Q.Productivity is the rate of production of biomass expressed in terms of:
i. (kcal m^-3) yr^-1
ii. g^-2 yr^-1
iii. g^-1 yr^-1
iv. (kcal m^-2) yr^-1
Concept understanding — Ecological Interactions
Ecological Interactions: A First Look
Imagine a city. People live in apartments, work in offices, buy food from shops, and throw away garbage that someone else collects. Some people compete for the same job. Others help each other—a landlord provides space, a tenant pays rent. Now shrink that city to a forest, a pond, or even your backyard garden. Replace people with plants, animals, fungi, and bacteria. What you get is a web of relationships between living organisms—that is what ecologists call ecological interactions.
The Core Idea
Every living thing on Earth is connected to others. No organism exists in isolation. A tiger needs deer to eat; the deer needs grass; the grass needs sunlight and soil nutrients made available by bacteria and fungi. These connections are not random—they follow patterns. Some interactions help both partners, some help one at the expense of the other, and some harm both.
The NCERT textbook defines ecological interactions as the relationships between different species in a community. These interactions shape who lives where, how many of them exist, and how energy flows through an ecosystem.
Why Should a Commerce/Humanities Student Care?
You might think this is only for biology students. But consider this: every business operates within an ecosystem of suppliers, competitors, customers, and regulators. A startup that helps its suppliers grow (mutualism) survives longer than one that squeezes them dry (parasitism). A company that competes aggressively with rivals (competition) may drive prices down for consumers. The same logic that governs a forest governs a market—because both are systems of interacting agents.
Ecological interactions are not just "nature facts." They are a lens to understand any system where different entities depend on, compete with, or exploit each other—including economies, societies, and organizations.
The Main Types of Interactions
Ecologists classify interactions based on who benefits (+) and who is harmed (−). A zero (0) means no effect.
1. Mutualism (+ / +)
Both species benefit. Think of bees and flowers: bees get nectar (food), flowers get pollinated (reproduction). In human terms, this is a win-win partnership—like a coffee shop and a bookstore sharing the same space to attract more customers.
2. Competition (− / −)
Both species are harmed because they fight for the same limited resource—food, water, space, light. When two businesses open identical stores on the same street, both may earn less profit. In nature, two species of birds eating the same insect will both struggle if insects become scarce.
3. Predation (+ / −)
One species (predator) kills and eats the other (prey). The predator benefits; the prey is harmed. This is the tiger-deer example. In business, think of a large corporation acquiring a smaller competitor—the acquirer grows, the acquired loses independence.
4. Parasitism (+ / −)
One species (parasite) lives on or inside another (host) and feeds on it, usually without killing it immediately. The parasite benefits; the host is harmed. A tick on a dog, or a virus in a human. In economics, this resembles a monopolist that extracts value from suppliers without providing fair returns.
5. Commensalism (+ / 0)
One species benefits; the other is neither helped nor harmed. Barnacles attaching to a whale get a free ride to food-rich waters; the whale is unaffected. In a city, a street vendor setting up near a popular metro station benefits from foot traffic without affecting the station.
6. Amensalism (− / 0)
One species is harmed; the other is unaffected. A large tree casts shade that kills smaller plants beneath it—the tree does not care. In business, a giant retailer opening next to a small shop may drive the shop out of business without intending to.
| Interaction | Effect on Species A | Effect on Species B | Real-world analogy |
|-------------|---------------------|---------------------|---------------------|
| Mutualism | + | + | Joint venture |
| Competition | − | − | Price war |
| Predation | + | − | Acquisition |
| Parasitism | + | − | Exploitative contract |
| Commensalism | + | 0 | Free rider |
| Amensalism | − | 0 | Collateral damage |
The Bigger Picture
No interaction exists in isolation. A single species may be involved in multiple relationships simultaneously. A tree competes with other trees for sunlight, provides shelter for birds (commensalism), hosts fungi that help it absorb nutrients (mutualism), and is eaten by insects (predation). This complexity is what makes ecosystems resilient—or fragile.
When one interaction is disrupted—say, bees decline due to pesticides—the entire web trembles. Plants that depended on bees for pollination produce fewer fruits. Animals that ate those fruits starve. The lesson for any student of systems: interdependence means no action is without consequence.
