Chapter 18 — Ecology and biological reference

Begin with a place and its interactions

An ecosystem consists of organisms and the nonliving environment interacting in a defined setting. A pond includes algae, aquatic plants, animals and microorganisms together with water, dissolved substances, light and temperature. A forest includes trees but is not simply a count of trunks. A habitat is the place or type of environment where an organism lives; a niche describes its role and relationships in that setting. These are related concepts, not synonyms. A question may ask where a frog lives or what it eats and does; the first points to habitat, the second to niche.

Biotic components are living organisms; abiotic components include physical and chemical factors such as light, water, temperature and mineral nutrients. Dead organic matter is not alive but participates in the ecosystem through decomposition. A decomposition question should not assume that fallen leaves disappear without material transformation. Bacteria and fungi can break down organic matter, returning nutrients to forms that can move through the environment. Energy, however, is not recycled in the same closed loop as atoms: energy enters, moves through organisms and is dissipated as heat.

Producers such as green plants use light to build organic matter. Herbivores consume producers; predators consume other animals; decomposers process dead material and wastes. A food chain represents one route of feeding and energy transfer. A food web combines connected chains because a species often has more than one food source or consumer. The arrow in a food-chain diagram conventionally points from food to eater, showing direction of energy and matter transfer. If grass is eaten by a grasshopper, write grass → grasshopper, not the reverse merely because the grasshopper moves toward the grass.

Trophic levels and transfer

A trophic level is a feeding position in an ecological pathway. Producer is the first level in a simple grazing chain, primary consumer the next, then secondary consumer. An organism may occupy different levels in different feeding relationships: a human eating rice is a primary consumer in that route; a human eating an herbivorous fish may be at a higher level. Labels attach to the specific chain under discussion, not permanently to the species in all contexts. An omnivore illustrates why a web is often more accurate than a single ladder.

At each transfer, only a portion of energy captured at one level becomes biomass available to the next; much is used in metabolism and dissipated. A common school illustration uses about 10% transfer, but it is a rough teaching approximation, not an invariant physical law. If a question explicitly says “assume 10%,” use the arithmetic. For example, 10,000 units at producers would give 1,000 at primary consumers and 100 at secondary consumers under that assumed rule. If no assumption is supplied, avoid claiming that every ecosystem has exactly those fractions.

Biomass pyramids and energy pyramids differ. An energy pyramid tracks energy flow per unit area and time and is upright in the conventional ecological account because transfer loses usable energy at each step. A biomass pyramid describes standing material at a given time; in some aquatic systems it can appear inverted because small producer biomass turns over quickly. A question that says “all ecological pyramids are always upright” mixes these measures. Read the axis and unit. Numbers of organisms can have still another shape, depending on the size and abundance of species.

Biomagnification occurs when a persistent substance becomes more concentrated at successive trophic levels under suitable food-web conditions. It does not happen to every pollutant or every nutrient. Bioaccumulation refers to buildup in an individual organism over time; biomagnification compares levels along feeding relationships. A question may offer these two similar terms. Ask whether it describes one organism's exposure history or increasing concentration among consumers. Do not infer a specific contaminant level from the trophic position alone without measurements.

Cycles of matter

Water evaporates or transpires into the atmosphere, condenses and returns through precipitation, runoff or infiltration. The water cycle moves water among reservoirs; it does not create new water with each rainfall. Carbon moves among atmosphere, organisms, oceans and rocks through processes including photosynthesis, respiration, decomposition and combustion. A tree can take in atmospheric CO₂ during growth, but it also respires and ultimately returns carbon through other processes. A single arrow “tree absorbs carbon” is too incomplete for questions about a full cycle.

Nitrogen gas is abundant in air, but many organisms cannot use N₂ directly. Nitrogen-fixing microorganisms and other processes convert it into biologically usable forms. Plants take up suitable nitrogen compounds; animals obtain nitrogen largely through food; decomposition and microbial processes return forms to soil and atmosphere. A question that says fertilizer “adds energy” to plants mislabels the role of mineral nutrient supply. Mineral cycles track atoms; sunlight supplies much of the energy entering a typical green-plant food web.

