OCR gateway a higher biology b2
- Created by: Zoe caplan
- Created on: 25-05-19 10:02
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
Lastly MITOSIS
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
Osmosis
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…
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