Plant cells and animal cells
- Even though they belong to different organisms, plant and animal cells have some features in common:
- Cell Membrane – separates the contents of the cell and its surroundings. It controls the movement of substances like glucose, oxygen and carbon dioxide in and out of the cell.
- Cytoplasm – many of the chemical reactions needed to carry out life processes take place here. It also contains organelles.
- Nucleus – an organelle that contains DNA which is the genetic material. The nucleus controls all activities of the cell.
- Mitochondria – these are organelles where respiration occurs. They are incredibly small and cannot be seen easily with a light microscope.
- Plant cells have other structures:
- Cell Wall – made of tough cellulose which supports the cell and helps it keep its shape.
- Large vacuole– this fills up a space in the cytoplasm and is filled with cell sap and keeps the cells rigid, thus supporting the plant.
- Chloroplasts – organelles which contain chlorophyll which is a green substance that absorbs light energy, used for photosynthesis.
A bacterium
- Bacteria are single celled organisms that are much smaller than plant or animal cells. They do not contain a nucleus.
- Bacterial cells contain two types of DNA; chromosomal DNA and Plasmid DNA. The former is a giant loop of DNA containing most of the genetic material. It is not neatly packaged like plant or human chromosomes. Plasmid DNA comes in small loops and carries extra information.
- Using information from electron microscopes we know that bacterial cells have a cell wall but it is different to that of plant cell walls. It is more flexible and not made of cellulose, but does a similar job.
- Some bacteria also have flagella on the outside of the cell; they are long whip-like structures that bacteria can use to move themselves along.
