cell membrane transport methods Flashcards
What are the two different types of transport method?
Passive and active
What are the three different types of passive transport methods?
lipid diffusion, facilitated diffusion and osmosis (water diffusion)
What are the two different types of active transport methods?
Active transport and bulk transport (endocytosis and exocytosis)
What is a passive transport method?
How do they take place?
A process that does not require any energy other the thermal energy of the surroundings
They take place as a result of concentration, pressure or electrochemical gradients
Why do substances move around within the cell?
They move around randomly due to thermal motion
What is regular diffusion?
A net movement of substances across a cell membrane down the concentration gradient (from an area of high concentration to low concentration)
Do substances diffuse in both directions across a membrane or in just one direction?
Both, but there is a net movement down the concentration gradient
What are the factors that affect the rate of diffusion and why do they affect it?
(4 things)
- The steepness of the concentration gradient - the greater the difference in concentration the faster the rate
- Temperature - molecules have more kinetic energy at high temperatures therefore diffuse faster
3 The type of molecule or ion - large molecules diffuse more slowly than small ones. Non-polar molecules diffuse faster than polar molecules. - Surface area - the greater the surface area, the more molecules or ions that can cross it
What is another name for lipid diffusion?
Simple diffusion
What is lipid diffusion?
When a substance can diffuse directly through the lipid bilayer part of the membrane
What substances can undergo lipid diffusion?
Hydrophobic (lipid-soluble) molecules such as steroids, and very small hydrophilic molecules such as water oxygen and carbon dioxide.
What is facilitated diffusion?
The diffusion of a substance across the membrane through a trans-membrane transport protein molecule
i.e. with the aid of transport proteins
Are transport proteins specific or non-specific?
Specific-this means that substances can only cross membranes that contains the appropriate protein
How do channel proteins help facilitated diffusion?
They form a water filled pore or channel in the membrane which allows charged substances to defuse across
Are the channels gated or not?
Gated -this means that they can be open or closed, allowing the cell to control the entry and exit ions
Can cells change their permeability to certain ions using channel proteins?
Yes - due to the gated channels they get along certain substances in but not others
What are some examples of ions that can defuse across the membrane through specific ion channels?
Na+, K+, Ca2+ and Cl-
How do the carrier proteins help facilitated diffusion?
They have binding site for a specific solutes and constantly flip between two states so the site is alternately open to opposite side of the membrane
Where will the substance bind?
On the side with the highest concentration
Where will the substance be released?
On the side with the lowest concentration
What type of solutes can diffuse across the membrane through specific carrier proteins?
Amino acids and glucose
What is co-transport?
When a carrier proteins have two binding sites so can therefore carry two molecules at once
What is an example of co- transport?
The sodium/glucose co-transport found in the small intestine
What must be present for co-transport to take place?
Both the molecules
What is osmosis?
The diffusion of water molecules from a more dilute solution to a more concentrated solution across a partially permeable membrane
What two ways can water diffuse across the membrane?
Partly the phospholipids bilayer (which is an example of lipid diffusion) or partly through the protein channels called aquaporins (which is the example of facilitated diffusion)
Why is the concentration of water in most cells very high but is not free to diffuse?
Because water is the solvent in all cells however most of the water is bound to solvent molecules as a hydration shell
What is a hydration shell?
When the solvent is water, it is the number of solvent molecules surrounding each unit of solute
What happens when the solution is concentrated?
The more concentrated the solution, the more solute molecules are in a given volume and more water molecules are bound in hydration shells so there are less free water molecules
What happens when there is a concentration difference of solutes across the membrane?
There will also be a concentration difference of free water molecules across the membrane, so water will diffuse across.
What will a dilute solution have?
3 things
- A low concentration of solute
- A high concentration of free water
- A high solute potential
What will a concentrated solution have?
3 things
- A high concentration of solute
- A low concentration of free water
- A low solute potential
What is an active transport method?
A process that needs energy to occur
What is ATP?
adenosine triphosphate
How is ATP broken down?
What is it used for?
ATP is broken down by removing a phosphate ion
All active processes use ATP is their immediate source of energy
What is ATP synthesised from?
How is ATP synthesised?
ADP - adenosine diphosphate and phosphate (Pi)
Using hydrolosis and energy released from glucose in respiration in mitochondria
What is hydrolysis?
The splitting of ATP back to ADP and the phosphate which will release energy which drives the processes.
What is active transport?
The pumping of substances across a membrane by a trans membrane protein pump molecule using energy from ATP
What protein molecule does active transport involve?
ATPase enzymes
What do ATPase enzymes do?
They catalyse the hydrolysis of ATP to release energy
What are ATPase enzymes?
Transport proteins that have an active site on their cytoplasm side
How do ATPase enzymes aid active transport?
The protein binds a molecule of the substance to be transported on one side of the membrane,, changes the shape using energy from ATP spitting and releases the molecule on the other side.
Are ATPase enzymes specific?
Yes - therefore there is a different protein pump for each molecule type to be transported.
Does active transport always appear in same direction?
Yes
Is active transport movement of substances down a concentration gradient or up the concentration gradient?
Up
What is an example of an active transport pump?
the sodium/potassium ATPase (Na/K pump) which pumps sodium ions out of an animal cell and potassium ions in.
What is the bulk transport?
The transport of a large macromolecules like proteins and polysaccharides using membrane vesicles.
What is a membrane vesicle?
Small structures within the cell consisting of fluid enclosed by lipid bilayer
What does the movement and fusion of vesicles require?
Metabolic energy in the form of ATP
What is endocytosis?
Transport of substances into a cell.
Part of the membrane folds to form pockets that deepen and pinch shut to form a vesicle containing whatever material was captured outside the cell.
What is exocytosis?
Transport of substances out of the cell
The part of the membrane that formed a pocket opens and releases the material that was inside the cell
