NCERT Exemplar Class 12 Biology Solutions Chapter 13 Organisms and Population

Question:1

Autecology is the:
a. Relation of heterogeneous populations to their environment
b. Relation of an individual to its environment
c. Relation of a community to its environment
d. Relation of a biome to its environment

Answer:

Autecology focuses on the study of an individual organism’s relationship with its environment, including how it responds to abiotic factors like light, temperature, and soil, and biotic interactions like competition and predation. This is in contrast to synecology, which studies groups or communities.

Hence, the correct answer is option (b) relation of an individual to its environment.

Question:2

Ecotone is:
a. A polluted area
b. The bottom of a lake
c. A zone of transition between two communities
d. A zone of developing community

Answer:

An ecotone is a transition zone between two different ecological communities, where species from both communities may coexist and interact. It often shows higher biodiversity due to this blending of species. These zones are considered areas of tension as well as richness. They are never polluted areas or developing communities, but rather serve as bridges between established ecosystems.

Hence, the correct answer is option (c), a zone of transition between two communities.

Question:3

Biosphere is:
a. a component in the ecosystem
b. composed of the plants present in the soil
c. Life in outer space
d. composed of all living organisms present on Earth, which interact with the physical environment

Answer:

The biosphere is defined as the sum of all living organisms on Earth interacting with each other and with the air, water, and land. It includes every ecosystem on the planet and forms a narrow layer where life is possible. It is much broader than just soil or a single ecosystem component, encompassing the entirety of Earth’s life-supporting zone.

Hence, the correct answer is option (d), composed of all living organisms present on Earth which interact with the physical environment.

Question:4

The ecological niche is:
a. the surface area of the ocean
b. an ecologically adapted zone
c. the physical position and functional role of a species within the community
d. formed of all plants and animals living at the bottom of a lake

Answer:

The ecological niche of a species refers to its “profession” in a community — how it uses resources, interacts with other organisms, and fits into the ecosystem’s structure. It describes both the habitat (physical space) and the functional role the species plays. It does not mean an ocean area or just a zone, but its specific place and function in the system.

Hence, the correct answer is option (c), the physical position and functional role of a species within the community.

Question:5

According to Allen’s Rule, the mammals from colder climates have:
a. shorter ears and longer limbs
b. longer ears and shorter limbs
c. longer ears and longer limbs
d. shorter ears and shorter limbs

Answer:

Allen’s Rule explains that mammals living in colder regions tend to have shorter ears and limbs to minimize heat loss. Smaller appendages reduce the surface area through which heat can escape, helping the organism conserve body heat. By contrast, mammals in hot climates usually have longer limbs and ears to release more heat.

Hence, the correct answer is option (d), shorter ears and shorter limbs.

Question:6

Salt concentration (Salinity) of the sea measured in parts per thousand is:
a. 10 – 15
b. 30 – 70
c. 0 – 5
d. 30 – 35

Answer:

Seawater salinity is typically measured in parts per thousand (ppt). On average, oceans have a salinity ranging between 30 to 35 ppt, making them moderately salty compared to freshwater (close to zero ppt) or brackish water (less than 30 ppt). Salinity in this range supports marine life adapted to moderate salt levels.

Hence, the correct answer is option (d), 30–35.

Question:7

Formation of tropical forests needs the mean annual temperature and mean annual precipitation as:
a. 18 – 25°C and 150 – 400 cm
b. 5 – 15°C and 50 – 100 cm
c. 30 – 50°C and 100 – 150 cm
d. 5 – 15°C and 100 – 200 cm

Answer:

Tropical forests require warm and wet conditions to thrive. These forests usually form where the mean annual temperature ranges between 18–25 °C, and rainfall is abundant, typically between 150–400 cm annually. Such climates support dense, biodiverse, and evergreen vegetation with multi-layered canopies.

Hence, the correct answer is option (a), 18–25°C and 150–400 cm.

Question:8

Which of the following forest plants controls the light conditions at the ground?
a. Lianas and climbers
b. Shrubs
c. Tall trees
d. Herbs

Answer:

In forests, tall trees form a dense overhead canopy that directly controls how much sunlight reaches the ground. By doing so, they regulate the light availability for understory plants like shrubs, herbs, and climbers. Other vegetation does not affect light as strongly as the dominant tall trees do.

Hence, the correct answer is option (c), tall trees.

