MP Board Class 12th Biology Solutions Chapter 13 Organisms And Population

MP Board Class 12th Biology Solutions Chapter 13 Organisms And Population

Organisms And Population NCERT Text Book Questions and Answers

Question 1.
How is diapauses different from hibernation?
Answer:
Diapauses is a stage of suspended development to cope with unfavorable conditions. Many species of zooplankton and insects exhibit diapauses to tide over adverse climatic conditions during their development. On the other hands hibernation or winter sleep is a resting stage where in animals escape winters (cold) by hiding themselves in their shelters. They escape the winter season by entering a state of inactivity by slowing their metabolism. The phenomenon of hibernation is exhibited by bats, squirrels, and other rodents.

Question 2.
If a marine fish is placed in a fresh water aquarium, will the fish be able to survive? Why or why not?
Answer:
If a marine fish is placed in a freshwater aquarium, then its chances of survival will diminish. This is because their bodies are adapted to high salt concentrations of the marine ‘ environment. In freshwater conditions, they are unable to regulate the water entering then- body (through osmosis). Water enters their body due to the hypotonic environment outside. This results in the swelling up of the body, eventually leading to the death of the marine fish.

Question 3.
Define phenotypic adaptation. Give one example.
Answer:
Phenotypic adaptation involves changes in the body of an organism in response to genetic mutation or certain environmental changes.These responsive adjustments occur in an organism in order to cope with environmental conditions present in their natural habitats For example, desert plants have thick cuticles and sunken stomata on the surface of their leaves to prevent transpiration. Similarly, elephants have long ears that act as thermoregulators.

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Question 4.
Most living organisms cannot survive at temperature above 45° C. How are some microbes able to live in habitats with temperatures exceeding 100° C ?
Answer:
Archaebacteria (Thermophiles) are ancient forms of bacteria found in hot water springs and deep sea hydrothermal vents. They are able to survive in high temperatures because their bodies have adapted to such environmental conditions. These organisms contain specialized thermo-resistant enzymes, which carry out metabolic functions that do not get destroyed at such high temperatures unlike other enzymes.
Most living organism can not survive above 45° because :

  • Above 45° C enzymes get denatured
  • Protoplasm precipitates at high temperature.

Question 5.
List the attributes that populations but not individuals possess.
Answer:
A population has the following attributes that an individual does not possess :

  • Birth rates and death rates
  • Sex ratio
  • Population density
  • Age distribution
  • Population growth.

Question 6.
If a population growing exponentially double in size in 3 years, what is the intrinsic rate of increase (r) of the population?
Answer:
A population grew exponentially if sufficient amounts of food resources are available to the individual. Its exponential growth can be calculated by the following integral form of the exponential growth equation:

Nt = N0 en
Where,

Nt = Population density after time t.
N0 = Population density at time zero.
r = Intrinsic rate of natural increase.
e = Base of natural logarithms (d-434).

From the above equation, we can calculate die intrinsic rate of increase (r) of a population. Now, as per the question,
Present population density = x
Then, Population density after two years = 2x
t = 3 years
Substituting these values in the formula, we get:
⇒ 2x=xe3r
⇒  2 = e3r
Applying log on both sides :
⇒ log 2 = 3r log e
\(\frac { log 2 }{ 3 log e }\)=r

\(\frac { 0.301 }{ 3X0.434 }\)=r

\(\frac { 0.301 }{ 1.302 }\)=r

0.2311=r
Hence, the intrinsic rate of increase for the above illustrated population is 0.2311.

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Question 7.
Name important defence mechanisms in plants against herbivory.
Answer:
Several plants have evolved various mechanisms both morphological and chemical to protect themselves against herbivory.
(1) Morphological defence mechanisms :

  • Cactus leaves (Opuntia) are modified into sharp spines (thorns) to deter herbivores from feeding on them.
  • Sharp thorns along with leaves are present in Acacia to deter herbivores.
  • In some plants, the margins of their leaves are spiny or have sharp edges that prevent herbivores from feeding on them.

(2) Chemical defence mechanisms :

  • All parts of Calotmpis weeds contain toxic cardiac glycosides, which can prove to be fatal in ingested by herbivores.
  • Chemical substances such as nicotine, caffeine, quinine and opium are produced in plants as a part of self-defense.

Question 8.
An orchid plant is growing on the branch of mango tree. How do you describe this interaction between the orchid and the mango tree ?
Answer:
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. Therefore, the relationship between a mango tree and an orchid is an example of commensalisms, where one species gets benefited while the other remains unaffected. In the above interaction, the orchid is benefited as it gets support while the mango tree remains unaffected.

Question 9.
What is the ecological principle behind die biological control method of managing with pest insects ?
Answer:
The ecological principle behind the biological control method of managing with pest insects is to keep their population in check by using their natural predators and parasites.

Question 10.
Distinguish between the following:
(a) Hibernation and Aestivation
(b) Ectotherms and Endotherms.
Answer:
(a) Differences between Hibernation and Aestivation:
MP Board Class 12th Biology Solutions Chapter 13 Organisms And Population 1

(b) Difference between Ectotherms and Endotherms.
MP Board Class 12th Biology Solutions Chapter 13 Organisms And Population 2

Question 11.
Write a short note on:
(a) Adaptations of deserts plants and animals
(b) Adaptations of plants to water scarcity
(c) Behavioural adaptations id animals
(d) Importance of light to plants
(e) Effect of temperature or water scarcity and the adaptations of animals.
Answer:
(a) Adaptations of desert plants and animals :

1. Adaptations of desert plant : Plants have an extensive root system to tap underground water. They bear thick cuticles and sunken stomata on the surface of their leaves to reduce transpiration. In Opuntia, the leaves are entirely modified into spines and photosynthesis is carried out by green stems. Desert plants have special pathways to synthesize food, called CAM (C4 pathway). It enables the stomata to remain closed during the day to reduce the loss of water through transpiration.

2. Adaptations of desert animals : Animals found in deserts such as desert Kangaroo rats, Lizards, Snakes, etc. are well adapted to their habitat. The Kangaroo rat found in the deserts of Arizona never drinks water in its life. It has the ability to concentrate its urine to conserve water. Desert lizards and snakes bask in the sun during early morning and burrow themselves in the sand during afternoons to escape the heat of the day. These adaptations occur in desert animals to prevent the loss of water.

