essay qn

Question 1

describe the process of protein synthesis and secretion

Answer 1

1. polypeptide chains synthesized at ribosomes and folded at RER to form proteins
2. transport vesicles containing proteins made by RER pinch off RER
   transport vesicles fuse and release their substances into Golgi apparatus
3. chemically modified in Golgi apparatus
4. packaged into secretory vesicles which pinch off Golgi apparatus
5. secretory vesicles move towards and fuse with cell membrane, releasing proteins outside cell by exocytosis

Question 2

describe the process of the formation of lysosome

Answer 2

1. lysosomal enzymes synthesised on the rough ER and transported via transport vesicles to Golgi apparatus for chemical modification
2. vesicle containing enzymes pinches off Golgi apparatus, forming lysosome
   - enzymes must be kept apart from rest of cell or else they wld destroy the cell

Question 3

explain enzymatic reaction

Answer 3

1. effective collision between specific substrate(s) and enzyme at the correct orientation causes substrate molecules to enter active site of enzyme
2. substrate molecules bind to the active site of the enzyme –> enzyme-substrate complex
3. formation lowers activation energy
4. chemical reaction –> products formed
5. products dissociate from enzyme and the chemically unchanged enzyme is ready for another cycle of chemical reaction

Question 4

explain the lock-and-key hypothesis [5]

Answer 4

• substrate is “key” and enzyme is “lock”
• substrate has a shape complementary to the shape of active site (x same shape)
• with active site of enzyme having a specific shape into which the substrate fits exactly
• substrate binds to the active site of enzyme, forming ES-complex
• once products formed, no longer fit into active site if the enzyme and released into surrounding medium

Question 5

explain the induced fit model [5]

Answer 5

• active site of enzymes is complementary in shape but not a perfect fit to substrate it catalyses
• when substrate binds to active site of enzyme, induces a change in shape of active site
• allows substrate to fit more tightly into active site
• binding of substrate to active site of enzymes occurs and ES-complex forms
• chemical reaction occurs –> forming products –> released into the surrounding medium as they no longer fit into active site of enzyme

Question 6

Explain the process of digestion in the mouth

Answer 6

Chewing breaks up larger pieces of food to smaller pieces (physical digestion)
Tongue rolls food into boli
Salivary glands secrete saliva, which is mixed with the food by tongue
Saliva contains mucin which softens food
Salivary amylase digests starch to maltose

Question 7

explain the liver function of detoxification

Answer 7

Liver cells convert harmful substances into harmless ones – detoxification.
Hydrogen peroxide is a toxic by-product of cellular activities. It is broken down into water and oxygen by the enzyme catalase in the liver cells.
Alcohol is broken down in the liver and then removed from the body system.
Liver cells produce enzymes that break down alcohol to acetaldehyde, which can be further broken down to glucose that can be used in respiration to provide energy for cellular activities.

Question 8

explain the liver function of regulation of blood glucose

Answer 8

Blood glucose concentration increases after a meal.
Excess glucose will stimulate the pancreas to secrete insulin.
Insulin, a hormone, transported to the liver by blood will stimulate the liver cells to convert excess glucose into glycogen that will be stored in the liver .
However, during fasting or after a long time after a meal, blood glucose concentration will decrease.
Low blood glucose concentration will stimulate the pancreas to secrete glucagon, a hormone, which will stimulate the liver cells to break down the stored glycogen to glucose to be released into the bloodstream

Question 9

explain the assimilation of lipids

Answer 9

required in the production of cell membranes, steroid hormones, etc
fats oso protect vital organs
inadequate glucose –> fats broken down
excess fats stored in adipose tissues under skin

Question 10

Assimilation of glucose

Answer 10

Glucose is a substrate for respiration to release energy for cellular activities
Excess glucose is converted and stored as glycogen by liver cells. (stimulated by insulin — produced by pancreas)
Glycogen converted back into glucose by liver cells when blood glucose level is low. (stimulated by glucagon — produced by pancreas)

Question 11

Assimilation of amino acids

Answer 11

Amino acids are required in making new cell material for growth and repair of worn-out parts
Required to make enzymes, hormones, antibodies, etc. (proteins)
Excess is deaminated in liver. Amino group is removed and converted into urea. (carbon residue converted into glucose)