Question:9

What will happen to a well-growing herbaceous plant in the forest if it is transplanted outside the forest in a park?
a. It will grow normally
b. It will grow well because it is planted in the same locality
c. It may not survive because of a change in its micro-climate
d. It grows very well because the plant gets more sunlight

Answer:

A herbaceous plant growing in a shaded forest is adapted to its specific micro-climate. If transplanted to a park with more light and less humidity, it may fail to adjust to the new micro-climate, leading to poor growth or death. Micro-climate shifts can disrupt survival despite being in the same geographic area.

Hence, the correct answer is option (c), it may not survive because of a change in its micro-climate.

Question:10

If a population of 50 Paramoecium present in a pool increases to 150 after an hour, what would be the growth rate of the population?
a. 50 per hour
b. 200 per hour
c. 5 per hour
d. 100 per hour

Answer:

The population rose from 50 to 150 in one hour, meaning 100 new individuals were added per hour. Growth rate is generally calculated as the change in population over time, so (150–50) individuals per hour = 100 per hour. This is a classic example of rapid growth in simple unicellular organisms under ideal conditions.

Hence, the correct answer is option (d), 100 per hour.

Question:11

What would be the per cent growth or birth rate per individual per hour for the same population mentioned in the previous question (Question 10)?
a. 100
b. 200
c. 50
d. 150

Answer:

Here, 100 new Paramoecium individuals formed from an initial population of 50. Hence, the percent growth rate is (100/50) × 100 = 200%. This gives the per-individual birth or growth rate per hour, showing exponential increase in favorable conditions.

Hence, the correct answer is option (b), 200.

Question:12

A population has more young individuals compared to older individuals. What would be the status of the population after some years?
a. It will decline
b. It will stabilise
c. It will increase
d. It will first decline and then stabilize

Answer:

A population with more young individuals means a higher reproductive potential for the future, leading to rapid population growth. Since there are more individuals capable of reaching reproductive age, the birth rate will exceed the death rate, and the population will expand.

Hence, the correct answer is option (c), it will increase.

Question:13

What parameters are used for tiger census in our country’s national parks and sanctuaries?
a. Pugmarks only
b. Pugmarks and faecal pellets
c. Faecal pellets only
d. Actual headcounts

Answer:

In Indian tiger reserves, census methods rely on indirect evidence like pugmarks (footprints) and faecal pellets to estimate population sizes. These indicators are reliable and non-invasive, and help track elusive animals like tigers in large forest areas where direct counting is impractical.

Hence, the correct answer is option (b), pugmarks and faecal pellets.

Question:14

Which of the following would necessarily decrease the density of a population in a given habitat?
a. Natality > mortality
b. Immigration > emigration
c. Mortality and emigration
d. Natality and immigration

Answer:

Population density decreases when individuals die (mortality) or leave the area (emigration). These two processes directly remove members from the habitat, reducing total numbers. Births and immigration, on the other hand, add to the population density.

Hence, the correct answer is option (c), mortality and emigration.

Question:15

A protozoan reproduces by binary fission. What will be the number of protozoans in its population after six generations?

a. 128
b. 24
c. 64
d. 32

Answer:

A protozoan population doubling by binary fission grows exponentially. After six generations, its population would be 2⁶ = 64. Each division doubles the previous number, leading to a geometric progression of the population in successive generations.

Hence, the correct answer is option (c), 64.

Question:16

In 2005, for each of the 14 million people present in a country, 0.028 were born and 0.008 died during the year. Using the exponential equation, the number of people present in 2015 is predicted as:
a. 25 million
b. 17 million
c. 20 million
d. 18 million

Answer:

Birth rate minus death rate gives a net growth rate of 2% per year. Applying the compound growth formula over 10 years to the initial 14 million yields about 17 million people in 2015. This is an example of an exponential population growth calculation.

Hence, the correct answer is option (b), 17 million.

Question:17

Amensalism is an association between two species where:
a. one species is harmed, and the other is benefited
b. one species is harmed and the other is unaffected
c. one species is benefited, and the other is unaffected
d. Both species are harmed.

Answer:

Amensalism is a type of ecological interaction where one species is harmed while the other remains unaffected. For example, certain fungi release antibiotics that harm bacteria, but the fungi themselves are not affected. This is different from parasitism, which benefits the harming species.

