Exams

Describe the applications of PCR. (4 marks)

Forensics, paternity testing, diagnosis of genetic disorders, detecting pathogens.

Osmoregulation

Compare and contrast the use of external energy sources in photoautotrophs and chemoautotrophs (4 marks)

Both require an external energy source.

Both use the ATP to convert inorganic nutrients to organic/carbon compounds.

Photoautotrophs use light as the external energy source and chemoautotrophs use ions.

Photoautotrophs use light to photolyse water/manufacture ATP and chemoautotrophs oxidise an external energy source to manufacture ATP.

Discuss the use of CRISPR sequences, the enzyme Cas9 and the gene knockout technique for investigating the function of genes. (7 marks)

1. CRISPR and Cas9 used to change a specific gene.

2. Gene knockout investigates gene function.

3. Gene knockout disables a gene.

4. Knockout organism libraries exist.

5. CRISPR-Cas9 used in human medical treatments.

6. Example of diseases treated (e.g., cancer, HIV, etc.).

7. Ethical issues raised by CRISPR - editing germ cells makes it heritable.

8. Example of unethical use (bonus point for covering more!).

Distinguish between germ line mutations and somatic mutations. (3 marks)

Germ line mutations are inherited from parents and somatic are not inherited.

Mutations can cause cancer in somatic cells but not in germ cells.

Somatic mutations occur in the individual after birth/later in life.

Somatic mutations are present only in specific organs but germ line mutations are present in

all cells (of the organism)

What is the role of cyclins?

A group of proteins that controls the cell cycle.

State where melatonin is produced in the body.

Pineal gland.

What are tandem repeats?

Short DNA sequences repeated one after another at a specific location. They don’t code for proteins but can play structural or regulatory roles.

One similarity between tandem repeats and genes?

Both are made of DNA and are inherited from parents.

One difference between tandem repeats and genes?

Genes make proteins; tandem repeats usually don’t.

What is the role of short tandem repeats (STRs) in DNA profiling?

PCR used for copying/amplifying STRs.
Tandem repeats allow individuals to be distinguished as they are different for everyone.

Explain how the structure of a prokaryotic cell allows it to survive and reproduce in diverse environments.

• Absence of membrane-bound nucleus/nuclear envelope 1 mark

• DNA is free in cytoplasm allowing rapid replication/binary fission 1 mark

• Rigid cell wall provides:

  • Protection from osmotic lysis

  • Structural support

  • Shape maintenance 2 marks

• Presence of flagella enables:

  • Movement towards nutrients/favorable conditions

  • Movement away from harmful substances 2 marks

• Plasmids contain additional genes for:

  • Antibiotic resistance

  • Specialized metabolic functions

  • Horizontal gene transfer between cells 2 marks

Describe how cyclins control the cell cycle.

It binds to CDKs and that cyclin-CDK complex gets phosphorylated to form an activated cyclin-CDK complex which starts the next phase of the cell cycle. Cyclins also regulate checkpoints to make sure everything is correct before moving on. There are different cyclins for each stage of the cell cycle.

Stages of blood clotting.

* Damaged cells release chemicals that stimulate platelets to adhere to damaged area.

* damaged cells and platelets release chemicals called clotting factors that convert prothrombin (clotting protein) into thrombin.

* Thrombin is an active enzyme that catalyses the conversion of soluble fibrinogen (another clotting protein) into insoluble fibrin which is a fibrous protein that forms a mesh-like network to stabilize the platelet plug.

* More and more cellular debris becomes trapped in the fibrin mesh until stable clot is formed.