Topic 5: Gaseous Exchange And Respiration – Biology Notes Form 2

Topic 5: Gaseous Exchange And Respiration – Biology Notes Form 2

Welcome to our website scholars.co.tz. In this article, are you looking for  Topic 5: Gaseous Exchange And Respiration – Biology Notes Form 2

GASEOUS EXCHANGE AND RESPIRATION

The Concept of Gaseous Exchange

GASEOUS EXCHANGE

Is the movement of oxygen and carbon dioxide across a respiratory surface.

VENTILATION

Refers to the movement of air into and out of the lungs.

RESPIRATORY GASES
Are gases that take part in gaseous exchange.
Example of respiratory gases

i. Oxygen

ii. Carbon dioxide.

IMPORTANCE OF GASEOUS EXCHANGE

i. Gaseous exchanges enable animals and plants to get oxygen for use in respiration.

ii. It enables plants to get carbon dioxide used in photosynthesis.

iii. Enable organisms to get rid of carbon dioxide which is toxic to cells if it allowed to accumulate in large amounts.

GASEOUS EXCHANGE IN SMALL (UNICELLULAR) ORGANISMS

Gaseous exchange in small (unicellular) organism takes place by diffusion through cell membrane.

Example of unicellular organisms

i. Amoeba

ii. Bacteria

iii. Hydra

GASEOUS EXCHANGE IN LARGE ORGANISMS

Gaseous exchange in large organisms like mammals takes place through specialized organs called respiratory surfaces or organs.

RESPIRATORY SURFACES

Are specialized organs for gaseous exchange.
Example of respiratory surfaces includes

i. Lungs

ii. Gills

iii. Skin

ORGANS OR RESPIRATORY SURFACES RESPONSIBLE FOR GASEOUS
EXCHANGE IN LIVING ORGANISMS

ADAPTIVE FEATURES OF RESPIRATORY SURFACES

Respiratory surfaces (gaseous exchange surfaces) have the following adaptive features:

1. They are thin to reduce diffusion distance of gases.

2. They are moist to allow gases to dissolve before diffusion.

3. They have large surface area for maximum exchange of gases.

4. They have a dense network of blood capillaries for transportation of gases to and from the gaseous exchange surfaces.

5. They highly folded surfaces to provide area for rapid exchange of gases.

6. They are well ventilated so that gases can pass through them easily.

RESPIRATORY SYSYTEM

The respiratory system consists of the trachea and the lungs.

Function/ role of the respiratory system

1. o take in oxygen and expel carbon dioxide gas.

DIAGRAM OF HUMAN RESPIRATORY SYSTEM

Parts of the human respiratory system

The components of the gaseous exchange system in mammals include:

i) The nostril

ii) Nasal cavity

iii) Trachea

iv) Lungs

v) Intercostal muscles

vi) Diaphragm

vii) Ribs

THE FEATURES OF DIFFERENT PARTS OF THE RESPIRATORY SYSTEM AND
THEIR ADAPTIVE FEATURES

The following are Features of Different Parts of the Respiratory System

EXAMINATION QUESTIONS

1. Why is it better to breathe through the nose than through the mouth? Explain.

Answer.

i. Because the nose has mucus and cilia which traps and filters dust and microorganism.

ii. Nasal cavity has a rich supply of blood which helps to warm and moisten the incoming air.

2. What will happen if the epiglottis is removed from the human body?
Answer

— Foods and drinks will pass into the trachea during swallowing hence chocking will occur.

BREATHING

Is the process of taking in and out of respiratory gases.

TYPES OF BREATHING

Breathing is divided into two types, namely:

1. Breathing in (inhalation)

2. Breathing out (exhalation)

1. INHALATION (INSPIRATION)

Is the process whereby air is taken inside the lungs.

2. EXHALATION (EXPIRATION)

Is the process whereby air is taken outside the lungs.

The mechanism of gaseous exchange (breathing) in mammals

Gaseous exchange in mammals happens as a result of inhalation and exhalation.

