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AS level biology
Difference between Prokaryotes and Eukaryotes

Prokaryotic cells are smaller and simpler organisms, whereas Eukaryotic
cells are more complex. The organelles found inside a Eukaryotic cell are:

Organelle Description Function
Nucleus A large organelle surrounded Chromatins is made from
by a nuclear envelope (double proteins and DNA. The…

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There are many differences between Eukaryotes and prokaryotes, these
include the size of ribosomes, the size of the cell, and the cell walls involved;
most of the differences are listed below:

Eukaryotes Prokaryotes
Larger cells (2-200um) Extremely small cells less and 2.0um
DNA is linear DNA is circular
Nucleus present-(DNA…

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1. Transcription occurs changing DNA to mRNA, where the mRNA leaves
the nucleus via pores in the nuclear envelope.
2. Proteins are made on ribosome's
3. The ribosomes sometimes attach to the rER where the protein made
moves through making the 3-D shape en route. (ribosomes on the rough

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The Cell cycle and Mitosis

The cell cycle is a process that all body cells
from multicellular organisms use to grow and
divide. The cell cycle starts when a cell is
produced by cell division and ends with the cell
dividing to produce two identical cells. Mitosis
ensures genetic consistency.…

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The chromatids uncoil and come long and thin again.
They are now called chromosomes again.
The nuclear envelope forms around each group of
chromosomes, so there are two nuclei.
The cytoplasm divides and there are now two
daughter cells that are genetically identical to each
Mitosis is finished and…

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The way the gametes divide is by meiosis; meiosis is a type of cell division that
happens in the reproductive organs to produce gametes. Cells that divide by
meiosis have the full number of chromosomes to start off with (23 pairs).
Without meiosis the number of chromosomes would be double…

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Fertilisation is where male and female gametes fuse. It is a term to describe
the exact moment when the nuclei from the male and female gamete fuse.
Since each gamete contains half the required number of chromosomes the
fusion of the nuclei will create a complete set.

In mammals…

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these specialised cells all originally came from stem cells. Stem cells are cells
which are unspecialised and they can develop into any type of cell. Stem cells
divide by mitosis to become specialised; the process of which cells become
specialised is called differentiation.

In humans stem cells can be found…

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Stem cells in Medicine

Stem cells could be used to treat some diseases, as they can develop into any
type of cell; scientists think they could be used to create a range of tissues
which can replace damaged cells.

Some stem cell treatment already exists, such as treatment for leukaemia,…

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many guidelines which are involved. They also provide evidence and advice to
governmental officials. There are no ethical objections to a person using
multipotent stem cells derived from adults. In the UK the HFEA regulates
research on human embryos.

Different genes are switched on and off. Such as the b-galactosidase…


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