Cells transport questions

Question 1

The phospholipids are orientated in a particular way. Explain why

Answer 1

• Phospholipids have hydrophilic heads and hydrophobic tails
• Hydrophilic heads are attracted to water
• Hydrophobic tails are repelled by water and point inwards

Question 2

Give 2 differences between facilitated diffusion and active transport

Answer 2

• Facilitated moves down a concentration gradient and active transport moves against a convcentration gradient
• Facilitated is passive and doesnt require external sources of energy whilst active transport is an active process and requires ATP

Question 3

Explain the shape of the curve (when levelled off) with glucose diffusing into blood

Answer 3

• Number of carrier proteins working at maximum
• Limiting rate of uptake

Question 4

The student washed the beetroot discs at the start of the procedure. Explain why

Answer 4

• This to wash away/ remove pigment of cells damaged by cutting during preparation
• If not removed the experiment would get false readings

Question 5

Use your knowledge of the fluid-mosaic model of membrane structure to explain results

Answer 5

• As phospholipids are heated the molecules move around at low temps some pigment escapes
• Above 40c phospholipids absorb heat and become more mobile pigment further leaks. Proteins may denature and allow pigment to leak
• Above 50.c membrane is freely permeable and pigment diffuse out

Question 6

Why did the student dry the pieces

Answer 6

• So excess liquid on the surface didnt affect mass cause mass to vary

Question 7

Why did the student calculate percentage change

Answer 7

1. Potatoes had different starting masses
2. So there is a comparable result/ can make comparison to rest of results

Question 8

Why is Mitochondria important in the processes in the uptake of glucose

Answer 8

• Site of (aerobic) respiration;
• provide ATP / release energy (for active transport);

Question 9

Sodium ions are pumped out of the epithelial cells into the bloodstream. Explain how this helps glucose to be absorbed from the lumen of the ileum

Answer 9

• Concentration of sodium ions in the cell becomes less than concentration in the lumen of ileum / concentration gradient is established;
• sodium ions diffuse into the cell down the concentration gradient;
• glucose moves in with sodium ions via co-transport protein;

Question 10

Explain why the data above is described as processed results

Answer 10

• The results were calculations from the raw results.
• Raw reults measured the initial and final masses

Question 11

Explain why the structure of a membrane is described as fluid-mosaic.

Answer 11

• idea of molecules / named molecules moving= Fluid;
• idea of both proteins and phospholipids= Mosaic;

Question 12

How does the bilayer formed by substance A affect entry and exit of substances into and out of a cell?

Answer 12

• allows movement of lipid soluble / non-polar molecules / namede.g. water / gases;
• prevents movement of water soluble/ polar molecules / namede.g. ions / amino acids;
• idea of selection / membrane partially / differentially permeable / large molecules do not move through, small molecules do;(accept semi-permeable)

Question 13

Explain why an electron microscope shows more detail of cell structure than a light microscope.

Answer 13

• electron microscope has a greater resolvingpower / objects closer together can be distinguished;
• electron (beams) have a shorter wavelength;