NEET AIPMT Biology Chapter Wise Solutions – Organisms and Populations

NEET AIPMT Biology Chapter Wise Solutions – Organisms and Populations

NEET AIPMT Biology Chapter Wise SolutionsPhysicsChemistry

1. In which of the following interactions both partners are adversely affected?
(a) Parasitism
(b) Mutualism
(c) Competition
(d) Predation. (AIPMT 2015)

2. An association of individuals of different species living in the same habitat and having functional interactions is
(a) ecosystem
(b) population
(c) ecological niche
(d) biotic community. (AIPMT 2015)

3. The following graph depicts changes in two populations (A and B) of herbivores in a grassy field. A possible reason for these changes is that

(a) Population A produced more offspring than population B
(b) Population A consumed the members of population B
(c) Both plant populations in this habitat decreased
(d) Population B competed more successfully for food than population A. (AIPMT 2015, Cancelled)

4. Just as a person moving from Delhi to Shimla to escape the heat for the duration of hot summer, thousands of migratory birds from Siberia and other extremely cold northern regions move to
(a) Western Ghat
(b) Meghalaya
(c) Corbett National Park
(d) Keolado National Park. (AIPMT 2014)

5. Besides paddy fields, cyanobacteria are also found inside vegetative part of
(a) Equisetum
(b) Psilotum
(c) Pinus
(d) Cycas. (NEET 2013)

6. A sedentary sea anemone gets attached to the shell lining of hermit crab. The association is
(a) commensalism
(b) amensalism
(c) ectoparasitism
(d) symbiosis. (NEET 2013)

7. A biologist studied the population of rats in a bam. He found that the average natality was 250, average mortality 240, immigration 20 and emigration 30. The net increase in population is
(a) 05
(b) zero
(c) 10
(d) 15. (NEET 2013)

8. The age pyramid with broad base indicates
(a) high percentage of old individuals
(b) low percentage of young individuals
(c) a stable population
(d) high percentage of young individuals. (Karnataka NEET 2013)

9. Which one of the following is not a parasitic adaptation?
(a) Development of adhesive organs
(b) Loss of digestive organs
(c) Loss of reproductive capacity
(d) Loss of unnecessary sense organs. (Karnataka NEET 2013)

10. Benthic organisms are affected the most by 
(a) light reaching the forest floor
(b) surface turbulence of water
(c) sediment characteristics of aquatic ecosystems
(d) water-holding capacity of soil. (Karnataka NEET 2013)

11. Cuscuta is an example of
(a) ectoparasitism
(b) brood parasitism
(c) predation
(d) endoparasitism. (Mains 2012)

12. What type of human population is represented by the following age pyramid?

(a) vanishing population
(b) stable population
(c) declining population
(d) expanding population. (Prelims 2011)

13. Large woody vines are more commonly found in
(a) temperate forests
(b) mangroves
(c) tropical rainforests
d) alpine forests. (Prelims 2011)

14. Consider the following four conditions (1-4) and select a correct pair of them as adaptations to environment in desert lizards.
Conditions:
1. Burrowing in soil to escape high temperature.
2. Losing heat rapidly from the body during high temperature.
3. Bask in sun when temperature is low.
4. Insulating body due to thick fatty dermis.
(a) 3,4
(b) 1,3
(c) 2,4
(d) 1,2 (Prelims 2011)

15. Which one of the following is categorised as a parasite in true sense?
(a) the female Anopheles bites and sucks blood from humans
(b) human foetus developing inside the uterus draws nourishment from the mother
(c) head louse living on the human scalp as well as laying eggs on human hair
(d) the cuckoo (koel) lays its eggs in crow’s nest. (Prelims 2011)

16. The logistic population growth is expressed by the equation

17. The figure given below is a diagrammatic representation of response of organisms to abiotic factors. What do (i), (ii) and (iii) represent respectively?

