Maharashtra Board Class 12 Biology Important Questions Chapter 13 Organisms and Populations

Balbharti Maharashtra State Board 12th Biology Important Questions Chapter 13 Organisms and Populations Important Questions and Answers.

Maharashtra State Board 12th Biology Important Questions Chapter 13 Organisms and Populations

Multiple Choice Questions

Question 1.
All ecosystems on the earth together form
(a) biosphere
(b) biome
(c) living world
(d) environment
Answer:
(a) biosphere

Question 2.
What is the mean annual temperature in the region of Arctic and Alpine tundra ?
(a) About -10 to 2 °C
(b) About -2 to 2 °C
(c) About 0 to 5 °C
(d) About 5 to 10 °C
Answer:
(a) About -10 to 2 °C

Question 3.
Which out of the following are the major biomes in India ?
(I) Desert (II) Grassland (III) Tropical rain forest (IV) Temperate forest (V) Coniferous forest (VI) Deciduous forest (VII) Sea coast (VIII) Tundra
(a) (II) (IV) (VI) (VII)
(b) (I) (II) (V) (VIII)
(c) (I) (III) (VI) (VII)
(d) (II) (III) (VI) (VIII)
Answer:
(c) (I) (III) (VI) (VII)

Question 4.
Important key elements that bring about variations in the different habitats are
(a) temperature, water, light and soil
(b) salinity, pollutants, water
(c) modern developmental parameters in the region
(d) scientific progress and technological innovations
Answer:
(a) temperature, water, light and soil

Question 5.
Which out of the following is the most ecologically relevant factor?
(a) Water
(b) Temperature
(c) Salinity
(d) Wind speed
Answer:
(b) Temperature

Question 6.
Animals that can tolerate a narrow range of temperature are
(a) stenothermal
(b) eurythermal
(c) poikilothermic
(d) homeothermic
Answer:
(a) stenothermal

Question 7.
Animals that can tolerate a narrow range of salinity are
(a) euryhaline
(b) anadromous
(c) catadromous
(d) stenohaline
Answer:
(d) stenohaline

Question 8.
What is the source of energy in the depths of more than 500 m in the oceans?
(a) Sunlight
(b) Wind energy
(c) Dead and decaying matter
(d) Phytoplankton
Answer:
(c) Dead and decaying matter

Question 9.
Which factor does not determine percolation and water holding capacity of the soil?
(a) Soil composition
(b) Grain size
(c) Aggregation of soil particles
(d) Vegetation on that soil
Answer:
(d) Vegetation on that soil

Question 10.
Which factors of soil does not determine the vegetation in any area?
(a) pH
(b) mineral composition
(c) topography
(d) types of microorganisms
Answer:
(d) types of microorganisms

Question 11.
Find the odd one out
(a) Dormancy
(b) Hibernation
(c) Aestivation
(d) Migration
Answer:
(d) Migration

Question 12.
Which of the following ability is present in the desert animals?
(a) Ability to concentrate urine.
(b) Ability to remain inside the shelters and escape need of water.
(c) Ability to derive water from all the fruits.
(d) Ability to absorb water from air.
Answer:
(a) Ability to concentrate urine.

Question 13.
Which of the statement does not describe the adaptation of the desert plants ?
(a) Desert plants have a thick cuticle on their leaf surfaces.
(b) Desert plants have their stomata arranged in sunken pits.
(c) Desert plants have a special photosynthetic pathway called CAM.
(d) Desert plants have soft stems and large leaves.
Answer:
(d) Desert plants have soft stems and large leaves.

Question 14.
What is the use of CAM type of photosynthetic pathway for the desert plants ?
(a) It enables their stomata to remain closed during day time.
(b) It requires less sunlight for the photosynthesis.
(c) It requires less amount of chlorophyll during photosynthesis.
(d) The water absorbed from the soil by the plants during CAM photosynthetic pathway is less.
Answer:
(a) It enables their stomata to remain closed during day time.

Question 15.
In which plant photosynthetic function is taken over by the flattened stems?
(a) Nephrolepis
(b) Cycas
(c) Opuntia
(d) Zea mays
Answer:
(c) Opuntia

Question 16.
What is Allen’s rule?
(a) Mammals from colder climates generally have shorter ears and limbs to minimise heat loss.
(b) Mammals have constant temperature of the body in spite of their varied habitats.
(c) Mammals can be oviparous at times.
(d) The ecosystem of cold climate regions is equally occupied with mammals, birds and reptiles.
Answer:
(a) Mammals from colder climates generally have shorter ears and limbs to minimise heat loss.

