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AS Biology > 3B - Digestion and absorption > Flashcards

3B - Digestion and absorption Flashcards

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1
Q

Why is digestion necessary?

A

To break large biological molecules into smaller molecules as they are too big to cross cell membranes so can’t be absorbed from the gut into the blood.

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2
Q

What are carbohydrates broken down into in hydrolysis?

A

Disaccharides and then monosaccharides.

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3
Q

What are fats broken down into in hydrolysis?

A

Fatty acids and monoglycerides.

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4
Q

What are proteins broken down into in hydrolysis?

A

Amino acids

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5
Q

What are digestive enzymes used for?

A

To break down biological molecules in food.

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6
Q

What are carbohydrates broken down by in digestion?

A

Amylase and membrane-bound disaccharidases.

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7
Q

What is amylase?

A

An enzyme

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8
Q

What is the function of amylase?

A

An enzyme that catalyses the conversion of starch (a polysaccharide) into the smaller sugar maltose (a disaccharide).

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9
Q

What bonds in starch are broken during hydrolysis?

A

Glycosidic

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10
Q

Where is amylase produced?

A

Salivary glands (into the mouth) and also by the pancreas (into the small intestine).

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11
Q

What are membrane-bound disaccharidases?

A

Enzymes that are attached to the cell membranes of epithelial cells lining the ileum.

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12
Q

What do membrane-bound disaccharidases do?

A

Help to break down disaccharides into monosaccharides.

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13
Q

How can monosaccharides be transported across the cell membranes of the ileum epithelial cells?

A

Via specific transporter proteins.

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14
Q

What are lipids broken down by?

A

Lipase (with the help of bile salts).

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15
Q

What does lipase do?

A

Catalyses the breakdown of lipids into monoglycerides and fatty acids.

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16
Q

When lipids are broken up into fatty acids and monoglycerides, what bond is broken?

A

Ester

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17
Q

Where are lipases made?

A

Pancreas

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18
Q

Where do lipases work?

A

Small intestine.

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19
Q

Where are bile salts produced?

A

Liver

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20
Q

What do bile salts do?

A

Emulsify lipids - cause the lipids to form small droplets.

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21
Q

Why are bile salts important in lipid digestion?

A

Several small lipid droplets have a bigger SA than a single large droplet. So the formation of small droplets greatly increases the SA of lipid that’s available for lipases to work on.

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22
Q

What happens to the monoglycerides and fatty acids once a lipid has been broken down?

A

They stick with the bile salts to form tiny structures called micelles.

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23
Q

What is a monoglyceride?

A

A glycerol molecule with 1 fatty acid attached.

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24
Q

What does the digestive system consist of?

A

A long tract of muscular tubing with a range of enzyme secreting glands and sections of increased SA for absorption.

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25
Q

What is digestion?

A

The breaking down of large biological molecules, so they can be absorbed.

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26
Q

What are the major components of the digestive system?

A 
Salivary glands
Oesophagus
Stomach
Pancreas
Ileum
Large intestine
Rectum
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27
Q

What are the salivary glands/what are their functions?

A

Secrete saliva which helps to lubricate food - also contains amylase.

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28
Q

What enzyme do the salivary glands secrete?

A

Amylase

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29
Q

What is the oesophagus/what is its function?

A

A smooth tube that transports food to the stomach.

30
Q

What is the stomach/what is its function?

A

Stores and digests food, especially proteins. Has sphincter muscles at each end to control its opening and closing and therefore the movement of food through the digestive system.

31
Q

Why does the stomach digest proteins especially well?

A

Because it has a low pH due to the hydrochloric acid, giving the optimum pH for the enzymes to break them down.

32
Q

What does the stomach have at each end?

A

Sphincter muscles at each end to control its opening and closing and therefore the movement of food through the digestive system.

33
Q

What do the sphincter muscles in the stomach do?

A

Sphincter muscles at each end to control its opening and closing and therefore the movement of food through the digestive system.

34
Q

What is the pancreas/what is its function?

A

A large gland that secretes pancreatic juice just after the stomach - contains proteases, lipases and amylase.

35
Q

What enzymes does the pancreas secrete?

A

Proteases, lipases and amylase.

36
Q

What is peristalsis?

A

The process by which food moves through the digestive system by contraction of the muscles.

37
Q

What is the name of the process in which food moves through the digestive system?

A

Peristalsis.

38
Q

What is peristalsis controlled by?

A

Contraction of the muscles.

39
Q

What is a bolus?

A

A ball of food after it is passed through the digestive system.

40
Q

What does bile do?

A

Neutralises the hydrochloric acid.

41
Q

Where is bile released from?

A

Liver

42
Q

What is the scientific name for the small intestine?

A

Ileum

43
Q

What is the ileum?

A

The small intestine.

44
Q

What is the ileum/what is its function?

A

The small intestine - secrete many digestive enzymes and has a massive SA due to epithelial cells covered in villi (and microvilli).