18. Which one of the following is one of the characteristics of a biological community?
(a) stratification
(b) natality
(c) mortality
(d) sex-ratio. (Prelims 2010)

19. Which one of the following is most appropriately defined?
(a) host is an organism which provides food to another organism
(b) amensalism is a relationship in which one species is benefitted whereas the other is unaffected
(c) predator is an organism that catches and kills other organism for food
(d) parasite is an organism which always fives inside the body of other organism and may kill it. (Mains 2010)

20. A country with a high rate of population growth took measures to reduce it. The figure below shows age-sex pyramids of populations A and B twenty years apart. Select the correct interpretation about them

Interpretations:
(a) “B” is earlier pyramid and shows stabilized growth rate.
(b) “B” is more recent showing that population is very young
(c) “A” is the earlier pyramid and no change has occurred in the growth rate
(d) “A” is more recent and shows slight reduction in the growth rate (Prelims 2009)

21. Reduction in vascular tissue, mechanical tissue and cuticle is characteristic of
(a) mesophytes
(b) epiphytes
(c) hydrophytes
(d) xerophytes. (Prelims 2009)

22. Consider the following four statements (1-4) about certain desert animals such as kangaroo rat
(1) they have dark colour and high rate of reproduction and excrete solid urine
(2) they do not drink water, breathe at a slow rate to conserve water and have their body covered with thick hairs
(3) they feed on dry seeds and do not require drinking water
(4) they excrete very concentrated urine and do not use water to regulate body temperature.
Which two of the above statements for such animals are tme?
(a) 3 and 1
(b) 1 and 2
(c) 3 and 4
(d) 2 and 3. (Prelims 2008)

23. Quercus species are the dominant component in
(a) scrub forests
(b) tropical rain forests
(c) temperate deciduous forests
(d) alpine forests. (Prelims 2008)

24. Geometric representation of age structure is a characteristic of
(a) population
(b) landscape
(c) ecosystem
(d) biotic community. (2007)

25. The population of an insect species shows an explosive increase in numbers during rainy season followed by its disappearance at the end of the season. What does this show?
(a) the food plants mature and die at the end of the rainy season
(b) its population growth curve is of J-type
(c) the population of its predators increases enormously
(d) S-shaped or sigmoid growth of this insect. (2007)

26. If the mean and the median pertaining to a certain character of a population are of the same value, the following is most likely to occur
(a) a bi-modal distribution
(b) a T-shaped curve
(c) a skewed curve
(d) a normal distribution.(2007)

27. A high density of elephant population in an area can result in
(a) intraspecific competition
(b) interspecific competition
(c) predation on one another
(d) mutualism. (2007)

28. Niche overlap indicates
(a) mutualism between two species
(b) active cooperation between two species
(c) two different parasites on the same host
(d) sharing of one or more resources between the two species. (2006)

29. More than 70% of world’s freshwater is contained in
(a) polar ice
(b) glaciers and mountains
(c) Antartica
(d) Greenland. (2005)

30. At which lattitude, heat gain through insolation approximately equals heat loss through terrestrial radiation?

31. Animals have the innate ability to escape from predation. Examples for the same are given below. Select the incorrect example.
(a) colour change in Chamaeleon
(b) enlargement of body size by swallowing air in puffer fish
(c) poison fangs in snakes
(d) melanism in moths. (2005)

32. Which one of the following pairs is mismatched?permafrost Acacia trees epiphytes evergreen trees.
(a) Tundra
(b) Savanna
(c) prairie
(d) coniferous forestv (2005)

33. Certain characteristic demographic features of developing countries are
(a) high fertility, low or rapidly falling mortality rate, rapid population growth and a very young age distribution
(b) high fertility, high density, rapidly rising mortality rate and a very young age distribution
(c) high infant mortality, low fertility, uneven population growth and a very young age distribution
(d) high mortality, high density, uneven population growth and a very old age distribution. (2004)

34. What is a keystone species?
(a) a species which makes up only a small proportion of the total biomass of a community, yet has a huge impact on the community’s organization and survival
(b) a common species that has plenty of biomass, yet has a fairly low impact on the community’s organization
(c) a rare species that has minimal impact on the biomass and on other species in the community
(d) a dominant species that constitutes a large proportion of the biomass and which affects many other species. (2004)

35. In which one of the following pairs is the specific characteristic of a soil not correctly matched?

36. The maximum growth rate occurs in
(a) stationary phase
(b) senescent phase
(c) lag phase
(d) exponential phase. (2004)

37. In which one of the following habitats does the diurnal temperature of soil surface vary most?
(a) shrub land
(b) forest
(c) desert
(d) grassland. (2004)

