Previous Year Examination Questions
1 Mark Questions
1.Give an example of an organism that enters ‘diapause’ and why?[Delhi 2014]
Ans.Many zooplanktons in lakes and ponds enter diapause. They enter diapause to escape unfavourable environmental conditions and to delay the overall development.
Ans.Many zooplanktons in lakes and ponds enter diapause. They enter diapause to escape unfavourable environmental conditions and to delay the overall development.
2.Mention how do bears escape from stressful time in winter. [Delhi 2013c]
Ans.Bears escape from stressful time in winter by going into hibernation
Ans.Bears escape from stressful time in winter by going into hibernation
3.Write the basis on which an organism occupies a space in its community/natural surroundings.[All India 2013]
Ans.An organism occupies individual or species level in its community. This level is occupied on the basis of ecological level of organisation or ecological hierarchy. Individual-> Population -> Biotic community -> Biome
Ans.An organism occupies individual or species level in its community. This level is occupied on the basis of ecological level of organisation or ecological hierarchy. Individual-> Population -> Biotic community -> Biome
4.Why are some organisms called as eurythermals and some other as stenohaline? [Foreign 2011]
Ans.Organisms, which can tolerate and thrive in a wide range of temperatures are called as eurythermal while organisms, which can tolerate and thrive in a narrow range of salinities are stenohaline
Ans.Organisms, which can tolerate and thrive in a wide range of temperatures are called as eurythermal while organisms, which can tolerate and thrive in a narrow range of salinities are stenohaline
5.Why are green plants not found beyond a certain depth in the ocean? [HOTS; Delhi 2011]
Ans.Beyond a certain depth, green plants are not found, because light is unavailable in that zone.
Ans.Beyond a certain depth, green plants are not found, because light is unavailable in that zone.
6.Mention any two activities of animals, which get cues from diurnal and seasonal variations in light intensity, [Delhi 2011 c]
Ans.The two activities of animals which get cues from diurnal and seasonal variations in light intensity are:
(i) Timing their foraging
(ii) Migratory activities
(iii) Reproduction (any two)
Ans.The two activities of animals which get cues from diurnal and seasonal variations in light intensity are:
(i) Timing their foraging
(ii) Migratory activities
(iii) Reproduction (any two)
7.How do animals like fishs and snails avoid summer related unfavourable conditions? [Delhi 2010]
Ans.Fish migrate and snails go into aestivation or summer sleep to avoid summer-related problems.
Ans.Fish migrate and snails go into aestivation or summer sleep to avoid summer-related problems.
8.How do prickles help cactus survive in desert? Give two methods.[All India 2010 C]
Ans.The two methods by which prickles help cactus survive in desert are:
(i) By reducing and altering outer surface to reduce evaporation of water.
(ii) By providing defense against grazing animals.
Ans.The two methods by which prickles help cactus survive in desert are:
(i) By reducing and altering outer surface to reduce evaporation of water.
(ii) By providing defense against grazing animals.
9.Which one of the two, stenothermals or eurythermals shows wide range of distribution on earth and why?[HOTS; Delhi 2008]
Ans.Eurythermals show a wide range of distribution on earth, as they can tolerate and thrive in a wide range of temperatures
Ans.Eurythermals show a wide range of distribution on earth, as they can tolerate and thrive in a wide range of temperatures
10.When and why do some animals like snails go into aestivation?[All India 2008]
Ans.During stressful conditions of the habitat and inability to migrate, animals like snails undergo aestivation and protect themselves
Ans.During stressful conditions of the habitat and inability to migrate, animals like snails undergo aestivation and protect themselves
11.Why is the polar region not a suitable habitat for tiny humming birds? [HOTS; All India 2008]
Ans.Humming birds have a larger surface area compared to body volume. They tend to lose body heat very fast, when it is cold outside. Due to this, they need to spend more energy to generate body heat. Hence, polar region being a cold habitat is not suitable for tiny hummingbirds
Ans.Humming birds have a larger surface area compared to body volume. They tend to lose body heat very fast, when it is cold outside. Due to this, they need to spend more energy to generate body heat. Hence, polar region being a cold habitat is not suitable for tiny hummingbirds
12.When and why do some animals go into hibernation? [Foreign 2008]
Ans.When unfavourable conditions are for a short time and if the animals could not migrate, they undergo hibernation to avoid stressful winter conditions.
Ans.When unfavourable conditions are for a short time and if the animals could not migrate, they undergo hibernation to avoid stressful winter conditions.
13.List any two physiological responses that help you to gradually get acclimatised to high altitudes when you go from the plains. [Delhi 2008 C]
Ans.The physiological condition or responses in order to get accl imatised to high attitudes are:
(i) To compensate low oxygen, the production of red blood cells is increased.
(ii) High haemoglobin content and its decreased binding capacity.
(iii) Faster breathing rate (any two).
Ans.The physiological condition or responses in order to get accl imatised to high attitudes are:
(i) To compensate low oxygen, the production of red blood cells is increased.
(ii) High haemoglobin content and its decreased binding capacity.
(iii) Faster breathing rate (any two).
14.Define homeostasis. [All India 2008 C]
Ans.The process to maintain the constancy of internal environment of the body, despite varying external environmental conditions is called homeostasis
Ans.The process to maintain the constancy of internal environment of the body, despite varying external environmental conditions is called homeostasis
15.When and why do some animals like frogs hibernate? [Delhi 2008]
Ans.When unfavourable conditions are for a short time period and animals are unable to migrate, they hibernate to avoid the stres winter.
Ans.When unfavourable conditions are for a short time period and animals are unable to migrate, they hibernate to avoid the stres winter.
16.Between amphibians and birds, which will be stable to cope with global warming? Give reason.[HOTS; All India 2008]
Ans.Birds will be stable to cope with global warming because they can tolerate a wide range of temperatures (eurythermals).
Ans.Birds will be stable to cope with global warming because they can tolerate a wide range of temperatures (eurythermals).
17.How do herbs and shrubs survive under the shadow of big canopied trees in forests? [Delhi 2008C]
Ans.The herbs and shrubs are adapted to perform photosynthesis optimally under very low light conditions due to growing in the forests under the shadow’ of big canopied trees
Ans.The herbs and shrubs are adapted to perform photosynthesis optimally under very low light conditions due to growing in the forests under the shadow’ of big canopied trees
18.Why many of the freshwater animals cannot live for long in seawater or vice versa?[HOTS; Delhi; All India 2008 C]
Ans.Seawater contains high quantity of salt that is not favourable for freshwater animals. They face osmotic problems, hence they cannot survive in seawater for long.
Ans.Seawater contains high quantity of salt that is not favourable for freshwater animals. They face osmotic problems, hence they cannot survive in seawater for long.
2 Marks Questions
19.Some organisms suspend their metabolic activities to survive in unfavourable condition. Explain with the help of any four examples.[Delhi 2012]
Ans.Examples of organisms that suspend their metabolic activities in unfavourable condition.
(i) Bacteria, fungi and lower plants They form thick-walled spores, which help them to survive in unfavourable conditions. Spores germinate on return of favourable conditions.
(ii) Higher plants Seeds and some other vegetative reproductive structures serve as means to tide over periods of stress. They reduce their metabolic activity and undergo dormancy.
(iii) Animals They undergo hibernation or aestivation, if unable to migrate. For example, some snails and fishes.
(iv) Zooplanktons They enter diapause (suspended development) under unfavourable conditions.
Ans.Examples of organisms that suspend their metabolic activities in unfavourable condition.
(i) Bacteria, fungi and lower plants They form thick-walled spores, which help them to survive in unfavourable conditions. Spores germinate on return of favourable conditions.
(ii) Higher plants Seeds and some other vegetative reproductive structures serve as means to tide over periods of stress. They reduce their metabolic activity and undergo dormancy.
(iii) Animals They undergo hibernation or aestivation, if unable to migrate. For example, some snails and fishes.
(iv) Zooplanktons They enter diapause (suspended development) under unfavourable conditions.
20.Explain the response of all communities to environment over time. [All India 2011]
Ans.Response of communities to environment:
(i) Some organisms maintain homeostasis by physiological or behavioural means (regulate).