What NCERT Expects You to Know
The NCERT Class 12 Biology textbook (Chapter 11, Organisms and Populations) presents these interactions as part of "population interactions." The key points are:
- Interactions can be intraspecific (within same species) or interspecific (between different species).
- The six types above cover all interspecific interactions.
- Competitive exclusion principle: Two species competing for the same resource cannot coexist indefinitely—one will outcompete the other.
- Resource partitioning: Sometimes competitors evolve to use different parts of the resource to reduce conflict (e.g., birds feeding at different heights in the same tree).
For a commerce/humanities student, the competitive exclusion principle is especially valuable. It explains why identical businesses cannot survive in the same niche—differentiation is not just strategy, it is biology.
A Final Thought
Ecological interactions are not a list to memorize. They are a vocabulary for describing how entities relate. Once you see the world through this lens, you will notice mutualism in a shared office space, competition in a bidding war, and parasitism in a loan shark's contract. The forest and the marketplace are not so different after all.
Ecological interactions as a whole are a high-weightage topic within the NCERT Class 12 Biology chapter on Organisms and Populations, and searches like "types of ecological interactions class 12 biology" or "population interactions important questions with examples" are common during exam revision. This umbrella topic ties together predation, competition, mutualism, commensalism, and parasitism — all frequently tested together in CBSE boards and NEET.
Productivity is the rate at which biomass is produced per unit area over a given time. In ecology, it is expressed in terms of weight (grams) per unit area per year, or in terms of energy (kilocalories) per unit area per year. The NCERT textbook clearly states that productivity is measured as weight (g⁻² yr⁻¹) or energy (kcal m⁻² yr⁻¹).
- Option i uses m⁻³, which is volume, not area — incorrect.
- Option ii uses g⁻² yr⁻¹ — correct.
- Option iii uses g⁻¹ yr⁻¹, which lacks area — incorrect.
- Option iv uses kcal m⁻² yr⁻¹ — correct.
Therefore, the correct combination is ii and iv.
Productivity is expressed in terms of g⁻² yr⁻¹ and (kcal m⁻²) yr⁻¹, so the correct choice is (C) ii and iv.
Productivity is measured as biomass produced per unit area per unit time, so the correct units are those that include area (m⁻²) and time (yr⁻¹), making options ii and iv the valid ones.
When we talk about productivity in ecology, we are referring to the rate at which biomass — the organic matter produced by plants through photosynthesis — is generated in an ecosystem. This is a fundamental concept in the study of energy flow and nutrient cycling. The NCERT textbook defines productivity as the rate of biomass production, and it expresses this rate in terms of weight (grams) or energy (kilocalories) per unit area per unit time.
The key here is the phrase "per unit area." Productivity is always measured over a specific area of land or water, because we need to compare how productive different ecosystems are. For example, a tropical rainforest produces far more biomass per square metre than a desert. So the units must include an area component, typically square metres (m⁻²).
Now look at the options given:
-
i. (kcal m⁻³) yr⁻¹ — This uses cubic metres (m⁻³), which is a unit of volume, not area. This would be appropriate for measuring productivity in a three‑dimensional space like a water column, but the standard ecological definition for terrestrial ecosystems uses area. The NCERT, however, does mention that for aquatic ecosystems, productivity can be expressed per unit volume, but the question is about the general expression of productivity. In the standard NCERT treatment, productivity is given as weight or energy per unit area per year. So option i is not the typical expression.
-
ii. g⁻² yr⁻¹ — This is grams per square metre per year. It correctly includes area (m⁻²) and time (yr⁻¹). This is a standard unit.
-
iii. g⁻¹ yr⁻¹ — This is grams per gram per year, which is a ratio (like relative growth rate), not a rate of biomass production per unit area. This is not a measure of productivity in the sense used in ecosystem ecology.
-
iv. (kcal m⁻²) yr⁻¹ — This is kilocalories per square metre per year. It also correctly includes area and time, and is the energy‑based equivalent of option ii.
The NCERT textbook explicitly states that productivity is expressed in terms of weight (g⁻² yr⁻¹) or energy (kcal m⁻² yr⁻¹). It does not use volume‑based units for the general definition.