38. Mycorrhiza is an example of
(a) symbiotic relationship
(b) ectoparasitism
(c) endoparasitism
(d) decomposers. (2003)

39. What is true for individuals of same species?
(a) live in same niche
(b) live in same habitat
(c) interbreeding
(d) live in different habitat. (2002)

40. Which type of association is found in between entomophilous flower and pollinating agent:
(a) mutualism
(b) commensalism
(c) cooperation
(d) co-evolution. (2002)

41. Two different species cannot live for long duration in the same niche or habitat. This law is
(a) Allen’s law
(b) Gause’s hypothesis
(c) Dollo’s rule
(d) Weisman’s theory. (2002)

42. Which part of the world has a high density of organisms?
(a) deciduous forests
(b) tropical rain forests
(c) grasslands
(d) savannahs. (1999)

43. In desert grasslands, which type of animals are relatively more abundant?
(a) aquatic
(b) fossorial
(c) diurnal
(d) arboreal. (1998)

44. Plants such as Prosopis, Acacia and Capparis represent examples of tropical
(a) deciduous forests
(b) evergreen forests
(c) grass lands
(d) thorn forests. (1998)

45. Which of the following communities is more vulnerable to invasion by outside animals and plants?
(a) temperate forests
(b) oceanic island communities
(c) mangroves
(d) tropical evergreen forests. (1998)

46. During adverse season, therophytes survive by
(a) rhizomes
(b) seeds
(c) bulbs
(d) corms. (1997)

47. Benthoic animals are those, which
(a) are submerged in area
(b) float on the sea surface
(c) are deep dweller in sea
(d) are floating (free) organisms. (1996)

48. The ‘niche’ of a species is meant for
(a) habitat and specific functions of a species
(b) specific place where an organism lives
(c) specific species function and its competitive power
(d) none of these. (1996)

49. The abundance of a species population, within its habitat, is called
(a) relative density
(b) regional density
(c) absolute density
(d) niche density. (1995)

50. Which one of the following pairs is correctly matched?
(a) parasitism – intra-specific relationship
(b) uricotelism – aquatic habitat
(c) excessive perspiration – xeric adaptation
(d) stream lined body – aquatic adaptation. (1995)

51. Study of inter-relationships between organisms and their environment is
(a) ecology
(b) ecosystem
(c) phytogeography
(d) ethology. (1993)

52. The sum total of the populations of the same kind of organisms constitute
(a) colony
(b) genus
(c) community
(d) species. (1993)

53. Association of animals when both partners are benefitted
(a) colony
(b) mutualism
(c) commensalism
(d) ammensalism. (1993)

54. Fertility of soil is measured by its ability to
(a) retain nutrients
(b) hold organic materials
(c) hold water
(d) support life. (1992)

55. Soil particles determine its
(a) texture
(b) field capacity
(c) water holding capacity
(d) soil flora. (1992)

56. Homeostasis is
(a) tendency of biological systems to change with change in environment
(b) tendency of biological systems to resist change
(c) disturbance of self regulatory system and natural controls
(d) biotic materials used in homeopathic medicines. (1991)

57. Deep black soil is productive due to high proportion of
(a) sand and zinc
(b) gravel and calcium
(c) clay and humus
(d) silt and earthworm. (1991)

58. Which one is true?
(a) commensalism when none of the interacting populations affect each other
(b) symbiosis when the interaction is useful to both the populations
(c) symbiosis when neither populations affects each other
(d) commensalism when the interaction is useful to both the populations. (1991)

59. The relation between algae and fungi in a lichen is
(a) symbiosis
(b) parasitism
(c) commenalism
(d) protocooperation. (1989)

60. Competition for light, nutrients and space is most severe between
(a) closely related organism growing in different niches
(b) closely related organisms growing in the same area/niche
(c) distantly related organisms growing in the same habitat
(d) distantly related organisms growing in different niches. (1988)

61. A mutually beneficial association necessary for survival of both partners is
(a) mutualism/symbiosis
(b) commensalism
(c) amensalism
(d) both A and B. (1988)

EXPLANATIONS

1. (c) :
Competition is the rivalry between two or more organisms for obtaining the same resources such as food, light, water, space, shelter, mate etc. Competitors adversely affect each other.