(b) Adaptations of plants to water scarcity :
Plants found in deserts are well adapted to cope with water scarcity and scorching heat of the desert. Plants have an extensive root system to tap underground water. They bear thick cuticles and sunken stomata on the surface of their leaves to reduce transpiration. In Opuntia, the leaves are modified into spines and the process of photosynthesis is carried out by green stems. Desert plants have special pathways to synthesize food, called CAM (C4 pathway). It enables their stomata to remain closed during the day to reduce water loss by transpiration.

(c) Behavioural adaptations in animals :
Certain organisms are affected by temperature variations. These organisms undergo adoptions such as hibernation, aestivation, migration, etc. to escape environmental stress to suit their natural habitat. These adaptations in the behaviour of an organism are called behavioural adaptations. For example, ectothermal animals and certain endosperms exhibit behavioural adaptations. Ectotherms are cold blooded animals such as fish, amphibians, reptiles, etc. Their temperature varies with their surroundings. For example, the desert lizard basks in the sun during early hours when the temperature is quite low.

However, as the temperature begins to rise, the lizard burrows itself inside the sand to escape the scorching sun. Similar burrowing strategies are exhibited by other desert animals. Certain endotherms (warm blooded animals) such as birds and mammals escape cold and hot weather conditions by hibernating during winters and aestivating during summers. They hide themselves in shelters such as caves, burrows, etc. to protect against temperature variations.

(d) Importance of light to plants :
Sunlight acts as the ultimate source of energy for plants. Plants are autotrophic organisms, which need right for carrying our the process of photosynthesis. Light also plays an important role in generating photoperiodic responses occurring in plants. Plants respond to changes in intensity of light during various seasons to meet their photoperiodic requirements for flowering. Light also plays an important role in aquatic habitats for vertical distribution of plants in the sea.

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(e) Effects of temperature or water scarcity and the adaptations of animals :
Temperature is the most important ecological factor. Average temperature on the Earth varies from one place to another. These variations in temperature affect the distribution of animals on the Earth. Animals that can tolerate a wide range of temperature are called eurythermals. Those which can tolerate’a narrow range of temperature are called stenothermal animals. Animals also undergo adaptations to suit their natural habitats.

Animals found in polar regions have thick layers of fat below their skin and thick coats of fur to prevent the loss of heat. Some organisms exhibit various behavioural changes to suit their natural habitat. These adaptations present in the behaviour of an organism to’ escape environmental stresses are called behavioral adaptations. For example, desert lizards are ectotherms. This means that they do not have a temperature regulatory mechanism to escape temperature variations.

These lizards bask in the sun during early hours when the temperature is quite low. As the temperature begins to increase, the lizard burrows itself inside the sand to escape the scorching sun. Similar burrowing strategy is seen in other desert animals.Water scarcity is another factor that forces animals to undergo certain adaptations to suit their natural habitat. Animals found in deserts such as desert kangaroo rats, lizards, snakes, etc. are well adapted to stay in their habitat.

The kangaroo rat found in the deserts of Arizona never drinks water in its life. It has the ability to concentrate its urine to conserve water. Desert lizards and snakes bask in the sun during early morning and burrow in the sand as the ‘ temperature rises to escape the heat of the day. Such adaptations can be seen to prevent the loss of water.

Question 12.
List the various abiotic environmental factors.
Answer:

  • Atmospheric factors: Light, temperature, wind and water.
  • Lithosphere: Rock, soil.
  • Hydrosphere: Pond, river, lake and ocean.
  • Edaphic factors: Soil texture, soil water, soil air, soil microorganism, soil pH, minerals.
  • Topographic factors: Slope, altitude, valley.

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Question 13.
Give an example for:
(a) An endothermic animal .
(b) An ectothermic animal
(c) An organism of benthic zone.
Answer:
(a) An endothermic animals : Birds such as crows, sparrows, pigeons, cranes, etc. and mammals such, as bears, cows, rats, rabbits etc. are endothermic animals.

(b) An ectothermic animals : Fishes such as sharks, amphibians frogs, and reptiles, tortoise, snakes, and lizards are ectothermic animals.

(c) An organism of benthic zone : Decomposing bacteria is an example of an organism found in the benthic zone of a water body.

Question 14.
Define population and community.
Answer:
Population : Population is a group of individuals of same species, which can reproduce among themselves and occupy a particular area in a given time.

Community : It is an assemblage of several population in a particular area and time and exhibit interaction and interdependence through trophic relationship.

Question 15.
Define the following terms and give one example for each:
(a) Commensalism
(b) Parasitism
(c) Camouflage
(d) Interspecific competition.
Answer:
(a) Commensalism :
(a) Difference between Parasitism and Symbiosis:
MP Board Class 12th Biology Solutions Chapter 13 Organisms And Population 3
(b) Differences between Mutualism and Commensalism:
MP Board Class 12th Biology Solutions Chapter 13 Organisms And Population 7
(c) Differences between Hydrosere and Xerosere:
MP Board Class 12th Biology Solutions Chapter 13 Organisms And Population 8

Odum (1971) distinguished interactions into two broad categories:
(A) Positive interactions and
(B) Negative interactions.

(A) Positive Interactions :
In this type, those type of interactions are considered in which both interacting species are mutually involved to help each other. Here, one interacting species helps the other either one way or on reciprocal terms and may be in the form of nutrition or shelter or substratum or transport. Here interaction may be obligatory or facultative. The positive interactions include three types of interactions. They are :

1. Commensalism : This type of interaction occurs in between two organisms of two different species in which one species benefits and the other is neither benefited nor harmed. e.g., Lichens.

2. Protocooperation : The type of interaction where both population are benefited but not obligatory i.e., not essential for the survival of either population is called protocooperation. This is also known as non-obligatory mutualism. The relationship between hermit crab and sea anemone is an example of proto-cooperation. The crab pses the gastropod (mollusc) shell as a portable shield and the sea anemone eats the leftover food of the crab, which is protected from its predators by the stinging cells of the sea anemone.

3. Mutualism or Symbiosis : When two different species grow together and are mutually benefited, the plants are known as symbiotic plants and the phenomenon is called symbiosis or mutualism. It is a sort of obligatory association. This type the organisms are dependent upon each other for survival. In this type of association, two types of species are physiologically related. This type of relationship may exist in between two plants or in between one plant and one animal or in between two animals.

(B) Negative Interactions :
Those interaction of two different species in which both are harmed or one organism is benefited while other is more or less harmed is referred to as negative interaction. In this type of interaction one population eats the other type of population or one organism does not allow other organisms to grow near it by using the food supply of the other or producing toxic substances. The negative interactions be categorised into following types :

  1. Competition,
  2. Parasitism,
  3. Predation and
  4. Antibiosis.

1. Competition : When interaction occurs between two species for the use of same resources and when resources are in short supply is referred to as competition. It is a relationship which involves struggle amongst the organisms for food, shelter, water, sunlight and climate.

