Transport Across the Membrane Flashcards
(29 cards)
Why is the Cell membrane described as a fluid-mosaic?
It is described as fluid as the phospholipids are constantly moving and mosaic as the proteins of different sizes and shapes look like a mosaic when looked at from above.
What are the main components of the cell membrane?
- Phospholipids
- Cholesterol
- Glycolipids and Glycoproteins
- Extrinsic proteins are found on the top and bottom of the membrane, and intrinsic proteins are found throughout the membrane ( channels and carrier proteins).
What is the function of phospholipids in the cell membrane?
When placed in an aqueous environment, the hydrophilic heads face outwards toward the water, and the hydrophobic tails face away from the water and towards each other. This forms a hydrophobic layer that only allows lipid-soluble substances to pass through via simple diffusion.
What is the function of cholesterol in the cell membrane and how does it carry out it’s function?
It controls the fluidity of the membrane. When the temperature increases the hydrophobic regions of the cholesterol bind to the fatty acid tails preventing the phospholipids from moving too far away from each other and the membrane becoming too fluid. They also lay between the phospholipid and prevent them from packing too closely together and the membrane freezing in colder temperatures.
What are glycolipids and glycoproteins?
- Glycolipids are lipids attached to carbohydrates and glycoproteins are proteins attached to carbohydrates.
- They are used for cell adhesion ( cells sticking to other cells), cell recognition and cell signalling between cells.
What is the function of carrier proteins in the cell membrane and how do they carry out that function?
- Carrier proteins are used to transport large molecules like glucose and amino acids across the membrane.
- The molecule attaches to the protein. Then ATP binds to the carrier protein and the hydrolysis of ATP causes the protein to change shape and let the molecule pass to the other side of the membrane.
What is the function of channel proteins in the cell membrane and how do they carry out that function?
- Channel proteins are used to transport ions across the membrane.
- They form pores in the membrane that allow the ions to pass through.
What is diffusion?
The movement of small, lipid-soluble substances from an area of high concentration to an area of low concentration.
What substances move across the membrane via diffusion?
Small and lipid-soluble substances like oxygen and carbon dioxide.
Why does diffusion decrease overtime?
The particles diffuse down a concentration gradient, and as they do this, the concentration gradient starts decreasing as it evens out. This means the rate of diffusion also decreases.
What factors affect the rate of diffusion?
- Thickness of the membrane.
- Concentration gradient.
- Surface Area.
How does the concentration gradient affect the rate of diffusion?
As the concentration gradient increases the rate of diffusion increases.
How does the thickness of the membrane affect the rate of diffusion?
As the thickness of the membrane increases the rate of diffusion decreases as the diffusion distance increases.
How does the surface area affect the rate of diffusion?
As the surface area increases the rate of diffusion increases as more particles can move past the membrane at one time.
What is facilitated diffusion?
The movement of large, polar substances down a concentration gradient with the help of transport proteins.
What substances are transported across the membrane via facilitated diffusion?
Large, polar substances.
What factors affect the rate of facilitated diffusion?
- The thickness of the membrane.
- Surface Area of the membrane.
- The concentration gradient.
- The number of channel and carrier proteins present.
What is active transport?
The movement of substances from an area of low concentration to an area of high concentration with the use of carrier proteins and the energy released by ATP.
Compare and contrast the movement of substances across the cell membrane via active transport, diffusion and facilitated diffusion?
- Diffusion and facilitated diffusion involve the movement of substances down a concentration gradient and active transport involves movement against a concentration gradient.
- Facilitated diffusion and diffusion do not require any energy to work active transport does.
- Diffusion does not require the use of transport proteins but facilitated diffusion and active transport do.
- Facilitated diffusion requires both the use of channel and carrier proteins but active transport only requires the use of carrier proteins.
What is water potential?
The tendency of water to move out of a solution.
What is osmosis?
The movement of water from an area of high water potential to an area of low water potential across a partially permeable membrane.
What is a hypertonic solution?
The water potential of the solution is lower than the cells inside it.
What is a hypotonic solution?
The water potential of the solution is higher than the cells inside it.
What happens when you place an animal cell in a hypertonic solution?
The water potential inside the cell is higher compared to the water potential of the solution. This means water will move down a concentration gradient, out of the cell and into the solution via osmosis. This will cause the the animal cell to shrink ( lysis).
