Notes On Environment & Biodiversity For WBCS Main Exam.

পরিবেশের নোট –  WBCS মেইনস  পরীক্ষার জন্য  – জীব বৈচিত্র্য।

Amongst the vast syllabus of W.B.C.S Examination, this part is quite easy to read and recollect and also fetches good marks.Biological diversity, or biodiversity, is the scientific term for the variety of life on Earth. It refers not just to species but also to ecosystems and differences in genes within a single species. Biodiversity is the key indicator of the health of an ecosystem.Continue Reading Notes On Environment & Biodiversity For WBCS Main Exam.

Environment is everything that is around us. It can be living or nonliving things. It includes physical, chemical and other natural forces. Living things live in their environment. They constantly interact with it and adapt themselves to conditions in their environment.Also read, Notes on Environment-Climate Change And Agriculture.

Food Chain

• For example, plants are eaten by insects, who are eaten by frogs, these frogs are eaten by fish, who are eaten by human beings.
• Plant > insect > frog > fish > human.
• This sequence is known as Food chain.

What is Trophic Level?

• Each step in the food chain is called a “Trophic level”.
• In this food chain: Plant > Insect > Frog > Fish > human= five steps.
• The trophic level to which an organism belongs, indicates how far it is away from plants in the food chain.

1. green plants (producers)= trophic level I
2. herbivores (primary consumers)= trophic level II
3. carnivores (secondary consumers)=trophic level III
4. top carnivores (tertiary consumers)= trophic level IV

Starts with green plants.e.g. Grass> grasshoppers> birds> hawks.Also starts with green plants but here smaller organisms depending on larger organism. e.g. Grass> cow> lice.

NOTES ON, Environment and Biodiversity-For WBCS Main Exam Is Available Here.

Ecological Pyramids

• You already know about the food chain: grass –> Grasshoppers –>birds –>hawk.
• Each step or level is known as Trophic level.
• If we draw these trophic levels in a verticle fashion, a pyramid is created. This pyramid is known as Ecological pyramid.
• The Autotrophs (green plants) = base of the pyramid
• The top carnivores (lion tigers) = tip (apex) of this pyramid.

Food Web

• Food Chain:–> Grass> grasshopper >frog > fish > man
• Assume the isolated linear line. But in real life, frog could be eating other insects apart from grasshopper. Fish could be eating smaller fishes apart from frog. So there exists an interconnected Network of (Food Chain + Food Chain + Food chain…).
• This interconnected network of food chains = food web.

Why is Food web important?

• Suppose in a jungle, the deer species is wiped out due to some human poaching/ diseases / natural disaster.
• Then its predators (lion,tiger) can feed on other animals such as fox, wolf, crane, peacock etc. until deer population grows again.
• Thus, food web= help living organism survive in case of minor or major setbacks in their food chain.
• food web=provides stability to the ecosystem.

Energy Flow in the Ecosystem

• So far you know what is food chain and what is food web.
• You also know what is Trophic level. (each step in a food chain).
• When energy is passed from one tropic level to next trophic level, some part of energy is wasted. So energy declines as we move up in the chain/ web / pyramid.

Why?

1. Because some energy is wasted as body heat.
2. No herbivore (deer, cow) can entirely digest and absorb the plant nutrients.
3. Some energy is wasted while capturing the prey. (e.g. Tiger chasing a deer.)
4. Some energy remains trapped e.g. Tiger only eats the flash of a deer. He doesn’t eat the skin, hair, bone and teeth of a deer.

• So the energy stored in the skin, hair, bone and teeth of a deer =not moved up in the food chain.
• However this energy is later utilized when scavenger (hyena) comes into picture. Because Hyena’s stomach acid is so powerful, it can digest the skin, hair, bone, teeth and other remnants of a deer corpse.

2^nd law of themodynamics

• When energy changes from one form to another, some of the energy is Lost. Suppose a jungle receives 1000 calories worth Sunlight everyday.
• Most of the sunlight is not absorbed; some is reflected back to space.
• Out of the sunlight that is absorbed, only a small portion is utilized by green plants
• Out of which the plant uses up some for respiration, therefore only 100 calories are stored as energy rich materials.
• Now a deer, eats the green plant containing 100 cal of food energy.
• The deer uses some of it for its own metabolism and stores only 10 cal as food energy.
• A tiger eats the deer gets an even smaller amount of energy.
• Thus usable energy decreases from sunlight to producer(green plant) to herbivore(deer) to carnivore(tiger).
• Therefore, the energy pyramid will always be upright.

Connection: Trophic level vs Energy flow

• The loss of energy (explained in previous para) limits the number of trophic levels in the ecosystem.
• Hence trophic levels are seldom more than five.
• This also explains why the steps in a food chain are limited to four or five.Also Read, Essay composition on Environment Pollution.

Energy=Unidirectional

• Movement of Energy is Unidirectional (one-way).
• Because initial Solar energy trapped by an autotroph (plant) does not go back to Sun.
• Similarly, energy that passes from herbivore (deer) to carnivore (lion) does not pass back to herbivore (deer).
• This unidirectional (one-way) and continuous energy flow=prevents the collapse of Ecosystem.

DDT and Biomagnification

• DDT=dichloro-diphenyl trichloroethane.
• It is a “broad” spectrum pesticide (meaning it can kill variety of insects, not just one or two.)
• It lasts for a relatively long time (nearly 20 years) after one application.
• DDT is cheap to produce, been extensively used across world.
• Problem: DDT cannot be metabolized (digested) by any living organism.

To sumup

• Biomagnification is a man-induced process.
• Biomagnification occurs with non-degradable chemicals/substances/pollutants only.
• For example Pesticides, anti-knocking agents used in internal combustion engines, paints, artificial perfumes etc.

Biotic Potential

• Unlimited food + ideal environmental conditions =a species can produce offspring at maximum rate.
• It can be high or low, depending on how many offspring (children) can a species produce in ideal conditions.

Carrying Capacity

• It means the maximum population that an environment can support and sustain.
• When the carrying capacity is reached, birth rates equal death rates and the population should maintain a steady state equilibrium.Do follow previous years question papers for better understanding of the types of questions asked.

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