2. (d):
Biological or biotic community is an assemblage of populations of different species of plants, animals, bacteria and fungi which live in a particular area and interact with one another through competition, predation, mutualism, etc. Each biotic community has a specific composition and structure, e.g., pond community.

3. (d):
Both the populations are herbivorous, thus they cannot each other. If the food sources for these populations A and B have decreased, then both the populations A and B would have declined. If population A have produced more offspring then the graph A should have increased. Based on the graph, Population B is more successful in competing with population A, that is why number of organisms in population B increased while that in population A decreased, as they get access to limited resources.

4. (d)

5. (d):
Coralloid roots of Cycas have symbiotic association with blue-green algae like Nostoc and Anabaena. Coralloid roots are irregular, negatively geotropic, dichotomously branched coral like roots which do not possess root hairs and root caps.

6. (d):
Sea anemone gets associated to the shell of hermit crab. It provides camouflage and protection to the crab due to presence of stinging cells in sea anemone. In turn, sea anemone is transported to new places reaching new food sources. This is symbiosis as both the organisms are benefitted.

7. (b):
Natality and immigration positively contribute to the population growth while mortality and emigration are negative factors. In the given question,
The net increase in population is
natality + immigration = 250 + 20 = 270
The net decrease in population is
mortality + emigration = 240 + 30 = 270
Thus, net increase in population = 270 – 270 = 0

8. (d):
Age pyramid is a graphic representation of abundance of individuals of different age groups with pre-reproductive individuals at the base, reproductive individuals in the middle and post-reproductive individuals at the top.
Triangular age pyramid has high proportion of pre- reproductive individuals, moderate number of reproductive individuals and fewer post-reproductive individuals. It represents young or rapidly growing population. In bell-shaped age pyramid, the number of pre-reproductive and reproductive individuals is almost equal. Post -reproductive individuals are comparatively fewer. It represents stable or stationary population where growth rate is nearly zero. In urn¬shaped age pyramid, the number of reproductive individuals is higher than the number of pre- reproductive individuals. It represents declining or diminishing population.

9. (c):
Parasitism is a relationship between two living organisms of different species in which one organism called parasite obtains its food directly from another living organism called host. The parasite spends a part or whole of its life either on or inside the body of the host.
The general parasitic adaptations are (i) anaerobic respiration in internal parasites, (ii) loss of certain organs, (iii) presence of adhesive organs, (iv) excessive multiplication, (v) resistant cysts and eggs for safe transfer of their progeny to new hosts and (vi) well developed and complicated reproductive organs.

10. (c):
Benthic organisms are bottom dwelling forms found crawling or attached to the bottom. The sediment characteristics often determine the type of benthic animals that can thrive there.

11. (a) :
Cuscuta is a total stem parasite which is a good example of ectoparasitism. It is commonly found growing on hedge plants. It has lost chlorophyll and leaves in the course of evolution. It attaches and wraps itself around the stem of host plant and produces haustoria that gets inserted into the vascular system of host. The parasitic plant sucks all the nutrients from the host plant with the help of haustoria. Cuscuta is known to receive even the flower inducing hormone or florigen from the host.

12. (c) :
Refer answer 8.

13. (c) :
Lianas are large climbing woody vines that drape tropical rainforest trees. They have adapted to life in rainforest by having their roots in the ground and climbing high onto the tree canopy to reach available sunlight. Many lianas start life in the rainforest canopy and send roots down to the ground.

14. (b) :
Desert lizards lack the physiological ability that mammals have to deal with the high temperatures of their habitat, but manage to keep their body temperature fairly constant by behavioural means. They bask in the sun and absorb heat when their body temperature drops below the comfort zone, but move into shade when the ambient temperature starts increasing. Some species are capable of borrowing into the soil to hide and escape from the above-ground heat.

15. (c) :
Parasitism is an association in which one organism (the parasite) lives on (ectoparasitism) or in (endoparasitism) the body of another (the host), from which it obtains its nutrients. They also produce vast numbers of eggs there e.g., head louse living on the human scalp.

