Energy and Ecosystems

Notes taken from 2 AQA approved text books

HideShow resource information
Preview of Energy and Ecosystems

First 469 words of the document:

Energy and Ecosystems
Food chains and food webs
All living organisms rely on a source of energy to carry out every activity. The ultimate source of energy is the
sun, which is converted to chemical energy by photosynthesising organisms and is the passed as food between
other organisms. Organisms are divided into three groups, sorted by how they obtain energy and nutrients.
Producers. These are organisms Consumers. These are organisms Decomposers. When producers
that carry our photosynthesis. that obtain energy by eating other and consumers die, the energy
They manufacture organic organisms, rather than taking that they contain can be used
substances using light energy, energy straight from the sun. by a group of organisms that
water and carbon dioxide. Green Animals are consumers. The break down these complex
Plants are producers. consumers that eat plants, are materials into simple
called primary consumers, the components again. This means
animals that eat primary consumers that minerals are released in a
are secondary consumers and the form that can be used and
animals that eat secondary recycled by plants. Most of this
consumers are called tertiary is carried out by fungi and
consumers. Secondary and tertiary bacteria called decomposers.
consumers are usually predators And to a lesser extent by certain
but may also be scavengers or animals such as earthworms
parasites. called detritivores.
Food Chains- The term `food chain' describes a feeding relationship. Producers eaten by primary consumers,
primary consumers eaten by secondary consumers, secondary consumers eaten by tertiary consumers, tertiary
consumers sometimes eaten by quaternary consumers. Each stage is called a trophic level. The arrows show
the direction of energy flow. Food chains can be different lengths.
Grass Sheep Human
(producer) (primary consumer) (secondary consumer)
Nettle Aphid Lady Bird Blue tit Sparrowhawk
(producer) (primary (secondary (tertiary (quaternary
consumer) consumer) consumer) consumer)
Food Webs- Most animals don't rely on a single food source
within a single habitat. Many food chains are linked together
in a food web.
However the problem with food webs is their complexity. For
example, in the diagram the nettle leaf is shown to be only
eaten by aphids but in reality it's eaten by up to twenty
organisms It is likely that all organisms within a habitat are
linked in a food web. Showing all the inter-relationships is not
possible. The relationships that organisms have in relation to
feeding change with different factors such as time of year,
age and population size. Despite this it's still useful to have
an idea of food webs and it helps us to understand

Other pages in this set

Page 2

Preview of page 2

Here's a taster:

Energy transfer between trophic levels
Energy loss in food chains- Producers
Plants convert between 1 and 3% of the suns energy
available to them into organic matter. Most of the suns
energy is not converted into organic matter by
photosynthesis because;
·Over 90% of the suns energy is reflected back into space
by clouds and dust or absorbed by the atmosphere.
·Not all wavelengths of light can be absorbed and used for
·Light may not fall on a chlorophyll molecule.…read more

Page 3

Preview of page 3

Here's a taster:

Ecological pyramids
Pyramids are used to show quantative data at each trophic level. They can show number, mass or amount of
energy stored by organisms at each trophic level.
Pyramids of number- Usually the number of
organisms at a lower trophic level is greater than the
ones further up. This can be shown by drawing bars
with lengths that are proportional to the number of
each organism present at each trophic level.…read more

Page 4

Preview of page 4

Here's a taster:

Agricultural Ecosystems
What is an agricultural ecosystem?- Agricultural ecosystems are largely made up of domesticated animals and
plants to used to feed humans. Humans are the 3rd or 4th trophic level therefore they only take in a tiny amount
of the energy available from the sun in their food. Agriculture tries to ensure that as much of the available energy
from the sun as possible is transferred to humans.…read more

Page 5

Preview of page 5

Here's a taster:

Chemical and biological control of agricultural pests
What are pests and pesticides? A pest is an organism that competes with humans for
food or space, or it could be a danger to health. Pesticides are poisons chemicals that kill
pests. They are named after the pest that they destroy. An effective pesticide should;
·Be specific- Only toxic to the organism at which its directed. Should be harmless to
humans and other organisms.…read more

Page 6

Preview of page 6

Here's a taster:

Intensive rearing of domestic livestock
Intensive rearing and energy conservation
Intensive rearing of domestic livestock is about converting the
smallest possible amount of food energy into the greatest quantity
of animal mass. This can be done by minimising the energy that is
lost from the animals during their lifetime. This means that more
energy will be converted into body mass and passed onto the next
link in the food chain.…read more


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all resources »