A BRIEF DISCUSSION OF THE PREVIOUS CLASS (5:03 PM)

ECOSYSTEMS (5:07 PM)

• Classification of Ecosystems
• 1. Terrestrial Ecosystem (land-based)
• Forest
• Grassland
• Desert
• Polar
• 2. Aquatic Ecosystem
• a) Freshwater
• Lentic- standing water moving slowly
• Lotic- moving water river system
• b) Brackish- a mixture of freshwater with saline water
• Estuarine ecosystem
• Lagoons- a body of ocean that has been cut off from the ocean by some kind of a barrier
• Lagoons can be brackish or marine ecosystems depending on whether freshwater flows into such lagoons or not
• Backwaters- they are formed at the mouth of the river by the deposition of sediments by the rivers, making water calm but leaving scope for ingression of seawater during high tides
• Backwaters in Kerala are termed Kayals
• c) Marine Ecosystem
• Littoral ecosystem - the ecosystem in the continental shelf where the depth is not more than 200 m
• Bathyal ecosystem- ecosystem at the continental shelf
• Abyssal ecosystem- ecosystem formin the abyssal zone of the ocean
• Photic zone- It is the entire region of the ocean surface up to the depth of 200m which receives sunlight
• Aphotic zone- It is the zone of the ocean that doe not receive any sunlight
• Benthos is the life form that leaves on the sea floor of the continental shelf, slope, and abyssal plain
• Nektons are very strong swimmers like fish
• Planktons are the microscopic life form that leaves close to the water's surface and are not swimmers, rather they are drifted by waves or currents
• Planktons can be either phytoplanktons (plants) or zooplankton (animals)
• Artificial Ecosystems
• They are anthropogenic or man-created ecosystems and are highly restrictive
• They are also called cultural ecosystems
• It includes agricultural regions, reservoirs, local lakes/dams/tanks
• Structure of Biotic Components (6:00 PM)
• The biotic component comprises all living organisms
• They can be broadly classified into the following categories:
• 1. Producers:
• They produce food on their own
• All the green plants which use the photosynthesis process are called autotrophs or phototrophs, as they use sunlight to produce food
• Chemotrophs are those micro-organisms that break down minerals to make their food
• 2. Heterotrophs:
• It comprises organisms that do not make their own food and feed on other life forms for food
• 3. Decomposers:
• Detritivores are the animals that feed on dead animals. e.g. vulture
• Decomposers are those organisms that feed on dead plants and animals
• Saprophytes are those micro-organism bacteria and fungi that secrete digestive juice on dead plant or animal material which breaks and thereafter absorbs digested organic materials
• Saprophytes digest their food outside their cells and absorb the digested food
• Trophic Structures
• It was proposed by RC Lindeman
• The trophic Structure of the biotic component refers to the organization of life forms based on the mode of getting/procuring food 
• Each trophic level is a feeding level
• All life forms at a given trophic level obtain food by the same method involving the same steps
• The maximum trophic levels for any ecosystem are only four
• This includes trophic level one for primary producers, trophic level two for primary consumers (herbivores), trophic level three for the secondary consumers (carnivores), and trophic level four for tertiary consumers (omnivores)
• Energy pathways   (6:31 PM)
• This refers to the movement of solar energy from one trophic level to another
• This is because the tissue material of green plants contains stored solar energy in a form that can be used by other life forms
• Therefore, when green plants are eaten by herbivores, it is the solar energy moves into the trophic level two
• The flesh and bones of herbivores again represent solar energy
• Therefore, when carnivores eat herbivores, it is solar energy moves from trophic level two to level three
• Similarly, energy moves from level three to level four when omnivores eat carnivores
• Therefore, it is solar energy that links different trophic levels
• In the movement of solar energy across the trophic levels, only 10% of the total solar energy stored at a given level moves up to the next level
• This is termed the 10% rule given by Lindeman
• The movement of solar energy in the biotic component is unidirectional and non-cyclical
• Food Chain
• The trophic structure depicts the food chain
• Therefore, the food chain represents the path taken by solar energy as it moves in the biotic component of the ecosystem
•  There are two types of food chains that are
• 1. Grazing foodchains
• This always starts with living green plants
• 2. Detritus food chain
• They always start from dead plant and animal material involving detritivores and decomposers
• Food Webs
• Food webs are linked to food chains
• This is possible because a single ecosystem can have many food chains which are separate and linear
• When these foodchains are interlinked because of alternate predator-prey relations
• Food webs represent the flexibility in the availability of food for life forms in a single ecosystem
• The concept of food webs is based on the column presence of such linked food chains in many ecosystems
• Very simple and small ecosystems may not have food webs, because of the limited number of life forms
• Ecological Pyramids (7:27 PM)
• The concept was given by Charles Elton
• This represents life forms in terms of their number, biomass, and energy at different trophic levels
• In the energy pyramid, the rate of transfer of energy across different trophic levels is shown
• Since only 10% of the energy moves up from one trophic level to another, the energy pyramid should be upright
• The number pyramid shows the absolute number of life forms at each trophic level
• This can be upright or inverted
• Generally when insect lifeforms are present n some ecosystems the number pyramid can become inverted
• Biomass is the dry weight of organic matter
• This can be inverted or upright
• Generally, inverted biomass is true for an ecosystem that has large size herbivores

Topics: Types of species, the interaction between species, adaptation, abiotic components, biogeochemical cycles