Hence, the correct answer is option (b), one species is harmed and the other is unaffected.

Question:18

Lichens are an association of:
a. bacteria and fungus
b. algae and bacterium
c. fungus and alga
d. fungus and virus

Answer:

Lichens are formed through a mutualistic relationship between a fungus and an alga. The fungus protects and supports the alga, while the alga makes food via photosynthesis for both partners. This classic symbiotic relationship helps them colonize harsh environments.

Hence, the correct answer is option (c), fungus and algae.

Question:19

Which of the following is a partial root parasite?
a. Sandalwood
b. Mistletoe
c. Orobanche
d. Ganoderma

Answer:

Sandalwood is a partial root parasite, meaning it attaches its roots to the roots of other plants to draw water and nutrients, but can also photosynthesize on its own. By contrast, organisms like Orobanche are fully obligate parasites with no photosynthesis.

Hence, the correct answer is option (a), sandalwood.

Question:20

Which one of the following organisms reproduces sexually only once in its lifetime?
a. Banana
b. Mango
c. Tomato
d. Eucalyptus

Answer:

Eucalyptus is semelparous, meaning it reproduces sexually only once in its lifetime and then dies. This strategy is common in some plants, ensuring a massive reproductive output in a single event before death. Other listed plants reproduce multiple times.

Hence, the correct answer is option (d), Eucalyptus.

Access Answers to the Chapter 13 NCERT Exemplar for Class 12 Science (Very Short Answer Questions)

The detailed answers to the very short questions are given below:

Question:1

Species that can tolerate a narrow range of temperatures are called ______.

Answer:

Stenothermic

Question:2

What are Eurythmic species?

Answer:

Species which can tolerate and thrive in a wide range of temperatures are called eurythermic species.

Question:3

Species that can tolerate a wide range of salinity are called ______.

Answer:

Euryhaline

Question:4

Define stenohaline species.

Answer:

Species which thrive in a narrow range of salinity are called stenohaline species.

Question:5

What is the interaction between two species called?

Answer:

The interaction between two species is called interspecific interaction.

Question:6

What is commensalism?

Answer:

Relationship between two organisms in which one organism is benefitted, and there is a neutral effect on another organism; is called commensalism.
Many commensals live in the alimentary canal of humans to get shelter and food, but they have neither a positive nor negative impact on humans.

Question:7

Name the association in which one species produces a poisonous substance or a change in environmental conditions that is harmful to another species.

Answer:

Amensalism

Question:8

What is Mycorrhiza?

Answer:

Mycorrhiza is a mutualistic association between the fungus and the roots of higher plants. The fungi get shelter and food, and lieu of that helps the plant in absorption of phosphorous from the soil. It also provides resistance to the pant from root-borne pathogens.

Question:9

Emergent land plants that can tolerate the salinities of the sea are called.

Answer:

Euryhaline

Question:10

Why do high altitude areas have brighter sunlight and lower temperatures as compared to the plains?

Answer:

When sunlight reaches us, it undergoes refraction through several layers of the atmosphere. The relative degree of refraction at higher altitude is less than at lower altitude. Due to this, sunlight appears brighter at high altitudes than in plains. Temperature reduces with increase in altitude. Due to this, higher altitudes have a lower temperature compared to the plains.

Question:11

What is homeostasis?

Answer:

The process by which an organism maintains constancy in its internal environment is called homeostasis. Osmoregulation and thermoregulation are parts of homeostasis.

Question:12

Define aestivation.

Answer:

When an organism goes into summer sleep to avoid an unfavourable environment, this process is called aestivation.

Question:13

What are diapause and its significance?

Answer:

The period of suspended development to tide over the unfavourable conditions is called diapause.

Question:14

What would be the growth rate pattern when the resources are unlimited?

Answer:

When resources are unlimited, the growth rate of population is exponential. This gives a J- shaped curve on the graph.

Question:15

What are the organisms that feed on plant sap and other plant parts called?

Answer:

Organisms that feed on plant sap and other plant parts are called phytophagous.

Question:16

What is high altitude sickness? Write its symptoms.

Answer:

A range of symptoms due to the low atmospheric pressure of high altitudes, the body does not get enough oxygen is called high altitude sickness. The symptoms of altitude sickness are nausea, fatigue and heart palpitations.

Question:17

Give a suitable example for commensalism.

