Cells as the basic units of living organisms — common mistakes

Don't just list the MRS GREN characteristics; be prepared to briefly explain what each one means in the context of a living organism. For example, 'respiration' isn't just breathing; it's the cellular process of energy release.

The cell theory is a fundamental concept in Cambridge 9700 Biology, stating three key principles: all living organisms are made of cells, cells are the basic units of life, and all cells arise from pre-existing cells. Mastering these tenets is crucial for understanding biology.

For AS Biology, the main differences are that eukaryotic cells have a true nucleus and membrane-bound organelles (like mitochondria and ER), while prokaryotic cells lack these. Prokaryotic DNA is circular in a nucleoid region, and they have smaller 70S ribosomes, whereas eukaryotes have linear DNA in the nucleus and larger 80S ribosomes in the cytoplasm.

In Cambridge 9700 Biology, all living organisms share seven characteristics, remembered by the acronym MRS GREN: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, and Nutrition. You need to not only list these but also be able to explain what each characteristic means.

Use the formula: Magnification = Image size / Actual size. Make sure both 'Image size' and 'Actual size' are in the same units before you calculate. You can rearrange the formula to find any of the three variables if the other two are known.