45
Q

What is the large intestine/what is its function?

A

Absorbs water. Essential in reclaiming the water that is secreted by the many digestive enzymes.

46
Q

What is the rectum/what is its function?

A

Faeces are stored here prior to periodic egestion.

47
Q

What is ingestion?

A

Taking food into the digestive system OUTSIDE OF THE BODY.

48
Q

What is egestion?

A

Taking food out of the digestive system OUTSIDE OF THE BODY.

49
Q

Do ingestion and egestion occur inside or outside of the body?

A

Outside.

Food isn’t in the body unless it has diffused/been absorbed into the bloodstream.

50
Q

Is the food inside or outside the body when it is in the digestive system?

A

Outside - food isn’t in the body unless it has diffused/been absorbed into the bloodstream.

51
Q

Explain the process of digestion of carbohydrates:

A
  • Begins in the mouth with salivary amylase which begins to break down starch into maltose.
  • Then the pancreatic amylase is secreted by the pancreas into the ileum to break the maltose down into alpha glucose.
  • Alkaline (bile) salts are secreted in pancreatic juice and from the ileum wall to correct the pH for the enzymes.
52
Q

Explain the process of digestion of lipids:

A
  • Lipases digest lipids by breaking the ester bonds.
  • 2 fatty acids and a monoglyceride are released.
  • Bile salts emulsify lipids - breaking them into smaller droplets called micelles, increasing the SA of the lipid to accelerate the effect of digestive enzymes.
53
Q

What are the functions of bile salts?

A

Emulsify lipids and neutralise stomach (hydrochloric) acid.

54
Q

What is the better name for proteases?

A

Peptidases

55
Q

What are proteins broken down by?

A

Peptidases

56
Q

What are the 3 peptidases?

A

Endopeptidases.
Exopeptidases.
Dipeptidases.

57
Q

What do endopeptidases do?

A

Break peptide bonds in the central region of protein molecules creating several peptide molecules.

58
Q

What do exopeptidases do?

A

Hydrolyse peptide bonds on the terminals of the peptide molecules created by the endopeptidases - makes dipeptidases.

59
Q

What do dipeptidases do?

A

Hydrolyse peptide bonds at the centre of a dipeptide molecule releasing 2 amino acids.

60
Q

What are dipeptidases?

A

Membrane bound enzymes found in the ileum.

61
Q

What are examples of endopeptidases?

A

Trypsin and chymotrypsin.

Pepsin.

62
Q

What is pepsin?

A

An endopeptidase.

63
Q

Where is pepsin released and why?

A

Into the stomach by cells in the stomach lining as it only works in acidic conditions - which are provided by hydrochloric acid in the stomach.

64
Q

Where are dipeptidases located?

A

In the cell-surface membrane of epithelial cells in the ileum.

65
Q

How are monosaccharides absorbed across the ileum epithelium into the bloodstream?

A

Glucose is absorbed by active transport with sodium ions via a co-transporter protein.

Galactose is absorbed in the same way using the same co-transporter protein as above.

Fructose is absorbed via facilitated diffusion through a different transporter protein.

66
Q

How are monoglycerides and fatty acids absorbed across the ileum epithelium into the bloodstream?

A

Micelles help to move monoglycerides and fatty acids towards the epithelium.

Because micelles constantly break up and reform they can ‘release’ monoglycerides and fatty acids, allowing them to be absorbed - whole micelles are not taken up across the epithelium.

Monoglycerides and fatty acids are lipid-soluble, so can diffuse directly across the epithelial cell membrane.

67
Q

How are amino acids absorbed across the ileum epithelium into the bloodstream?

A

Amino acids are absorbed via co-transport.

Sodium ions are actively transported out of the ileum epithelial cells into the blood. This creates a sodium ion concentration gradient. Sodium ions can then diffuse from the lumen of the ileum into the epithelial cells through sodium-dependent transporter proteins, carrying the amino acids with them.

68
Q

What do peptidases do?

A

Enzymes that catalyse the conversion of proteins into amino acids by hydrolysing the peptide bonds between amino acids.

69
Q

What are the adaptations of villi for absorption?

A

Lots of capillaries for the absorption of glucose and amino acids.

Epithelial cells have microvilli increasing SA.

They have a lacteal (tiny lymphatic vessels) which absorbs fatty acids and glycerol.

70
Q

Describe how triglycerides are digested/absorbed:

A

Micelles are brought into contact with the ileum wall by peristalsis moving substance around in the ileum.

Once hydrolysed into monoglycerides and fatty acids the molecules, being non-polar, can easily diffuse across the cell-surface membrane of the epithelial cells.

The molecules are then taken to the ER and recombined into various triglycerides.

From the ER, they move to the golgi apparatus. Here, they associate with cholesterol and lipoproteins to form special lipid transport particles called chylomicrons.

Exocytosis moves these chylomicrons from the epithelial cells into lymphatic capillaries called lacteals.

AS Biology (47 decks)

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