1st MBr Test

Question 1

The scientists expressed their results as Percentage of lipid in plasma membrane by mass. Explain how they would find these values.

Answer 1

Divide mass of lipid by all lipids in the membrane

Then multiply by 100

Question 2

Suggest one advantage of the different percentage of cholesterol in red blood cells compared with cells lining the ileum.

Answer 2

Cells unsupported

Question 3

How does E. coli maintain a constant shape?

Answer 3

Cell wall

Question 4

“Push down hard on the cover slip, but do not push the cover slip sideways.”

Explain why she was given this instruction.

Answer 4

1. Push hard – spread/squash tissue;

2. Not push sideways – avoid rolling cells together/breaking chromosomes;

Question 5

One features of anaphase stage of mitosis as observable under a microscope

Answer 5

V-shape shows that (sister) chromatids have been pulled apart at their centromeres/that centromeres of (sister) chromatids have been pulled apart

Question 6

The pieces of leaf tissue examined were very thin. Explain why this was important.

Answer 6

1. Single/few layer(s) of cells;

2. So light can pass through;

Question 7

Give a piece of evidence supporting a photographed SEM image

Answer 7

3D

Question 8

Describe how the student could use an eyepiece graticule to determine the mean diameter of stomata.

Answer 8

1. Measure (each stoma) using eyepiece graticule;
2. Calibrate eyepiece graticule against stage micrometer / ruler / graph paper;
3. Take a number of measurements (to calculate a mean);

Question 9

List one way to contrast the processes of facilitated diffusion and active transport.

Answer 9

Facilitated diffusion takes place down a concentration gradient whereas active transport can occur against a concentration gradient;

Question 10

Describe how you could make a temporary mount of a piece of plant tissue to observe the position of starch grains in the cells when using an optical (light) microscope.

Answer 10

3. Stain with/add iodine in potassium iodide;

4. Lower cover slip using mounted needle;

Question 11

List 2 features of TEM image

Answer 11

1. High resolution;

2. Can see internal structure of organelles;

Question 12

Call magnification w/ scale bar

Answer 12

Length of bar in mm × 1000;

Question 13

Describe how phospholipids are arranged in a plasma membrane

Answer 13

Bilayer

Hydrophobic tails facing inwards

Question 14

In many trials of new drugs, a control group of patients is given a placebo that does not contain any drug.
The control group in this investigation had been treated with dacarbazine, which treats cancer. Suggest why they had not been given a placebo.

Answer 14

Unethical to not treat cancer

Question 15

Treatment
Median survival time (ST) / months (table)

Percentage of patients showing significant reduction in tumours
Dacarbazine
9.1

10.3

Dacarbazine and ipilimumab
11.2
15.2

A journalist who read this investigation concluded that ipilimumab improved the treatment of MM.
Why could the data in the table perhaps not support this conclusion? Give reasons for your answer.

Answer 15

No standard errors shown

So differences may be statistically significant

Question 16

LDL enters the liver cells

Using your knowledge of the structure of the cell-surface membrane, suggest how LDL enters the cell.

Answer 16

1. Attaches to receptor

2. Facilitated diffusion

Question 17

Describe the principles and the limitations of using a transmission electron microscope to investigate cell structure.

Answer 17

Principles

1. Use of electron beams on specimen
2. Denser parts absorb more electrons
3. Hence appearing darker

Limitations
Ignore ref to colour

Question 18

What about DNA replication leads to two identical daughter cells being formed post mitosis

Answer 18

Involvement of complementary base pairing

Question 19

Give four precautions that the researchers took to make their calculations of the mean number of capillaries per fibre in a diaphragm sample reliable.

Answer 19

Randomly chosen fields of view

Several FoVs taken

Same species

Same organ