2. Parasitism : Parasite is an organism which is dependent upon other living organism for their food and other requirements. Parasitism is an interspecific interrelation in which the individual of one species lives at the cost of the individual of another species, its host which it harms and eventually kills. In this case host is always larger than the parasite. The parasite that is seen on the surface of host plant is called ectoparasite or external parasite and if a parasite is found inside the plant body is said to be an endoparasite or internal parasite.

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Examples:

(i) Parasitic bacteria : Parasitic bacteria cause several diseases in plants and animals. For example, the citrus canker disease of lemon is caused by Xanthomonas citri, black rots of vegetables of Cruciferae group is caused by Xanthomonas campestris. The common diseases caused by bacteria in human beings are diarrhoea, pneumonia, tetanus, leprosy, plague etc.

(ii) Predation : To obtain food by hunting is predation. A predator is an animal or plant that kills and feeds on another organism, its prey. It represents a generalised carnivorous habit. Commonly predators are larger than their prey but this is not always true but predator is in any case always occur as a naturally better equipped hunter than its prey. Most of the predatory organisms are animals but there are some plants (carnivores) also especially fungi which feed upon other animals.

(b) Parasitism :
(a) Difference between Parasitism and Symbiosis:
MP Board Class 12th Biology Solutions Chapter 13 Organisms And Population 6
(b) Differences between Mutualism and Commensalism:
MP Board Class 12th Biology Solutions Chapter 13 Organisms And Population 15
(c) Differences between Hydrosere and Xerosere:
MP Board Class 12th Biology Solutions Chapter 13 Organisms And Population 16

(a) Parasitism : Parasite is an organism which is dependent upon other living organism for their food and other requirements. Parasitism is an interspecific interrelation in which the individual of one species lives at the cost of the individual of another species, its host which it harms and eventually kills. In this case host is always larger than the parasite. The parasite that is seen on the surface of host plant is called ectoparasite or external parasite and if a parasite is found inside the plant body is said to be an endoparasite or internal parasite.

Examples:

(i) Parasitic bacteria : Parasitic bacteria cause several diseases in plants and animals. For example, the citrus canker disease of lemon is caused by Xanthomonas citri, black rots of vegetables of Crticiferae group is caused by Xanthomonas campestris. The common diseases caused by bacteria in human beings are diarrhoea, pneumonia, tetanus, leprosy, plague etc.

(b) Species dominance : Presence of any biotic community or presence of more population of any species biosphere shown its dominance and it is called species dominance which has capacity to reduce other species in population. The effect of dominant speeds is more upon environment or other species.

(c) Biotic potential  : Biotic potential is the ability of a population of living species to increase under ideal environmental conditions sufficient food supply, no predators and a lack of disease. An organisms rate of reproduction and the size of each litter are the primary determining factors for biotic potential.

Odum (1971) distinguished interactions into two broad categories:
(A) Positive interactions and
(B) Negative interactions.

(A) Positive Interactions:
In this type, those type of interactions are considered in which both interacting species are mutually involved to help each other. Here, one interacting species helps the other either one way or on reciprocal terms and may be in the form of nutrition or shelter or substratum or transport. Here interaction may be obligatory or facultative. The positive interactions include three types of interactions. They are :
1. Commensalism : This type of interaction occurs in between two organisms of two different species in which one species benefits and the other is neither benefited nor harmed. e.g., Lichens.

2. Protocooperation : The type of interaction where both population are benefited but not obligatory i.e., not essential for the survival of either population is called protocooperation. This is also known as non-obligatory mutualism. The relationship between hermit crab and sea anemone is an example of proto-cooperation. The crab pses the gastropod (mollusc) shell as a portable shield and the sea anemone eats the leftover food of the crab, which is protected from its predators by the stinging cells of the sea anemone.

3. Mutualism or Symbiosis : When two different species grow together and are mutually benefited, the plants are known as symbiotic plants and the phenomenon is called symbiosis or mutualism. It is a sort of obligatory association. This type the organisms are dependent upon each other for survival. In this type of association, two types of species are physiologically related. This type of relationship may exist in between two plants or in between one plant and one animal or in between two animals.

(B) Negative Interactions :
Those interaction of two different species in which both are harmed or one organism is benefited while other is more or less harmed is referred to as negative interaction. In this type of interaction one population eats the other type of population or one organism does not allow other organisms to grow near it by using the food supply of the other or producing toxic substances. The negative interactions be categorised into following types :

  1. Competition,
  2. Parasitism,
  3. Predation and
  4. Antibiosis.

1. Competition : When interaction occurs between two species for the use of same resources and when resources are in short supply is referred to as competition. It is a relationship which involves struggle amongst the organisms for food, shelter, water, sunlight and climate.

2. Parasitism : Parasite is an organism which is dependent upon other living organism for their food and other requirements. Parasitism is an interspecific interrelation in which the individual of one species lives at the cost of the individual of another species, its host which it harms and eventually kills. In this case host is always larger than the parasite. The parasite that is seen on the surface of host plant is called ectoparasite or external parasite and if a parasite is found inside the plant body is said to be an endoparasite or internal parasite.

Examples:

(i) Parasitic bacteria : Parasitic bacteria cause several diseases in plants and animals. For example, the citrus canker disease of lemon is caused by Xanthomonas citri, black rots of vegetables of Cruciferae group is caused by Xanthomonas campestris. The common diseases caused by bacteria in human beings are diarrhoea, pneumonia, tetanus, leprosy, plague etc.

(ii) Predation : To obtain food by hunting is predation. A predator is an animal or plant that kills and feeds on another organism, its prey. It represents a generalised carnivorous habit. Commonly predators are larger than their prey but this is not always true but predator is in any case always occur as a naturally better equipped hunter than its prey. Most of the predatory organisms are animals but there are some plants (carnivores) also especially fungi which feed upon other animals.

(c) Camouflage : It is a strategy adapted by prey species to escape their predators. Organisms are cryptically coloured so, that they can easily mingle in their surroundings and escape their predators. Many species of frogs and insects camouflage in their surroundings and escape their predators.

(d) Mutualism :

Odum (1971) distinguished interactions into two broad categories:
(A) Positive interactions and
(B) Negative interactions.

