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ECOLOGY

1. Explain the meaning of the following terms

1. Community

Community refers to  all different species that live in one area and interact with each other .

1. Ecosystem

An ecosystem is a complex system that consists of all the living organisms in a particular area, as well as the environment with which the organisms interact. The living organisms and non-living components of the ecosystem interact in such a way as to maintain balance. Ecosystems are divided into biotic (living) and abiotic (non-living) components respectively.

(c ) Habitat

A habitat is a place where an organism makes its home. A habitat meets all the environmental conditions an organism needs to survive. For an animal, that means everything it needs to find and gather food, select a mate, and successfully reproduce.

1. Differentiate between antecology and synecology

Autecology & Synecology are two main branches of ecology. Autecology is the study of individual organism or individual species. It is also known as population ecology. Synecology is the study of group of organisms of different species which are associated together as a unit in form of a community. Also known as community ecology. Autecology helps us to understand the relationships between individual plants and environment. Synecology helps us to understand the relationships between communities and environment.

2. Functions of Ecosystem

The functions of the ecosystem are as follows

• It regulates the essential ecological processes, supports life systems and renders stability.
• It is also responsible for the cycling of nutrients between biotic and abiotic components.
• It maintains a balance among the various trophic levels in the ecosystem.
• It cycles the minerals through the biosphere.

3. Explain the importance of The abiotic components in the ecosystem

Abiotic components  help in the synthesis of organic components that involves the exchange of energy.

4. Classify the types of ecosystems

The ecosystem is the structural and functional unit of ecology where the living organisms interact with each other and the surrounding environment. In other words, an ecosystem is a chain of interactions between organisms and their environment.

An ecosystem can be as small as an oasis in a desert, or as big as an ocean, spanning thousands of miles. There are two types of ecosystem:

1. Terrestrial Ecosystem
2. Aquatic Ecosystem

Terrestrial Ecosystems

Terrestrial ecosystems are exclusively land-based ecosystems. There are different types of terrestrial ecosystems distributed around various geological zones. They are as follows:

1. Forest Ecosystems
2. Grassland Ecosystems

• Tundra Ecosystems

1. Desert Ecosystem
2. Forest Ecosystem

• A forest ecosystem consists of several plants, animals and microorganisms that live in coordination with the abiotic factors of the environment. Forests help in maintaining the temperature of the earth and are the major carbon sink.
• Grassland Ecosystem

In a grassland ecosystem, the vegetation is dominated by grasses and herbs. Temperate grasslands, savanna grasslands are some of the examples of grassland ecosystems.

• Tundra Ecosystem

Tundra ecosystems are devoid of trees and are found in cold climates or where rainfall is scarce. These are covered with snow for most of the year. The ecosystem in the Arctic or mountain tops is tundra type.

• Desert Ecosystem

Deserts are found throughout the world. These are regions with very little rainfall. The days are hot and the nights are cold.

Aquatic Ecosystem

Aquatic ecosystems are ecosystems present in a body of water. These can be further divided into two types, namely:

1. Freshwater Ecosystem
2. Marine Ecosystem

Freshwater Ecosystem

The freshwater ecosystem is an aquatic ecosystem that includes lakes, ponds, rivers, streams and wetlands. These have no salt content in contrast with the marine ecosystem.

Marine Ecosystem

The marine ecosystem includes seas and oceans. These have a more substantial salt content and greater biodiversity in comparison to the freshwater ecosystem.

5. Discuss the structure of the Ecosystem

The structure of an ecosystem is characterised by the organisation of both biotic and abiotic components. This includes the distribution of energy in our environment. It also includes the climatic conditions prevailing in that particular environment. 

The structure of an ecosystem can be split into two main components, namely: 

1. Biotic Components
2. Abiotic Components

The biotic and abiotic components are interrelated in an ecosystem. It is an open system where the energy and components can flow throughout the boundaries.

Biotic Components

Biotic components refer to all life in an ecosystem.  Based on nutrition, biotic components can be categorised into autotrophs, heterotrophs and saprotrophs (or decomposers).

1. Producers include all autotrophs such as plants. They are called autotrophs as they can produce food through the process of photosynthesis. Consequently, all other organisms higher up on the food chain rely on producers for food.
2. Consumers or heterotrophs are organisms that depend on other organisms for food. Consumers are further classified into primary consumers, secondary consumers and tertiary consumers.
   1. Primary consumersare always herbivores that they rely on producers for food.
   2. Secondary consumersdepend on primary consumers for energy. They can either be a carnivore or an omnivore.
   3. Tertiary consumersare organisms that depend on secondary consumers for food.  Tertiary consumers can also be an omnivore.
   4. Quaternary consumers are present in some food chains. These organisms prey on tertiary consumers for energy. Furthermore, they are usually at the top of a food chain as they have no natural predators.

• Decomposers include saprophytes such as fungi and bacteria. They directly thrive on the dead and decaying organic matter.  Decomposers are essential for the ecosystem as they help in recycling nutrients to be reused by plants.

Abiotic Components

Abiotic components are the non-living component of an ecosystem.  It includes air, water, soil, minerals, sunlight, temperature, nutrients, wind, altitude, turbidity, etc. 

6. State and explain
   1. Food Chain

A food chain is a series of nutrient and energy changes that moves through a chain of organisms. It always begins with a producer and terminates with decomposers.

The sun is the ultimate source of energy on earth. It provides the energy required for all plant life. The plants utilise this energy for the process of photosynthesis, which is used to synthesise their food.

During this biological process, light energy is converted into chemical energy and is passed on through successive levels. The flow of energy from a producer, to a consumer and eventually, to an apex predator or a detritivore is called the food chain.

Dead and decaying matter, along with organic debris, is broken down into its constituents by scavengers. The reducers then absorb these constituents. After gaining the energy, the reducers liberate molecules to the environment, which can be utilised again by the producers.

 

1. Food Web

Food web is a network of interconnected food chains. It comprises all the food chains within a single ecosystem. It helps in understanding that plants lay the foundation of all the food chains. In a marine environment, phytoplankton forms the primary producer.

1. Ecological Pyramids

An ecological pyramid is the graphical representation of the number, energy, and biomass of the successive trophic levels of an ecosystem. Charles Elton was the first ecologist to describe the ecological pyramid and its principals in 1927.

The biomass, number, and energy of organisms ranging from the producer level to the consumer level are represented in the form of a pyramid; hence, it is known as the ecological pyramid.

The base of the ecological pyramid comprises the producers, followed by primary and secondary consumers. The tertiary consumers hold the apex. In some food chains, the quaternary consumers are at the very apex of the food chain.

