Nitrogen cycle refers to a
biochemical cycle in the environment whereby nitrates in the soil are taken up
by plant roots and may pass along food chains into animals absorb it in this
form. It must first be converted into either nitrates or ammonium compound.
Figure below shows the nitrogen cycle.
- Nitrogen-fixing bacteria in the root nodules of legumes
plant carry out fixation by converting atmospheric nitrogen to nitrates.
- Lightning converts atmospheric nitrogen into nitrates.
The nitrates get into the soil and are later absorbed by
plants.
Plants use nitrogen compounds to produce plant proteins.
Plants are eaten by animals. Animals use the nitrogen to produce animal
proteins. When plants and animals die, decomposers such as bacteria and
fungi feed on them. The decomposers release ammonia gas (NH3)
which contains nitrogen. The ammonia is converted into nitrites and then
nitrates by bacteria. Denitrifying bacteria release nitrogen from nitrates
back into the atmosphere.
INTERACTION
AMONG LIVING ORGANISM
The relationship among organisms in
the environment can be explained in the form of predation, competition and
symbiosis.
PREDATION – This happens when one organism captures, kills and feeds
on another in order to get nutrients. Example cats eat mice and sharks eat
fishes.
COMPETITION – This is a relationship where organisms both need the same
limited environment resources for survival. Examples lions and leopards both
hunt antelope and zebra. Hence lions and leopards are competitors. Organism
from the same places can also be competitors, Example cow competing for grass
SYMBIOSIS – This is a relationship whereby there is a close
association between organisms. This association could take various forms, such
as mutualism, commensalism, Neutralism, syn-necrosis, amensalism and
parasitism.
MUTUALISM – This is the relationship in which two organisms benefit
each other. Example: The rhizobium bacteria in the root nodules of legumes
convert nitrogen into nitrates for use by the plant. The bacteria get
protection and nutrients from the plants.
COMMENSALISM – This is interaction that is beneficial to one organism and
is neutral to the other organism. Example when a bird builds a nest in a hole,
in a tree.
PARASITISM – In this association one organism benefits while the others
is harmed. Example: Plasmodium that causes malaria in human beings.
FOOD CHAINS AND FOOD WEBS
Food chains and food webs show the
flow of nutrients and energy among organisms in the environment.
- Each organism in a food chain or food web represents a
trophic level a food chain.
- Trophic level -
is a position that organism occupies in food chain or food web.
- Examples; producers like green plants, primary
consumers like herbivores and secondary consumers like carnivores
PRODUCERS: These are organisms that can manufacture their own food
example: green plants and photosynthesis bacteria, this is the first trophic
level.
- Producers
are eaten by primary consumers
- Primary consumers are mostly herbivores such as
rabbits, cows, buffaloes, wild beasts, goat and sheep.
- Primary consumers form the second trophic level.
SECONDARY
CONSUMERS:
These form
the third trophic level.
- They feed on primary consumers
- They are mostly carnivores such as – domestic
cats, dogs, hyenas, lions, leopards and cheetahs.
- This level can be followed by tertiary consumers which
feed on secondary consumer then quaternary consumer feed on tertiary
consumers.
DECOMPOSERS
These are
organisms that decompose dead organic matter
- This is the final trophic level.
- These organisms feed on dead matter and break it down
there by facilitating decomposition.
- The two main decomposers are the saprophytic fungi
and saprophytic bacteria.
- The relationship between organisms at different trophic
levels can be presented diagrammatically as follows;
FOOD CHAINS- a food chain is a linear relationship among the organisms of
a community in which each organism feeds on the one preceding it.
- It presents energy flow from one trophic level to the
next.
- Each organism feeds on therefore derives energy from
the proceedings one in return it is eaten by the other and therefore
provides energy for the one following it.
- The arrows indicate the direction of energy flow
Example of
food chain:
FOOD WEBS
A food web refers to the several
food chains interlinking together(A network of food chain).
- Most herbivores consume more than one kind of plants
and omnivores consume more than one kind of plant and animal and the
decomposer consume more than one kind of herbivore
Example
of food web
SIGNIFICANCE OF FOOD CHAINS AND FOOD
WEBS
i) Food chains and food webs
facilitate the flow of energy in the environment.
ii) Helps to maintain the balance of
the total numbers of organisms in the environment
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