Membranes Flashcards
What is diffusion?
The net movement of particles from a high to low concentration
What is osmosis?
The net movement of water particles from an area of high water potential to an area of low water potential through a partially permeable membrane
What is active transport?
Movement of particles from a low to high concentration where energy is needed for it to happen (movement happens against a substance’s concentration gradient)
What are organelles?
Sub structure of the cell (all the things inside a cell)
What are eukaryotic cells?
Cells that contain membrane bound organelles eg. nucleus, mitochondria and chloroplasts. Eukaryotic cells are found in plants and animals
What are prokaryotic cells?
Cells that do not contain membrane bound organelles. Prokaryotic cells are found in bacteria
What is a plasma membrane?
The membrane at the cell surface (the same as a cell membrane)
What are the plasmodesmata?
The strips of shared cytoplasm between neighbouring plant cells
What is the middle lamella?
The gap between two cells that is sticky and joins them together
What are the cristae?
The cristae are folds in the inner membrane
When you add solutes does the water potential increase or decrease?
The water potential decreases when you add solutes
As you increase the pressure does the water potential increase or decrease?
The water potential increases as you increase the pressure
What does hypotonic mean?
When a cell has a higher water potential than another cell it is hypotonic to that cell
What does hypertonic mean?
When a cell has a lower water potential than another cell it is hypertonic to that cell
What does isotonic mean?
Equal concentration of solutes in solution meaning an equal water potential
What is water potential?
A measure of the tendency of water molecules to diffuse from one region to another
What is a glycolipid?
Lipid/phospholipid with a chain of carbohydrate molecules attached
What is a glycoprotein?
A protein with a chain of carbohydrate molecules attached
What does hydrophilic mean?
When a molecule is attracted to water
What does hydrophobic mean?
When a molecule is repelled by water
What is cholesterol?
A waxy type of lipid that gives mechanical stability and flexibility
What is a phospholipid?
A molecule with a phosphate head and a fatty acid tail, forms the phospholipid bilayer
What is an integral protein?
A protein/group of proteins permanently attached to a biological membrane
What is a peripheral protein?
A protein on the outside of the membrane
What are protein receptors?
Sensors embedded in the outer membrane that give information about the cell’s immediate surroundings
What are carrier proteins?
Proteins that carry substances from one side of a biological membrane to the other
What is bulk transport?
Some cells need to transport large molecules and particles that are too large to pass through the plasma membrane. They do this by bulk transport.
What is the equation for water potential?
Water potential = solute concentration (number becomes smaller as you add more solute) + pressure
Are the heads of phospholipids hydrophobic or hydrophilic?
Hydrophilic, they are attracted water and face outwards in the phospholipid bilayer
Are the tails of the phospholipids hydrophobic or hydrophilic?
Hydrophobic, they repel water and face inwards in the phospholipid bilayer
What is the role of the plasma membrane?
- Partially permeable so controls the transport of molecules in and out of the cels
- Separates content of cell from outside environment
- Allows other cells to recognise the cell as belonging to the body
- Allows molecules to bind to the receptors in membranes
- Holds components of some chemical reactions in place
What is the function of a phospholipid?
Maintains the shape of the phospholipid bilayer so they indirectly control what enters and exits the cell
What is the function of an integral protein?
Transport molecules in and out of the cell
What is the function of glycoproteins and glycolipids?
Cell recognition, cell signalling and receptors
What is the function of a peripheral protein?
Peripheral proteins act as enzymes
What is the effect of temperature on the plasma membrane?
The membrane components of the membrane gain more kinetic energy so phospholipids and proteins move about faster increasing the fluidity and permeability of the plasma membrane, when the temperature becomes too high the proteins will denature.
How does cholesterol maintain the mechanically stability of the membrane?
It partially immobilises nearby phospholipids and decreases the permeability of the membrane, cholesterol also prevents phospholipids from packing too close together and freezing when it’s too cold
How can solvents affect membranes?