Therefore, the correct choices are ii and iv.
Always remember: productivity is a rate per unit area per unit time. If the unit lacks an area component (like m⁻²), it is not a measure of productivity in the standard ecological sense.
In short, productivity is expressed as biomass per unit area per year, so the correct options are ii (g⁻² yr⁻¹) and iv (kcal m⁻² yr⁻¹), which corresponds to answer (C).
Check each unit option against the two things a productivity unit must always specify — an AREA term and a TIME term. Any unit missing either one (a bare ratio like g⁻¹yr⁻¹, or a volume like kcal m⁻³yr⁻¹) can be discarded immediately, without needing to recall the exact NCERT wording.
- AP EAPCET 2026Set ap-2026-05-19-FN1 markMCQQ.Assertion (A): According to Gause, two species competing for the same limiting resource can not coexist indefinitely in the same habitat. Reason (R): Competing species promote resource partitioning. (A) Both (A) and (R) are true. (R) is correct explanation for (A) (B) Both (A) and (R) are true. (R) is not correct explanation for (A) (C) (A) is true. But (R) is false (D) (A) is false. But (R) is true
›Reveal solutionSolution
Gause's principle and resource partitioning are both real, true ecological ideas, but they describe two different (almost opposite) outcomes of competition — so while both statements are individually true, the reason does not causally explain the assertion.
Concept and Intuition
Gause's competitive exclusion principle states that when two species compete strongly for the exact same limiting resource within the same niche, one will eventually outcompete and exclude the other — they cannot coexist indefinitely with total niche overlap. Separately, ecologists observe that competing species often evolve resource partitioning — dividing up how, where, or when they use a shared resource (e.g., MacArthur's warblers foraging in different parts of the same tree) — which is precisely the mechanism that lets ecologically similar species coexist despite competition, by reducing niche overlap. So resource partitioning is the escape hatch from competitive exclusion, not a restatement or explanation of why exclusion happens when it does.
Step-by-Step Solution
- Assertion: two species competing for the same limiting resource cannot coexist indefinitely — this is Gause's principle, a true, well-established statement.
- Reason: competing species promote resource partitioning — also a true ecological observation on its own.
- Check causality: does resource partitioning explain competitive exclusion? No — resource partitioning is the process by which species reduce competitive overlap and thereby manage to coexist, which is a different (and arguably opposite) phenomenon from exclusion under complete overlap.
- So both statements are true, but R is not the correct explanation of A.
Common Mistakes
- Assuming any two true ecological statements placed together as assertion-reason must be causally linked; here they describe two related but distinct competition outcomes.
✓Final answerThe correct option is (B) — Both (A) and (R) are true. (R) is not correct explanation for (A).
ANSWER: B
- AP EAPCET 2026Set ap-2026-05-20-FN1 markMCQQ.Assertion (A): Closely related species of warbler birds co-exist on the same tree. Reason (R): The behavioral differences in their foraging activities exhibit competitive release. (A) Both (A) and (R) are true. (R) is correct explanation for (A) (B) Both (A) and (R) are true. (R) is not correct explanation for (A) (C) (A) is true. But (R) is false (D) (A) is false. But (R) is true
›Reveal solutionSolution
The assertion describes MacArthur's real warbler study (true), but the reason mislabels the mechanism — the behavioural foraging differences among the warblers are an example of resource partitioning, not "competitive release," which is a distinct ecological phenomenon.
Concept and Intuition
When multiple similar species share the same habitat without one outcompeting the others, ecologists look for how they divide up the available resources. Resource partitioning (niche differentiation) is exactly this: species reduce competition by using different parts of the resource spectrum — different feeding zones, times, or prey types. Competitive release, in contrast, refers to a species expanding its realized niche or population size after a competing species is removed from the community — it describes a change following the loss of competition, not a mechanism that lets two species coexist side by side.
Step-by-Step Solution
- Evaluate A: Robert MacArthur's famous 1958 study documented five species of closely related warblers all feeding on the same spruce trees. This is a real, well-established ecological example, so A is true.
