GASEOUS EXCHANGE AND RESPIRATION

Gaseous exchange is the process which enables mammals to obtain

oxygen gas in their body for various uses such as energy production.

Gaseous exchange is possible through the respiratory system.

Characteristics of respiratory surfaces

❖ They are thin in Order to reduce the diffusion distance.

❖ They moist in order to dissolve gases that diffuse in a solution

form.

Note; this is confirmed when a person breathes onto the plain

mirror where by tiny liquid droplets formed the mirror

❖ They are highly branched, folded, or flattened in order to increase

the surface area for gaseous exchange.

❖ They are surrounded by blood capillaries so that gases can be taken

to and from the cells easily.

❖ They are well ventilated so that gases can pass through them

easily.

The components of the respiratory system of mammals include

❖ The nostril, nasal cavity, pharynx, trachea, bronchi, lungs,

bronchioles, alveoli, intercostal muscles, diaphragm, and ribs,

Mechanism of gaseous exchange in mammals

Gaseous exchange in mammals occurs as a result of inhalation and

exhalation. Inhalation is the process of breathing in air into the lungs.

Exhalation is process of breathing out air from the lungs. The composition

of inhaled air is different from exhaled air,

Constituent

In haled

Exhaled air

Oxygen gas

20.95%

0.03%

16.40%

Carbon dioxide gas

Nitrogen gas

78.10%

0.94%

78.100/0

0.94%

Noble gases

Note; exhaled air(Carbon dioxide gas) can be confirmed by person

breathing onto lime water whereby colour change turn into milky; this

confirms the presence of carbon dioxide in the exhaled air.

Factors affecting the rate of gaseous exchange in mammals

Gaseous exchange is affected by many factors including the following:

❖ Carbon dioxide concentration

High concentration of carbon dioxide in the blood increases the

rate of gaseous exchange. The increase in the rate of gaseous

exchange provides the cells with adequate concentration of

oxygen and lager concentration of carbon dioxide in the blood.

❖ Haemoglobin concentration

Haemoglobin is a reddish protein molecule containing an Iron

atom, which is responsible for transporting oxygen and carbon

dioxide in the blood of vertebrates. Haemoglobin transports

oxygen gas from the lungs to the body cells and carbon dioxide

from the body cells to the lungs. Efficient transportation of gases

takes place When the body has adequate concentration of

haemoglobin. When a person is anemic, the body has a low

concentration of haemoglobin therefore, a low level of oxygen can

be transported at a time. This results into the increase of the rate of

gaseous exchange so that the body cells can get enough oxygen.

❖ Physical activity

A more active body requires more oxygen than a active body.

During physicalexercise the muscle cells respire more than when

the body is at rest. Therefore, the rate and depth of breathing

increases. This ensures that more oxygen is absorbed into the

blood and more carbon dioxide is removed, As a result, therefore

gaseous exchange increases when there is increased body activity.

❖ Health status

Generally, the rate of gaseous exchange increases when a person

is sick. This is due to increased metabolism by the liver during

removal of the toxins released by disease-causing micro-

organisms or break down of the drugs taken

❖ Altitude

Altitude is the height above sea level at high altitudes; the

concentration of oxygen is lower than at low altitudes. This is due

to reduced pressure at high altitudes compared to low altitudes.

❖ Age

Young people are generally more active than old people. Also,

many growth processes take place in the bodies of young people

compared to adults. This increases the demand for oxygen hence

increases the rate of gaseous exchange.

Gaseous exchange in plants

Gaseous exchange in plants is the process whereby oxygen gas leaves and

carbon dioxide gas enters the plant during the day. During the night

oxygen gas enters and carbon dioxide gas leaves the plant. Gaseous

exchange mostly takes place through the stomata on the leaves and

lenticels on the stem. In some plants such as mangrove, gaseous exchange

is carried through breathing roots, also called pneumatophores, which

usually project above the water surface,

During the day, green plants carry out photosynthesis to produce glucose.

This takes place also within the guard cells that surround the stomata. As a

result, the cell sap of guard cells becomes hypertonic and draws in water

from the neighbouring cells by osmosis.

The guard cells become turgid and the stomata open, Air from the

atmosphere enters into the air spaces in the spongy mesophyll. The cells

next to the air spaces have more oxygen that is produced by the cells

during photosynthesis and less carbon dioxide as it is used up during

photosynthesis.

