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Q1. What does the sigmoid growth curve of a population mean? 

Solution

The sigmoid growth curve indicates rapid multiplication and then equilibrium of population.

Q2. Egrets are often seen along with grazing cattle. How do you refer to this interaction? Give a reason for this association.

Solution

The interaction in egrets and grazing cattle is called commensalism. (i) In this association, egrets are found close to the grazing cattle. (ii) During movement, the cattle flush out various insects which may be difficult for the egrets to catch. (iii) The egrets are benefitted, but the cattle are neither benefitted nor harmed.

Q3. What are the two types of population growth curves? What are the phases involved in both types of curves?

Solution

The two types of growth curve of a population are S-shaped and J-shaped. The phases of the S-shaped growth curve are lag phase, exponential phase and stationary phase. In the J-shaped growth curve, there are only two phases - the lag phase and exponential phase. 

Q4. How do organisms cope with stressful external conditions which are localised or of short duration?

Solution

To cope with stressful conditions, organisms (i) Migrate temporarily from the stressful habitat to a hospitable area (ii) Aestivate during summer (iii) Hibernate during winter (iv) Form thick-walled spores

Q5. Describe habitat and ecological niche.

Solution

A habitat is the living place of an organism; for example, coastal areas of sea by Scoliodon. An ecological niche indicates not only the habitat of a species but also the functional role of a species in the community. 

Q6. How does the human body maintain constant temperature both in summers and winters? Explain.

Solution

Human beings maintain a constant temperature of 37°C. In summers, the outside temperature is much higher than our body temperature. Therefore, we sweat profusely. This results in evaporative cooling, and our body temperature is reduced to normal. In winters, the outside temperature is much lower than our body temperature. Therefore, we shiver, which is a kind of exercise, which produces heat and raises the body temperature.

Q7. Name the organisms which form lichens.

Solution

Lichens are formed by the association between alga and fungus. This association is called symbiosis. 

Q8. Explain brood parasitism with the help of an example.

Solution

Brood parasitism is a method in which the parasitic bird lays its eggs in the nest of its host and the host incubates them. The eggs of the parasites resemble the eggs of the host bird and these eggs are raised by the host. Example: The cuckoo bird lays its eggs in the nest of a crow. The eggs of the cuckoo are incubated by the crow.

Q9. Name the animal which finds its path using echolocation phenomenon.

Solution

The echolocation phenomenon is shown by horseshoe bat.

Q10. While walking in the garden, Amit got hurt by a thorn present on a twig bearing beautiful rose flowers. He started analysing the role of different parts of the rose plant such as leaves, flowers etc. but was not able to understand the need of thorns on the rose plant. Read the above passage and answer the following questions: (i) Why plants produce thorn/spine-like structures on their body? (ii) What is meant by adaptation? (iii) What are other methods of adaptations of organisms in specific environments?

Solution

(i) Many plants have thorns or spines to protect themselves from the attack of grazing animals. (ii) Adaptation refers to the ability of a species to survive in a particular ecological niche, especially because of alterations of form or behaviour brought about through natural selection. (iii) Other methods of adaptations of organisms are some of the anatomical changes which include mimicry, hibernation and aestivation.

Q11. Differentiate between S-shaped and J-shaped growth curve.

Solution

 S-shaped curve   J-shaped curve (i) It comprises the lag phase, exponential phase and stationary phase. (i) It comprises only two phases - lag phase and exponential phase. (ii) Population becomes stable with zero growth rate and the curve levels. (ii) Population faces mass mortality, and the curve stops. (iii) It is observed by most species including humans. (iii) It is observed in few organisms such as reindeer and annual plants.  

Q12. What is adaptation? Describe the adaptations of plants and animals in the desert.

Solution

Adaptation is the quality of the organism which enables the organism to survive and reproduce in its habitat. It helps organisms to live in different types of habitats. The adaptation of desert plants are (i) Desert plants have a cuticle to minimise transpiration. (ii) In some desert plants, the leaves modify into spines to minimise loss of water. (iii) They have long roots and adaptations to reduce transpiration. Example: Acacia The adaptations of desert animals are (i) Urine of desert animals is concentrated for minimum loss of water. Example: Kangaroo rat (ii) Desert animals absorb heat from the Sun when the body temperature drops below the comfort zone. (iii) They live in burrows during the hot season and have little water requirement.

Q13. State one difference between biotic community and ecosystem.

Solution

A biotic community represents only the populations of different species of an era, while an ecosystem represents both abiotic and biotic components of an area.

Q14. Explain three types of interspecific interactions. 

Solution

Three types of interspecific interactions are (i) Competition: It is a type of interaction in which both the species suffer due to limited resources. Example: Carnivorous animals compete for prey (ii) Parasitism: It is a type of interaction in which one species is benefitted and the other species is harmed. Example: Malarial parasite inside the female Anopheles mosquito causes malaria in humans. (iii) Mutualism: In this type of interaction, both the species are benefitted. Example: The sea anemone and hermit crab stay in mutual relationship with each other.

Q15. An orchid plant is growing on the branch of a mango tree. How do you describe the interaction between the orchid and mango tree? 

Solution

The interaction between an orchid and the mango tree is commensalism because the orchid is benefitted by getting shelter from the mango tree, whereas the mango tree is neither harmed nor benefitted.

Q16. Write four characteristics of a biotic community. 

Solution

Four characteristics of a biotic community are species diversity, stratification, dominance and succession.

