Download energy and ecosystems

ENERGY AND ECOSYSTEMS
A habitat is where an organism lives e.g. giant panda in mountain
forests, Gobi bear in the Gobi Desert.
A population is a group of the same species living in an area at the
same time that can interbreed with each other e.g. all the people in
Shenzhen, the barnacles on a rocky shore
A community is made up of all of the different species living in a
habitat e.g. all the organisms in a rock pool.
An ecosystem is made up of all the living organisms together with all
of the non living factors that are in an area and how they interact e.g.
the mountain forest community with the rainfall, soil, temperature,
light etc. or a mangrove ecosystem.
A niche is an organism’s role in an ecosystem and the sum total of its
use of the abiotic (non living) and biotic (living) resources e.g. a
hibiscus tree is a producer, provider of food, habitat etc. No two
organisms can occupy the same ecological niche for a long time as
they compete for the same resources.
A producer can make its own food e.g. lily. A consumer must eat
ready made food. Herbivores eat plants e.g. cows eat grass,
carnivores e.g. tigers eat meat and omnivores e.g. pigs eat both
plant and animal food. Decomposers are bacteria and fungi
that ?break down dead and decaying things also waste substances
and help to release materials that can be used again. Detritivores
tend to be the larger animals that do this e.g. earthworm.
A trophic level is a feeding level, for example the trophic level of
producers and primary consumers.
From page 95 the oak and grass are producers. The rabbit and
sparrowhawks are consumers. The fox is an omnivore. The
sparrowhawk belongs to the tertiary consumer trophic level.
A food chain can show what eats what in an area and the flow of
energy through it.
Grass
cow
man
In nature a complicated food chain is a food web.
Grass
sheep
Grass
cow
man
man
Energy is never recycled but enters the ecosystem as light energy
from the sun. Plants convert this light energy into chemical energy.
Not all of the light falling on the plant is used. Some is reflected,
passes through the leaves etc and the plant uses some of this energy
for its own activities e.g. active transport. Only one tenth of the
energy in a producer passes to a primary consumer. Not all of the
plant may be eaten, not all of the plant may be digestible. A lot of
energy is lost as heat into the environment from respiration. Only
one tenth of the energy will pass onto the secondary consumer and
so on. Between levels energy can pass to the decomposers as dead
leaves, urine, faeces etc. These energy loses limit the numbers of
trophic levels and top carnivores in a food chain.
The rate at which plants convert light energy into chemical potential
energy is productivity or primary productivity. It is usually
measured in kilojoules of energy transferred per square metre per
year. The total energy transferred is the gross primary productivity
and the net primary productivity is the gross primary productivity
minus the loss from respiration.
The efficiency of transfer between trophic levels is calculated by
comparing the energy available to a trophic level with the energy
available to the next trophic level, for example
Energy available to tertiary consumers x
Energy available to secondary consumers
100%
Matter cycles round ecosystems but energy does not. Nitrogen is
found in proteins, amino acids and nucleic acids. Although 78% of
the air is nitrogen, most organisms cannot use it. It has to be
converted into a more reactive form by nitrogen fixation. One type
of nitrogen fixing bacteria is Rhizobium, which lives in the soil and in
some plants including leguminous plants (have a pod). The
bacteria and legume live together and both benefit from the
relationship. This is called mutualism. The roots of a germinating
legume seed make lectins which join to polysaccharides on the
surface of the bacteria. The bacteria enter the roots and stimulate
some cells to divide to form nodules. There are colonies of bacteria
in the lumps. The bacteria make an enzyme nitrogenase that is a
catalyst for the conversion of N gas to ammonium ions. Hydrogen,
ATP and anaerobic conditions are needed for this nitrogen fixation.
The fixed nitrogen is used to make amino acids. These are
transported to other plant cells in the xylem, where they are used to
make proteins
Fixation can also be caused by lightning, where nitrogen oxides
are formed when nitrogen and oxygen join. The oxides dissolve in
rain and this falls to the ground. In the Haber process when fertilizers
are made, nitrogen and hydrogen gas are reacted together to form
ammonia.
Other plants take up nitrates by active transport in their root hairs.
In many plants the nitrate is changed to nitrite, then to ammonia and
then to amino acids, which are transported in xylem. Cells convert
most of these to proteins. Other plants transport nitrates in the
xylem. Most N becomes part of proteins.
Animals get their nitrogen from eating, mainly from proteins.
Proteins are digested into amino acids before they enter the blood.
They are used by cells to make proteins. Excess amino acids are
deaminated by the liver and urea is made. Urea is excreted in
urine.
When plants and animals die decomposers – mainly bacteria and
fungi - break down the proteins into amino acids. Those amino
acids that are not used by the decomposers for growth are broken
down into ammonia, which is also broken down from urea in urine.
The process is ammonification. Ammonia is converted to nitrite
ions during an oxidation process by bacteria e.g. Nitrosomonas and
then by oxidation into nitrate ions by bacteria e.g. Nitrobacter. This
process is nitrification and needs well aerated soils. Denitrifying
bacteria gain energy by converting nitrates into nitrogen gas that
goes into the air. This happens in places such as waterlogged soils
where there is little or no oxygen.