Oxygen is produced in oxygenic photosynthesis and used in many respiration and combustion processes. The global oxygen cycle has multiple reservoirs and time scales. Do not infer that a single plant “produces all the oxygen it needs” at every moment. Respiration occurs day and night, while photosynthesis in a given leaf depends on light. At the ecosystem scale, exchange depends on growth, decomposition and many organisms. This is a good example of why local and global statements may differ.

Biodiversity, adaptation and conservation

Biodiversity includes variation within species, among species and among ecosystems. Species count is one measure but does not cover all genetic or ecological variation. An endemic species is restricted naturally to a particular geographic area; an invasive species establishes outside its native range and can cause ecological harm in a new setting. The terms require geographic and ecological context. A species common in one district is not automatically endemic there. A newly introduced species is not automatically invasive merely because it is foreign; evidence of establishment and impact matters.

Adaptation is an inherited characteristic shaped over generations that improves performance in a particular environment under the relevant conditions. An individual can also acclimatise during its lifetime, but that is not the same process as evolutionary adaptation. A cactus-like water-storing stem and reduced leaf area can help conserve water in some arid-adapted plants, but no single structure defines every dryland species. An organism's trait may have trade-offs: a feature useful in one habitat may carry costs in another. A multiple-choice statement claiming an adaptation gives “perfect survival” is too absolute.

Conservation can occur in situ, protecting species and habitats where they live, or ex situ, maintaining living or genetic material outside its usual habitat. Protected areas can support in-situ conservation; seed banks and some captive-breeding programmes are ex-situ examples. Neither category alone guarantees long-term success: habitat quality, genetic diversity, ecological interaction and management matter. A seed bank cannot store every organism in the same form, and a protected area is not automatically free from all human influence. The exam-safe distinction is location and method, not a claim of universal effectiveness.

Pollution, habitat change, overuse and climate shifts can alter ecosystems. Causation must be matched to evidence rather than inferred from one observation. If fish die in a pond, possible causes include low dissolved oxygen, toxic exposure, disease or other stressors; a green algal bloom may support a hypothesis but does not alone prove a specific pollutant or source. A well-posed data question gives measurements, timing and a comparison. This reasoning carries the same scientific-method theme introduced in Physics.

Biological names and evidence

Scientific names help distinguish species across local languages. In binomial nomenclature, the first part is the genus and the second is the specific epithet. Homo sapiens is a familiar example: genus capitalised, epithet lower case, both conventionally italicised in print. A common name can refer to multiple species, and one species can have multiple common names. An MCQ might ask which is the genus in a two-part name; choose the first word rather than treating both words as two separate organisms.

Classification changes with evidence, especially genetic evidence. Two organisms with similar body shape may have evolved that shape independently. A whale's streamlined form does not make it a fish; its mammalian ancestry and traits provide a better classification. Fossils, anatomy and molecular data can each contribute to evolutionary inference. A school-level tree diagram shows proposed shared ancestry, not a ranking in which one living species is “more advanced” than another. Avoid reading its vertical position as a ladder of worth.

Worked food-web route

Suppose a simplified chain reads grass → grasshopper → frog → snake. Grass is producer, grasshopper primary consumer, frog secondary consumer and snake tertiary consumer in this chain. If the frog also eats a plant-feeding insect from another route, that is compatible with the same broad level here. If a question asks which organism loses energy to its predators, every consumed organism can do so; if it asks where energy first enters the chain, the green producer capturing sunlight is the answer. Trace the arrow meanings before assigning labels.

For a stated 10% transfer exercise, give producers 20,000 kJ of captured energy available in the stated model. Primary consumers receive 2,000 kJ, secondary consumers 200 kJ and tertiary consumers 20 kJ. This is arithmetic under an explicit assumption. It does not imply that an individual frog contains exactly 200 kJ or that transfer efficiency is always 10% in nature. The unit kJ is energy; if the diagram asks for biomass in kg, the energy numbers cannot simply be relabelled.