(A) Positive Interactions :
In this type, those type of interactions are considered in which both interacting species are mutually involved to help each other. Here, one interacting species helps the other either one way or on reciprocal terms and may be in the form of nutrition or shelter or substratum or transport. Here interaction may be obligatory or facultative. The positive interactions include three types of interactions. They are :
1. Commensalism : This type of interaction occurs in between two organisms of two different species in which one species benefits and the other is neither benefited nor harmed. e.g., Lichens.

2. Protocooperation : The type of interaction where both population are benefited but not obligatory i.e., not essential for the survival of either population is called protocooperation. This is also known as non-obligatory mutualism. The relationship between hermit crab and sea anemone is an example of proto-cooperation. The crab pses the gastropod (mollusc) shell as a portable shield and the sea anemone eats the leftover food of the crab, which is protected from its predators by the stinging cells of the sea anemone.

3. Mutualism or Symbiosis : When two different species grow together and are mutually benefited, the plants are known as symbiotic plants and the phenomenon is called symbiosis or mutualism. It is a sort of obligatory association. This type the organisms are dependent upon each other for survival. In this type of association, two types of species are physiologically related. This type of relationship may exist in between two plants or in between one plant and one animal or in between two animals.

(B) Negative Interactions :
Those interaction of two different species in which both are harmed or one organism is benefited while other is more or less harmed is referred to as negative interaction. In this type of interaction one population eats the other type of population or one organism does not allow other organisms to grow near it by using the food supply of the other or producing toxic substances. The negative interactions be categorised into following types :

  1. Competition,
  2. Parasitism,
  3. Predation and
  4. Antibiosis.

1. Competition : When interaction occurs between two species for the use of same resources and when resources are in short supply is referred to as competition. It is a relationship which involves struggle amongst the organisms for food, shelter, water, sunlight and climate.

2. Parasitism : Parasite is an organism which is dependent upon other living organism for their food and other requirements. Parasitism is an interspecific interrelation in which the individual of one species lives at the cost of the individual of another species, its host which it harms and eventually kills. In this case host is always larger than the parasite. The parasite that is seen on the surface of host plant is called ectoparasite or external parasite and if a parasite is found inside the plant body is said to be an endoparasite or internal parasite.

Examples:

(i) Parasitic bacteria : Parasitic bacteria cause several diseases in plants and animals. For example, the citrus canker disease of lemon is caused by Xanthomonas citri, black rots of vegetables of Cruciferae group is caused by Xanthomonas campestris. The common diseases caused by bacteria in human beings are diarrhoea, pneumonia, tetanus, leprosy, plague etc.

(ii) Predation : To obtain food by hunting is predation. A predator is an animal or plant that kills and feeds on another organism, its prey. It represents a generalised carnivorous habit. Commonly predators are larger than their prey but this is not always true but predator is in any case always occur as a naturally better equipped hunter than its prey. Most of the predatory organisms are animals but there are some plants (carnivores) also especially fungi which feed upon other animals.

(e) Interspecific competition : It is an interaction between individuals of different species where both species get negatively affected. For example, the competition between flamingoes and resident fishes in South American lakes for common food resources i.e., zooplankton.

Question 16.
With the help of suitable diagram describe the logistic population growth curve.
Answer:
Logistic Growth:

  1. The resources become limited at certain point of time so, no population can grow exponentially.
  2. This growth model is more realistic.
  3. Every ecosystem or environment or habitat has limited resources to support a particular maximum number of individuals called is carrying capacity (K).
  4. When N is plotted in relation to time t, the logistic growth show sigmoid curve and is also called Verhulst-Pearl logistic growth. It is given by the following equation:

MP Board Class 12th Biology Solutions Chapter 13 Organisms And Population 9
Where, N = Population density at time t
R = Intrinsic rate of natural increase
K = Carrying capacity.
MP Board Class 12th Biology Solutions Chapter 13 Organisms And Population 10
a = When resources are not limiting the growth, plot is exponential
b = When resources are limiting die growth. Plot is logistic, k is carrying capacity.

Question 17.
Select the statement which explains best parasitism:
(a) One organism is benefited
(b) Both the organism are benefited
(c) One organism is benefited, other is not affected
(d) One organism is benefited, other is affected.
Answer:
(d) One organism is benefited, other is affected.

Question 18.
List any three important characteristics of a population and explain.
Answer:
The three important characteristic of a population are:

1. Population density : The number of individuals of a species per unit area, or a volume is called population density.
PD=\(\frac { N }{ s }\)

Where, PD = Population density
N = Number of individuals in a region
S = Number of unit area in a region.

2. Birth rate : It is expressed as the number of births per 1000 individuals of a population per year.

3. Death rate : It is expressed as the number of deaths per 1000 individuals of a population per year.

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Organisms And Population Other Important Questions and Answers

Organisms And Population Objective Type Questions

1. Choose the Correct Answer:

Question 1.
Unit, easily subjected for identification at level of organisation is:
(a) Cell
(b) Tissue
(c) Organ
(d) Individual organism.
Answer:
(d) Individual organism.

Question 2.
Useful chemical compound in interspecific communication is:
(a) Allochemix
(b) Caromones
(c) Auxin
(d) Pheromones.
Answer:
(d) Pheromones.

Question 3.
Study of one species and its inter-relation with environment is called:
(a) Community ecology
(b) Autecology
(c) Ethology
(d) Forest ecology.
Answer:
(b) Autecology

Question 4.
The factor which does not effect the magnitude of population is:
(a) Migration
(b) Emigration
(c) Imigration
(d) Natality.
Answer:
(a) Migration

Question 5.
Availability of two various forms of an organism of a species is called:
(a) Dimorphism
(b) Trimorphism
(c) Polymorphism
(d) None of these.
Answer:
(a) Dimorphism

Question 6.
Birth of 1000 persons/annually in unit time is called:
(a) Death rate
(b) Biotic rate
(c) Birth rate
(d) Growth rate.
Answer:
(c) Birth rate

Question 7.
The permanent stage of succession is known as:
(a) Ecosere
(b) Climax stage
(c) Successive stage
(d) Ecotone.
Answer:
(b) Climax stage

Question 8.
The plant groups present in between two communities are called:
(a)Ecad
(b) Ecotype
(c) Ecotone
(d) None of these.
Answer:
(c) Ecotone

Question 9.
Xerosere starts from:
(a) Water
(b) Rock
(c) Marshy place
(d) All of the above.
Answer:
(b)Rock

Question 10.
The successive development of plant communities is called:
(a) Aggregation
(b) Succession
(c) Reaction
(d) None of these.
Answer:
(b) Succession

Question 11.
Which one is the example of mangrove:
(a) Rhizophora
(b) Eichhomia
(c) Avicennia
(d) Both (a) and (b).
Answer:
(d) Both (a) and (b).