- Evaluate R: MacArthur found that each warbler species foraged in a different zone of the tree (e.g., outer twigs vs. inner branches, different heights) and used different feeding behaviours/timing — this differential resource use is precisely resource partitioning, the standard explanation for how these species coexist.
- "Competitive release" describes something else entirely — it's what happens when a competing species is removed and the remaining species' niche/population expands into the vacated space. That is not what is happening among the coexisting warblers.
- Since the reason names the wrong phenomenon, R is false, even though the underlying observation (behavioural differences reduce competition) is correctly gestured at — the specific term used is incorrect.
- Therefore: A is true, R is false.
Common Mistakes
- Confusing "resource partitioning" (mechanism allowing coexistence) with "competitive release" (consequence of a competitor's removal) — these are commonly mixed up but describe opposite situations (presence vs. absence of a competitor).
- Assuming that because the general idea ("behavioural differences reduce competition") sounds right, the specific named term must also be correct.
✓Final answerThe correct option is (C) — (A) is true. But (R) is false.
ANSWER: C
- AP EAPCET 2024Set ap-2024-05-16-FN1 markMCQQ.Match the following: List-1: A. Parasitic castration, B. Neoplasia, C. Hyperplasia, D. Hypertrophy List-2: I. Fasciola hepatica, II. Sacculina, III. Larvae of Fasciola, IV. Some viruses, V. Plasmodium (A) A-II, B-IV, C-III, D-V (B) A-II, B-IV, C-I, D-V (C) A-V, B-I, C-IV, D-II (D) A-IV, B-V, C-I, D-III
›Reveal solutionSolution
Parasitic castration–Sacculina, neoplasia–viruses, hyperplasia–Fasciola hepatica, hypertrophy–Plasmodium gives option (B).
Concept and Intuition
Different parasites provoke characteristic host tissue responses: destruction/suppression of gonads (parasitic castration), uncontrolled new growth (neoplasia), increase in cell number (hyperplasia), and increase in cell size (hypertrophy). Each is classically linked to a particular parasite.
Step-by-Step Solution
- Parasitic castration is the textbook effect of the barnacle parasite Sacculina on crabs ⇒ A–II.
- Neoplasia (tumour formation) is induced by certain oncogenic viruses ⇒ B–IV.
- Hyperplasia of the bile-duct epithelium is caused by the adult liver fluke Fasciola hepatica ⇒ C–I.
- Hypertrophy (enlargement of host cells) is associated with Plasmodium ⇒ D–V.
- Combining: A-II, B-IV, C-I, D-V ⇒ option (B); 'Larvae of Fasciola' (III) is the unused distractor.
Common Mistakes
- Assigning hyperplasia to the larval stage (III) rather than the adult fluke Fasciola hepatica (I) that resides in the bile ducts.
- Swapping castration and neoplasia agents.
✓Final answerThe correct option is (B) — A-II, B-IV, C-I, D-V.
ANSWER: B
- AP EAPCET 2024Set ap-2024-05-16-FN1 markMCQQ.Identify the incorrect statement (A) Both the species are benefitted in mutualism (B) Both species are not benefitted in parasitism (C) Both species get harm in competition (D) One species is benefitted and the other is neither benefitted nor harmed in commensalism
›Reveal solutionSolution
Parasitism is a (+, −) interaction: the parasite gains, the host loses — so the statement that neither species benefits is factually wrong.
Concept and Intuition
Species interactions are classified by their net effect on each partner:
- Mutualism (+, +): both benefit.
- Parasitism (+, −): parasite benefits, host is harmed.
- Competition (−, −): both are harmed (each reduces the other's access to a shared limited resource).
- Commensalism (+, 0): one benefits, the other is neither helped nor harmed.
Step-by-Step Solution
- (A) Mutualism — both benefited — correct statement.
- (B) Parasitism — claims neither species benefits, but the parasite clearly benefits (gets nutrition at host's expense) — this statement is factually wrong.
- (C) Competition — both harmed — correct statement.
- (D) Commensalism — one benefited, other unaffected — correct statement.
- Hence (B) is the incorrect statement being asked for.
Common Mistakes
- Thinking parasitism harms both parties equally; in reality it is asymmetric — the parasite always benefits.
