Digestion and absorption Flashcards – AQA A-Level Biology - (7402)

What does hydrolysis accomplish in carbohydrate digestion?

It breaks glycosidic bonds, producing monosaccharides that can be absorbed.

What reaction do amylases catalyse in carbohydrate digestion?

They hydrolyse starch into smaller carbohydrates, including maltose.

Where are the disaccharidases involved in carbohydrate digestion located?

They are membrane-bound on epithelial cells of the small intestine.

What reaction does maltase catalyse?

It hydrolyses maltose to glucose.

What reaction does sucrase catalyse?

It hydrolyses sucrose to glucose and fructose.

What reaction does lactase catalyse?

It hydrolyses lactose to glucose and galactose.

What are the main products of triglyceride hydrolysis by lipase?

Monoglycerides and free fatty acids.

How do bile salts make lipids more accessible to lipase?

They emulsify large lipid droplets into smaller droplets, increasing the surface area available for lipase.

Are bile salts lipid-digesting enzymes?

No. Bile salts are not enzymes and do not themselves hydrolyse lipids.

What happens to peptide bonds during protein digestion, and what is the final product?

Peptide bonds are hydrolysed, producing amino acids.

What is the role of endopeptidases in protein digestion?

They hydrolyse bonds within polypeptide chains, forming shorter peptides.

What is the role of exopeptidases in protein digestion?

They remove amino acids from the ends of peptide chains.

What is the role of membrane-bound dipeptidases in protein digestion?

They hydrolyse dipeptides into amino acids.

Where are membrane-bound dipeptidases involved in protein digestion located?

On small-intestinal epithelial cells.

Which three types of solute are absorbed by sodium-dependent co-transport in the ileum?

Glucose, galactose and amino acids.

Where are sodium-dependent co-transport proteins located in ileum epithelial cells?

In the membrane facing the intestinal lumen.

How does sodium co-transport drive solute absorption into an ileum epithelial cell?

Sodium moves down its concentration gradient, driving a sugar or amino acid into the cell against its gradient.

How do sodium-dependent co-transport proteins differ in the solutes they carry?

Different co-transport proteins carry different solutes.

How is the sodium gradient for co-transport maintained in ileum epithelial cells?

Sodium–potassium pumps in the opposite membrane use ATP to move sodium out of the cell.

Where do absorbed solutes go after entering an ileum epithelial cell?

They leave across the opposite membrane and enter the blood.

How does fructose enter ileum epithelial cells?

By facilitated diffusion, not sodium co-transport.

How do micelles form in the small intestine?

Bile salts associate with lipid digestion products, including fatty acids and monoglycerides, in the watery intestinal contents.

What role do micelles play in lipid absorption?

They carry poorly water-soluble lipid digestion products to the surface of ileum epithelial cells.

How do fatty acids and monoglycerides enter ileum epithelial cells from micelles?

They leave the micelles and cross the cell membranes.

What happens to bile salts after fatty acids and monoglycerides leave micelles?

They remain in the intestinal lumen and can be reused.