Question 12

absorption of digested products and water

Answer 12

• glucose and amino acids absorbed by facilitated diffusion into the blood capillaries (active transport when lower concentration in intestinal lumen than blood capillaries)
• blood capillaries join to form venules which then join to form hepatic portal vein (mainly carries glucose & amino acids to liver to be processed)
• fatty acids and glycerol diffuse into epithelium of villi and recombine to form fat globules before diffusing into the lacteal and transported away
  Most water and minerals absorbed in small intestine

Question 13

explain process of transpiration pull

Answer 13

1. Water evaporates from the thin film of moisture on the surface of mesophyll cells and into the intercellular air spaces.
2. Water vapour diffuses out of the stomatal pore and into the surrounding air via transpiration.
3. Water leaves to replenish film of moisture –> cell water potential decrease.
4. Water from neighbouring cells move into mesophyll cells by osmosis
5. Neighbouring cells draw water from cells deeper inside the leaves which draw water from the xylem
6. A suction force known as transpiration pull is generated, pulling the whole column of water up the xylem vessels.

Question 14

what happens to glucose formed during photosynthesis

Answer 14

1. when rate of photosynthesis higher than rate of respiration, excess glucose is converted into starch for storage. when photosynthesis stops, starch converted back to glucose for usage
2. glucose converted to sucrose for transport to other parts of plant via phloem
   - substrate for respiration to produce ATP for cellular activities
   - form cellulose cell walls
   - converted to lipids for storage and synthesis of cell membranes
   - reacts with nitrates and other mineral salts from soil to form amino acids in leaves. amino acids form proteins to make new cellular material

Question 15

describe the sequence of events for deoxygenated blood in the cardiac cycle (7)

Answer 15

1. deoxygenated blood from various parts of the body is returned to the right side of the heart
2. muscles of right and left atria contract
3. blood enters right ventricle
4. left and right ventricles contract
5. tricuspid valve closes
6. blood enters pulmonary arteries and is sent to the lungs
7. pulmonary valve closes

Question 16

describe the sequence of events for oxygenated blood in the cardiac cycle (7)

Answer 16

1. oxygenated blood from lungs is sent to the left side of the heart
2. muscles of right and left atria contract
3. blood enters left ventricle
4. left and right ventricles contract
5. bicuspid valve closes
6. blood enters aorta and is sent to the other body parts
7. aortic valve closes

Question 17

summarise the sequence of events and changes in pressure in the left side of the heart. (9)

Answer 17

1. Muscles of the left atrium contract. Pressure in the left atrium increases until it becomes higher than the pressure in the left ventricle. Bicuspid valve opens. Blood is forced into the left ventricle.
2. Muscles of the left atrium relax while muscles of the left ventricle start to contract
3. Pressure in the left ventricle increases until it becomes higher than the pressure in the left atrium. The bicuspid valve closes
4. Muscles of the left ventricle continue to contract.
5. Pressure in the left ventricle continues to increase until it becomes higher than the pressure in the aorta. The semi-lunar valve in the aorta opens. Blood enters the aorta.
6. Muscles of the left ventricle begin to relax.
7. Pressure in the aorta becomes higher than that of the left ventricle. The semi-lunar valve in the aorta closes
8. Muscles of the left ventricle continue to relax and its pressure decreases
9. Pressure in the left ventricle becomes lower than that in the left atrium. The bicuspid valve opens

Question 18

Describe the production of lactic acid in muscles during vigorous exercise

Answer 18

1. vigorous muscle contractions –> cells respire aerobically
2. limit to increase in the rate of breathing and heartbeat –> insufficient oxygen –> oxygen debt
3. anaerobic respiration –> extra energy –> supplements energy released by aerobic respiration to allow muscles to continue contracting vigorously
   buildup up of lactic acid in muscle cells

Question 19

Describe what happens to lactic acid in muscles during recovery

Answer 19

1. breathing continues to be high for some time to provide ‘extra’ oxygen repay the oxygen debt
2. lactic acid removed from muscles –> transported to liver –> some oxidised using extra oxygen –> release energy –> convert rest of lactic acid into glucose
3. when all converted, oxygen debt repaid
4. glucose transported back to muscles

Question 20

describe how oxygen is carried into the blood (5)

Answer 20

1. Alveolar air contains higher conc. of oxygen than in blood
2. Oxygen dissolve in thin layer of moisture on inner surface of wall
3. Diffuses through walls of alveoli and into blood capillaries – > diffuses into rbc
4. binds with haemoglobin to form oxyhaemoglobin
5. pass through oxygen-poor tissues, oxyhaemoglobin releases oxygen which will then diffuse through walls of capillaries into body cells