2.40 understand that respiration continues during the day and night, but that the net exchange of carbon dioxide and oxygen depends on the intensity of light

Respiration is a continuous process in living things, so won't stop at any time. But photosynthesis depends on light and so will stop in the dark. This means that in the night carbon dioxide will be being given out by respiration but not taken in for photosynthesis, so the net exchange of carbon has an increased out put. In the same way at night oxygen will not be being given out as there is no photosynthesis.

2.39 understand gas exchange (of carbon dioxide and oxygen) in relation to respiration and photosynthesis

In photosynthesis: 6CO2 + 6H2O > C6H12O6 + 6O2 + 6H2O
So the plant takes up carbon dioxide and gives out oxygen

In respiration: C6H12O6 + 6O2 > 6CO2 + 6H2O
So the plant gives out carbon dioxide

2.48 describe experiments to investigate the effect of exercise on breathing in humans.

During exercise cells respire more quickly (to provide more energy for movement) this means oxygen has to be delivered more quickly and carbon dioxide taken away more quickly. As a result of this the lung muscles contract and relax more rapidly and the heart beats faster.

Measure a persons breaths per 10 seconds when stationary.
Then after one minute after running at 5mph then at two minutes and so on.
You will find a linear relationship as described above between the two.

2.47 understand the biological consequences of smoking in relation to the lungs and the circulatory system, including coronary heart disease

Tar can cause cancerous mutations in the lungs.
Smoke removes the cilia- tiny hairs- which keep the lungs clean.
Smoking also hardens the arteries, constricting the blood flow and putting strain on the heart, resulting in coronary heart disease.

2.46 explain how alveoli are adapted for gas exchange by diffusion between air in the lungs and blood in capillaries

The alveoli have are thin, this allows gasses to diffuse through them easily.
They are small and there are many of them meaning there is a large surface area through which much gas can diffuse at once. It also means there is a lot of surface in contact with the blood stream for gasses to diffuse into.
Alveoli have a moist lining for gasses to dissolve into.

2.45 understand the role of the intercostal muscles and the diaphragm in ventilation

Breathing in

The intercostal muscles contract

The ribs move up and out

The diaphragm contracts and moves down

The trachea carries air towards the lungs; it splits into two bronchi- one leading to the left lung, and one o the right- which then split into even smaller tubes, called bronchiles; these end in alveoli where gas exchange takes place.
The pleural membranes prevent friction.

Breathing out

The intercostal muscles relax

The ribs drop down

The diaphragm also relaxes and moves upward

These things reduce the space inside the lungs, pushing the air out.

2.44 describe the structure of the thorax, including the ribs, intercostal muscles, diaphragm, trachea, bronchi, bronchioles, alveoli and pleural membranes

Once air is breathed in through the mouth or nose it travels down the trachea. The trachea splits into two- one going into the left lung and one going into the right lung- these pipes are called bronchi. Each bronchus will then divide further into many bronchioles: each ending in a sac called an alveoli.

The trachea and bronchi have walls of muscle that are supported by cartilage. The cartilage is in partial rings so that the tubes can be moved in any direction. Cilia on the walls move mucus out of the breathing system and into the stomach.

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2.43 describe experiments to investigate the effect of light on net gas exchange from a leaf, using hydrogen-carbonate indicator

hydrogen-carbonate indicator is an indicator for carbon dioxide: under normal levels (atmospheric) of carbon it is orange; an increase turns it yellow; a decrease turns it purple.

Fill a test tube quarter full with HCIS, attach a leaf to a bung and put in the test tube; observe the indicator colour in different light intensities.

2.42 describe the role of stomata in gas exchange

Stomata are minute wholes in the lower epidermis of the leaf. Guard cells regulate the opening and closing of the stomata; allowing carbon dioxide and oxygen to be exchanged between the leaf and the atmosphere. The guard cells absorb water and become turgid- opening the stomata- during the day. At night the guard cells are flaccid and so close the stomata.

2.41 explain how the structure of the leaf is adapted for gas exchange

Leaves are thin which allows gasses to diffuse quickly through them. In addition the stomata at the bottom of the leaf allow the diffusion of gasses in to the leaf- when a guard cell is shrunk gasses can enter the leaf.

2.38 understand the role of diffusion in gas exchange

Diffusion is the movement of particles from an area of high density to an area of low density. In this way gasses will move from an area dense with gas to an area of low density.

In the circulatory system oxygen enters the blood and carbon dioxide leaves the blood via gaseous exchange. Gasses move across the walls of alveoli to an area of lower density than they are in: Oxygen moves into the blood as there is a low density of oxygen in the blood; Carbon dioxide moves into the lungs as it is an area of lower density.