A2 OCR Biology Ecosystems and Sustainability

All the notes you need for A2 OCR Biology Ecosystems and Sustainability

HideShow resource information
  • Created by: h
  • Created on: 12-06-12 16:08
Preview of A2 OCR Biology Ecosystems and Sustainability

First 336 words of the document:

A2 Biology Revision Notes Ecosystems and sustainability
Ecosystems
Ecosystem ­ all the living organisms and all the non-living components in a specific habitat, and their
interactions
Ecosystems are dynamic
In most ecosystems, population sizes rise and fall, either very slightly or very noticeably. This is
because the community of living things in an ecosystem interact with each other and their physical
environment. Any small changes in one can affect the other. For example;
If a predator's population size increases, population size of prey will go down (as more are
being eaten more quickly)
Nitrogen levels in the soil can affect the population sizes of plants growing there.
Nitrogen-fixing plants would grow successfully in nitrogen-deficient soil, but they would
affect their environment by increasing the soil nitrogen levels. This change would then help
other plants to grow there as well
Biotic factor ­ the effects of one living organism on another. Biotic factors include food supply,
predation and disease
Abiotic factors ­ the effects of the non-living components of an ecosystem. Abiotic factors include
pH, temperature and soil type.
Producer ­ plants and other photosynthetic organisms that supply chemical energy to all other
organisms
Consumer ­ all other animals and fungi which feed on other organisms
Decomposer ­ living things that feed on waste material or dead organisms (bacteria, fungi and some
animals)
Trophic level ­ the level at which an organism feeds in a food chain
Understanding energy transfer
How energy is transferred
Within an ecosystem, living organisms are usually members of more than one food chain and often
feed at different trophic levels in different chains. Drawing these food chains together as a food web
helps us understand how energy flows through the whole ecosystem. The arrows in a food chain
show the direction of energy transfer, rather than just `who eats what'
Measuring efficiency of energy transfer
1

Other pages in this set

Page 2

Preview of page 2

Here's a taster:

A2 Biology Revision Notes Ecosystems and sustainability
Pyramids of biomass
Each bar within the pyramid is proportional to the dry mass of all organisms at that trophic level. An
ecologist must collect all the organisms within that trophic level and put them in an oven at 80 C until
all the water is evaporated out of the organism.…read more

Page 3

Preview of page 3

Here's a taster:

A2 Biology Revision Notes Ecosystems and sustainability
Animals can be treated with antibiotics. This means that less energy is used in fighting off
pathogens and more energy is invested in growth.
Animals are often kept indoors in cages and not allowed to move. This means less energy is
used on movement and less energy is wasted by having to keep a high core body
temperature.…read more

Page 4

Preview of page 4

Here's a taster:

A2 Biology Revision Notes Ecosystems and sustainability
Randomly position the quadrats across the habitat, using random numbers to plot
coordinated for each one
Take samples at regular distances across the habitat, so you sample every part of the habitat
to the same extent.
Transects
A transect is a line taken across the habitat.…read more

Page 5

Preview of page 5

Here's a taster:

A2 Biology Revision Notes Ecosystems and sustainability
Nitrogen-fixing bacteria live freely in the soil and fix nitrogen gas, which is in the air in the
soil, using it to manufacture amino acids
Some of these bacteria also live in the root nodules of plants such as peas and beans. They
have a mutualistic relationship with the plant: bacteria provide plant with fixed nitrogen and
receive carbon compounds such as glucose, in return
Proteins in the nodules absorb oxygen and keep the conditions anaerobic.…read more

Page 6

Preview of page 6

Here's a taster:

A2 Biology Revision Notes Ecosystems and sustainability
Competition
Carrying capacity
Carrying capacity ­ the maximum population size that can be maintained over a period of time in a
particular habitat
Predators and prey
A predator is an animal that hunts other animals for food. Predation can act as a limiting factor on a
prey's population size, which in turn can affect the predator's population size.…read more

Page 7

Preview of page 7

Here's a taster:

A2 Biology Revision Notes Ecosystems and sustainability
more effectively than Paramecium caudatum. Over 20 days, Paramecium caudatum reduced and
died out.
Gause concluded that more overlap between two species' niches would result in more intense
competition. If two species have exactly the same niche, one would be out-competed by the other
and would die out or become extinct in that habitat. This idea was called the competitive exclusion
principle, and can be used to explain why particular species only grow in particular places.…read more

Page 8

Preview of page 8

Here's a taster:

A2 Biology Revision Notes Ecosystems and sustainability
Managing large-scale timber
Large-scale production of wood for timber often involved clear-felling all the trees in one area. This
can destroy habitats on a large scale and is now rarely practised in the UK. Clear-felling the trees
reduces soil mineral levels and leave soil susceptible to erosion. Soil may run off into waterways,
polluting them.…read more

Page 9

Preview of page 9

Here's a taster:

A2 Biology Revision Notes Ecosystems and sustainability
Natural environments are a valuable source of potentially beneficial resources. Many of the
drugs we use today were discovered in wild plant species
Natural predators of pests can act as biological control agents. This has advantages over the
use of synthetic chemicals, although each solution is different
Many species also have indirect economic value;
Wild insect species are responsible for pollinating crop plants.…read more

Page 10

Preview of page 10

Here's a taster:

A2 Biology Revision Notes Ecosystems and sustainability
(lonesome George) now lives in the grounds of the Charles Darwin Research Station, which
has begun a captive breeding programme to supplement tortoise numbers
More recent fishing boom for exotic species in the 1990s has left populations seriously
depleted
Depletion of sea cucumber populations has led to a dramatic effect on underwater ecology
International market for shark find has led to the deaths of 150,000 sharks each year around
the islands
Introduced species
Many species, such as goats,…read more

Comments

No comments have yet been made

Similar Biology resources:

See all Biology resources »See all resources »