1).DEFINE FOOD CHAIN AND FOOD WEB.
Ans)
FOOD CHAIN
A food chain is a linear sequence of links in a food web starting from species that are
called producers in the web and ends at species that are called decomposers in the web.
A food chain also shows how the organisms are related with each other by the food they
eat. The length of a chain is the number of links between a trophic consumer and the base
of the web and the mean chain length of an entire web is the arithmetic average of the
lengths of all chains in a food web.
Food chains were first introduced by the African-Arab scientist and philosopher Al-Jahiz
in the 9th century and later popularized in a book published in 1927 by Charles Elton,
which also introduced the food web concept.
FOOD WEB
A food web (or food cycle) is the natural interconnection of food chains and generally a
graphical representation (usually an image) of what-eats-what in an ecological
community.
Another name for food web is a consumer-resource system.
Ecologists can broadly lump all life forms into one of two categories called trophic levels:
1) the autotrophs, and 2) the heterotrophs.
To maintain their bodies, grow, develop, and to reproduce, autotrophs produce organic
matter from inorganic substances, including both minerals and gases such as carbon
dioxide. These chemical reactions require energy, which mainly comes from the sun and
largely by photosynthesis, although a very small amount comes from hydrothermal vents
and hot springs.
The linkages in a food web illustrate the feeding pathways, such as where heterotrophs
obtain organic matter by feeding on autotrophs and other heterotrophs.
The food web is a simplified illustration of the various methods of feeding that links an
ecosystem into a unified system of exchange. There are different kinds of feeding
relations that can be roughly divided into herbivory, carnivory, scavenging and
parasitism.
Some of the organic matter eaten by heterotrophs, such as sugars, provides energy.
Autotrophs and heterotrophs come in all sizes, from microscopic to many tonnes - from
cyanobacteria togiant redwoods, and from viruses and bdellovibrio to blue whales.)
2) WHAT ARE CONSUMERS IN AN ECOSYSTEM?
CLASSIFY IT WITH SUITABLE EXAMPLE.
Ans)
CONSUMERS(food chain)
Consumers are organisms of an ecological food chain that receive energy by consuming
other organisms. These organisms are formally referred to as heterotrophs, which include
animals, bacteria and fungus. Such organisms may consume by various means, including
predation, parasitization, and biodegradation.
Four type of consumer in ecosystem.
Herbivores are animals that feed only on plants.
Carnivores are animals that feed on other animals.
Omnivores are animals that feed on both plants and animals.
Saprobes are organisms that get nutrients by breaking down the remains of dead plants
and animals. Examples of saprobes are bacteria and fungi.
Herbivores.
Herbivores are living organisms that mostly feed on plant based products like leaves,
grass, some fruits and shrubs.
Carnivores.
carnivores are meat eating animals that acquire their food and energy and nutrients needs
of their bodies through feeding on other animal tissues. Carnivores can either be
scavengers or predators. Scavengers are those consumers who feed on dead organisms
that have either died through the natural way or were killed by predators like the lion. The
predators rarely eat dead organisms but instead hunt and kill their pray before they eat
them. The carnivores are mostly to be found in the animal kingdom but there exists some
few of them in the plant kingdom. There are carnivorous plants that feed on such things
as insects that come near them.
Omnivores.
Omnivores are types of consumers that are similar to both herbivores and carnivores in
one way or another in terms of the types of foods they happen to eat. They eat both
animals and plants products to derive energy and nutrients. Note that omnivores usually
don’t eat every plant or animal that comes their way but are selective in nature on what
they prey on. They only consume on things that good for them and their general being
and avoid on food substances may not be suitable for consumption or that poses a health
threat to them. A typical example of an omnivore is man.
Saprophytes.
Saprophytes are types of consumers or organisms that generally get their food and
nutrients from decaying or non living organisms. Fungi are a good example of a
saprophyte.
3) WHAT ARE ECOLOGICAL PYRAMIDS? EXPLAIN
WHY SOME OF THESE PYRAMIDS ARE UPRIGHT
WHILE OTHERS ARE INVERTED IN DIFFERENT
ECOSYSTEMS?
Ans)
Ecological Pyramid
An ecological pyramid (also trophic pyramid, energy pyramid, or sometimes food
pyramid) is a graphical representation designed to show the biomass or biomass
productivity at each trophic level in a given ecosystem.
Biomass is the amount of living or organic matter present in an organism. Biomass
pyramids show how much biomass is present in the organisms at each trophic level, while
productivity pyramids show the production or turnover in biomass.
Ecological pyramids begin with producers on the bottom (such as plants) and proceed
through the various trophic levels (such as herbivores that eat plants, then carnivores that
eat herbivores, then carnivores that eat those carnivores, and so on). The highest level is
the top of the food chain.
