pair (+ / −), the gain of one coming at the other's cost.
'+' is benefit, '−' is harm, '0' is no effect. The stem states benefit for one and no effect on the other, which is the (+ / 0) row.
- Symbiosis carries two readings — broadly, close living-together with the sign pair left open; in common textbook usage, the association in which both partners gain. Neither reading is (+ / 0).
- Options that require harm — parasitism, exploitation — are excluded by "neither harmed" alone; symbiosis needs the second half, "nor benefitted", to be eliminated — which is why both signs must be read.
- Amensalism carries the same '0' but the opposite sign on the first partner: (+ / 0) and (− / 0) differ only in the first sign, and swapping them swaps commensalism for amensalism.
- The classification follows the effect on fitness, not physical contact: an epiphyte is attached to its tree and the tree still scores 0.
- An interaction can look one-sided until a return benefit is identified, which is why the same pair of organisms is sometimes reclassified from commensalism to mutualism.
Revise the idea in three shapes. Work it first as a definition: given benefit to one partner and no effect on the other, name the term.
Then work it as an example. Take a named pair of organisms — the orchid on a mango branch, Rhizobium in root nodules, Cuscuta on its host — and decide which interaction each pair illustrates.
Then work it as a matching exercise, setting the interaction names against their sign pairs, (+ / +), (+ / 0), (− / 0). Whichever shape you use, the work is the same: fix the effect on each partner independently, then read off the label.
No eligible match among this question's citable set.
- practice — not a real PYQ
In the notation used for interactions between species, an interaction represented as (+ / 0) is called:
- (a)Mutualism
- (b)Amensalism
- (c)Commensalism
- (d)Competition
Answerc — In this notation '+' marks benefit and '0' marks no effect, so (+ / 0) is benefit to one partner with no effect on the other, which is commensalism by definition.(a) Mutualism is (+ / +), with both partners gaining. (b) Amensalism is (− / 0): one partner harmed, the other unaffected. (d) Competition is (− / −), with both partners losing.
- practice — not a real PYQ
An orchid growing as an epiphyte on the branch of a mango tree is an example of:
- (a)Parasitism
- (b)Commensalism
- (c)Mutualism
- (d)Predation
Answerb — The orchid uses the branch as a perch, gaining light and space, while the mango tree's growth, survival and reproduction are unchanged. That is the (+ / 0) pattern.(a) Parasitism would need the orchid to draw nutrition from the tree and reduce its fitness. (c) Mutualism would need the tree to gain something in return. (d) Predation involves one organism killing and consuming another.
- practice — not a real PYQ
Which interaction is one in which one species is harmed while the other is neither harmed nor benefited?
- (a)Commensalism
- (b)Amensalism
- (c)Mutualism
- (d)Parasitism
Answerb — Amensalism carries the sign pair (− / 0): the first species suffers a loss of fitness and the second is left exactly as it was.(a) Commensalism has the opposite first sign, benefit rather than harm. (c) Mutualism is (+ / +), both gaining. (d) Parasitism is (+ / −), where the harm to the host is matched by a gain to the parasite, so the second partner is not unaffected.
- practice — not a real PYQ
The koel laying its eggs in the nest of a crow, which then rears the young, is an example of:
- (a)Commensalism
- (b)Brood parasitism
- (c)Mutualism
- (d)Camouflage
Answerb — The koel gains parental care for its offspring at the crow's expense, since the crow spends its effort on another bird's young. Being a gain to one at a cost to the other, it is classed as a form of parasitism.(a) Commensalism would require the crow's fitness to be unchanged. (c) Mutualism would require the crow to gain. (d) Camouflage is a concealment device, not a category of interaction, although the resemblance of the parasite's eggs to the host's in size and colour is what allows the deception to work.