(ii)The internal environment in majority of animals and nearly all plants change with the change of external environment (conform).
(iii)Some organisms leave their habitats temporarily during unfavourable conditions and return back when conditions become favourable (migrate).
(iv)Some organisms suspend their metabolic activities to avoid stress by timely escaping, e.g. hibernation and aestivation.
Ans.Response of communities to environment:
(i) Some organisms maintain homeostasis by physiological or behavioural means (regulate).
(ii)The internal environment in majority of animals and nearly all plants change with the change of external environment (conform).
(iii)Some organisms leave their habitats temporarily during unfavourable conditions and return back when conditions become favourable (migrate).
(iv)Some organisms suspend their metabolic activities to avoid stress by timely escaping, e.g. hibernation and aestivation.
21.Bear hibernates, whereas some species of zooplanktons enter diapause to avoid stressful external conditions. How are these two ways different from each other?[Foreign 2011]
Ans.Difference between diapause and hibernation:
Ans.Difference between diapause and hibernation:
22.How does our body adapt to low oxygen availability at high altitudes?[Foreign 2011]
Ans.Body adaptations at high altitudes are:
The physiological condition or responses in order to get accl imatised to high attitudes are:
(i) To compensate low oxygen, the production of red blood cells is increased.
(ii) High haemoglobin content and its decreased binding capacity.
(iii) Faster breathing rate (any two).
Ans.Body adaptations at high altitudes are:
The physiological condition or responses in order to get accl imatised to high attitudes are:
(i) To compensate low oxygen, the production of red blood cells is increased.
(ii) High haemoglobin content and its decreased binding capacity.
(iii) Faster breathing rate (any two).
23.Why are small animals rarely found in the polar regions? Explain.[HOTS; Foreign 2010]
Ans.Small animals have a large surface area relative to their volume. So, they tend to lose body heat very fast during cold conditions. They need to spend more energy to generate body heat. Due to this smaller animals are rarely found in polar regions.
Ans.Small animals have a large surface area relative to their volume. So, they tend to lose body heat very fast during cold conditions. They need to spend more energy to generate body heat. Due to this smaller animals are rarely found in polar regions.
24.How do seals adapt to their natural habitat? Explain. [Foreign 2010]
Ans.Seals adapt to the natural habitat (cold climate) by developing a thick layer of fat (blubber) below their skin that acts as an insulator and reduce excess loss of body heat.
Ans.Seals adapt to the natural habitat (cold climate) by developing a thick layer of fat (blubber) below their skin that acts as an insulator and reduce excess loss of body heat.
25.Humming birds v live among the bushes in tropics, while penguins live on icebergs. They cannot survive if their habitats are reversed. Justify. [HOTS; Delhi 2010 C]
Ans.Humming birds are natural habitats of tropics. They have large surface area relative to their volume. So, they tend to lose heat very fast, even when it is cold outside.Penguins live on icebergs (natural habitat). They have less surface area to volume ratio. The lesser the ratio, more effective will be the thermoregulation. Also, they hide in group to escape from cold conditions. Therefore, both of them will not survive if their habitats are reversed
Ans.Humming birds are natural habitats of tropics. They have large surface area relative to their volume. So, they tend to lose heat very fast, even when it is cold outside.Penguins live on icebergs (natural habitat). They have less surface area to volume ratio. The lesser the ratio, more effective will be the thermoregulation. Also, they hide in group to escape from cold conditions. Therefore, both of them will not survive if their habitats are reversed
26.How does human body maintain constant temperature both in summers and winters? Explain.[Delhi 2009 C]
Ans.Human body maintains constant body temperature (37°C) as follows:
In summers, the outside temperature is very high than our body temperature. Due to this, profuse sweating occurs. This causes evaporation and cooling effect on the body.
In winters, the outside temperature is much lower than our body temperature. This causes shivering, a kind of exercise that produces heat and raises the body temperature.
Ans.Human body maintains constant body temperature (37°C) as follows:
In summers, the outside temperature is very high than our body temperature. Due to this, profuse sweating occurs. This causes evaporation and cooling effect on the body.
In winters, the outside temperature is much lower than our body temperature. This causes shivering, a kind of exercise that produces heat and raises the body temperature.
3 Marks Questions
27.(i)State how the constant internal environment is beneficial to organisms.
(ii)Explain any two alternatives by which orgnaisms can overcome stressful external conditions.[All India 2014]
Ans.(i)Constant internal environment is beneficial to organisms as it permits all biochemical reactions and physiological functions to proceed with maximal efficiency, thereby enhancing the overall efficiency of organism.
(ii) The two alternatives by which organisms can overcome stressful external conditions are
(ii)Explain any two alternatives by which orgnaisms can overcome stressful external conditions.[All India 2014]
Ans.(i)Constant internal environment is beneficial to organisms as it permits all biochemical reactions and physiological functions to proceed with maximal efficiency, thereby enhancing the overall efficiency of organism.
(ii) The two alternatives by which organisms can overcome stressful external conditions are
- Migration-organisms move temporarily to a favourable area under stressful conditions and return back when the period is over.
- Hibernation and aestivation are ways to escape the stress during winters and summers respectively.
28.Water is very essential for life. Write any three features both for plants and animals which enable them to survive in water scarce environment,
or
How do organisms cope with stressful external environmental conditions which are localised or of short duration? [ah India 2011]
Ans.Adaptation in plants
(i) Thick cuticle on their leaf surface.
(ii) Stomata are arranged in deep pits (sunken) to minimise water loss through transpiration.
(iii) Leaves are reduced to spines. The photosynthetic function is carried out by thick, fleshy flattened stems.
Adaptation in animals
(i) Kangaroo rat meets the water requirement through internal oxidation of fat. They concentrate their urine, so that minimum volume of water is excreted.
(ii) Snails undergo aestivation during summers.
Organisms either migrate or suspend their metabolic activities when conditions are stressful for short duration.In such conditions, organisms are as follow:
(i) Moving away from stressful habitat to more favourable area and return to their habitat when stressful period is over. For example, birds from Siberia and other cold countries migrate to Bharatpur Sanctuary of Rajasthan.
(ii) Hibernating (frogs) or aestivating (snails) or undergo diapause (zooplanktons).
(iii) Thick-walled spores are formed in stressful conditions and germinate under suitable conditions, e.g. bacteria, fungi and lower groups of plants.
or
How do organisms cope with stressful external environmental conditions which are localised or of short duration? [ah India 2011]
Ans.Adaptation in plants
(i) Thick cuticle on their leaf surface.
(ii) Stomata are arranged in deep pits (sunken) to minimise water loss through transpiration.
(iii) Leaves are reduced to spines. The photosynthetic function is carried out by thick, fleshy flattened stems.
Adaptation in animals
(i) Kangaroo rat meets the water requirement through internal oxidation of fat. They concentrate their urine, so that minimum volume of water is excreted.
(ii) Snails undergo aestivation during summers.
Organisms either migrate or suspend their metabolic activities when conditions are stressful for short duration.In such conditions, organisms are as follow:
(i) Moving away from stressful habitat to more favourable area and return to their habitat when stressful period is over. For example, birds from Siberia and other cold countries migrate to Bharatpur Sanctuary of Rajasthan.
(ii) Hibernating (frogs) or aestivating (snails) or undergo diapause (zooplanktons).
(iii) Thick-walled spores are formed in stressful conditions and germinate under suitable conditions, e.g. bacteria, fungi and lower groups of plants.
29.How do organisms like fungi, zooplanktons and bears overcome the temporary short-lived climatic stressful conditions? Explain.[All India 2010; Delhi 2008]
Ans.(i)Fungi They produce various kinds of thick-walled spores to survive under unfavourable conditions, which germinate on return of favourable conditions.
(ii) Zooplanktons They enter diapause, a stage of suspended development under unfavourable conditions.
(iii)Bears They hibernate during winter to escape the time of unfavourable conditions.
Ans.(i)Fungi They produce various kinds of thick-walled spores to survive under unfavourable conditions, which germinate on return of favourable conditions.
