Cell membrane transports Flashcards
(28 cards)
What is osmosis?
The diffusion of water across a partially permeable membrane from a dilute solution (high concentration of water) to a concentrated solution (low concentration of water).
What does a partially permeable membrane allow?
It allows water through, but won’t let larger molecules dissolved in water pass through
Why does water move?
To make the concentrations the same on both sides of the membrane. The likelihood of water molecules diffusing is the water potential.
Which direction does water move?
Water moves through the membrane in both directions, but the net movement will be from the dilute solution to the concentrated one
Which substance has the greatest and lowest water potential?
Pure water has the greatest water potential and concentrated solutions have lower. Isotonic solutions have equal water potentials on either side of the membrane.
What factors affect the rate of osmosis?
The lower the water potential gradient, the slower the rate.
The thicker the membrane, the slower the rate.
The smaller the surface area, the slower the rate.
What is diffusion?
The net movement of particles from an area of high concentration to an area of lower concentration
How do molecules move in diffusion?
They move randomly but tend to move into any space available until it is evenly distributed
What are examples of substances that move via diffusion?
CO2, O2 and urea can move in and out of cells across cell membranes via diffusion
What is facilitated diffusion?
Molecules diffuse through carrier proteins or channel proteins spanning across the membrane
Why do some materials move by facilitated diffusion?
Some materials are too large to move through the membrane. Other materials are polar molecules that are repelled by the hydrophobic part of the membrane.
What are channel proteins?
They allow polar compounds to avoid the non-polar central layer of the plasma membrane that would slow or prevent entry in
What are carrier proteins?
When a substance binds to carrier proteins, there is a change in the shape of the carrier protein. This change moves the substance from the outside of the cell to the inside.
What factors affect the rate of diffusion?
Concentration gradient
Temperature
Membrane surface area
Thickness of membrane
Channel or carrier proteins
How does concentration gradient affect the rate of diffusion?
The bigger the difference in concentration between two areas, the greater the concentration gradient and the faster the rate of diffusion
How does temperature affect the rate of diffusion?
The higher the temperature, the faster the rate of diffusion
How does membrane surface area affect the rate of diffusion?
The larger the surface area of the membrane that a substance is diffusing through, the faster the rate of diffusion
How does thickness of membrane affect the rate of diffusion?
The thicker the exchange surface, the slower the rate of diffusion
How does channel or carrier proteins affect the rate of diffusion?
The higher the concentration gradient, the faster the rate of facilitated diffusion until an equilibrium is reached and the rate will level off. The more proteins, the faster the rate.
What is active transport?
Moving ions and molecules across a membrane against the concentration gradient, using energy
What is an important membrane adaptation for active transport?
The presence of specific carrier proteins to facilitate movement
What are examples of active transport?
Sugar absorption in the gut
Mineral absorption in plants
What factors affect the rate of active transport?
The surface area of cell membranes
The number of carrier proteins in cell membranes
What are two ways substances can be actively transported across membranes using ATP?
Endocytosis
Exocytosis