GASEOUS EXCHANGE ACROSS THE ALVEOLUS

Alveoli: are tiny air sacs covered by a dense network of blood capillaries.

> 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 a network of capillaries.

Gaseous exchange across the alveolus

> When we breathe in, air accumulates in the alveoli.

> There is a higher concentration of oxygen in the alveoli than in the blood stream.

> Therefore, oxygen diffuses out of the alveoli into the blood in the capillaries.

> Oxygen combines with hemoglobin to form oxyhaemoglobin.

> The Oxygen is then transported to the heart then to all body tissues.

> Once in the tissues, the oxyhaemoglobin breaks down to release oxygen and haemoglobin.

The tissue use oxygen and release carbon dioxide. This causes the levels of carbon dioxide to become higher in the tissues than in the bloodstream. When the concentration of carbon dioxide in the tissues is higher than in the bloodstream. Carbon dioxide diffuses into the bloodstream and combines with haemoglobin to form carbaminohaemoglobin.

The capillaries transport carbon dioxide in this form to the alveoli. The concentration of carbon dioxide in bloodstream is higher than in the alveoli. Carbon dioxide diffuses from the bloodstream into the alveoli. It is then transported through the bronchioles, trachea, glottis, pharynx, and finally nostrils into the atmosphere.

Fig: Gaseous exchange across the alveolus

COMPOSITION OF INHALED (INSPIRED) AND EXHALED (EXPIRED) AIR.

DIFFERENCES BETWEEN INHALED AND EXHALED AIR

EXAMINATION QUESTION

1. The table below shows changes in composition of inhaled and exhaled air. Carefully examine it and answer the questions that follow.

Explain why:

(i) The amount of oxygen was decreased?

(ii) The amount of carbon dioxide was increased?

(iii)The amounts of nitrogen remain constant?

(iv) Exhaled air is warmer than clean inhaled air?

ANSWER

1. The amount of oxygen was decreased because some oxygen is used in respiration process.

2. Amount of carbon dioxide was increased because carbondioxide is produced during respiration process

3. Amount of nitrogen remain constant because nitrogen does not used in the body of living thing.

4. Exhaled air is warmer than clean inhaled air because of the heat energy produced during respiration.

5. The composition of the air inside the lungs changes during breathing.

2. State three differences between inspired and expired air.

Gaseous exchange in the alveoli causes some of the changes to the inspired air.

3. Describe three features of the alveoli which assist gaseous exchange.

ANSWER

Inspired air contains more O2, less CO2, and less water vapor then expired air.

Three features from:

i. The wall of the alveolus is one cell thick (or very thin)

ii. There is a moist surface to the alveoli

iii. There are large numbers of alveoli

iv. The air in the alveoli is constantly being replaced.

FACTORS GOVERNING GASEOUS EXCHANGE AT ALVEOLI

i. Concentration of gases (oxygen & carbon dioxide) in the blood and alveoli,

ii. Walls of capillaries and alveoli are very thin to allow for easy diffusion of gases,

iii. Blood pressure in the blood capillaries surrounding the alveoli is high,

iv. Alveoli surfaces are moist and aid in rapid diffusion of gases.

FACTORS AFFECTING GASEOUS EXCHANG (BREATHING) IN MAMMALS

The following are factors affecting the rate of gaseous exchange (breathing) in mammals:

i. Physical activities or exercise

ii. Health status of the body

iii. Age

iv. Carbon dioxide concentration

v. Haemoglobin

vi. Altitude

i. PHYSICAL ACTIVITIES OR EXERCISE

Vigorous activities or exercise increases the breathing rate because more oxygen is required to burn glucose to release energy required by muscle.

ii. AGE

Young people have a higher metabolic rate and therefore breathe faster than old people.

iii. HEALTH STATUS OF THE BODY

The rate of breathing increases during sickness so as to remove toxins from the body.

iv. CARBON DIOXIDE CONCENTRATION

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.

v. HAEMOGLOBIN CONCENTRATION.