(ii) Zooplanktons They enter diapause, a stage of suspended development under unfavourable conditions.
(iii)Bears They hibernate during winter to escape the time of unfavourable conditions.
30.The following graph represents the organismic response to certain environmental condition (e.g. temperature)
(i)Which one of these A or B depicts conformers?
(ii)What does the other line graph depict?
(iii)How do these organisms differ from each other with reference to homeostasis?
(iv)Mention the category to which human belong. [All India 2009]
Ans.(i)A depicts conformers.
(ii) The other line B depicts regulators.
(iii) Differences between conformer and regulator are:
(iv) Humans are regulators.
(i)Which one of these A or B depicts conformers?
(ii)What does the other line graph depict?
(iii)How do these organisms differ from each other with reference to homeostasis?
(iv)Mention the category to which human belong. [All India 2009]
Ans.(i)A depicts conformers.
(ii) The other line B depicts regulators.
(iii) Differences between conformer and regulator are:
(iv) Humans are regulators.
5 Marks Questions
31.(i) Explain giving reasons why the tourists visiting Rohtang Pass or Mansarovar are advised to resume normal active life only after a few days of reaching there.
(ii) It is impossible to find small animals in the polar regions. Give reasons. [All India 2012]
Ans.(i)Tourists visiting to Rohtang Pass near Manali (> 3500 m) may suffer from altitude sickness. They resume normal active life only after a week because in low atmospheric pressure at high altitudes, the body does not get enough oxygen. Gradually, the body compensates low oxygen availability by
(a)Increasing red blood cell production.
(b)Decreasing the binding affinity of haemoglobin.
(c)Increasing the breathing rate.
(ii)Small animals have a large surface area relative to their volume. So, they tend to lose body heat very fast during cold conditions. They need to spend more energy to generate body heat. Due to this smaller animals are rarely found in polar regions.
(ii) It is impossible to find small animals in the polar regions. Give reasons. [All India 2012]
Ans.(i)Tourists visiting to Rohtang Pass near Manali (> 3500 m) may suffer from altitude sickness. They resume normal active life only after a week because in low atmospheric pressure at high altitudes, the body does not get enough oxygen. Gradually, the body compensates low oxygen availability by
(a)Increasing red blood cell production.
(b)Decreasing the binding affinity of haemoglobin.
(c)Increasing the breathing rate.
(ii)Small animals have a large surface area relative to their volume. So, they tend to lose body heat very fast during cold conditions. They need to spend more energy to generate body heat. Due to this smaller animals are rarely found in polar regions.
32.list the different ways by which organisms cope or manage with abiotic stresses in nature. Explain any three ways. [All India 2009c]
Ans.Organisms cope up with abiotic stress by:
(i)Regulating Some organisms maintain homeostasis by physiological and behavioural means. They are called regulators, e.g.
Ans.Organisms cope up with abiotic stress by:
(i)Regulating Some organisms maintain homeostasis by physiological and behavioural means. They are called regulators, e.g.
- In summers, when outside temperature is more, we sweat profusely that results in evaporative cooling to bring down the body temperature.
- In winters, when temperature is low, we shiver (a kind of exercise) that produces heat and raise the body temperature.
(ii) Conformating Organisms that cannot maintain a constant internal environment. Their body temperature changes with the ambient temperature. Such animals are called conformers. For example, small animals have larger surface area relative to their volume. They lose body heat very fast in low temperature. So, they expend energy to generate body heat through metabolism for adjusting.
(iii) Migrating The temporary movement of organisms from the stressful habitat to a more hospitable area and return when favourable conditions reappear is called migration. The long distance migration is very common in birds.
(iii) Migrating The temporary movement of organisms from the stressful habitat to a more hospitable area and return when favourable conditions reappear is called migration. The long distance migration is very common in birds.
33.(i) List any four abiotic components that lead to variations in the physical and chemical conditions of habitats.
(ii) Explain the impact of these components on the distribution of organisms in different habitats.
[All India 2009 C]
Ans.(i)Temperature, water, light and soil.
(ii) (a) Temperature influences the kinetics of enzymes and thereby the metabolism and other physiological functions of the organisms.
Organisms may be eurythermal and can tolerate a wide range of temperature and stenothermal that can tolerate only a narrow range of temperature.
(b)Water is important to sustain life and productivity and distribution of plants is dependent on water.
Freshwater forms cannot thrive in sea water and vice versa.
(c)Light influences photosynthesis of plants. Light also influences the flowering in plants and timing of foraging, reproduction and migratory activities of animals.
Aquatic plants occupy different depths depending on their pigments and the light available.
(d)Soil influences vegetation by the water holding capacity, topography and its composition.
(ii) Explain the impact of these components on the distribution of organisms in different habitats.
[All India 2009 C]
Ans.(i)Temperature, water, light and soil.
(ii) (a) Temperature influences the kinetics of enzymes and thereby the metabolism and other physiological functions of the organisms.
Organisms may be eurythermal and can tolerate a wide range of temperature and stenothermal that can tolerate only a narrow range of temperature.
(b)Water is important to sustain life and productivity and distribution of plants is dependent on water.
Freshwater forms cannot thrive in sea water and vice versa.
(c)Light influences photosynthesis of plants. Light also influences the flowering in plants and timing of foraging, reproduction and migratory activities of animals.
Aquatic plants occupy different depths depending on their pigments and the light available.
(d)Soil influences vegetation by the water holding capacity, topography and its composition.
1 Mark Questions
1.State Gause’s competitive exclusion principle. [Ail India 2014]
Ans.Gause’s competitive exclusion principle states that two competiting species for same resource cannot co-exist, if all other ecological factors are constant.
Ans.Gause’s competitive exclusion principle states that two competiting species for same resource cannot co-exist, if all other ecological factors are constant.
2.Write, what do phytophagous insects feed on? [Delhi 2012]
Ans.Phytophagous insects feed on sap and other parts of plants.
Ans.Phytophagous insects feed on sap and other parts of plants.
3.What is the interaction called between Cuscuta and shoe flower bush? [Delhi 2012]
Ans.The interaction between Cuscutaand shoe flower bush is called parasitism. Here, Cuscuta is the parasite which infests the shoe flower bush and derives nutrition from it
Ans.The interaction between Cuscutaand shoe flower bush is called parasitism. Here, Cuscuta is the parasite which infests the shoe flower bush and derives nutrition from it
4.What is an interaction called when an orchid grows on a mango plant?[Delhi 2012]
Ans.An orchid growing on the branch of a mango tree is an epiphyte. Epiphytes are plants growing on other plants which however, do not derive nutrition from them. Hence, the relationship between a mango tree and an orchid is an example of commensalism.
Ans.An orchid growing on the branch of a mango tree is an epiphyte. Epiphytes are plants growing on other plants which however, do not derive nutrition from them. Hence, the relationship between a mango tree and an orchid is an example of commensalism.
5.Mention the unique feature with respect to flowering and fruiting in bamboo species. [Delhi 2012]
Ans.Bamboo plants flower only once in their life time, generally after 50-100 years, produce large number of fruits and then die.
Ans.Bamboo plants flower only once in their life time, generally after 50-100 years, produce large number of fruits and then die.
6.In a pond, there were 20 Hydrilla plants. Through reproduction, 10 new Hydrilla plants were added in a year. Calculate the birth rate of the population. [Delhi 2012]
Ans.
Ans.
7.Pollinating species of wasps show mutualism with specific fig plants. Mention the benefits the female wasps derive from the fig trees from such an interaction. [All India 2011]
Ans.The wasp uses the ovary for oviposition.It also uses the developing seeds of the fruit to nourish its larvae.
Ans.The wasp uses the ovary for oviposition.It also uses the developing seeds of the fruit to nourish its larvae.
8.Why are cattle and goats not seen browsing on Calotropis growing in the fields? [Foreign 2011]
Ans.Calotropis plant produces poisonous cardiac glycosides. Therefore, cattle or goat do not graze these plants
Ans.Calotropis plant produces poisonous cardiac glycosides. Therefore, cattle or goat do not graze these plants
9. If 8 individuals in a laboratory population of 80 fruitflies died in a week, then what would be the death rate for population for the said period? [Delhi 2010]
Ans.
