WRONG QS T1

Question 1

Explain how decreasing pH to pH 2 effects enzyme activity (4 marks):

Answer 1

• increases H+ ions attracted to amino acids
• hydrogen/ ionic bonds disrupted which changes tertiary structure of enzyme
• changes shape of active site so E-S complexes can no longer form
• decreases rate of breakdown of starch

Question 2

Describe the induced fit model:

Answer 2

• substrate binds to active site of enzyme so E-S complex forms
• new IMFs with R groups cause the active site to change shape and this causes the bonds in the substrate to be strained
• reducing activation energy for the reaction

Question 3

Describe the structure of the cell surface membrane, including the biological molecules it is made of and their functions:

Answer 3

1. Fluid mosaic model
2. Phospholipids- selectively permeable and fluid barrier
3. Intrinsic proteins- carrier protein allows movement of substances across the membrane
4. Extrinsic proteins- enzymes/ receptors
5. Glycoproteins- cell receptors
6. Glycolipids- cell receptors/ membrane stability
7. Cholesterol- restricts movement of molecules within the membrane, increasing its strength

Question 4

Describe the gross structure of the human gas exchange system:

Answer 4

Trachea
Bronchi
Bronchioles
Alveoli

Question 5

Describe inhalation:

Answer 5

1. Diaphragm contracts
2. External intercostal muscles contract
3. Volume increase and pressure decrease in the thorax causing air to move in

Question 6

Describe exhalation:

Answer 6

1. Diaphragm and external intercostal muscles relax
2. Volume decrease and pressure increase in the thorax means air moves out

Question 7

Explain how the countercurrent mechanism in fish gills allows for the maximum amount of oxygen possible to be passed into the blood:

Answer 7

• water and blood flow in opposite directions
• blood always passing water with a higher oxygen concentration
• diffusion gradient maintained throughout length of gill
• if water and blood flowed in the same direction equilibrium would be reached

Question 8

Respiration produces more ATP per molecule of glucose in the presence of oxygen than it does when oxygen is absent, explain why (2 marks)

Answer 8

1. Oxygen is final/ terminal electron acceptor
2. Oxidative phosphorylation/ ETC provides most ATP

Question 9

Describe how acetyl CoA is formed in the link reaction (2 marks)

Answer 9

1. Hydrogen removed from pyruvate + CO2 released
2. Addition of CoA

Question 10

Explain why converting pyruvate to lactate allows the continued production of ATP during anaerobic respiration (2 marks)

Answer 10

1. Regenerates/ produces NAD
2. NAD used in glycolysis

Question 11

An advantage of lactate being converted back to pyruvate in muscles?

Answer 11

Pyruvate used in aerobic respiration

Question 12

Explain two ways in which the structure of the fish gills is adapted for sufficient gas exchange (2 marks):

Answer 12

1) lots of llamellae which ensure a large surface area
2) thin surface area so short diffusion distance

Question 13

Explain how the counter current mechanism in gills ensures the maximum amount of oxygen passes into teh blood flowing through the gills (3 marks):

Answer 13

1) blood and water flow in opposite directions
2) water always has a higher oxygen concentration than blood
3) diffusion gradient maintained throughout the length of the gill

Question 14

Describe three ways in which an insect’s tracheal gas exchange is adapted for sufficient gas exchange (3 marks):

Answer 14

1) tracheoles have thin walls so short diffusion distance to cells
2) highly branches system of tracheoles so short diffusion distance to cells
3) large number of tracheoles so large SA for gas exchange

Question 15

Describe how the structure of glycogen is related to its function (4 marks):

Answer 15

1. Helical/ coiled with branches so it is compact
2. Polymer of glucose so easily hydrolysed
3. Branched with more ends for faster hydrolysis
4. Polymer of glucose- respiratory substrate for energy release
5. Large so insoluble and doesn’t affect water potential

Question 16

Some substances can cross the cell-surface membrane of a cell by simple diffusion through the phospholipid bilayer. Describe other ways which substances cross this membrane (5 marks)

Answer 16

1. Active transport, against a concentration gradient, using a carrier protein and ATP hydrolase
2. Bulk transport, using endo and exocytosis
3. Co transport- molecules moving the same way- e.g. AA’s
4. Osmosis….

Question 17

When a vaccine is given to a person, it leads to the production of antibodies against a disease causing organism. Describe how. (5 marks)

Answer 17

1. Vaccine contains antigen from pathogen
2. Macrophage presents antigen on its surface
3. T cell with complementary receptor protein binds to antigen
4. T cell stimulates B cell
5. With complementary antibody on its surfaces
6. B cell secretes large amounts of antibody
7. B cell divides by mitosis to form clone all secreting/ producing same antibody

Question 18

Describe the difference between active and passive immunity (5 marks)

Answer 18

1. Active involves memory cells, passive does not
2. Active involves production of antibody by plasma cells/ memory cells
3. Passive involves antibody introduced into body from outside/ vaccine
4. Active = long term because antibody produced in response to antigen
5. Passive = short term because antibody given is broken down
6. Active can take time to develop/ work, passive is fast acting

Question 19

Describe how water is moved through a plant according to the cohesion-tension hypothesis (6 marks)

Answer 19

1. Water evaporates/ transpires from leaves
2. Reduces water potential in cell
3. Water is drawn out of xylem
4. Creates tension
5. cohesive forced between water molecules
6. Water pulled up as a column

Question 20

Describe the process involved in the transport of sugars in plant stems (5 marks):

Answer 20

1) Sucrose actively transported into the phloem
2) By companion/ transfer cells
3) Lowers WP in phloem and water enters by osmosis
4) Produces high hydrostatic pressure
5) Mass flow towards sink
6) At sink, sugars are removed

Question 21

How are T helper cells activated?

Answer 21

1. Macrophage engulfs pathogen and presents antigens on cell membrane
2. T helper cell with complementary antigen receptor binds to presented antigen
3. Release of cytokines activates T helper cell
4. T helper cell divides by mitosis to produce more active T helper cells

Question 22

What is the role of cytoxic T cells>

Answer 22

Biden to antigens on surface of, and destroy infected body cells by making cell membrane permeable

Question 23

What happens after B cells are activated?

Answer 23

• B cell divides rapidly by mitosis
• some B cells become memory cells
• others differentiate into plasma cells and poridyce antibodies which are complementary to pathogen’s antigen