The Biosphere - Standard Grade

Revision for Standard Grade Prelims

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Abiotic Factors

Abiotic Factors are non-living conditions which can influence where plants or animals live... 

e.g. temperature, light, ph of the environment, moisture content of the soil

Light meters can be used to measure light intensity. Errors can be made when shading light meter. Moisture meters can be used to measure moisture content of the soil. Errors made when probe is not wiped between samples.


Daisies - The more light, the more daisies will be present this is because daisies need light to be able to photosynthesise.

Grasses - Found in full sunlight of a field for photosynthesis.

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Light Meters - How to Minimise Errors

1. Make sure all observers stand to one side of the light meter

2. Take all measurements at the same time, or, take lots of samples and take the       average of them.

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Quadrats and Pitfall Traps

A QUADRAT is used to sample non-living organisms like plants. 

ERRORS : Plants may be wrongly identified or wrongly counted.

  The Quadrat sample may not be representative of the area if it is not placed           randomly.

  Because of chance - it may not be reliable.

A PITFALL TRAP is used to sample invertebrates living on the ground surface.

ERRORS : Pitfall traps badly set will not catch many animals - estimates unreliable

 Unreliable because of predators and escape (flying insects).

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Eco-System Terms

  • Habitat - The place where an organism lives
  • Population - All of the members of one species living in an area
  • Community - All the living things, animals and plants, living in a particular habitat
  • Ecosystem  - Habitat + Community
  • Green Plants are PRODUCERS
  • CONSUMERS obtain their food from other living things ( animals are consumers
  • HERBIVORES eat plants
  • CARNIVORES eat other animals
  • OMNIVORE - eat plants and animals
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Food Chains And Webs

Producer -  An organism that can make its own food e.g. green plants change light energy into chemical energy (food) by the process of photosynthesis. All food chains start with a producer.

Consumer - An organism that must eat other organisms to get energy. All animals are consumers.

Food Chain;

A simple diagram showing the feeding relationship between organisms in a habitat;

Floating algae → Water fleas → Minnows

Food Web - A complex diagram showing the interconnecting food chains in a habitat.

→   -  Shows the direction of energy flow in a food chain/web

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Energy Loss in Food Chains And Webs

Energy is lost at each stage of a food chain or web. This is due to the organisms using some of the energy they get to survive. Energy is lost from food chains/webs because the organisms need to:

 1. move

 2. heat

 3. reproduce

 4. carry out chemical reactions

The energy that is passed on is that from growth. The bigger the organism eaten the more energy the next organism can get. Only about 10% of the energy is passed on in a food chain. Fewer links in a food chain mean less energy loss.

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Pyramid Of Numbers And Biomass


  • The even looking one 
  • A Pyramid Of Numbers shows the relative number of organisms at each stage of the food chain.
  • Sometimes is not the best way to represent a food chain 


  • The wonky looking one
  • A pyramid of biomass shows the total mass of organisms at each stage of a food chain. 
  • In general, all producers have a higher biomass than the primary consumer, so a pyramid will always be produced. The total energy (and biomass) present at a lower tier of the pyramid, must be greater than the higher tiers in order to support the energy requirements of the subsequent organisms.
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Population Growth

The growth of any population depends on the birth rate and death rate. A population will: increase if the birth rate is higher than the death rate                             decrease if the birth rate is lower than the death ratestay the same if the birth rate is equal to the death rate. Under ideal conditions a population would have a growth with a slow start, then a very fast rate of increase and finally the growth slows down and stops. Factors which can limit the growth of a population include:

  • predation
  • shortage of food
  • disease
  • lack of water
  • lack of space
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Competition occurs when more then one species need the same resources to survive, which are in short supply.

Animals often compete for food or space. Plants often compete for light and moisture.

If organisms are in competition with each other, one of the species will normally die out or have to move to another habitat, leaving the stronger competitor with the resources they need. Neither organism will grow as well as they would have done had there been no competition.

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The Nitrogen Cycle

The Nitrogen Cycle

  • Nitrogen is a chemical element which is needed to make protein in plants.
  • The protein in dead animals and plants, or their waste material, is converted into ammonia. This is done by bacteria and fungi which eat the protein and produce ammonia as their waste product.
  • Special bacteria convert ammonia into nitrites.
  • Other bacteria convert nitrites into nitrates.
  • Plant roots absorb nitrates and use the nitrates to make their protein.
  • Animals eat some of the plants to make their protein.

This basic cycle happens continuously in the soil. In addition there are some other factors which affect the recycling of nitrates and proteins.

  • Some bacteria, which are known as denitrifying bacteria, use up soil nitrate by converting it to nitrogen gas.
  • Some plants, such as peas and clover, have nitrogen-fixing bacteria in root nodules which take nitrogen gas from the air to make nitrates which the plant then uses to make protein.
  • Humans make fertilisers from nitrogen gas. They are an artificial method of adding nitrates to the soil.
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Control And Management - Sources of Pollution

The main sources of pollution are from 

  • industry
  • agriculture
  • domestic (households)

There are disadvantages with the two main ways of producing energy. They are 

  • Nuclear Power - carries a risk of dangerous leaks of radiation at high levels and involves the constant release of low level radiation in the cooling water from power stations. Radiation is known to increase the risk of cancer. The used fuel has to be stored and the long term effects of storing highly radioactive materials are unknown.
  • Burning Fossil Fuels - Burning fossil fuels creates soot and smogs which restrict photosynthesis in plants and coats the environment with grime. In addition sulphur dioxide and carbon dioxide are produced. These lead to acid rain and global warming. We are also using up resources which can never be replaced.
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Controlling Pollution

Here are ideas of how pollution could be controlled;

  • legislation by parliament, for example the Clean Air Acts
  • European agreements to decrease sulphur dioxide emissions
  • world agreements to reduce carbon dioxide production
  • removal of sulphur and nitrogen oxides from flue gases from power station chimneys
  • fitting catalytic converters to car exhausts
  • use of lead free petrol
  • treatment of sewage before releasing it into rivers
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Effect Of Sewage On Water Eco-Systems

Organic waste is material which is living, such as bacteria or yeasts, or once formed part of a living organism.

An increase in organic pollution leads to a large increase in the numbers of bacteria present in water. This causes a drop in the oxygen available to other water living organisms, and therefore a reduction in the number of species which can live in the water. Sewage polluted water, with its lack of oxygen can support a much poorer and less diverse community than water with little pollution and abundant oxygen.

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Indicator Species

Indicator species are organisms that can tell us about the levels of pollution in an area by their presence or absence.

For example, the Stonefly nymph shown in the diagram is only found in water which does not have any sewage pollution.

Another example of indicator species are lichens. The presence or absence of a particular type of lichen tells us about the level of an air pollutant, such as sulphur dioxide, in the area.

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Examples of Poor Management and Possible Solutions

Examples of bad management;

  • Rainforest is being destroyed to provide land for crops. This leads to loss of species, erosion and loss of soil fertility.
  • Overgrazing of grassland leads to soil erosion
  • Overfishing leads to reduced fish stocks.

Possible Solutions;

  • Improve existing farmland or provide alternative work for farmers.
  • Plant trees for shelter and develop irrigation schemes.
  • Enforce strict quotas
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Other ...

Man controls components of the eco-system in both agriculture and forestry to produce large quantities of a single crop. This is done by;

  • Addition of fertilisers - To replace nutrients which would normally be returned by recycling
  • Addition of fertilisers - To remove competing species e.g. weeds
  • Addition of pesticides - To prevent crops being eaten by animal pests. 
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