✓Final answerThe correct option is (B) — Both species are not benefitted in parasitism.
ANSWER: B
- AP EAPCET 2024Set ap-2024-05-17-AN1 markMCQQ.Identify A, B, C plants in a series based on these characters of roots A. Roots at lower nodes of stem B. Roots absorb water and food from host plant C. Root forming nodules (A) Vanda, Viscum, Cuscuta (B) Avicinnea, Striga, Pisum (C) Maize, Viscum, Vanda (D) Sugarcane, Rafflesia, Groundnut
›Reveal solutionSolution
This tests matching three distinct root modifications to their classic textbook examples: nodal/stilt roots, total-parasite roots absorbing both water and food, and nitrogen-fixing nodule roots.
Concept and Intuition
Root modifications serve varied functions beyond anchorage and absorption. Stilt/prop roots arise adventitiously from lower stem nodes to give extra mechanical support to tall grass-like stems (classic examples: maize, sugarcane). A hemi-parasite (like Viscum) retains chlorophyll and draws only water/minerals from its host, but a true holo-parasite lacking chlorophyll entirely (like Rafflesia, which grows almost entirely embedded within its host Tetrastigma vine's tissue) must draw both water and organic food/nutrients from the host through its haustorial roots. Legumes characteristically develop root nodules that house symbiotic nitrogen-fixing Rhizobium bacteria, converting atmospheric nitrogen into usable forms — groundnut and pea are the standard textbook examples.
Step-by-Step Solution
- A — 'Roots at lower nodes of stem': Sugarcane (and maize) develop adventitious stilt roots from the lower nodes for extra support.
- B — 'Roots absorb water and food from host plant' (both, implying no photosynthesis of its own): Rafflesia is a total root-parasite with no chlorophyll, fully dependent on its host for water and food.
- C — 'Root forming nodules': Groundnut, a legume, forms nitrogen-fixing root nodules.
- Matching gives Sugarcane–Rafflesia–Groundnut, exactly option (D).
- Cross-check other options: (C)'s third entry Vanda is an epiphyte (aerial roots absorbing moisture from air, not forming nodules) — fails criterion C; (B)'s Avicinnea has pneumatophores (breathing roots), not nodal stilt roots — fails criterion A.
Common Mistakes
- Confusing a hemi-parasite (only water/minerals, still photosynthesises) with a holo-parasite (both water and food, no chlorophyll) when the clue explicitly says 'water AND food'.
- Mistaking an epiphyte's aerial/velamen roots for nodule-forming roots.
✓Final answerThe correct option is (D) — Sugarcane, Rafflesia, Groundnut.
ANSWER: D
- AP EAPCET 2024Set ap-2024-05-17-FN1 markMCQQ.Study the following and pick up the incorrect statements: I. In commensalism both partners are benefitted due to each other. II. In amensalism no partner is benefitted. III. In parasitism, one partner is benefitted and the other is harmed. IV. In competition both the partners are benefitted (A) I, II (B) II, III (C) III, IV (D) I, IV
›Reveal solutionSolution
This tests the precise definitions of interspecific interactions; commensalism (I) and competition (IV) are misstated, so they are the incorrect statements.
Concept and Intuition
Ecological interactions between two species are classified by the net effect on each partner (using +, 0, − notation):
- Commensalism (+, 0): one species benefits, the other is neither harmed nor helped.
- Amensalism (0, −): one species is harmed, the other is unaffected — so indeed "no partner is benefitted" is a true description.
- Parasitism (+, −): one species (parasite) benefits, the other (host) is harmed.
- Competition (−, −): both competing species are negatively affected as they vie for the same limited resource; neither "benefits."
Step-by-Step Solution
- Statement I claims commensalism benefits both partners — false, since by definition only one benefits.
- Statement II claims no partner is benefited in amensalism — true, since the interaction is (0, −).
- Statement III claims parasitism has one benefited, one harmed — true, matches (+, −).
- Statement IV claims competition benefits both partners — false, since competition is (−, −), harming both.
- The incorrect statements are I and IV, i.e., option (D).
Common Mistakes
- Confusing commensalism with mutualism (mutualism is the one where both partners genuinely benefit).