Question 12.
Pneumatophores are the characteristic feature of:
(a) Mangrove plants
(b) Mesophytes
(c) Hydrophytes
(d) Xerophytes.
Answer:
(a) Mangrove plants

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Question 13.
Vascular bundles are feebly developed in:
(a) Hydrophytes
(b) Xerophytes
(c) Psammophytes
(d) Halophytes.
Answer:
(a) Hydrophytes

Question 14.
Phyllode is a modification of:
(a) Root
(b) Stem
(c) Leaf
(d) None of these
Answer:
(c) Leaf

Question 15.
Phyllodade is a modification of:
(a) Root
(b) Stem
(c) Leaf
(d) Petiole.
Answer:
(b) Stem

Question 16.
Rootless plant is:
(a) Wolffia
(b) Eichomia
(c) Lenina
(d) Jussiaea.
Answer:
(a) Wolffia

Question 17.
Free floating plant is:
(a) Pistia
(b) Eichomia
(c) Azolla
(d) All of the above
Answer:
(d) All of the above

Question 18.
Vivipary is found in:
(a) Hydrophytes
(b) Xerophytes
(c) Epiphytes
(d) Mangrove plants.
Answer:
(d) Mangrove plants.

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2. Fill in the Blanks:

  1. …………………………… is a rootless free floating aquatic plant.
  2. Respiratory roots are found in ……………………………. plants.
  3. The germination of seeds over parent plants is called ……………………………..
  4. Stem become flattened leaf like and succulent is called ………………………….
  5. In Pistia …………………………. is present in place of root cap.
  6. The relation between root of pinus and fungus is known as ……………………………….
  7. Refflesia is ……………………………… parasite.
  8. The part of earth where organism live is known as ………………………….
  9. The organisms which feed on other dead organisms are known as …………………………..
  10. …………………………………. are known as woody climbers.
  11. Orchid is …………………………… plant.
  12. The offspring of male donkey and female horse is known as ………………………………….
  13. Santhalum is a ………………………………. parasitic plant.

Answer:

  1. Wolffia
  2. Mangrove
  3. Vivipary
  4. Phylloclade
  5. Root pocket
  6. Mutualism
  7. Total root
  8. Lithosphere
  9. Saprophytes
  10. Lianas
  11. Epiphytes
  12. Mule
  13. Partial root.

3. Match the Following:

MP Board Class 12th Biology Solutions Chapter 13 Organisms And Population 11
Answer:

  1. (d)
  2. (e)
  3. (a)
  4. (b)
  5. (c)

MP Board Class 12th Biology Solutions Chapter 13 Organisms And Population 12
Answer:

  1. (b)
  2. (d)
  3. (a)
  4. (c)
  5. (e).

MP Board Class 12th Biology Solutions Chapter 13 Organisms And Population 13
Answer:

  1. (d)
  2. (a)
  3. (b)
  4. (e)
  5. (c).

4. Answer in One Word/Sentence:

  1. Give the term for scientific study of human population.
  2. Name any animal which lays egg in the nest of other animal.
  3. What is the name of woody climbers ?
  4. Give an example of species polymorphism.
  5. Give an example of sexual dimorphism.
  6. Name two symbiotic partners of lichen.
  7. Which type of association is found between two partners of lichens ?
  8. Give an example of proto-cooperation.
  9. How many groups of plants are given by warming on the basis of water relations ?
  10. Name any rootless angiospermic plant.
  11. Name any two free floating plants.
  12. Name any two amphibian plants.
  13. Name the adaptations found in the plants of Eichhomia and Trapa due to which their plants become able to float on water.
  14. Name any one mangrove plants.
  15. Name the plant in which pneumatophores are found.
  16. Name any plant in which stem is modified into leaf like structure and leaves are modified into spines.

Answer:

  1. Demography
  2. Cuckoo
  3. Liana
  4. Honeybee
  5. Honeybee
  6. Algae and Fungi
  7. Mutualism
  8. Lichen
  9. Three groups
  10. Wolffia
  11. Hydrilla, Salvia
  12. Ranunculus, Sagittaria
  13. Aquatic
  14. Rhizophora
  15. Marshy
  16. Opuntia.

MP Board Solutions

Organisms And Population Very Short Answer Type Questions

Question 1.
Howmany groups of plants are given by warming on the basis of water relations?
Answer:
Three group.

Question2.
Name any rootless angiospermic plant.
Answer:
Wolffia.

Question 3.
Name any four free floating plants.
Answer:
Pistia, Trapa, Lemna and Echinus.

Question 4.
What is called the flattened leaf like structure of Opuntia?
Answer:
Phylloclade.

Question 5.
Name any two mangrove plants.
Answer:
Rhizophora, Avicennia.

Question6.
Name the vegetation found in sundarban delta.
Answer:
Mangrove vegetation.

Question 7.
Name the plant in which pneumatophores are found.
Answer:
Rhizophora.

Question 8.
Give the term for scientific study of human population.
Answer:
Demography.

Question9.
What is sex ratio of India according to 2001 census?
Answer:
933 females per 1000 of males.

Question 10.
Name any animal which lays egg in the nest of other animal.
Answer:
Koyal.

Question 11.
Give the name of larva of frog, salamander and moths.
Answer:
Tadpole, Axolotal, Catterpillar.

Question 12.
Give the reason for increase in population.
Answer:
Decrease in death rate.

Question 13.
Give example of species polymorphism.
Answer:
Honeybee.

Question 14.
Name the species found in different geographical areas.
Answer:
Allopatric.

Question 15.
Write the name of any saprophytic angiospermic plant
Answer:
Monotropa.

Question 16.
What is called the relationship between hermit crab and sea-anemone ?
Answer:
Protocooperation.

Question 17.
Why insectivores eat insects ?
Answer:
To fulfill the need of nitrogen.

Question 18.
Which are main abiotic factor ?
Answer:
Temperature, water, light, soil.

Question 19.
Give the name of one insectivores plant.
Answer:
Utricularia.

MP Board Solutions

Organisms And Population Short Answer Type Questions

Question 1.
What is ecological competition ?
Answer:
Ecological competition is the struggle between two organisms for the same resources within an environment.

Question 2.
Name the speciality of any population.
Answer:
Any population has some speciality these are :

  1. Population density
  2. Growth rate
  3. Death rate
  4. Age distribution
  5. Biotic capacity
  6. Population growth form
  7. Changes of population
  8. Populatidn dispersion.