Population, community and ecosystem: identify what is included

A population is a group of individuals of the same species in a defined area and time. A community includes populations of different species interacting in that area. An ecosystem also includes the nonliving environment and its interactions with organisms. “All frogs of one species in a pond” can identify a population; “frogs, insects, algae and other organisms in the pond” identifies a community; adding water chemistry, light and material exchange moves the description towards an ecosystem. The boundary is chosen for the question and need not coincide with a district boundary.

Population size changes through births, deaths, immigration and emigration. In a simple accounting model, next population = initial population + births + immigrants − deaths − emigrants. If a population starts at 500, has 70 births and 20 immigrants, and loses 40 through death and 10 through emigration, the result is 540. Net increase is 40, or 8% of the initial population. This calculation assumes the categories are measured over the same interval and that individuals are not counted twice. It does not predict the next year's numbers without further assumptions.

Density expresses population relative to area or volume. Forty individuals in 2 hectares give 20 per hectare, while 100 individuals in 10 hectares give 10 per hectare. The second area has more individuals but a lower density. Comparing density requires comparable habitat, sampling method and time. Some organisms are clustered rather than evenly distributed, so the mean does not describe every small patch. An abundance estimate is stronger when its method and uncertainty are stated than when a single observed group is treated as the whole population.

Sampling: quadrats and capture estimates

A quadrat defines a sampled area for counting or estimating cover, often used for plants and relatively immobile organisms. Suppose five randomly placed 1-square-metre quadrats contain 4, 6, 3, 5 and 7 individuals of a plant species. Mean count is 25/5 = 5 per square metre. A 200-square-metre plot with comparable distribution would have an estimated 1,000 individuals using that simple extrapolation. This is an estimate, not a census. Non-random placement only in lush patches could bias it upwards; selecting bare patches could bias it downwards.

A transect samples along a line or band and can reveal changes across an environmental gradient, such as distance from water. It answers a different design need from scattering quadrats randomly over a homogeneous plot. Repeated samples improve the evidence but do not repair every biased design. If all quadrats are placed near a convenient path, taking many of them may still fail to represent the interior. Exam questions about reliability often require identifying representative sampling, controlled methods and sufficient replication rather than merely choosing the largest count.

A simple mark–recapture teaching estimate uses N approximately equal to M × C/R, where M is the number initially marked and released, C is the later sample size, and R is the number of marked individuals recaptured. With M = 40, C = 50 and R = 10, estimated population is 200. This assumes a sufficiently closed population, retained marks, mixing and comparable capture chances. If marks make animals easier to catch or disappear between samples, the estimate can be biased. It is a mathematical illustration of sampling, not an instruction to handle wildlife without appropriate expertise and permissions.

Productivity is a flow; biomass is a stock

Gross primary productivity is the rate at which producers capture energy into organic material in the defined account. Producers use some of that energy in respiration. Net primary productivity is what remains after producer respiration: NPP = GPP − R. If GPP is 1,200 energy units per square metre per year and producer respiration is 450 in the same units, NPP is 750. Keep the area and time terms attached because productivity is a rate. A standing biomass measurement in kilograms on one date is a stock and cannot simply be substituted into the same equation without a rate interpretation.

Consumers do not receive all primary production as growth. Some material is uneaten, some ingested material is not assimilated, and assimilated energy supports respiration as well as new tissue. A question may give separate efficiencies for these stages. If 1,000 units are ingested, 600 assimilated and 120 retained as new biomass, assimilation efficiency is 600/1,000 = 60%, while production as a fraction of assimilated energy is 120/600 = 20%. Dividing 120 by 1,000 answers a third question: 12% of ingested energy becomes new biomass in that example.

Under an explicitly assumed 10% transfer model, reverse calculations divide by 0.1 for each step towards the producer level. If a tertiary consumer level receives 30 units, the secondary level requires 300, the primary level 3,000 and the producer level 30,000 in that model. There are three transfers from producer to tertiary consumer. Counting trophic levels as if each were a transfer produces an extra factor of ten. Draw the arrows and count the gaps between levels before multiplying or dividing.

Interactions: use the effect on both partners

In mutualism, both partners benefit in the relationship being described. In commensalism, one benefits while the other has no substantial measured benefit or harm in the simplified account. In parasitism, the parasite benefits while the host is harmed. Predation also benefits a consumer and harms its prey but usually involves capture and consumption rather than the sustained association typical of many parasites. Competition can reduce access to limited resources for both participants. These labels describe interactions, so the effect on each partner matters more than whether the organisms are physically close.

