An introduction to CELL SPECIALISATION

Specialised cell examples are described, their different functions explained

Doc Brown's Biology Revision Notes

Suitable for GCSE/IGCSE/O level Biology/Science courses or equivalent

 This page will help you answer questions such as ...

 Why do cells become specialised?

 What is the function of an egg cell?

 What is the function of a sperm cell?

 Why are cells described as haploid or diploid?

Know and understand that cells may be specialised to carry out a particular function.

Pre-reading: Introduction to plant and animal cell structure and function gcse biology revision notes

These notes about cell specialisation and specialised cell function are developed in detail on other pages.



The specialisation of cells

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

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


Examples of specialised animal cells - adapted to their functions

Note that stem cells are undifferentiated and have not changed into a specialised cells in the developing embryo.

Gamete cells - the function of egg cells and sperm cells in sexual reproduction

Egg cells and sperm cells are the specialised cells of sexual reproduction.

In sexual reproduction the nucleus of an egg cell fuses with the nucleus of a sperm cell to produce a fertilised egg.

The fertilised egg develops into an embryo.

Both the sperm cell and an egg cell are referred to as being haploid, because their nuclei only contain half the number of chromosomes that you find in a normal body cell.

This ensures that when the egg and sperm nuclei combine at fertilisation the created cell will have the right number of chromosomes (now referred to as a diploid cell).

 

The egg cell - its structure and its adapted functions

  Simple diagram of egg cell

The principal function of the egg cell is to convey the female DNA and to provide nutrients for the developing embryo in the early stages of the organism's development. The egg cell has a haploid nucleus (half set of chromosomes) and the cytoplasm contains the nutrients to feed the growing embryo. Immediately after fertilisation the egg cell's membrane changes structure to stop another sperm getting into the egg cell and this ensures the right amount of DNA is present in the fertilised cell.

 

The sperm cell - its structure and its adapted functions

  Simplified diagram of sperm cell

The sperm cell, like the egg cell has a haploid nucleus (half of the full set of required chromosomes). The principal function of a sperm cell is to convey the male's DNA to the female's egg. The sperm cell has a long tail to enable it to swim to the egg. A sperm cell contains lots of mitochondria (sites of energy releasing respiration) in the middle section to provide the energy for it to swim to the egg cell. At the front of the head of a sperm cell is an acrosome where enzymes are stored. These enzymes are needed so that the sperm cell can digest its way through the membrane of the egg cell to fertilise it.

 

Ciliated Epithelial Cells

  Simple diagram of epithelial cells

Organ surfaces are lined with epithelial cells. Some types of epithelial cells are adapted with hairs called cilia on the top of the cell's surface. The function of these ciliated epithelium cells is to move substances in one particular direction along the surface of the tissue. The hair-like structure of the cilia beat to move the material along. A good example is the lining of your air passage, the surface of which is covered in lots of epithelial cells. The 'beating' cilia move mucous and any particles from air trapped on the surface up the throat and away from your delicate lungs. This allows the mucous to be swallowed or blow out through your nose.

 

Muscle cells

Muscle cells form soft tissue found in most animals. They contain protein filaments of actin and myosin that slide past one another. This adaptation produces a contraction that changes both the length and the shape of the cell. The contraction can be reversed and allows muscle tissue cells to function in such a way as to produce force and motion. Muscle cells contain lots of mitochondria to supply the larger amounts of energy to work the muscles.

 

Nerve cells

Neurones are nerve cells that carry information as tiny electrical signals. These sensory neurones are adapted to carry signals from receptors to the spinal cord and brain.

 

Red blood cells

Red blood cells are adapted to carry oxygen via the haemoglobin molecules inside them. Without this adapted cell transportation of oxygen you could not have efficient energy releasing respiration in mitochondria.

 

White blood cells

White blood cells are part of the immune system. White blood cell can ingest disease-causing bacteria to destroy them produce antibodies to destroy pathogens. White cells can change shape to engulf a microbe.

 


Specialised Plant cells

Root hair cells - are adapted to absorb water and minerals from soil and then through the root system to transport these minerals around the plant.

Xylem cells - are not living cells, but rod-like cells that form hollow tubes that can move water and dissolved minerals from the roots around the plant.

Phloem cells - phloem vessels (columns of living cells) move dissolved sugars, produced during photosynthesis, and other soluble food molecules from the leaves to growing tissues (e.g. the tips of roots and shoots) and storage tissues (e.g. in the roots).

Palisade leaf cells - their structure is adapted to support the sites of photosynthesis. They allow light to be absorbed and contain chloroplasts, subcellular structures that contain the chlorophyll needed for photosynthesis.

Guard leaf cells - can open and close the pores (stomata) in leaves and allow oxygen and carbon dioxide to pass in and out.


Pre-reading: Introduction to plant and animal cell structure and function gcse biology revision notes

These notes about cell specialisation and specialised cell function are developed in detail on other pages.


Edexcel gcse 9-1 biology: Be able to describe how specialised cells are adapted to their function, including: (a) sperm cells acrosome, haploid nucleus, mitochondria and tail (b) egg cells nutrients in the cytoplasm, haploid nucleus and changes in the cell membrane after fertilisation (c) ciliated epithelial cells


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