Biology - Differentiation

These are complete notes copied out of my textbook completed for homework, on differentiation. Diagrams included. It is based on the OCR specification for AS Biology. Happy revising! =P

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  • Created on: 12-01-13 23:35
Preview of Biology - Differentiation

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Reianna Shakil L6EFBiology10/11/12
Your body contains about 1013 cells. They have all developed from the single cell with
which you began your life ­ the zygote that was formed by the fusion of an egg cell and
a sperm cell. The zygotes divided to form a tiny ball of cells called a blastocyst, which
continued to divide to form an embryo.
In multicellular organisms, there are usually many different kinds of cells. These cells have
become specialised to carry out different functions. There is `division of labour' amongst
The body is made up of `teams' of cells, usually grouped together into tissues, which
work together closely while each performing their own specialist functions.
The specialisation of a cell to carry out a particular function is called differentiation.
Once a human cell had differentiated, it usually cannot change into another kind of cell.
Heart muscle cell can't change into a bone cell. A bone cell can't change into a skin cell.
This is very different from the abilities of the cells in the blastocyst. These cells have the
potential to become any of the many different kinds of cells within a human. They are
stem cells.
Stem cells differ from most human cells because:
They are unspecialised
They can divide repeatedly to make new cells
They can differentiate into several kinds of specialised cells.
All the cells in a blastocyst are stem cells, and they can differentiate into any kind of
specialised cell. They are therefore said to be `totipotent'. Even in an adult person, there
are still some stem cells.
So far, all the ones that have been found are only able to differentiate into a limited
range of cells ­ for example, there are stem cells in bone marrow that can form white
and red blood cells. But they cannot differentiate into neurones, or any other kind of cell.
There is much interest in stem cells, as they could cure many diseases. For example,
Parkinson's disease is caused by the death of a particular group of cells in the brain. One
day, it may be possible to use stem cells to replace these brain cells.

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Reianna Shakil L6EFBiology10/11/12
Some specialised plant cells
Plants do not have stem cells ­ most of their cells retain the ability to differentiate into
other kinds of cells throughout their lives.
However, there are several parts of a plant where cells are able to divide, and places
where this occurs at a high rate are called meristems.…read more

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Reianna Shakil L6EFBiology10/11/12
Tissues, organs and organ systems
The millions of cells inside a multicellular organism (i.e. you) are not scattered about
randomly.…read more

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Reianna Shakil L6EFBiology10/11/12
tissue. Tissues may be further grouped into organs, and organs into systems. We can define
these terms as follows:
A tissue is a collection of cells together with any intercellular (`between cells') secretion
produced by them, that is specialised to perform one or more particular functions. The
cells are often of the same type, such as palisade tissue on a plant leaf or squamous
epithelium in animals.…read more

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Reianna Shakil L6EFBiology10/11/12
The cells rest on a basement membrane, which, despite its name, is not a cell
membrane at all. It is a network of collagen and glycoproteins that is secreted by the
underlying cells, and that holds the epithelial cells in position.
Squamous epithelium covers many surfaces in the human body, including the inner
linings of the cheeks, the inner surfaces of blood vessels, and the inner surfaces of the
atria and ventricles in the heart.…read more

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Reianna Shakil L6EFBiology10/11/12
Pulling the activities of all the different parts of the body together, so that they work
with each other and do appropriate things at appropriate times, is essential if a
multicellular organism is to survive.
As we have seen, this communication involves cell signalling.
Much of it is done by means of molecules that are produced by one cell and that affect
the behaviour of another. These include hormones.
In animals, electrical signals, carried by neurones, are another method of
communication.…read more

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