Question 17.
Sunken stomata is the characteristic feature of
(a) hydrophyte
(b) mesophyte
(c) xerophyte
(d) halophyte
Answer:
(c) xerophyte

Question 18.
Which of the following pairs is correctly matched ?
(a) Uricotelism-aquatic habitat
(b) Parasitism-intra-specific relationship
(c) Excessive perspiration-xeric adaptation
(d) Stream-lined body-aquatic adaptation
Answer:
(d) Stream-lined body-aquatic adaptation

Question 19.
World population day is observed on
(a) 11th July
(b) 16th September
(c) 23rd October
(d) 1st December
Answer:
(a) 11th July

Question 20.
World Environment day is celebrated on
(a) 22nd April
(b) 5th June
(c) 1st October
(d) 16th November
Answer:
(b) 5th June

Question 21.
World Earth day is observed on
(a) 22nd April
(b) 5th June
(c) 21st October
(d) 26th November
Answer:
(a) 22nd April

Question 22.
World ozone day is celebrated on
(a) 5th June
(b) 16th September
(c) 1st October
(d) 23rd October
Answer:
(b) 16th September

Question 23.
A group of individuals belonging to the same species within an ecosystem is called a
(a) community
(b) habitat
(c) population
(d) specific group
Answer:
(c) population

Question 24.
The populations of different species that live and interact together in the ecosystem are called
(a) community
(b) habitat
(c) population
(d) interspecies
Answer:
(a) community

Question 25.
If do not occur in an ecosystem, the survival of organisms may not take place and functioning of ecosystem is lost.
(a) interactions
(b) struggle
(c) reproduction
(d) none of the above
Answer:
(a) interactions

Question 26.
If in a pond there were 200 lotus plants last year and through reproduction 20 new plants are added, taking the current population to 220, what is the natality rate of the lotus for that year ?
(a) 0.2
(b) 0.4
(c) 0.1
(d) 1.0
Answer:
(c) 0.1

Question 27.
During laboratory experiments, 30 fishes died from an aquarium tank having 150 fishes during one month. What is the rate of mortality of fishes per month ?
(a) 0.2
(b) 0.3
(c) 0.4
(d) 0.5
Answer:
(a) 0.2

Question 28.
Which of the following is correct statement?
(a) Natality can never be controlled in any population.
(b) If mortality is more than natality, the density of population declines.
(c) Natality and mortality are always same for every population.
(d) If natality is more than mortality the population size declines.
Answer:
(b) If mortality is more than natality, the density of population declines.

Question 29.
What is the apt definition of density?
(a) The capacity of a population to sustain.
(b) The total number of genes in a population.
(c) The total number of individuals in a population per unit area.
(d) The total number of births taking place.
Answer:
(c) The total number of individuals in a population per unit area.

Question 30.
On which of the following factors is growth rate of a population dependent ?
(a) Density and natality
(b) Natality and age structure
(c) Mortality and density
(d) Natality and mortality
Answer:
(a) Density and natality

Question 31.
When pre-reproductive age group is large in a population, what will be the growth rate of that population?
(a) Steady
(b) Rapid
(c) Declining
(d) None of these
Answer:
(b) Rapid

Question 32.
When pre-reproductive and post-reproductive age group is same in structure, the population is
(a) declining
(b) increasing
(c) steady
(d) disappearing
Answer:
(c) steady

Question 33.
In which type of interactions, interacting species do not live closely together ?
(a) Competition
(b) Parasitism
(c) Commensalism
(d) Predation
Answer:
(d) Predation

Question 34.
Name the interaction in which one species is harmed but the other remains unaffected,
(a) Commensalism
(b) Parasitism
(c) Amensalism
(d) Competition
Answer:
(c) Amensalism

Question 35.
Choose the correct statement from the following
(a) Carnivores are the only predators in any ecosystem
(b) Herbivores are in a broad ecological context not very different from predators.
(c) Sparrow eating grain is not a predator.
(d) Predation and parasitism are one and the same.
Answer:
(b) Herbivores are in a broad ecological context not very different from predators.

Question 36.
What is the meaning of symbiosis?
(a) Living together
(b) Breeding together
(c) Fighting with each other
(d) Feeding together
Answer:
(a) Living together

Question 37.
Gause’s ‘Competitive Exclusion Principle’ can work only when
(a) the resources are limited
(b) the resources are abundant
(c) the inferior species and superior species do not need same resources
(d) only when there is interspecific competition
Answer:
(a) the resources are limited

Question 38.
The word commensalism means
(a) on the either side of the table
(b) sharing the table
(c) eating at the table of other
(d) on the top of the table
Answer:
(b) sharing the table

Question 39.
Which of the following is not a classical example of commensalism?
(a) An orchid growing as an epiphyte on a mango branch.
(b) Barnacles growing on the back of a whale.
(c) The cattle egret and grazing cattle.
(d) Lichen seen on the tree.
Answer:
(d) Lichen seen on the tree

Question 40.
Calotropis plant is poisonous for herbivores as it is rich in
(a) opium
(b) cardiac glycosides
(c) quinine
(d) strychnine
Answer:
(b) cardiac glycosides

Question 41.
Term ecology was first used by
(a) Grinnell
(b) Reiter
(c) Haeckel
(d) Darwin
Answer:
(b) Reiter

Question 42.
Who introduced subject ecology to the world.
(a) Reiter
(b) Grinnell
(c) Darwin
(d) E. Haeckel
Answer:
(d) E. Haeckel

Question 43.
The term niche was first time used by
(a) Grinnell
(b) Haeckel
(c) Mendel
(d) Darwin
Answer:
(a) Grinnell

Match the columns

Question 1.

