S-Cool Revision Summary
S-Cool Revision Summary
Plants and animal cells share the same basic structural features, although plant cells have a few extra bits.
Animal cells come in all kinds of shapes and sizes but have the same basic features.
The control centre is the nucleus; this contains all the genetic information for the cell and controls all its activities.
The cytoplasm is like a big soup of chemicals in which the reactions occur.
Then forming the outside of the cell is the cell membrane, which acts as a barrier and controls the transfer of materials into and out of the cell.
Plant cells also come in a variety of forms but share similar features. In addition to the three basic features found in animal cells, plant cells have some useful extra ones.
Firstly they have a rigid cell wall made of fibres of cellulose (which we use to make paper!) that gives them shape and strength. The cell wall fits closely just outside the cell membrane like a plastic box with an inflated balloon stuffed inside.
Secondly they have a vacuole, which stores extra water and gives extra support to the cell by pressing hard against the cell wall.
Thirdly, most plant cells also contain small round structures called chloroplasts, which contain the green pigment chlorophyll, which is needed for photosynthesis.
Tissues, organs and organisms
A living plant or animal is called an organism and is made up of lots of cells all working together.
Some of these cells are all of the same type, collectively they are called a tissue. They all do the same job, for example connective tissue, which is used in animals to connect other tissues together - and stop us falling apart!
Next, some different tissues are grouped together to make up an organ such as the stomach or a leaf.
Finally, some organs work together to form an organ system such as the digestive system.
Characteristics of Life
All living things show 7 characteristics of life. All plants and animals are alive.
The 7 characteristics are:
Diffusion: Molecules move from a place of high concentration into a place of low concentration.
Osmosis: a special kind of diffusion, which is very important in Biology; it keeps us alive!!
- Osmosis only involves water molecules- nothing else. Osmosis is water diffusion.
- Osmosis occurs across a barrier such as a cell membrane which is 'selectively permeable', which means it only lets through small molecules like water.