The human digestive system Flashcards – AQA GCSE Combined Science: Trilogy (8464) — Biology — Foundation

What happens to food molecules during chemical digestion?

Large, insoluble food molecules are broken down into small, soluble molecules.

Why is chemical digestion necessary for absorption?

It produces molecules that can be absorbed from the digestive system.

What does amylase break down, and what does it produce?

It breaks down starch into simple reducing sugars.

Where do the salivary glands secrete amylase?

Into the mouth, where it acts on starch in food.

Where does the pancreas secrete amylase?

Into the small intestine, where it continues starch digestion.

What do proteases break proteins down into during digestion?

Amino acids.

Where are the proteases that act in the stomach secreted?

In the stomach.

Which two organs secrete proteases that act in the small intestine?

The pancreas and the small intestine.

What is an enzyme?

A protein that acts as a biological catalyst, increasing reaction rates in living organisms without being used up.

How does the lock and key model explain enzyme specificity?

A particular substrate fits an enzyme’s active site because their shapes are complementary.

What happens after a substrate binds to an enzyme’s active site?

The enzyme catalyses the reaction, and the products are released.

What is metabolism?

The sum of the chemical reactions in an organism.

What role do enzymes play in metabolism?

They catalyse metabolic reactions.

Why does enzyme activity increase as temperature rises up to the optimum?

Particles gain kinetic energy, so enzyme and substrate molecules collide more frequently.

Why does enzyme activity fall rapidly above the optimum temperature?

The enzyme denatures: its structure changes and its active site loses its complementary shape.

How do low temperatures affect enzyme activity and denaturation?

They slow enzyme activity but do not normally denature the enzyme.

What is an enzyme’s optimum pH?

The pH at which the enzyme works fastest.

What happens to enzyme activity as pH moves away from the optimum?

It decreases.

How can extreme pH prevent an enzyme from working effectively?

It can denature the enzyme, changing its structure and active-site shape so the substrate no longer fits effectively.

Do different enzymes necessarily have the same optimum pH?

No. Different enzymes can have different optimum pH values.

How is the average rate of a chemical reaction calculated?

Divide the amount of reactant used up or product formed by the time taken.

How are the units of an average reaction rate determined?

Express the measured quantity’s unit per unit of time, using consistent quantity and time units.

What is the word equation for lipid digestion by lipase?

Lipid → glycerol + fatty acids

Which two organs produce lipase?

The pancreas and small intestine.

Where does lipase act during digestion?

In the small intestine.

Why can the products of lipid digestion be absorbed?

They are small molecules.

Where is bile made, stored and released?

Made in the liver, stored in the gall bladder and released into the small intestine.

How does bile provide conditions that increase lipase activity?

Alkaline bile neutralises hydrochloric acid from the stomach, providing alkaline conditions.

What does it mean for bile to emulsify fat?

It breaks fat into small droplets.

Why does emulsification increase the rate of fat breakdown?

It increases the surface area available to lipase.

Is bile an enzyme?

No, bile is not an enzyme.