- Assuming competition always has a "winner who benefits" — ecologically, competitive interactions are classified as harmful to both parties even if one suffers less.
✓Final answerThe correct option is (D) — I, IV.
ANSWER: D
- AP EAPCET 2023Set ap-2023-05-22-AN1 markMCQQ.Assertion (A): Life cycle of ectoparasites is more complex with many developmental stages. Reason (R): Developmental stages of endoparasites have better chances to reach definitive host. (A) Both A and R are correct and R is the correct explanation of A. (B) Both A and R are correct but R is not the correct explanation of A. (C) A is correct but R is incorrect. (D) A is incorrect but R is correct.
›Reveal solutionSolution
The complex, multi-stage life cycle belongs to endoparasites, not ectoparasites, so the Assertion is wrong — but the Reason's point about developmental stages and reaching the definitive host is a correct, independent statement about parasite biology.
Concept and Intuition
Parasites are broadly classed as ectoparasites (living on the host's external surface, e.g. lice, ticks, leeches) and endoparasites (living inside the host's body, e.g. tapeworms, liver flukes, Plasmodium). Ectoparasites, being already in direct contact with a host's exterior, generally have comparatively simpler life cycles and can move between hosts more directly. Endoparasites, by contrast, must get their offspring out of one host's body and into a new one (often via intermediate hosts, vectors, or environmental stages), a much harder journey — which is exactly why endoparasites have evolved elaborate, multi-stage life cycles (and produce huge numbers of eggs/larvae) to compensate for the difficulty of successfully completing the cycle.
Step-by-Step Solution
- Evaluate the Assertion: it claims ectoparasites have the more complex, many-staged life cycle — this reverses the standard biology, where endoparasites are the ones with complex multi-stage, often multi-host cycles; Assertion is incorrect.
- Evaluate the Reason as an independent statement: whether a developmental stage of a parasite can successfully reach a new definitive host is indeed a central factor governing parasite life-cycle evolution and strategy; taken on its own, this is a correct, sound biological statement.
- Since the Assertion is false while the Reason is an independently true statement, the matching option is the one recording exactly that combination.
Common Mistakes
- Assuming 'ecto-' (external, more exposed) intuitively sounds like it should face more challenges and hence have a 'more complex' cycle — the textbook classification is actually the opposite.
- Trying to judge R only in the context of a false A rather than assessing it as its own standalone factual claim.
✓Final answerThe correct option is (D) — A is incorrect but R is correct.
ANSWER: D
- AP EAPCET 2022Set ap-2022-07-12-FN1 markMCQQ.The response and behavior of an organism with environment and other organisms of its biotic community is called (A) Camouflage (B) Homeostasis (C) Niche specialization (D) Speciation
›Reveal solutionSolution
An organism's specific functional role — how it behaves and interacts with its physical environment and with other organisms of its community — defines its ecological niche, i.e. niche specialization.
Concept and Intuition
The ecological niche of a species describes its complete functional role within an ecosystem: what it eats, where and how it lives, and how it behaves and interacts with both the physical (abiotic) environment and other organisms of its biotic community. Niche specialization refers to this specific, defined set of behaviors/interactions/adaptations a species has evolved. Homeostasis refers to internal physiological regulation (not interaction with the environment/community), camouflage is a specific anti-predator adaptation, and speciation is the process of new species formation — none of these describe the broad behavior-with-environment-and-community concept being asked about.
Step-by-Step Solution
- The question describes 'behavior of an organism with environment and other organisms of its biotic community.'
- This functional-role description matches the concept of ecological niche.
- Among the options, niche specialization is the term for a species' defined niche/role, distinguishing it from homeostasis (internal regulation), camouflage (an adaptation), and speciation (species formation).
Common Mistakes
- Confusing niche (an organism's role/interactions) with habitat (merely where it lives) or homeostasis (internal, not environmental, regulation).
✓Final answerThe correct option is (C) — Niche specialization.
