Plant transport systems
- Plants have two specialised tissue: xylem and phloem which carry minerals, salts and water up and down the plant.
- Xylem tissue consisting of long dead cells that die and form hollow tubes. These tubes also give support to the plant. Xylem transports water and minerals.
- Phloem tissue is living. This transports food from the leaves which is used to make food at the tip.
Transpiration
- This is caused by the evaporation and diffusion of water from inside the leaves.
- This creates a slight shortage of water in the leaf, and so more water is drawn up from the rest of the plant through the xylem vessels to replace it. This means more water is drawn up from the roots so there is a constant stream of transpiration through the plant.
- Transpiration is a side effect of the way leaves are adapted for photosynthesis. They have stomata for easier diffusion which means the water can get out more easily too, as well as due to the fact there is less water outside than inside the plant.
- But the transpiration stream does provide the plant with a constant supply of water for photosynthesis.
- A potometer can be used to measure the rate of transpiration.
- As the stem takes up water, the air bubble moves along the capillary tube and the length of which it moves can be recorded.
Organisms and their environment
- A habitat is a place where an organism lives. The distribution of an organism is where the organism is found.
- The conditions in an environment determine what kind of animal will live there. Different environments may present different challenges (such as the Artic vs the rainforest) and the organisms must adapt to their environment in order to survive there.
- Ecologists study the biodiversity of life found in an ecosystem or habitat and where particular organisms are found. The data they collect on their population are used to monitor changes in population or test hypotheses about what sort of organisms exist in a certain place.
Sampling techniques
- Sampling means looking at a small portion of an area. In random sampling every point within an area has an equal chance of being selected. This means it is more likely to be representative of the whole area.
Pooter
- This is used to catch small invertebrates through an inlet tube by sucking sharply on a second tube connected to the container.
Sweep net
- This is used for catching insects in long grass. It is a net lined with strong cloth.
- It should be quickly swept through the grass and the insects collected should be put into a container.
Pond net
- This is a net used for catching insects, water snails etc. from ponds.
- The net should be swept along the bottom of the pond or river to collect the organisms.
Pitfall traps
- These are useful for trapping small animals, such as spiders, beetles and woodlice. They can be set up and left overnight so it is possible to catch organisms that might not be active during the day.
Quadrats
- These are square frames of a known size, which is typically used to sample plant species in a habitat.
- The quadrat is placed in random locations numerous times, and each time the number of plants desired to be counted are recorded. For spreading plants like clover, the percentage of the quadrat area that is covered by the plant is estimated.
- There are different reasons for a varying number of the same organisms due to the different conditions. For example, observing how light intensity varies might help to explain the distribution of different species of plants.
- Other factors such as temperature, soil or water pH may also have an effect in determining which organisms can survive in any given part of a habitat.
- Systematic sampling along a line can be useful when investigating changes in a habitat caused by one environmental factor. The quadrat could be placed at regular intervals along a straight line.
Distribution of organisms in an ecosystem
- It is important to know the distribution of living organisms in an area. This is particularly true if something in the environment is going to change such as houses being built or a road developed.
- In these cases, local environment impact surveys are carried out. They involve collecting data about the numbers and distribution of several species in an area which will be affected.
- The use of sampling techniques is extremely important in this kind of work.