Question 3.
Give definition of:

  1. Population
  2. Population density
  3. Biotic potential
  4. Growth rate
  5. Birth rate.

Answer:
1. Population : A community of animals, plants or humans among whose members inbreeding occurs.

2. Population density : Population density is a measurement of population per unit area or unit volume.

3. Biotic potential : Biotic potential is the ability of a population of living species to increase under ideal environmental conditions sufficient food supply, no predators and a lack of disease. An organisms rate of reproduction and the size of each litter are the primary determining factors for biotic potential.

4. Growth rate : Human population growth is the increase in the number of individuals in a population. Global human population growth amounts to around $5 million annually.
Growth rate=\(\frac { Annually birth }{ Mid year population }\)X100

5. Death rate : The death rate is the number of people per thousand who die in a particular are during a particular period of time.
Death rate=\(\frac { Annual death }{ Mid year population }\)X100

Question 4
What suggestions will you give for awakening people towards population control ?
Answer:
Following things can be done for controlling the population:

  • Promotion of education : Misunderstanding can be avoided by promotion of education such as:
    • Children are gift of god,
    • More income from the more children
  • To introduce for reality of population growth.
  • Uses of family planning techniques
  • Restriction of more than one marriage.
  • To decrease birth rate.

MP Board Solutions

Question 5.
Give two examples of each:
Symbiotic, commensal, phytoplankton, zooplankton and rooted floating plant
Answer:

  • Symbiotic – (i) Escherichia, (ii) Triconimpha
  • Commensal – (i) Orchid and Trees, (ii) Hermit crab
  • Phytoplankton – (i)Nostoc, (ii) Anabaena
  • Zooplankton – (i) Paramocium, (ii) Euglena
  • Rooted floating plant – (i)Wolffia,(ii)Lemna.

Question 6.
Write the differences:

  1. Species and Population
  2. Population growth and Population density
  3. Mono-specific and Polyspecific Population
  4. Competition and Scattering.

Answer:
1. Species and Population : Population on defined as organisms that belong to the identical species and identical geographical niche or area. The said area should enable these species to interbreed with each other.

2. Population growth and Population density : In biology, Population growth is the increase in the number of individuals in a population but population density is a measurement of population per unit area, it is a quantity of type number density.

3. Monospecific or Polyspecific population : Monospecific population is the population of individuals of only one species but polyspecific or mixed population is the population of individuals of more than one species and it is generally referred to as a community.

4. Competition and Scattering : Competition is in general a contest between two or j more rivalry between two or more entities, organisms, animals, economic groups or social groups etc. Population scattering is a method which shows equilibrium by interaction of population. In population, scattering seeds away from the parent plant.

Question 7.
Give four reasons ofpopulation growth in India.
Answer:
Four reasons of population growth in India are as follows :

  1. Increasing growth rate.
  2. Decreasing death rate.
  3. No importance of education and promotion of education is less.
  4. Conservative.

Question 8.
Explain, The formation of New species.
Answer:
Although all life on earth shares various genetic similarities, only certain organisms combine genetic information by sexual reproduction and have offspring that can than successfully reproduce. Scientists call such organisms members of the same biological species.

Question 9.
What do you mean by population equilibrium?
Answer:
Population equilibrium : When growth pattern of any population is observed then it becomes clear that any population increases at faster rate in the beginning in a new area and reaches to a maximum limit and then remain constant for long time.This phase is called as population equilibrium. At equilibrium birth and death rate of any population become equal.

Question 10.
Write cooperative interactions between the members of a species.
Answer:
The cooperative intraspecific interactions involve help to other members. The co-operative interaction amongst the individuals of a species is necessary for reproduction, perpetuation, parental care of young ones, social organization, territoriality, protection and food, etc.

1. Cooperation for protection and food : For protection and food, members of a species may form groups. Such organisms which live in group are called as gregarious.

2. Cooperation for reproduction : It is necessary for reproduction in which adult male and female comes together for mating,

3. Social organization : Active association for mutual benefits amongst the individuals of same species often bring social organization. Success of these organizations is measured in the terms of the survival or colony. Honey-bees, ants, wasps and termites, etc. form well-organized societies showing division of labour and polymorphism. In these social insects, a large number of individuals of different kinds live together in the colony aftd vyprk collectively for the benefit of the group.

The insect societies are formed of different castes such as workers, drones (male) and queen which are specialized for the different kind of work. The workers collect and store food, build houses of complicated design and pay special attention to the queen. The drones (male) and queen (female) are mainly concerned with reproduction.

MP Board Solutions

Question 11.
Explain population dispersal in brief.
Answer:
Population dispersal: The movement of individuals of a population from a particular place to another is known as population dispersal. Dispersal of members of population may occur for search of food, escape from enemies or for breeding purpose. There are three types of population dispersal:

1. Immigration : Inward movement of members of other population and settle with local population. It causes increase in population.

2. Emigration : Outward movement of individuals of a population to shift in some other place. It causes decrease in population.

3. Migration : It can be observed in birds. It is periodic departure of organism and returning back to its original place, e.g., Siberian cranes visit India during winters and go back to north during summer.

Question 12.
Write short note on population growth form or pattern.
Answer:
Population growth pattern: The way of growth of population is known as population growth pattern. Population growth shows two patterns :

  • J-shaped form : In some organisms the population increases very fast in the beginning because of some environmental factors, the growth is checked abruptly.
  • S-shaped form : In this pattern, the increase in population is very slow in the beginning, then there is a fast growth rate and then becomes stable.

Question 13.
Give only five examples of communication of informations in animals.
Answer:
Communication of information within a species: Communication may be defined as an act which influences the activity of one individual by some behaviour of another. Most of the animal Species have some mechanism of exchanging information among their members through sight, sound, touch or chemicals. The evolution of the techniques of communication in the animal kingdom is progressive but complex.
Following are few examples:

  • The honeybee gives the information to the other worker bees of the hive regarding availability of nectar in the vicinity by dancing in a special manner on the surface of the hive. Through the round dance they communicate that the availability of the food is very near to the hive and the waggle dance (by moving abdomen) shows the direction and the distance of the food source from the hive.
  • Croaking of male frog attract female frog during breeding season.
  • The dogs express their various intensions by facial expressions and movement of the tail and by making typical sound.
  • Rabbits inform their group members about any sort of danger by tapping their tails.
  • Certain chemical compounds called pheromones are secreted by animals to transmit message to other members of the species. Pheromones are detected by smell or taste.