A pollinating insect may receive food while helping a plant reproduce, illustrating a mutualistic relationship when both effects occur. A parasite taking resources from its host does not become mutualistic merely because it spends a long time there. Two plant species competing for limited light may affect each other without touching. The strength and even outcome of an interaction can depend on environmental conditions. For a well-posed introductory MCQ, use the effects stated in the stem and do not add an unmentioned benefit to make a favourite label fit.

An ecological niche includes resource use, environmental tolerances and relationships. Two species living in the same habitat need not occupy identical niches. Different feeding times, food sizes or nesting sites can reduce direct overlap. Habitat answers where the organism lives; niche describes more of how it lives within the ecological system. A tree can provide habitat for several organisms with different niches, so “same tree” does not imply “same ecological role.” This is often a stronger discriminator than memorising one sentence for each term.

Nitrogen-cycle verbs that should not be swapped

Nitrogen fixation converts atmospheric nitrogen into forms that can enter biological use. Ammonification releases ammonium from organic nitrogen during decomposition. Nitrification oxidises ammonium through nitrite to nitrate in the conventional aerobic account. Denitrification converts oxidised nitrogen compounds towards gaseous nitrogen forms under suitable conditions, often in oxygen-limited environments. These processes involve different transformations. A question asking which process returns nitrogen gas to the atmosphere should not be answered with fixation simply because both involve nitrogen gas somewhere in the description.

Plants assimilate suitable inorganic nitrogen compounds into organic molecules. Animals obtain much of their nitrogen by eating organic material, and decomposition returns nitrogen from wastes and dead organisms to environmental pools. Fertiliser can increase available nutrients but does not create a new source of sunlight energy. Excess nutrient loss into water can contribute to eutrophication. The cycle therefore links agricultural inputs, plant growth, decomposition and water quality without treating every nitrogen compound as interchangeable.

Carbon-cycle questions also require verbs. Photosynthesis incorporates carbon from carbon dioxide into organic compounds; respiration and decomposition can release carbon dioxide; combustion of carbon-containing fuel transfers carbon to gases and other products. A growing forest may accumulate carbon overall, yet its organisms still respire. Net storage depends on gains and losses over the stated boundary and time. An isolated photograph of a green area does not quantify its annual carbon balance.

Succession, disturbance and conservation choices

Ecological succession describes changes in community composition over time. Primary succession begins where developed soil and many biological legacies are initially absent, as in an idealised newly exposed substrate. Secondary succession occurs after a disturbance where soil or other biological remnants persist. The distinction is the starting condition, not simply whether trees are present on the observation date. A fire does not necessarily remove all soil and seed sources, so succession after fire is commonly secondary in the usual school comparison.

Succession is not a guarantee that every place moves through one identical list of species towards an unchanging endpoint. Climate, disturbance, available colonists, soil and land use affect the course. Pioneer species can alter conditions for later organisms, but later arrival is not a ranking of moral worth or biological perfection. Exam descriptions often supply enough information to identify the starting condition or a mechanism, such as soil formation or shade. Use that evidence rather than forcing every example into the same memorised sequence.

In-situ conservation protects organisms within their ecological setting, preserving relationships as well as individual specimens. Ex-situ approaches can provide backup populations, genetic material or controlled propagation when suitable. Maintaining a species in a collection does not automatically preserve its entire wild ecosystem, while designating a protected area does not automatically solve every threat. A practical comparison asks what is being protected, where it is protected and how success is assessed. Statutory categories and current protected-area counts belong to dated legal or current-affairs sources and should be verified separately.

Biomagnification calculations and measurement limits

Suppose measured concentrations of a persistent substance are 0.02 mg/kg in producers, 0.10 mg/kg in herbivores and 0.50 mg/kg in predators in a simplified food chain. Concentration rises fivefold at each displayed step and twenty-fivefold from producer to predator. The pattern is consistent with magnification in this supplied example. It does not mean a predator contains more total pollutant mass than the entire producer population, because concentration and total mass differ. Total amount requires both concentration and the amount of material considered.

