cell membranes

Question 1

Why are sodium ions important in the transport of glucose from the ileum into the blood?

Answer 1

Sodium ions diffuse from the lumen of the ilium into the intestinal epithelial cells down their concentration gradient through a sodium glucose co transporter protein.
At the same time, the co transporter carries glucose into the epithelial cell against its concentration gradient.
Glucose is then able to diffuse into blood from the epithelial cell

Question 2

What are the factors affecting the rate of facilitated diffusion?

Answer 2

The concentration gradient
The number of channel or carrier proteins (once all the proteins in a membrane are in use, facilitated diffusion can’t happen any faster)

Question 3

describe the role of cholesterol in a cell membrane

Answer 3

membrane stability
fits between the phospholipid, restricting movement
binds to hydrophobic tails of phospholipids, causing them to pack more closely together
maintain shape of animal cells
contains hydrophobic regions so it can create a barrier to polar substances

Question 4

why is the molecules in a membrane structure described as the fluid mosaic model?

Answer 4

• phospholipds constantly moving
• proteins scattered through the bilayer

Question 5

What is the difference between isotonic/hypotonic & hypertonic?

Answer 5

Isotonic - same water potential
Hypotonic - solutions with a higher water potential compared with the inside of the cell (water moves into the cell)
Hypertonic - solution with a lower water potential (water moves out of cell)

Question 6

What is diffusion?

Answer 6

Diffusion is the net movement of particles (molecules or ions) from an area of high concentration to lower concentration down a concentration gradient

Question 7

What do channel, carrier and receptor proteins do?

Answer 7

They allow large molecules and ions to pass through the membrane
The receptor proteins allow the cell to detect chemicals released from other cells

Question 7

What are the factors affecting the rate of osmosis?

Answer 7

water potentail gradient (higher, faster)
thickness of exchange surface (thinner, faster)
surface area of exchange surface (larger, faster)

Question 8

How do you lower the water potential of pure water (0) ?

Answer 8

Adding solutes to pure water lowers its water potential
The water potential of any solution is always negative
The more negative the water potential, the stronger the concentration of solutes in the solution

Question 9

What is the structure of phospholipids?

Answer 9

Hydrophilic head (attract water- faces outwards)
Hydrophobic tail (repels water - faces inwards)

Question 10

what is the difference between a glycoprotein and a glycolipid

Answer 10

glycoproteins : proteins + carbohydrates
glycolipids : carbohydrates+ lipids

Question 11

Factors affecting the rate of diffusion

Answer 11

The concentration gradient (higher it is, faster the rate)
The thickness of the exchange surface (thinner, faster the rate)
The surface area (larger,faster)

Question 12

What is osmosis?

Answer 12

Osmosis is the diffusion of water molecules across a partially permeable membrane, from an area fo high water potential to an area of low water potential

Question 13

What is facilitated diffusion?

Answer 13

This is the process where large, charged molecules diffuse through the bilayer through carrier and channel protein

Question 14

How do co transporters transport substances?

Answer 14

They bind two molecules at a time. The concentration gradient of one molecule is used to move the other molecule against its concentration gradient

Question 15

what is the structure of the bilayer?

Answer 15

glycoprotein
glycolipids
proteins
channel protein
cholesterol

Question 16

What is active transport?

Answer 16

This uses energy to move molecules and ions across a plasma membranes from a low to high concentration against the gradient using ATP as a source of energy

Question 17

What substances can/cannot go through the bilayer?

Answer 17

water soluble substances such as ions and polar molecules cannot diffuse
small, non polar substances and water can diffuse

Question 18

How does a carrier protein transport molecules across a cell membrane?

Answer 18

A large molecule attaches to a carrier protein in the membrane
The protein then changes shape
This releases the molecule on the opposite side of the membrane

Question 19

how does temperature affect the permeability of phospholipids

Answer 19

The higher the temperature up to a certain point before denaturation mean the phospholipds can move around more which increases permeability

Question 20

how do channel proteins help facilitated diffusion?

Answer 20

They form pores in the membrane for charged particles to diffuse through

Different channel proteins facilitate the diffusion of different charged particles

Question 21

What is water potential?

Answer 21

The likelihood of water molecules to diffuse out of or into a solution