transport in and out of cells

Question 1

What are the two main ways proteins are embedded in the cell surface membrane?

Answer 1

they can be integral or peripheral

Question 2

describe integral proteins

Answer 2

some never extend completely across it,

they act either to give mechanical support to the membrane

they can be in conjunction with glycolipids, as cell receptors for molecules such as hormones

Question 3

describe peripheral proteins

Answer 3

some completely span the phospholipid bilayer from one side to the other.

these can be protein channels or carrier proteins

Question 4

what are the two different proteins in the bilayer

Answer 4

protein channels

carrier proteins

Question 5

explain the function of carrier proteins

Answer 5

they bind to ions or molecules like glucose and amino acids, then change shape in order to move these molecules across the membrane

Question 6

explain the function of protein channels

Answer 6

form water-filled tubes to allow water soluble ions to diffuse across the membrane.

Protect polar molecules from the non-polar central layer of the plasma membrane.

Question 7

What is the significance of cholesterol molecules within the phospholipid bilayer of the cell-surface membrane (functions)

Answer 7

add strength to the membranes

they are very hydrophobic and hence play an important role in preventing loss of water and dissolved ions from the cell

they pull together the fatty acid tails of the phospholipid molecules, reducing their lateral movement as well as for other molecules, without making the membrane as a whole too rigid

make the membrane less fluid at high temperatures

Question 8

What is the function of phospholipids in the membrane?

Answer 8

• allow lipid-soluble substances to enter and leave the cell
• prevent water-soluble substances from entering and leaving the cell by having a hydrophobic centre
• make the membrane flexible and self-sealing

Question 9

What are the functions of proteins in the membrane?

Answer 9

provide structural support

act as channels transporting water-soluble substances across the membrane

allow active transport across the membrane through carrier proteins

form cell-surface receptors for identifying cells

help cells adhere together

act as receptors

Question 10

What are the functions of glycolipids

Answer 10

act as recognition sites

help maintain the stability of the membrane

help cells to attach to one another and so form tissues

Question 11

What are the functions of glycoproteins

Answer 11

act as recognition sites

help cells to attach to one another and so form tissues

allows cells to recognise one another

Question 12

how does a low temperature affect cell membranes permeability?

Answer 12

not packed as tightly and can move around each other (partially permeable)

Question 13

how does an increase in temperature affect the permeability of a membrane

Answer 13

when the temperature increases the phospholipids move more

because they have more kinetic energy,

increasing the permeability of the membranbe

Question 14

how does a temperature above 45 degrees affect the permeability of the membrane

Answer 14

phospholipids start to break down and become more permeable.

Water inside the cell expands and puts pressure on the membrane.

Both channel and carrier proteins in the membrane denature

so they cannot control what enters or leaves a cell

resulting in increasing permeability

Question 15

what are the two main factors that affect cell membranes permeability

Answer 15

solvents and temperatures

Question 16

How do solvents affect cell membranes permeability?

Answer 16

Since water is important in creating membrane stability with phospholipids, less polar substances (e.g. alcohol) can move into the bilayer disrupting the structure = membrane becomes more fluid and permeable

some solvents dissolve the phospholipids = cell loses structure

Question 17

Why are beetroot dabbed with a paper towel before being placed in different concentrations during practical

Answer 17

to remove excess water so concentration is not affected

Question 18

What should you do every time you use calorimeter

Answer 18

recalibrate with water

Question 19

A student investigated the stages of mitosis in a garlic root. The root tip was placed on a microscope slide with a stain. A coverslip was placed on top and the root tip was firmly squashed. A different set of results was obtained when the count was repeated on another occasion with a different garlic root tip. Give two reasons for the difference in results.

Answer 19

genetic differences/different types of garlic

time of day

chance

age of root tip

water availability

temperature

nutrient availability

Question 20

describe the phospholipid bilayer

Answer 20

the hydrophobic heads of both