IGCSE Chapter 04 Food & Digestion

Define assimilation.

The incorporation of absorbed food molecules into new parts of the cell.

Describe how you would test for glucose.

Add an equal volume of Benedict's solution (blue).

Heat.

If positive, it will turn green/yellow/orange/brick-red depending on the concentration of glucose.

Describe how you would test for protein.

Add Biuret solution (pale blue).

If positive a lilac colour will form.

(No heating required.)

Describe how you would test for starch.

Add iodine solution (orange colour.

If positive, it will turn blue-black.

Describe the emulsion test for lipids.

Add food to ethanol.

Shake.

Add cold water.

White emulsion forms if lipid is present.

Give two functions of bile.

Neutralises acid (from the stomach).

Emulsification of lipids.

How do you calculate the energy content of a sample of food?

Burn a known mass of food under a test tube of known volume of water.

Record maximum temperature rise.

Calculate energy released by using heat capacity of 4.2 kJ per degree Celcius per ml of water.

Divide by mass of food to get energy per gram.

In what form do animals store glucose?

Glycogen.

In which part of the digestive system are most villi found?

Ileum.

Name the food molecule that amylase breaks down.

Starch.

Name the food molecule that maltase breaks down.

Maltose.

Name the process by which muscles move food through the gut.

Peristalsis.

Name the substance used to test for starch.

Iodine.

Name the two veins connected to the liver.

Hepatic vein and hepatic portal vein.

State the components of a balanced diet.

Protein / carbohydrate / lipid / minerals / vitamins / fibre / water.

State the function of fibre in the diet.

To allow peristalsis to move digested food through the colon.

Prevents constipation.

State the function of iron in the diet.

Iron is a component of haemoglobin in red blood cells.

To where does blood go after absorbing food molecules in the ileum?

The liver, via the hepatic portal vein.

What biological term describes the process of removing undigested food from the body?

Egestion.

What disease results from a lack of vitamin A?

Night blindness.

What disease results from a lack of vitamin C?

Scurvy.

What disease results from a lack of vitamin D?

Rickets.

What do proteases break down proteins into?

Amino acids.

What does lipase break down lipids into?

Fatty acids and glycerol.

What does maltose get broken down into?

Glucose.

What does starch get broken down into in the mouth?

Maltose.

What is a balanced diet?

One that provides enough of all the food groups in the correct proportions.

What is the difference between saturated and unsaturated lipids?

Saturated have only single carbon‐carbon bonds in the fatty acids.

What is the function of the lacteal in a villus?

To absorb lipids.

What is the main function of the hydrochloric acid secreted by the stomach?

To kill bacteria.

What is the purpose of mechanical digestion?

To increase the surface area of food for chemical digestion by enzymes.

What substance is dietary fibre made of?

Cellulose.

What two types of digestion take place in the mouth?

Mechanical and chemical.

Where is bile stored?

Gall bladder.

Where is fat emulsified?

Duodenum.

Where is protein first digested?

Stomach.

Which enzyme is secreted by the stomach?

Pepsin.

Why do animals need lipids?

Energy source.

Insulation.

Make cell membranes.