VisionIAS - Video Classroom Lecture

Environment Class 02

THE CLASS STARTED WITH A BRIEF OVERVIEW OF THE PREVIOUS TOPICS (09:06 AM)

PRIMARY PRODUCTION (09:08 AM)

It is the storage of energy through the formation of organic matter from inorganic compounds, For Example- Photosynthesis done by plants represents the first step in the capture-storage-transfer of energy in most ecosystems.
Gross Primary Productivity (GPP) is defined as "Rate of production of organic matter" i.e. Amount of biomass per unit area over a time period. A considerable amount of gross primary productivity is utilized by plants in respiration.
We define Net Primary Productivity (NPP) as Gross Primary productivity - Respiration losses, Thus NPP is the available Biomass for the consumption of heterotrophs.
Primary productivity depends upon a variety of environmental factors like sunlight, water, availability of nutrients, and the photosynthetic capacity of plants.
Photosynthetically Active radiation: The Portion of light spectrum utilized for photosynthesis. (400-700nm)
Chemosynthesis: It is the process by which certain microbes can reach energy rich molecules from chemicals present in their environment, typically in the absence of sunlight. For Example: In deep sea hydrothermal vents some bacteria use hydrogen sulfide to produce carbohydrates.
Chemical Reaction: 6CO₂ + 6H₂O +3H₂S -> C₆H₁₂O₆ +3H₂SO₄

ENERGY FLOW THROUGH FOOD CHAIN (09:40 AM)

The transfer of food energy through a series of organisms that consume and are consumed is termed as "Food Chain"
It shows the movement of energy within any ecosystem.
There are two major food chains: the Grazing Food Chain and the Detritus Food Chain.
The distinction between these two is the source of energy for primary consumers in the grazing food chain is living plant biomass and in the detritus food chain, it is dead organic matter.
Dead organic matter will be decomposed by microbes such as fungi and bacteria.
They convert complex organic molecules into simple inorganic molecules.
Organisms that consume detritus directly are called "Detritivores", They break organic matter into smaller pieces, for Example Earthworms, woodlice, etc.
In aquatic ecosystems, the Grazing food chain is a major conduit for energy flow while in terrestrial ecosystems, it is a detritus food chain.
Based on the source of food, organisms occupy a specific place in the food chain i.e. known as their "Trophic level", Thus Producers have the first trophic level, primary consumers have the second, and so on.
The percentage of energy in the biomass produced by one trophic level that is incorporated into the biomass produced by the next higher trophic level is called "Ecological efficiency"
It can vary from 5% to 40%, on average above 10% is transferred to each trophic level from the lower trophic level. (Lindeman's Rule)
While the Food chain is simple, the actual scenario will include the food web's interconnected food chains in an ecosystem where heterotrophs can occupy different trophic levels and we can find interconnections between detritus and grazing food chains.

ECOLOGICAL PYRAMID (10:09 AM)

Ecological pyramids are graphic representations of trophic levels in an ecosystem, the producers make the base of the pyramid and subsequently makes a higher trophic layer
for Example: In the Pyramid of numbers, the number of organisms at each trophic level will be presented generally they are upright however, in some cases, the pyramid of numbers can be inverted such as a large tree as an ecosystem.
Pyramid of Biomass: In the pyramid of biomass each trophic level will represent dry biomass per unit area, generally, they are upright but in aquatic ecosystems, there can be inverted pyramids of biomass.
Pyramid of Energy:
It represents the total amount of energy at each trophic level, they are never inverted.
Ecological pyramids have limitations because they do not accommodate food webs, or decomposers and assume that one species can only occupy one trophic level.

BIOACCUMULATION AND BIOMAGNIFICATION (10:23 AM)

Bioaccumulation occurs when pollutants build up in a single organism's body over time, for example- Mercury poisoning in fish.
Biomagnification occurs if the concentration of toxins increases as they are passed after the food chain, for toxins to magnify they have to be long-lived, fat-soluble, mobile, biologically active, etc.
Examples: DDT, Polychlorinated biphenyl (PCB), etc.

