environments of cells all cells exist in a watery environment – extracellular fluid mullticellular...
TRANSCRIPT
Environments of cells• All cells exist in a watery environment –
extracellular fluid
• Mullticellular organisms have an outer layer that acts as a barrier and creates an internal environment
Aspects of the internal environment that need to be regulated:
•Salt concentrations
•Temperature
•Levels of nutrients
•pH
•Removal of wastes
•Ion concentrations
CELL MEMBRANE (look pg 58)
The role of the membrane is very important in maintaining cell stability and enabling the cell to operate at optimum levels.
The cell membrane (plasma membrane),
- selectively controls the molecules entering & leaving the cell.
- allows the cytoplasm to have a different composition from the the surrounding environment
Membrane Structure.
• The membrane is partially permeable. Some substances pass freely across the membrane while others are excluded.
Phosopholipid bi-layer
• The cell membrane is formed from a double layer of lipids with proteins embedded in it forming ion channels.
• The lipid layer is capable of much movement, i.e. it is fluid.
• Cholesterol molecules reduce the membrane fluidity
• It is impermeable to water soluble substances.
• Lipid soluble substances e.g. alcohol pass through.
Hydrophobic,
‘water hating’ end
Hydrophillic,
‘water loving’ endWhen in contact with an aqueous solution, the phospholipid molecules line up with tails pointing in (away from sol)
EXAMPLE! Detergents cause fats to form micelles.
Protein Channels• These are large proteins with
openings on both sides of the membrane.
• Allow flow of
ions
•Carbohydrates on the outer surface are important in cell adhesion and cell recognition. These are attached to recognition proteins.
Phospholipid Bilayer
Embedded Cholesterol Protein channel
Embedded protein
Carbohydrate
(1) Fluid (2) Mosaic Model (Draw)
Surface area to volume ratio
Movement in and out of Cell
• Diffusion (simple)
• Osmosis
• Facilitated diffusion
• Active Transport
• Endocytosis and Exocytosis
Diffusion (simple)
Comments: Moves down Con~ gradient (high to low) The diffusion rate increases with a high concentration gradient, heat, small particles and with gaseous substances. Movement is from a strong solution to a weak solution. (think sugar cube /water) (lungs, CO2)
Where? What? Energy?
Through the phospholipid bilayer
small uncharged particles (water, urea, Oxygen, carbon dioxide) & lipid soluble substances such as alcohol, ether, chloroform.
NO
Facilitated DiffusionWhere? What? Energy?
Through the protein molecules spanning the membrane. Either by channel proteins or by carrier proteins.
Charged ions &larger molecules (glucose).
- the lipid insoluble molecules.
NO
Comments: The process is the same as for simple diffusion.
Osmosis
Comments: Osmosis is a special type of diffusion. The process is the same but only water moves to even up concentrations. Movement of water is from a weak solution into a strong solution.Example: water from the gut (diarrhoea) Cell wall in plants
Where? What? Energy?
Through the phospholipid bilayer
Water only NO
Diffusion across the (partially permeable) membrane.
12
Active Transport.
Comments: Active transport is movement against the concentration gradient to ‘build up’ rather than to‘even up’.
Where? What? Energy?
Through the protein molecules spanning the membrane.
Nutirent molecules, ions such as chloride ions (Cl-), sodium ions (Na+), potasssium ions (K+) and water
Yes
Bulk Transport (endocyctosis and exocytosis).
Comments: Phagocytosis (solids - cell eating) and pinocytosis (cell drinking – entry of liquid) are forms of endocytosis.
Where? What? Energy?
Small sections of the plasma membrane.
Large molecules such as enzymes, hormones and antibodies and foreign material.
YES