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AQA AS (A-level) Biology > 3.3.3 Digestion and Absorption > Flashcards

3.3.3 Digestion and Absorption Flashcards

1
Q

Where are digestive enzymes released and what type of enzymes are they?

A

Released by gland cells and are hydrolytic enzymes

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2
Q

What do hydrolytic enzymes hydrolyse?

A

Large insoluble food molecules (polymers) into smaller, soluble molecules (monomers)

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3
Q

Where are small, soluble molecules absorbed and accumulated?

A

Lining of the ileum (small intestine)

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4
Q

Carbohydrates are hydrolysed into ___________ ___________ by _____________________

A
  • Simple sugars
  • Carbohydrases
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5
Q

Fats are hydrolysed into __________________, _____________ __________ and ______________________ by _______________

A
  • Glycerol
  • Fatty acids
  • Monoglycerides
  • Lipases
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6
Q

Why are assimilated molecules useful?

A

Can be used by the body for specific functions e.g., glucose used in respiration

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7
Q

Name the glands which produce enzymes

A
  • Salivary glands
  • Stomach
  • Pancreas
  • Ileum
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8
Q

Where is amylase secreted from?

A

Pancreas and salivary glands

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9
Q

What is mechanical digestion?

A

Mouth breaking down foods giving a large surface area

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10
Q

What does amylase break down?

A

Starch into maltose

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11
Q

Which enzymes does the stomach produce?

A
  • Endopeptidases
  • Exopeptidases
  • Dipeptidases
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12
Q

Which enzymes does the pancreas secrete?

A

Pancreatic amylase, lipase and exopeptidases

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13
Q

Which enzymes does the ileum secrete?

A

Membrane bound dipeptidases and disaccharides

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14
Q

State what is meant by digestion (1)

A

Hydrolysis of large insoluble substances (polymers) to smaller, soluble substances (monomers)

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15
Q

What is the purpose of hydrochloric acid in the stomach?

A
  • Denatures salivary enzymes
  • Kills microorganisms
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16
Q

Where does digestion stop?

A

Ileum

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17
Q

Where is membrane bound maltase found?

A

Ileum

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18
Q

Which enzyme breaks down maltose into glucose?

A

Maltase

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19
Q

Explain the complete digestion of starch (6)

A
  1. Mechanical digestion by teeth (larger surface area), then mixed with saliva
  2. Salivary amylase starts to hydrolyse glycosidic bonds in starch producing the dimer maltose
  3. In the stomach, salivary amylase is denatured due to acidic pH
  4. In small intestine, pancreatic amylase continues to hydrolyse starch into maltose
  5. Maltose is hydrolysed to glucose by membrane bound maltase embedded in CSM of epithelial cells in ileum
  6. Glucose absorbed by ileum
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20
Q

A healthy person has amylase in their blood.

Explain why it has no harmful effects on the body (2)

A
  1. Amylase is an enzyme;
  2. Specific and complementary to starch so has no effect on other molecules;
21
Q

Explain how endopeptidases are involved in the digestion of proteins

A

Endopeptidases found in the stomach and pancreas
• Polypeptides are hydrolysed by proteases
• Endopeptidases hydrolyse internal peptide bonds within polypeptide chain
• Produces many smaller, shorter polypeptide chains and increases surface area for the next enzyme making digestion more efficient

22
Q

Explain how exopeptidases are involved in the digestion of proteins

A

Exopeptidases made in the pancreas
• Hydrolyse peptide bonds and terminal ends of polypeptide chain (—COOH and —H2N)
• Produces dipeptides and single amino acids
• They are specific: one group are complementary to the N terminal end and another group is complementary to C terminal end.

23
Q

Explain how dipeptidases are involved in the digestion of proteins

A

Dipeptidases found in the small intestine
• Embedded in cell surface membrane of epithelial cells
• Hydrolyse single peptide bond in the dipeptide to produce single amino acids
• Amino acids absorbed by co-transport

24
Q

Why are monosaccharides only able to be transported across epithelial cell membranes?

A

Small enough and complementary to specific channel/carrier proteins

25
Q

Why do monosaccharides require carrier proteins, and have to be transported by facillitated diffusion?

