Certain cells within an organism are specialised. This means that they have developed to carry out a specific function. See the table below for some examples.
|To fertilise a female egg cell (the ovum)
Helps prevent dirt and bacteria entering your lungs
|It’s very small and has a tail which allows it to swim and find the ovum.Its head contains enzymes which allow it to digest its way through the membrane of the egg.Its nucleus only contains 23 chromosomesIt has a large surface so that it can absorb as much light as possible
It’s located on the top side of the leaf so that it can easily absorb light and carbon dioxide
It’s full of chloroplasts which are required for photosynthesis
It’s found in all air passages connected to the lungs
It has minute hairs which filter the air as it moves past
Mucus with trapped dirt and bacteria can be swept to the back of the throat where it’s swallowed
Dissolved substances are able to enter and leave a cell through its cell membrane. One way in which they can achieve this is through a process known as diffusion.
Diffusion can occur in either a liquid or gas. It involves the particles of a substance moving from an area in which there’s a high concentration of it to an area in which there’s a lower concentration. The bigger the difference in concentration, the faster the rate at which diffusion occurs.
There are a number of ways diffusion is used by living organism:
- lungs: oxygen from the alveoli in the lungs is able to move across into the red blood cells so that carbon dioxide can then diffuse into the alveoli and then be expelled out of the body via the lungs.
- photosynthesis: similarly, green plants take in carbon dioxide from the air via chloroplasts by diffusion and release oxygen back into the atmosphere also by diffusion.
- respiration: this process also involves diffusion. In animals, for example, oxygen diffuse from the red blood cells into the tissue cells and then carbon dioxide diffuses in the other direction.