Column A	Column B
(1) Organism	(a) Large unit with specific climatic zone
(2) Population	(b) Different species in particular area
(3) Community	(c) Same species in a geographical area
(4) Biome	(d) Basic unit of ecological hierarchy

Answer:

Column A	Column B
(1) Organism	(d) Basic unit of ecological hierarchy
(2) Population	(c) Same species in a geographical area
(3) Community	(b) Different species in particular area
(4) Biome	(a) Large unit with specific climatic zone

Question 2.

Water body A	Salinity values B
(1) Streams	(a) 340 ppt
(2) Indian Ocean	(b) 5 ppt
(3) Hyper saline lagoon	(c) 30-35 ppt
(4) Dead sea	(d) 100 ppt

Answer:

Water body A	Salinity values B
(1) Streams	(b) 5 ppt
(2) Indian Ocean	(c) 30-35 ppt
(3) Hyper saline lagoon	(d) 100 ppt
(4) Dead sea	(a) 340 ppt

Classify the following to form Column B as per the category given in Column A

Question 1.
Emigration, Immigration, More mortality, Unlimited resources, More natality, Continuous reproduction.

Column A	Column B
(1) Decrease in population density	————–
(2) Increase in population density	—————
(3) Exponential growth	————–

Answer:

Column A	Column B
(1) Decrease in population density	Emigration, More mortality
(2) Increase in population density	Immigration, More natality
(3) Exponential growth	Unlimited resources, Continuous reproduction.

Question 2.
Hungary, United States, Denmark, Italy, Australia, Kenya, Nigeria, Germany

Pattern of population growth	Name of the countries
(1) Rapid growth	————–
(2) Slow growth	—————
(3) Zero growth	————–
(4) Negative growth	————–

Answer:

Pattern of population growth	Name of the countries
(1) Rapid growth	Kenya, Nigeria
(2) Slow growth	United States, Australia
(3) Zero growth	Denmark, Italy
(4) Negative growth	Hungary, Germany

Question 3.
Epiphytic orchid and mango tree, Ascaris and human, Egret and cattle, Lichen having alga and fungus, Bumblebee and flowering plant, Plasmodium vivax and man.

Column A	Column B
(1) Mutualism	————–
(2) Commensalism	—————
(3) Parasitism	————–

Answer:

Column A	Column B
(1) Mutualism	Lichen having alga and fungus, Bumblebee and flowering plant.
(2) Commensalism	Epiphytic orchid and mango tree, Egret and cattle.
(3) Parasitism	Ascaris and human, Plasmodium vivax and man.

Very short answer questions

Question 1.
What are the key abiotic factors that influence all habitats?
Answer:
Key abiotic factors that influence all habitats are ambient temperature, availability of water, light and type of soil.

Question 2.
What is homeostasis?
Answer:
Homeostasis is the state of steady interned, physical and chemical conditions maintained by living systems.

Question 3.
What is meant by eurythermal?
Answer:
Eurythermal are those organisms that can tolerate and thrive in a wide range of temperatures.

Question 4.
What is meant by stenothermal?
Answer:
Stenothermal are those organisms which are restricted to only narrow range of temperatures.

Question 5.
What is euryhaline?
Answer:
Organisms which can tolerate wide range of salinities are called euryhaline.

Question 6.
What is stenohaline?
Answer:
Organisms which are restricted only to a narrow range of salinity are called stenohaline.

Question 7.
What are the various characteristics of soil?
Answer:
Characteristics of the soil are soil composition, grain size, the percolation and water holding capacity, pH, mineral composition of the soil.

Question 8.
What decides the vegetation of an area?
Answer:
The soil characteristics along with pH, mineral composition and topography, and climatic factors determine the vegetation of an area.

Question 9.
What is Population ecology?
Answer:
Population ecology is an important area of ecology because it links ecology to population dynamics, genetics and evolution.

Question 10.
In which interaction of species, both the species are at a loss?
Answer:
Competition is the type of interaction where . both the species are at a loss.

Question 11.
What is parasitism?
Answer:
Parasitism is the type of interaction between two species in which parasitic species is benefited and the host species is harmed.

Question 12.
What are ectoparasites?
Answer:
Parasites that feed on the external surface of the host organism are called ectoparasites.

Question 13.
Name blood sucking ectoparasites.
Answer:
Lice, mosquito feeding on human blood and ticks parasitic on dogs.

Question 14.
Name the malarial parasite and its vector.
Answer:
The malarial parasite is Plasmodium vivax which needs a vector anopheles mosquito.

Question 15.
Name the secondary metabolites that act as defensive substances against grazers and browsers.
Answer:
Nicotine, caffeine, quinine, strychnine, opium, etc. are secondary metabolites which act as defensive substances produced by plants against grazers and browsers.

Question 16.
Name the ectoparasites which infest the marine fish.
Answer:
Copepods are the ectoparasites which infest the marine fish.

Question 17.
What do you mean by ‘evolutionary arms race’? In which kind of interactions is it observed?
Answer:
In order to save their lives, prey species : have evolved various defence mechanisms. This are called ‘evolutionary arms race’. These defence mechanisms are seen in prey-predator interactions.

Give Definitions of the following

Question 1.
Habitat
Answer:
The physical space of an organism with the other living or non-living factors is called its habitat.

