Biology IGCSE Edexcel - Gas exchange

When water is abundant,

the plants can afford to lose water, so it opens the stomata to allow gases to diffuse

Leaves are adapted for efficient gas exchange:

1. broad - large surface area for diffusion

2. thin - gases only have to travel a short distance to reach cells

3. air spaces - allows gases to move easily between cells

4. stomata - let gases and water to diffuse and escape. also closes at night when photosynthesis cannot occur

Hydrogen carbonate indicator colours

yellow - high

red - atmospheric

purple - low

Respiration continues...

during the day and night, but the net exchange of carbon dioxide and oxygen depends on the intensity of light

Thorax...

part of the body which contains the heart and lungs within a rib cage

Trachea...

main windpipe, which is supported by C-shaped cartilage which keeps it open

Intercoastal muscles...

join each rib to the next. Move the rib cage when they contract.

Bronchioles...

branches from the bronchus which air passes through to reach the alveoli.

Rib...

encloses the lungs

Alveoli...

air sacs where gas exchange takes place between the air and blood

Pleural membranes...

two thin, moist membranes which separate the lungs and the thorax.

Diaphragm...

dome shaped sheet of muscle which separates the thorax from the abdomen and moves air in and out of the lungs when it contracts/relaxes.

Breathing in...

external intercoastal muscles contract, intercoastal muscles relax, ribs move up, diaphragm contracts and flattens, volume of chest increases, pressure in chest decreases, air pressure in lungs is lower than atmospheric pressure, air rushes into the lungs.

Breathing out...

external intercoastal muscles relax, intercoastal muscles contract, ribs move down, diaphragm relaxes and curves, volume of chest decreases, pressure in chest increases, air pressure in lungs is higher than atmospheric pressure, air rushes out of the lungs.

What happens in the alveoli?

deoxygenated blood arrives into the alveolus. oxygen and carbon dioxide are exchanged between the blood in the capillaries and the air in the lungs. oxygenated blood leaves the alveolus.

Alveoli are specialised for gas exchange:

1. enormous surface area - huge number of microscopic alveoli

2. moist lining - easier for gases to dissolve

3. thin walls - one cell thick

4. great blood supply - keeps high concentration gradient

5. permeable walls - gases can diffuse across easier

6. surrounded by a network of capillaries - allows O2 and CO2 to be exchanged between the blood in the capillaries and the air in the lungs

7. ventilation - helps keep a high concentration gradient

Smoking can cause...

emphysema - damages wall of alveoli, reducing surface area for gas exchange

chest infections - tar damages cilia in lungs and trachea meaning they can no longer sweep mucus towards mouth.

smoker's cough - tar irritates bronchi and bronchioles, encouraging mucus to be produced

coronary heart disease - carbon monoxide reduces the amount of oxygen blood can carry, forcing an increase in blood pressure, damaging artery walls and making blood clots more common

cancer - tobacco smoke contains carcinogens

exercise...

increases rate of respiration and creates a higher conc of CO2 in blood.

brain detects this and causes breathing to become deeper and faster.

means more carbon dioxide can be breathed out at a quicker rate.

what measures the rate and volume of someone's breathing?

spirometer