Carbon dioxide and oxygen diffuse in opposite directions depending on

their concentration gradients. Carbon dioxide diffuses to neighbouring

cells until it reaches the site of photosynthesis. Oxygen moves out through

the open stomata to the atmosphere.

At night, there is no sunlight, therefore light reaction of photosynthesis

ceases. This means that little or no glucose is produced hence the guard

cells do not absorb water by osmosis. Therefore, the stomata remain

partially closed. On the other hand respiration continues during the night.

The partially open stomata allow in a small amount of air to accumulate in

the air spaces.

Oxygen diffuses into the plant cells while carbon dioxide diffuses out into

the intercellular spaces and eventually into the atmosphere through the

partially opened stomata.

Fermentation in the laboratory can be investigated by mixing glucose

solutions and 10% of yeast granules in a closed container and left for 15

minutes .bubbles will be observed on the surfaces of liquid with the smell

of alcohol. Bubbles are caused by rising up of carbon dioxide

C₆H₁₂O₆→2C₂H₅OH+2CO₂+Energy

In animals, anaerobic respiration leads to the formation of lactic acid and

energy as shown in the following equation:

C₆H₁₂O₆→2C₃H₆O₃+Energy

Anaerobic respiration occurs when the body's oxygen supply does not

meet the body's needs. For example, during vigorous activity such as

sports, lactic acid is accumulated in the muscles prevents from contracting

and relaxing due to its toxicity. and can also cause pain. When this occurs,

oxygen is required to oxidise lactic acid into water and carbon dioxide, the

oxygen required in such situation is known as oxygen debt. Accumulation

of lactic acid in the muscles prevent them from contracting and relaxation

due its toxicity and cause pain .

Oxygen debt causes the animal to breathe rapidly and deeply in Order to

get enough oxygen required to convert the lactic acid to carbon dioxide

and water. Some of the lactic acid is converted to glucose. Breathing goes

back to normal when the acid has been broken down.

Application of anaerobic respiration

❖ Bread making

❖ Beer brewing

❖ Distiller industries

❖ Production in citric acid.

PRACTICAL QUESTIONS

2. You are provided with solution P in the test tube. By using delivery

tube, breathe in the solution P by using delivery tube until its colour

changes.

Question

The specimen was tilapia fish

PRACTICAL ACTIVITY

1 You are provided with two beakers labeled with letter A and B

stirring rod rubber band plain paper and sample labeled C(glucose

crystals)),D(starch powder) and E(yeast). A beaker wit letter B

containing distilled water. Carry out experiment under the procedure

(i)-(v) and then answer the question that follow;

(i) Put a sample labeled C into beaker A followed by sample

labeled D

(ii) Add sample labeled E into a beaker A, then use stirring rod

to mix the contents

(iii)Add distilled water from beaker B into beaker A, then stir

the solution mixture

(iv) Use a rubber band and plain paper to cover on top of the

solution on a beaker A

(v) Leave the experiment for 15 minutes then remove cover

Questions

(a) (i) what did you observe

(ii) What brought about your observation in (a) (i) above?

(b) (i) Name the physiological process which takes place in

beaker. Give reasons for your answer

(ii) Define the physiological process you mentioned above

(c) (i)write a balanced chemical equation for the physiological

process

(ii) Write the main product and byproduct for the

physiological process

(d) (i)which byproduct is useful to the yeast in C(ii) and why

(ii) Where does the physiological process occur in the

human body?

(e) What was the aim of experiment

(f) Explain briefly four industrial application physiological

process you named in b(i)

Answer

(a) (i)Bubbles was observed on the surface of the liquid

(ii)Bubbles are caused by rising up of carbon dioxide

(b) (i)Anaerobic respiration (fermentation)

(ii)Anaerobic respiration (fermentation) takes place in the absence

of oxygen.

(c) (i)C₆H₁₂O₆→2C₂H₅OH+2CO₂+Energy

(ii)Mai product is 2C₂H₅OH and Energy, byproduct is 2CO₂

(d) (i) CO₂which makes dough rise

(ii) In the skeletal muscles

(e) The aim of the was to investigate anaerobic respiration in yeast

(f) Application of anaerobic respiration

❖ Bread making

❖ Beer brewing

❖ Distiller industries

❖ Production in citric acid.