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Differences between individuals of the same species are called 'Variation'. Variation maybe due to genetic factors or environmental factors.

Stem cells are cells in the early stages of development, that are not yet specialised. They have the potential to develop into any type of cells and can replace damaged tissues.

 Most organisms are made of specialised cells with different structures.

There's an issue as to whether it's right or wrong to clone embryos and use stem cells.

Cells carry out instructions by producing proteins. These proteins can be for cell growth/repair which are called structural proteins, or they can speed up chemical reactions which are called Enzymes.

DNA = Deoxyribonucleic  acid

All organisms have DNA. This means its possible to introduce genetic information from one organism into another. This will produce a new combination of genes and characteristics. This is called Genetic Modification.

DNA molecules are made up of 2 strands and are coiled to form a double helix.

Genes are sections of DNA. Genes control the development of different characteristics by issuing instructions to the cell.

Genes occur in long strips called chromosomes and are located inside the nucleus of every cell. Chromosomes come in pairs. Both chromosomes in a pair have the same sequence of genes.

Genes carry out the information needed for you to develop. Different genes control different characteristic e.g. colour of eyes. Genetic diagrams and family trees are used to identify how you inherit a characteristic.

Different species have different numbers of pairs. Human cells contain 23 pairs of chromosomes (46 in total).

One of the 23 pairs of chromosomes in a human body cell is the sex chromosomes.

Human sex cells contain single chromosomes. We have a total of 23 chromosomes; half the number of a normal body cell. Chromosomes are made of DNA molecules.

DNA molecules form a set of instructions for how the organism should be constructed and how each cell should function.




this is really useful, thanks!


Like how you have highlighted the key words!! :D

Antonia **

Thanks, just trying to help people pass their exams !!

and you welcome x


buddy buddo 

good work 

Sara Gure

Really Helpful


lisa linsdell

Very good revision notes for any revision session on cells, very comprehensive with highlighted key words.  Suitable for Higher papers.

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