16. (b):
Logistic population growth is expressed by following equation:

17. (d) :
Some organisms are able to maintain homeostasis by physiological (sometimes behavioural also) means which ensures constant body temperature, constant osmotic concentration, etc. They are known as regulators. A majority of animals and plants cannot maintain a constant internal environment. Their body temperature changes with the ambient temperature. These animals and plants are simply conformers. During the course of evolution, the costs and benefits of maintaining a constant internal environment are taken into consideration. Some species have evolved the ability to regulate, but only over a limited range of environmental conditions, beyond which they simply conform. They are known as partial regulators.

18. (a):
The characteristics of biological community are dominance, species diversity, trophic organisation, stratification, dynamism and stability. Organisms are not uniformly distributed throughout a community. They usually occur in definite zones. This spatial arrangement of populations is called stratification. Structurally a community may be divided horizontally into subcommunities. This horizontal division constitutes the zonation in the community. Natality, mortality, age structure and sex ratio are the basic characteristics of a population.

19. (c) :
Predation is an interaction between members of two species in which members of one species capture, kill and eat up members of other species ‘Host’ is a term which is specifically related to parasitism. Amensalism is an interspecies interaction in which one species is harmed whereas the other one is unaffected. Parasitic organism can live both over the surface of their host or inside their body.

20. (d):
“A” is more recent and shows slight reduction in growth rate.

21. (c) :
In hydrophytes mechanical tissue i.e. sclerenchyma, conducting tissue xylem, absorbing tissues are in reduced form or absent. Cuticle is either completely absent or if present it is thin and poorly developed.

22. (c):
Kangaroo rat (Dipodomys merriami) feeds on dry seeds. It seldom drinks water. The requirement of water is met by food (10%) and metabolic water (90%). Water loss is prevented by living in burrows during the day, concentration of urine and solidification of faeces. It has a thick coat to minimise evaporative desiccation.

23. (c):
Temperate broad leaf (deciduous) forests have warm summer and moderately cool winter. Rainfall is 100 – 250 cm. Dominant trees are oak, elm, birch, maple ash, chestnut, hickory, beech, poplar and Magnolia. Indian temperate broad leaves forests are1 dominated by oak like Quercus semecarpifolia (Brown oak of Himalayas, Khrsu oak), Q. floribunda (Tilonaj oak), Q. lanuginose (Rianj oak) and Q. leucotrichophora (Banj oak). Fauna of latitudinal temperate broad leaf forests consists of deer, fox, beaver, wild cat, racoon etc.

24. (a) :
Population has several characteristics or attributes which are a function of the whole group and
not of individual. Age distribution is one of them that is the number or the percentage of individuals in a population in different age groups. This is represented geometrically in the form of age pyramid.

25. (b) :
J-shape of growth pattern can be easily observed in algae blooms, some insects, annual plants and the lemmings of Tundra. In the beginning density of the population increases rapidly in compound interest fashion and then stops abruptly as the environmental resistance or other limiting factors become effective. These factors may be food, space, seasonal (frost, excessive rain etc.) or the termination of reproduction session.

26. (d) :
If the mean and the median pertaining to a certain character of a population are of the same value a normal distribution is most likely to occur.

27. (a) :
Competition is rivalry for obtaining the same resource. Competition is of two types, intraspecific and interspecific. Intraspecific competition is the competition amongst members of the same species for a common resource. It may be for food, space, and mate. So if the density of elephant population in an area increases, it will lead to intraspecific competition. This will lead to the establishment of territories in elephants which will result in pushing out of the extra number securing shelter, mate and food for the rest.

28. (d) :
Niche/ecological niche is specific part of habitat occupied by individuals of a species which is circumscribed by its range of tolerance, range of movement, microclimate, type of food and its availability, shelter, type of predator and timing of activity. A habitat has several ecological niches and supports a number of species. An ecological niche is used by a single species. Two or more species cannot use the same niche despite having a mutualistic association. Organisms or populations in competition have a niche overlap of a limited resource for which they compete.
Both owl and cat feed on shrews and mice. They occupy the same niche because of being ecological equivalents though their habitats are different.

29. (a):
Nearly about 97% of the earths water is saline in the oceans and seas. 3% of the earths water is locked up on the polar ice caps. 85% of the frozen freshwater is in the Antarctic is ice cap, 15% of the frozen freshwater is in the northern polar ice cap and glaciers.