Answer:

Egrets ride on the back of cattle. When cattle forage for grass, insects fly away abruptly. This gives the egrets a chance to feed on those insects. In this relationship, cattle get no benefit from egrets. This can be considered a suitable example of commensalism.

Question:18

Define ectoparasite and endoparasite and give suitable examples.

Answer:

Ectoparasite: Parasites which live on the body of hosts are called ectoparasites, e.g. leeches and ticks.
Endoparasites: Parasites which live inside the body of hosts are called endoparasites, e.g. roundworms and hookworms.

Question:19

What is brood parasitism? Explain with the help of an example.

Answer:

In this type of parasitism, a bird lays its eggs in the nest of another bird. The eggs resemble those of the host bird. The host bird incubates the eggs, unaware of its actual identity. This is seen in the Koyal (cuckoo), which lays its eggs in a crow’s nest.

Get Answers to the Science Class 12 Chapter 13 NCERT Exemplar (Short Answer Questions)

The detailed answers to the short questions are given below:

Question:1

Why are coral reefs not found in the regions from West Bengal to Andhra Pradesh but are found in Tamil Nadu and on the east coast of India?

Answer:

In West Bengal and Andhra Pradesh, freshwater is released from the Ganges and some other rivers. Due to this, coral reefs are not found in regions from West Bengal to Andhra Pradesh. From Tamil Nadu to the southern tip of the east coast, coral reefs are present because of no interference from freshwater.

Question:2

If a freshwater fish is placed in an aquarium containing seawater, will the fish be able to survive? Explain giving reasons.

Answer:

Freshwater is adapted to maintain its homeostasis in freshwater. It is unable to do so in saline water. Hence, the fish will not survive in an aquarium, which contains seawater.

Question:3

Why do all the freshwater organisms have contractile vacuoles, whereas the majority of marine organisms lack them?

Answer:

In freshwater organisms, the concentration of solute inside the cell is higher than that in the external environment. This means that the external environment is hypotonic. This leads to a movement of water inside the cells because of osmosis. Contractile vacuoles work like safety devices and prevent lysis of the cell. In marine organisms, the concentration of solute inside the cell is lower than that in the external environment.
This means that the external environment is hypertonic. Hence, the cell does not have to face the risk of lysis. This explains the absence of contractile vacuoles in marine organisms.

Question:4

Define heliophytes and sciophytes. Name a plant from your locality that is either a heliophyte or sciophyte.

Answer:

Heliophyte: Plants, which are adapted to live under plenty of sunlight, are called heliophytes, e.g. banyan. Heliophytes form the roof of a forest.
Sciophyte: Plants, which are adapted to live under low light conditions, are called sciophtyes, e.g. herbs. Sciophytes form the understory of a forest.

Question:5

Why do submerged plants receive weaker illumination than exposed floating plants in a lake?

Answer:

Most of the colours from the visible spectrum fail to reach deep into a water body. This happens because of the refraction of light through different layers of water. Due to this, floating plants get plenty of sunlight, but submerged plants get weaker illumination.

Question:6

In a seashore, the benthic animals live in sandy, muddy, and rocky substrata and accordingly developed the following adaptations.
a. Burrowing
b. Building cubes
c. Holdfasts/peduncle
Find a suitable substratum against each adaptation.

Answer:

(a) These animals live in the sandy substratum and make burrows, e.g. lobsters, crabs, etc. (b) These animals live in muddy substratum as cube-like aggregates. The small size of the cube helps in passive feeding mechanisms, e.g. zooplanktons.
(c) These animals live in the rocky substratum and attach to the substratum with the help of a holdfast, e.g. sponges.

Question:7

Categorise the following plants into hydrophytes, halophytes, mesophytes and xerophytes. Give reasons for your answers.
a. Salvinia
b. Opuntia
c. Rhizophora
d. Mangifera

Answer:

Question:8

In a pond, we see plants which are free-floating, rooted-submerged, rooted emergent, and rooted with floating leaves. Write the type of plants against each of them.

Answer:

Plant Name - Type
(a) Hydrilla - Rooted submerged
(b) Typha - Rooted emergent
(c) Nymphaea - Rooted with floating leaves
(d) Lemna -Free-floating
(e) Vallisnaria- Rooted emergent

Question:9

The density of a population in a habitat per unit area is measured in different units. Write the unit of measurement against the following:
a. Bacteria _______________
b. Banyan _______________
c. Deer _______________
d. Fish _______________

Answer:

(a) Number unit volume
(b) Biomass/ square kilometre (Area)
(c) Number/of square kilometres (Area)
(d) Weight/square kilometre (Area)

Question:10

Label the three tiers 1, 2, 3 given in the above age pyramid.
b. What type of population growth is represented by the above age pyramid?