If a 2 kg sample contains the substance at 0.50 mg/kg, the amount in that sample is 1.0 mg. If a 100 kg sample is at 0.02 mg/kg, its amount is 2.0 mg despite the lower concentration. Units expose the distinction. Real assessments also require comparable tissues, moisture basis, sampling and analytical methods. A higher measured value at one site does not by itself identify the source of contamination or establish a complete food-web pathway.

Retrieval practice with reasons

Problem A: A population starts at 300, gains 50 births and 10 immigrants, and loses 20 deaths and 15 emigrants. Final size is 325 and increase is 25. Problem B: Mean density is 8 plants per square metre over a representative sample; the estimated number in 50 square metres is 400. Problem C: GPP is 900 and producer respiration 350 in matching rate units. NPP is 550 in those units.

Problem D: A return of nitrogen to atmospheric gas points towards denitrification in the stated nitrogen-cycle comparison. Problem E: Soil remains after a disturbance, making secondary succession the usual school classification. Problem F: A 4 kg sample at 0.25 mg/kg contains 1 mg of the substance. Problem G: Two organisms share a pond but feed on different resources at different times. Sharing habitat does not prove identical niches. Write the relevant process or unit beside each answer before moving to the chapter practice set.

Recall and review

Separate ecosystem, habitat and niche. Identify producer, consumer and decomposer in a food web and draw arrows from food to eater. Use a stated transfer percentage without treating it as universal. Distinguish energy flow from cycling of water, carbon and nitrogen. Compare bioaccumulation with biomagnification and in-situ with ex-situ conservation. Finally, read a scientific name and a simple evolutionary tree without turning either into a hierarchy of value. Attempt the chapter practice set, then use the explanations to revisit any uncertain concepts.

Figure 18. Original chapter diagram.

Practice 32 questions

Choose one answer for each item. The answer key and explanations follow this chapter set.

1. Who introduced binomial nomenclature, the two-word system of naming species?

A. Gregor Mendel B. Carl Linnaeus C. Charles Darwin D. R.H. Whittaker

2. The hump of a camel stores which substance that can be metabolised for energy and water?

A. Fat B. Water C. Protein D. Salt

3. World Heart Day is observed every year on which date?

A. 1 December B. 29 September C. 14 June D. 10 October

4. Cushing syndrome is associated with prolonged exposure to excessive amounts of which hormone or hormone-like medicine?

A. Insulin B. Thyroxine C. Cortisol or a glucocorticoid D. Vasopressin

5. In an ecological community, two bird species feed on the same limited insect prey. Which interaction is most likely when both reduce each other’s access to food?

A. Mutualism B. Commensalism C. Competition D. Parasitism

6. Among glands whose primary role is endocrine hormone secretion, which is usually the largest in a human adult?

A. Adrenal B. Pineal C. Pituitary D. Thyroid

7. Match List I (Observance) with List II (Scientist whose birthday or discovery it marks):
List I: A. World Diabetes Day B. World Hepatitis Day C. World Blood Donor Day D. World Tuberculosis Day
List II: 1. Robert Koch 2. Baruch Blumberg 3. Karl Landsteiner 4. Frederick Banting

A. A-3, B-2, C-4, D-1 B. A-4, B-2, C-1, D-3 C. A-2, B-4, C-3, D-1 D. A-4, B-2, C-3, D-1

8. Match each vitamin with the named form: A vitamin A (retinol); B vitamin B1; C vitamin C; D vitamin K1. Forms: 1 thiamine; 2 retinol; 3 phylloquinone; 4 ascorbic acid.

A. A-2, B-4, C-1, D-3 B. A-2, B-1, C-4, D-3 C. A-1, B-2, C-4, D-3 D. A-2, B-1, C-3, D-4

9. A freshwater pond has many microscopic algae and relatively few fish, yet fish biomass at one instant exceeds algal biomass. Which ecological pyramid can then be inverted?

A. Pyramid of energy B. Pyramid of biomass C. Pyramid of trophic energy flow D. Pyramid of ecological efficiency

10. An ecosystem has gross primary productivity of 950 kJ per square metre per year. Producers use 350 kJ per square metre per year in respiration. What is its net primary productivity?