A

Not lipid soluble

26
Q

Explain how glucose moves into the bloodstream using co transport in the ileum (5)

A
  1. Na+ are actively transported out of epithelial cells into blood (by sodium potassium pump requiring ATP)
  2. This creates a concentration gradient of Na+ (between lumen of ileum and epithelial cell)
  3. Na+ and glucose enter by facilitated diffusion using complementary co-transporter proteins - this has 2 binding sites - one complementary to Na+ and one complementary to glucose.
  4. Na+ diffuses into cell down concentration gradient, glucose moves into cell against concentration gradient.
  5. Glucose moves into blood by facilitated diffusion
27
Q

Describe and explain three features you would expect to find in a cell specialised for absorption (3)

A
  • Microvilli and villi - increased surface area
  • Large number of co-transport/carrier/channel proteins - faster rate of diffusion
  • Epithelial cells contain many mitochondria - produces ATP for active transport by sodium, potassium pump
28
Q

Why are humans unable to digest cellulose?

A

Don’t have enzyme cellulase

29
Q

Explain lactose intolerance

A
  • No lactase
  • No lactose hydrolysed
  • Bacteria in large intestine produces enzymes releasing monosaccharides for bacteria to absorb and assimilate it for their own respiration
30
Q

Where does the digestion and absorption of lipids take place?

A

Only in the ileum

31
Q

What happens to lipids in the stomach?

A

Churned into fat droplets

32
Q

Why do lipids not dissolve in stomach acid?

A

Insoluble

33
Q

Where is bile produced?

A

Liver

34
Q

Where is bile released?

A

Small intestine

35
Q

By which process do lipids move across a cell surface membrane?

A

Simple diffusion

36
Q

Bile contains ______ _______

A

Bile salts

37
Q

What is the purpose of bile salts?

A

Emulsifies fat droplets and forms micelles increasing surface area for action of lipases

38
Q

Name the enzyme that hydrolyses lipids and the products it produces

A
  • Lipases
  • Monoglycerides and fatty acids
39
Q

How are lipids emulsified?

A

Lipid droplets are mixed with bile salts to form small droplets

40
Q

What is the advantage of emulsification?

A

Smaller droplets increase surface area for faster hydrolysis by pancreatic lipase

41
Q

What are micelles formed of?

A

Bile salts, glycerol and fatty acids

42
Q

Describe and explain the process of digestion of lipids (5)

A
  1. Lipid droplets mixed with bile salts to form small droplets - emulsification
  2. Smaller droplets increase surface area for faster hydrolysis by pancreatic lipase
  3. Triglycerides hydrolysed into fatty acids and monoglycerides
  4. Bile salts, glycerol and fatty acids form micelles
  5. Micelles make fatty acids soluble in water and bring them to surface of epithelial cell membrane, this maintains a higher concentration relative to epithelial cells
43
Q

State the primary function of micelles

A

Transport fatty acids and glycerol to the cell surface membrane

44
Q

Why are fatty acids able to pass through the phospholipid bilayer?

A

They are non-polar and lipid-soluble, so dissolve in the bilayer and diffuse across it

45
Q

Chylomicrons

A

Modified lipids, where a protein is added

46
Q

Describe and explain the process of absorption of lipids (4)

A
  1. Fatty acids enter epithelial cells by simple diffusion (micelles don’t cross CSM, they transport FA and glycerol to CSM) - only small, non-polar molecules pass CSM, bile salts contain phospholipid on exterior so allow passage.
  2. At sER, fatty acids and glycerol recombined to form triglycerides
  3. At Golgi apparatus, triglycerides modified, proteins added to form lipoproteins (chylomicrons) and packaged into vesicles (chylomicrons are water soluble)
  4. Chylomicrons are transported into a lymph system vessel by exocytosis, then entering blood.
47
Q

What happens at the smooth endoplasmic reticulum to absorbed lipids?

A

Fatty acids and glycerol recombine to form triglycerides

48
Q

What happens at the Golgi apparatus to triglycerides?

A

Modified, proteins added to form lipoproteins (chylomicrons) and packaged into vesicles

AQA AS (A-level) Biology (16 decks)

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