The producers generally outnumber the primary consumers and similarly, the primary consumers outnumber the secondary consumers. And lastly, apex predators also follow the same trend as the other consumers; wherein, their numbers are considerably lower than the secondary consumers.

7. Give an example of an organism that enters ‘diapause’ and why?
   Many zooplanktons in lakes and ponds enter diapause. They enter diapause to escape unfavourable environmental conditions and to delay the overall development.
8. Mention how do bears escape from stressful time in winter. Bears escape from stressful time in winter by going into hibernation
9. Why are green plants not found beyond a certain depth in the ocean? Beyond a certain depth, green plants are not found, because light is unavailable in that zone.
10. How do animals like fishs and snails avoid summer related unfavourable conditions?

Fish migrate and snails go into aestivation or summer sleep to avoid summer-related problems.

11. Explain why green plants are referred to  as primary producers in an ecosystem

Green plants use sunlight and carbon dioxide from the atmosphere to produce carbohydrates by the process of photosynthesis. Since, plants produce food for themselves, they are known as producers.

12. State four adaptation of cactus plant to its environment

Leaves are reduced to spines to reduce water loss through transpiration. Wide and deep roots absorb rainwater on the surface and reach the underground deep water. Sunken stomata to reduce water loss. Fleshy and thick stems to store water and perform photosynthesis, waxy coating on the stem to retain water.

13. How do prickles help cactus survive in desert? Give two methods.
    The two methods by which prickles help cactus survive in desert are:

(i) By reducing and altering outer surface to reduce evaporation of water.

(ii) By providing defense against grazing animals.

14. When and why do some animals like snails go into aestivation?
    During stressful conditions of the habitat and inability to migrate, animals like snails undergo aestivation and protect themselves
15. When and why do some animals go into hibernation?  
    When unfavourable conditions are for a short time and if the animals could not migrate, they undergo hibernation to avoid stressful winter conditions.
16. List any two physiological responses that help you to gradually get acclimatised to high altitudes when you go from the plains.

The physiological condition or responses in order to get acclimatised to high attitudes are:

(i) To compensate low oxygen, the production of red blood cells is increased.

(ii) High haemoglobin content and its decreased binding capacity.
(iii) Faster breathing rate (any two).

17. Define homeostasis. The process to maintain the constancy of internal environment of the body, despite varying external environmental conditions is called homeostasis
18. When and why do some animals like frogs hibernate?
    When unfavourable conditions are for a short time period and animals are unable to migrate, they hibernate to avoid the stress winter.
19. Some organisms suspend their metabolic activities to survive in unfavourable condition. Explain with the help of any four examples.

.Examples of organisms that suspend their metabolic activities in unfavourable condition.

(i) Bacteria, fungi and lower plants They form thick-walled spores, which help them to survive in unfavourable conditions. Spores germinate on  return of favourable conditions.
(ii) Higher plants Seeds and some other vegetative reproductive structures serve as means to tide over periods of stress. They reduce their metabolic activity and undergo dormancy.
(iii) Animals they undergo hibernation or aestivation, if unable to migrate. For example, some snails and fishes.
(iv) Zooplanktons they enter diapause (suspended development) under unfavourable conditions.

20. Explain the response of all communities to environment over time. 
21. Response of communities to environment:

(i) Some organisms maintain homeostasis by physiological or behavioural means (regulate).

(ii)The internal environment in majority of animals and nearly all plants change with the change of external environment (conform).

(iii)Some organisms leave their habitats temporarily during unfavourable conditions and return back when conditions become favourable (migrate).

(iv)Some organisms suspend their metabolic activities to avoid stress by timely escaping, e.g. hibernation and aestivation.

22. Distinguish between Diapause and hibernation
    
23. How does our body adapt to low oxygen availability at high altitudes?

The physiological condition or responses in order to get accl imatised to high attitudes are:

• To compensate low oxygen, the production of red blood cells is increased.
  (ii) High haemoglobin content and its decreased binding capacity.
  (iii) Faster breathing rate (any two).

 

24. Why are small animals rarely found in the polar regions?

Small animals have a large surface area relative to their volume. So, they tend to lose body heat very fast during cold conditions. They need to spend more energy to generate body heat. Due to this smaller animals are rarely found in polar regions.

25. How does human body maintain constant temperature both in summers and winters? Explain.

Human body maintains constant body temperature (37°C) as follows:
In summers, the outside temperature is very high than our body temperature. Due to this, profuse sweating occurs. This causes evaporation and cooling effect on the body.
In winters, the outside temperature is much lower than our body temperature. This causes shivering, a kind of exercise that produces heat and raises the body temperature.

26. State how the constant internal environment is beneficial to organisms.
    (ii)Explain any two alternatives by which organisms can overcome stressful external conditions.

Constant internal environment is beneficial to organisms as it permits all biochemical reactions and physiological functions to proceed with maximal efficiency, thereby enhancing the overall efficiency of organism.
(ii) The two alternatives by which organisms can overcome stressful external conditions are

1. Migration-organisms move temporarily to a favourable area under stressful conditions and return back when the period is over.
2. Hibernation and aestivation are ways to escape the stress during winters and summers respectively.
3. Water is very essential for life. Write any three features both for plants and animals which enable them to survive in water scarce environment,

Adaptation in plants

• Thick cuticle on their leaf surface.
• Stomata are arranged in deep pits (sunken) to minimise water loss through transpiration(iii) Leaves are reduced to spines. The photosynthetic function is carried out by thick, fleshy flattened stems.

Adaptation in animals

(i) Kangaroo rat meets the water requirement through internal oxidation of fat. They concentrate their urine, so that minimum volume of water is excreted.

(ii)Snails undergo aestivation during summers. Organisms either migrate or suspend their metabolic activities when conditions are stressful for short duration. In such conditions, organisms are as follow:
(i) Moving away from stressful habitat to more favourable area and return to their habitat when stressful period is over. For example, birds from Siberia and other cold countries migrate to Bharatpur Sanctuary of Rajasthan.

(ii) Hibernating (frogs) or aestivating (snails) or undergo diapause (zooplanktons).
(iii) Thick-walled spores are formed in stressful conditions and germinate under suitable conditions, e.g. bacteria, fungi and lower groups of plants.

28. How do organisms like fungi, zooplanktons and bears overcome the temporary short-lived climatic stressful conditions? Explain.

(i)Fungi They produce various kinds of thick-walled spores to survive under unfavourable conditions, which germinate on return of favourable conditions.

