Digestion

Question 1

Physical digestion (breaking down food into smaller pieces) is important because:

Answer 1

• It allows the food to pass more easily through the digestive system
• It prepares the food for chemical digestion by giving it a larger surface area

Question 2

In chemical digestion, carbohydrates, fats and proteins are broken down by specific enzymes, in three places:

Answer 2

• In the mouth, where carbohydrase breaks down starch to sugar.
• In the stomach, where protease breaks down protein to amino acids.
• In the small intestine, where lipase breaks down fat into fatty acid and glycerol.

Question 3

The strong stomach acid

Answer 3

Provides the optimum condition for protease to work.

Question 4

The chemical breakdown of starch involves two steps:

Answer 4

• Breakdown of starch (many linked units) to maltose (two lose units).
• Breakdown of maltose to glucose (one unit).

Question 5

What do protease enzymes need?

Answer 5

Protease enzymes, such as pepsin in the stomach, require a low pH (acidic) while other protease enzymes in the mouth and small intestines require a high pH (alkaline). Those in the mouth require a slightly acidic/neutral pH

Question 6

How is bile used in chemical digestion?

Answer 6

The gall bladder stores bile. Bile is released into the small intestine to emulsify fats, increasing their surface area for efficient digestion.

Question 7

What happens to the food molecules in the small intestine?

Answer 7

• Food molecules need to be able to pass through the walls of the small intestine and dissolve in the blood or lymph. This means they have to be small and soluble.
• The digestived carbohydrates and protein molecules (glucose and amino acids) are soluble. They diffuse through the walls of the small intestine and into the blood.
• The digested fat molecules (fatty acids) are not soluble in water or plasma, so would block up blood vessels. They diffuse through the walls of the small intestine and into the lympth.

Question 8

How is the small intestine adapted for absorption?

Answer 8

• The small intestine is adapted for efficient absorption of food by having an extensive system of blood capillaries and an extensive lymphatic system of lacteals, which contain lymph. The small intestine also has a large surface area, created by:
  
  • Many villi in the walls of the small intestine.
  • Many microvilli (projection) from the walls of the villi