3.2.2 Transport Across Cell Membranes Flashcards
Water is dipolar. What do we mean by dipolar?
One end of the molecule has a slight positive charge, the other end is slightly negative
Why is water important for living things?
It is used in metabolism (condensation/ hydrolysis), it is a solvent for many substances, water potential has to be at the right level so cells don’t shrivel or burst due to osmosis
How does ATP release energy to a cell?
ATP undergoes hydrolysis to form ADP + Pi, releasing energy.
Which part of a phospholipid is hydrophobic?
Tail
What is the role of cholesterol in the plasma membrane?
add strength, reduce lateral movement, stop leakage
Describe the importance of a partially permeable membrane.
The membrane will only allow certain molecules through- regulates movements of solutes
What does the fluid mosaic model describe?
The phospholipid bilayer is interspersed with proteins (like tiles in a mosaic), & constantly move (fluid)
The centre of the bilayer is hydrophobic. So which type of molecules can diffuse through.
Small & non-polar. (Water also does! As it’s so small).
How would chloride (Cl-) ions move across the membrane?
Across a channel protein
What is a glycoprotein?
Proteins with a carbohydrate attached- usually protrude from the membrane.
Would you expect a red blood cell, or an epithelial cell of the small intestine, to contain more cholesterol in the plasma membrane?
Red blood cell- unsupported & free-floating cell, so needs to maintain own shape.
If high temperatures are applied to the Plasma membrane, what happens?
Channel/carrier proteins denature, so membrane becomes more permeable (it can’t control what is going in/out)
What is diffusion?
The net movement of molecules from an area of high concentration to an area of low concentration (DOWN the conc. gradient)
Is diffusion a passive or active process?
Passive-no energy is needed.
Give an example of a molecule which can use simple diffusion to pass through the membrane.
Small, non-polar e.g. oxygen, carbon dioxide
Describe the role of a carrier protein.
Use to move large molecules across the membrane- when ion/molecule attaches to protein, it changes shape & releases molecules on other side of membrane.
What is facilitated diffusion?
Movement of particles from a high to low concentration, down the conc. gradient, using a membrane protein.
Which types of molecules would be transported using facilitated diffusion across the membrane?
Large, polar, water-soluble (e.g. glucose, amino acids)
Describe the role of a channel protein.
Acts as a pore in the membrane to allow larger/polar molecules to diffuse across.
A graph showing the uptake of glucose by GLUT1 carrier proteins, shows that the rate increases as the number of glucose molecules increases. However the graph plateaus, why?
The system reaches equilibrium- there are only so many carrier proteins- if most of these are in use, then the rate of glucose uptake would slow.
How can the gradient of a straight line or tangent by calculated?
Change in y / change in x
Is facilitated diffusion a passive or active process?
Passive-no energy is needed.
What is osmosis?
The net movement of water molecules through a partially permeable membrane, from an area of high water potential (less negative) to an area of lower water potential (more negative).
What is the water potential of pure water?
Water potential ψ = 0
If more of a solute (e.g. salt) is added to a beaker of water, what would happen to the water potential of the solution?
More solute = less water molecules, so LOWER water potential (more negative)
Describe how you would use a calibration curve to identify the water potential of a sample.
Identify the point at which the curve meets the x axis (where % change in mass is 0). Find the concentration at this point & look up water potential.
Pieces of potato with a ψ of -350 kPa are placed into a solution with a ψ of -275 kPa. Explain what will happen to the potato.
Potato gains mass (has a lower ψ than the solution OR MORE negative ψ) so water moves from solution into the potato.
what words describe what happens to red blood cells if placed in solutions of high, the same, and low water potential?
what words describe what happens to plant cells if placed in solutions of high, the same, and low water potential?
What is active transport?
The movement of particles from an area of lower concentration to higher concentration, requiring energy. (AGAINST a conc. gradient)
Will the rate of active transport increase or decrease if the number of carrier proteins in the membrane is increased?
Increase
Describe the importance of sodium ions in the transport of glucose from the ileum into the blood.
Na + ions diffuse through a carrier protein down their conc. gradient, carrying glucose in simultaneously, which is moving AGAINST it’s gradient. Glucose can then diffuse into the blood & be transported around the body.
Describe the importance of the villi in the small intestine.
Villi- increase surface area of ileum, so more products of digestion can be absorbed.
Define facilitated diffusion
Larger molecules and charged particles cannot diffuse through the phospholipid bilayer as they are insoluble. They diffuse through carrier or channel proteins in the cell membrane instead. Passive process
What are carrier proteins?
Move large molecules into or out of the cell down their concentration gradient. Different carrier proteins facilitate the diffusion of different molecules
How do carrier proteins work?
A large molecule binds to a specific site in the carrier protein. The protein changes shape and releases the molecule on the opposite side of the membrane
What is a channel protein?
Channel proteins - Form pores in the membrane for charged particles to diffuse through. Different channel proteins facilitate the diffusion of different charged particles. All have a specific shape and can be opened or closed
Define active transport
Active transport - Uses energy to move molecules and ions across the plasma membranes against a concentration gradient. Use carrier proteins
Explain how active transport works
A molecule attaches to the carrier protein. ATP is hydrolysed in the cell to release energy. This energy is used to make the carrier protein change shape. This moves the molecule across the membrane, releasing it on the other side.