Cell Structure

In the early 1800s, Scottish scientist Robert Brown was examining plant cells under a microscope when he noticed that there was a similar structure in each and every cell he looked at. It had been seen before but it was Brown who first realized it was present in all plant cells, and he called it ‘the nucleus’.

We now know that animal and plant cells have many features in common - a nucleus, cytoplasm, mitochondria, ribosomes and a cell membrane. Plant cells have chloroplasts for photosynthesis, a permanent vacuole and a cell wall. Brown had no idea of the importance of the nucleus, or that it was also found in animal cells too, but scientists have gradually discovered more and more about how cells work.

In a test or exam, you could be asked to draw and label a plant or animal cell; fill in missing labels or show the examiners that you understand what each part of a cell does, so here's a recap:

The nucleus contains the DNA of an organism and it is this that instructs the cell what to do and how to do it. Most cells contain DNA but bacterial cells do not have a nucleus as the DNA is simply found in the cytoplasm. The cytoplasm is a jelly-like liquid that contains the chemicals required for the cell to function. Cell membranes allow some substances into and out of the cell whilst blocking others. It is because of this that it is said to be a semi-permeable membrane. Mitochondria are the engines of life as they provide energy from respiration. The cell wall (where present) provides support and structure for a cell and is freely permeable. All cell types have ribosomes for making proteins.

In organisms other than single celled ones, you will always find a variety of different cells. Each one of these is perfectly adapted to its job, for example, sperm cells have a tail that they use to propel themselves to the ovum; root hair cells in plants have a long and very fine process that has a large surface area allowing it to absorb water and minerals more efficiently. For the exam, you need to know how each of the specialist cells are adapted to their function.