Plasma Membranes

Question	Answer
Why do plant cells not burst?	They have a cellulose cell wall to give the cell structural integrity. When water enters the cell, the increased hydrostatic pressure pushes against the cell wall, giving it turgor. Turgor pressure resists the entry of more water.
What is crenation?	When too much water leaves an animal cell, causing it to shrivel.
What happens is too much water enters an animal cell?	The volume of solution inside the cells increases, increasing hyrdrostatic pressure. Because animal cells cannot withstand a very large increase in hydrostatic pressure so they can burst if too much water enters. this is cytolysis.
What is oncotic pressure?	The tendency for water to move into the blood by osmosis as a result of plasma proteins.
How does adding a solute to pure water affect its water potential?	It lowers its water potential
What is the water potential of pure water?	0kPa
What is water potential?	The pressure exerted by water molecules as they collide with a membrane or container.
Why is ATP needed for endo and exocytosis?	For movement of vesicles along the cytoskeleton, changing the shape of cells to engulf materials and to fuse cell membranes with vesicles.
Describe the two types of endocytosis	Endocytosis is the bulk transport of materials into cells. The two types are phagocytosis and pinocytosis. Both processes are the same but phagocytosis is the movement of solids and pinocytosis is the movement of liquids. First the membrane invaginates (bends inwards) when material comes into contact with it. The membrane surrounds the material, forming a vesicle. The vesicle pinches off and moves into the cytoplasm.
Describe the process of exocytosis	This is the bulk transport of material out of cells. Vesicles containing the material fuse with the cell membrane. The contents are then released out of the cell.
How do carrier proteins actively transport molecules into the cell?	1) A molecule or ion binds to receptors inside the carrier protein 2) ATP binds to the other end of the protein and it is hydrolysed into ADP and phosphate. 3) The phosphate binds to the carrier protein, which causes it to change shape, and the channel opens up to allow molecules to exit. 4) The phosphate molecule is released from the carrier protein and recombines with the ADP to form ATP 5) The protein returns to its original shape
What is facilitated diffusion?	Diffusion across a membrane through protein channels
What is the rate of facilitated diffusion dependent on?	Temperature, concentration gradient steepness, membrane surface area, membrane thickness, number of channel proteins present.
What kinds of solvent disrupt the phospholipid bilayer?	Solvents that are less polar than water or ones that are non-polar
What is cholesterol? Describe its role in the cell surface membrane.	It is a lipid with a hydrophilic end and a hydrophobic end, positioned between phospholipids in the cell surface membrane. The hydrophilic end interacts with the hydrophilic heads of the phospholipids and the hydrophobic end interacts with the hydrophobic tails of the phospholipids. This adds stability to membranes and regulates the fluidity of it.
How does temperature affect the permeability of the plasma membrane?	An increase in temperature increases the kinetic energy of the phospholipids, which causes the membrane to lose its structure. This increases permeability. Carrier and channel proteins can also denature at higher temperatures, which will allow molecules to pass through. This also increases permeability.
What are the two types of cell surface membrane proteins?	Intrinsic - Transmembrane proteins that are embedded through both layers of a membrane. They have amino acids with hydrophobic R-groups on their external surfaces, which interact with the hydrophobic core of the membrane, keeping them in place. Extrinsic- present on one side of the bilayer. They normally have hydophilic R-groups on their outer surfaces and interact with the polar heads of the phosphlipids or with intrinsic proteins to keep them in place.
Describe the role of channel proteins	They provide a hydrophilic channel that allows the passive movement of polar molecules and ions down a concentration gradient through membranes.
Describe the fluid mosaic model	Phospholipids are free to move like a fluid, giving the membrane flexibility. proteins are embedded in the various positions in the membrane.
Why is it important that the hydrophilic phosphate heads of the phospholipid bilayer are facing outwards?	Cells exist in aqueous environments and the inside of cells and organelles are also aqueous. The phospholipid bilayer is suited as a membrane in this environment because the outer hydrophilic phosphate layers can interact with the water.
What are glycoproteins? Describe their functions.	Glycoproteins are intrinsic proteins that are embedded into the cell surface membrane and have carbohydrates attached to them. They play a role in cell adhesion. They also act as receptors for chemical signals. Chemicals bind to the receptor, which causes a response from the cell. This is cell communication or cell signalling.
Describe the role of carrier proteins	They allow passive and active transport of polar and non polar molecules through them
What is compartmentalisation?	The formation of separate membrane bound areas in a cell. This allows separate parts of the cell to have the specific conditions needs for cellular reactions, such as chemical gradients to be maintained. This protects other vital cell components.
What is a plasma membrane?	The barrier which separates a cell from its external environment
What is the structure of a phospholipid bilayer?	Hydrophilic phosphate heads form both the inner layer and outer surface of the bilayer and hydrophobic fatty acid tails are together in a hydrophobic core between the two phosphate layers.
What is the function of glycolipids?	Glycolipids act as antigens. They helps the immune system recognise the cell as self so it doesn't attack it.
What happens when a plant cell loses too much water?	It plasmolyses - the cell-surface membrane pulls away from the cell wall
What give beetroot its colour?	Red Betalain pigment

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	Created by Kayla Price about 8 years ago