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A2 Biology > Topic 3B: Digestion and Absorption > Flashcards

Topic 3B: Digestion and Absorption Flashcards

1
Q

Why does digestion occur?

A

To break down large molecules into small molecules which can be absorbed from the gut into the blood, to be transported around the body for use by the body cells.

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2
Q

Digestion of carbohydrates: Amylase

A
  • Amylase is produced by the salivary glands where it is secreted into the mouth, and also in the pancreas where it is secreted into the small intestine.
  • Amylase catalyses the hydrolysis of glycosidic bonds in starch to produce maltose.
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3
Q

Digestion of carbohydrates: Sucrase

A
  • Sucrase is attached to the cell membranes of the epithelial cell’s lining the ileum.
  • Sucrase catalyses the hydrolysis of glycosidic bonds in sucrose to produce glucose and fructose.
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4
Q

Digestion of carbohydrates: Maltase

A
  • Maltase is attached to the cell membranes of the epithelial cell’s lining the ileum.
  • Maltase catalyses the hydrolysis of glycosidic bonds in maltose to produce glucose and glucose.
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5
Q

Digestion of carbohydrates: Lactase

A
  • Lactase is attached to the cell membranes of the epithelial cell’s lining the ileum.
  • Lactase catalyses the hydrolysis of glycosidic bonds in lactose to produce glucose and galactose.
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6
Q

Digestion of lipids: Lipase

A
  • Lipase is made in the pancreas, where it is secreted into the small intestine.
  • Lipase catalyses the hydrolysis of ester bonds in lipids to produce monoglycerides and fatty acids.
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7
Q

Digestion of lipids: Bile

A
  • Bile salts are made in the liver.
  • Bile salts emulsify lipids causing the lipids to form small droplets. This increases the surface area, allowing lipases to hydrolyse the lipid droplets more effectively.
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8
Q

Digestion of proteins: Endopeptidase

A

Hydrolyse the peptide bonds within a protein, to form two polypeptide fragments.

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9
Q

Digestion of proteins: Exopeptidase

A

Hydrolyse the peptide bonds at the end of a protein molecule, to remove a single amino acid from the protein.

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10
Q

Digestion of proteins: Dipeptidase

A

Hydrolyse the peptide bonds between dipeptides, to separate the amino acids.

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11
Q

Absorption: Monosaccharides

A
  • Glucose and galactose are absorbed by active transport with sodium ions via co-transporters.
  • Fructose is absorbed via facilitated diffusion.
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12
Q

Absorption: Monoglycerides and fatty acids

A

• Miscelles help to move monoglycerides and fatty acids towards the epithelium, where they diffuse directly across the epithelial cell membrane.

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13
Q

Absorption: Amino acids

A

1) Sodium ions are actively transported out of the epithelial cell’s into the ileum.
2) They then diffuse back into the cells through sodium-dependent transporter proteins, carrying the amino acids with them.

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14
Q

What is the role of haemoglobin?

A

To carry oxygen around the body

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15
Q

What is the structure of haemoglobin?

A

A large protein with a quaternary structure made up of four polypeptide chains. A haem group which contains an iron ion is attached to each chain.

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16
Q

What is oxyhaemoglobin?

A

The molecule formed when oxygen joins to haemoglobin.

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17
Q

Why does oxygen association occur in the lungs?

A

1) There is a high oxygen concentration.
2) Therefore there is a high partial pressure of oxygen (pO₂).
3) This means the haemoglobin (Hb) has a higher affinity for oxygen (O₂).
4) Consequently, oxygen (O₂) loading occurs.

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18
Q

Why does oxygen dissociation occur in the respiring tissues?

A

1) There is a low oxygen concentration.
2) Therefore there is a low partial pressure of oxygen (pO₂).
3) This means the haemoglobin (Hb) has a lower affinity for oxygen (O₂).
4) Consequently, oxygen (O₂) unloading occurs.

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19
Q

What are the features of a dissociation curve?

A

Where pO₂ is high, Hb has a high affinity for oxygen, and therefore a high saturation of oxygen.

Where pO₂ is low, Hb has a low affinity for oxygen, and therefore a low saturation of oxygen.

IMAGE

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20
Q

Why is a dissociation curve shaped as it is?

A

1) When haemoglobin combines with the first O₂ molecule, it’s shape changes making it easier for the next O₂ molecule to bind.
2) However, As haemoglobin becomes more saturated, it gets harder for more O₂ molecules to join.

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21
Q

What is the Bohr effect?

A

1) When cell’s respire, the pCO₂ raises, increasing the rate of oxygen unloading.
2) Therefore the curve shifts to the right.

