biology AS chapter 4

Question	Answer
why are phospholipids important in cell surface membranes?	the hydrophillic heads face outward in the bilayer meaning both sides attract water hydrophobic tails face inward due to repulsion from water on either side of the membrane
What are the functions of the phospholipids in the cell membrane?	1) allow movement of the lipid soluble substances 2) prevent movement of water soluble substances 3) ensure membrane is flexible and self sealing
what are the main ways proteins are embedded into the phospholipid bilayer?	1) on the surface of the membrane as a receptor for molecules such as hormones 2) across the whole membrane as protein channels (moves water soluble ions) or as as carrier proteins (molecules like glucose bind to them and they change shape to allow molecule to move into the cell)
what are the basic uses of proteins in the cell membrane?	1) provide structural support 2) act as channels to move substances 3) identify cells 4) act as receptors 5) help cells adhere together in a tissue
what are the functions of cholesterol?	1) reduce movement of molecules 2) make membrane more stable at high temperatures 3) prevent water and dissolved ions leaking from cells
what is the functions glycolipids in the cell membrane?	1) recognition site 2) maintain stability of cell 3) help cells to adhere to for tissues
what are the main functions of glycoproteins in a cell membrane?	1) act as recognition sites for the cell 2) help cells adhere to form tissues 3) allow cell recognition e.g. lymphocytes recognising own cells
why don't many substances diffuse across cell membranes?	1) substance isn't soluble in lipid so cant move through phospholipid layer 2) molecules are too large 3) same charge as protein channel so are repelled 4) molecules are charged so cant pass through phospholipid layer (uncharged)
explain the fluid mosaic model.	FLUID: phospholipid molecules can move against each other making it flexible, changing shape MOSAIC: proteins embedded are differently shaped and sized so look almost mosaic like
define diffusion	the net movement of molecules or ions from a region of high concentration to a region of low concentration until the particles are evenly distributed
why is diffusion described as a passive process?	because diffusion is due to the natural inbuilt motion of particles due to their own kinetic energy rather than being due to an external source of energy such as ATP
why is facilitated diffusion necessary?	diffusion only allows small uncharged molecules through, as the charged phospholipid molecules make it difficult for charged molecules to pass through
what is the mechanism of facilitated diffusion?	it is a passive process similar to diffusion, however requires the use of two protein types: protein channels and carrier proteins.
how do protein channels act in facilitated diffusion?	they are hydrophillic channels across the membrane which allow water soluble molecules through but the channels are specific to specific ions which bind to the protein, causing it to change shape allowing the molecule to move into or out of the cell. if the ion trying to bind to the protein is not the specific ion for the protein, the protein will remain closed.
how do carrier proteins act in facilitated diffusion?	specific molecules (e.g. glucose) bind to specific proteins causing them to change shape so that the molecule is released to the inside of the membrane. this is a passive process.
define osmosis	the passage of water from a region of higher water potential to a region of lower water potential through a selectively permeable membrane
define solution	a solute which has dissolved into a solvent
how is water potential measured	in pressure, usually kilopascals (KPa)
what is the water potential of pure water at standard conditions, and what are standard conditions?	standard condidtions: 25 degrees centigrade, 100KPa water potential of pure water: 0KPa
what does the addition of a solute do to water potential?	the addition of solute to water makes water potential lower (more negative). themore solute added, the lower the water potential.
how do the values of water potential work?	the highest possible value for water potential is 0 all other values are negative, so osmosis moves water from less negative areas to more negative areas
explain what happens to animal cells if the external conditions are: a) higher in water potential b) the same water potential c) lower water potential	a) the water potential is less negative outside, so water moves into the cell until it swells and bursts b) water enters and leaves cell at same rate so nothing happens to the cell c) the water potential is more negative outside, so water leaves the cell so it shrivels
define active transport	the movement of molecules or ions into or out of a cell from a region of low concentration to a region of high concentration using ATP and carrier proteins
how do carrier proteins work?	a molecule attaches to the protein causing it to change shape and therefore pushing the molecule into or out of the cell
what are the two main differences between active transport and facilitated diffusion?	1. active transport is against the concentration gradient 2. active transport uses energy
how do co-transport carrier proteins work?	two molecules bind to the protein at once causing the protein to change shape allowing the molecules into or out of the cell. one of these is against the concentration gradient.
explain the glucose-sodium co-transport process.	1) sodium ions are actively transported out of the epithelial cells and into the blood by the sodium potassium pump creating a concentration gradient due to more sodium in the blood 2) sodium diffuses into the epithelial cell through sodium-glucose co-transport carriers also carrying glucose 3) glucose concentration in the cell increaces 4) glucose diffuses out of the cell into the blood down its concentration gradient by facilitated diffusion

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biology AS chapter 4

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	Created by Olivia McKenzie-Allen almost 7 years ago