Answer:

(a) 1: Pre-reproductive, 2: Reproductive, 3: Post-reproductive
(b) This age pyramid shows an expanding population.

Question:11

In an association of two animal species, one is a termite which feeds on wood, and the other is a protozoan Trichonympha present in the gut of the termite. What type of association do they establish?

Answer:

Termite and Trichonympha show mutualism; a relationship in which both the organisms are benefited from each other. Trichonympha breaks down cellulose in the wood and thus help the termite in the digestion of wood. Trichonympha also feeds on fragments of wood.

Question:12

Lianas are vascular plants rooted in the ground and maintain the erectness of their stem by making use of other trees for support. They do not maintain a direct relationship with those trees. Discuss the type of association the lianas have with the trees.

Answer:

Lianas compete with other trees. While taking support from other trees, lianas usually strangulate the other tree. They also compete for sunlight and water, and in the process, harm the host tree.

Question:13

Give the scientific names of any two microorganisms inhabiting the human intestine.

Answer:

Propionibacterium and E. coli

Question:14

What is a tree line?

Answer:

The edge of the habitat at which trees are capable of growing is called the tree line. Trees show stunted growth at the tree line. They cannot grow beyond the tree line because of unfavourable environmental conditions.
Treeline shows a gradual transition from dense cover to sparse cover.

Question:15

Define ‘zero population growth rate’. Draw an age pyramid for the same.

Answer:

Zero population growth rate is seen when the population of a location neither grows nor declines. The following pyramid shows a population with zero growth rate.

Question:16

List any four characters that are employed in the human population census.

Answer:

The following are the four characteristics that are employed in the human population census:

1. Sex-ratio

2. Age group

3. Occupation

4. Income

Question:17

Give one example for each of the following types.
a) Migratory animal
b) Camouflaged animal
c) Predator animal
d) Biological control agent
e) Phytophagous animal
f) Chemical defence agent

Answer:

(a) Siberian crane (b) Chameleon (c) Lion (d) Dragonfly (e) Honey bee (f) Capsaicin produced by bell pepper

Question:18

Fill in the blanks

Answer:

Question:19

Observe the set of 4 figures A, B, C and D and answer the following questions
i. Which one of the figures shows mutualism?
ii. What kind of association is shown in D?
iii. Name the organisms and the association in C.
iv. What role is the insect performing in B?

Answer:

(a) Figure ‚’ A’ shows mutualism because the butterfly gets the food from the plant and helps the plant in pollination.
(b) This shows predation in which a carnivore is eating an herbivore.
(c) This shows the association between egrets and buffaloes. This shows commensalism.
(d) The insect is performing the role ectoparasite.

Get Answers to the Science Class 12 Chapter 13 NCERT Exemplar (Long Answer Questions)

The detailed answers to the long questions are given below:

Question:1

Comment on the following figures: 1, 2 and 3:

Answer:

Figure 1 shows a population of species A. All the individuals are interacting among themselves.
Figure 2 shows a community with three populations of A, B and C. They are interacting with each other and their environment.
Figure 3 shows a biome with three communities. One of the communities is in the climax, and the other two are at different stages of development. All the three communities are in the same environment, and they interact with each other and with the environment.

Question:2

An individual and a population have certain characteristics. Name these attributes with definitions.

Answer:

A population has certain characteristics that an individual does not have. The following are the main attributes of the population:

1. Birth Rate: An individual is born, but a population shows the birth rate. The birth rate is usually expressed in terms of the number of births per thousand population.

2. Death Rate: An individual dies, but a population shows the death rate. The death rate is usually expressed in terms of several deaths per thousand population.

3. Sex Ratio: An individual is either a male or a female, but a population shows a sex ratio. The ratio of males to the number of females is called the sex ratio. For example, the sex ratio in India is 934 females to 1000 males.

4. Age Distribution: An individual can be of a certain age, but a population has people of different ages. For convenience, age groups are taken into consideration. Age group is normally categorised as pre-reproduction, reproduction, and post-reproduction age groups.