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22
Q

Haemoglobin: Low oxygen environments

A
  • Haemoglobin has a higher affinity for oxygen because there isn’t much oxygen available.
  • Therefore their curve is to the left of ours.
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23
Q

Haemoglobin: High activity levels

A
  • Haemoglobin has a lower affinity for oxygen because they need to unload oxygen easily so that it’s available for aerobic respiration.
  • Therefore their curve is to the right of ours.
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24
Q

Haemoglobin: Small animals

A
  • Haemoglobin has a lower affinity for oxygen because they need a high metabolic rate to maintain body temperature, as they have a very large SA:Vol.
  • Therefore their curve is to the right of ours.
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25
Q

Function: Pulmonary artery

A

Carries blood from the heart to the lungs.

26
Q

Function: Pulmonary vein

A

Carries blood from the lungs to the heart.

27
Q

Function: Aorta

A

Carries blood from the heart to the body.

28
Q

Function: Vena Cava

A

Carries blood from the body to the heart.

29
Q

Function: Renal artery

A

Carries blood from the body to the kidneys.

30
Q

Function: Renal vein

A

Carries blood from the kidneys to vena cava.

31
Q

What does blood transport around the body?

A
  • Respiratory gases
  • Products of digestion
  • Metabolic waste
  • Hormones
32
Q

What is the structure/function of the arteries?

A
  • Carry blood from heat to the body.
  • Thick muscular walls with elastic tissue stretch and recoil as the heart beats to help maintain high pressure.
  • Highly folded endothelium allowing the artery to stretch.
33
Q

What is the structure/function of the arterioles?

A
  • Form a network to direct blood to different parts of the body.
  • Arteries divide into these smaller arterioles.
  • Purely muscular tissue, to contract and relax in order to control blood flow.
34
Q

What is the structure/function of the veins?

A
  • Return blood to the heart at a lower pressure from the rest of the body.
  • A very wide lumen, with little elastic/muscular tissue, and calves which prevent back flow.
  • Contraction if surrounding bodily muscles aids blood flow through the veins.
35
Q

What is the structure/function of the capillaries?

A
  • Arterioles branch into capillaries which exchange substances with cells.
  • Their walls are only one cell thick to reduce the length of diffusion pathway and therefore increase the rate of diffusion.
  • There are many capillaries which provide a very large surface area.
36
Q

How is tissue fluid formed?

A

1) At the start of the capillary bed, the hydrostatic pressure inside the capillaries is greater than that in tissue fluid.
2) Therefore, fluid is forced out of the capillaries into the spaces around cells down it’s pressure gradient, forming tissue fluid.
3) As fluid leaves, pressure reduces inside the capillaries, lowering the hydrostatic pressure at the end of the capillary bed.
4) Due to fluid loss, water potential at the end of the capillary bed is lower than that in tissue fluid.
5) Therefore, water re-enters the capillaries from the tissue fluid via osmosis.

37
Q

How do heart valves work?

A

The valves only open one way, meaning that blood flow is unidirectional.

38
Q

Atrial systole

A

1) Atria contract and ventricles relax.
2) This decreases the volume and therefore increases the pressure inside the atria.
3) Therefore, blood is pushed into the ventricles down its pressure gradient through AV valves.
4) The SL valves then close to prevent back flow.

39
Q

Ventricular systole

A

1) Ventricles contract and atria relax.
2) This decreases the volume and therefore increases the pressure inside the ventricles.
3) Therefore, blood is pushed into the pulmonary artery down its pressure gradient through the SL valves.
4) The AV valves then close to prevent back flow.

40
Q

Diastole

A

1) Both the ventricles and atria relax.
2) This increases the volume and therefore decreases the pressure in the atria and the ventricles.
3) This pushes the blood into the atria from the pulmonary artery, down its pressure gradient.
4) The AV valves open and blood passively flows into ventricles, and the SL valves close to prevent backflow.

41
Q

How does an atheroma form?

A

1) Damage occurs to the endothelium of the arteries due to high blood pressure.
2) Therefore, white blood cells and lipids from the blood are deposited under the lining of the arteries forming an atheroma.
3) The atheroma partially blocks the lumen of the artery, restricting blood flow and therefore increases blood pressure.

42
Q

What is an aneurysm?

A

• An aneurysm is a balloon like swelling of the artery.

1) An atheroma forms, causing the walls of the artery to weaken.
2) When blood at high pressure passes through, it forces the inner walls of the artery through the outer elastic layer forming an aneurysm.
3) If this bursts, a haemorrhage is caused.

