Wednesday 18th January 2012

Question 1

Describe the function of a chloroplast. 2 marks

Answer 1

• Absorbs sunlight
• For photosynthesis
• Produces carbs/ sugars/ lipids/ proteins

Question 2

Describe what happens during anaphase that results in the production of two genetically identical cells. 2 marks

Answer 2

• Sister chromatids

- To opposite poles

Question 3

Use your knowledge of the cell cycle to explain why some cells had 8.4 units of DNA and other had only 4.2 units. 2 marks

Answer 3

• 8.4 - cells with twice DNA content as the DNA had replicated.
• 4.2 = DNA not replicated

Question 4

How many units of DNA would you expect to be present in a gamete formed in this animal as a result of meiosis?

Answer 4

2.1

Question 5

A scientist carried out breeding experiments with catfish from different populations. Describe how the results could show that the catfish belong to the same species. 1 mark

Answer 5

Fertile offspring produced

Question 6

The variety of colours displayed by catfish is important in courtship. Give 2 ways in which courtship increases the probability of successful mating. 2 marks

Answer 6

• Recognise opposite sex
• Recognise same species
• Synchronises mating

Question 7

Explain how this mutation leads to the formation of non-functioning PAH. 3 marks

Answer 7

• Change in amino acids
• Change in hydrogen bonds
• Alters active site of enzyme
• Substates can’t bind as they are no longer complementary so no E-S complexes can form.

Question 8

One mutation causing phenylketonuria was originally only found in one population in Central Asia. It is now found in many different populations across Asia. Suggest how the spread this mutation may have occurred. 1 mark

Answer 8

Interbreeding - reproduction between individuals from different populations

Question 9

Vancomycin acts on the cell wall - explain why vancomycin does not affect human cells. 1 mark

Answer 9

Human cells don’t have cell walls

Question 10

Tetracycline acts on ribosomes - how does tetracycline prevent bacterial growth. 1 mark

Answer 10

Affects protein synthesis

Question 11

Frequent treatment with vancomycin can result in resistant strains of bacteria. Explain how. 3 marks

Answer 11

• Mutation occurs
• Resistant allele
• Resistant bacteria survive and reproduce
• Vertical gene transmission

Question 12

Use your knowledge of gene transmission to explain how the gene was passed from one species of bacterium to another. 3 marks

Answer 12

• Horizontal gene transmission
• Via conjugation
• Plasmid copied
• Plasmid transferred to s.aureus

Question 13

Scientists can use protein structure to investigate the evolutionary relationships between different species. explain why. 2 marks

Answer 13

• Amino acid sequences
• Close the amino acid sequence the closer the relationship.
• Protein structure related to DNA base sequence.

Question 14

Comparing the base sequence of genes provides more evolutionary information than comparing the structure of proteins. Explain why. 2 marks

Answer 14

• More bases than amino acids
• Introns
• More than once code for each amino acid.

Question 15

Explain the importance of taking a large number of samples at each site. 1 mark

Answer 15

• Produces a more reliable mean

Question 16

Explain the importance of taking samples at random. 1 mark

Answer 16

• Removes bias

Question 17

Explain the effect of developing this golf course on the index of diversity of insects. 3 marks

Answer 17

• Increase in variety of plants
• More habitats
• Greater variety of food sources

Question 18

Root pressure moves water through the xylem. Describe what causes root pressure. 3 marks

Answer 18

• Active transport by endodermis
• Ions into xylem
• Lowers water potential in xylem
• Water enters by osmosis

Question 19

Explain how oxygen is loaded, transported and unloaded in the blood. 6 marks

Answer 19

• Haemoglobin carries oxygen
• In red blood cells
• At high potential of oxygen
• Unloads to respiring cells
• At low potential of oxygen
• Unloading linked to higher oxygen

Question 20

The larvae in this investigation were kept at a temperature of 17 degrees, why was it important that the larvae of both species were kept at the same temperatures? 2 marks

Answer 20

• Allows comparison
• Different temperature affects enzymes
• Different temperature affects metabolism
• Different temperature affects amount of dissolved oxygen.

Question 21

Apart from age, suggest two factors that the scientists should have considered when selecting volunteers for this trial. 2 marks

Answer 21

• Sex
• Health
• Ethnicity

Question 22

In analysing the results of the investigation, the scientists took into account the age of the volunteers. Suggest why. 1 mark

Answer 22

Age affects risk of cancer

Question 23

Tea and coffee contain caffeine. A newspaper reported the results of this investigation under the headline ‘ Caffeine helps cut cancer risk’. Explain why scientists could not support this view solely on the basis of this investigation. 4 marks

Answer 23

• Correlation does not mean causation
• Tea/coffee contains other substances
• Contain different amounts of caffeine
• No control group
• Only one type of cancer studied
• Further studies required.

Question 24

Describe how the control group should have been treated. 2 marks

Answer 24

• Treated the same

- No caffeine

Question 25

Volunteers who drank the same concentration of caffeine solution often had different concentrations of caffeine in their blood. Suggest one reason for the difference in concentration of caffeine in the blood of volunteers. 1 mark

Answer 25

• Absorb different amounts
• Broken down by enzymes
• Difference in metabolisms

Question 26

The investigation showed that caffeine reduces the blood flow to certain parts of the brain. Suggest one way in which this could lead to a reduced risk of brain cancers. 1 mark

Answer 26

• Less oxygen to cancer cells

- Reduced spread of cancer cells