Chapter 3 Cell Membrane and Transport Flashcards
What is the function of the cell membrane?
Controls the exchange of materials between the cell and its environment.
What are the characteristics of a phospholipid?
A phospholipid has a glycerol and two fatty acids with a phosphate. The phosphate end is the head which is hydrophilic. The glycerol and fatty acids make up the tail which is hydrophobic.
Define hydrophilic
Polar ; a molecule that can interact with water molecules because of its charge.
Define hydrophobic
Non-polar ; a molecule that cannot interact with water molecules because it has no charge.
What two types of proteins are embedded in the cell membrane?
Intrinsic proteins
Extrinsic proteins
What are the function of intrinsic proteins?
Transporting water soluble substances across the bilayer by forming channels.
What is the function of cholesterol in the cell membrane?
It limits the movement of the phospholipids giving the membrane stability. It stops the cell leaking water because it is hydrophobic.
What is the structure and function of glycoprotein in the cell membrane?
A carbohydrate attached to a protein. It is a receptor site for chemicals and hormones
What is the structure and function of glycolipids in the cell membrane?
A branching carbohydrate attached to a phospholipid. It is a receptor site for chemicals/hormones.
Why is the model of membrane structure called the ‘fluid-mosaic’ model?
The phospholipid molecules are constantly moving and therefore fluid.
The proteins embedded in the bilayer vary in shape, size and pattern like a mosaic.
What is exocytosis?
The active process of a vesicle fusing with the cell membrane, releasing the molecules it contains. Used for cell secretions.
What is endocytosis?
The active process of the cell membrane engulfing material, bringing it into the cell in a vesicle.
What are the two types of endocytosis?
Phagocytosis
Pinocytosis
What is phagocytosis?
The active process of the cell membrane engulfing large particles, bringing them into the cell in a vesicle, and breaking them down by releasing digestive enzymes.
What is pinocytosis?
The active process of the cell membrane engulfing droplets of fluid, bringing them in a vesicle.
How is the cell membrane selectively permeable?
The cell surface membrane is selectively permeable to water and some solutes depending if they are lipid soluble or water soluble.
How do lipid-soluble substance move through the cell membrane?
Lipid soluble substances such as vitamin A and Oxygen dissolve into the phospholipids and diffuse across the membrane. The bilayer is hydrophobic so lipid soluble molecules can move through easily.
How do water-soluble substances move through the cell membrane?
Water soluble substances such as glucose cannot diffuse through the phospholipids and must pass through intrinsic protein molecules which form water filled channels across the membrane.
Define diffusion
The passive movement of a molecule or ion down a concentration gradient, from a region of high concentration to a region of low concentration.
What is Fick’s law of diffusion?
Rate of diffusion= Surface area x difference in conc. / distance
What 4 factors effect diffusion?
Concentration gradient
Distance
Surface area
Thickness of membrane
Define facilitated diffusion
The passive movement of molecules or ions down a concentration gradient by protein carriers.
What are the factors that effect facilitated diffusion?
Surface area Thickness of membrane Distance Concentration gradient Saturation of proteins
Define active transport
The movement of molecules or ions against a concentration gradient using ATP
What factors effect active transport?
Surface area Thickness of membrane Distance Concentration gradient Saturation of proteins ATP
Define Osmosis
The ent passive movement of water molecules across a semipermeable membrane from a region of high water potential to a region of low water potential.
Define water potential
The tendency for water to move into a system; water moves from a region of high water potential to low water potential.
What is the water potential of pure water in kPa?
Zero (0) kPa
Define solute potential
A measure of the osmotic strength of a solution. It is the reduction in water potential due to the presence of solute molecules
What is the water potential equation?
Water potential= pressure potential + solute potential
Ψ= Ψp+ Ψs
Define pressure potential
The pressure exerted by the cell wall contents on the cell wall
Define turgid
A plant cell wall that holds as much water as possible. Further entry of water is prevented as the cell wall cannot expand further.
Define plasmolysis
The retraction of the cytoplasm and cell membrane from the cell wall as it loses water
Define incipient plasmolysis
Cell membrane and cytoplasm are partially detached from the cell wall due to insufficient water to make the cell turgid.
What is the pressure potential at incipient plasmolysis?
0kPa
Define haemolysis
If water moves into red blood cells by osmosis, without the cell wall they burst.
Define hypotonic
The water potential of the external solution has a high water potential (less negative) than the solution inside the cell.
Water moves into the cell by osmosis
Define hypertonic
The water potential of the external solution is lower (more negative) than the solution inside the cell.
Water moves out of the cell by osmosis
Define isotonic
The water potential of the external solution is equal to the water potential of the solution inside the cell.
There is no net movement of water
