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AS level biology
Difference between Prokaryotes and Eukaryotes

The organelles found inside a Eukaryotic cell are:

Organelle Description Function
Nucleus A large organelle surrounded by Chromatins is made from
a nuclear envelope (double proteins and DNA. The pores
membrane) which contains allow substances to move
many pores. The nucleus between…

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There are many differences between Eukaryotes and prokaryotes,:

Eukaryotes Prokaryotes
Larger cells (2-200um) Extremely small cells less and 2.0um
DNA is linear DNA is circular
Nucleus present-(DNA is inside) No nucleus-DNA is free in cytoplasm
No cell wall in animal cells, cellulose Cell wall made of polysaccharides but
cell wall…

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mutations. The master gene produces mRNA which is translated into signal
proteins. These proteins switch on the genes responsible for producing the
proteins needed for the specialisation of the cell in each segment.

The Cell cycle and Mitosis

The cell cycle consists of a period of cell growth
and DNA…

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Production of a gametes

In animals the male gamete is sperm, and in female it is an egg cell (ova). In plants
the male gamete is pollen grains, and the female gametes are ovules.

Gametes contain only half the normal amount of chromosomes, so in one gamete
in humans it…

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Genetic variation:

Crossing over of chromatids is when before the first division of meiosis the
homologous pairs of chromosomes come together and pair up, two of the
chromatids in each pair twist around each other. The twisted bit breaks off
their original chromatid and rejoins onto the other chromatid recombining…

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3. When the tube reaches the ovary, it grows through the micropyle, and into
the embryo sac within the ovule.
4. In the embryo sac, the tube nucleus disintegrates and the tip of the pollen
tube bursts releasing two male nuclei
5. One male nucleus fuses with the egg nucleus…

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Stem cells in Medicine

Some stem cell treatment already exists, such as treatment for leukaemia, where
bone marrow transplants are given. Scientists are researching treatments for
injuries such as: spinal cord injuries, and heart disease. The treatments can save
many lives, and also improve the quality of lives for many…

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There are many for and against arguments.

To help these arguments many authorities have been set up. These include looking
at the proposals of research to see if it should be allowed. This ensures that any
research involving embryos is carried out for a good reason. The licensing and

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Since 1850 the human population has on average got 8cm taller. This can be due to
many reasons such as:

Taller men have more children, resulting in a gradual change
Greater movements of people have lead to less inbreeding
Improved health, especially in protein
The end of child labour has…




thank u soooooo much these are sooo helpful:):*



How can I access these? :)



Sorry about that! Really great notes. 



really great simplified notes with diagrams



A massive life saver! thank you!

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