ANSWER: C
- AP EAPCET 2021Set ap-2021-09-03-AN1 markMCQQ.Match the following? List I | List IIi) Calotropis | a) Predator of Americana Pacificii) Cactus | b) Insects and frogs cryptically colorediii) Pisaster | c) Distasteful glycosidesiv) Monarch Butterfly | d) Cardiac glycosidesv) Camouflage | e) Predator is moth (A) (i – c), (ii – e), (iii – a), (iv – d) & (v – b) (B) (i – d), (ii – e), (iii – a), (iv – c) & (v – b) (C) (i – a), (ii – d), (iii – e), (iv – c) & (v – b) (D) (i – e), (ii – d), (iii – c), (iv – a) & (v – b)
›Reveal solutionSolution
This tests five classic ecology examples of anti-predator/defense strategies and species interactions.
Concept and Intuition
Organisms defend themselves from predation through chemical defense (toxic/distasteful compounds), being preyed upon by a specific natural enemy (biological control), acting as a keystone predator in an ecosystem, or through camouflage (cryptic colouration).
Step-by-Step Solution
- Calotropis — a weed abundant in dry areas, produces highly poisonous cardiac glycosides, which is why herbivores avoid browsing it → (i–d).
- Cactus — the prickly-pear cactus (Opuntia), introduced in Australia, became invasive until it was controlled biologically by the Cactoblastis moth, whose larvae feed on the cactus (i.e., its predator is a moth) → (ii–e).
- Pisaster — the sea star Pisaster ochraceus is the textbook keystone predator of the American Pacific coast, famous from Robert Paine's removal experiment → (iii–a).
- Monarch butterfly — its caterpillar feeds on milkweed and sequesters cardiac-glycoside-like compounds, making the butterfly highly distasteful to bird predators → (iv–c).
- Camouflage — classically illustrated by insects and frogs that are cryptically coloured, matching their background to avoid detection → (v–b).
Common Mistakes
- Confusing "cardiac glycosides" (Calotropis, a plant defense) with "distasteful glycosides" (Monarch butterfly, an acquired defense) since both involve glycosides.
- Not recognising the Cactoblastis-moth/Opuntia-cactus biological control story, which is the only sensible fit for "predator is moth."
✓Final answerThe correct option is (B) — (i – d), (ii – e), (iii – a), (iv – c) & (v – b).
ANSWER: B
- AP EAPCET 2021Set ap-2021-09-03-AN1 markMCQQ.Match the following. The correct combinations are List I | List II | List IIIa) Fig tree | i) Highly distasteful | p) petals of its flowerb) Ophrys | ii) Cryptically colored | q) special chemical presentc) Sea anemone | iii) Wasp | r) clown fishd) Camouflage | iv) Sexual deceit | s) developing seedse) Monarch butterfly | v) Stinging cells | t) Insects & frogs (A) (a – iv – p), (b – iii – t), (c – v – r), (d – ii – q), (e – i – s) (B) (a – i – q), (b – iii – s), (c – v – r), (d – ii – t), (e – iv – p) (C) (a – iii – s), (b – iv – p), (c – v – r), (d – ii – t), (e – i – q) (D) (a – iii – p), (b – iv – s), (c – v – r), (d – ii – t), (e – i – q)
›Reveal solutionSolution
This tests five classic species-interaction/defense examples, each requiring the correct mechanism AND the correct associated structure/organism.
Concept and Intuition
Each row links a species/phenomenon (List I) to its defense/interaction type (List II) and a specific structural/biological detail (List III). These are the standard textbook case studies of species interactions and predator-avoidance strategies.
Step-by-Step Solution
- Fig tree — has an obligate one-to-one relationship with its pollinating wasp (iii); the wasp lays eggs inside the fig's syconium, and its larvae feed on some of the developing seeds (s) → (a–iii–s).
- Ophrys (bee orchid) — practises sexual deceit (iv): its petals (p) mimic the appearance/scent of a female bee, luring male bees to "pseudocopulate" and thereby pollinate the flower → (b–iv–p).
- Sea anemone — has stinging cells/nematocysts (v) in its tentacles that deter most predators, yet the clownfish (r) lives safely among them, immune to the stings, gaining protection → (c–v–r).
- Camouflage — achieved by being cryptically coloured (ii), classically shown by insects & frogs (t) that blend into their background → (d–ii–t).
- Monarch butterfly — is highly distasteful (i) to predators because of a special chemical (q) sequestered from the milkweed it feeds on as a caterpillar → (e–i–q).
