Size and surface area to volume ratio

Question 1

Why is surface area important for exchange?

Answer 1

Cell or organisms need to exchange materials and heat with their environment.
More chemical reactions happen every second in the organisms with a larger volume than in ones with smaller volumes.
Therefore more oxygen, nutrients, waste products and heat need to be exchanged across the membrane of cells of larger organisms.
With increasing volume this becomes an ever-increasing problem.

Question 2

What makes a good experiment?

Answer 2

Precise results are repeatable if the same person repeats the experiment using the same methods and equipment, they will get the same results. And reproducible if someone different does the experiment or a slightly different method or piece of equipment is used, the results will still be the same.
Valid results are precise and answer the original question. To get valid results you need to make sure you control all the variable to make sure you are testing the only thing you want to be testing.

Question 3

How do you work out magnification?

Answer 3

size of image/size of real object

Question 4

What is centrifugation?

Answer 4

The process by which the fragments in the filtered homogenate are separated in a machine called a centrifuge. This spins tubes of homogenate at very high speeds in order to create a centrifugal force.

Question 5

What happens in centrifugation of animal cells?

Answer 5

1. The tube of filtrate is placed in the centrifuge and spun at a slow speed.
2. The heaviest organelles, the nuclei, are forced to the bottom of the tube, where they form a thin sediment or pellet.
3. The fluid at the top of the tube called the supernatent is removed, leaving just the sediment of nuclei.
4. The supernatent is then transferred to another tube and spun in the centrifuge at a faster speed than before.
5. The next heaviest organelle, the mitochondrion are forced to the bottom of the tube.
6. The process is continued in this way so that at each increase in speed the next heaviest organelle is sedimented and separated out.

Question 6

What is homogenation?.

Answer 6

Cells are broken up by homogeniser. This releases the organelles from the cell. The resultant fluid, known as homogenate, is the filtered to remove any complete cells and large pieces of debris.

Question 7

What is a cold buffered solution?

Answer 7

a solution with the same water potential as the tissue.

Question 8

Why is the buffer solution cold?

Answer 8

To reduce enzyme activity that might break down the organelles.

Question 9

Why does the buffer solution have the same water potential as the tissue?.

Answer 9

to prevent organelles bursting or shrinking as a result of osmotic gain or loss of water.

Question 10

Why is the buffered solution buffered?

Answer 10

so that the pH does not fluctuate. Any change in pH could alter the structure of the organelles or affect the functioning of enzymes.