Q17. (i) Write the importance of measuring the size of a population in a habitat or an ecosystem. (ii) Explain how age structure plays an important role in population growth.

Solution

(i) The size of the population depends on its state in the habitat. The impact of a predator or the effect of a pesticide application can be determined by evaluating the size of the population. (ii) The age structure of a population is the percentage of individuals of different ages such as young, adult and old. The ratio of various age groups in a population determines the current reproductive status of the population. The age groups are classified as pre-reproductive, reproductive and post-reproductive.

Q18. How do protocooperation and mutualism resemble and differ?  

Solution

In protocooperation and mutualism, the two species are benefitted. However, the difference is that in protocooperation, the two species can live equally well without association, but this does not happen in mutualism.

Q19. List the different population attributes which an individual does not possess. Explain any three.

Solution

The different population attributes which an individual does not possess are population density, population growth, mortality rate, natality rate, sex ratio and age distribution. (i) Population density: It is the number of individuals of a species per unit area or volume. (ii) Population growth: Increase in the number of population which resides in a particular geographical area. (iii) Mortality rate: It is expressed as the number of deaths per 1000 individuals of a population per year. (iv) Natality rate: It is expressed as the number of births per 1000 individuals of a population per year. (v) Sex ratio: The ratio of males to females in a population. (vi) Age distribution: The proportionate numbers of persons in different age categories in a given population. (Any three)

Q20. What is aerenchyma? Mention any two specific functions of this tissue in hydrophytes. 

Solution

Aerenchyma is a modified parenchyma, where the cells are arranged with regular air spaces or air chambers to facilitate diffusion of gases to provide buoyancy to aquatic plants such as lotus and water hyacinth. Two functions of hydrophytes are (i) It helps in the diffusion of oxygen, both in and out. (ii) It provides buoyancy to aquatic plants.

Q21. What are ectoparasites and endoparasites? Give two examples of each. 

Solution

Parasites which live on the body surface of the host are called ectoparasites. Examples: Lice, bed bug Parasites which live inside the body of the host are called endoparasites. Examples: Malarial parasite, Ascaris

Q22. Why are mammals the most successful animals on Earth? 

Solution

The mammals are the most successful animals on Earth because they can maintain a constant body temperature with high range of tolerance whether in Antarctica or in the Sahara desert.

Q23. Define population and community. 

Solution

A population can be defined as a group of individuals of the same species residing in a particular geographical area at a particular time and functioning as a unit. A community is defined as a group of individuals of different species, living within a certain geographical area.

Q24. Mention any two significant roles which predation plays in nature.

Solution

(i) Predation transfers energy from plants to a higher trophic level. (ii) Predation keeps prey population under control.

Q25. (i) What is carrying capacity? (ii) Write any four population attributes.

Solution

(i) Carrying capacity is the uppermost limit of population size beyond which no major increase can occur, so there is zero growth rate. (ii) The attributes which populations possess are population density, population growth, mortality rate, natality rate, sex ratio and age distribution. (Any four) 

Q26. Write adaptations of submerged, rooted hydrophytes.

Solution

To withstand movement of water, submerged, rooted hydrophytes have ribbon-shaped or greatly dissected leaves. The stems are soft, spongy and with long internodes.

Q27. Write short notes on (i) Mutualism, (ii) Competition, (iii) Predation and (iv) Parasitism

Solution

(i) Mutualism: It is a positive interaction in which both the interacting species favour the growth and survival of each other. It is of two types: (1) Protocooperation, in which both the species are mutually beneficial but association is facultative so that the partners can live separately. Example: Hermit crab and sea anemone association (2) Symbiosis, in which both the species are mutually beneficial but the association is obligatory. Example: Lichens, a symbiotic relationship of fungus with alga (ii) Competition: It is a type of interaction in which both the interacting species decrease the chances of growth and survival of each other as these compete for common resources. Example: Visiting flamingos and resident fish compete for zooplankton in the lakes of South America (iii) Predation: It is a type of interaction in which larger species (predator) attacks smaller species (prey) and kills for food. Example: All carnivorous animals are predators. (iv) Parasitism: It is a type of interaction in which smaller species (parasite) is benefitted, but the larger species (host) is harmed. Different types of parasites include ectoparasites (lice, bed bugs), endoparasites (malarial parasite), holoparasites (Cuscuta), partial parasites and brood parasites (cuckoo).

Q28. (i) What is ‘r’ in the population equation? (ii) How does the increase and decrease in the value of ‘r’ affect the population size?

Solution

(i) ‘r’ in the population equation is the intrinsic rate of natural increase in the population. (ii) An increase in the value of ‘r’ will increase the population size. When ‘r’ decreases, the population size also decreases.

Q29. Bear hibernates whereas some species of zooplankton enter diapause to avoid stressful external conditions. How are these two ways different from each other?  

Solution

Hibernation is the winter sleep in cold-blooded animals in polar regions. During hibernation, these animals suspend their metabolic activities when the external temperature becomes unfavourable. Diapause is the phenomenon seen in insects during their developmental stages. During diapause, the metabolic activities are suspended due to unfavourable conditions.

Q30. Give an example where percentage cover is a more meaningful measure of the population size.

Solution

In an area if there are 200 Parthenium plants but only a single huge banyan tree with a large canopy, the population density of banyan is low relative to that of Parthenium. The banyan tree plays an enormous role in that community. In such cases, the percent cover or biomass is a measure of the population size.