A. 350 kJ per square metre per year B. 600 kJ per square metre per year C. 950 kJ per square metre per year D. 1,300 kJ per square metre per year

11. Indian-origin scientist Har Gobind Khorana shared the 1968 Nobel Prize in Physiology or Medicine for work on:

A. Interpretation of the genetic code B. Discovery of human blood groups C. Discovery of the double-helix structure of DNA D. Cloning of the first mammal

12. The Cell Theory, stating that all living organisms are made of cells, was proposed by:

A. Matthias Schleiden and Theodor Schwann B. Watson and Crick C. Robert Hooke and Antonie van Leeuwenhoek D. Walter Sutton and Theodor Boveri

13. Consider the following statements:
Statement I: The polio vaccine developed by Jonas Salk is given as an injection.
Statement II: The polio vaccine developed by Albert Sabin is given orally as drops.
Which of the above is/are correct?

A. Only I B. Only II C. Both I and II D. Neither I nor II

14. Which of the following 'human body record' pairs is NOT correctly matched?

A. Longest bone — Femur B. Largest muscle — Gluteus maximus C. Largest vein — Pulmonary vein D. Largest artery — Aorta

15. Which of the following is NOT one of the three ear ossicles?

A. Malleus B. Stapes C. Incus D. Stapedius

16. In which year did Robert Hooke observe and name 'cells' while examining a thin slice of cork?

A. 1674 B. 1838 C. 1665 D. 1590

17. Ronald Ross, who worked in India, received the 1902 Nobel Prize in Physiology or Medicine for his work on which disease?

A. Malaria B. Cholera C. Plague D. Kala-azar

18. The specific functional role of an organism in its habitat — what it eats, when it is active and how it interacts with others — is called its:

A. Community B. Habitat C. Population D. Niche

19. Arrange the following organisms in the correct order of a food chain, starting from the producer:
P. Frog Q. Grass R. Eagle S. Grasshopper T. Snake

A. Q, P, S, T, R B. Q, S, T, P, R C. S, Q, P, T, R D. Q, S, P, T, R

20. In an ecosystem, a mushroom growing on a fallen log functions as a:

A. Decomposer B. Producer C. Secondary consumer D. Primary consumer

21. In which of the following situations is the pyramid of numbers inverted?

A. A single large tree supporting thousands of insects B. A pond with numerous phytoplankton and fewer small fish C. A crop field with many plants and a few grasshoppers D. A grassland with many grass plants, fewer deer and a few tigers

22. What is the main advantage of a food web over a single food chain in an ecosystem?

A. It allows energy to be recycled back to producers B. It contains no decomposers, so nutrients stay in living organisms C. It provides alternative pathways for energy flow, making the ecosystem more stable D. It eliminates energy loss between trophic levels

23. Which ecological pyramid is always upright and can never be inverted?

A. Pyramid of biomass B. None of these pyramids C. Pyramid of energy D. Pyramid of numbers

24. Which behaviour is especially well documented in emperor penguins as a way to reduce heat loss during Antarctic winter?

A. Huddling together in large groups B. Storing water in a hump C. Becoming nocturnal D. Shedding all their feathers

25. Match List I (Interaction) with List II (Effect on the two species):
List I: A. Mutualism B. Commensalism C. Parasitism D. Competition
List II: 1. One benefits, the other is harmed 2. Both benefit 3. Both are harmed 4. One benefits, the other is unaffected

A. A-4, B-2, C-1, D-3 B. A-2, B-4, C-1, D-3 C. A-2, B-4, C-3, D-1 D. A-2, B-1, C-4, D-3

26. If the producers in an ecosystem trap 20,000 J of energy, how much energy will be available to the tertiary consumers according to the 10% law?

A. 200 J B. 20 J C. 2 J D. 2,000 J

27. A persistent pollutant enters a lake at low concentration and accumulates in living tissues. Which organism is most likely to have the highest concentration after many feeding steps?