(ii) Zooplanktons They enter diapause, a stage of suspended development under unfavourable conditions.

(iii)Bears They hibernate during winter to escape the time of unfavourable conditions.

29. The following graph represents the organismic response to certain environmental condition (e.g. temperature)
    
30. (i)Which one of these A or B depicts conformers?

(ii)What does the other line graph depict?
(iii)How do these organisms differ from each other with reference to homeostasis?

(iv)Mention the category to which human belong.  
(i) A depicts conformers.

The other line B depicts regulators.

Differences between conformer and regulator are:

(iv) Humans are regulators.

30. List the different ways by which organisms cope or manage with abiotic stresses in nature. Explain any three ways.    
    Organisms cope up with abiotic stress by:
    (i)Regulating Some organisms maintain homeostasis by physiological and behavioural means. They are called regulators, In summers, when outside temperature is more, we sweat profusely that results in evaporative cooling to bring down the body temperature. In winters, when temperature is low, we shiver (a kind of exercise) that produces heat and raise the body temperature.

Conformating Organisms that cannot maintain a constant internal environment. Their body temperature changes with the ambient temperature. Such animals are called conformers. For example, small animals have larger surface area relative to their volume. They lose body heat very fast in low temperature. So, they expend energy to generate body heat through metabolism for adjusting.
(iii) Migrating The temporary movement of organisms from the stressful habitat to a more hospitable area and return when favourable conditions reappear is called migration. The long distance migration is very common in birds.

31. (i) List any four abiotic components that lead to variations in the physical and chemical conditions of habitats.
    (ii) Explain the impact of these components on the distribution of organisms in different habitats.

(i)Temperature, water, light and soil.

(ii) (a) Temperature influences the kinetics of enzymes and thereby the metabolism and other physiological functions of the organisms.
Organisms may be eurythermal and can tolerate a wide range of temperature and stenothermal that can tolerate only a narrow range of temperature.

(b)Water is important to sustain life and productivity and distribution of plants is dependent on water.
Freshwater forms cannot thrive in sea water and vice versa.
(c)Light influences photosynthesis of plants. Light also influences the flowering in plants and timing of foraging, reproduction and migratory activities of animals.
Aquatic plants occupy different depths depending on their pigments and the light available.
(d)Soil influences vegetation by the water holding capacity, topography and its composition.

32. State Gause’s competitive exclusion principle.  
    Gause’s competitive exclusion principle states that two competiting species for same resource cannot co-exist, if all other ecological factors are constant.
33. In a pond, there were 20 Hydrilla plants. Through reproduction, 10 new Hydrilla plants were added in a year. Calculate the birth rate of the population.  
    

32. If 8 individuals in a laboratory population of 80 fruitflies died in a week, then what would be the death rate for population for the said period?
    
33. In a pond, there were 200 frogs.40 more were bom in a year. Calculate the birth rate of the population.
    

36. State four benefits of recycling wastes in environmental conservation
    • helps in restoration of nutrients back to the environment
    • helps to reduce accumulation of waste in the environment
    • helps in enhancing resource efficiency
    • helps in ensuring  environmental sanitation and hygiene
37. Explain how deforestation  influences the level of atmospheric carbon dioxide

Forests store large amounts of carbon. Trees and other plants absorb carbon dioxide from the atmosphere as they grow. This is converted into carbon and stored in the plant’s branches, leaves, trunks, roots and in the soil.

When forests are cleared or burnt, stored carbon is released into the atmosphere, mainly as carbon dioxide. Whilst forests are important carbon sinks, meaning they draw down carbon dioxide from the atmosphere, the carbon stored in these sinks is part of an active, relatively quick carbon cycle. As living things (including trees) die and decay, the carbon that they once stored is released back into the atmosphere.

By contrast, carbon stored underground in the form of fossil fuels such as coal, oil and gas, is much more stable, and is part of a much slower carbon cycle. Without the influence of humans burning these fossil fuels for energy, this carbon would be unlikely to reach the atmosphere. When fossil fuels are burned, carbon from dead and decayed plants, animals and phytoplankton that lived hundreds of millions of years ago (before dinosaurs existed), is released into the atmosphere in the form of carbon dioxide.

38. .In capture-recupture experiment, 300 beetles  were captured, marked and released . After a few days, a 100 beetles from the same habitats were captured and 50 of them were found to be marked. calculate the population size of the beetles in  this habitat

EPS = TFC  X  TSC

                   TRS

Where

EPS =  Estimated population size

TFC =  Total number captured in 1^st sample

TSC=  total number captured in 2^nd  sample

TRS=   Total number of marked individuals recaptured

Therefore  300 x 100

                          50

                       = 600

Suggest any four reasons as to why the population size calculated in (a) above is just an estimate

Marked individuals distribute evenly

No migration in and out of the population

There are few births and deaths

Method of marking does not affect the individuals

Marks made does not come off

39. A pest control technician captures and applies ear tag to 23 brown rats which he then releases. A week later  he traps 29 brown rats , 11 of which  have ear tags . Calculate the estimated population of brown rats  in that ecological zone.

EPS = TFC  X  TSC

                 TRS

            Therefore  23 x 29

                               11          = 60

40. Why do predators avoid eating Monarch butterfly? How does the butterfly develop this protective feature?   

Predators avoid the monarch butterfly as it is highly distasteful to its predators (birds) because of a special chemical present in its body. It acquires this chemical during the caterpillar stage by feeding on a poisonous weed

41. Mention any two significant roles predation plays in nature.
    Significant roles played by predators are predators keep prey population under control. They help in maintaining species diversity in a community by reducing the intensity of competition
42. List two advantages that a mycorrhizal association provides to the plant.  

Mycorrhizal association helps plants in
(i) Providing resistance to root borne pathogens.
(ii) Absorbing nutrients.

43. (a)  Define the term  trophic level
    • Identify two trophic levels  in an ecosystem
44. (a)Name two denitrifying bacteria
    • Explain the role of  denitrifying bacteria in the nitrogen cycle
45. (a)Highlight two sources of errors  during measurement of light intensity
    • State the precaution to be taken against each error
46. Construct an age pyramid which reflects an expanding growth status of human population.  
    

The age pyramid geometrically represents the proportions of different age groups in population. The triangular shape of age pyramid represents the expanding growth status of human population.

