OCR gateway a higher biology b2



Cell cycle – cells grow and divide

G = new structures and proteins are made

S = cells replicate dna so when it splits each cell has identical dna

G2 = proteins are made and cell keeps growing


Cell differentiation

  • Becomes specialised

In animal cels they can only differentiate at an early stage but not with plant cells. It makes the cells become more efficient

Palisade leaf cell = photosynthesis so lots of chloroplasts

Tall = large surface area absorbs lots of carbon dioxide

Thin shape = fit lots at top of leaf nearer sun light

Sperm cell=get male DNA. To female DNA in reproduction

Tails and streamline = swim

Mitochondria and enzymes = energy and to digest through the egg cell membrane

Specialised cells group to from tissues which do a function. Different tissues form organs

Stem cells differentiate into different cells depending on instruction they can then divide

Embryonic stem cells are found in human embryos v important for the growth and development of cells

Adult stem cells only found in certain places like bone marrow not as versatile

In animals stem cells replace damaged cells

Meristems contain plant stem cells – only found in the parts of the plant that grow and produce unspecialised cells . They are like embryonic cells but can divide the whole life of the plant. Hey can become specialised and form xylem and phoelem

Diffusion – net movement of particles from area of high to low concentration

Only small molecules can diffuse lie water and oxygen

Active transport – movement of particles across a membrane against the concentration gradient using ATP released during respiration

Example nutrients from gut to blood if there is a lower concentration of nutrients in gut than blood it still works

Plants obtain mineral from soil using this


Net movement of water molecules across a partially permeable membrane from a region of higher water concentration to lower water concentration

Plant cells draw water till they become turgid ( swollen ) and the contents of the cell push against the cell wall ( turgor pressure ) this supports the plant cells

When the cell loses water it becomes flaccid

Investigating osmosis using potato cylinders

Potato cylinders in different concentrations of sucrose solution

Cut potatoes into 1 cm diameter cylinders and measure the mass and put groups of 3 in each concentration of sucrose

Remove the cylinders dry them and weigh the.

Final mass – initial mass

Initial mass. X 100

If the potato cylinder is in solution with a higher water potential then the mass will have increased

Factors affecting movement of substance

Sa : v ratio higher rate In larger ratio

Temp as temp increases rate of diffusion is faster

Concentration gradient bigger difference in concentration it will move faster

Single called organisms = diffuse quickly short difference and large surface area – volume ratio

Multicellular organisms – diffusion across outer membrane is too slow because of long distance and a low sa- v…


Zoe caplan


The word turgor would be turgid