2.1.5 Flashcards
What is the function of a plasma membrane?
barrier between the cell and it’s environment
What does the plasma membrane control?
the transfer of substances in and out of the cell
e.g water, ions , gases
What substances can pass through the plasma membrane?
water, ions, gases
What are the roles of membranes?
- compartmentalisation
- site of chemical reactions
- site of cell commuication / cell signalling
What are 2 key roles of membranes within organelles?
allows for concentration gradients to be established and maintained
Embedding of enzymes into the membrane
How do cells communicate?
signals like hormones bind to a specific receptor with a complimentary shape
What is cell signalling?
communication between cells
cell recognition / identification
cells working together
to trigger a response
How does insulin regulate blood sugar levels?
1) Insulin is produced from beta cells in the islet of langerhans in the pancreas in reponse to high blood sugar
2) Insulin binds to receptors in the cell memrane of cells such as muscle and liver cells
3)This triggers a response inside the muscle or liver cell causing glucose to be taken up from the blood and reducing blood sugar level
How do beta blockers work to reduce the chance of a heart attack?
beta blockers stop neurotransmitters binding to heart muscle therefore decreasing the chance of a heart attack
How does botox work?
botox blocks receptors in muscke fibres
stopping them from working and causing paralysis
How does HIV get into a cell?
mimicking the receptor sites for a white blood cell
What is the structure of a phospholipid?
2 fatty acids, 1 glycerol molecule and a phosphate group
What part of the phospholipid is hydrophobic?
Fatty acid chains
What part of the phospholipid is hydrophillic?
glycerol and phosphate
Why do the phospholipids arrange themselves in a bilayer at the cell surface?
hydrophillic heads oreintate themselves towards water and the hydrophobic tails orenitate themselves away from water
Intracellular fluid inside the cell and extracellular fluid outside the cell
Why is it called the fluid mosaic model?
fluid - components in the membrane move around, flexible
Mosaic - proteins embedded in the membrane give it a mosaic look
What are the functions of glycoproteins and glycolipids?
- Cell recogition / identification
- Cell signalling
- acts as antigens
- Acts as receptors
- Adhesion
What are the roles of the proteins in the fluid-mosaic model?
Carrier proteins transport large and polar substances
Channel proteins transport polar substances
What is the role of cholesterol in the membrane?
found between tails of phospholipids and regulates fluidity
more cholestrol - less fluid the membrane is
What factors affect membrane permeability?
- heat
- ethanol
- detergent / soap / washing-up liquid
How does heat affect membrane permeability?
- As temperature increases, phospholipids gain kinetic energy
- causes gaps to appear between phospholipids
- membrane becomes more permeable
- At high temperatures proteins in the membrane denature
How does ethanol affect membrane permeability?
- Alcohol dissolves the phospholipid bilayer
- the higher the alcohol concentration the more permeable the membrane becomes
How does detergent affect the membrane permeability?
Detergents dissolve the phospholipid bilayer making the membrane more permeable
What are the control variables in the beetroot experiment?
Mass / length of beetroot
Same species of beetroot
Same volume of water
All beetroot cylinders in water for the same time
What should you do after cutting the beetroot?
pat beetroot dry once samples are cut to remove any excess pigment caused by damaging the membranes
What is the process of the beetroot experiment
Take samples of beetroot and place into water at different temperatures. Compare colour change.
What happens to the colour when the temperature is increased?
As temp increases, colour is darker
Colorimeter absorption increases
as more pigment has been released from samples of beetroot into the water
How do you calibrate the colorimteter?
Fill cuvette water (blank)
put blank into colorimeter
press calibrate and it should be 0%
ensure red fliter and blue light
Remove and blank and add a cuvette with solution from beetroot
What is the reasoning why absorption increases with temperature?
as temperature increases,
phospholipids gain KE,
Causes gaps to appear between the phospholipids
membrane becomes more permeable
therefore more pigment will leak out of the cell
at high temperatures the proteins in the membrane will denature
What is diffusion?
net movement of molecules form an area of higher concentration to an area of lower concentration
passive
continues until particles are uniformly distributed throughout system in equilibrium
What is a concentration gradient?
the difference in concentration between 2 regions
What factors affect diffusion?