47. Construct an age pyramid which reflects as stable growth status of human population.
    

The age pyramid that reflects a stable growth status of human population can be represented as follows

48. Differentiate between commensalism arid mutualism by taking one example each from plants only.  

Commensalism is the kind of interaction between species in which one is benefitted and other is neither benefitted nor-harmed. Example of such association is orchid growing as an epiphyte on a mango tree, which remains unaffected by its growth.
Whereas mutualism is the type of interaction in which both the species involved are benefitted. e.g. lichen representing mutual ‘ association between algae and fungi, in which algae is protected by fungi, which also provides nutrients for synthesis of food, while algae provides food to fungi, as they are incapable of synthesising their own food.

49. Provide two reasons that make the count of prokaryotic species difficult.

The two reasons that make the count of prokaryotic species difficult is
(i) they are microscopic not visible by naked eyes.
(ii)they form dense colonies, i.e. population size is so, huge that counting is time taking and almost possible.
(iii) the rate of growth is very fast in prokaryotic species, which may almost double itself while counting

50. How do plants benefit from having mycorrhizal symbiotic association?
    Benefits to plants having mycorrhizal association are:
    (i) The fungus absorbs nutrients from the soil and passes it to the plant.
    (ii) Mycorrhiza provide resistance to root-borne pathogens.
    (iii) They show increased tolerance to salinity and drought.
    (iv) An overall increase occurs in plant growth and development.
51. .In a pond, there were 40 lotus plants. After a year, the number rose to 56. Calculate birth rate of a lotus plant.

                The birth rate of lotus plant

50. Draw and explain expanding age pyramids of human population. Why is it so called?
    .The age pyramid geometrically represents the proportions of different age groups in population. The triangular shape of age pyramid represents the expanding growth status of human population.
    
    Expanding age pyramid is so called as it represents the growing status of populations growth.
51. (i) Write the importance of measuring the size of a population in a habitat or an ecosystem.

(ii) Explain with the help of an example, how the percentage  cover is a more meaningful measure of population size than mere numbers?    

(i) Measurement of population in a habitat determines the relative abundance of a particular species and its effect on the available resources of that particular habitat.
(ii) The percentage cover is more meaningful measure of population size than mere numbers because the relative abundance of a species is not only determined by number of individuals but by both the relative abundance in biomass and number.
e.g. in a unit area the number of grass species or relative abundance in number is high but not the relative biomass, if the same area has one or two Ficus bengalensis tree, it is very low in relative abundance but high in relative abundance of biomass

54. Study the three different age pyramids, for human population given below and answer the questions that follow
    
    
    
55. (i)Write the names given to each of these age pyramids.
    (ii)Mention the one which is ideal for human population and why?
    (i) A – Expanding, B – Stable,C -Declining
    (ii) Stable population is preferred.It is beneficial for survival and better living of the human population. It is helpful for planning welfare activities.
56. Why is predation required in a community of different organisms?
    .Requirement of predation:

(i) Acts as a conduit for energy transfer across trophic levels.
(ii) Keep the prey population under control.
(iii) Helps in maintaining species diversity in a community by reducing the intensity of competition.

(iv) Biological control of pests is based on predation.

57. (i) What is an age pyramid?

(ii) Explain with the help of figures, the three different types of age pyramids represented by human population.
(i)The graphic representation of the no. of individuals in the different age groups of a population, at a given time is known as age pyramid.

(ii)Age pyramid

When the age distribution (per cent individuals of a given age or age group) is plotted for the population, this is called age pyramid.

Population at any given time is composed of individuals of different ages.

For human population, the age pyramids generally show age distribution of males and females in a combined diagram.

The shape of the pyramids reflects the growth status of the population that whether it is expanding (triangular shaped), stable (bell-shaped) or declining.

58. (ii) Differences between mutualism and competition are
    
59. (b) Difference between commensalism and amensalism is:
    

59. State what does standing crop of a trophic level represent.
    Standing crop represents the total mass of living material or energy content of all the organisms of a trophic level at a particular time and location
60. Mention the role of pioneer species in primary succession on rocks. 

Lichens are the pioneer species in the succession on rocks. They secrete acids to dissolve the rock and help in weathering and soil formation and pave way to small plant like bryophytes.

61. List any two ways of measuring the standing crop of a trophic level.

Standing crop can be measured as:
(i) Biomass of living organism in a unit area.
(ii)Number in a unit area 

62. Explain how nitrogen is incoperated  into a food chain

• Nitrogen is important to living organisms and is used in the production of amino acids, proteins and nucleic acids (DNA, RNA).Nitrogen (N) makes up most of the gas in the atmosphere (about 78%).

• Nitrogen gas present in the air is notavailable to organisms and thus has to be made available in a form absorbable by plants and animals.
• Only a few single-cell organisms, like bacteria can use nitrogen from the atmosphere directly.
• For plants, nitrogen has to be changed into other forms, eg. nitrates or ammonia. This process is known as nitrogen fixation.
• The nitrogen cycle involves the following steps:
• Lightning: Nitrogen can be changed to nitrates directly by lightning. The rapid growth of algae after thunderstorms is because of this process, which increases the amount of nitrates that fall onto the earth in rain water, acting as fertiliser.
• Absorption: Ammonia and nitrates are absorbed by plants through their roots.
• Ingestion: Humans and animals get their nitrogen supplies by eating plants or plant-eating animals.
• Decomposition: During decomposition, bacteria and fungi break down proteins and amino acids from plants and animals.
• Ammonification: The nitrogenous breakdown products of amino acids are converted into ammonia (NH3}  by these decomposing bacteria.
• Nitrification: Is the conversion of the ammonia to nitrates (NO3) by nitrifying bacteria.
• Denitrification: In a process called denitrification, bacteria convert ammonia and nitrate into nitrogen and nitrous oxide (N2 O). Nitrogen is returned to the atmosphere to start the cycle over again.

63. Explain standing crop in an ecosystem. Draw a pyramid of biomass when a small standing crop of phytoplanktons supports a large standing crop of zooplankton in the sea.
    Standing crop represents the total mass of living material or energy content of all the organisms of a trophic level at a particular time and location
    
    Inverted pyramid of biomass small standing crop of phytoplankton supports large standing crop of zooplankton
64. State the purpose of each of the following tools

• Quadrant

A quadrat is a frame, traditionally square, used in ecology, geography and biology to isolate a standard unit of area for study of the distribution of an item over a large area

• Altimeter

An altimeter is a device used in ecology to measures altitude, the distance of a point above sea level.

• Seechi disc

Seechi disk  is a plain white, circular disk 30 cm (12 in) in diameter used to measure water transparency or turbidity in bodies of water. The disc is mounted on a pole or line and lowered slowly down in the water. The depth at which the disk is no longer visible is taken as a measure of the transparency of the water. This measure is known as the Secchi depth and is related to water turbidity.