Question 14.
Write distinguish between:
(a) Parasitism and symbiosis.
(b) Parasitism and Symbiosis.
(c) Mutualism and Commensalism.
Answer:
(a) Difference between Parasitism and Symbiosis:
MP Board Class 12th Biology Solutions Chapter 13 Organisms And Population 14
(b) Differences between Mutualism and Commensalism:
MP Board Class 12th Biology Solutions Chapter 13 Organisms And Population 15
(c) Differences between Hydrosere and Xerosere:
MP Board Class 12th Biology Solutions Chapter 13 Organisms And Population 16

MP Board Solutions

Question 15.
Write short notes on:
(a) Parasitism
(b) Species dominance
(c) Biotic potential.
Ans
(a) Parasitism : Parasite is an organism which is dependent upon other living organism for their food and other requirements. Parasitism is an interspecific interrelation in which the individual of one species lives at the cost of the individual of another species, its host which it harms and eventually kills. In this case host is always larger than the parasite. The parasite that is seen on the surface of host plant is called ectoparasite or external parasite and if a parasite is found inside the plant body is said to be an endoparasite or internal parasite.

Examples: (i) Parasitic bacteria: Parasitic bacteria cause several diseases in plants and animals. For example, the citrus canker disease of lemon is caused by Xanthomonas citri, black rots of vegetables of Crticiferae group is caused by Xanthomonas campestris. The common diseases caused by bacteria in human beings are diarrhoea, pneumonia, tetanus, leprosy, plague etc.

(b) Species dominance : Presence of any biotic community or presence of more population of any species biosphere shown its dominance and it is called species dominance which has capacity to reduce other species in population. The effect of dominant speeds is more upon environment or other species.

(c) Biotic potential : Biotic potential is the ability of a population of living species to increase under ideal environmental conditions sufficient food supply, no predators and a lack of disease. An organisms rate of reproduction and the size of each litter are the primary determining factors for biotic potential.

Question 16.
Explain population fluctuation.
Answer:
Population is generally a group of individuals of a particular species occupying a particular area at a specific time.
Population fluctuation: Any increase or decrease in number of individuals in a population from its equilibrium state is known as population fluctuation. It may occur due to various reasons, such as due to change in climate or due to change in physical environment or due to predators.

Question 17.
Give an example for:

  • Heliophytes
  • Sciophytes
  • Viviparous.

Answer:

  • Heliophytes: Sunflower, AmranthuS.
  • ciophytes: Java moss, Lycopodium, Polytrichus.
  • Viviparous : Rhizophora, Salicomia, Sonneratia.

MP Board Solutions

Organisms And Population Long Answer Type Questions

Question 1.
Write characteristic features of aquatic plants.
Answer:
Characteristic features of aquatic plants (Hydrophytes):

  • The cuticle is either absent or very thinly deposited on the epidermis.
  • Usually stomata are absent, if present they are non-functional.
  • Many air chambers or large intercellular spaces are present inside the plant body of hydrophytes.
  • The whole body of the plant helps in the absorption of water and minerals.
  • Root system is feebly developed and usually non-branched or less branched. Some hydrophytes like Wolffia lack roots.
  • The mechanical tissues are less distributed.
  • The vascular tissues are either absent or feebly developed in the case of hydrophytes.

Question 2.
Describe the anatomical adaptation of xerophy tic plants.
Answer:
The anatomical adaptations of xerophytic plants are :

1. The epidermis of xerophytic plant organs is covered by thick cuticle. It protects plants against heavy transpiration and also provides mechanical strength to some extent.

2. Epidermis may be multiple layered which also reduces the rate of transpiration. Examples: Banyan, Nerium etc.

3. Except some monocotyledonous plants the stomata are restricted to the lower surface of the leaves. The stomata are generally sunken and surrounded by many hairs.

4. Hypodermis in xerophytes is multilayered and sclerenchymatous which checks evaporation of water.
Example: Pinus needle.
MP Board Class 12th Biology Solutions Chapter 13 Organisms And Population 17

5. Mesophyll tissue is well differentiated into palisade and spongy parenchyma but palisade parenchyma is more in number than spongy parenchyma.
Examples: Pinus needle, Nerium leaf.

6. Vascular bundles are well developed and differentiated into xylem and phloem. Vascular bundles are comparatively more in number. Besides vascular bundles, mechanical tissues are well developed.

7. Leaves of some xerophytes have some rolling devices due to presence of motor cells of bulliform cells in the epidermal zone.
Examples: Poa pratensis, Agropyron, Ammophila etc.

8. Stomata in certain desert plants such as Capparis spirwsa and Aristida ciliata may sometimes get blocked due to deposition of resinous matter or wax. This adaptation is also known to reduce the loss of water during transpiration.

Question 3.
Describe the morphological adaptations of aquatic plants.
Or
Describe morphological adaptations found in the stem and leaves of xerophytic plants.
Or
Explain in brief, xerophytic plants along with examples.
Answer:
The morphological adaptations of aquatic plants are :

1. Adaptations in roots :

1. Root system is feebly developed and unbranched. Some floating plants like Wolffia, Utricularia etc. and submerged plants like Ceratophyllum lack roots.

2. Root hairs are absent except rooted floating hydrophytes. In most of the hydrophytes roots are meaningless as the entire surface of the plant body is in direct contact with water and acts as absorptive surface. This may probably be the reason why roots in hydrophytes are reduced or absent.

3. True root caps are absent in some free floating hydrophytes and in lieu of that they develop root pockets or root sheaths which protect their tips from injuries.

4. If roots are present they are always of adventitious type e.g., Nymphaea, Nelumbo etc. In Jussiaea modified spongy negative geotrophic floating roots are present whifch provide buoyancy to the plants and also do the job of gaseous exchange.

2. Adaptations in stems :

1. In submerged hydrophytes like Hydrilla, Potamogeton etc. stems are long, slender and flexible.

2. In free floating hydrophytes, stems are modified as thick, stout, stoloniferous or as offset and occur horizontal on the water surface. It bears vegetative bud at their apex and helps in vegetative propagation.

3. In rooted floating hydrophytes or rooted submerged hydrophytes or in marshy plants, stem may be modified as runner or rhizome.

4. The stem may be modified as runner, stolon, tuber to perform vegetative propagation effectively. Usually stems are of perennial nature.

3. Adaptations in leaves :

1.Leaves are thin, long, ribbon shaped in the submerged forms.
Example : Vallisneria, Ceratophyllum etc. or they are finely dissected as found in Ranunculus aquatilis.