A. An aquatic top predator B. A single-celled producer C. A decomposed leaf before it enters the lake D. Pure lake water with no organisms

28. Food chains in nature rarely have more than four or five links mainly because:

A. Decomposers consume all consumers after the fifth level B. Grass cannot grow in a chain longer than five links C. Most of the energy is lost as heat at each trophic level, leaving too little for further levels D. Predators refuse to hunt beyond that point

29. Raymond Lindeman is associated with which influential ecological idea?

A. Ernst Haeckel B. Arthur Tansley C. Charles Elton D. Raymond Lindeman

30. A food chain that begins with dead organic matter such as fallen leaves and animal remains is called a:

A. Detritus food chain B. Food web C. Parasitic food chain D. Grazing food chain

31. Barnacles attached to the skin of a whale get transport and access to food, while the whale is neither harmed nor benefited. This relationship is:

A. Competition B. Parasitism C. Mutualism D. Commensalism

32. Ecological succession that begins on a bare, lifeless surface with no soil, such as newly cooled lava rock, is called:

A. Secondary succession B. Biomagnification C. Primary succession D. Eutrophication

Answers and explanations

1. B. Carl Linnaeus formalised the two-part scientific naming convention: a genus name followed by a specific epithet. Names are customarily italicised, with the genus capitalised. The other researchers are associated with heredity, evolution and classification rather than this naming system.

2. A. The hump stores fat, not a reservoir of water. Breaking down fat can provide energy and some metabolic water. Camels conserve water through several adaptations; no single hump mechanism explains their desert tolerance.

3. B. The World Heart Federation observes World Heart Day on 29 September. The distractor dates correspond to World AIDS Day (1 December), World Blood Donor Day (14 June) and World Mental Health Day (10 October).

4. C. Cushing syndrome results from too much cortisol action over time. It can arise from excess cortisol produced in the body or from prolonged use of glucocorticoid medicines. An adrenal tumour is only one possible endogenous cause; pituitary ACTH excess is another.

5. C. When two species use the same limited resource and each reduces availability to the other, the interaction is competition. Mutualism benefits both, commensalism benefits one without a measurable effect on the other, and parasitism benefits one while harming a host.

6. D. The thyroid is commonly taught as the largest purely endocrine gland. It produces thyroid hormones and calcitonin. The pancreas has both endocrine and exocrine roles; the liver is a larger gland overall but is not counted as a purely endocrine gland.

7. D. World Diabetes Day (14 Nov) marks Banting's birthday; World Hepatitis Day (28 Jul) marks Blumberg's birthday; World Blood Donor Day (14 Jun) marks Landsteiner's birthday; World TB Day (24 Mar) marks Koch's 1882 announcement of the TB bacillus.

8. B. The pairings are A-2, B-1, C-4, D-3. Vitamin K1 is phylloquinone; “vitamin K” more broadly also includes other forms such as K2. The question uses K1 deliberately to keep the chemical-name match exact.

9. B. In some aquatic systems, algae have rapid turnover and low standing biomass at a snapshot, while consumers can have higher standing biomass. The biomass pyramid can therefore be inverted. Energy flow over time still decreases across trophic levels, so an energy pyramid remains upright.

10. B. Net primary productivity equals gross primary productivity minus producer respiration: 950 − 350 = 600 kJ per square metre per year. Retain both the area and time units because this is a productivity rate, not a standing biomass measurement.

11. A. Har Gobind Khorana shared the 1968 Nobel Prize in Physiology or Medicine with Robert W. Holley and Marshall W. Nirenberg for work interpreting the genetic code and its role in protein synthesis. The other discoveries belong to different investigators and periods.

12. A. Schleiden and Schwann formulated the classical cell theory in the 1830s from plant and animal observations. Virchow later stressed that new cells arise from existing cells. Hooke named cells after observing cork; Leeuwenhoek observed living microscopic organisms.

13. C. Both are correct. Salk's inactivated (killed-virus) polio vaccine is injected, while Sabin's live attenuated vaccine is given as oral drops — the form used in India's Pulse Polio campaign. Memory hook: Salk = Shot, Sabin = Sip.

14. C. The pulmonary vein is not the largest vein: the inferior vena cava is the major large-diameter vein returning blood from the lower body. The femur is the longest bone, the aorta the largest artery, and gluteus maximus is commonly cited as the largest skeletal muscle.

