To enable normal functioning all cells in the human body need to be in a relatively stable environment
Some like brain and retinal cells are very susceptible to even slight variations in glucose, oxygen and temperature
Other cells such as skin cells are able to cope with a much wider range of conditions e.g. temperature
One of the ârolesâ of the body systems is to maintain a continual supply of the materials needed and a continued removal of waste materials
Body systems work together to make sure that the cellular environment is kept constant
Called homeostasis
Systems operate in such a way that if a particular factor becomes too high or too low they will function to return the factor to its best or optimal level
Cell Membrane Structure
Composed mainly of lipids and proteins
Arranged into 2 layers that make up the single membrane
Called a bilayer
Substances and molecules move through the membrane in different ways
How they are moved depends on their size and if they are organic or inorganic
Very small molecules e.g. oxygen can pass through the small gaps between the lipids
Fat soluble such as alcohol and steroid hormones can diffuse across the membrane by âdissolvingâ into the lipid (fat)
Proteins are embedded through the membrane and they carry out most of the functions of the membrane
Divided into 2 types
Integral proteins bridge the 2 sides of the membranes
Peripheral proteins embedded in the outside of the membrane
Transport Across the Cell Membrane
Cell membranes are described as being differentially permeable
Allow some ions and molecules to pass through
Restrict movement of others, usually based on size
Differentially permeable membranes are also known as semi-permeable or selectively permeable membranes
Passive and Active Processes
Materials may pass through cell membrane in a number of different ways
Some transfer mechanisms are passive processes which means there is no requirement to spend energy
Passive processes will occur in both living and dead cells and are almost impossible to prevent
Diffusion
Osmosis
Facilitated Diffusion
Active processes require the cellâs energy for the transfer to occur. It only occurs in living cells
Cytosis
Active Transport
Diffusion
Movement of molecules from area of high concentration to area of low concentration
Only occurs when there is a difference in concentration between 2 areas (concentration gradient)
Passive Process
Occur in almost any circumstance where cells can move, it does not need a cell membrane