Topic 2 Revision - Divide and Develop - GCSE Edexcel B2

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Topic 2 Revision ­ Divide and Develop
Cell division
HAPLOID half the normal number of chromosomes (23)
DIPLOID the normal number of chromosomes (46)
Mitosis Meiosis
Where it happens Most parts of the body Reproductive organs
Number of daughter cells Two identical nuclei Four genetically different cells
Number of chromosomes Diploid ­ chromosomes replicate, Haploid from a diploid parent cell
then replicas separate
Purpose For making body cells, growth, Produces gametes for variation
repair, replacement of older cells
1. 2. 3. 4. 5.
Growth and Development
Growth is a permanent increase in size of a living organism
In humans growth can mean an increase in height, mass/weight or number of cells.
Cell division, elongation and differentiation all contribute to the growth and development of an
Length is not a good measure of growth because it doesn't take into account growth in other
directions, e.g. width or body mass.
GROWTH ­ an increase in size, length, wet/dry mass
ELONGATION ­ when cells absorb water and get longer
DIFFERENTIATION ­ when cells become specialised to do a particular job
What happens to Cells for Growth and Development to occur in an Organism?
1. Cells divide by mitosis
2. Cells elongate and absorb nutrients and water
3. Differentiation occurs (cells become specialised)
4. Some cells stay as stem cells
DIFFERENTIATION: Different genes are switched on/off so different proteins are produced
How is growth measured?
DRY MASS ­ A way to measure growth. It's mass without water (organism is dried in an oven until all
the water has evaporated out of it).
WET MASS ­ Total mass of a living organism

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Embryonic Stem Cells
Embryos have stem cells which can grow into any type of body cell
Embryos left over from fertility treatment are used
1. They have no Hayflick limit
2. Can grow into any cell
3. May be used to replace/repair damaged cells/tissue or grow organs
4. Transplanted organs produced from stem cells are less likely to be rejected.…read more

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Stomata function Yellow leaves with dark spots
Phosphorous Making roots
Making DNA, RNA, ATP, phospholipids,
Purple leaves, small roots
enzymes, proteins, membranes
To prevent/ resist disease
In photosynthesis and respiration
How mineral ions from the soil are absorbed into root hair cells
1. Mineral ions are dissolved in water in the soil
2. Cell membrane contains molecular `pumps'
3. Mineral ions move through the molecular `pumps' in root cells by active transport
4. Mineral ions are transported in the plant by xylem vessels
5.…read more

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Changes that occur in the stump to allow the leg to regenerate
1. The wound is sealed by a scab
2. A ball of cells which are undifferentiated stem cells (no Hayflick limit) grows by mitosis
3. The cells differentiate
Benefit to humans from research into leg regeneration in newts.
Regrow human limbs
Cheaper compared to prosthetics
Better chance of survival if injured
Produce stem cells
SELECTIVE BREEDING: Breeding plants or animals from individuals that have the characteristics
you most want.…read more

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How to produce dwarf wheat plants from normal size wheat plants
1. Select the wheat plants with shorter stems
2. Cross breed individual wheat plants with shorter stems
3. Collect seeds and grow offspring
4. Repeat for many generations
Nearly all the bananas we buy today are the same variety. They come from the Cavendish banana tree
which is sterile and seedless. Farmers grow new trees from cuttings.…read more

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Is it right to clone body parts?
Pros: Could provide tissue/organ transplants to treat human disease
Cons: Many embryos die
Premature ageing/death of clones
Unknown consequences e.g.…read more

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Help reduce food shortages
Bacteria can be used to produce human insulin for people with diabetes
Ready source of product
Pollution free/environmentally friendly
Greater yield
Possibility of disease free livestock
How bacteria are genetically modified to produce human insulin:
· Human genes are removed from DNA using enzymes
· Human genes are inserted into the bacterial plasmids using enzymes
Reasons why food cannot be simply transported from the country with plenty of food to the country
with a food shortage: War, politics, transport problem/cost, cost…read more


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