BIOGEOCHEMICAL CYCLES AND NUTRIENT CYCLES (11:00 AM)

The movement of nutrient elements through the various components of an ecosystem is called "Nutrient Cycling"
They are of two types:

Gaseous Cycle	Sedimentary Cycle
Most of the cycle occurs in the atmosphere.	The reservoir of these nutrients is the earth's crust and thus most of the cycle occurs on the lithosphere.
Example: the Carbon Cycle, Nitrogen Cycle, etc.	Example: Sulphur and Phosphorous cycle.
The gaseous cycle is much quicker than the sedimentary cycle.

A) Carbon Cycle:
It comprises of following major processes Photosynthesis, respiration, decomposition, etc.
Decomposers break down organic matter releasing CO₂ back into the atmosphere in the absence of oxygen (Anaerobic condition)
Organic matter can decay into Methane.
Combustion, Burning of fossil fuel releases stored carbon into the atmosphere as CO₂
There are many places where carbon is stored sediments, rock, snow, and Ice among others.
B) Nitrogen Cycle:
Nitrogen is a vital component of amino acids, proteins, and nucleic acids in living organisms even though it is the most abundant gas in the atmosphere.
Most organisms can not use it directly.
Stages of Nitrogen Cycle:
1) Nitrogen Fixation:
This involves the conversion of atmospheric Nitrogen into ammonium ions which can be used by plants.
There are three processes in Nitrogen Fixation:

Atmospheric Fixation

Bacterial Fixation

Industrial Fixation

Lightening, Combustion, Volcanic activity, etc. help in the fixation of nitrogen.

This can occur in two ways:

a) Symbiotic bacteria: for example, Rhizobium in the root nodules of legume plants helps in nitrogen fixation.

Examples of legume plants are beans, chickpeas, Soyabean among others.

b) Free-living bacteria: They do not require mutualistic association. like Azotobactor, Cyanobacteria such as Nostoc, Anabaena, and Bluegreen algae.

At high temperatures and high pressure, Molecular nitrogen is broken into atomic nitrogen which then combines with hydrogen to form ammonia.

Example: Urea (Nitrogen-based fertilizer)

2) Nitrification:
Conversion of ammonia to Nitrite or Nitrate.
This also occurs because of microbes.
For Example: Nitrosomonas convert Ammonia to nitrites and Nitrobactor converts Nitrites to Nitrate.
3) Assimilation:
Plants absorb nitrates and ammonia from the soil to create amino acids, proteins, and nucleic acids.
4) Ammonification:
Decomposition of organic nitrogen from dead organisms and waste products into ammonia and uric acid.
5) Denitrification:
Conversion of Nitrate and Nitrite back into gaseous Nitrogen or Nitrous oxide.
This occurs because of bacteria such as Pseudomonas and Clostridium.
C) Phosphorous Cycle:
Phosphorous is crucial element as a component of DNA, RNA, ATP, and Phospholipids that form cellular membranes.
It is often limiting nutrients because of its scarcity, for Example: it limits growth in aquatic ecosystems.
The phosphorous cycle does not include a significant atmospheric component given that phosphorous and phosphorous-based compounds are usually solids at room temperature and pressure.
The important steps of the cycle are:
1) Weathering: It releases Phosphate ions in soils and water.
2) Assimilation: Conversion of inorganic phosphate into Organic molecules.
3) Mineralization: Decomposers like bacteria break organic matter and release phosphorous back into the soil.
4) Sedimentation: Some phosphorous can deposit in water and settle at the bottom of the water bodies forming new phosphate rocks through the process of geological uplift. These rocks get uplifted to land and again the process of weathering will start.
This process is very slow, an average phosphate ion usually stays 20,000 years in the ocean.

EUTROPHICATION (12:12 PM)

It is the process whereby water bodies such as lakes, rivers, and coastal oceans receive excess nutrients primarily Nitrogen and Phosphorus leading to excessive plants and algal growth.
The main sources of these excessive nutrients as agricultural runoff and wastewater discharge, among others.
An Explosive growth of algae can lead to harmful algal bloom because algae die and sink to the bottom, decompose, and break down the organic matter which needs a certain level of oxygen, thus oxygen availability of other organisms is reduced leading to high mortality and forming the dead zones.

TOPIC FOR THE NEXT CLASS: SULFUR CYCLE (To be Continued...)