CARBON AND NITROGEN CYCLE
THE CARBON CYCLE
Carbon is passed from the
atmosphere, as carbon dioxide, to
living things. It is then passed from
one organism to the next in
complex molecules, and returned
to the atmosphere as carbon
dioxide again. This is known as the
carbon cycle.
STAGES OF THE CARBON CYCLE
1-Carbon enters the atmosphere as carbon dioxide
from respiration and combustion.
2-Carbon dioxide is absorbed by producers to make
carbohydrates in photosynthesis.
3-Animals feed on plants, passing the carbon
compounds along the food chain. Most carbon they
consume is exhaled as carbon dioxide during
respiration. The animals and plants eventually die.
4-Dead organisms are eaten by decomposers and
carbon in their bodies is returned to the atmosphere as
carbon dioxide. In some conditions decomposition is
blocked. The plant and animal material may then be
available as fossil fuel in the future for combustion.
Removing carbon dioxide from the atmosphere :
Plants use carbon dioxide from the atmosphere for photosynthesis. The carbon
becomes part of complex molecules in the plants, such as proteins, fats and
carbohydrates.
Passing carbon from one organism to the next:
When an animal eats a plant, carbon from the plant becomes part of the fats and
proteins in the animal. Microorganisms and some animals feed on waste material from
animals, and the remains of dead animals and plants. The carbon then becomes part of
these organisms.
Returning carbon dioxide to the atmosphere:
Carbon dioxide is released to the atmosphere through respiration by animals, plants
and microorganisms. It is also released by the combustion of wood and fossil
fuels (such as coal, oil and natural gas). The use of fossil fuels is gradually increasing
the carbon dioxide levels in the atmosphere.
Decomposition or decay also releases carbon dioxide. This process happens faster in
warm, moist conditions with plenty of oxygen because it involves microorganisms. Decay
can be very slow in cold, dry conditions, and when there is a shortage of oxygen.
DESCRIBE THE PROCESSES OF
PHOTOSYNTHESIS AND CELLULAR
RESPIRATION
THE NITROGEN CYCLE
Nitrogen compounds found in cells
include proteins. Nitrogen from the
air is converted into
soluble ions that plant roots can
absorb. It forms part of nitrogen
compounds in the plants, and is
then passed from one organism to
the next. It is returned to the
atmosphere as nitrogen gas. This is
the nitrogen cycle.
STAGE ONE - FIXATION
About 78 per cent of the air is nitrogen
gas. However, nitrogen is too unreactive
to be used directly by plants to make
protein. It must be converted into soluble
ions, such as nitrates. Nitrogen-fixing
bacteria in root nodules are able to do
this. Lightning can also convert nitrogen
gas into nitrates. The Haber
process converts nitrogen gas
into ammonia for use in
fertilisers. Nitrifying bacteria in the soil
can convert ammonium ions into nitrates.
STAGE TWO- NITRIFICATION
absorption into roots and incorporation
into plants
Plants absorb nitrates from the soil and
use these to make proteins.
STAGE THREE -DENITRIFICATION
moving along food chains and
excretion
When an animal eats a plant,
nitrogen from the plant’s
proteins becomes proteins in the
animal. Nitrogen is also passed
from one animal to another by
feeding.
STAGE FOUR – DECOMPOSING-DEATH OF
ANIMALS
Decomposers break
down urea, egested material (eg
faeces) and dead bodies. This
results in nitrogen being returned
to the soil as ammonium ions, which
nitrifying bacteria can convert into
nitrates for plants to absorb.
STAGE FIVE – DENITRIFICATION-RELEASE
INTO ATMOSPHERE
Denitrifying bacteria in the
soil break down nitrates
and return nitrogen gas to
the air.
WHAT IS THE NITROGEN CYCLE?
The nitrogen cycle describes how nitrogen is ‘recycled’ in the
environment
Nitrogen is needed to make the amino acids in found in protein
78% of the air is composed of nitrogen
Nitrogen is very unreactive and can’t be used by plants. Only in
the form of nitrates is it useful.
We rely on processes to convert nitrogen into nitrates
WATER CYCLE
Evaporation
Energy from the Sun heats the Earth’s surface and
water evaporates from oceans, rivers and lakes. The warm
air rises, carrying water vapour with it.
Transpiration
Transpiration from plants releases water vapour into the
air.
Condensation
The moist air cools down as it rises. Water
vapour condenses back into liquid water, and
this condensation process produces clouds.
Precipitation
As the water droplets in the cloud get bigger and heavier,
they begin to fall as rain, snow and sleet. This is
called precipitation
Infiltration is defined as the flow of water from aboveground into the subsurface.
Percolation (from Latin percolare, "to filter" or "trickle through") is the movement and filtering of fluids through
porous materials in physics, chemistry, and materials science.
Surface flow is flow that travels overland in a dispersed manner (sheet flow) or in natural channels or streams or
constructed conveyance system.
Groundwater flow is defined as the "part of streamflow that has infiltrated the ground, entered the phreatic zone,
and has been (or is at a particular time) discharged into a stream channel or springs.
Sublimation is the conversion between the solid and the gaseous phases of matter, with no intermediate liquid stage.