Chapter 5 - Plasma Membranes Flashcards
State three roles of membranes inside a cell
- Forms organelles
- Provide selective permeability of membrane so can control what goes in and out of a organelle
- Sites for attachment of ribosomes/enzymes
State three roles of membranes at the surface of a cell
- Controls what enters and exits the cell
- Allows cell communication/ contains receptors for cell signalling
- Allows creation of concentration gradient
How does the fluid mosaic model describe the structure of plasma membranes?
It shows that there is a phospholipid bilayer.
The phospholipids are free to move in the membrane causing it to be ‘fluid’
Proteins are randomly arranged between the phospholipids making it ‘mosaic’
Explain why progesterone can move across membranes.
Progesterone is hydrophobic and a lipid molecule, therefore it is not repelled by the hydrophobic tails.
Name one molecule that can cross plasma membranes.
Oxygen
State how the structure of the cell surface membrane allows potassium ions to enter or leave a cell.
There are carrier proteins
ATP is made up of phosphate groups and two other molecules.
Name the two other molecules
Adenine
Ribose
An investigation into how a change in sodium chloride concentration effects osmosis in potato cells concluded that the isotonic point of the potato was 0.25M.
Describe what is happening at the isotonic point?
The movement of water into the potato cells is equal to the movement of water out of the potato cells.
A student uses cubes of agar jelly containing universal indicator, which changes colour at different pH.
What was the role of the universal indicator in this experiment?
Detect the presence of acid / H+
Describe the role of cholesterol in cell surface membranes in the human body?
D - Cholesterol binds to phospholipid fatty acid tails increasing the packing of the membrane, therefore reducing the fluidity of the membrane.
The student plots the data on a graph about the effect of temperate on beetroot membrane permeability.
Describe and explain the pattern of data shown on the graph as temperature increases.
An increase in pigment leaking out of the cells increases absorbance.
At lower temperature little/no change in absorbance, membrane is still intact.
At higher temperature there is a steep increase in absorbance, pigment leaves cells, membrane becomes more permeable and proteins denature.
A student places cubes in beakers of dilute HCl, which caused the indicator to become colourless. They then measured how much of each cube became colourless over time.
State 2 ways the student could have ensured they had confidence in their results.
Repeat readings and calculate mean
identify anomalies
Explain why the surface area to volume ratio of an organism determines whether it needs a circulatory system.
Larger organisms have smaller SA : Vol ratio
Therefore rate of diffusion is slow
without circulatory sustain not all cells would be supplied quick enough to carry out its function
Name the process by which water leaves the cell
Osmosis
Describe the routes that water molecules take through the cell surface membrane.
fit between phospholipid bilayer
They can also travel via protein channels