An ecological pyramid of biomass shows the relationship between biomass and trophic
level by quantifying the biomass present at each trophic level of an ecological community
at a particular time. It is a graphical representation of biomass (total amount of living or
organic matter in an ecosystem) present in unit area in different tropic levels. The
pyramid of biomass may be "inverted". For example, in a pond ecosystem, the standing
crop of phytoplankton, the major producers, at any given point will be lower than the
mass of the heterotrophs, such as fish and insects. This is explained as the phytoplankton
reproduce very quickly, but have much shorter individual lives.
One problem with biomass pyramids is that they can make a trophic level appear to
contain more energy than it actually does. For example, all birds have beaks and
skeletons, which despite having mass are not eaten by the next trophic level.
There is also pyramid of numbers which represent the number of organisms in each
trophic level. They may be upright (e.g. Grassland ecosystem), inverted (parasitic
ecosystem) or dumbbell shaped (forest ecosystem).
Inverted Ecological Pyramids.
The concept of the ecological pyramid is one of the most important models described in
ecology. Classically defined, biomass and energy pyramids are wider at the bottom. This
indicates that there are more prey items than predators in a given environment, with
cumulative biomass and energy content being greater in prey than predators.
Inverted pyramids have predators stably outnumber prey, with the most biomass locked
up in the highest rung.i.e.:This inverted scheme goes against the convention generally
taught in basic biology, and for good reason. They’re rare, and, in fact, their existence is
debatable, depending upon semantics.
A popular example of biomass inversion comes from aquatic environments (particularly
closed off, nutrient poor lakes). Here, phytoplankton, the primary producers, can be much
reduced in biomass compared to the planktivores that eat them.This is usually explained
by the high turnover of plankton numbers. Their rapid synthesis and mortality ensures
that, although their overall biomass is less, because of the fast rates of death and
reproduction, more ENERGY is going through these lower rungs. So the energy
throughput of the phytoplankton is greatestamongst pyramid levels.
Conversely, predators live longer, grow slower, and arepredated less often, so it may
appear as though there is more biomass there, but the energy flowing through the top is
reduced.
This shows that energy pyramids arealways bottom up and can never be inverted.Nature
is inefficient. Due to requirements of organisms to “waste” energy maintaining
homeostasis (for starters), not all the energy taken from the lower food level gets
transferred to the next one up.
Another familiarly published inverted system describes coral reef habitats, whereshark
populations see significantly more accumulated biomass than those of smaller reef fish
species.Problems with the inversion concept include mobile predators with access to
multiple ecosystems, inconsistent ratios between predator/prey mass [i.e., in a lake, there
may be less algae than small fish (inverted scheme), but there are more small fish than
top predators (normal), resulting in only a partially inverted biomass pyramid], and just a
lack of understanding of the full complexities of food chains.
4) EXPLAIN THE ENERGY FLOW IN AN
ECOSYSTEM WITH A SUITABLE EXAMPLE.
Ans)
Energy flow in ecosystem:
Energy:
1. Energy has been defined as the capacity to do work.
2. Living organisms can use energy in several forms as radiant and fixed
energy.
3. Radiant energy is in the form of electromangetic waves such as light i.e.
solar energy.
4. Fixed energy is potential chemical energy bound in various organic
substances which can be broken down in order to release their energy
content.
5. Quantity of solar energy reaching to the ecosystem: Out of the total
incident light, about 34 % of sunlight is reflected back, 10 % is held by
ozone layer, water vapour and other atmospheric gases and 56%
reaches to the earth's surface.
6. Quantity of light energy used by green plants for photosynthesis: Of
the total sunlight reaching to the earth's atmosphere, only a fraction i.e.,
0.02 % is used for photosynthesis.
Flow of energy in ecosystem:
1. The transfer, of energy from one trophic level to another trophic level is
called energy flow.
2. The energy flow in the ecosystem is from producers to consumers in one
direction only i.e., unidirectional.
3. The organisms which utilitize the light energy and fix energy from inorganic
materials into organic molecules are called as producers or autotrophs.
4. Organisms that cannot prepare the organic food material but depend on
energy rich organic molecules synthesized by autotrophs are called
heterotrophs.
5. Thus in ecosystem, the source of energy is the light energy coming from
sun. This energy flows from producers to consumers i.e. from autotrophs
to heterotrophs in a cyclic manner.
6. The flow of energy is never in the reverse direction i.e. the energy fixed by
autotrophs does not go back to the solar system or the energy which
passes to herbivores does not go back to autotrophs.
7. In this transfer of energy from one trophic level to another, there is a
gradual loss of energy or it goes on decreasing.
8. This is due to the energy released as heat during various metabolic
activities of the organisms.
9. Hence the amount of energy available decreases from one trophic level to
another.
10. If the food chain is short, the energy reaching at tertiary consumsers
level may get more amount of energy and if the food chain is long, energy
upto the tertiary consumers level will be less.
11. In any ecosystem the energy flows from producers -> primary
consumers -> secondary consumers -> Tertiary consumers.