• Barometer

A barometer is a scientific instrument used to measure atmospheric pressure, also called barometric pressure. Barometers measure this pressure.

65. Describe the belt transect method

The belt transect method is used when there is a gradual change from one side of a habitat to another, like the change in light between the outer edges of a forest to the centre.

Procedure

• Extend a measuring tape from one side of the habitat to another.
• Place a quadrat at 0m on the tape.
• Count the numbers/estimate percentage cover of each species.
• Use a key to identify each species.
• Record results in a table.
• Move the quadrat along the measuring tape.
• Repeat step 3-5 at regular intervals along the measuring tape.
• Continue until the full length of the measuring tape has been sampled.
• Calculate the average of each species.
• A bar chart can be drawn to show the data obtained.

66. Construct a grazing food chain and detritus food chain using the following five links each. Earthworm, bird, snake, vulture, grass, grasshopper, frog, decaying plant matter.     
    Grass — >Grasshopper— > Bird— >Snake -> Vulture
    Detritus food chain
67. Dead and decaying plant matter— >Earthworm— >Bird — >Snake Vulture
68. Differentiate between two different types of pyramids of biomass with the help of an example.
    Pyramid of’ biomass refers to the relationship between producers and consumers in terms of biomass.It can be: Upright, e.g. in grasslands ecosystem

Inverted, e.g. in pond ecosystem

69. Name the pioneer species on a bare rock. How do they help in establishing the next type of vegetation? Mention the type of climax community that will ultimately get established. (i)Lichens are the pioneer species on a bare rock.
    (ii) The lichens secrete some acid to dissolve rock and help in weathering and soil formation.

(iii) Later, some small bryophytes invade and hold the small amount of soil.

(iv)The bryophytes are succeeded by herbs, shrubs and ultimately big trees.

(v)At last, a stable climax forest is formed.

(vi)Mesophytic climax community will be established from xerophytic habitat.

70. Construct an ideal pyramid of energy, when 1000000 J of sunlight is available. Label all its levels.
    

70. Construct a pyramid of biomass starting with phytoplanktons, label three trophic levels. Is this upright  or inverted? Why?         

The pyramid is inverted because the biomass of fishes is much more than that of the phytoplanktons.

72. Define a climax community. Climax community can be defined as a community which gets established at the terminal stage of succession and remains in equilibrium with the environment,
73. (i) Differentiate between primary and secondary ecological successions.

In primary succession, newly exposed or newly formed rock is colonized by living things for the first time. In secondary succession, an area that was previously occupied by living things is disturbed, then re-colonized following the disturbance.

(ii)Explain the different steps of xerarch succession occurring in nature.   .(i)The differences between primary and secondary ecological succession can be summarised as:

(ii)The different succession in occurring in xerarch re can be summarised as:

The pioneer species lichens grows on hare rocks

They secrete some acids that dissolve rock, help in weathering and soil formation.

Allows small plants, e.g. bryophytes to invade and hold some soil. These are succeeded by bigger plants in order as herbs, shrubs and finally big trees.

(ii) Write any two limitations of ecological pyramids.
(i)The energy flows unidirectionally from the first trophic level (producers) to last trophic level (consumers), and as the energy flows from one trophic level to another, some energy is always lost as heat into the surrounding environment. So, the amount of energy flowing decreases at each successive trophic levels.

This can be explained with the help of a diagram of a grazing food chain.

The pyramid of energy is always upright and each bar in the pyramid indicates the amount of energy the present at each trophic level in a given time or per unit area:

(ii) The limitations of ecological pyramids are:

• It does not consider the same single species operating at two or more trophic levels.
• It assumes simple food chains that do not exist in nature and do not accomodate food web.
• Saprophytes, detritivores and decomposers are not given any place in pyramids, despite their vital role in

ecosystem (any two).     

74. Define the term succession

Succession is the order of colonization of species in an ecosystem from a barren or destroyed area of land. Ecological succession is the steady and gradual change in a species of a given area with respect to the changing environment. It is a predictable change and is an inevitable process of nature as all the biotic components have to keep up with the changes in our environment.

The ultimate aim of this process is to reach equilibrium in the ecosystem. The community that achieves this aim is called a climax community. In an attempt to reach this equilibrium, some species increase in number while some other decrease.

Mosses and lichens are the first species that inhabit an area. They make the area suitable for the growth of larger species such as grasses, shrubs and finally trees.

75. What are the various types of succession

In an area, the sequence of communities that undergo changes is called sere. Thus, each community that changes is called a seral stage or seral community. All the communities that we observe today around us have undergone succession over a period of time since their existence. Thus, we can say that evolution is a process that has taken place simultaneously along with that of ecological succession. Also, the initiation of life on earth can be considered to be a result of this succession process.

If we consider an area where life starts from scratch by the process of succession, it is known as primary succession. However, if life starts at a place after the area has lost all the life forms existing there, the process is called secondary succession.

It is obvious that primary succession is a rather slow process as life has to start from nothing whereas secondary succession is faster because it starts at a place which had already supported life before. Moreover, the first species that comes into existence during primary succession is known as pioneer species.

Types of Ecological Succession

These are the following types of ecological succession:

1. Primary Succession

Primary succession is the succession that starts in lifeless areas such as the regions devoid of soil or the areas where the soil is unable to sustain life.

When the planet was first formed there was no soil on earth. The earth was only made up of rocks. These rocks were broken down by microorganisms and eroded to form soil. The soil then becomes the foundation of plant life. These plants help in the survival of different animals and progress from primary succession to the climax community.

If this primary ecosystem is destroyed, secondary succession takes place.

1. Secondary Succession

Secondary succession occurs when the primary ecosystem gets destroyed. For eg., a climax community gets destroyed by fire. It gets recolonized after the destruction. This is known as secondary ecological succession. Small plants emerge first, followed by larger plants. The tall trees block the sunlight and change the structure of the organisms below the canopy. Finally, the climax community arrives.

1. Cyclic Succession

This is only the change in the structure of an ecosystem on a cyclic basis. Some plants remain dormant for the rest of the year and emerge all at once. This drastically changes the structure of an ecosystem.

76. Explain how does a primary succession start on a bare rock and reach a climax community?

Primary succession rocks The species of organisms that first invade a bare area are called pioneer species. The pioneer species on a bare rock are usually lichens. Lichens secrete acids which dissolve rocks, thereby leading to weathering and soil formation. This paves the way for small plants or bryophytes which hold the soil. They are succeeded by bigger plants and ultimately an entire forest gets established. Forests represent the climax community in this succession.

