TOPIC 1.CLASSIFICATION KINGDOM FUNGI

Gaseous exchange across the alveolus

The actual exchange of oxygen and carbon dioxide takes place in the alveoli. One mammalian lung has millions of alveoli. The alveoli are surrounded by network of capillaries
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Gases exchange across alveolus

When we breathe in, air accumulates in the alveoli. There is a higher concentration of oxygen in the air in the alveoli than in the alveoli than in the bloodstream.

Therefore, oxygen diffuses out the alveoli into the blood in the capillaries. It combines with haemoglobin to form oxyhaemoglobin           

The oxygen is then transported to the tissues. Once in the tissues, the oxyhaemoglobin breaks down to lease oxygen and haemoglobin. The tissues use release oxygen and release carbon dioxide.

This causes the levels of carbon dioxide to become higher in the tissues than in the blood. Carbon dioxide therefore diffuses into the blood in the capillaries and combines with haemoglobin to form carbominohaemoglobin. The capillaries transport carbon dioxide in this form to the alveoli.

The concentration of carbon dioxide is higher in lie blood in the capillaries than in the air in the

alveoli. Carbon dioxide therefore diffuses from the Capillaries into the alveoli. It is then transported through the bronchioles, trachea, glottis, pharynx and finally nostrils into the atmosphere

       Composition of inspired and expired air

gas	Inspired air	Expired air
Oxygen	20.95%	16.40%
Carbon dioxide	0.03%	4.00%

Factors affecting the rate of gaseous exchange

      1. Concentration of carbon dioxide

High concentration of carbon dioxide in the blood increases the rate of gaseous exchange. This provides the tissues with adequate amounts of oxygen and lower carbon dioxide concentration in the blood.

       2. Concentration of haemoglobin

Haemoglobin is responsible for the transportation of gases from the lungs to the tissues and back. Efficient transportation of gases takes place when the body has adequate amounts of haemoglobin.

When a person is anaemic, the body has a low concentration of haemoglobin. Only small amounts of oxygen can be transported at a time. As a result, the rate of gaseous exchange has to increase so that the tissues get adequate amounts of oxygen.

       3. Physical activity

A more active body requires more oxygen than a less active body. As a result, gaseous exchange takes place faster when there is increased body activity.

        4. Health status of the body

Generally, the rate of gaseous exchange increases when somebody is sick. This is as a result of increased metabolism by the liver in order to remove the toxins released by disease-causing microorganisms or break down the drugs taken. Certain diseases also make the body weak and cause slowing down of the breathing process.

       5.  Altitude

Altitude is the height above sea level. At high altitudes, the concentration of oxygen is lower compared to low altitudes. Breathing is therefore faster at high altitudes. At high altitudes, there is also decreased atmospheric pressure. This makes breathing difficult. Organisms therefore have to breathe in faster in order to get enough oxygen.

        6. Age

Young people are generally more active than old people. Also, a lot of growth processes take place in the bodies of young people. This increases the demand for oxygen and therefore increases the breathing rate.

Gaseous exchange in plants

In plants, gaseous exchange mostly takes place through the stomata on the leaves and lenticels on the stem. Some plants such as mangrove and ficus also carry out gaseous exchange through breathing roots.

Gaseous exchange in the leaves

Atmospheric air moves into and out of the leaf through the stomata. Gaseous exchange mostly takes place in the air spaces in the spongy mesophyll.