Tag: o level biology notes

Cells need food materials which they can oxidise for energy or use to build up their cell structures. They also need salts and water, which play a part in chemical reactions in the cell. Finally, they need to get rid of substances such as carbon dioxide, which, if they accumulated in the cell, would upset some of the chemical reactions or even poison the cell. Substances may pass through the cell membrane either passively by diffusion or actively by some form of active transport.

If a very thin slice of a plant stem is cut and studied under a microscope, it can be seen that the stem consists of thousands of tiny, box-like structures. These structures are called cells. There is no such thing as a typical plant or animal cell because cells vary a great deal in their size and shape depending on their function.

It is useful to have an overview of the classification of the plant kingdom, although only two groups (ferns and flowering plants) will be tested in the examination.

Animals are multicellular organisms whose cells have no cell walls or chloroplasts. Most animals ingest solid food and digest it internally.

All living organisms, whether they are single celled or multicellular, plants or animals, show the characteristics included in the definitions above: movement, respiration, sensitivity, growth, reproduction, excretion and nutrition.