State what is meant by cell theory and give evidence to support it (4) Living things are made from cells Cells are the smallest living units Cells are the building blocks of life Cells can survive on their own- organelles can not Cells divide by mitosis Viruses require a host cell Evidence-Organisms appear to be made of cells when viewed under a light microscope

Explain how single celled organisms contradict cell theory and explain why these organisms have limited growth (5) Organisms made from only one cell Can still carry out all the characteristics of life Fungal hyphae and skeletal muscle can be multinucleated Diffusion/osmosis effective only over short distances As volume increases surface area for diffusion decreases Refer to surface area to volume ratio

Explain why scientists think that Eukaryotes may have developed from Prokaryotes, how are the first cells believed to have come in to existence? (3) Endosymbiotic theory- endocytosis of other cells e.g. cells attained organelles by engulfing/symbiosis other cells All new cells are derived from existing cells The first cells must have arisen from non-living material

What is meant by cell differentiation, how are cells able to differentiate and why is differentiation beneficial to the organism (4) Specialisation of a cell Multi-cellular organisms have cells which interact Differentiated cells form tissues, organs and organ systems Differentiation involves the expression of some genes and the switching off of others No one cell needs to perform all characteristics of life This removes the limitations of cell size