Ans.
10.In a pond, there were 200 frogs.40 more were bom in a year. Calculate the birth rate of the population. [Delhi 2010]
Ans.
Ans.
11.Why do predators avoid eating Monarch butterfly? How does the butterfly develop this protective feature? [Foreign 2010]
Ans.Predators avoid the monarch butterfly as it is highly distasteful to its predators (birds) because of a special chemical present in its body. It acquires this chemical during the caterpillar stage by feeding on a poisonous weed
Ans.Predators avoid the monarch butterfly as it is highly distasteful to its predators (birds) because of a special chemical present in its body. It acquires this chemical during the caterpillar stage by feeding on a poisonous weed
12.Comment on the interaction between a clown fish living among the tentacles of a sea anemone.[Delhi 2010]
Ans.The interaction between a clown fish living among the tentacles of sea anemone is called commensalism.
Ans.The interaction between a clown fish living among the tentacles of sea anemone is called commensalism.
13.Comment on the interaction between certain species of fig trees and Wasps. [Delhi 2010c]
Ans.The relation between fig trees and wasps is of mutualism.
Ans.The relation between fig trees and wasps is of mutualism.
14.Name the type of interaction seen between whale and barnacles growing on its back. [Foreign 2009]
Ans.The type of interaction observed between whale and barnacles growing on its back is commensalism.
Ans.The type of interaction observed between whale and barnacles growing on its back is commensalism.
15.How does camouflage help an insect? [All India 2009 C]
Ans.Camouflage is a prey defence mechanism to avoid being detected easily by the predators.
Ans.Camouflage is a prey defence mechanism to avoid being detected easily by the predators.
16.Mention any two significant roles predation plays in nature.[All India 2008]
Ans.Significant roles played by predators are predators keep prey population under control. They help in maintaining species diversity in a community by reducing the intensity of competition
Ans.Significant roles played by predators are predators keep prey population under control. They help in maintaining species diversity in a community by reducing the intensity of competition
17.List two advantages that a mycorrhizal association provides tO the plant. [All India 2008 C]
Ans.Mycorrhizal association helps plants in
(i) Providing resistance to root borne pathogens.
(ii) Absorbing nutrients.
Ans.Mycorrhizal association helps plants in
(i) Providing resistance to root borne pathogens.
(ii) Absorbing nutrients.
18.Give one example where population estimation of an organism is done indirectly without actually counting the organism. [All India 2008 c]
Ans.The number of fish caught per trap is a population estimation method done indirectly without actually counting them.
Ans.The number of fish caught per trap is a population estimation method done indirectly without actually counting them.
2 Marks Questions
19.Describe the mutual relationship between fig tree and wasp and comment on the phenomenon that operates in their relationship.[All India 2014]
Ans.The relationship between fig tree and wasp shows mutualism. The wasp while searching for sites to lay its eggs, pollinates the fig’s inflorescence. On the other hand, the fig not only provides shelter (fruit) for oviposition to wasp but also allows its larva to feed on seeds.
Ans.The relationship between fig tree and wasp shows mutualism. The wasp while searching for sites to lay its eggs, pollinates the fig’s inflorescence. On the other hand, the fig not only provides shelter (fruit) for oviposition to wasp but also allows its larva to feed on seeds.
20.Construct an age pyramid which reflects an expanding growth status of human population. [All India 2014]
Ans.The age pyramid geometrically represents the proportions of different age groups in population. The triangular shape of age pyramid represents the expanding growth status of human population.
Ans.The age pyramid geometrically represents the proportions of different age groups in population. The triangular shape of age pyramid represents the expanding growth status of human population.
21.Construct an age pyramid which reflects as stable growth status of human population. [All India 2014]
Ans.The age pyramid that reflects a stable growth status of human population can be represented as follows
Ans.The age pyramid that reflects a stable growth status of human population can be represented as follows
22.Differentiate between commensalism arid mutualism by taking one example each from plants Only. [All India 2014]
Ans.Commensalism is the kind of interaction between species in which one is benefitted and other is neither benefitted nor-harmed. Example of such association is orchid growing as an epiphyte on a mango tree, which remains unaffected by its growth.
Whereas mutualism is the type of interaction in which both the species involved are benefitted. e.g. lichen representing mutual ‘ association between algae and fungi, in which algae is protected by fungi, which also provides nutrients for synthesis of food, while algae provides food to fungi, as they are incapable of synthesising their own food.
Ans.Commensalism is the kind of interaction between species in which one is benefitted and other is neither benefitted nor-harmed. Example of such association is orchid growing as an epiphyte on a mango tree, which remains unaffected by its growth.
Whereas mutualism is the type of interaction in which both the species involved are benefitted. e.g. lichen representing mutual ‘ association between algae and fungi, in which algae is protected by fungi, which also provides nutrients for synthesis of food, while algae provides food to fungi, as they are incapable of synthesising their own food.
23.Explain Verhulst-Pearl Logistic Growth of a population. [All India 2014]
Ans.The population growing in a habitat with limited resources initially shows a lag phase, followed by exponential phase and finally a declining or stationary phase, when the growth or density of population reaches carrying capacity is called Verhulst-Pearl logistic growth.
It can be explained by following equation
Where, N – Population density at time t.
r – Intrinsic rate of natural increase K – Carrying capacity
Ans.The population growing in a habitat with limited resources initially shows a lag phase, followed by exponential phase and finally a declining or stationary phase, when the growth or density of population reaches carrying capacity is called Verhulst-Pearl logistic growth.
It can be explained by following equation
Where, N – Population density at time t.
r – Intrinsic rate of natural increase K – Carrying capacity
24.Explain mutualism with the help of an example. [All India 2014]
Ans.The type of interaction where both the species involved are benefitted is called mutualism. For the relationship between fig and wasp is mutualism. The wasp while in search of egg laying sites pollinate the fig’s inflorescence, while the fig offers fruit or ovary for oviposition (egg laying). It also offers its seeds to the developing larva
Ans.The type of interaction where both the species involved are benefitted is called mutualism. For the relationship between fig and wasp is mutualism. The wasp while in search of egg laying sites pollinate the fig’s inflorescence, while the fig offers fruit or ovary for oviposition (egg laying). It also offers its seeds to the developing larva
25.Provide two reasons that make the count of prokaryotic species difficult. [All India 2014]
Ans.The two reasons that make the count of prokaryotic species difficult is
(i) they are microscopic not visible by naked eyes.
(ii)they form dense colonies, i.e. population size is so, huge that counting is time taking and almost possible.
(iii) the rate of growth is very fast in prokaryotic species, which may almost double itself while counting
Ans.The two reasons that make the count of prokaryotic species difficult is
(i) they are microscopic not visible by naked eyes.
(ii)they form dense colonies, i.e. population size is so, huge that counting is time taking and almost possible.
(iii) the rate of growth is very fast in prokaryotic species, which may almost double itself while counting
26.How does Monarch butterfly defend itself from predators? Explain.[Delhi 2013 C]
Ans.Predators avoid the monarch butterfly as it is highly distasteful to its predators (birds) because of a special chemical present in its body. It acquires this chemical during the caterpillar stage by feeding on a poisonous weed
Ans.Predators avoid the monarch butterfly as it is highly distasteful to its predators (birds) because of a special chemical present in its body. It acquires this chemical during the caterpillar stage by feeding on a poisonous weed
27.Why do clown fish and sea anemone pair up? What is this relationship called ? [Delhi 2012; All India 2008]
Ans.Clown fish maintains commensalism with the sea anemone. In this interaction, one species is benefitted and the other is neither harmed nor-benefitted. Sea anemone has stinging tentacles that provide protection to clown fish from predators. The anemone does not appear to derive any benefit from the clown fish
Ans.Clown fish maintains commensalism with the sea anemone. In this interaction, one species is benefitted and the other is neither harmed nor-benefitted. Sea anemone has stinging tentacles that provide protection to clown fish from predators. The anemone does not appear to derive any benefit from the clown fish
28.Explain brood parasitism with the help of an example. [All India 2012]
Ans.The phenomenon in which one organism(parasite) lays its eggs in the nest of another organism is called brood parasitism. e.g. cuckoo (parasite) lay eggs which resemble the host’s (crow) egg in size and colour in crow’s nest and let it incubate them.
