Exam Q's

Question 1

Describe the roles of iron ions, sodium ions, and phosphate ions in cells.

Answer 1

1. Haemoglobin binds/associates with oxygen OR Haemoglobin transports/loads oxygen
2. Co-transport of glucose/amino acids (into cells);
3. (Because) sodium moved out by active transport/Na - K pump;
4. Creates a sodium concentration/diffusion gradient; 5. Affects osmosis/water potential
5. Affects osmosis/water potential;
6. Joins nucleotides/in phosphodiester bond/in backbone of DNA/RNA/in nucleotides;
7. Used in/to produce ATP;
8. Phosphorylates other compounds (usually) making them more reactive;
9. Hydrophilic/water soluble part of phospholipid bilayer/membrane;

Question 2

Contrast how an optical microscope and a transmission electron microscope work and contrast the limitations of their use when studying cells.

Answer 2

1. TEM use electrons and optical use light
2. TEM allows a greater resolution
3. so with TEM smaller organelles can be observed
4. TEM can only view dead specimens whereas optical can view life specimens.
5. TEM does not show colour and optical can
6. TEM required thinner specimens
7. TEM requires more complex preparation
8. TEM focusses using magnets and optical uses lenses

Question 3

Describe the appearance and behaviour of chromosomes during mitosis.

Answer 3

1. Chromosomes
   coil / condense / shorten / thicken / become visible;

2.(Chromosomes) appear as (two sister) chromatids joined at the centromere;

(During metaphase)
3. Chromosomes line up on the equator / centre of the cell;

4. (Chromosomes) attached to spindle fibres;
5. By their centromere;

(During anaphase)
6. The centromere splits / divides;

7. (Sister) chromatids / chromosomes are pulled to opposite poles / ends of the cell / separate;

(During telophase)
8. Chromatids / chromosomes
uncoil / unwind / become longer / thinner.

Question 4

Name and describe five ways substances can move across the cell-surface membrane into a cell.

Answer 4

1. (Simple) diffusion of small/non-polar molecules down a concentration gradient;
2. Facilitated diffusion down a concentration gradient via protein carrier/channel;
3. Osmosis of water down a water potential gradient;
4. Active transport against a concentration gradient via protein carrier using ATP;
5. Co-transport of 2 different substances using a carrier protein;

Question 5

The movement of substances across cell membranes is affected by membrane structure. Describe how.

Answer 5

1. Phospholipid (bilayer) allows movement/diffusion of non-polar/lipid-soluble substances;
2. Phospholipid (bilayer) prevents movement/diffusion of polar/ charged/lipid-insoluble substances
3. Carrier proteins allow active transport;
4. Channel/carrier proteins allow facilitated diffusion/co-transport;
5. Shape/charge of channel / carrier determines which substances move;
6. Number of channels/carriers determines how much movement;
7. Membrane surface area determines how much diffusion/movement;
8. Cholesterol affects fluidity/rigidity/permeability;

Question 6

In the UK, children are vaccinated against this disease. Describe how vaccination can lead to protection against bacterial meningitis.

Answer 6

1. Antigen on surface of N. meninigitis binds to surface receptor on a (specific / single) B cell.
2. (Activated) B cell produces clone;
3. (Division) stimulated by cytokines / by T cells;
4. B cells / plasma cells release antibodies;
5. (Some) B cells become memory cells;
6. Memory cells produce plasma / antibodies faster