The rate of gaseous exchange increases when the concentration of haemoglobin is low due to anaemic condition, hence small amount of oxygen reaches the cells. Breathing rate increases so that to compensate the shortfall and meet the oxygen demand in the body.

vi. ALTITUDE

The breathing rate is higher at high altitudes than at low altitude because there is a lower concentration of oxygen in the atmosphere at higher altitudes.

vii. EXAMINATION QUESTIONS

Explain why the rate of breathing increases quickly during exercise?

ANSWER

— Because more oxygen is required to breakdown glucose to release energy.

— To remove more carbon dioxide in the blood which arise from the process of respiration.

Why your breathing rate does not go back to normal as soon as you stop exercising?

ANSWER

— In order to provide extra oxygen for breaking down available glucose to release energy for muscle and to remove carbon dioxide from the body.

GASEOUS EXCHANGE IN PLANTS

Gaseous exchange in plants involves exchange of oxygen and carbon dioxide.

> During the day, plants take in carbon dioxide for photosynthesis and give out oxygen.

> At night plants take in oxygen for respiration and give out carbon dioxide.

> Some of oxygen produced during photosynthesis is used for respiration.

EXAMINATION QUESTION

1. Why it is not healthy to sleep in a closed or poorly ventilated room with many potted plants? Briefly explain

Answer: Because potted plants also use oxygen during the night for respiration, this will result into a competition in intake of oxygen between a person and a plant which sometimes may cause suffocation and eventually death to a person.

2. Why it is not healthy to sleep in a poorly ventilated room with charcoal burning? Give reason

Answer: Because the burning charcoal produces carbon monoxide gases which combine with haemoglobin permanently and prevent haemoglobin to combine with oxygen as a result a person will lack oxygen in the body and will die because of suffocation.

PARTS OF PLANT RESPONSIBLE FOR GASEOUSE EXCHANGE

In plants gaseous exchange takes place in three main organs namely:

i. Leaves(stomata)

ii. Stems (lenticels)

iii. Roots (breathing roots)

THE PROCESS OF GASEOUS EXCHANGE IN PLANTS

The process of gaseous exchange in plants takes place in the following parts;

i. Leaves

ii. Stems

iii. Roots

I. GASEOUS EXCHANGE IN LEAVES

Gaseous exchange in a leaf occurs through stomata

Function of stomata

— Are small holes through which gaseous exchange take place.

Qn: Why in many plants numerous stomata are found on the lower surface of the leaf?

Answer: To prevent excessive loss of water through transpiration.

Adaptation of leaf for gaseous exchange

a. A leaf has numerous numbers of stomata, to increase the surface area for taking in and out of gases.

b. A leaf has air spaces in the spongy mesophyll layer, to allow the easily movement of gases.

c. A leaf has numerous guard cells which control the opening and closing of stomata.

II. GASEOUS EXCHANGE IN THE STEMS

Gaseous exchange in the stem takes place through the lenticels

Function of lenticels

— Lenticels are small holes through which gaseous exchange occurs.

Adaptations of the stem for gaseous exchange

i. Have lenticels to increase the surface area for taking in and out gases.

ii. Lenticels are made up of loosely packed cork cells to facilitate the movement of gases between them.

III. GASEOUS EXCHANGE THROUGH ROOTS

Gaseous exchange in roots occurs through breathing roots.

Function of breathing roots

— Used for gaseous exchange in roots

Adaptation of roots for gaseous exchange

(i) Breathing roots have a very thin epidermal layer which enables the root to carry out gaseous exchange.

IMPORTANCE OF GASEOUS EXCHANGE IN PLANTS

i. It enables the plants to eliminate excess carbon dioxide at night of which if left will harm the plants.

ii. It enables plants to obtain carbon dioxide which is one of the raw materials necessary for photosynthesis

(iii) Plants obtain oxygen which is necessary for production of energy which is produced during respiration through gaseous exchange.