30. (b) :
Earth does not receive equal radiation at all points. The east west rotation of earth provides equal exposure to sunlight but lattitude and dispersion do affect the amount of radiation received. The poles receive far less radiation than equator. This uneven heating is called differential insolation. At 40° North and South, approximately the heat gain is equal to heat loss through terrestrial radiation.

31. (c) :
Colour change in chameleon and melanism in moths are examples of camouflage in animals adapted to prevent predation from prey. As a defence mechanism puffers have the ability to inflate rapidly, filling their extremely elastic stomach with water (or air) until they are almost spherical. This prevents them from being identified by the predator. But poison fangs in snakes are a method adopted for preying and not escaping predation.

32. (c) :
A biome is a major terrestrial community characterized by a distinct climate and inhabited by a particular species of plants and animals.
Tundra is characterized by precipitation of less than 25 cm annually. Permafrost or permanent ice is found about a meter down from the surface, it never melts and is impenetrable to both water and roots. Savannahs are open grasslands with scattered shrubs and trees. Coniferous forest contain evergreen trees. In these forests all plants do not shed their leaves at the same time hence forest remains always evergreen. But pairies is a grassland and epiphytes and ephemerals are found in deserts.

33. (a) :
In developing countries the conditions are becoming better for survival of human beings. So the mortality rate or the number of individuals dying per unit of time is low.
Mortality or the average number of individuals produced by a population in a unit of time is high. So that there is rapid population growth and there are more individuals in the pre-reproductive age group. So there is young age distribution. ”

34. (a) :
Keystone species are those species which has significant and disproportionately large influence on the community structure and characteristics. It has often considerably low abundance and biomass as compared to dominant species. Removal of such species causes serious disruption in structure and function of community.

35. (d) :
Black soil forms the largest group. It is developed mainly on the Deccan traps of Maharashtra, Madhya Pradesh and Kathiawar. Because of its hydrology and climatic conditions of the environment, the medium and deep black soils are very suitable for cotton cultivation. Laterite soil is rich in insoluble iron oxides and aluminium compounds, which gives laterites a reddish appearance. Chernozems are rich in nutrients (due to abundant organic rich compounds) and consequently the most fertile in the world.

36. (d):
Maximum growth rate occurs in exponential or acceleration or log phase. The point at which the exponential growth begins to slow down is known as inflexion point.

37. (c) :
Deserts are places where the diurnal temperatures very greatly. It is extremely hot during the day time and very cold at night. This change in temperature also affects the temperature condition of the soil.

38. (a) :
In mutalism or symbosis both the organisms in association are mutually benefitted and further this association is obligatory, i.e., necessary for existence of both organisms. Mycorrhiza is a example of symbiosis.
It is association between roots of higher plants and fungal hyphae. The fungal hyphae supply water and nutrients to the plant and in turn get food form the plant. So both the organism are mutually benefitted.

39. (c) :
Species may be defined as the uniform interbreeding population of individuals which freely interbreed among themselves. Niche represents the habitat and functions of a species. Habitat is a specific place where an organisms lives.

40. (d) :
Coevolution can occur in any interspecific relationship like symbiosis or mutualism. The relation between an entomophilous flower and pollinating insect shows co-evolved mutualism. In this the plant depends exclusively on the insect for pollination and the insect relies on the plant for food.

41. (b) :
Interspecific competition is rivalry amongst members of different species. The severity of competition depends upon similarity in the requirement of food and shelter. Every type of organism has a particular niche, no two organisms can live in same niche. One of the two is eliminated. This phenomenon is called Gause hypothesis of competitive exclusion. Different organisms develop different types of variations in order to exploit niches, e.g. 14 species of Finches in Galapagos Islands. Allen’s law states that there is tendency of smaller extremities like ear, nose, tail etc. in animals living in colder climate. Weisman’s germplasm theory was the ultimate blow to discard lamarckism. Dollo’s law proposed that evolution is irreversible.

42. (b) :
Trophical forests are found in trophical zone of the world and are characterized by very high temperature with rainfall in abundance. The flora of trophical rain forest is very rich and highly diversified. The trophical forests have a very rich fauna both in density as well as in varieties. The reason for this high diversity and variety of flora and fauna is the occurrence of suitable conditions in these forests.

43. (b) :
Deserts animals prefer to live under the earths surface. Such animals are called fossorial. The animal residing either permanently or for most of life inside the burrows or under the earth surface are known as burrowing or fossorial animals and their mode of existence is described as subterranean or underground.

