CBSE Class 12 Biology Organisms and Populations diagrams based questions

CBSE Class 12 Biology Organisms and Populations diagrams based questions. Please refer to the examination notes which you can use for preparing and revising for exams. These notes will help you to revise the concepts quickly and get good marks.

DIAGRAM BASED QUESTIONS IN BIOLOGY FOR CLASS XII

13. Organisms and Populations

13.1 Introduction of goats in Galapagos Islands caused extinction of this animal. Name this animal

[Figure: Photograph of a large, dome-shelled land tortoise walking on dry ground.]

Answer: The animal is the Galapagos giant tortoise (Chelonoidis species), the native land tortoise of the Galapagos Islands.

Teacher's Note:
a) Goats were introduced by sailors and settlers and fed on the vegetation that the tortoises depended on for food.
b) Goats also trampled nests and competed with the tortoises for food and water, which reduced their population.

13.2 This is an example of predation.
a) If tigers / carnivores stop eating animals, herbivores will be saved. Comment upon the statement.
b) If they don't stop eating animals, a day will come when there will be no herbivores. Justify.

[Figure: A cheetah running after a gazelle-like antelope across dry grassland.]

Answer:
a) The statement is not correct. If carnivores stopped eating herbivores, the herbivore population would grow very large, overgrazing would destroy the vegetation, and the herbivores would then starve.
b) Predators keep the prey population under control. If carnivores ate all the herbivores, the carnivores would themselves lose their food supply and decline, so the ecosystem would be disturbed.

Teacher's Note:
a) Predators regulate prey populations, which keeps the food chain balanced.
b) Removing either predators or prey upsets the population balance of the whole community.

13.3 How do these animals survive in such cold waters?

[Figure: Two seals resting on ice at the edge of icy water.]

Answer: These seals are mammals with a thick layer of blubber (subcutaneous fat) under the skin, which insulates the body against the cold water. They also have dense fur, a streamlined body, and a lower surface-to-volume ratio that reduces heat loss, and they can hold their breath for long periods.

Teacher's Note:
a) Blubber is the main insulating layer, and it also stores energy.
b) Being warm-blooded (homeothermic) lets them keep a constant body temperature in cold water.

13.4 a) Identify the plant.
b) Why cattle avoids browsing this plant?
Name any two such chemical produced by plants for its protection but commercially used by human.

[Figure: A shrub with broad, thick, pale green leaves and clusters of pinkish-white flowers.]

Answer:
a) The plant is Calotropis (madar or crown flower, Calotropis procera).
b) Cattle avoid it because the plant contains bitter and toxic cardiac glycosides, and its milky latex irritates the mouth and gut.
Two such chemicals are alkaloids such as quinine, and glycosides such as digitoxin, which are used in medicine.

Teacher's Note:
a) Plants make these chemicals as defence against herbivores, which is why they are called secondary metabolites.
b) Quinine (from cinchona) is used against malaria, and digitoxin (from Digitalis) is used for heart conditions.

13.5 Can the animal easily be spotted?
a) If no, Why?
b) Give technical term to this phenomenon.
Why animals do such?

[Figure: A moth with wings patterned in brown and grey that match the bark of a tree trunk.]

Answer:
a) No, the animal cannot easily be spotted, because its colour and pattern match the tree bark.
b) The technical term is cryptic colouration (camouflage).
Animals do this to avoid being detected by predators, and sometimes to approach prey without being noticed.

Teacher's Note:
a) Camouflage is an adaptation that increases survival by reducing the chance of being seen.
b) Animals with good camouflage often stay still, which makes the effect stronger.

13.6 This plant was introduced in Australia in 1920s and later became invasive spreading over millions of hectares of rangeland.
a) Why it spread so fast?
b) How was it controlled?
Name this plant.

[Figure: A dense clump of flat, spiny green stem pads (cladodes) bearing reddish fruits.]

Answer:
a) It spread fast because it had no natural predators or herbivores in Australia, it reproduced both by seeds and by vegetative pieces of stem, and birds and animals dispersed its seeds.
b) It was controlled by biological control, using a moth, Cactoblastis cactorum, whose larvae feed on the cactus pads.
The plant is prickly pear (Opuntia).