Ans.The phenomenon in which one organism(parasite) lays its eggs in the nest of another organism is called brood parasitism. e.g. cuckoo (parasite) lay eggs which resemble the host’s (crow) egg in size and colour in crow’s nest and let it incubate them.
29.How does the floral pattern of mediterranean orchid Ophrys guarantee cross-pollination?[Delhi 2010; Foreign 2009]
Ans.In the flowers of Ophrys
(i) One petal resembles the female of a bee species in size, colour, markings, etc.
(ii) Male bee perceives it as a female and pseudocopulates with it.
(iii)During the process, the pollen grains from the anthers become dusted on the body of the bee.
(iv)When the bee is attracted to another flower of this orchid species, the process is repeated and the pollen grains from the body of the bee get dusted on the stigma thus, pollination is achieved.
Ans.In the flowers of Ophrys
(i) One petal resembles the female of a bee species in size, colour, markings, etc.
(ii) Male bee perceives it as a female and pseudocopulates with it.
(iii)During the process, the pollen grains from the anthers become dusted on the body of the bee.
(iv)When the bee is attracted to another flower of this orchid species, the process is repeated and the pollen grains from the body of the bee get dusted on the stigma thus, pollination is achieved.
30.How do plants benefit from having mycorrhizal symbiotic association?[Foreign 2010]
Ans.Benefits to plants having mycorrhizal association are:
(i) The fungus absorbs nutrients from the soil and passes it to the plant.
(ii) Mycorrhiza provide resistance to root-borne pathogens.
(iii) They show increased tolerance to salinity and drought.
(iv) An overall increase occurs in plant growth and development.
Ans.Benefits to plants having mycorrhizal association are:
(i) The fungus absorbs nutrients from the soil and passes it to the plant.
(ii) Mycorrhiza provide resistance to root-borne pathogens.
(iii) They show increased tolerance to salinity and drought.
(iv) An overall increase occurs in plant growth and development.
31.Mention the changes the koel must have undergone in order to achieve brood parasitism, during the course of evolution. [All India 2010C]
Ans.During the course of evolution, the eggs of koel have evolved to resemble the host’s (crow) egg in size and colour to reduce the chances of the host bird detecting the koel’s eggs and ejecting them out of the nest.
Ans.During the course of evolution, the eggs of koel have evolved to resemble the host’s (crow) egg in size and colour to reduce the chances of the host bird detecting the koel’s eggs and ejecting them out of the nest.
32.Explain the two defense mechanisms evolved in preys to avoid overpopulation of their predator. [Ail India 2010 C]
Ans.Defense mechanism evolved in preys:
(i) To avoid being detected easily by the predators, some species of insects and frogs are cryptically coloured (camouflaged).
(ii) Some plants have thorns or spines for defence mechanism, e.g. Acacia, cactus.
Ans.Defense mechanism evolved in preys:
(i) To avoid being detected easily by the predators, some species of insects and frogs are cryptically coloured (camouflaged).
(ii) Some plants have thorns or spines for defence mechanism, e.g. Acacia, cactus.
33.Egrets are often seen along with grazing cattle. What do you refer to this interaction? Give a reason for this association. [Delhi 2009]
Ans.The egrets are seen in close association with grazing cattle as the cattle egrets are benefitted by it. Cattle while grazing stir up the bushes and insects are flushed out from the vegetation to be detected by the cattle egrets. This association is called commensalism as cattles are neither benefitted nor-harmed.
Ans.The egrets are seen in close association with grazing cattle as the cattle egrets are benefitted by it. Cattle while grazing stir up the bushes and insects are flushed out from the vegetation to be detected by the cattle egrets. This association is called commensalism as cattles are neither benefitted nor-harmed.
34.(i) What is r in the population equation given below dN/dt = rN
(ii)How does the increase and the decrease in the value of r affect the population size? [Delhi 2009]
Ans.(i) r is an intrinsic factor assessing impacts of biotic and abiotic factor on population growth.
(ii) When r increases, population size • increases, while a decrease in r decreases the population size
(ii)How does the increase and the decrease in the value of r affect the population size? [Delhi 2009]
Ans.(i) r is an intrinsic factor assessing impacts of biotic and abiotic factor on population growth.
(ii) When r increases, population size • increases, while a decrease in r decreases the population size
35.(i) How is Cuscuta adapted to be a parasitic plant?
(ii) Why do cattle avoid grazing on Calotropis plants? Explain.[Foreign 2009]
Ans.(i)Cuscutahas lost its chlorophyll during evolution and developed haustoria through which it derives its nutrition from host plant. Thus, it is adapted as a parasitic plant.
(ii) Cattle avoid grazing on Calotropis plants because it produces poisonous cardiac glycosides.
(ii) Why do cattle avoid grazing on Calotropis plants? Explain.[Foreign 2009]
Ans.(i)Cuscutahas lost its chlorophyll during evolution and developed haustoria through which it derives its nutrition from host plant. Thus, it is adapted as a parasitic plant.
(ii) Cattle avoid grazing on Calotropis plants because it produces poisonous cardiac glycosides.
36.Identify the curves A and B shown in the graph given below. List the conditions responsible for growth patterns A and B. [Foreign 2009]
Ans.A-Exponential growth curve When the resources are not limiting, this form of curve appears.
B-Logistic growth curve When the resources are limiting, this form of growth curve appears, hereK is the carrying capacity
Ans.A-Exponential growth curve When the resources are not limiting, this form of curve appears.
B-Logistic growth curve When the resources are limiting, this form of growth curve appears, hereK is the carrying capacity
37.In a pond, there were 40 lotus plants. After a year, the number rose to 56. Calculate birth rate of a lotus plant.[All India 2009 C]
Ans.The birth rate of lotus plant
Ans.The birth rate of lotus plant
38.Name the interaction in each of the following
(i)Cuscuta growing on a shoe flower plant.
(ii)Mycorrhizae living on the roots of higher plants.
(iii)Clown fish living among the tentacles of sea anemone.
(iv)Koel laying her eggs in crow’s nest. [All India 2008; Foreign 2008]
Ans.The interactions are identified as:
(i) Parasitism (ii) Mutualism
(iii) Commensalism (iv) Brood parasitism
(i)Cuscuta growing on a shoe flower plant.
(ii)Mycorrhizae living on the roots of higher plants.
(iii)Clown fish living among the tentacles of sea anemone.
(iv)Koel laying her eggs in crow’s nest. [All India 2008; Foreign 2008]
Ans.The interactions are identified as:
(i) Parasitism (ii) Mutualism
(iii) Commensalism (iv) Brood parasitism
39.Certain species of wasps are seen to frequently visit flowering fig trees. What type of interaction is seen between them and why? [All India 2008]
Ans.Mutualism is seen between them because both are equally benefitted. Female wasps lay eggs in fruits and uses developing seeds within the fruit for nourishing its larvae. In return, the wasp pollinates the fig’s inflorescence, while searching for suitable egg laying site.
Ans.Mutualism is seen between them because both are equally benefitted. Female wasps lay eggs in fruits and uses developing seeds within the fruit for nourishing its larvae. In return, the wasp pollinates the fig’s inflorescence, while searching for suitable egg laying site.
3 Marks Questions
40. Study the graph given below and answer the questions that follow
(i)Write the status of food ans space in the curves (A) and (J3)
(ii)In the absence of predators, which one of the two curves would appropriately depict the prey population?
(iii)Time has been shows on x-axis and there is a parallel doted line above it. Given the significance of this dotted line. [Delhi 2014]
Ans.(i)The status of food and space in curves ‘a’ is unlimited resources, while in curve ‘b’ the sources of food and space are limited.
(ii)In the absence of predators, the curve ‘B’ would appropriately depict the competition for limited food and shelter resources within the prey population.
