5.5Chapter 5: Respiration and the Respiratory System

The lungs and gas exchange — Alhussan Biology - Stage 8 Revision Notes & Topical Questions

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Biology 5.5 The lungs and gas exchange — Alhussan International Academy — Biology (Stages 7–9) notes: Describe the structure of the human gas exchange system, relate each part to its function and explain how oxygen and carbon dioxide are exchanged.Respiration — every cell carries…

Mouth and nose
Cilia and mucus
Carbon monoxide
Protection
Respiration — every cell carries out aerobic respiration to release energy for all the characteristics of life
Oxygen and carbon dioxide — cells need oxygen and produce toxic carbon dioxide as waste

Part 1 of 6Why gas exchange is needed

Why gas exchange is needed

Respiration

Respiration every cell carries out aerobic respiration to release energy for all the characteristics of life.

Oxygen and carbon dioxide

Oxygen and carbon dioxide cells need oxygen and produce toxic carbon dioxide as waste.

Gas exchange

Gas exchange the process in which the body exchanges oxygen from the air for waste carbon dioxide from the blood.

The respiratory system is also called the gas exchange system.

Part 2 of 6The respiratory system

The respiratory system

Path

Path it leads from the nose and mouth down into the lungs, which sit in the chest protected by the ribs.

Lungs

Lungs an adult's lungs have a volume of about 6000 cm³ (6 litres).
The right lung is wider and shorter to make room for the liver below.
The left lung is smaller overall because the heart sits behind it.

Airway

Airway air enters through the nose or mouth, passes down the trachea, which divides into two bronchi, one to each lung.
Inside the lungs the bronchi branch into smaller tubes (bronchioles) that end in clusters of alveoli.

Part 3 of 6Structure and function of each part

Structure and function of each part

Mouth and nose

Mouth and nose air moving in and out passes through them.
The nose warms and moistens the air, which makes gas exchange easier.
Nose hairs and mucus trap microorganisms that might cause disease.

Trachea

Trachea a tube carrying air from the nose down into the chest and back out.
Rubbery cartilage rings hold it open so you can breathe easily.

Bronchi

Bronchi tubes from the trachea to the lungs, branching into smaller and smaller tubes that carry air deep into the lung tissue.
The lining cells are specialisedgoblet cells make sticky mucus that traps dust, dirt and microorganisms.
Ciliated cells have hair-like cilia that move the mucus, dirt and microorganisms away from the lungs, and they contain mitochondria for energy.

Alveoli

Alveoli tiny air sacs at the ends of the tubes, forming clusters like bunches of grapes, where gas exchange takes place.
There are millions of them, about 300 million in each lung, with a total surface area of roughly 70 to 100 m².
Each has a good blood supply to take oxygen from the air and remove carbon dioxide.

Pleura

Pleura tough, slippery membranes around the lungs that make a liquid and slide over each other,
- so the lungs can get bigger and smaller as you breathe.

Diaphragm

Diaphragm a sheet of muscle that divides the chest from the other organs and moves air in and out of the lungs.

Part 4 of 6Gas exchange in the alveoli

1Oxygen

Oxygen it dissolves in the moisture lining an alveolus and diffuses across the thin alveolus wall and the neighbouring capillary wall into the blood,
- where red blood cells pick it up.

2Carbon dioxide

Carbon dioxide it diffuses the opposite way, from the blood into the alveolus, and is breathed out.

3Process

Process both movements are by diffusion, from a region of higher to lower concentration.

4Barrier

Barrier air is separated from the blood by only two thin layers of cells.

Part 5 of 6Composition of inhaled and exhaled air

Gas	Inhaled air (%)	Exhaled air (%)
Nitrogen	78–79	78–79
Oxygen	21	16
Carbon dioxide	0.04	4
Water vapour	Variable	Higher (saturated)

Oxygen

Oxygen exhaled air has less because some is absorbed into the blood.

Carbon dioxide

Carbon dioxide exhaled air has far more because it is a waste product of respiration.

Nitrogen

Nitrogen it is unchanged because the body does not use it.

Exhaled air is warmer and moister, which shows on a cold mirror.

Part 6 of 6Keeping the lungs healthy

Cilia and mucus

Cilia and mucus they keep the lungs clean, and cilia are paralysed and destroyed by tar from smoking.

Smoking

Smoking mucus and dirt build up causing a cough and infections, tar contains carcinogens that can cause lung cancer,
- and smoke damages alveoli (emphysema).

Carbon monoxide

Carbon monoxide it binds to haemoglobin and reduces oxygen carried by the blood.

Protection

Protection avoiding smoking and polluted air, exercising regularly and treating infections early.

Key terms

Term	Meaning
Trachea	The windpipe leading from the throat to the bronchi.
Bronchus	One of two tubes leading from the trachea to the lungs.
Alveolus	A tiny air sac where gas exchange takes place.
Gas exchange	Swapping oxygen from the air for carbon dioxide from the blood.
Cilia	Tiny hairs that move mucus.
Diaphragm	A sheet of muscle below the lungs used in breathing.
Pleura	The slippery membranes around the lungs.