2. In rooted floating plants, like Nymphaea, Nelumbo etc. the petioles of leaves show indefinite power of growth and they keep the laminae of leaves always on the surface of water.

3. In free floating plants like Eichomia, Trapa etc. the petioles become characteristically swollen and develop sponginess which keep the plant afloat.

4. Occurrence of two or more than two different types of leaves in a plant is called heterophylly. Examples are Limnophila, Heterophylla, Sagittaria, Ranunculus aquatilis etc. They bear leaves of many types viz., submerged leaves, floating leaves, aerial leaves, linear, ribbon shaped leaves or dissected leaves. Floating leaves are entire and lobed. The ’ broad leaves found on the surface of water transpire actively and regulate the hydrostatic pressure in the plant body. The submerged leaves act as water absorbing orgAnswer: Hetero- phylly is also associated with quantitative reduction in transpiration.

5. In the amphibious or marshy plants, the leaves that are exposed to air show typical mesophytic features. They are leathery and more tough than the submerged and floating hydrophytes.

MP Board Solutions

Question 4.
What do you mean by biotic community ? Describe characteristic features of any biotic community.
Answer:
Biotic community : A biotic community is a localized association of several populations of different species living in a given geographic area of habitat. It represents heterogeneous assemblage of different groups of organisms both plants and animals. Biotic community is composed of smaller units of intimately associated members belonging to different species.

The different species of a community share common environment and their relationships are based on direct or indirect functional interactions. The nature or relationship is determined by the requirements of the members of a community.

Characteristics of a community: Each community has its own characteristics which are not shown by its individual component species.

1. Species diversity : Each community is made up of much different organisms: Plants, animals, microbes, which differ taxonomically from each other. The number of species and population abundance in community also vary greatly.

2. Growth form and structure : Each community have a definite growth form. This different growth form determines the structural pattern of a community.

3. Dominance : In each community, all the species are not equally important. There are relatively only a few of these, which determine the nature of community. These few species exert a major controlling influence on the community. Such species are known as dominants.

4. Succession : Each community has its own development history. It develops as a result of a directional change in it with time.

5. Trophic structure (Self-sufficiency) : Nutritionally, each community, a group of autotrophic plants as well as heterotrophic animals exists as a self-sufficient, perfectly balanced assemblage of organism.

Question 5.
Write cooperative interactions between the members of a species.
Answer:
The cooperative intraspecific interactions involve help to other members. The co-operative interaction amongst the individuals of a species is necessary for reproduction, perpetuation, parental care of young ones, social organization, territoriality, protection and food, etc.

1. Cooperation for protection and food : For protection and food, members of a species may form groups. Such organisms which live in group are called as gregarious.

2. Cooperation for reproduction : It is necessary for reproduction in which adult male and female comes together for mating.

3. Social organization : Active association for mutual benefits amongst the individuals of same species often bring social organization. Success of these organizations is measured in the terms of the survival or colony. Honey-bees, ants, wasps and termites, etc. form well- organized societies showing division of labour and polymorphism. In these social insects, a large number of individuals of different kinds live together in the colony and work collectively for the benefit of the group.

The insect societies are formed of different castes such as workers, drones (male) and queen which are specialized for the different kind of work. The workers collect and store food, build houses of complicated design and pay special attention to the queen. The drones (male) and queen (female) are mainly concerned with reproduction.

Question 6.
Explain interrelationship between various species of a biotic community along with examples.
Answer:
Odum (1971) distinguished interactions into two broad categories:
(A) Positive interactions and
(B) Negative interactions.

(A) Positive Interactions :
In this type, those type of interactions are considered in which both interacting species are mutually involved to help each other. Here, one interacting species helps the other either one way or on reciprocal terms and may be in the form of nutrition or shelter or substratum or transport. Here interaction may be obligatory or facultative. The positive interactions include three types of interactions. They are :
1. Commensalism : This type of interaction occurs in between two organisms of two different species in which one species benefits and the other is neither benefited nor harmed. e.g., Lichens.

2. Protocooperation : The type of interaction where both population are benefited but not obligatory i.e., not essential for the survival of either population is called protocooperation. This is also known as non-obligatory mutualism. The relationship between hermit crab and sea anemone is an example of proto-cooperation. The crab pses the gastropod (mollusc) shell as a portable shield and the sea anemone eats the leftover food of the crab, which is protected from its predators by the stinging cells of the sea anemone.

3. Mutualism or Symbiosis : When two different species grow together and are mutually benefited, the plants are known as symbiotic plants and the phenomenon is called symbiosis or mutualism. It is a sort of obligatory association. This type the organisms are dependent upon each other for survival. In this type of association, two types of species are physiologically related. This type of relationship may exist in between two plants or in between one plant and one animal or in between two animals.

(B) Negative Interactions :
Those interaction of two different species in which both are harmed or one organism is benefited while other is more or less harmed is referred to as negative interaction. In this type of interaction one population eats the other type of population or one organism does not allow other organisms to grow near it by using the food supply of the other or producing toxic substances. The negative interactions be categorised into following types :

  1. Competition
  2. Parasitism
  3. Predation and
  4. Antibiosis.

1. Competition : When interaction occurs between two species for the use of same resources and when resources are in short supply is referred to as competition. It is a relationship which involves struggle amongst the organisms for food, shelter, water, sunlight and climate.

2. Parasitism : Parasite is an organism which is dependent upon other living organism for their food and other requirements. Parasitism is an interspecific interrelation in which the individual of one species lives at the cost of the individual of another species, its host which it harms and eventually kills. In this case host is always larger than the parasite. The parasite that is seen on the surface of host plant is called ectoparasite or external parasite and if a parasite is found inside the plant body is said to be an endoparasite or internal parasite.

Examples:

(i) Parasitic bacteria : Parasitic bacteria cause several diseases in plants and animals. For example, the citrus canker disease of lemon is caused by Xanthomonas citri, black rots of vegetables of Cruciferae group is caused by Xanthomonas campestris. The common diseases caused by bacteria in human beings are diarrhoea, pneumonia, tetanus, leprosy, plague etc.

(ii) Predation : To obtain food by hunting is predation. A predator is an animal or plant that kills and feeds on another organism, its prey. It represents a generalised carnivorous habit. Commonly predators are larger than their prey but this is not always true but predator is in any case always occur as a naturally better equipped hunter than its prey. Most of the predatory organisms are animals but there are some plants (carnivores) also especially fungi which feed upon other animals.

MP Board Class 12th Biology Solutions

 

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