77. i) Explain the significance of ecological pyramids with the help of an example.

(ii) Why are the pyramids referred to as upright or inverted? Explain. 
.(i)Significance of ecological pyramids

They graphically represent the relation between producers and consumers. To calculate energy. content, biomass or numbers, organisms of that trophic level needs to be calculated. A trophic level represents only a functional level not a species as such. A given species may occupy more than one trophic level in the same ecosystem at the same time. The ecological pyramids provide an over all idea of the trophic levels occupied by an organism in an ecosystem.
Example A sparrow is a .primary consumer, when it eats seeds, fruits, peas and a secondary consumer when it eats insects and worms.
(ii)Upright pyramids When producers are more in number and biomass than the herbivoes and herbivores are more in  number and biomass than the carnivores. Energy at a lower trophic level is always more than at a higher trophic level. Pyramid of energy is ah rays upright.
Inverted pyramids When the numbers of producers are less and consumers increase and become largest in top consumer level.Pyramid pf number and biomass may be inverted

78. Explain the function of reservoir in nutrient cycle. List the two types of nutrient cycles in nature.

Reservoir in an ecosystem meets the deficit that arises due to the imbalance in the influx and efflux of nutrients. The two types of nutrient cycles are:

(i) Gaseous cycle (ii) Sedimentary cycle

79. Name the two types of nutrient cycles existing in nature. Where are their reservoirs present? State the function of reservoirs.   Two types of nutrient cycles in nature:
    (i) (a) Gaseous cycles (carbon and nitrogen cycle).
                 (b) Sedimentary cycles (phosphorus and sulphur cycle).
    (ii) (a) Reservoir for gaseous cycle is atmosphere.
            (b) Reservoir for sedimentary cycle is earth’s crust.
    Function of Reservoir 

     It meets the deficit which occurs due to the imbalance in the state of influx and efflux of nutrients

1. State the function of a reservoir in a nutrient cycle. Explain the simplified model of carbon cycle in nature.

For function of a reservoir in a nutrient cycle.

Two types of nutrient cycles in nature:

(i) (a) Gaseous cycles (carbon and nitrogen cycle).
        (b) Sedimentary cycles (phosphorus and sulphur cycle).
(ii) (a) Reservoir for gaseous cycle is atmosphere.
         (b) Reservoir for sedimentary cycle is earth’s crust.
Function of Reservoir It meets the deficit which occurs due to the imbalance in the state of influx and efflux of nutrients

80. Define the term ‘biological oxygen demand.

Biochemical oxygen demand, or BOD, measures the amount of oxygen consumed by microorganisms in decomposing organic matter in stream water. BOD also measures the chemical oxidation of inorganic matter (i.e., the extraction of oxygen from water via chemical reaction). A test is used to measure the amount of oxygen consumed by these organisms during a specified period of time (usually 5 days at 20 C). The rate of oxygen consumption in a stream is affected by a number of variables: temperature, pH, the presence of certain kinds of microorganisms, and the type of organic and inorganic material in the water.

BOD directly affects the amount of dissolved oxygen in rivers and streams. The greater the BOD, the more rapidly oxygen is depleted in the stream. This means less oxygen is available to higher forms of aquatic life. The consequences of high BOD are the same as those for low dissolved oxygen: aquatic organisms become stressed, suffocate, and die.

Sources of BOD include leaves and woody debris; dead plants and animals; animal manure; effluents from pulp and paper mills, wastewater treatment plants, feedlots, and food-processing plants; failing septic systems; and urban stormwater runoff.

81. Procedure for determining BOD

The procedures for collecting samples for BOD testing consist of the same steps described for sampling for dissolved oxygen (see above), with one important difference. At each site a second sample is collected in a BOD bottle and delivered to the lab for DO testing after the 5-day incubation period. Follow the same steps used for measuring dissolved oxygen with these additional considerations:

• Make sure you have two BOD bottles for each site you will sample. The bottles should be black to prevent photosynthesis. You can wrap a clear bottle with black electrician’s tape if you do not have a bottle with black or brown glass.
• Label the second bottle (the one to be incubated) clearly so that it will not be mistaken for the first bottle.
• Be sure to record the information for the second bottle on the field data sheet.
• The first bottle should be analyzed just prior to storing the second sample bottle in the dark for 5 days at 20 C. After this time, the second bottle is tested for dissolved oxygen using the same method that was used for the first bottle.

 The BOD i s expressed in milligrams per liter of DO using the following equation:

DO (mg/L) of first bottle – DO (mg/L) of second bottle

= BOD (mg/L)

82. Define the term ‘Chemical  oxygen demand.

Chemical oxygen demand (COD) is the amount of dissolved oxygen that must be present in water to oxidize chemical organic materials, like petroleum. COD is used to gauge the short-term impact wastewater effluents will have on the oxygen levels of receiving waters.

 

83. Why  do we Measure Chemical Oxygen Demand (COD)?

When treated wastewater is discharged into the environment, it can introduce pollution in the form of organic content to receiving waters. High levels of wastewater COD indicate concentrations of organics that can deplete dissolved oxygen in the water, leading to negative environmental and regulatory consequences. To help determine the impact and ultimately limit the amount of organic pollution in water, oxygen demand is an essential measurement.

84. Distinguish between COD and  BOD

Like COD, biochemical oxygen demand (BOD) measurement can be used to estimate the amount of pollution in a water sample. COD describes the amount of oxygen required to chemically break down pollutants, while BOD indicates the amount of oxygen required to breakdown organic pollutants biologically with microorganisms.

There is a correlation between COD and BOD, however, it must be experimentally established before using one parameter to express another. Usually COD analysis (which is a much faster and more accurate method) is used to estimate BOD using the established correlation.

85. Explain the consequence of sudden phosphate and nitrogen enrichment by sewage discharge

Too much nitrogen and phosphorus in the water causes algae to grow faster than ecosystems can handle. Significant increases in algae harm water quality, food resources and habitats, and decrease the oxygen that fish and other aquatic life need to survive. Large growths of algae are called algal blooms and they can severely reduce or eliminate oxygen in the water, leading to illnesses in fish and the death of large numbers of fish. Some algal blooms are harmful to humans because they produce elevated toxins and bacterial growth that can make people sick if they come into contact with polluted water, consume tainted fish or shellfish, or drink contaminated water.

Nutrient pollution in ground water can be harmful, even at low levels. Infants are vulnerable to a nitrogen-based compound called nitrates in drinking water. Excess nitrogen in the atmosphere can produce pollutants such as ammonia and ozone, which can impair our ability to breathe, limit visibility and alter plant growth. When excess nitrogen comes back to earth from the atmosphere, it can harm the health of forests, soils and waterways.

