In this chapter of I/GCSE Biology, we will discuss about how plants make food.
Diffusion
Substances move through cells via the process of DIFFUSION. Diffusion is the overall movement of a substance from a region where it is in high concentration to an area where it is in lower concentration. Diffusion is a passive process as it does not need an energy input to happen.
For example diffusion is the main method by which gases enter and leave the plant. Gases such as carbon dioxide and oxygen exchange between the leaf and the surrounding air through small holes on the underside of a leaf, called STOMATA.
Osmosis
OSMOSIS is a specific type of diffusion – it is the overall movement of water from a dilute to a more to a more concentrated solution through a partially permeable membrane. A partially permeable membrane allows water molecules through, but not solute molecules because they are too large.
When it comes to I/GCSE Biology, the movement water into plant roots occur by osmosis.
Active transport
ACTIVE TRANSPORT is the overall movement of a chemical substance across a cell membrane (from where the substance is in low concentration to where it is in higher concentration). This requires energy, which is provided by respiration. Active transport is used in the absorption of nitrates by plant roots.
There are several factors that can limit the rate the rate of photosynthesis:
- Temperature – too low and photosynthesis stops until the temperature rises again. Too high and the enzymes stop working permanently
- Carbon dioxide concentration – as carbon dioxide concentration increases, so does the rate of photosynthesis
- Light intensity – light is needed for photosynthesis. The greater the availability of light the quicker photosynthesis will take place
In I/GCSE Biology, to identify the effect of light on plants, biologists have to carry out fieldwork. This involves using a variety of techniques to measure the amount of available light and to see how this has affected the growth of plants.
- A light meter can measure the amount of light that is hitting the leaf. The amount of light is measured in units of lux. Data-loggers can be fitted with a light meter and readings taken over a period of time.
- A quadrat is a square shape, often divided up into smaller squares. The quadrat is placed randomly on sections of the area in question and the plants that fall inside the quadrat are vaunted
- It is vital to use an identification key to ensure that plants are correctly identified. A key enables the rapid identification of plants and animals by asking questions such as ‘does the plant have parallel veins in its leaves?’
Sometimes it is preferable to measure the changes in plant life along a straight line – in this case a transect may be taken. A line is drawn and the quadrat is placed at set intervals along the line and the plants are counted. This gives a picture of the changes in plant life over the line of the transect.
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