2018 A2 Paper 1

Question 1

Evidence that a cell is undergoing mitosis

Answer 1

Chromosomes are visible because they have condensed

Chromosome made up of 2 chromatids because DNA has replicated

Not meiosis because crossing over not seen

Question 2

How does water entering a cell cause the chromosomes to move further apart

Answer 2

Water moves into the cells by osmosis

Cell gets bigger

Question 3

How could the chromosome differ along its length to result in the stain binding more in some areas

Answer 3

Differences in base sequences

Differences in histones

Question 4

Homologous pair of chromosomes definition

Answer 4

Chromosomes that carry the same genes

Question 5

How is the arrangement of prokaryotic DNA is different from human DNA

Answer 5

Prokaryotic DNA is:

Circular as opposed to linear

Not associated with histones

Present as plasmids

Question 6

Species richness

Answer 6

A measure of the number of different species in a community

Question 7

How can scientists ensure their ways of collecting organisms is ethical

Answer 7

Must not harm organism

Must allow organism to be released unchanged

Question 8

How can scientists ensure their ways of collecting organisms allows them to identify accurately the species to which they belong

Answer 8

Must allow close examination

Use a key to identify the species

Use photographs to identify species

Question 9

How could scientists improve methods of data collection

Answer 9

Collect data at more times of the year SO more points on graph

Collected from more sites TO increase accuracy of data

Question 10

What about the evolutionary relationships can be suggested by species with similar names

Answer 10

More closely related

Because they are in the same genus

Question 11

How does the formation of an E-S complex increase rate of reaction

Answer 11

Reduces activation energy

Due to bending bonds

Question 12

Degenerate genetic code

Answer 12

More than one codon codes for a single amino acid

Question 13

Why is treating antivenom with passive immunity better than usng active immunity

Answer 13

In passive immunity antibodies bind to the antigen causes its destruction

Active immunity would be too slow

Question 14

Why is it beneficial to use mixture of venoms from several snakes of same species in antivenom

Answer 14

May be different form of antigen within one species

Different antibodies needed in the antivenom

Question 15

During vaccination, each animal is initially injected with a small volume of venom

Two weeks later, it is injected with a larger volume of venom

Use your knowledge of the humoral immune response to explain this vaccination programme

Answer 15

B cells specific to the venom reproduce by mitosis

B cells produce plasma cells and memory cells

Second dose produces antibodies in higher concentration AND quickly

Question 16

Describe the role of 2 named enzymes in semi conservative replication of DNA

Answer 16

DNA helicase causes breaking of H bonds between DNA strands

DNA polymerase joins the DNA nucleotides

Forming phosphodiester bonds

Question 17

Describe the gross structure of the human gas exchange system and how we breathe in and out

Answer 17

Trachea, bronchi, bronchioles, alveoli

Breathing in - Diaphragm contracts AND external intercostal muscles contract

Causes volume increase and pressure decrease in thoracic cavity

Breathing out - Diaphragm relaxes AND internal intercostal muscles contract

Causes volume decrease and pressure increase in thoracic cavity

Question 18

Compare the structure and properties of triglycerides and phospholipids

Answer 18

Both contain ester bonds

Both contain glycerol

Fatty acids on both can be saturated or unsaturated

Both are insoluble in water

Question 19

Contrast the structure and properties of triglycerides and phospholipids

Answer 19

Both contain C, H and O BUT phospholipids also contain P

Triglyceride has 3 fatty acids AND phospholipid has 2 fatty acids + phosphate group

Triglycerides are hydrophobic AND phospholipids have hydrophilic and hydrophobic region

Phospholipids form monolayer on bilayer BUT triglycerides dont

Question 20

Mucus also contains glycoproteins. One of these glycoproteins is a polypeptide with the sugar, lactose, attached

Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein

Answer 20

Glucose and galactose

Joined by condensation reaction

Joined by glycosidic bond

Added to polypeptide in golgi