Cell Structure

A typical animal cell

- All cells have structures inside them - these are called sub-cellular structures. - In an animal cell, the sub-cellular structures include:  - nucleus, which controls the activities of the cell and contains the genetic material.  - cytoplasm, in which most of the chemical reactions take place.  - a cell membrane, which controls the passage of substances in and out of the cell.  - mitochondria, where areobic reputation takes place.  - ribosomes, where proteins are made.

Plant cells

- Plant cells and algal cells conatin all the sub-cellular structures found in animal cells.- They also have:   - a cell wall, made of cellulose, which strengthens the cell.   - a permanent vacuole, that is filled with cell sap, which supports the plant.- Plants need to make their own food, so some of their cells contain chloroplasts.- Chloroplasts  absorb light to make food (glucose) through photosynthesis. 

Prokaryotic and Eukaryotic cells

- There are two main types of cell:   - Prokaryotic    - Eukaryotic - Plant, animal and fungal cells are all eukaryotic.-  Bacterial cells are prokaryotic.- Prokaryotic cells are much smaller in size and:   - the genetic material is not enclosed in a nucleus.   - the genetic material is a single DNA loop and there may                                   be one or more small rings of DNA, called plasmids.    - they do not contain mitochondria or chloroplasts.

A typical bacteria cell

- Bacterial cells have many different shapes - some are round, some are rod-shaped and some are spiral - but they are all prokaryotic cells.- In bacterial cells, the roles of mitochondria and chloroplasts are taken over by the cytoplasm.- There may be one or more flagella, which are tail-like structures that move the bacterium.- Plasmids are present, which are loops of DNA that can be transferred from one cell to another.- Plasmids allow bacterial cells to move genes from one cell to another.

Key points

Not all plant cells have chloroplasts. For example, they are not present in root cells because those cells do not receive any light.  

Prokaryotic cells are much more simpler in structure than eukaryotic cells. 

Key point

Plasmids have become very useful to scientists. They allow genes to be inserted into bacteria in genetic engineering.

Key words

- sub-cellular structures- nucleus - cytoplasm  - cell membrane - mitochondria - ribosome- cell wall- cellulose- vacuole- chloroplast- prokaryotic - eukaryotic - plasmid- flagella