Cell Membranes

?
  • Created by: vimal__
  • Created on: 18-11-17 22:29
What is the most basic cell membrane?
Cell-surface membrane (Plasma membrane).
1 of 46
What do they do?
Cell-surface membranes surround cells. They are a barrier between the cell and its environment controlling which substances enter and leave the cell.
2 of 46
Cell membranes are partially permeable. What does this mean?
They let some molecules through but not others.
3 of 46
Name the three main ways substances can move across cell membranes.
Diffusion, osmosis and active transport.
4 of 46
There can be membranes within cells as well. Give an example of a membrane within a cell, and what it encloses.
The substances needed for respiration are kept together inside a mitochondrion by the membrane surrounding the mitochondrion.
5 of 46
Some of the membranes within cells are partially permeable. Give an example of a partially permeable membrane within a cell.
RNA leaves the nucleus via the nuclear envelope. DNA is too large to pass through the partially permeable membrane so it stays in the nucleus.
6 of 46
What are most cell membrane composed of?
Phospholipids, proteins and carbohydrates.
7 of 46
Cell membranes have a continuous, double layer. What is this double layer called?
Phospholipid bilayer.
8 of 46
Why is it called the Fluid Mosaic Model?
Fluid; Phospholipids are constantly moving. Mosaic: Proteins are scattered through the bilayer like tiles in a mosaic.
9 of 46
What type of proteins does the bilayer have? What do they do?
Channel and carrier proteins allow large molecules and ions to pass through the membrane.
10 of 46
What are glycoproteins? What are glycolipids?
Glycoproteins are proteins with a carbohydrate attached. Glycolipids are lipids with a protein attached.
11 of 46
Is cholesterol present in the bilayer?
Yes.
12 of 46
What do phospholipids form a barrier to?
Water-soluble substances.
13 of 46
Phospholipids have a head and a tail. Draw the bilayer. How do the head and tail respond to water?
The head is hydrophilic and the tail is hydrophobic.
14 of 46
The molecules automatically arrange themselves into a bilayer. How do they do this?
The heads face out towards the water on either side of the membrane.
15 of 46
The centre of the bilayer is hydrophobic. What does this mean?
That the membrane doesn't allow water soluble substances to diffuse through it. It only allows small, non-polar molecules (e.g. water and CO2) to diffuse through it.
16 of 46
What is cholesterol and what does it do?
Cholesterol is a type of lipid that fits in between the phospholipids, giving the membrane stability.
17 of 46
What does cholesterol restrict the movement of? What is the importance of this?
Cholesterol restricts the movement of phospholipids by binding to the hydrophobic tails. This makes the membrane less fluid and more rigid.
18 of 46
Cholesterol helps to maintain the shape of animal cells, which don't have cell walls. What is this important for?
This is important for cells that aren't supported by other cells (e.g. red blood cell which float free in the blood)
19 of 46
Describe the permeability of the membrane below 0 degrees celsius.
Phospholipids have little energy, so they don't move much. They're packed closely together so membrane is rigid. But channel + carrier proteins denature, increasing permeability. Ice crystals pierce the membrane, increasing permeability when it thaws
20 of 46
Describe the permeability of the membrane between 0 and 45 degrees celsius.
Phospholipids can move around and aren't packed as closely together, the membrane is partially permeable. As temperature increases, phospholipids move more as they have more energy, increasing permeability of the membrane.
21 of 46
Describe the permeability of the membrane above 45 degrees celsius.
Phospholipid bilayer begins to melt and the membrane becomes more permeable. Channel and carrier proteins denature so they can't control what comes in/goes out, so the permeability of the membrane increases.
22 of 46
Define diffusion.
Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration.
23 of 46
Molecules will diffuse both ways, but the net movement of particles will always be in the direction of the area of lower concentration. When does this happen until?
This continues until particles are evenly distributed in the liquid/gas.
24 of 46
What is the concentration gradient?
The path from an area of high to low concentration. Particles diffuse down the concentration gradient.
25 of 46
Is diffusion an active or passive process?
Diffusion is a passive process - no energy is required for it to happen.
26 of 46
