~ quadrats should be placed randomly so that a representative sample is taken
~ you should look at the results from several quadrats in an area to reduce the effect of an unusual distribution
~ the results are more reliable when you look at the results from many quadrats
~ quadrats may also be used for slow moving animals such as snails/slugs
- light intensity
- moisture content of soil
- pH of the environment
Measuring Light Intensity
Light meters can be used to measure light intensity. The meter is held at the soil surface and pointed in the direction of the maximum light intensity, then the meter is read. Errors can be made when measuring light intensity by accidentally shading the light meter. Results can be made more reliable by taking many samples.
Measuring Moisture Content of Soil
Soil moisture and soil pH meters are also available - both are used by simply pushing the probe into the soil and reading the meter.
Errors can be made when measuring abiotic factors when the soil moisture or pH meter probes are not cleaned between readings. As always the results can be made more reliable by taking many samples.
Energy lost from a food chain/web
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:
~ 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.
The growth rate of any population depends on the birth rate and the 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 rate
~ stay the same if the birth rate is equal to the death rate
If the birth rate is greater than the death rate the population will rise. Populations with a birth rate smaller than the death rate will decrease. Equal birth and death rates give a population that stays the same
Factors which can limit the growth of a population include:
~shortage of food
~lack of water
~ lack of space
Competition occurs when more then one species need the same resources to survivem, 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.
Habitat = Place where oranisms live.
Population = All of the members of one species living in an area.
Community = All the living things living in a particuar habitat.
Ecosystem = Habitat + Community
Producer = An organism that can make its own food eg. Green plants change light energy into chemical energy (food) by the photosynthesis. All food chains start with a producer.
Consumer = An organism that