(iii)The dotted line in the above graph represents the carrying capacity (K). The carrying capacity signifies the limit of habitat, i.e. limited resources in a given habitat to support growth upto a certain level beyond which no further growth can take place
(i)Write the status of food ans space in the curves (A) and (J3)
(ii)In the absence of predators, which one of the two curves would appropriately depict the prey population?
(iii)Time has been shows on x-axis and there is a parallel doted line above it. Given the significance of this dotted line. [Delhi 2014]
Ans.(i)The status of food and space in curves ‘a’ is unlimited resources, while in curve ‘b’ the sources of food and space are limited.
(ii)In the absence of predators, the curve ‘B’ would appropriately depict the competition for limited food and shelter resources within the prey population.
(iii)The dotted line in the above graph represents the carrying capacity (K). The carrying capacity signifies the limit of habitat, i.e. limited resources in a given habitat to support growth upto a certain level beyond which no further growth can take place
41Draw and explain expanding age pyramids of human population. Why is it so called?
Ans.The age pyramid geometrically represents the proportions of different age groups in population. The triangular shape of age pyramid represents the expanding growth status of human population.
Expanding age pyramid is so called as it represents the growing status of populations growth.
Ans.The age pyramid geometrically represents the proportions of different age groups in population. The triangular shape of age pyramid represents the expanding growth status of human population.
Expanding age pyramid is so called as it represents the growing status of populations growth.
42.Explain brood parasitism with the help of an example. [Delhi 2013c]
Ans.Brood parasitism is a phenomenon in which one organism (parasite) lays its eggs in the nest of another organism.e.g. eggs of cuckoo (koel) and the crow resemble in size and colour, to reduce the chances of the crow (host) detecting the foreign eggs (cuckoo’s) and ejecting them out from the host, cuckoo lay eggs in the crow’s nest.
Ans.Brood parasitism is a phenomenon in which one organism (parasite) lays its eggs in the nest of another organism.e.g. eggs of cuckoo (koel) and the crow resemble in size and colour, to reduce the chances of the crow (host) detecting the foreign eggs (cuckoo’s) and ejecting them out from the host, cuckoo lay eggs in the crow’s nest.
43.(i) Write the importance of measuring the size of a population in a habitat or an ecosystem.
(ii) Explain with the help of an example, how the percentage cover is a more meaningful measure of population size than mere numbers? [All India 2013]
Ans.(i) Measurement of population in a habitat determines the relative abundance of a particular species and its effect on the available resources of that particular habitat.
(ii) The percentage cover is more meaningful measure of population size than mere numbers because the relative abundance of a species is not only determined by number of individuals but by both the relative abundance in biomass and number.
e.g. in a unit area the number of grass species or relative abundance in number is high but not the relative biomass, if the same area has one or two Ficus bengalensis tree, it is very low in relative abundance but high in relative abundance of biomass
(ii) Explain with the help of an example, how the percentage cover is a more meaningful measure of population size than mere numbers? [All India 2013]
Ans.(i) Measurement of population in a habitat determines the relative abundance of a particular species and its effect on the available resources of that particular habitat.
(ii) The percentage cover is more meaningful measure of population size than mere numbers because the relative abundance of a species is not only determined by number of individuals but by both the relative abundance in biomass and number.
e.g. in a unit area the number of grass species or relative abundance in number is high but not the relative biomass, if the same area has one or two Ficus bengalensis tree, it is very low in relative abundance but high in relative abundance of biomass
44.(i)Explain death rate in a population by taking a suitable example.
(ii) Write the other two characteristics, which only a population shows but an individual cannot. [All India 2013]
Ans.Death or mortality rate is expressed as the number of deaths of individual of a population per year.
Example If 80 individuals in a laboratory population of 800 fruit fly died in a week then death rate is 80/800=0.1/fruityfly/week
(ii)Characteristics of population, not exhibited by individual are:
(ii) Write the other two characteristics, which only a population shows but an individual cannot. [All India 2013]
Ans.Death or mortality rate is expressed as the number of deaths of individual of a population per year.
Example If 80 individuals in a laboratory population of 800 fruit fly died in a week then death rate is 80/800=0.1/fruityfly/week
(ii)Characteristics of population, not exhibited by individual are:
- Population size or density
- Population interactions
45.(i) Explain birth rate in a population by taking a suitable example.
(ii) Write the other two characteristics, which only a population shows but an individual cannot. [All India 2013]
Ans.(i) Due to natality or birth rate, population increases continuously. It is covering the production of new individual by birth, hatching, by asexual mode, etc. It is expressed as the number of birth per 1000 individual of a population per year.
(ii) The characteristic, which are unique to the group (population) and not shown by an individual are.
(ii) Write the other two characteristics, which only a population shows but an individual cannot. [All India 2013]
Ans.(i) Due to natality or birth rate, population increases continuously. It is covering the production of new individual by birth, hatching, by asexual mode, etc. It is expressed as the number of birth per 1000 individual of a population per year.
(ii) The characteristic, which are unique to the group (population) and not shown by an individual are.
- Population dynamics theories to explain population growth. Size of population for any species is not a static parameter.Population growth change during time and depend upon food availability, predation, pressure, weather and also depend upon natality and mortality, immigration, emigration.
- Regulation of population Govern population density or population size. It is the number of individual of a species per unit area or volume
46.(i) List any three ways of measuring population density of a habitat.
(ii) Mention the essential information that can be obtained by studying the population density of an organism.[All India 2013]
Ans.(i)Three ways of measuring population density of a habitat
A- Per cent cover for trees with larger canopy.
B- Number of fishes caught per trap.
C- Pug marks or faecal pellets for tiger census.
(ii) The population density tells us about the status of a species, i.e. the outcome of competition, impact of predation or effect of pesticides, etc.
(ii) Mention the essential information that can be obtained by studying the population density of an organism.[All India 2013]
Ans.(i)Three ways of measuring population density of a habitat
A- Per cent cover for trees with larger canopy.
B- Number of fishes caught per trap.
C- Pug marks or faecal pellets for tiger census.
(ii) The population density tells us about the status of a species, i.e. the outcome of competition, impact of predation or effect of pesticides, etc.
47.Name the type of interaction seen in each of the following examples
(i)Ascaris worm living in the intestine of human.
(ii)Wasp pollinating fig’s inflorescence.
(iii)Clown fish living among the tentacles of sea anemone.
(iv)Mycorrhizae living on the roots of higher plants.
(v)Orchid growing on a branch of mango tree.
(vi)Disappearance of smaller barnacles when Balanus dominated in the coast of Scotland. [Delhi 2011]
Ans.(i) Parasitism (ii) Mutualism
(iii) Commensalism (iv) Mutualism
(v)Commensalism (vi) Competition
(i)Ascaris worm living in the intestine of human.
(ii)Wasp pollinating fig’s inflorescence.
(iii)Clown fish living among the tentacles of sea anemone.
(iv)Mycorrhizae living on the roots of higher plants.
(v)Orchid growing on a branch of mango tree.
(vi)Disappearance of smaller barnacles when Balanus dominated in the coast of Scotland. [Delhi 2011]
Ans.(i) Parasitism (ii) Mutualism
(iii) Commensalism (iv) Mutualism
(v)Commensalism (vi) Competition
48.Study the three different age pyramids, for human population given below and answer the questions that follow
(i)Write the names given to each of these age pyramids.
(ii)Mention the one which is ideal for human population and why?[Foreign 2011]
Ans.(i) A – Expanding, B – Stable,C -Declining
(ii) Stable population is preferred.It is beneficial for survival and better living of the human population. It is helpful for planning welfare activities.
(i)Write the names given to each of these age pyramids.
(ii)Mention the one which is ideal for human population and why?[Foreign 2011]
Ans.(i) A – Expanding, B – Stable,C -Declining
(ii) Stable population is preferred.It is beneficial for survival and better living of the human population. It is helpful for planning welfare activities.
49.Why is predation required in a community of different organisms?[Foreign 2009]
Ans.Requirement of predation:
(i) Acts as a conduit for energy transfer across trophic levels.
(ii) Keep the prey population under control.
(iii) Helps in maintaining species diversity in a community by reducing the intensity of competition.
(iv) Biological control of pests is based on predation.
