StemUp: AQA A level Biology 3.3.3 Digestion and Absorption

What is meant by the term 'digestion'? (2)

- The process by which larger biological molecules are hydrolysed into smaller molecules ‎‏‏‎‎‏

- That can be absorbed across cell membranes

Which enzyme is involved in the hydrolysis of starch in the mouth and what does it do? (2)

- Salivary amylase

- Which hydrolyses the starch into maltose

Why is only a small amount of starch broken down in the mouth? (1)

Due to the short time food remains in the mouth

How does chewing affect the hydrolysis of carbohydrates in the mouth? (3)

- Chewing breaks the food into smaller particles

- Which increases the surface area

- Allowing hydrolysis by enzymes to occur more rapidly

What enzyme hydrolyses the remaining starch into maltose in the small intestine? (1)

- Pancreatic amylase

- Which hydrolyses the remaining starch into maltose

What are the three membrane-bound disaccharidases involved in the complete hydrolysis of carbohydrates in the small intestine? (3)

- Maltase

- Lactaste

- Surcase

Which enzyme is responsible for the complete hydrolysis of maltose? (1)

Maltase

Which enzyme is responsible for the complete hydrolysis of lactose? (1)

Lactase

Which enzyme is responsible for the complete hydrolysis of surcose? (1)

Surcase

What enzyme is responsible for the hydrolysis of lipids in our body? (1)

Lipase

Describe how bile salts are involved in the hydrolysis (4)

- Bile salts emulsify lipids

- Causing them to form small droplets

- This increases the surface area of the lipids

- Which speeds up the hydrolysis by lipase

What kind of process is emulsification? (2)

- Physical process

- Does not cause chemical breakdown

What are the three enzymes involved in the complete digestion of proteins? (3)

- Endopeptidases

- Exopeptidases

- Dipeptidases

What is the function of endopeptidases in the hydrolysis of proteins? (2)

- Hydrolyse the internal peptide bonds between the amino acids of proteins

- To form small polypeptides and peptides

What is the function of exopeptidases in the hydrolysis of proteins? (2)

- Hydrolyse the terminal (end) peptide bonds at either end of a polypeptide

- To form dipeptides

What is the function of dipeptidases in the hydrolysis of proteins? (2)

Hydrolyse dipeptides into amino acids

How does the ileum in the small intestine achieve a large surface area for absorption? (2)

- Long length

- Presence of villi and microvilli

What role do the blood capillaries in the ileum play in absorption? (2)

- Absorbs monosaccharides and amino acids

- Which maintains a high diffusion gradient for further absorption

How do lymph vessels (lacteals) in the villi contribute to absorption? (2)

- Absorbs digested lipids

- Which maintains a high diffusion gradient for absorption

How does the structure of the villus wall facilitate absorption in the ileum? (2)

- Consists of a single layer of epithelial cells

- Which provide a short diffusion pathway for absorption

Describe the co-transport absorption mechanism of amino acids and monosaccharides (3)

1. Sodium ions are actively transported from the ileum cells into the blood

2. This forms a diffusion gradient for sodium ions to enter the cells

3. Glucose enters the blood by facilitated diffusion coupled with the sodium ions

Describe the role of micelles in absorption of lipids

1. Micelles contain fatty acids, monoglycerides, and bile salts

2. These transport poorly soluble fatty acids and monoglycerides to the surface of epithelial cells where they can be absorbed

3. They then release the fatty acids and monoglycerides

4. Fatty acids and monoglycerides are absorbed into epithelial cells by diffusion.

5. Smaller fatty acid chains diffuse from the epithelial cells directly into the blood

What do micelles contain? (3)

- Fatty acids

- Monoglycerides

- Bile salts

What is the role of micelles in the absorption of poorly soluble fatty acids and monoglycerides? (2)

- Micelles transport them to the surface of the epithelial cells

- Where they can be absorbed

What happens after micelles transport fatty acids and monoglycerides to the epithelial cells? (1)

They release the fatty acids and monoglycerides

How are fatty acids and monoglycerides absorbed into epithelial cells? (1)

By diffusion

What happens to smaller fatty acid chains after they are absorbed into epithelial cells? (2)

- Smaller fatty acid chains diffuse from the epithelial cells

- Directly into the blood

How are longer-chained fatty acids and monoglycerides are absorbed? (5)

1. Triglycerides are reformed in the epithelial cell using the longer-chained fatty acids and monoglycerides

2. They are then packaged into proteins by the Golgi body

3. To form chylomicrons

4. Chylomicrons are absorbed into the lacteals (lymphatic vessels) in the villi

5. Which eventually drain into the blood