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Biology Unit 2 Edexcel AS notes, Liam Johnson.




Section 1, Cells:

Cells can be Eukaryotic or Prokaryotic.

Eukaryotic Prokaryotic
Large cells Small celss
Dna is linear Dna is circular
Nucelus present (dna inside) No nucleus (dna in cytoplasm)
No cell wall for animals, cellulose wall in plants Cell wall of…

Page 2

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Biology Unit 2 Edexcel AS notes, Liam Johnson.




Oval shaped, double membrane. Inner one folded to make cristae. Matrix inside which has enzymes
for respiration. Site of aerobic respiration, ATP made here.

Protein Transport:

Protein made at ribosome (RER makes ones for transport, lone ones make protein to stay in…

Page 3

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Biology Unit 2 Edexcel AS notes, Liam Johnson.




Mitosis:

4 stages. Remember PMAT.

Prophase:

Chromosomes condense, centrioles start to move to opposite sides of the cells. Nuclear envelope
breaks down and the chromosomes lie free in the cytoplasm. Spindles form from the centriole.



Metaphase:

Chromosomes line up along the middle…

Page 4

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Biology Unit 2 Edexcel AS notes, Liam Johnson.




Section 2: Reproduction

Production of gametes:

Gametes are sex cells that are found in an organism that produces sexually.

Form together to form a zygote.

Males = sperm Female = Egg

In plants male gametes inside pollen grains and females inside ovules.…

Page 5

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Biology Unit 2 Edexcel AS notes, Liam Johnson.




Genetic differentiation:

Occurs in Meiosis.

Before first division, homologous pairs pair up.

Two of the chromatids in each pair twist around eachother. The twisted bits break off and rejoin the
other chromatid.

Chromatids still contain the same genes but have a different…

Page 6

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Biology Unit 2 Edexcel AS notes, Liam Johnson.




When tube reaches ovary it grows through the microphyte (hole in the ovule wall) and into the ovule
sac inside. Once inside the tube nucleus disintegrates and the two gametes are released.

One gamete fuses with the egg nucleus to form a…

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Biology Unit 2 Edexcel AS notes, Liam Johnson.

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Biology Unit 2 Edexcel AS notes, Liam Johnson.

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Biology Unit 2 Edexcel AS notes, Liam Johnson.

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Biology Unit 2 Edexcel AS notes, Liam Johnson.

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