86. Write short notes on eutrophication under the following subheading
    1. Definition

Eutrophication is an enrichment of water by nutrient salts that causes structural changes to the ecosystem such as: increased production of algae and aquatic plants, depletion of fish species, general deterioration of water quality and other effects that reduce and preclude use”.

1. Causes of Eutrophication

• Fertilizers (nitrates and phosphates)

Eutrophication is predominantly caused by human actions due to their dependence on using nitrate and phosphate fertilizers. Agricultural practices and the use of fertilizers on lawns, golf courses and other fields contribute to phosphate and nitrate nutrient accumulation.

When these nutrients are washed by surface runoff into lakes, rivers, oceans and other surface waters when it rains, the hungry plankton, algae and other aquatic plant life are well fed, and their photosynthesis activity is increased. This causes a dense growth of algal blooms and plant life, such as the water hyacinths in the aquatic environments.

• Concentrated Animal Feeding Operations

Concentrated animal feeding operations (CAFOs) are as well the main contributor of phosphorus and nitrogen nutrients responsible for eutrophication.

The concentrated animal feeding operations normally discharge high scores of the nutrients that find a way into rivers, streams, lakes and oceans where they accumulate in high concentrations, thereby plaguing the water bodies by recurring cyanobacterial and algal blooms.

• Direct Sewage Discharge and Industrial Waste into Water Bodies

In some parts of the world, especially the developing nations, sewage water is directly discharged into water bodies such as rivers, lakes and oceans.

As a result, it introduces high amounts of chemical nutrients, thereby stimulating the dense growth of algal blooms and other aquatic plants, which threatens the survival of aquatic life in many ways.

• Aquiculture

Aquiculture is a technique of growing shellfish, fish and even aquatic plants (without soil) in water containing dissolved nutrients. As a highly embraced practice in recent times, it also qualifies as a top-ranking contributor to eutrophication.

If aquiculture is not properly managed, the unconsumed food particles together with the fish excretion can significantly increase the levels of nitrogen and phosphorous in the water, resulting in dense growth of microscopic floating plants.

• Natural Events

Natural events such as floods and the natural flow of rivers and streams can also wash excess nutrients off the land into the water systems, this causing excessive growth of algal blooms.

• Also, as lakes grow old, they naturally accumulate sediments as well as phosphorus and nitrogen nutrients which contribute to the explosive growth of phytoplankton and cyanobacterial blooms.
  1. Effects of Eutrophication
• Causes abundance of inorganic chemicals such ammonia, nitrites, hydrogen sulphide etc. that in the drinking water treatment plants induce the formation of harmful substances such as nitrosamines suspected of mutagenicity;
• Causes abundance of organic substances that give the water disagreeable odours or tastes, barely masked by chlorination in the case of drinking water.
• These substances, moreover, form complex chemical compounds that prevent normal purification processes and are deposited on the walls of the water purifier inlet tubes, accelerating corrosion and limiting the flow rate;
• Causes the water acquires disagreeable odours or tastes (of earth, of rotten fish, of cloves, of watermelon, etc.) due to the presence of particular algae;
• Causes the disappearance or significant reduction of quality fish with very negative effects on fishing (instead of quality species such as trout undesirable ones such as carp become established);
• Leads possible affirmation of toxic algae with potential damage to the population and animals drinking the affected water;
• Causes prohibition of touristic use of the lake and bathing, due to both the foul odour on the shores caused by the presence of certain algae, as well as the turbidity and anything but clean and attractive appearance of the water; bathing is dangerous because certain algae cause skin irritation;reduction of oxygen concentration, especially in the deeper layers of the lake at the end of summer and in autumn.
• In the light of these significant repercussions and serious consequent economic and naturalistic damage, there is a clear need to curb the progress of eutrophication, avoiding the collapse of the affected ecosystems.

Measurement of eutrophication

• Nutrients are the leading cause of eutrophication. Nitrogen and phosphorus both stimulate plant growth. Both are measured from samples of water and reported in units of ug/l (micrograms per liter), or ppb (parts per billion). Phosphorus is the most important nutrient, and is often used directly as a measure of eutrophication.
• Plants are the primary users of nutrients. Chlorophyll a is a component of the cells of most plants, and can be used to measure the concentration of small plants in the water, such as algae. Chlorophyll a is measured from samples of water and reported in units of ug/l. Macrophytes are aquatic plants with stems and leaves. The location of different species of plants can be mapped, and the density can be measured in pounds of plants per acre of lake.
• Transparency, or the clarity of water, is measured using a device known as a Secchi disk. This is an eight inch diameter target painted black and white in alternate quadrants. The disk is attached to a marked line, or measuring tape, and lowered from a boat into the lake. The distance into the water column the disk can be seen is the transparency, measured in feet or meters. A short distance of visibility means that there are suspended particles or algae cells in the water, an indication of nutrient enrichment.
• Dissolved Oxygen (DO) which is oxygen dissolved in the water, is necessary to sustain fish populations. Fish, such as trout, require more DO than warm water species. Eutrophic lakes occasionally have levels of DO below the minimum for fish to survive, and fish kills can result.
• Sediments can be measured to determine how fast material is depositing on the bottom. This may indicate watershed erosion, or a large die-off of aquatic plants.
• Fish can be sampled using nets. In an oligotrophic lake there are likely to be cold water species, such as trout. Warm water fish, such as sunfish, bass, bullheads, and carp are more typical of a eutrophic lake.
• Temperature affects the growth of plants, the release of nutrients, and the mixing of layers of water in the lake. Temperature measurements can determine if mixing occurs, moving nutrients from the lake bottom up into the surface waters promoting algae blooms.