Ans.Requirement of predation:
(i) Acts as a conduit for energy transfer across trophic levels.
(ii) Keep the prey population under control.
(iii) Helps in maintaining species diversity in a community by reducing the intensity of competition.
(iv) Biological control of pests is based on predation.
50.Study the population growth curves in the graph given below and answer the questions which follow
(i) Identify the growth curves A and B
(ii)Which one of them is considered a more realistic one and why?
(iii)If
equation of the logistic growth curve, what does K stand for?
(iv)What is symbolised by N?[Delhi 2008]
Ans.(i)A – Exponential growth curve B – Logistic growth curve
(ii) Logistic growth curve B is considered more realistic one because the resources are finite and become limiting sooner or later.
(iii) K-stands for carrying capacity. It is the maximum number of individuals of a population, that the given environment can sustain.
(iv) N-symbolises population density. It is the number of individuals in a given population per unit area
(i) Identify the growth curves A and B
(ii)Which one of them is considered a more realistic one and why?
(iii)If
equation of the logistic growth curve, what does K stand for?
(iv)What is symbolised by N?[Delhi 2008]
Ans.(i)A – Exponential growth curve B – Logistic growth curve
(ii) Logistic growth curve B is considered more realistic one because the resources are finite and become limiting sooner or later.
(iii) K-stands for carrying capacity. It is the maximum number of individuals of a population, that the given environment can sustain.
(iv) N-symbolises population density. It is the number of individuals in a given population per unit area
51.Study the population growth curves shown below
(i)Identity curves A and B,
(ii)Mention the conditions responsible for the curves A and B respectively,
(iii)Give the necessary equation for the curve B. [All India 2008]
Ans.(i)A-Exponential growth curve B-Logistic growth curve.
(ii) A- Any species growing exponentially under unlimited resource conditions, shows this growth curve.
B- A population growing in a habitat with limited resources shows an initial lag phase, an accelerated log phase and a decelerated steady phase.
(iii)
(i)Identity curves A and B,
(ii)Mention the conditions responsible for the curves A and B respectively,
(iii)Give the necessary equation for the curve B. [All India 2008]
Ans.(i)A-Exponential growth curve B-Logistic growth curve.
(ii) A- Any species growing exponentially under unlimited resource conditions, shows this growth curve.
B- A population growing in a habitat with limited resources shows an initial lag phase, an accelerated log phase and a decelerated steady phase.
(iii)
52.Study the graph below and answer the questions which follow
(i)The curve A is represented by the equation
dN /dt=rN represent in the equation and what is its importance?
(ii)Which one of the two curves is considered a more realistic one for most of the animal population?
(iii)Which curve would depict the population of a species of deer if there are no predators in the habitat? Why is it SO? [Foreign 2008]
Ans.(i) r is intrinsic rate of natural increase. It is an important parameter for assessing the impact of any abiotic or biotic factors on the population growth.
(ii) Curve-B is more realistic for animal population
(iii) Curve-B. When the predators are absent, there will be competition among large prey population for resources.
(i)The curve A is represented by the equation
dN /dt=rN represent in the equation and what is its importance?
(ii)Which one of the two curves is considered a more realistic one for most of the animal population?
(iii)Which curve would depict the population of a species of deer if there are no predators in the habitat? Why is it SO? [Foreign 2008]
Ans.(i) r is intrinsic rate of natural increase. It is an important parameter for assessing the impact of any abiotic or biotic factors on the population growth.
(ii) Curve-B is more realistic for animal population
(iii) Curve-B. When the predators are absent, there will be competition among large prey population for resources.
5 Marks Questions
53.(i) Name the population growth pattern the equation{dN/dt=rN} represents. What does ‘r’ represent in the equation? Write its importance in population growth.
(ii) Explain the principle of carrying capacity by using population Verhulst-Pearl logistic growth curve. [Delhi 2014 C]
Ans.The logistic growth pattern is represented by equation {dN/dt=rN}
Here Y represents the intrinsic factor a rate of natural increase.Since, the growth for most of the organisms’s population becomes limiting due to limited resources, this logistic growth pattern provides a realistic model for study of population growth.
(ii)The Verhulst-Pearl logistic growth curve iexplained by
where, K represents the carrying capacity. It can be referred to nature’s limit of natural resources that a habitat provides to its individuals of a growing population, beyond which there is no growth in that particular habitat.
(ii) Explain the principle of carrying capacity by using population Verhulst-Pearl logistic growth curve. [Delhi 2014 C]
Ans.The logistic growth pattern is represented by equation {dN/dt=rN}
Here Y represents the intrinsic factor a rate of natural increase.Since, the growth for most of the organisms’s population becomes limiting due to limited resources, this logistic growth pattern provides a realistic model for study of population growth.
(ii)The Verhulst-Pearl logistic growth curve iexplained by
where, K represents the carrying capacity. It can be referred to nature’s limit of natural resources that a habitat provides to its individuals of a growing population, beyond which there is no growth in that particular habitat.
54.What is the association between the bumble bee and its favourite orchid Ophrys? How would extinction or change of one affect he other?[Delhi 2012]
Ans.Mutualism is an association seen between the bumble bee and the orchid In this, both species are benefitted. One petal of its flower bears an uncanny resemblance to the female of the bee in size, colour and markings.
The male bee is attracted to what it perceives as a female and pseudocopulates with the flower. During the process, the bee gets dusted with pollen from the flower. When this same bee pseudocopulates with another flower, it transfers pollen to it and thus, pollinates the flower.
Extinction of bumble bee will definitely affect the orchid flower because these bees are the means of pollination for the flower and if they get extinct, the pollination percentage will be reduced. But, the extinction of the orchid will not affect the bumble bee population.
Ans.Mutualism is an association seen between the bumble bee and the orchid In this, both species are benefitted. One petal of its flower bears an uncanny resemblance to the female of the bee in size, colour and markings.
The male bee is attracted to what it perceives as a female and pseudocopulates with the flower. During the process, the bee gets dusted with pollen from the flower. When this same bee pseudocopulates with another flower, it transfers pollen to it and thus, pollinates the flower.
Extinction of bumble bee will definitely affect the orchid flower because these bees are the means of pollination for the flower and if they get extinct, the pollination percentage will be reduced. But, the extinction of the orchid will not affect the bumble bee population.
55.(i) What is an age pyramid?
(ii) Explain with the help of figures, the three different types of age pyramids represented by human population. [Delhi 2011c]
Ans.(i)The graphic representation of the no. of individuals in the different age groups of a population, at a given time is known as age pyramid.
(ii)Age pyramid
(ii) Explain with the help of figures, the three different types of age pyramids represented by human population. [Delhi 2011c]
Ans.(i)The graphic representation of the no. of individuals in the different age groups of a population, at a given time is known as age pyramid.
(ii)Age pyramid
- When the age distribution (per cent individuals of a given age or age group) is plotted for the population, this is called age pyramid.
- Population at any given time is composed of individuals of different ages.
- For human population, the age pyramids generally show age distribution of males and females in a combined diagram.
- The shape of the pyramids reflects the growth status of the population that whether it is expanding (triangular shaped), stable (bell-shaped) or declining.
56.(i) Explain the birth rate and death rate in the population with the help of an example each.
(ii) What is age pyramid? Draw an age pyramid of an expanding population. [All India 2011 C]
Ans.(i) The no. of organisms added to a population by birth in a given period is known as birth rate, e.g. if in a pond there are 20 lotus plants last year and through reproduction 8 new plants are added, the birth rate =8/20=0.4 plants per lotus per year.
The no. of individuals removed from a population due to death in a given period of time is called death rate, e.g. if 4 individuals in a lab population of 40 fruit flies died during a specified time interval, say a week, the death rate in the population=4/40=0.1 individuals per fruit fly per week.
(ii)The age pyramid geometrically represents the proportions of different age groups in population. The triangular shape of age pyramid represents the expanding growth status of human population.
The graphic representation of the no. of individuals in the different age groups of a population, at a given time is known as age pyramid.