5. Population Density: Population density is usually taken in terms of the number of individuals per square km. Population density depends on various abiotic factors. The plains usually have extremely high population density, while mountains have very low population density.

Question:3

The following diagrams are the age pyramids of different populations. Comment on the status of these populations.

Answer:

• Figure A shows a population in which the ratio of individuals in pre-reproductive age is highest, followed by reproductive age and post-reproductive age. This pyramid shows a growing population.
• Figure B shows a population in which the number of individuals in pre-reproductive and reproductive age is equal. Several individuals in post-reproductive age is fewer. This pyramid shows that a stable population, i.e. population growth, is negligible.
• Figure C shows a population in which the number of individuals in the pre-reproductive age is the least. The number of individuals of reproductive age is the highest. A smaller number of individuals in the pre-reproductive age shows a negative growth rate in the population. This pyramid shows a population in degrowth.

Question:4

Comment on the growth curve given below.

Answer:

The growth curve in this figure shows logistic growth of the population. We know that resources are limited in nature, and they cannot support unlimited growth in population. Limited resources mean tough competition for resources among individuals.

• Only those survive which are fit to survive in such a condition.
• This is what happens in a real-life situation.
• In the initial phase, the population shows a lag phase, i.e. it grows at a slow pace.
• The lag phase is followed by a phase of acceleration, during which population growth is rapid. The acceleration phase is followed by a phase of deceleration, during which population growth slows down.
• Finally, a phase comes when population density reaches the carrying capacity.
• Carrying capacity defines the load limit of nature, in terms of sustaining a particular population density. Once the population density reaches the carrying capacity, it reaches the phase of the asymptote.
• This is the phase when the population begins to show negative growth.

Question:5

A population of Paramoecium caudatum was grown in a culture medium. After 5 days, the culture medium became overcrowded with Paramoeium and had depleted nutrients. What will happen to the population, and what type of growth curve will the population attain? Draw the growth curve.

Answer:

The population of Paramoecium will show logistic growth, which can be shown by a sigmoid curve. The population growth will show the following phases:
(a) Lag phase
(b) Acceleration phase
(c) Deceleration phase
(d) Asymptote phase
The asymptote phase shall be reached on the fifth day. The following figure shows the growth curve:

Question:6

Discuss the various types of positive interactions between species.

Answer:

The following are the positive interactions between species:
(a) Mutualism: This is a relationship between two organisms in which both the organisms are benefitted. Lichen is a particularly good example of mutualism. Lichen is an association of fungi and algae. The fungal part attaches to the substratum and gets water and minerals for the algal part. The algal part carries out photosynthesis and provides food to the fungal part.
(b) Commensalism: This is a relationship between two organisms in which one organism benefits, while another organism neither gains nor loses. Egrets keep on sitting on the back of herbivore animals, like buffalo, cow, etc. When the cattle forage for grass, the insects under the grass fly away haphazardly. This gives a chance for the egrets to feed on insects. Without the help of cattle, it will be difficult for egrets to find insects in the grass. In this relationship, there is no benefit to the cattle.

Question:7

In an aquarium, two herbivorous species of fish are living together and feeding on phytoplankton. As per Gause’s Principle, one of the species is to be eliminated in due course of time, but both are surviving well in the aquarium. Give possible reasons.

Answer:

Gause proposed that when resources are limited then out of the two competing species, one of the species will eventually become extinct. The species with superior predatory skills will survive in the end. But the evidence for such conclusive extinction is rare in nature. Many recent studies do not support Gause’s Principle of competitive exclusion. One of the means to survive is called resource partitioning.
For example, if two species compete for the same resource, they partition their time for foraging or use different foraging patterns. MacArthur showed that five species of warblers living on the same tree effectively change their feeding patterns to survive in limited resources. The same thing can happen in the given aquarium. Either the resources are unlimited, or two herbivorous species of fish may have changed their feeding times or feeding patterns to survive in the aquarium.

Question:8

While living in and on the host species, the animal parasite has evolved certain adaptations. Describe these adaptations with examples.

