Transport across membranes

Explain why the data in the table above are described as processed results

Calculations have been made from raw data

Describe how you would use a 1.0 mol dm-3 solution of sucrose to produce 30 cm3 of a 0.15 mol dm-3 solution of sucrose

1. 0.15/1.0 x 30 = 4.5
2. 30-4.5 = 25.5
3. You take 4.5cm3 of the original 1.0 mol dm-3 solutions of sucrose
4. Add it to 25.5 cm3 of water
5. Makes 30 cm3 of a 15 mol dm-3 solution of sucrose

Explain the change in mass of potato tissue in the 0.40 mol dm-3 solution of sucrose

1. Water potential of solution is less than that of the potato tissue
2. Tissue loses water by osmosis

Describe how phospholipids are arranged in a plasma membrane

1. Arranged in a continuous bilayer
2. Hydrophobic tails to inside
3. Hydrophilic head to outside

Cells that secrete enzymes contain a lot of RER and a large golgi apparatus
i) Describe how the RER is involved in the production of enzymes
ii) Describe how the Golgi apparatus is involved in the secretion of enzymes

i) RER has ribosomes to make proteins (which an enzyme is)
ii) Golgi apparatus modifies proteins and transports them to the cell surface

A student investigated the effect of putting cylinders cut from potato into sodium chloride solutions of different concentration. He cut cylinders from a potato and weighed each cylinder. He then placed each cylinder in a test tube. each test tube contained a different concentration of sodium chloride solution. The tubes were left overnight. He then removed the cylinders from the solutions and reweighed them.

i) Before reweighing the student blotted dry the outside of each cylinder. Explain why.

ii) The student calculated the percentage change in mass rather than the change in mass. Explain the advantage of this.

i) Water will affect the mass
Amount of water on cylinders varies so this ensures the same amount of water is on the outside
ii) Allows comparison
Cylinders have different starting masses but can still be compared

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

Fluid - movement and interchanging of molecules
Mosaic - contains phospholipids and proteins

The student carried out several repeats at each concentration of sodium chloride solution. Explain why the repeats were important.

1. Allows anomalies to be identified
2. Can calculate a reliable mean

During treatment in veterinary surgery, any of the mammals in the figure above may be given an infusion of sodium chloride solution directly into a vein. The concentration of sodium chloride solution used is 0.9% rather than 0.5%, regardless of the species of mammal.

Explain the advantage to the vet of using this concentration.

1. Use of 0.9% will not cause haemolysis in any of the mammals
2. Therefore will not kill any of the animals
3. Only need to buy and store one concentration of sodium chloride solution

Give two functions of proteins in plasma membranes

1. cell recognition
2. Active transport
3. Facilitated diffusion

Explain why the potato cylinder in distilled water increased in length

1. Higher water potential in the distilled water
2. Water enters by osmosis causing cells to extend

Explain why the potato cylinder in the 1.0 mol dm-3 sucrose solution showed no further decrease in length after 40 minutes

1. Water potentials are equal
2. So no net movement of water

After 45 minutes the potato cylinder in the 0.8 mol dm-3 solution was removed and blue dye added to this solution. Some of this blue-stained solution was drawn into a syringe. A drop was then released, slowly, halfway down a test tube of fresh 0.8 mol dm-3 sucrose solution. The blue drop quickly moved to the surface of the liquid in the test tube.

i) The density of a solution depends on its concentration. The more concentrated the solution the greater its density. Explain why the blue drop had a lower density and therefore moved up.

ii) A sucrose solution of concentration 0.3 mol dm-3 has a water potential which is equivalent to that of the potato cells. Describe and explain what would happen to the blue drop from this solution.

i) Water moved into the solution from the potato
Solution diluted
ii) No net movement of water in or out
Drop would not move as densities are the same

Suggest two reasons for keeping the fluid in the dialysis machine at 40 degrees rather than room temperature

1. Higher rate if diffusion
2. Prevents cooling of the blood

The blood and the dialysis fluid flow in opposite direction in the dialysis machine. Explain the advantage of this.

1. Concentration gradient maintained
2. Diffusion along the whole length of surface

Give one similarity in the way in which active transport and facilitated diffusion transport substances across the membranes

Involves carrier/transport proteins

Give one way in which active transport diffres from facilitated diffusion

Active transport uses energy