Question 2.
Microhabitat
Answer:
The immediate surrounding of an organism is called microhabitat.

Question 3.
Niche
Answer:
Niche is defined as the processes about how that organism is linked with its physical and biological environment.

Question 4.
Fundamental niche
Answer:
Fundamental niche is the niche in the absence of all competitors, this is highly improbable in nature.

Question 5.
Realized niche
Realized niche is more realistic approach, in the presence of competition for the resources available in the habitat.

Question 6.
Competition
Answer:
Competition is defined as a process in which the fitness of one species is significantly lowered in the presence of another species.

Give one or two examples of the following

Question 1.
Intraspecific competition
Answer:
Two dogs fighting for same food. Two tomcats fighting for their territory.

Question 2.
Commensalism
Answer:
An orchid growing as an epiphyte on a branch of mango tree, is benefited due to support offered by mango tree but the mango tree does not get any benefit.

Question 3.
Ectoparasites
Answer:
Mosquito, louse sucks blood from human host.

Question 4.
Endoparasites
Answer:
Round worm. Ascaris and tape worm are endoparasites in the intestine of humans.

Name the type of association

Question 1.
Cattle egret birds with buffalo.
Answer:
Commensalism

Question 2.
Tiger and the deer.
Answer:
Predator and prey relationship

Question 3.
Visiting flamingos and fishes in the estuarine water.
Answer:
Interspecific competition.

Distinguish between the following

Question 1.
Natality and Mortality.
Answer:

Natality	Mortality
1. Birth rate of any population is called its natality.	1. Death rate of any population is called its mortality.
2. Rise in natality increase the population density.	2. Rise in mortality decrease the population density.
3. Decline in natality decrease the population.	3. Decline in mortality increase the population.
4. Natality is the positive factor for population growth.	4. Mortality is the negative factor for population growth.
5. Absolute natality will always be more than realized natality.	5. Absolute mortality will always be less them realized mortality.

Question 2.
Eurythermal and stenothermal.
Answer:

Eurythermal	Stenothermal
1. Animals which can tolerate wide range of temperatures are called eurythermal.	1. Animals which can tolerate only narrow range of temperature fluctuations are called stenothermal.
2. Eurythermal animals show reduced temperature sensitivity.	2. Stenothermal animals show high temperature sensitivity.
3. Body functions of eurythermal animals can occur at wide range of temperature range. E.g. Goat, man, cat, dog, tiger, cow, sheep, monkey, crab, etc.	3. Body functions of stenothermal animals can occur at only narrow range of temperature range. E.g. Insects, fishes, reptiles, snakes, etc.

Give scientific reasons

Question 1.
Temperature is said to be the most ecologically relevant environmental factor.
Answer:

1. Temperature fluctuations on the earth are quite marked.
2. The distribution of plants and animals on the earth depends upon temperature range.
3. For the organisms ambient temperature affects their enzyme kinetics of the cell.
4. Entire metabolism, activity and other physiology of the organism is dependent on temperature. Therefore, it is said to be the most ecologically relevant environmental factor.

Question 2.
Adaptation is an important attribute of the organism.
Answer:

1. Organisms adapt to their surrounding environment by showing physiological, behavioural or morphological changes which are called adaptations.
2. Due to adaptations, organisms can survive and reproduce in its environment. Therefore, adaptation is said to be am important attribute of the organisms.

Question 3.
Both host and the parasite tend to co¬evolve, against each other.
Answer:

1. Host and parasitic relationship is most specific. This means that for a particular parasite there is specific host.
2. Many parasites have evolved to be host-specific as they can parasitize only a single species of host. Therefore, during evolution, they both co-evolve together, against each other.

Question 4.
Cuscuta plant does not have chlorophyll.
Answer:

1. Cuscuta is a parasitic plant. It is commonly found growing on hedge plant.
2. It derives its nutrition directly from the host plant on which it thrives by parasitizing it.
3. Since it does not prepare its own food by photosynthesis, it loses chlorophyll from the leaves.

Question 5.
Predators in nature are called prudent.
Answer:

1. Predators control the prey population but if a predator over exploits its prey, then the prey might become extinct.
2. If prey species is not available, the predator will also starve and become extinct. Predators, therefore, do not kill the prey unnecessarily. They act as prudent.

Write short notes

Question 1.
Temperature fluctuations on the earth.
Answer:

1. The temperatures vary from subzero levels in polar areas and high altitudes, to about 50 °C in tropical deserts during summer.
2. There are also seasonal changes in the temperature.
3. Temperature also shows progressive decrease from the equator towards the poles and from plains to the mountain tops.
4. Some unique habitats such as hot springs may show very high temperatures of about 80 to 100 °C.
5. In deep-sea hydrothermal vents average temperatures may rise up to 400 °C.

Question 2.
Adaptations of mammals in colder regions.
Answer:

1. Mammals inhabiting colder regions have shorter snout, ears, tail and limbs to minimize the loss of body heat. This is called Allen’s Rule.
2. Aquatic mammals such as whales and seals living in the polar seas, have a thick layer of fat which is called a blubber below their skin.
3. Blubber acts as an insulator and thus helps to keep the body warm by reducing loss of body heat.
4. Some animals like polar bears undergo hibernation and thus tide over the stressful winters.