How lipid soluble a substance is
the thickness of the cell membrane
surface area
difference in concentration
How does lipid solubility affect diffusion?
charged particles like ions and large molecules like glucose cannot pass readily through the plasma membrane
How does thickness of the membrane affect diffusion?
the thicker the membrane, the more time it takes for diffusion to occur
How does surface area affect diffusion?
when increased, we can increase the rate of diffusion
How does difference in concentration / maintaining a concentration difference affect diffusion?
steep concentration difference
means particles move more rapidly in order to achieve an eqiulbrium
What is the difference between channel proteins and carrier proteins?
Channel proteins are pores that allow the movement of ions. Channels proteins are specific to different ions
Carrier proteins allow movement of larger molecules across the membrane.
Larger molecules are specific to the molecule they transport and involve a shape change to release the molecule on the opposite side of the membrane
What is faciliated diffusion?
Passive process
requires a channel or carrier protein
molecules move down the concentration gradient
What is active transport?
movement against concentration gradient
from an area of low concentration to an area of higher concenration
ATP required -> to change shape of carrier protein
carrier proteins used
How does exocytosis occur?
Cytoskeleton contracts
to move the vesicle to the plasma membrane
the membrane of the vesicle and plasma membrane fuse
releasing contents
How does endocytosis occur?
influx of substances that push into membrane
membrane pinches off to form vesicle
What is osmosis?
net movement of water molecules from a region of higher water potential to a region of lower water potential
across a partially permeable membrane
What is water potential?
ability of water to move depending on solute
What is the water potential of pure water?
0 - the highest W.P
What would happen if you dissolved solutes into water?
W.P will become more and more negative
What would happen if cell A has a W.P of -450 and B has a water potential of 0?
B has a higher water potential than A
so water moves from B to A
down the water potential gradient by osmosis
What happens id cell B has a water potential of 0 and cell C has a water potential of -375?
B has a higher water potential than C
so water moves down the concentration gradient by osmosis from B into C
What happens if cell A has a water potential of -450 and cell C has a water potential of -375?
Cell C has a higher water potential than A
so water moves from Cell C to Cell A down the concentration gradient by osmosis
What happens if a cell is surrounded by pure water or a solution with a higher water potential ?
Water flows into the cell by osmosis
What is the name for the external solution if a cell is surrounded by pure water or a solution with a high water potential?
external solution is hypotonic
What happens if a cell is surrounded by a solutionw itha lower water potential than the cell content ?
water will flow out of the cell
What is the name for the external solution if a cell is surrounded by a solution with a lower water potential than the cell contents?
external solution is hypertonic
What happens if a cell and the surrounding solution have the same water potential?
no net movement of water
What is the name for a solution where the surrounding solution has the same water potential as the cell contents?
isotonic
What happens with red onion cells in a hypotonic solution>
Water enters cells by osmosis and they have become turgid
What would happen with red onion cell in a hypertonic solution?
Water has left the cells by osmosis and they have become flaccid
Plant cells become plasmolysed as cell membrane pulls away from cell wall
What type of solution would cause RBC to appear shrivelled?
hypertonic solution
water potential surrounding RBC is lower than water inside RBC
so water moves out of RBC
down the concentration gradient by osmosis
What type of solution woulf cause RBC to burst?
Hypotonic solution
RBC in pure water
water potential outside is higher
so water moves into the cell by osmosis
down the concentration gradient by osmosis
causing cell to burst as there is no cell wall in animal cells
What are the control variables for the potato osmosis practical?
Same length cyclinders
same potato
sAMEvolume of solution
Same length of time
Why is it important to dry the potato pieces?
to remove excess water as water has mass
What is the procedure of the potato osmosis practical?
1) Cut potato pieces
2) Prepare solutions
3) Weigh the mass of the potato pieces before placing them into solutions
4)Place potao into solution
5) After 40 minutes, take potato pieces out and pat dry
6) Weigh mass of potato pieces
Why do we use % change?
takes into consideration the starting masses / potatoes have different starting masses
Why did the potato lose weight in the sugar water?
- higher water potential inside the potato
- water moves out of the potato into the solution by osmosis
- down water potential gradient
- so mass decreases
Why did the potato gain weight in the distilled water?
- higher water potential in solution/water
- so water moves into the potato from the solution
- by osmosis down the water potential gradient
-so mass of potato increases