Draw a diagram showing the diffusion of CO2 through the membrane.
....
27 of 46
How does the concentration gradient affect rate of diffusion?
The higher it is, the faster the rate of diffusion. As diffusion takes place, the difference in concentration between both sides of the membrane decreases until it reaches an equilibrium. This means diffusion slows down over time.
28 of 46
How does the thickness of the exchange surface affect rate of diffusion?
The thinner the exchange surface, the faster the rate of diffusion.
29 of 46
How does the surface area affect rate of diffusion? Give an example.
The larger the surface area, the faster the rate of diffusion. E.g. Some specialised cells have microvilli, which give the cell-surface membrane a larger surface area.
30 of 46
What is facilitated diffusion?
Large particles or charged particles diffuse through carrier proteins or channel proteins in the cell membrane.
31 of 46
In what direction does facilitated diffusion move particles? Is facilitated diffusion active or passive?
Facilitated diffusion moves particles down a concentration gradient - from a high to low concentration. It is passive, so no energy is needed for it to happen.
32 of 46
What do carrier proteins do?
Carrier proteins move large molecules across the membrane down the concentration gradient.
33 of 46
How do carrier proteins work?
A large molecule attaches to a carrier protein in the membrane. Then, the protein changes shape. This releases the molecule on the opposite side of the membrane.
34 of 46
Draw a diagram showing how carrier proteins work.
....
35 of 46
How do channel proteins work?
Channel proteins form pores in the membrane for charged particles to diffuse through (down the concentration gradient).
36 of 46
Draw a diagram showing how channel proteins work.
.....
37 of 46
How does the concentration gradient affect the rate of facilitating diffusion?
The higher the concentration, the faster the rate of facilitating diffusion. As equilibrium is reached, the rate of facilitating diffusion levels off.
38 of 46
How does the number of channel and carrier proteins affect the rate of facilitating diffusion?
Increasing the number of channel/carrier proteins in a membrane would increase the rate of facilitating diffusion as more particles would be allowed to be transported across the membrane at the same time.
39 of 46
What happens when all the proteins in a membrane are in use?
Facilitated diffusion can't happen any faster, even if the concentration gradient was increased.
40 of 46
Some cells are adapted for rapid facilitated diffusion across their membranes by having more transport proteins in their membranes. Give an example of this.
Kidney cells are adapted to have lots of aquaporins (a type of channel protein). The aquaporins allow the cells to reabsorb a lot of the water that would otherwise be excreted by the body.
41 of 46
Define osmosis.
The diffusion of water molecules across a partially permeable membrane, from an area of higher water potential to an area of lower water potential. (e.g. higher concentration of water molecules to lower concentration of water molecules).
42 of 46
Define water potential.
The potential of water molecules to diffuse into or out of a solution.
43 of 46
What is meant by the term isotonic?
If two solutions have the same water potential, they're isotonic. There's no net movement of water molecules in cells of an isotonic solution. This is because there's no difference in water potential between the cell + the surrounding solution.
44 of 46
What is meant by the term hypotonic?
Solutions with a higher water potential compared with the inside of the cell. There's a net movement of water molecules into the cell.
45 of 46
What is meant by the term hypertonic?
Solution with a lower water potential compared with the inside of the cell. There's a net movement of water out of the cell.
46 of 46

Other cards in this set

Card 2

Front

What do they do?

Back

Cell-surface membranes surround cells. They are a barrier between the cell and its environment controlling which substances enter and leave the cell.

Card 3

Front

Cell membranes are partially permeable. What does this mean?

Back

Preview of the front of card 3

Card 4

Front

Name the three main ways substances can move across cell membranes.

Back

Preview of the front of card 4

Card 5

Front

There can be membranes within cells as well. Give an example of a membrane within a cell, and what it encloses.

Back

Preview of the front of card 5
View more cards

Comments

No comments have yet been made

Similar Biology resources:

Cells
Cells
See all Biology resources »See all Cellular processes resources »