(1) Introduction: The specialisation of cells - stem cells and differentiation

Undifferentiated cells are called stem cells and develop into all the different types of cells an organism needs to grow and develop.

A stem cell nucleus contains ALL the instructions to switch genes 'on and off' so it has the ability to change into any specialised cell needed by an organism.

Depending on the instructions a stem cell receives, it can divide by mitosis producing new cells which can then differentiate into various types of cells for specific functions.

Multicellular organisms (eukaryotic) contain a variety of cells, with different structures, which are adapted - specialised, to perform a variety of functions.

Differentiation is the process by which a cell develops into a form to do its specialised role.

Cells which have a particular structure adapted for a particular function are called specialised cells.

After this the cells from mitosis start to become specialised and the process of cell differentiation begins in earnest to ensure growth and development.

Always be aware of how the cell structure and its organelles is adapted to fulfill its function e.g. human blood cells contain haemoglobin to transport oxygen.

In a multicellular organisms, many different types of cell adopt different roles to ensure the organism functions correctly in its life sustaining behaviours.

In cell differentiation, cells become specialised by switching genes off and on to form tissues with particular functions.

In the process of differentiation the stem cells develop different sub-cellular structures to turn into the different types of cells - specialisation.

The specialised cells can now carry out their important specific functions - essential for the efficient and healthy viability of any organism.

The cell's size, shape and internal structures (e.g. organelles) must be all adapted for its function in the organism.

The derived specialised cells include:

Bone cells in skeletal systems.

Blood cells in the circulatory transport system.

Nerve cells in the nervous system.

Sperm cells and egg cells in the reproductive systems.

Most differentiation occurs as an organism develops - lots of stem cells are found in early human embryos.

However, these same stem cells are only found in small numbers in most adult tissues, such as bone marrow or fat and compared with embryonic stem cells, adult stem cells have a much more limited ability to differentiate giving rise to various cells of the body.

Some typical learning objectives for this section on stem cells, cell differentiation & specialisation

Be able to describe how human specialised cells are adapted to their function, including:

(a) sperm cells – acrosome, haploid nucleus and mitochondria and tail,

(b) egg cells – nutrients in the cytoplasm, haploid nucleus and changes in the cell membrane after fertilisation,

(c) ciliated epithelial cells for moving mucous along.

(d) white and red blood cells

Human reproduction systems, menstrual cycle, pregnancy, contraception, fertility treatments

Cell division - mitosis, meiosis, sexual/asexual reproduction

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Summary of learning objectives and key words or phrases

Be able to describe the idea and need for the specialisation of cells and stem cells that can differentiate in an embryo to become various types of specialised cells.

Know that in a developed organism the principal source of stem cells is in bone marrow.

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