Answer:

Parasites show the following types of adaptations:
(a) Morphological Adaptations: Many parasites are bigger than their free-living counterparts. This helps in producing more eggs, necessary for survival. Endoparasites lose unnecessary sense organs to conserve resources. Endoparasites lose their gut, or the gut is reduced in size. They absorb nutrients through the skin. Special organs for attachment are present, e.g. suckers.
(b) Life Cycle Adaptations: An endoparasite needs some way to enter another host. Many parasites use a secondary host for this purpose. For example, plasmodium uses mosquitoes as secondary hosts so that they can easily infect another primary host. Some parasites lay their eggs in the lower portion of the alimentary canal of the host so that eggs or cysts can go out along with stool. Later on, the cysts get transmitted to another host through contaminated food and water, e.g. Entamoeba histolytica.
(c) Immunological Adaptations: Some parasites engulf antigens from the host. Some parasites disturb the immunological function of the host. These mechanisms help the parasite survive immunological response of the host.
(d) Biochemical Adaptations: Many endoparasites do not produce digestive enzymes. They rely on the host’s digestive enzymes and absorb the simple nutrients. Endoparasites do not carry out the synthetic reaction. This is possible because their energy need are very low, which is fulfilled from the host’s resources.

Question:9

Do you agree that regional and local variations exist within each biome? Substantiate your answer with a suitable example.

Answer:

A biome is a climatically and geographically contiguous area with similar climatic conditions. Both organic and inorganic components are similar in a particular type of biome. However, regional and local variations exist within each biome. To understand this, let us consider the following examples.
Coniferous forest is a type of biome which mainly contains trees which bear cones with sees inside. In all the coniferous forests around the world, coniferous trees are the main plant species. But regional variations exist in coniferous forests. The coniferous forests of North America are dominated by black spruce. On the other hand, the coniferous forests of northeast Europe are dominated by Norway spruce. Forests of Siberia are dominated by pine. This shows regional variations in a particular type of biome.
In the case of coniferous forests, the canopy is so thick that negligible sunlight reaches the ground. This results in sparse vegetation on the ground. The dense canopy on top and sparse vegetation at ground show local variations in a particular type of biome.

Question:10

Which element is responsible for causing soil salinity? At what concentration does the soil become saline?

Answer:

Minerals are responsible for causing soil salinity. The following are some of the causes for the increase in soil salinity:
High level of salt in the soil.
Water table movement is caused by landscape features.
Human activities, like the clearing of land and the excessive use of synthetic fertilizers.
Salt runoff from streets can happen in cold climates because salt is applied on the road to prevent snow accumulation.
Measurement of Soil Salinity: Soil salinity is measured in terms of a gram per litre of soil solution or electrical conductivity in dS/m. Soil salinity is usually determined from an extract of the saturated paste of soil, and then EC is termed ECe. When 4 < ECe < 8, the soil is termed as slightly saline. When 8 < ECe < 16, the soil is termed moderately saline. When ECe > 16, the soil is termed as highly saline.

Question:11

Does light factor affect the distribution of organisms? Write a brief note giving suitable examples of either plants or animals.

Answer:

Light is an important factor in determining the distribution of organisms. We know that green plants need sunlight to carry out photosynthesis, and hence the distribution of green plants is highly dependent on the amount of illumination. This is the reason; tropics have dense plant cover, but poles have negligible plants. Moreover, plants also need sunlight for flowering. This phenomenon is called photoperiodism.
Hence, based on photoperiodism, plants are categorized as short-day plants, long-day plants and day-neutral plants. The area near the equator gets a long duration of light as compared to the area near the poles. Thus, this affects the distribution of plants on Earth. Animals, too, depend on light and show certain behavioural patterns based on diurnal and seasonal variations in light. Many animals get up early in the morning and start foraging. The nocturnal animals remain active during the night only, e.g. owl. Reproductive and migratory activities are also governed by the amount of period of illumination in many animals.

Question:12

Give one example for each of the following:
i. Eurythermal plant species _______________
ii. A hot water spring organism _______________
iii. An organism seen in deep ocean trenches _______________
iv. An organism seen in the compost pit _______________
v. A parasitic angiosperm _______________
vi. A stenothermal plant species _______________
vii. Soil organism _______________
viii. A benthic animal _______________
ix. Antifreeze compound seen in Antarctic fish _______________
x. An organism which can conform _______________

Answer:

(a) Gracilaria

(b) Alycyclobacillus

(c) Giant tube worms

(d) Earthworm

(e) Misteltoe

(f) Pine

(g) Earthworm

(h) Sponge

(i) Antifreeze glycoproteins

(j) Mangifera