Exam Questions

Question 1

Starch is a carbohydrate often stored in plants

describe and explain two features of starch that make it good for storage

Answer 1

Any two from:
Insoluble (in water), so doesn’t affect water potential;
Branched / coiled / (a-)helix, so makes molecule compact;
OR
Branched / coiled / (a-)helix so can fit many (molecules) in small area;
Polymer of (a-)glucose so provides glucose for respiration;
Branched / more ends for fast breakdown / enzyme action;
Large (molecule), so can’t cross the cell membrane

Question 2

describe the structure of glycogen

Answer 2

• Polysaccharide of alpha glucose
• branched structure

Question 3

explain the difference in the structure of the starch molecule and the cellulose molecule

Answer 3

Starch formed from a-glucose but cellulose formed from B-glucose;

Position of hydrogen and hydroxyl groups on carbon atom 1 inverted.

Question 4

Explain one way which starch molecules are adapted for their function in plant cells

Answer 4

Insoluble; Don’t affect water potential;
Helical; Compact;
Large molecule; Cannot leave cell.

Question 5

explain how cellulose molecules are adapted for their function in plant cells

Answer 5

• long and straight chains
• become linked together by many hydrogen bonds to form fibrils
• provide strength (to cell wall)

Question 6

explain why the fatty acid is unsaturated (1 mark)

Answer 6

contains double bond between carbon atoms in hydrocarbon chain

Question 7

suggest one advantage of different percentage of cholesterol in red blood cells compared with cells lining the ileum (1 mark)

Answer 7

red blood cells are free in the blood so cholesterol helps maintain shape

Question 8

E. coli has no cholesterol in its surface membrane. But the cell maintains a constant shape. explain why

Answer 8

• cell is unable to change shape because it has a cell wall
• wall is rigid made of murein

Question 9

other than ethical reasons, suggest two reasons why they chose to use cats as model organisms.

Answer 9

• are mammals so likely to have the same physiology/ reactions as humans
• small enough to keep in laboratory
• can use a large extract

Question 10

test for some seeds that contain lipids:

Answer 10

• crush / grind then describe ethanol test

Question 11

from how many molecules is a triglyceride formed?

Answer 11

4

Question 12

substance contains only the elements,emits carbon, hydrogen and oxygen

Answer 12

starch
glycogen
deoxyribose

Question 13

substance is made from amino acid monomers:

Answer 13

DNA helicase

Question 14

substance is found in both animal and plant cells:

Answer 14

deoxyribose
DNA helicase

Question 15

hydrogen bonds are important in cellulose molecules. explain why.

Answer 15

• holds chains/ forms cross links between chains/ forms microfibrils
• hydrogen bonds strong in large numbers

Question 16

explain two ways in which fatty acids are important in the formation of new cells.

Answer 16

• fatty acids used to make phospholipids, more phospholipids means more membranes made
• fatty acids respired to release more energy which is used for cell production