Nutrient Exchange

Write the correct words to complete the following sentences:

​ (a)   are small finger-like projections on the cells of the small intestine that increase the surface area.

The singular form of villi is ​ (b)  

• Villi
• villus

Describe the role of digestive enzymes (amylase, protease, lipase) in chemical digestion.

Select the correct words to complete the sentence below:

By increasing the surface area, villi ​ (a)   absorption, thereby ​ (b)   the surface area: volume ratio.

• increase
• increasing
• decreasing
• decrease

What are the projections on the surface of the epithelial cells of the villi called?

• Microvilli

• Goblet cells

• Secretory cells

• Cilia

How large is the absorptive surface of your small intestine?

• 2.5 square metres

• 25 square metres

• 250 square metres

• 2500 square metres

Describe how absorption is increased in the small intestine.

Answer explanation

The small intestine wall has many finger-like structures called villi. The epithelial cells have a border of microvilli. These villi and microvilli vastly increase the surface area of the small intestine, which in turn increase the rate of absorption.

The small intestine has a dense network of capillaries to absorb amino acids and sugars, and lacteals to absorb fatty acids and glycerol. These help maintain a steep concentration gradient for absorption.

The epithelium is thin and a single layer of cells to increase absorption. It has proteins to act as channels and facilitate active transport where needed.

Intestinal secretions also include enzymes that digest protein, fats, and carbohydrates, and mucus, which keeps the lining moist and protects the epithelia.

What molecule is broken down to produce nitrogenous waste?

• Cellulose

• Lipid

• Protein

• Carbohydrate

The small intestine is specialised for absorption, whilst the alveoli in the lungs are specialised for gas exchange.

Compare the adaptations of the two regions for their functions.

Answer explanation

Both the villi and alveoli help increase transport (largely diffusion) by having a large surface area, a transport system, thin epithelia and moist surfaces.

The transport in the small intestine is of digested food (glucose, amino acids, fatty acids and glycerol) into the capillaries and lacteals. It is transported in one direction only and whilst some transport is by diffusion, there is also active transport.

The transport in the lungs is of gases - oxygen from the alveoli into the capillaries and carbon dioxide from the capillaries into the alveoli, so it is in two directions and only involves diffusion.

What is a biological catalyst?

• A protein that can slow a reaction.

• A substance that increases activation energy in cells.

• A substance that speeds up reactions in living things.

• A chemical that can react with a substrate.

Why do we need digestive enzymes?

• Enzymes are an important source of protein in our diet.

• Digestive enzymes help physically breakdown down food.

• Without enzymes our food would take too long to digest.

• Enzymes make our food taste better.