Question 3.
Natality.
Answer:

1. Natality is the birth rate of a population. Due to increased natality the population density rises.
2. Natality is a crude birth rate or specific birth rate.
3. Crude birth rate : Number of births per 1000 population/year gives crude birth rate. Crude birth rate is helpful in calculating population size.
4. Specific birth rate : Crude birth rate is relative to a specific criterion such as age. E.g. If in a pond, there were 200 carp fish and their population rises to 800. Then, taking the current population to 1000, the birth rate becomes 800/200 = 4 offspring per carp per year. This is specific birth rate.
5. Absolute Natality : The number of births under ideal conditions when there is no competition and the resources such as food and water are abundant, then it give absolute natality.
6. Realized Natality : The number of births under different environmental pressures give realized natality. Absolute natality will be always more than realized natality.

Question 4.
Mortality.
Answer:

1. Mortality is the death rate of a population. It gives a measure of the number of deaths in a particular population, in proportion to the size of that population, per unit of time.
2. Mortality rate is typically expressed in deaths per 1,000 individuals per year.
   A mortality rate of 9.5 (out of 1,000) in a population of 1,000 would mean 9.5 deaths per year in that entire population or 0.95% out of the total.
3. Absolute Mortality : The number of deaths under ideal conditions when there is no competition, and all the resources such as food and water are abundant, then it gives absolute mortality.
4. Realized Mortality : The number of deaths under environmental pressures come into play gives realized mortality.
5. It must be remembered that absolute mortality will always be less than realized mortality.

Question 5.
Populations Interactions
Answer:

1. In nature, every species requires interactions with at least one other species for its food.
2. Even autotrophic plant species needs soil microbes to break down the organic matter in soil and return the inorganic nutrients for absorption.
3. The plants need animal agents . for pollination.
4. Animals, plants and microbes cannot live in isolation but interact in various ways to form a biological community.
5. Such interactions can be interspecific (within two different species) or intraspecific (within the same species).
6. Interspecific interactions are of broad four types viz, neutralism, negative or harmful, positive or beneficial, and both positive and negative interactions.
7. Interacting species live closely together in interactions such as predation, parasitism and commensalism.
8. Neutralism interaction have no significant effect on either species. Negative interactions are of competition or amensalism type. Positive interactions occur in the form of mutualism, protocooperation and commensalism. Parasitism and predation are both positive and negative type of interaction.

Question 6.
Mutualism
Answer:

1. Mutualism is an obligatory and interdependent interaction. It is an association of two species in which both of them are benefited.
2. The classic example of mutualism is lichens. Lichen is an intimate, mutualistic relationship between a fungus and photosynthetic algae or cyanobacteria.
3. Most of the plant and animal interactions are of mutualistic type.
4. For pollination and seed dispersal, plants depend on the animals.
5. Animals in turn feed on pollen and nectar during pollination. During seed dispersal juicy and nutritious fruits are used by the animals.
6. In animal-animal interactions also mutualism is seen in many instances.

Question 7.
Brood parasitism
Answer:

1. Brood parasitism is a type of parasitic behaviour shown by Asian Koel. Koel lays its eggs in the nest of crow.
2. Crow acts as a host bird and incubate the eggs of koel.
3. The eggs of koel show resemblance to the host’s egg in size and colour. This reduces the chances of the crow detecting koel’s eggs and ejecting them from the nest.
4. Eggs of koel hatch before the host’s eggs and hence parasitic bird is in advantage.

Short answer questions

Question 1.
What are the three main types of niches?
Answer:

1. Spatial or habitat niche : Spatial or habitat niche means the physical space occupied by the organisms.
2. Trophic niche : This kind of niche is based on the trophic level of an organism in a food chain.
3. Multidimensional or hypervolume niche : In multidimensional niche, number of abiotic and biotic environmental factors are considered. The resulting space by the niche is called hypervolume. Therefore it is also called hypervolume niche.
4. It shows the position of an organism in the environmental gradient.

Question 2.
Why do animals need to maintain homeostasis?
Answer:

1. Homeostasis keeps the body in equilibrium.
2. All the internal functions are maintained due to homeostasis.
3. Survival, growth and reproduction can be achieved due to this steady state.
4. The external environment changes constantly but by homeostasis, organisms can cope up with this change.
5. Thus homeostasis is a way of adaptation for survival.

Question 3.
How is sunlight important for every ecosystem ?
Answer:

1. Sunlight is essential for the plants for photosynthesis.
2. It is the only source of energy for the entire ecosystem.
3. Without sunlight the food chains will not exist.
4. Survival of plants is therefore dependent on sunlight.
5. In case of animals diurnal and seasonal variations in light intensity and duration decide the feeding, foraging and reproductive activities.
6. Migrations shown by certain animals also depend on light.
7. Almost all animals have behaviour based on photoperiod. The proportion of sunlight on land also decides the ambient temperature. Thus, life is dependent on light.