Age pyramid
(ii) What is age pyramid? Draw an age pyramid of an expanding population. [All India 2011 C]
Ans.(i) The no. of organisms added to a population by birth in a given period is known as birth rate, e.g. if in a pond there are 20 lotus plants last year and through reproduction 8 new plants are added, the birth rate =8/20=0.4 plants per lotus per year.
The no. of individuals removed from a population due to death in a given period of time is called death rate, e.g. if 4 individuals in a lab population of 40 fruit flies died during a specified time interval, say a week, the death rate in the population=4/40=0.1 individuals per fruit fly per week.
(ii)The age pyramid geometrically represents the proportions of different age groups in population. The triangular shape of age pyramid represents the expanding growth status of human population.
The graphic representation of the no. of individuals in the different age groups of a population, at a given time is known as age pyramid.
Age pyramid
- When the age distribution (per cent individuals of a given age or age group) is plotted for the population, this is called age pyramid.
- Population at any given time is composed of individuals of different ages.
- For human population, the age pyramids generally show age distribution of males and females in a combined diagram.
- The shape of the pyramids reflects the growth status of the population that whether it is expanding (triangular shaped), stable (bell-shaped) or declining.
57.(i) Explain the equation
Nt+)=Nt +[{B + 1) – (D – E)] on the basis of the flow chart given below:
(ii)Mention the different ways by which the population density of different species can be measured. [Delhi 2011 c]
Ans.(i)If Nis the population density at time t, then its density at time t +1 is Nt + [(B + 1) -(D -E)]
The population density will increase if the no. of births and the no. of immigrants, i.e. (8 + 1) is more than the no. of death and the no. of emigrants, i.e. (D + 1)
(ii)Three ways of measuring population density of a habitat
A- Per cent cover for trees with larger canopy.
B- Number of fishes caught per trap.
C- Pug marks or faecal pellets for tiger census.
Nt+)=Nt +[{B + 1) – (D – E)] on the basis of the flow chart given below:
(ii)Mention the different ways by which the population density of different species can be measured. [Delhi 2011 c]
Ans.(i)If Nis the population density at time t, then its density at time t +1 is Nt + [(B + 1) -(D -E)]
The population density will increase if the no. of births and the no. of immigrants, i.e. (8 + 1) is more than the no. of death and the no. of emigrants, i.e. (D + 1)
(ii)Three ways of measuring population density of a habitat
A- Per cent cover for trees with larger canopy.
B- Number of fishes caught per trap.
C- Pug marks or faecal pellets for tiger census.
58.Study the table given below and answer the questions that follow
Identify A, B, C and D in the given table and explain any three of them with the help of an example each.[Delhi 2011 C]
Ans.A-Mutualism B-Competition C-Predation D-Amensalism
Mutualism It is an interaction, where both species derive benefit from the interaction, e.g. lichens.
Competition This is an interaction, where both species suffer due to same requirement of resources, that are limited, e.g. In some South American lakes, visiting flamingoes and resident species compete for the common food.
Predation It is an interaction between two species in which one species (parasite) depends on the other species (host) for food and shelter and in the process damages the host, i.e. one is benefitted and other harmed, e.g. tiger and the deer.
Amensalism This is an interaction, where one species is harmed, while other neither benefitted nor harmed, e.g. antibiotics for pathogens.
Identify A, B, C and D in the given table and explain any three of them with the help of an example each.[Delhi 2011 C]
Ans.A-Mutualism B-Competition C-Predation D-Amensalism
Mutualism It is an interaction, where both species derive benefit from the interaction, e.g. lichens.
Competition This is an interaction, where both species suffer due to same requirement of resources, that are limited, e.g. In some South American lakes, visiting flamingoes and resident species compete for the common food.
Predation It is an interaction between two species in which one species (parasite) depends on the other species (host) for food and shelter and in the process damages the host, i.e. one is benefitted and other harmed, e.g. tiger and the deer.
Amensalism This is an interaction, where one species is harmed, while other neither benefitted nor harmed, e.g. antibiotics for pathogens.
59.Draw and explain a logistic curve for a population of density (N) at time (it) whose intrinsic rate of natural increase in (r) and carrying capacity (K). [Delhi 2010]
Ans.(i)Population initially shows a lag phase and then shows a phase of acceleration or exponential growth followed by phase of deceleration
(ii)Population can grow exponentially for a certain period of time and then assumes a steady state, as the resource availability becomes limited at some point of time.
(iii)Every environment has resources to support a particular maximum number of individuals, called its carrying capacity. Beyond that, there is no increase in the size/density of a population.
(iv)A population showing logistic growth shows a sigmoid curve, when the number of individuals is plotted as a function of time
(v)Equation can be described as
where, N = Population density at time t, r = Intrinsic rate of natural increase,
K = Carrying capacity
(vi)The model is more realistic in nature, because no population can sustain the exponential growth indefinitely.
60.(i) Why are herbivores considered similar to predators in the ecological context? Explain.
(ii) Differentiate between the following interspecific interactions in a population
(a)Mutualism and competition
(b)Commensalism and amensalism [All India 2010]
Ans.(i)Herbivores feed on plants. They are considered as predators because they also transfer energy across the trophic levels. Besides this, they also keep the population of their prey under control. For example, when the prickly pear cactus was introduced in Australia in early 1920, they spread rapidly causing havoc.Their population was controlled by introducing cactus-feeding predator (a moth).
(ii) (a) Differences between mutualism and competition are
(b) Difference between commensalism and amensalism is:
Ans.(i)Population initially shows a lag phase and then shows a phase of acceleration or exponential growth followed by phase of deceleration
(ii)Population can grow exponentially for a certain period of time and then assumes a steady state, as the resource availability becomes limited at some point of time.
(iii)Every environment has resources to support a particular maximum number of individuals, called its carrying capacity. Beyond that, there is no increase in the size/density of a population.
(iv)A population showing logistic growth shows a sigmoid curve, when the number of individuals is plotted as a function of time
(v)Equation can be described as
where, N = Population density at time t, r = Intrinsic rate of natural increase,
K = Carrying capacity
(vi)The model is more realistic in nature, because no population can sustain the exponential growth indefinitely.
60.(i) Why are herbivores considered similar to predators in the ecological context? Explain.
(ii) Differentiate between the following interspecific interactions in a population
(a)Mutualism and competition
(b)Commensalism and amensalism [All India 2010]
Ans.(i)Herbivores feed on plants. They are considered as predators because they also transfer energy across the trophic levels. Besides this, they also keep the population of their prey under control. For example, when the prickly pear cactus was introduced in Australia in early 1920, they spread rapidly causing havoc.Their population was controlled by introducing cactus-feeding predator (a moth).
(ii) (a) Differences between mutualism and competition are
(b) Difference between commensalism and amensalism is:
61.(i) Explain with the help of a graph the population growth curve when resources are (A) limiting (B) not limiting.
(ii) Nature has a carrying capacity for a species. Explain. [Foreign 2010]
Ans.
(a)Resources are limiting The population growth curve is sigmoid. It is represented by the equation
where, N = Population density at time t, r – Intrinsic rate of natural increase
K = Carrying capacity
(b)Resources are unlimited The population growth curve is J-shaped. It is represented by the equation
dN/dt = rN or Nt = N0en
where, Nt = Population density after time t, N0 = Population density at time zero r = Intrinsic rate of natural increase, e = The base of natural logarithm (2.71828).
(ii) The resources become limited at certain point of time. So, no population can grow exponentially. Every environment or habitat has limited resources to support a particular maximum number of individuals. This is called its carrying capacity (K).
(ii) Nature has a carrying capacity for a species. Explain. [Foreign 2010]
Ans.
(a)Resources are limiting The population growth curve is sigmoid. It is represented by the equation
where, N = Population density at time t, r – Intrinsic rate of natural increase
K = Carrying capacity
(b)Resources are unlimited The population growth curve is J-shaped. It is represented by the equation
dN/dt = rN or Nt = N0en
where, Nt = Population density after time t, N0 = Population density at time zero r = Intrinsic rate of natural increase, e = The base of natural logarithm (2.71828).
(ii) The resources become limited at certain point of time. So, no population can grow exponentially. Every environment or habitat has limited resources to support a particular maximum number of individuals. This is called its carrying capacity (K).