Some solvents dissolve lipids so can permanently damage plasma membrane
How can some membranes withstand extremely high temperatures?
Some organisms contain heat-tolerant lipids in their membranes which make the membranes less permeable at higher temperatures
What is facilitated diffusion?
Movement of larger or polar molecules from an area of higher concentration to an area of low concentration with the help of a channel protein. They need a channel protein as they can’t pass between the phospholipids
What is bulk transport?
Large molecules have to be taken in and out of the cells by bulk transport. Endocytosis is movement into the cell with the help of vesicles, exocytosis is the movement of molecules out of the cell with the help of secretory vesicles
What factors affect the rate of simple diffusion?
- Temperature, as molecules have more kinetic energy, the membrane becomes more fluid and more molecules are able to pass through, also the molecules diffusing across the membrane also have more kinetic energy and therefore a faster rate of diffusion
- Diffusion distance, as the thickness of a membrane that a molecule is diffusing across increases, the rate of diffusion decreases
- Surface area, as the surface area increases, more molecules can diffuse across a larger surface area, cells specialised for absorption have extensions to their cell surface membranes called microvilli, they provide a larger surface area for diffusion
- Size of diffusing molecules, smaller molecules/ions diffuse faster than larger molecules
- Concentration gradient, the steeper the concentration gradient, the faster the rate of diffusion is down the gradient
What happens to an animal cell when it is in a solution of a higher water potential than itself?
Water enters the cell by osmosis and the cell becomes cytolysed as it bursts open
What happens to a plant cell when it is in a solution of a higher water potential than itself?
Water enters the cell by osmosis and the cell becomes turgid, the rigid cellulose cell wall prevents it from bursting
What happens to an animal cell when it is in a solution of a lower water potential than itself?
The animal cell shrinks as water leaves the cell by osmosis, the cell appears wrinkles and is crenated
What happens to a plant cell when it is in a solution of a lower water potential than itself?
The plant cell wall pulls away from the cell membrane as water leaves the cell by osmosis, the cell is plasmolysed
What is endocytosis?
- The process of bringing large molecules into the cell
- A part of the plasma membrane surrounds and encloses a molecule that can’t pass through the plasma membrane
- This forms a vesicle which is brought into the cell, carried by motor proteins along cytoskeleton threads
- Forming the vesicle and the movement of the vesicle by the motor proteins requires energy from ATP
What is exocytosis?
- The process of exporting large molecules out of cells
- A membrane bound vesicle containing the molecule that can’t pass through the plasma membrane is moved to the plasma membrane by motor proteins that walk along the cytoskeleton threads
- The vesicle fuses with the plasma membrane and the contents of the vesicles are released outside the cell
What happens to the cell surface membrane as temperature decreases?
- Saturated fatty acids become compressed
- As unsaturated fatty acids become compressed the kinks in their tails push adjacent phospholipids way therefore maintaining the fluidity
- This means that the proportions of saturated and unsaturated fatty acids determine the fluidity of the membrane at low temperatures
- Cholesterol also maintains the fluidity of the membrane by preventing phospholipid molecules from packing together too closely
What happens to the cell surface membrane as temperature increases?
- Permeability increases as phospholipids acquire more kinetic energy and therefore move around more, this increases the membranes fluidity
- As the fluidity of the membrane increases, the infolding of the plasma membrane for phagocytosis is affected
- Increase in membrane fluidity may also affect the ability of cells to signal to other cells by releasing chemicals, often by exocytosis
- Cholesterol buffers the effects of increasing heat as it reduces the increase in membrane fluidity
What is the ingestion of liquids by endocytosis called?
Pinocytosis
What is the effect of an increase of temperature on the proteins embedded in the plasma membrane?
- The increase in temperature causes the atoms within the protein to vibrate, this disrupts the hydrogen and ionic bonds that hold together the protein’s tertiary structure. This causes the embedded proteins and the cytoskeleton threads underneath the plasma membrane to denature. This causes the plasma membrane to fall apart and become more permeable as holes appear in the membrane