15. D. The middle-ear ossicles are the malleus, incus and stapes; the stapes is also the smallest bone in the body. Stapedius is not a bone but the smallest skeletal muscle, which steadies the stapes and dampens loud sounds.

16. C. Robert Hooke published Micrographia in 1665 and used “cells” for the compartments he saw in cork. They were cell walls of dead plant tissue, not live cells with visible internal activity. The other dates refer to different developments.

17. A. Ronald Ross received the 1902 Nobel Prize for research on malaria and mosquito transmission. His observations in Secunderabad in 1897 helped establish that the parasite develops in mosquitoes. The question asks the disease, not sole credit for every part of the transmission cycle.

18. D. An ecological niche describes a species’ functional role and its use of resources, including where and when it feeds and interacts. Habitat is its physical setting. Population means members of one species in an area; community includes multiple interacting populations.

19. D. Grass (producer) is eaten by the grasshopper (primary consumer), which is eaten by the frog (secondary consumer), which is eaten by the snake (tertiary consumer), which is eaten by the eagle (top consumer): Q, S, P, T, R.

20. A. A mushroom is a fungus; it lacks chlorophyll, cannot photosynthesise and feeds saprotrophically on dead organic matter, making it a decomposer. Decomposers release nutrients back into the soil for producers to reuse.

21. A. One tree can support many herbivorous insects, giving fewer producers than primary consumers in a count-based snapshot. The pyramid of numbers may therefore be inverted at its base. This does not imply that the tree provides more energy to insects than it captured.

22. C. A food web records several feeding links, allowing some alternative routes for energy flow if one link weakens. Such redundancy can contribute to stability, although a web does not guarantee resilience to every disturbance. Energy flows and dissipates; nutrients cycle.

23. C. An energy pyramid is upright because less energy is available at successive trophic levels over a specified period. Numbers and standing biomass can be inverted under particular ecological conditions. Transfer efficiencies vary, so the pyramid is not based on an exact universal 10% ratio.

24. A. Emperor penguins huddle and change positions within the group, reducing exposure and sharing a warmer local environment. Other penguin species have different behaviours, so specifying emperor penguins avoids treating every species alike.

25. B. Mutualism is +/+ (bee and flower), commensalism +/0 (barnacle on whale), parasitism +/- (tapeworm in human intestine) and competition -/- (two species needing the same limited resource). So A-2, B-4, C-1, D-3.

26. B. Using the exam’s simplifying 10% transfer rule, 20,000 J at producers becomes 2,000 J for primary consumers, 200 J for secondary consumers and 20 J for tertiary consumers. Real transfer efficiency varies; energy is also used in metabolism or remains in uneaten and waste material.

27. A. Biomagnification can raise the concentration of a persistent, poorly excreted pollutant at successive trophic levels. A top predator may therefore carry the highest concentration. The pattern depends on the pollutant and food web; not every substance biomagnifies.

28. C. Energy available to higher trophic levels generally declines because organisms respire, generate heat and leave some biomass uneaten or unassimilated. Thus food chains tend to be short. The “10% law” is a teaching approximation, not an exact limit of four or five links in every ecosystem.

29. D. Lindeman’s trophic-dynamic work analysed energy flow between feeding levels. The classroom “10% law” is commonly associated with him, but actual transfer efficiencies vary across ecosystems. Tansley introduced the ecosystem concept; Haeckel coined ecology; Elton developed influential food-chain and pyramid ideas.

30. A. A detritus food chain begins with dead organic material and proceeds through detritivores and decomposers and their consumers. A grazing chain begins with live producers. The distinction concerns the starting resource, not whether decomposers ever occur in a wider food web.

31. D. Barnacles may gain a place to attach and access moving water, while the whale is commonly treated as unaffected: +/0 commensalism in the textbook model. Real ecological effects can be context-dependent, but the relationship as described is commensalism.

32. C. Primary succession starts where no soil exists, so it is very slow. Secondary succession begins on land that already has soil, such as a forest after a fire, and proceeds faster. Biomagnification and eutrophication are unrelated pollution concepts.