Teacher's Note:
a) This is a classic example of an introduced species becoming invasive because its natural enemies were absent.
b) Biological control must be tested carefully, because the control agent can itself become a pest.

13.7 This butterfly is highly distasteful to its predators (birds).
a) Name the butterfly
b) Why is it distasteful?
How did it develop such characteristics?

[Figure: A large orange and black butterfly with white-spotted black wing borders.]

Answer:
a) The butterfly is the monarch butterfly (Danaus plexippus).
b) It is distasteful because its larvae feed on milkweed (Calotropis and Asclepias), which contain cardiac glycosides. These toxins are stored in the adult body. The bright orange and black colours warn birds of this (warning colouration, or aposematism).
The characteristic developed through natural selection, because birds that ate the monarchs got sick and learned to avoid them.

Teacher's Note:
a) Bright warning colours are only useful when the prey is truly distasteful, so the warning and the toxin evolved together.
b) Mimics such as the viceroy butterfly copy this warning pattern to gain protection.

13.8 a) What type of interaction do you find here?
b) Define the type of interaction.
c) Cite any other example.

[Figure: Two white cattle egrets standing close to a grazing cow, with the cow's body beside them.]

Answer:
a) The interaction is commensalism between cattle egrets and the cow.
b) Commensalism is an interaction in which one species benefits and the other is neither harmed nor benefited. The egrets feed on insects and other small animals that the moving cattle disturb, while the cow is unaffected.
c) Another example is the clownfish living among sea anemone tentacles, or barnacles attached to the skin of whales.

Teacher's Note:
a) In commensalism, the host is neither helped nor harmed, which distinguishes it from mutualism.
b) The egrets are sometimes said to clean the cattle of ticks, but this is not the main form of the interaction.

13.9 It is an observation made by Mac Arthur.
a) What was the observation?
b) Give technical term to it?
c) Why do birds behave in this way?

[Figure: Diagram of a spruce tree divided into vertical zones, with five warbler species feeding at different heights and branch positions, and a height scale from 0 to 60 feet.]

Answer:
a) MacArthur observed that five warbler species living in the same spruce tree each fed in a different part of the tree, at different heights and on different branch zones.
b) The technical term is niche partitioning (resource partitioning).
c) The birds divide the tree's resources so that they reduce competition for food, which allows them to coexist.

Teacher's Note:
a) Niche partitioning means closely related species occupy slightly different niches, so they compete less.
b) The result shows how competition shapes the way species use shared resources.

13.10 This is a picture of a Kangaroo rat living in North American desert.
a) How does it survive there?
b) Write any 4 features developed in plants for survival in deserts.

[Figure: A small, stout rodent with a large head, large eyes, and a long tail, sitting on the ground.]

Answer:
a) The kangaroo rat is nocturnal and spends the day in cool underground burrows, which reduces water loss. It gets almost all its water from the metabolic breakdown of the dry seeds it eats, and it produces very concentrated urine and dry faeces.
b) Four features developed in desert plants are: (i) reduced leaves or leaves modified into spines, which lower water loss; (ii) a thick waxy cuticle on the leaves and stems; (iii) stems that store water (succulence), as in cactus; (iv) sunken stomata and CAM photosynthesis, which open at night.

Teacher's Note:
a) Nocturnal behaviour and burrowing are behavioural adaptations, while concentrated urine is a physiological adaptation.
b) Any four correct plant adaptations are acceptable, such as deep roots or a shallow spreading root system.

13.11 The diagram shows Biome distribution with respect to annual temperature and precipitation. Label A and B.

[Figure: Climograph with annual mean temperature (degrees Celsius, from -15 to 30) on the vertical axis and annual mean precipitation (cm, from 100 to 400) on the horizontal axis. Shaded biome regions are drawn, with a large green region labelled A, a blue region labelled B, and a light blue region at the bottom left labelled Arctic and alpine tundra. Pictures of a forest, a coniferous forest and a river or wetland are shown at the right.]

Answer:
A = Temperate deciduous forest.
B = Coniferous forest (taiga).