43
Q

What is thrombosis?

A

• Thrombosis is the formation of a blood clot.

1) An atheroma forms causing the endothelium of the artery to burst.
2) This damages the artery wall, leaving a rough surface where platelets and fibrins accumulate to form a blood clot.
3) This clot can either completely block the artery, or become dislodged and block a blood vessel elsewhere in the body.

44
Q

Risk factors for cardiovascular disease: High blood pressure

A

1) High blood pressure increases the risk of damage to artery walls.
2) Therefore, atheromas are more likely to form increasing blood pressure even further.
3) Also, blood clots could occur, possibly leading to myocardial infarction.

45
Q

What is a myocardial infarction?

A

• A heart attack where an infected person may experience chest pains or heart failure.

1) A thrombus forms preventing an area of the heart from receiving any oxygen.
2) Therefore, myocardial infarction occurs as that area of the heart is no longer able to function properly.

46
Q

Risk factors for cardiovascular disease: High blood cholesterol

A

1) A diet high in cholesterol contributes to the deposits formed underneath the arteries endothelium and therefore the risk of atheroma formation is larger.
2) Therefore, blood pressure increases, and blood clots may form.
3) Therefore, myocardial infarction could occur.

47
Q

Risk factors for cardiovascular disease: Salt

A

1) A diet high in salt increases blood pressure and therefore the risk of atheroma formation is larger.
2) Therefore, blood pressure increases, and blood clots may form.
3) Therefore, myocardial infarction could occur

48
Q

Risk factors for cardiovascular disease: Smoking

A

1) Carbon monoxide and nicotine found in cigarette smoke combine with haemoglobin to reduce the amount of oxygen transported in the blood.
2) This reduces the amount of oxygen delivered to the heart meaning a myocardial infarction may occur.

49
Q

Function: Xylem

A

Transport water and mineral ions in solution from the roots to the leaves.

50
Q

Function: Phloem

A

Transport organic substances in solution, both up and down the plant.

51
Q

Structure: Xylem

A
  • Very long, tube-like structures formed from dead vessel elements joined end to end.
  • There are no end walls on these cells, allowing water to easily pass through the middle of them.
52
Q

Water movement up a plant

A

1) Water evaporates from the leaves through transpiration.
2) This creates tension which pulls more water into the leaf.
3) Because water molecules are cohesive, the whole column of water in the xylem moves upwards.
4) Water then re-enters the stem through the leaf.

53
Q

What is transpiration?

A

The evaporation of water from a plant’s surface, through the stomata down a water potential gradient.

54
Q

Factors affecting transpiration: Light intensity

A

1) When it is light, the stomata open to let carbon dioxide in for photosynthesis.
2) Therefore, the transpiration rate increases.

55
Q

Factors affecting transpiration rate: Temperature

A

1) When it is warmer the water molecules have more energy so evaporate from the cells inside the leaf faster.
2) Therefore, there is a greater water potential gradient between the inside and outside of the leaf.
3) Consequently, the transpiration rate increases.

56
Q

Factors affecting transpiration: Humidity

A

1) If the humidity is low, the air around the plant is dry.
2) Therefore, the water potential gradient between the leaf and air is increased.
3) Consequently, transpiration rate increases.

57
Q

Factors affecting transpiration: Wind

A

1) If it is windy, water molecules are blown from around the stomata.
2) This increases the water potential gradient which increases the rate of transpiration.

58
Q

Structure: Phloem

A
  • Sieve tube elements form the tube for transporting solutes, but have no nucleus.
  • A companion cell is attached to each sieve tube element and carries out the living functions for each sieve cell.
59
Q

What is translocation?

A

Translocation is an energy-requiring process involving the movement of solutes to the location of usage.

60
Q

Translocation: Mass flow hypothesis

A

SOURCE:

1) Solutes move from companion cells into sieve tube via active transport, lowering the water potential inside the sieve tubes.
2) Therefore water enters the sieve tubes from the companion cell and xylem via osmosis creating a high pressure.

SINK:

3) Solutes move out of the phloem to be used which increases the water potential.
4) Therefore water leaves the sieve tubes via osmosis, lowering the pressure.

FLOW:
5) Because of the pressure gradient, solutes move down the tube.

61
Q

Mass flow evidence

A
  • Pressure inside the phloem suggests there is a pressure gradient.
  • If you use an inhibitor to stop the production of ATP, translocation stops suggesting active transport is involved.
  • If a ring of bark is removed a bulge forms suggesting there is a downward flow.
  • Radioactive tracers can be used to track the movement of substances.

A2 Biology (20 decks)

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