Friday, 13 October 2017

All About ... Cells

In quite a few of my blogs recently I have mentioned cells; epithelial cells, muscle cells, bone cells nerve cells etc.  Although, I vaguely remember learning about cells in Biology at school I don't remember much about them - so I thought I would find out!

Just about all living things are made of cells 

·         cells are the building blocks of living organisms
·         new cells only appear when existing cells divide
·         cells contain inherited information - which controls their activities
·         the chemical reactions of life take place inside cells

Animal cells are different from plant cells!

Animal cells have:

·         a surface membrane which encloses the contents
·         inside the membrane there is a nucleus (like a ball) and cytoplasm
·         inside the nucleus there is chromatin (fibrous material), it is this material which condenses to form chromosomes during cell division
·         the chromatin contains DNA - which is the inherited material controlling cell activity
·         scattered within the cytoplasm are mitochondria - these supply energy to the cell
·         within the cytoplasm are also particles of stored food (often glycogen)

Plant cells also have:

·         a vacuole - a large sap filled cavity, sap is a fluid which contains salts and sugars
·         the vacuole is surrounded by a membrane called the tonoplast
·         the cytoplasm also contains starch grains (food storage for plants)
·         plant cells (only in the green parts of a plant) also have chloroplasts in the cytoplasm.  These contain pigments used in photosynthesis.

Knowing about the ultra-structure of animal cells helps to understand how they work ....  the surface membrane (cell membrane) is selectively permeable, which means it lets some substances through but not all, it controls the exchange of these substances between the cell and its surrounding environment.   The cytoplasm is made up of cytosol, which is a fluid containing molecules, and different organelles: -

·         nucleus - is enclosed by 2 membranes (nuclear envelope) which have pores controlling the exchange of substances between the nucleus and the outside environment ie: the cytoplasm.  As well as the chromatin in the cytoplasm there are nucleoli which make ribosomes

·         endoplasmic reticulum and ribosomes - endoplasmic reticulum (ER) comes in 2 types, smooth and rough.  Smooth ER does not have any ribosomes.  ER is a system of sacs, each sac is full of fluid.  In the Rough ER the sacs transport proteins - proteins made by the ribosomes.  In the Smooth ER carbohydrates and lipids and other products (but not proteins) are made, stored and secreted.  NB - in liver cells the Smooth ER contains enzymes which break down chemicals. 

·         mitochondria - are also enclosed by 2 membranes.  They enclose a watery substance which contains DNA, ribosomes, enzymes and calcium phosphate granules.  Mitochondria are involved with the generation of ATP (a form of energy used to form biological activities).

·         golgi apparatus and lysosomes - the golgi apparatus 'processes and packs'  cell material into small sacs (vesicles) so that it can pass through the cell membrane.  It is also involved in the formation of lysosomes which remove worn out organelles (such as mitochondria).  Lysosomes are also involved with the breakdown of tissue and will digest substances which white blood cells have ingested eg: bacteria.

·         Centrioles - are involved in cell division.

·         Flagella and cilia are involved in cell locomotion.

The cell membrane forms the barrier between the cell and the environment around it.  It is strong but flexible because the cells must be able to move, grow and divide.  It also provides a surface for hormone and neurotransmitter receptor sites.

As I mentioned at the beginning of this blog there are many different types of cells in a horses' body.  They are all very similar in structure and ultra-structure BUT have specialised, this makes them more efficient.  However, some have specialised and so lost their ability to carry out other functions - red blood cells do not have a nucleus so they cannot reproduce.

Cells of the same type are grouped together to form tissue.  All the cells in the tissue will act together to perform the same function.

Tissue may join with tissue of a different type to form an organ: muscle tissue, nerve tissue and connective tissue all work together in the heart.   So an organ is a group of tissues which work together to   perform a specific function.  

 So, cells are pretty important .... to everything we do consciously and unconsciously!  

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