2.5.11 Absorption

Question 1

Food taken into the body goes through several different stages during its passage through the alimentary canal (the gut), what are they?

Answer 1

Ingestion
Mechanical digestion
Chemical digestion
Absorption
Assimilation
Egestion

Question 2

What is Absorption

Answer 2

Absorption is the movement of small digested food molecules from the digestive system into the blood (glucose and amino acids) and lymph (fatty acids and glycerol)

Question 3

Absorption of small soluble molecules occurs through, what?

Answer 3

diffusion and sometimes active transport

Question 4

Where is water primarily absorbed

Answer 4

in the small intestine, but also in the colon (by osmosis)

Question 5

After absorption, what occurs

Answer 5

assimilation and egestion occurs

Question 6

What is assimilation

Answer 6

Assimilation is the movement of digested food molecules into the cells of the body where they are used, becoming part of the cells

Question 7

What is egestion

Answer 7

Egestion is the passing out of food that has not been digested or absorbed (as faeces) through the anus

Question 8

The small intestine is adapted for, what?

Answer 8

absorption

Question 9

Why is the small intestine adapted for absorption

Answer 9

as it is very long and has a highly folded surface with millions of villi (tiny, finger-like projections)

• These adaptations massively increase the surface area of the small intestine, allowing absorption to take place faster and more efficiently

Question 10

How does Peristalsis help absorption

Answer 10

helps by mixing together food and enzymes and by keeping things moving along the alimentary canal

Question 11

Villi have several specific adaptations which allow for the rapid absorption of substances, such as?

Answer 11

A large surface area
- Microvilli on the surface of the villus further increase the surface available for absorption

A short diffusion distance
- The wall of a villus is only one cell thick

A steep concentration gradient
- The villi are well supplied with a network of blood capillaries that transport glucose and amino acids away from the small intestine in the blood

A lacteal (lymph vessel) runs through the centre of the villus to transport fatty acids and glycerol away from the small intestine in the lymph

Enzymes produced in the walls of the villi assist with chemical digestion

The movement of villi helps to move food along and mix it with the enzymes present

Question 12

Exam Tip

Answer 12

The way in which the structure of a villus is related to its function comes up frequently in exam questions so it is worth ensuring you have learned these adaptations and how they influence the rate of absorption.

Question 13

How does a short diffusion distance affect the rapid absorption of substances for villi

Answer 13

The wall of a villus is only one cell thick

Question 14

How does a large surface area affect the rapid absorption of substances for villi

Answer 14

Microvilli on the surface of the villus further increase the surface available for absorption

Question 15

How does a steep concentration gradient affect the rapid absorption of substances for villi (4 answers)

Answer 15

1. The villi are well supplied with a network of blood capillaries that transport glucose and amino acids away from the small intestine in the blood