Common Mistakes
- Swapping the Fig-tree/wasp row with the Monarch-butterfly row, since both involve a specific chemical/relationship with an insect.
- Assigning "developing seeds" to the Ophrys row instead of the Fig-tree row.
✓Final answerThe correct option is (C) — (a – iii – s), (b – iv – p), (c – v – r), (d – ii – t), (e – i – q).
ANSWER: C
- AP EAPCET 2021Set ap-2021-09-07-FN1 markMCQQ.Roots in some gymnospermic genera have fungal association in the form of A in B. Here A and B refers to ____ (A) A – lichen; B – cycas (B) A – lichen; B – pinas (C) A – mycorrhiza; B – cycas (D) A – mycorrhiza; B – pinas
›Reveal solutionSolution
This tests gymnosperm root symbioses; the FUNGAL association (mycorrhiza) is a documented feature of Pinus roots, distinct from the cyanobacterial (BGA) coralloid-root association seen in Cycas.
Concept and Intuition
Gymnosperms show two different types of symbiotic root associations that are often confused:
- Mycorrhiza — a symbiotic association between roots and certain fungi, well known in genera like Pinus, aiding mineral/water absorption.
- Coralloid roots — specialized roots in Cycas that harbor symbiotic, nitrogen-fixing cyanobacteria (blue-green algae, e.g., Anabaena), not fungi.
Step-by-Step Solution
- The question specifically asks about a fungal association ("in the form of A"), which points to mycorrhiza, not the cyanobacterial coralloid-root symbiosis.
- Mycorrhiza in gymnosperms is classically associated with Pinus roots.
- So A = mycorrhiza, B = Pinus (printed as "pinas", a typographic rendering of Pinus).
- This matches option (D).
Common Mistakes
- Confusing mycorrhiza (fungal, found in Pinus) with the coralloid root–cyanobacteria symbiosis (found in Cycas) — both are gymnosperm root symbioses but with completely different microbial partners.
- Mistaking "lichen" (a fungus-alga symbiotic organism, unrelated to gymnosperm roots) for the correct term.
✓Final answerThe correct option is (D) — A – mycorrhiza; B – pinus.
ANSWER: D
- AP EAPCET 2021Set ap-2021-09-06-FN1 markMCQQ.Match the following related to effects of parasites on host? Parasite | Effect on host | Host effecteda) Sacculina | i) Hypertrophy | p) Sheepb) Larva of Fasciola | ii) Hyperplasia | q) Snailc) Plasmodium | iii) Parasitic castration | r) Carcinusd) Fasciola hepatica | iv) Gigantism | s) Man (A) (a – iii – r), (b – ii – p), (c – i – s), (d – iv – q) (B) (a – iv – r), (b – ii – p), (c – i – s), (d – iii – q) (C) (a – iii – r), (b – iv – q), (c – i – s), (d – ii – p) (D) (a – iii – r), (b – ii – p), (c – iv – s), (d – i – q)
›Reveal solutionSolution
This tests the specific pathological effect each parasite (or life-stage) produces on its host; the correct match is (C).
Concept and Intuition
Different parasites — and even different life-stages of the same parasite in different hosts — cause distinct pathological effects. This question specifically tests knowing that a larva can affect its intermediate host quite differently from how the adult affects its definitive host.
Step-by-Step Solution
- Sacculina, a parasitic barnacle, causes parasitic castration of its crab host Carcinus → (a – iii – r).
- The larval stages of Fasciola hepatica developing inside the snail (Lymnaea) cause gigantism of the snail → (b – iv – q).
- Plasmodium infection in man causes hypertrophy (enlargement) of the spleen → (c – i – s).
- The adult Fasciola hepatica living in a sheep's bile duct causes hyperplasia of the duct's epithelial lining → (d – ii – p).
Common Mistakes
- Assigning gigantism to the adult fluke in sheep rather than the larva in the snail.
- Swapping hypertrophy and hyperplasia between the Plasmodium/man and Fasciola/sheep rows.
✓Final answerThe correct option is (C) — (a – iii – r), (b – iv – q), (c – i – s), (d – ii – p).
ANSWER: C
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