Teacher's Note:
a) Temperate forests lie in the moderate temperature and precipitation range, with broad-leaved trees that shed their leaves in winter.
b) Coniferous forests occur at lower temperatures than temperate forests, and they are dominated by needle-leaved trees.

13.12 What is sexual deceit? How does it apply to this flower?

[Figure: Close view of an orchid flower whose petal-like lip is dark maroon and velvety, resembling the body of an insect.]

Answer: Sexual deceit is a form of pollination in which a flower mimics the appearance, colour, and scent of a female insect so that male insects are attracted to it. The male insect attempts to mate with the flower and picks up pollen in the process. In this bee orchid (Ophrys), the labellum looks like a female bee, so male bees are deceived and carry pollen to other orchids.

Teacher's Note:
a) Sexual deceit is also called pseudocopulation, and it is a type of pollinator attraction.
b) The orchid gains pollination without giving any reward such as nectar to the insect.

13.13 a) What do you find in the picture?
b) Mutualists should co-evolve. Why?
Why do you call them mutualists?

[Figure: A cut open fig fruit showing a central cavity lined with many small flowers, with tiny winged insects visible inside.]

Answer:
a) The picture shows a fig (syconium) cut open, with small fig wasps and the internal flowers inside.
b) The fig and the fig wasp must co-evolve because each depends on the other for reproduction. The wasp lays its eggs in the fig flowers, and the fig depends on the wasp to pollinate it, so a change in one affects the other.
They are called mutualists because both the fig and the wasp benefit from the interaction.

Teacher's Note:
a) Mutualism is an interaction in which both partners gain.
b) Co-evolution means each species evolves in response to the other over time.

13.14 a) A plant growing on another plant causing no harm is called_________
b) This type of interaction is called ________
Give term to the interaction where one is not benefitted and other is in loss.

[Figure: A bromeliad plant growing on the branch of a tree.]

Answer:
a) A plant growing on another plant without harming it is called an epiphyte.
b) This type of interaction is called commensalism.
The interaction in which one is not benefited and the other is harmed is called amensalism.

Teacher's Note:
a) Epiphytes such as bromeliads and orchids take water and minerals from rain and debris, not from the host tree.
b) The question's last part asks for amensalism, where one species is harmed and the other is unaffected.

13.15 a) What specific term can you propose to explain egg laying relationship between a crow and a cuckoo (koel)?
b) Is it a parasitic relationship? Why?

[Figure: A crow's nest containing several eggs, with a young cuckoo chick and a crow chick in the nest.]

Answer:
a) The specific term is brood parasitism.
b) Yes, it is a parasitic relationship. The cuckoo lays its eggs in the crow's nest and does not raise its own young. The crow raises the cuckoo chick, which often pushes out the crow's own eggs or chicks, so the cuckoo benefits and the crow is harmed.

Teacher's Note:
a) Brood parasitism is a specialised form of parasitism in which the host raises the parasite's young.
b) Cuckoo chicks often have a similar call to the crow's chicks, which helps the host keep feeding them.

13.16 Interaction between Clown fish and Sea anemone is called Commensalism. Who is benefitted in this association and how?

[Figure: An orange and white clownfish swimming among the tentacles of a sea anemone.]

Answer: The clownfish is benefited. It lives among the stinging tentacles of the sea anemone, which protect it from predators. The sea anemone is neither harmed nor benefited in a major way, so the interaction is commensalism.

Teacher's Note:
a) The clownfish has a special mucus coat that stops it being stung by the anemone.
b) Some clownfish also clean the anemone and bring it food, which is a minor benefit to the anemone.

13.17 In this picture a Female mosquito is biting a man and drawing blood. Is it parasitism? Justify.

[Figure: A female mosquito with its proboscis inserted into human skin, with a red blood-filled abdomen.]

Answer: Yes, it is parasitism. The female mosquito lives on or near the host and feeds on its blood, which benefits the mosquito. The host is harmed by irritation, blood loss and, in some cases, by diseases such as malaria and dengue that the mosquito can transmit.

Teacher's Note:
a) The mosquito is a temporary external parasite (ectoparasite), because it feeds on the host for a short time.
b) Only the female bites, because she needs protein from blood for egg production.