Control  of eutrophication

• The traditional eutrophication reduction strategies include ;
• the alteration of excess nutrients, physical mixing of the water, application of powerful herbicides and algaecides, have proven ineffective, expensive and impractical for large ecosystems
• Nowadays, the main control mechanism of the eutrophic process is based on prevention techniques, namely removal of the nutrients that are introduced into water bodies from the water.
• It would be sufficient to reduce the concentrations of one of the two main nutrients (nitrogen and phosphorus), in particular phosphorus which is considered to be the limiting factor for the growth of algae, acting on localised loads (loads associated with waste water) and widespread loads (phosphorus loads determined by diffuse sources such as land and rain). The load is the quantity (milligrams, kilograms, tons, etc.) of nutrients introduced into the environment due to human activity.
• The possible activities to be undertaken to prevent the introduction of nutrients and to limit phosphorus loads can be summarised as follows:
• Improvement of the purifying performance of waste water treatment plants, installing tertiary treatment systems to reduce nutrient concentrations;
• Implementation of effective filter ecosystems to remove nitrogen and phosphorus present in the run-off water (such as phyto-purification plants);
• Reduction of phosphorous in detergents;
• Rationalisation of agricultural techniques through proper planning of fertilisation and use of slow release fertilisers;
• Use of alternative practices in animal husbandry to limit the production of waste water.
• In cases where water quality is already so compromised as to render any preventive initiative ineffective, “curative” procedures can be implemented, such as: removal and treatment of hypolimnetic water (deep water in contact with the sediments) rich in nutrients since in direct contact with the release source;
• Drainage of the first 10-20 cm of sediment subject to biological reactions and with high phosphorus concentrations;
• Oxygenation of water for restore the ecological conditions, reducing the negative effects of the eutrophic process, such as scarcity of oxygen and formation of toxic compounds deriving from the anaerobic metabolism;
• Chemical precipitation of phosphorous by the addition of iron or aluminium salts or calcium carbonate to the water, which give rise to the precipitation of the respective iron, aluminium or calcium orthophosphates, thereby reducing the negative effects related to the excessive presence of phosphorus in the sediments.

87. State five benefits of nitrogen cycle

Understanding how the plant-soil nitrogen cycle works can help us make better decisions about what crops to grow and where to grow them, so we have an adequate supply of food. Knowledge of the nitrogen cycle can also help us reduce pollution caused by adding too much fertilizer to soils. Certain plants can uptake more nitrogen or other nutrients, such as phosphorous, another fertilizer, and can even be used as a “buffer,” or filter, to prevent excessive fertilizer from entering waterways.

88. Describe
    • Carbon cycle 

Carbon is the basic building block of all organic materials, and therefore, of living organisms. Most of the carbon on earth can be found in the crust. Other reservoirs of carbon include the oceans and atmosphere.

Carbon moves from one reservoir to another by these processes:

• Combustion: Burning of wood and fossil fuels by factory and auto emissions transfers carbon to the atmosphere as carbon dioxide.
• Photosynthesis: Carbon dioxide is taken up by plants during photosynthesis and is converted into energy rich organic molecules, such as glucose, which contains carbon.
• Metabolism: Autotrophs convert carbon into organicmolecules like fats, carbohydrates and proteins, which animals can eat.
• Cellular respiration: Animals eat plants for food, taking up the organic carbon (carbohydrates). Plants and animals break down these organic molecules during the process of cellular respiration and release energy, water and carbon dioxide. Carbon dioxide is returned to the atmosphere during gaseous exchange.
• Precipitate: Carbon dioxide in the atmosphere can also precipitateas carbonate in ocean sediments.
• Decay: Carbon dioxide gas is also released into the atmosphere during the decay of all organisms.
• Photosynthesisand gaseous exchange are the main carbon cycling processes involving living organisms. Figure 8.23 depicts the carbon cycle.

 

90. Nitrogen cycle 

Nitrogen (N) makes up most of the gas in the atmosphere (about 78%). Nitrogen is important to living organisms and is used in the production of amino acids, proteins and nucleic acids (DNA, RNA).

• Nitrogen gas present in the air is notavailable to organisms and thus has to be made available in a form absorbable by plants and animals.
• Only a few single-cell organisms, like bacteria can use nitrogen from the atmosphere directly.
• For plants, nitrogen has to be changed into other forms, eg. nitrates or ammonia. This process is known as nitrogen fixation.
• The nitrogen cycle involves the following steps:
• Lightning: Nitrogen can be changed to nitrates directly by lightning. The rapid growth of algae after thunderstorms is because of this process, which increases the amount of nitrates that fall onto the earth in rain water, acting as fertiliser.
• Absorption: Ammonia and nitrates are absorbed by plants through their roots.
• Ingestion: Humans and animals get their nitrogen supplies by eating plants or plant-eating animals.
• Decomposition: During decomposition, bacteria and fungi break down proteins and amino acids from plants and animals.
• Ammonification: The nitrogenous breakdown products of amino acids are converted into ammonia (NH3}  by these decomposing bacteria.
• Nitrification: Is the conversion of the ammonia to nitrates (NO3) by nitrifying bacteria.
• Denitrification: In a process called denitrification, bacteria convert ammonia and nitrate into nitrogen and nitrous oxide (N2 O). Nitrogen is returned to the atmosphere to start the cycle over again.
• The nitrogen cycle is shown below

                               The nitrogen cycle

89. State four mechanisms  through which atmosheric  nitrogen is fixed to usable form by plant

 Because the nitrogen gas present in the atmosphere can not be directly used by plants. There are certain bacteria and some natural phenomenon that help in Nitrogen fixation

Biological Nitrogen Fixation

Certain bacteria or prokaryotes are capable of converting atmospheric nitrogen to ammonia. This process is called biological nitrogen fixation. The enzyme nitrogenase converts dinitrogen to ammonia. Nitrogen-fixing bacteria may be free-living or symbiotic. Some of the free-living nitrogen fixers are Azotobacter, Beijernickia,  Rhodospirillum, cyanobacteria, etc. Examples of symbiotic nitrogen fixers are Rhizobium (in the root nodules of legumes) and Frankia (in the root nodules of non-leguminous plants), etc.

Symbiotic Nitrogen Fixation

A species of bacteria called Rhizobium, help in nitrogen fixation. These bacteria live in the roots of leguminous plants (e.g., pea and beans plants) and using certain types of enzymes, they help in fixing nitrogen in the soil. During this biological process, they convert the non-absorbable nitrogen form into a usable form. This form of nitrogen gets dissolved in the soil, and plants absorb the modified nitrogen from the soil. This is the reason behind farmers implementing crop rotation, where leguminous plants help to replenish nitrogen content in the soil without the necessity of fertilizers.

Nitrogen fixation by bacteria is an example of the symbiotic relationship between Rhizobium and leguminous plants. While bacteria fix nitrogen in the soil, plants provide them food.

Nitrogen Fixation by Lightning

Another process that helps in nitrogen fixation is lightning. It is a natural phenomenon where the energy of lightning breaks and converts the non-absorbable form of nitrogen into a usable form. Even though the contribution of lightning in the nitrogen fixation is small, they save plants from the deficiency of essential elements.

Nitrogen oxides, e.g. NO, N₂O and NO₂ are also produced in the atmosphere by industrial processes, automobile exhausts, power stations and forest fires.