Cell membranes Flashcards
Chloride ions (Cl-) need to pass through the cell surf membrane to get inside the cell. How might they move across membrane
Using carrier or channel proteins in the membrane
The protein content of a typical cell membrane is around 50%.
In energy-releasing organelles, such as mitochondria, the amount rises to around 75%. Suggest a reason for this difference.
energy-releasing organelles require lots of substances (e.g. nutrients, enzymes, ATP) to travel across their membranes. Some of these substances will require help from proteins to get across the membrane, so these membranes will have a higher protein content.
A person removes some raspberries from the freezer that have frozen solid and leaves them on a plate to defrost. When he returns, there’s a red puddle on the plate around the fruit. Use your knowledge of cell membranes to explain what has happened.
Freezing the raspberries will have caused ice crystals to form and pierce the cell-surface membranes, making the membranes highly permeable when they thawed. This will have caused the red pigment to leak out of the raspberry cells as they defrosted.
What are the functions of cell membrane
Surround cells.
Boundaries cell and environment. Control what enter and leave to enable signalling (Pp)
divide cell component eg enzymes for respiration in the mitochondria makes more efficient.
The movement of substances across cell membranes is affected by membrane structure. Describe how
5 marks
1 Phospholipid (bilayer) allows movement/diffusion of non-polar/lipid-soluble substances;
1 and 2. Accept correct named examples
1 and 2. Ignore water
Accept phospholipid (bilayer) allows movement/diffusion of 02/002
Accept water-insoluble
- Phospholipid (bilayer) prevents movement/diffusion of polar/ charged/lipid-insoluble substances
Or
(Membrane) proteins allow polar/charged substances to cross the membrane/bilayer;
Accept water-soluble - Carrier proteins allow active transport;
- Channel/carrier proteins allow facilitated diffusion/co-transport;
Accept aquaporins allow osmosis - Shape/charge of channel / carrier determines which substances move;
- Number of channels/carriers determines how much movement;
- Membrane surface area determines how much diffusion/ movement.
6 and 7. Accept correct reference to faster/slower/rate for
‘how much movement’
Accept microvilli / Golgi (apparatus) / ER / rER
Accept surface area to volume for ‘surface area’
- Cholesterol affects fluidity/rigidity/permeability;
Accept cholesterol affects vesicle formation/ endocytosis/exocytosis/phagocytosis;
The decrease in the percentage of light passing through the water between 25 °C and 60 °C is caused by the release of the red pigment from cells of the beetroot.
Suggest how the increase in temperature of the water caused the release of the red pigment.
2 marks
- Damage to (cell surface) membrane;
- (membrane) proteins denature;
- Increased fluidity / damage to the phospholipid bilayer;
In mammals, in the early stages of pregnancy, a developing embryo exchanges substances with its mother via cells in the lining of the uterus. At this stage, there is a high concentration of glycogen in cells lining the uterus.
Suggest and explain two ways the cell-surface membranes of the cells lining the uterus may be adapted to allow rapid transport of nutrients.
2 marks
- Membrane folded so increased / large surface area;
Or
Membrane has increased / large surface area for (fast) diffusion / facilitated diffusion / active transport / co-transport; - Large number of protein channels / carriers (in membrane) for facilitated diffusion;
- Large number of protein carriers (in membrane) for active transport;
- Large number of protein (channels / carriers in membrane) for co-transport;
1: Accept microi villi to increase surface area’
Note feature and function required for each marking point and reference to large / many / more.
List rule applies.