44. (d) :
Tropical shrubs or thorn forests are found in places where moisture conditions are intermediate between desert and savanna on one hand and seasonal or rain forests on the other hand. Acacia and Prosopis are non-succulent perennial plants and Capparis is a xerophytic shrub.

45. (d) :
Tropical forests are found in tropical zone of the world and are characterised by very high temperature with rainfall in abundance. The flora of tropical rain forest is very rich and highly diversified. The tropical forests have a very rich fauna both in density as well as in varieties. The reason for this high diversity and variety of flora and fauna is the occurence of suitable conditions in these forests. So these are more vulnerable to invasion by outside^ plants and animals.

46. (b) :
Therophytes are those plants that survive the winter as a seed and complete their life cycle between the spring and autumn.

47. (c) :
Benthoic organisms are attached or rest on the bottom sediments. Benthic animal may be divided into filter feeders, e.g. clams and deposit feeders e.g. snails.

48. (a) :
Niche is specific part of habitat occupied by individuals of a species which is circumscribed by its range of tolerance, range of movement, microclimate, type of food and its availability, shelter, type of predator, and timing of activity. A habitat has several ecological niches and supports a number of species. An ecological niche is used by a single species. Two or more species cannot use the same niche despite having a mutualistic association.

49. (d)

50. (d) :
Streaming body is a secondary aquatic adaption. It is found in animals that live permanently in water but most of them are amphibious in nature. The stream lined body consists of compression of head, body and tail into a curved stream lined form. There is no protruberance over the body so that the animal can move easily through water. Parasitism is a relationship between two organisms of different species in which one organism called parasite obtains its food directly from another living organism called host.In xeric adaptation perspiration is reduced to conserve water. Uricotelism is characteristic of terrestrial animals which excrete uric acid.

51. (a) :
Ecology is the branch of science which deals with the study of inter relationship between organisms and their environment. The scope of ecology is very vast as it treats the organisms at the level of population, community and ecosystem. Ethology is the study of evolution ary significant behaviour of people in their natural surroundings. Phytogeography is the branch of biogeography that is concerned with the geographic distribution of plant species.

52. (d) :
The sum total of the populations of the same kind of organisms constitute species. A species is a group of individuals of same kind of phenotypic characters and can interbreed.

53. (b):
Mutualism is a type of association where both the partners are benefitted. This is permanent and obligatory association involving a physiological inter¬dependence e.g. in lichens.

54. (d) :
Soil fertility is the characteristic of soil that supports abundant plant life. In particular the term is used to describe agricultural and garden soil.

55. (a) :
Soil particles determines its texture. The soil particles enclose living spaces in between them called pore space. In coarse textured soils, the pore space is wide but pore frequency is low. But in fine textured soil, the pore space is narrow but pore frequency is high.

56. (b) :
The ability to maintain a steady state within constantly changing environment is essential for the survival of living systems. The maintenance of a constant internal environment is called homeostasis.

57. (c) :
Deep black soil is productive due to high proportion of clay and humus. The organic matter present in the soil is contributed by the death and decay of living organisms. These are the richest in nutrients and therefore these soils are the most fertile.

58. (b) :
When the interactions is useful to both the populations it is called symbiosis. Symbiosis means living together. It is beneficial co-action between two or more different species in which one or both species are benefitted and neither species is harmed.

59. (a) :
Algae and fungi in a lichen show symbiotic relationship. Fungi give support to the algae, give protection and help in absorption of water while algae provide food to fungi which is achlorophyllous. No one is harmed but both are benefitted by each other.

60. (b) :
Competition is rivalry for obtaining the same resource. Competition of light, nutrients and space is most severe between closely related organisms growing in the same area/niche, due to overproduction of population in the same area/niche.

61. (a) :
Mutualism is an association between individuals of two species, both of which are benefitted but cannot live separately under natural conditions e.g. instances of mutualism exist between animals and plants and also in between plants e.g. lichens.
Ammensalism is an interaction in which one species causes harm to another spices with its toxic secretion often without gaining any benefit from the interaction. Commensalism is the relationship between individuals of two species of which one is benefitted and the other is almost unaffected i.e.; neither benefitted nor harmed.