Every living thing is made up from cells. Each cell is essentially a simple building block in which the chemical reactions needed for life take place. Cells have the ability to repeatedly divide into two. Some living things are so small that they are made up from only one cell. The amoeba, for example, is a single cell organism. Other, much larger, living things such as humans have millions of cells. In fact, the human body contains about one hundred million, million cells, each one being about one hundredth of a millimetre in diameter. Although all cells share some basic characteristics, there is variation in shape and size since different cells perform different functions. In plants, some cells produce food during the process of photosynthesis; others are involved in growth or transporting food around the plant. In the human body, cells are often grouped together to form tissues (which in turn group together to make organs) or have a function within of the blood or nervous system. Whatever their place each has a task to do.
Plant cells and animal cells are different but all living cells, whether plant or animal, contain three common features:
nucleus: the nucleus of a cell contains structures called chromosomes that are composed of DNA(Deoxyribonucleic Acid) that can replicate itself to transmit genetic information from parents to offspring. It also controls all the reactions inside the cell.
cytoplasm: the cytoplasm is a jelly like substance where most of the chemical reactions in the cell take place. It contains organelles each of which carry out different tasks.
cell membrane: this forms the boundary of the cell. It is a very thin layer of protein that allows food and water to pass into the cell whilst allowing waste to pass out.
Within the cells of a plant, there are three other features:
cell wall: this is outside the cell membrane and holds the plant cell together. It is made of cellulose and is tougher than the cell membrane. Its main function is to support and protect the cell.
chloroplasts: these are small bodies of chlorophyll and absorb light energy during the process of photosynthesis and are only found in green plant cells.
vacuole: this is an area of watery liquid at the centre of the cell. It has two main functions: as storage space for food and to create pressure to keep the cell wall rigid.