Exam Pack - Long Answers

Question 1

Explain how the ventilation mechanism of a fish and the structure of its gill result in the efficient uptake of O2 from water

Answer 1

1. Lots of lamellae and filaments along the entire length of the gill, provides large SA for oxygen to diffuse along entire length of gill.
2. Large no. of capillaries - good supply of blood - maintain high conc grad of oxygen
3. Thin epithelium - short diffusion pathway of oxygen
4. Counter current mechanism - this ensures that blood will always have a lower concentration of oxygen, maintaining high conc grad and equilibrium isnt reached.
5. Changes in pressure when the fish opens and closes in mouth - maintains conc grad of oxygen

Question 2

Describe and explain how fish maintain a flow of water over their gill.

Answer 2

1. Fish opens its mouth
2. Increase in volume and decrease in pressure
3. Water moves down pressure gradient into fish
4. Mouth close
5. Volume decrease and pressure increases
6. This forces water over the gills

Question 3

Describe and explain how the structures of a human breathing system enables efficient uptake of oxygen into the blood.

Answer 3

1. Have diaphragms muscles and intercostal muscles, which contract and flatten to increase the volume of thoracic cavity. This decreases the pressure and establishes a conc grad for air to move into lungs.
2. Lots of alveoli - large SA - more areas for O2 to diffuse into blood
3. Alveolar epithelium is very thin - short diffusion pathway
4. Lots of capillary close to the alveoli - maintains high concentration gradient and large surface area
5. Capillaries have thin walls - short diffusion pathway
6. Cell membrane permeable to gases

Question 4

Describe and explain the mechanism that causes forced expiration

Answer 4

1. Diaphragm relaxes and return to its dome shape
2. External intercostal muscles relax
3. Internal intercostal muscles contract
4. This decreases volume in thoracic cavity and increases pressure in thoracic cavity
5. Pressure in thoracic cavities is now higher than in atmosphere
6. So air moves down pressure gradient into atmosphere

Question 5

The epithelial cells that line the small intestine are adapted for the absorption of glucose. Explain how.

Answer 5

1. Have carrier/channel protein for facilities diffusion of glucose
2. Have symport protein on surface membrane for co transport
3. Has sodium ion/potassium ion pump
4. Many microvilli - provide large surface area and short diffusion pathway
5. Many mitochondria- ATP produced and hydrolysed for energy for active transport
6. Membrane bound enzymes - digest disaccharides to produce glucose.

Question 6

Vaccines protect people against disease. Explain how

Answer 6

1. Vaccines contain antigens
2. Memory cells are made
3. On second exposure, memory cells produce antibodies
4. Rapidly produce antibodies
5. Antibodies destroy pathogen

Question 7

Describe the difference between active and passive immunity

Answer 7

Active -
1. Body produces antibodies on it own actively by B-Plasma cells
2. Produces B memory cells, in case of a 2nd infection
3. Takes more time as it has to carry out the primary immune response
4. Long term - because antibody produced in response to antigen

Passive -
1. Antibodies are injected into the body
2. Not a long term solution as antibodies are later broken down
3. Faster acting
4. No B - memory cells are produced

Question 8

Explain how the structure of dna relates to its function

Answer 8

1. Weak h bonds btwn nucleotide strands - easily broken to produce 2 nucleotide strands for dna rep and protein synthesis
2. Long molecule - can store a lot of genetic information
3. Double helix - allows dna to be a compact storage molecule
4. Phosphodiester bonds between adjacent nucleotide - provides strong sugar - phosphate backbone
5. Base sequences - triplet of bases code for an amino acid each
6. Double stranded - allows dna replicator. To be semi conservative bc both nucleotides act as template

Question 9

Describe how mRNA is produced in nucleus of cell

Answer 9

1. DNA helicase
2. Break h bonds
3. 2 nucleotide strands formed
4. 1 act as template
5. Free rna nucleotides are attracted to exposed dna nucleotides on strand by complementary base pairs
6. RNA polymerase forms phosphodiester bonds between adjacent nucleotides
7. Forms pre-mRNA
8. Splicing removes introns - mRNA produced

Question 10

Describe how proteins are digested in the human gut

Answer 10

1. Exppeptidase, endopeptidase and dipeptidase
2. Hydrolyse peptide bonds
3. Form shorter polpeitde chains or amino acids

Question 11

Starting with mRNA in the nucleus of a cell, describe how a molecule of protein is produced

Answer 11

1. mRNA leaves nucleus via nuclear pores
2. Associate themselves w ribosome
3. tRNA w comelmentary anticodon is attracted to codon on mRNA by complementary base pairs
4. tRNA has a specific amino acid on its binding site
5. tRNA detaches and brings another amino acids
6. Condensation reaction. Tween 2 amino acids = peptide bond and water molecule
7. Process continues until stop codon reached
8. Translation stops
9. Polypeptide detaches from ribosome

Question 12

Explain why Maltese allows reaction to happen at body temp

Answer 12

1. Describe induced fit model
2. Enzyme is a biological catalyst - decreases activation energy of reaction by finding different pathway