Question 4.
What can be the causes of deviation from 1 : 1 sex ratio in natural habitat?
Answer:

1. In nature, when there is chromosomal sex determination, usually 1 : 1 sex ratio is obtained. But there are other causes for deviation from 1 : 1 sex ratio.
2. There are many other environmental sex determination methods where 1 : 1 sex
   ratio becomes skewed. This is due to mere chance of fertilization.
3. Also some lower animals show parthenogenesis e.g. as in honey bees. In such cases, offspring produced may not be in 1 : 1 proportion.

Question 5.
What are the special adaptations that endoparasites show?
Answer:

1. Endoparasites show loss of unnecessary sense organs as these are not needed for the parasite.
2. There are adhesive organs or suckers always present in the endoparasites which are needed to cling on to the host.
3. Endoparasites show loss of digestive system.
4. They have very high reproductive capacity.
5. The complex life cycles are seen in such parasites which involve intermediate hosts or vectors to facilitate transfer to the host.

Question 6.
What are the effects of parasite on the host?
Answer:

1. Most of the parasites cause harm to the host.
2. Host is affected by reducing its survival, growth and reproduction.
3. Some parasites can also be fatal to the host causing death of the host.
4. The population density of host species is reduced by parasites.
5. The host species become more vulnerable to predation by making it physically weak.

Question 7.
What is the role of predator in balancing the ecosystem?
Answer:

1. Predators keep prey population under control. If predators are lacking from the ecosystem, the prey population will rise without any control. Their high density may cause instability in ecosystem.
2. Predators also help in maintaining the species diversity in a community. This is done by reducing the intensity of competition among competing prey species.
3. Predators control the pest species and thus can be used for natural biological control measures in an ecosystem. E.g. frog controlling the locust population.
4. Predators also control the invading exotic species and stop their rapid spread of such species.

Question 8.
How does prey species defend themselves against predators?
Answer:
Prey species show following defence mechanisms:

1. Showing camouflage for concealment.
2. Moving at faster speed for escape.
3. Cryptic colouration to avoid the detection. This is seen in some insects. Also predators display such cryptic colouration to avoid detection. E.g. Colouration in frog.
4. Bad taste due to accumulated chemicals.
   E.g. The Monarch butterfly is highly distasteful to its predator bird as it stores a special chemical in the body during its caterpillar stage by feeding on a poisonous weed.

Question 9.
With suitable examples describe commensalism.
Answer:
I. Commensalism : Commensalism is the interaction between two species in which one species derives benefit and the other one is neither harmed nor benefited.
II. Examples of commensalism:

1. Orchid grows as epiphyte on other big trees. The tree do not get any benefit but is neither harmed. But orchid gets support.
2. Cattle egret is the insectivorous bird which forage close to cattle. When cattle move, the hidden insects in the grass are flushed out. These insects are then captured by egrets. Cattle do not get benefit but birds do.
3. Sea anemone has stinging cells on the tentacles which offer protection to clown fish. Clown fish gets the protection from other predators, whereas, sea anemone does not derive any benefit from this association.

Question 10.
What are different population attributes?
Answer:

1. Basic physical attributes of population are population size and population density.
2. Number of individuals in a population is its size whereas number of individuals present per unit space, in a given time is called its density.
3. The other attributes are natality or birth rate, mortality or death rate, immigration means coming into the population, emigration means leaving from the population, age pyramids, sex ratio and biotic potential etc.

Question 11.
What are the decisive factors for population density?
Answer:
The density of a population in a given habitat during a given period fluctuates due to changes in four basic processes, viz.

1. Natality i.e. birth rate (The number of births during a given period in the population that are added to the initial density).
2. Mortality i.e. death rate (The number of deaths in the population during a given period).
3. Immigration i.e. number of individuals of the same species that have come into the habitat from elsewhere during the time period under consideration.
4. Emigration i.e. the number of individuals of the population who left the habitat and gone elsewhere during the time period under consideration.
5. Natality and immigration increase in population density whereas mortality and emigration decrease it.

Question 12.
Should an ideal parasite be able to thrive within the host without harming it?
Answer:
A parasite that resides inside the body of host, will certainly cause discomfort to the host. But if the host dies, the parasite also will diminish. Therefore, Ideal parasite will not extract more benefits from the host. But ideal parasite cannot stay alive without association with host. They need host for various purposes like nutrition, food. Some need the host for completing their life cycle. So parasite will always harm the host in order to thrive.

Question 13.
Why didn’t natural selection lead to the evolution of such totally harmless parasites?
Answer:
Being a parasite means causing trouble or harm to the host. When host-parasite relationship is concerned both of them evolve together which is also called co¬evolution. If totally harmless parasite has to be evolved through natural selection, then such parasite will not remain as a parasite but will become commensal or can show amensalism. Therefore, natural selection does not lead to evolution of totally harmless parasite.

Question 14.
What will happen when carrying capacity of any habitat is exceeded?
Answer:
When the carrying capacity of any habitat is exceeded there is severe resource crunch. This may be in the form of food, shelter or availability of mates. This results into struggle for survival. This will result into death of those who cannot cope up with the struggle. They may die due to starvation or due to interactions such as fierce competitions. This causes the population again to come back to equilibrium. Thus when carrying capacity is exceeded, the natural way is to reduce the population in the habitat.

