NCERT Questions for Class 12 Biology Chapter 11 – Organisms and Populations

Important Questions with Solutions of Class 12 Biology Chapter 11 – Organisms and Populations

Short Answer Questions

1) What are the four levels of biological organisation that ecology primarily addresses?

Ans – Organisms, populations, communities, and biomes.

2) Differentiate between ectotherms and endotherms.

Ans – Ectotherms are animals whose body temperature changes in relation to their environment, whereas endotherms are animals which maintain a relatively constant body temperature due to physiological control.

3) Explain why Lichens are a good illustration of obligate mutualisms.

Ans – Lichens are an obligate mutualistic interaction between a fungus and algae or cyanobacterium, where the fungus is supposed to facilitate the absorption of nutrients to provide to bacteria, whereas the algae or cyanobacterium synthesises food.

4) How do desert lizards manage their body temperature to maintain a relatively constant level?

Ans – Desert lizards succeed in regulating their body temperature effectively through behavioral adjustments to survive when the temperature becomes very high. They bask in sun and absorb heat when their body temperature is below the optimal limit and return to shade when it exceeds the level.

5) Would a marine fish survive if kept in an aquarium containing freshwater? What are the reasons for or against?

Ans – Marine fish cannot survive well in a freshwater aquarium as they are adapted for saltwater seawater. They cannot control an external hypotonic environment due to failure of osmoregulation.

6) What is the role of a predator in the ecosystem?

Ans – Predators perform an important job in the ecology:-

• They act as conduits transferring energy to higher trophic levels
• They regulate the population of prey so that it never becomes too high densities.
• They assist in upholding species diversity in an ecosystem.

7) Almost all living things are susceptible to temperatures above 450°C. How can some microbes survive in an environment where the temperature is over 1000°C?

Ans – Some microbes can survive in environments with temperatures greater than 1000°C as they contain very little free water in their bodies. Removal of the water makes them resistant to high temperature.

3 mark questions

1) Mention how xerophytes are specially modified to their stem, leaves, and root system.

Ans –

(i) Root Adaptation – Xerophytes contain a developed and much-branched long root system. Certain perennial xerophytes having succulent features possess broad yet shallow root systems. They seem to absorb moisture from dew-drops and small rain droplets.

(ii) Changes in Stem – The stems of woody xerophytes are relatively short and stiff. In acacia, the main stem and their branches appear as a sturdy succulent flattened and green modified structure called a phylloclade.

(iii) Leaf Adaptations – Leaves are generally small in size, which lowers the chances of getting scorched by sun radiation, consequently slowing down transpiration. The leaves of xerophytes have the water-holding capacity; they are usually dense and thicker, green in color, and fleshy, leathery.

2) Define the features of population.

Ans – A population possesses four primary characteristics:

1. Population Density – Population density refers to the number of individuals inside a specified unit of area. The maximum density limit is contingent upon energy flow within an ecosystem, the nutritional state of trophic levels, and metabolic balance. Population density maybe computed mathematically as:
2. Birth Rate / Natality – The birth rate or natality refers to the amount of new individuals generated through natural processes during a specified time frame.
3. Mortality Rate – It signifies the rate of death among individuals within the population. It is quantified as the number of individuals who perish within a specified timeframe.
4. Carrying Capacity – A limited number of creatures can inhabit a specific area of a given habitat or ecosystem, contingent upon its dimensions and productivity. This concept is referred to as carrying capacity.

3) Mutualists co-evolve with each other, often. Describe from the viewpoint of mutualistic relationship between wasps and figs.

Ans –

• Plants necessitate the assistance of animals for the pollination of their blossoms and the dissemination of their seeds.
• Animals that assist plants in this process must receive compensation for their efforts.
• Plants provide incentives or compensation to animals in the capacity of seed dispersers.
• Plant-animal interactions frequently entail the co-evolution of mutualists, signifying that the evolution of flowers and their pollinator species transpires concurrently.
• A fig may alone be pollinated by its specific wasp species and no other kind.
• The female wasp utilises the fruit as an oviposition site and employs the developing seed within the fruit to nourish her larvae.
• In search of appropriate oviposition sites, the wasp pollinates the fig inflorescence.
• The fig provides the wasp with its developing seeds as sustenance for the maturing wasp larvae in return for pollination services.

4) What is the difference between diapause and hibernation?

Ans – Diapause refers to the phenomena of enduring adverse environmental conditions during developmental stages. Hibernation is a phenomena wherein cold-blooded creatures endure winter in a state of rest or dormancy to evade low temperatures, sometimes concealing themselves in hollow tree trunks, burrows, or caverns, exhibiting minimal physiological activity.

5) How does one develop mountain sickness? What is mountain sickness and what are its symptoms? How does the body try to counter the problem of mountain sickness?

Ans – Not being able to breathe at high elevations. There is low air pressure at high elevations, which keeps the body from getting enough oxygen. Symptoms: feeling sick, being tired, and having heart beats.

The body tries to change in the following ways:

1. The creation of red blood cells
2. making it harder for haemoglobin to bind
3. by making breathing easier

5 Marks Questions

1) Explain the logistic growth model of the population and show a good slope. Why is this curve more like real life?

Ans – The logistic growth graph looks like a S or sigmoid shape. There are three parts:-

i) Lag-phase: This is the early stage, when there is little to no growth. During the lag phase, the cells in the under-population get used to or stabilise the growing conditions before they start to multiply.

ii) Log phase or exponential phase: This is the middle phase of speedy or straight rise. Once the small population is stable, cells start to grow quickly. This is because there is plenty of food and other things that cells need to live.

iii) Stationary phase, also called the steady phase: Soon after, the amount of food drops in proportion to the number of cells, which starts the stationary phase. During this phase, the number of new cells made is about the same as the number of dead cells, so the total number of cells does not grow.

2) Distinguish between regulators and conformers. Why do tiny animals lack regulatory behaviours?

Ans – The distinctions between regulators and conformers are as follows:

• Regulators are organisms that sustain homeostasis by physiological or behavioural mechanisms, ensuring a stable internal environment.
• Regulators encompass avians, mammals, certain lower vertebrates, and invertebrates.
• During summer, when external temperatures exceed body temperature, individuals perspire extensively to reduce body temperature via evaporative cooling.
• Non-regulators are organisms unable of sustaining a stable internal environment, resulting in their body temperature fluctuating with the surrounding temperature.
• The majority of animals and almost all plants are non-regulators.
• Thermoregulation is an energetically costly process, and tiny organisms exhibit no regulation.
• Small animals rapidly dissipate body heat in cold environments due to their relatively large surface area compared to their bulk.
• Small animals must use significant energy to produce body heat via metabolism.