1. National 5 Biology Unit 2 – Cell Biology
Section 13
Absorption of Materials

2. We will be learning…
To be able to describe how oxygen and nutrients from food is absorbed into the bloodstream for the use in respiration
To be able to describe how waste materials, such as carbon dioxide, are removed from cells to the bloodstream.
To be able to describe the structure of a capillary network and how exchange of materials takes place there.
To be able to explain the features of surfaces involved in absorption and their features that they have in common that help increase efficiency of absorption.
To be able to describe the structure of lungs and how gas exchange takes place at the alveoli.
To be able to describe how nutrients are absorbed, via villi, into the small intestine.
To be able to describe the structure of villi and how this structure maximises absorption of glucose, amino acids and a lacteal to absorb fatty acids and glycerol.

3. Respiratory system
To carry out respiration, the body needs a supply of oxygen. It gets this from the air.
The respiratory system extracts oxygen form the air to make it available [via the blood] to all respiring cells.

4. Respiratory System Structures
nasal cavity
trachea
air sac
bronchus
intercostal muscle
Chest cavity
ribs
Left lung
heart
diaphragm

5. Lung Structure
Lungs are spongy organs full of tiny air sacs called alveoli.
They have a very large surface area.
They are pinky red because they have a good blood supply.
Rings of cartilage are found around the trachea and the bronchi to prevent them from collapsing.

6. Trachea
Air enters the breathing system through the mouth and nose. It then travels down the trachea to the lungs.
The trachea is lined with rings of cartilage. This provides strength and prevents the trachea collapsing during breathing.
National 4/5 Biology Course Unit 2

7. The Lining of Air Passages
Air contains dust and germs which could damage your lungs.
The cells lining the air passages have small hairs or cilia.
The cilia move in waves to push upwards and keep the lungs clear.
(produce mucus)

8. The airways of the lungs are lined by special cells which produce mucus – a sticky substance to trap micro- organisms, dust and dirt.
The airways also have special hair-like cells called cilia who move upwards in a wave-like motion to move the trapped germs and dirt out of the lungs.
This shows bacteria (orange) trapped by mucus (blue) on the tiny cilia cells.
National 4/5 Biology Course Unit 2

9. Gas Exchange in the Air Sacs
The bronchi divide into smaller and smaller tubes called bronchioles.
Each bronchiole ends in an air sac, which is lined in moisture.
Oxygen dissolves in moisture and diffuses from lungs into blood because there is a higher concentration in the air sac than in the blood.
Carbon dioxide diffuses in opposite direction because there is a higher concentration in the blood than in the air sac.

10. Alveoli Bronchiole Alveolus Capillary
At the end of the bronchioles are the alveoli. These are the site of gas exchange.
Bronchiole
Alveolus
Capillary
National 4/5 Biology Course Unit 2

11. Gas Exchange
Oxygen diffuses from an area of high concentration inside the lung to an area of low concentration in the red blood cells.
Carbon dioxide diffuses from an area of high concentration in the blood to an area of low concentration in the lung.
bronchiole
single celled wall of alveolus O2
CO2
single celled wall of capillary
layer of fluid
red blood cell
National 4/5 Biology Course Unit 2

12. Importance in Multicellular Organisms
To increase efficiency of Absorption alveoli –
Have a large surface area
Thin walls – one cell thick
Good supply of blood
oxygen
carbon dioxide

13. Gas Exchange Cellular Level in Tissues
Oxygen diffuses from the high concentration in the capillary blood across into the body cells. Carbon dioxide diffuses from the high concentration in the cells into the plasma .
diffuses
plasma
living cell
capillary
Blood from artery high oxygen low carbon dioxide
Blood to vein high carbon dioxide low oxygen
oxygen
CO2
Glucose also diffuses into cells in the same way that oxygen does

14. Digestive System Mouth Tongue Gullet or Oesophagus Stomach Liver
Gall Bladder
Bile Duct
Pancreas
Small Intestine
Large Intestine
Appendix
Rectum
Anus
Digestive System
National 4/5 Biology Course Unit 2

15. 00:00:00
Food is swallowed and crushed by the teeth. Mixed with saliva.
00:00:10
Food enters stomach, where it is mixed with acid.
03:00:00
Food is now a creamy liquid – goes to the small intestine
20:00:00
Food enters large intestine. Where water is absorbed.
06:00:00
Food reaches the mid-point of the small intestine
32:00:00 Undigested food leaves the body

16. Oesophagus and Peristalsis
Oesophagus is a muscular tube - connects the mouth to stomach.
It is the start of the alimentary canal, which is a long tube stretching from mouth to anus.
When food is swallowed wave-like muscular contractions called peristalsis ensures the food (bolus) moves down in a slow controlled way no matter what position the body is in.
The muscle ahead of the food is relaxed while the muscle behind the food contracts.

17. Peristalsis Muscles behind food contracted Muscles ahead of food
relaxed
Direction of
food
movement
Food

18. Stomach pepsin protein
The stomach is a muscular sac with longitudinal and circular muscles that contract and relax, churning or mixing food with acid and enzymes.
The mucus, lining the stomach protects the wall from being damaged by the acid ( pH 2).
Acid provides the correct pH for the protein digesting enzyme pepsin to work.
protein
pepsin
Peptides

19. Small Intestine
As food leaves the stomach, it enters the small intestine.
The first 12 inches make up the duodenum.
There are 2 ducts connected to this :
Pancreatic : enzymes made by the pancreas enter through this. ( lipases,amylases and proteases, an example of a protease is trypsin)
Bile : bile stored in the gall bladder enters through this.
Bile is made in the liver but stored in the gall bladder.
Bile emulsifies fats ( gets them to mix with water) and neutralises the acid soaked food coming from the stomach as it is an alkali.

20. Small Intestine
The main job of the small intestine is to absorb the products of digestion.
It is well adapted for this by :
Long and inner membrane is highly folded. This increases the surface area for absorption
Thin inner lining ,only one cell thick.
Many blood capillaries to absorb and transport products. Lacteals are present to transport fats

21. Small Intestine Villus
Capillary - Absorbs products of carbohydrate (glucose) and protein digestion (amino acids)
Lacteal – Absorbs the products of fat digestion (fatty acids and glycerol)

22. Fate of Digested Food
Glucose, amino acids ( products of carbohydrate and protein digestion) are absorbed into the blood capillaries
Fatty acids and glycerol are absorbed into the lacteal.
Next Step – Liver !
The liver decides how much sugar is needed in the blood and converts the excess to glycogen and stores it.

23. Liver
The liver decides how much amino acids should be in the blood and converts the excess to urea.
This urea is taken to the kidneys for excretion in urine.
Fatty acids and glycerol travel in the lymphatic system. Excess is stored as fatty tissue.

24. Large Intestine
Material passing into the large intestine consists of undigested matter ( fibre), bacteria and dead cells .
The colon absorbs water from this before eliminating the waste as faeces.