Question 15.
What could be the reasons behind enormous increase in human population?
Answer:

1. Human population has increased enormously in last century due to increased natality and reduced mortality.
2. Due to advances in medical sciences, vaccinations and better life expectancy mortality rate has been considerably reduced. With the exception of Covid 19 Pandemic, all the mortalities due to epidemics were controlled due to modern medical facilities.
3. Due to better food production and advances in agriculture methods, people are not starving anymore. This has considerably reduced the deaths due to starvations.
4. However, natality rate has not been reduced especially in developing countries. Lack of family planning measures, ignorance, illiteracy and traditional thinking about birth of male child, all such factors have caused tremendous increase in the human population.

Question 16.
What can be reason behind the different reproductive strategies adopted by monocot plants like cereals / pulses and dicot plants like mango?
Answer:
The monocot plants such as cereals and pulses and also mango are commercially important cash crops. Therefore, in order to obtain profitable harvest, different reproductive strategies are adopted.

Chart based / Table based questions

Question 1.
Complete the following table by placing the categories and the given signs + : Benefited ; – : Inhibited ; 0 : Not affected

Interactions	Species
	A	B
1. Neutralism – …………………..
2. Negative interactions …………………………
3. Positive interactions …………………….
4. Both positive and negative interactions …………………………..

Answer:

Interactions	Species
	A	B
1. Neutralism – no significant effect	O	O
2. Negative interactions a. Competition – direct interference type b. Competition – resource – use type c. Amemsalism	– – –	– – O
3. Positive interactions a. Symbiosis (Mutualism) b. Commensalism c. Protocooperation	+ + +	+ O +
4. Both positive and negative interactions a. Parasitism b. Predation	+ +	– –

Diagram based questions

Question 1.
Sketch and label the graph showing logistic growth curve of the population.
Answer:

Question 2.
Sketch and label the graph showing exponential growth curve of the population.
Answer:

Question 3.
Sketch the different types of Age Pyramids.
Answer:

Question 4.
From the age pyramids given in figure what will be your forecast for 15 years from now for the populations of 1. Kenya, 2. Australia, 3. Italy and 4. Hungary?

Answer:
(1) Forecast for Kenya : Kenya is showing rapid growth as its pre-reproductive group is large. Post-reproductive group is much reduced. Therefore, 15 years from now, the population will be large.

(2) Forecast for Australia : Australian age pyramid is showing larger post-reproductive group. In the years to come, they will be removed from the population. Also the pre-reproductive group is not much large. This will not add to the Australian population in the future. Thus, this country will show slow growth.

(3) Forecast for Italy : In Italy the reproductive and post-reproductive groups are almost similar. The pre-reproductive group is also limited. Hence, in future, the population will not expand. At the same time the post-reproductive group here is large which means that the population growth will be reduced in the next 15 years.

(4) Forecast for Hungary : Hungary is showing : typical age pyramid where the pre-reproductive and reproductive groups are small. On the contrary, the post-reproductive group is more, which shows that in the next 15 years, the old people will leave the population, causing negative growth.

Long answer questions

Question 1.
What are the characteristics of ecological niche ?
Answer:

1. A niche describes how that organism is linked with its physical and biological environment.
2. Niche is described as a position of a species in the environment. It gives the idea about how the organisms are surviving and fulfilling their needs of shelter and food.
3. By studying niche one can get idea of the flow of energy from one organism to another. This helps to understand the feeding habits and interactions involving food chain and food web.
4. If any niche is left vacant, other organisms\fill that position.
5. The niche is specific to each species. Two species can never share the same niche. By having specific niche, every organism tries to reduce competition for resources.
6. E.g. In birds, each one is specific in their eating habits, some are insectivorous, while some are frugivorous. Some are omnivorous, in this way birds living in the same habitat differ in their niches because of different eating habits.

Question 2.
What are the different ways in which organisms adapt to the changes in the environment?
Answer:
To survive and propagate further in any environment, organisms show one of the four possible ways, viz. regulate, conform, migrate and suspend.
(1) Regulate : In this method, organisms maintain homeostasis by physiological and behavioural changes. Due to homeostatic regulation, they can perform thermoregulation or osmoregulation. E.g. All birds and mammals show constant body temperature and osmotic concentration irrespective of external temperature.

(2) Conform : Most of the animals and plants are unable to maintain a constant internal environment. Their body parameters change according to outside environment. E.g. Poikilothermic animals cannot maintain body temperature but they are simple conformers. In few aquatic animals, the osmotic concentration of the body fluids changes according to surrounding osmotic concentration. Few conformers can regulate the parameters in limited range.

(3) Migrate : When organism is unable to cope up with surrounding temperatures, they migrate temporarily from such stressful habitat to a more favourable habitat. After the stressful period is over, they return back. Birds show long-distance migrations during severe winter.

(4) Suspend : Suspending the life activities for particular period is one of the methods to cope up with stressful conditions. Seeds of plants remain dormant over unfavourable period and once favourable conditions are resumed they start growing. This state is called dormancy during which metabolic activities are suspended. Hibernation and aestivation seen in some animals is also for escaping severe winter or summer respectively. E.g. Polar bear shows hibernation while snails and fish show aestivation. These are also suspension measures.

Question 3.
What are the adaptations in animals living under crushing pressure at great depths of ocean?
Answer:

1. Environment of depths of ocean are characterized by high pressure, low temperature, absence of light, calmness of water, absence of phytoplankton and other producers, scarcity of food and thus animals staying here show many adaptations.
2. Due to extreme pressure the bodies of deep- sea fish and other animals are very much compressed.
3. The bony skeletons are much reduced except for jaws. They have watery muscles. Some deep-sea fishes exhibit greatly enlarged eyes which act like telescope.
4. They are highly effective as in depths there is less light. Their retina is composed of a number of tiers of rods, presumably arranged to absorb all the limited light that enters the eye. However, the eye-size is small.
5. Some benthic fishes have eyes located on only one side of the body. E.g. Sole fish.
6. Many deep-sea animals are bioluminescent, i.e. they produce their own light by means of luminous organs.
7. In anglerfish, the light is used as a bait to attract prey and also for species and sex recognition.
8. The mouth of deep-sea fish is the enormous, which enables them to gulp large sized prey.
9. Many of the deep-sea animals have long appendages, abundant spines, stalks or other

Question 4.
With the help of suitable diagram describe the Exponential population growth curve.
Answer:

1. When the resources are abundant, organisms show continuous growth of a population without any hindrance. With unlimited resources, each species has the ability to realise fully its innate potential to grow in number.
2. Such growth of a population is called an exponential or geometric growth.
3. Any species growing exponentially under unlimited resource conditions can reach enormous population densities in a short time. E.g. Human population shows such exponential growth.
4. Exponential growth shows J-shaped curve.

Question 5.
Explain the ‘Competitive Exclusion Principle’ given by Gause.
Answer:
Gause’s ‘Competitive Exclusion Principle’:
(1) This principle states that two closely related species competing for the same resources cannot co-exist indefinitely and the competitively inferior one will be eliminated eventually.

(2) The Gause’s principle may be true if resources are limiting, but not otherwise. More recent studies do not support such gross generalisations about competition. The species during competition also show resource partitioning.

(3) In resource partitioning, the species facing competition might evolve mechanisms that promote co-existence rather than exclusion. If two species compete for the same resource, they could avoid competition by choosing, for instance, different times for feeding or different foraging patterns. E.g. Five closely related species of warblers living on the same tree were able to avoid competition and co-exist due to behavioural differences in their foraging activities. If there are two competing species and one is comparatively superior than the other, then the inferior one remains restricted to smaller geographical area. If this superior species is removed then only the inferior species expands its range.

Question 6.
What are the key differences that make such a great variation in the physical and chemical conditions of different habitats?
Answer:
Different abiotic factors make great variations in the physical and chemical conditions of different habitats.
The most important abiotic factors are temperature, water, light and soil. These abiotic factors act with the resident biotic factors in that habitat. Biotic components such as pathogens, parasites, predators and competitors keep on interacting continuously. All such interactions cause variations in different habitats.

Question 7.
Give names of eurythermal and stenothermal animals and plants?
Answer:

1. Eurythermal animals : Goat, man, cow, crab, bivalves, etc.
2. Stenothermal animals : Insects, reptiles, snakes, fishes, etc.
3. Eurythermal plants : Roses, daisies, oak trees, some fruits and vegetables.
4. Stenothermal plants : Croton, Bougainvillea, Frangipani, vines and orchids, some other fruits and vegetables

Question 8.
What will be the effect of increasing global temperatures on the different habitats and the organisms found in those habitats?
Answer:

1. Global temperature rise or global warming is having great impact on natural habitats.
2. Aquatic habitats like oceans are worst affected as 90% of extra heat enters marine waters. These elevated temperatures cause adverse effects on marine habitat.
3. Coral reefs are also affected due to increased temperature. It causes bleaching of coral reefs. Fish populations are adversely affected.
4. Due to rising temperature, the tundra regions and polar regions are showing melting of snow. These habitats are disappearing and the animals from these areas such as polar bears are on the verge of extinction. Increased temperatures also cause desertification of the once green habitats.
5. Nearly 50% of the species are under threat of extinction due to climate change. Global warming and climate change thus reduces biodiversity.
6. Every plant and animal species is adapted to a specific temperature conditions. But due to global warming and associated climate change, these species are affected. Some species show migrations to cooler places.
7. Temperatures also alter the life cycles of plants and animals. When temperatures rise, many plants grow rapidly and bloom earlier in the spring and survive longer into the fall. Some animals leave hibernation sooner.

Question 9.
Give examples of an animal and plant that can survive in fresh water as well as sea water.
Answer:
Few fish species such as salmons, crustacean prawns and crabs are able to survive in fresh water as well as sea water. Among plants, few phytoplankton, some algal species and mangorves show similar phenomena.

Question 10.
What is the source of energy for the life in deep ocean trenches where sunlight does not reach?
Answer:
In deep ocean trenches, the sunlight does not penetrate. Hence photosynthesis is not possible here. Most of the organisms that live here depend upon subsistence on falling organic matter. This organic matter falls off down from the upper photic zones, where phytoplankton can perform photosynthesis. This organic matter acts as source of energy for the life in deep oceanic trenches.