Respiratory System in animals and Plants

CONTENT

• Definition / Phases of Respiration
• Conditions Necessary for Respiration
• Characteristics of Respiratory Surface
• Types of Respiratory System
• Mechanism of Respiratory System in Lower Animals & Higher Animals
• Respiratory System in Mammals: Mechanism of Respiratory System
• Process of Inhalation / Inspiration in man
• Characteristics
• Process of Expiration in Man
• Internal Aerobic Respiration
• Respiration in Plants (Stomata & Lenticels)
• Mechanism of Gaseous Exchange in Plants.

DEFINITION/PHASES OF RESPIRATION

The process of respiration involves the taking in of oxygen its transport within the body of the organism, its exchange in the cells and the eventual release of energy in form of ATP, water and carbon(IV)oxide. The energy is utilized by the cells for their daily activities. Respiration can therefore be defined as a biochemical activity of the cell in which glucose is broken down in a series of reaction controlled by enzymes to release energy.

The following are the Different Phases of Respiration

• External Respiration (Breathing)

This is the taking in of oxygen (inhalation)into the respiratory organ(e.g. lungs or gills) and breathing out (exhalation) of carbon(IV)oxide and water vapour.

1. Internal (Tissue) Respiration

This is the oxidation of food substances within the cells leading to the release of energy,carbon(IV)oxide, and water. This is made possible by the oxygen taken in through the breathing process. This can be represented by the following equation

C₆H₁₂O₆ +6O₆ →6H₂O+6C0₂+Energy (ATP)

CONDITIONS NECESSARY FOR RESPIRATION

For effective exchange of gases to take place, the following conditions must be met:

Respiratory Medium: This refers to the environment from which the organism picks up oxygen e.g. air and water.

Respiratory Organ: This refers to the organ possessed by the organism needed to pick oxygen from the environment and pass out CO₂ and water vapour e.g. lungs in mammals and gills in fishes, etc.

Transport Medium: This is needed to transport dissolved oxygen to the various cells of the body which in turn picks up CO₂ and other waste productsfor elimination process e.g. blood in mammals.

Ventilation: This is the movement of air in the direction over the respiratory surface. This ensures the replacement of used oxygen and the elimination of waste products. Increase in the rate of gaseous exchange isfacilitated by ventilation mechanism e.g. breathing in human.

Respiratory surface: This refers to the actual surface of the body where gaseous exchange takes place e.g. alveoliin mammals and cell membrane in amoeba

CHARACTERISTICS OF RESPIRATORY SURFACE

The following characteristics must be exhibited by all respiratory surface be it in plant or animals

• Respiratory surface must be moistened because gases diffuse in solution through them.
• It must be permeable to allow gas to pass in and out of  them.
• It must be thin-walled to make diffusion easier and faster.
• It must have adequate supply of transport medium e.g. blood.
• The surface must be large to aid easy diffusion of gases.
• It must be highly vascularized i.e. it must have lots of capillaries or similar network to bring in and take away gases.

EVALUATION

1. What is respiration?
2. Mention five characteristics of a respiratory surface.

TYPES OF RESPIRATORY SYSTEM

Thesevary from organism to organism depending on their type, complexity, size and habitat in which they can be found. The table below reflects various organisms and respiratory structures related to them                    

	Organism	Respiratory Structure
1	Unicellular organism e.g. Amoeba and paramecium	Body surface
2	Hydra worm tapeworm	Cell membrane
3	Earth worm	Wet skin or body surface
4	Fishes e.g. Tilapia	Gills
5	Arthropod e.g. insects	Tracheal system
6	Arachnids e.g. spiders	Lungs books
7	Tadpoles	Gills
8	Reptiles e.g. lizards	Lungs
9	Amphibians e.g. toads	Mouth, skin, and lungs
10	Mammals	Lungs
11	Flowering plant	Stomata and lenticels

MECHANISM OF RESPIRATORY SYSTEM IN LOWER ANIMALS

Unicellular Organism

They require no elaborate respiratory system for they respire through their entire body surface (the cell membrane acts as the respiratory surface) through simple diffusion process.Oxygen which is highly concentrated in the environment is absorbed in the organism which diffuse into the region with lower concentration.

Insects

Tracheal system is what insects use for respiration. Air passes through a spiracle then enters tracheal trunk which diffuses throughout a complex, branching network of tracheal tubes that subdivides into smaller and smaller diameters and reaches every part of the body. At the end of each tracheal branch, a special cell (the tracheole) provides a thin, moist interface for the exchange of gasses between atmospheric air and a living cell. Oxygen in the tracheal tube first dissolves in the liquid of the tracheole and then diffuses into the cytoplasm of an adjacent cell. At the same time, carbon dioxide, produced as a waste product of cellular respiration, diffuses out of the cell and, eventually, out of the body through the tracheal system.

EVALUATION

1. State the organs of respiration in (a) Amoeba (b) cockroach (c) spider (d) scorpion (e) tadpole
2. Differentiate between the mechanism of respiration in Amoeba and cockroach

FISH

The gill is the respiratory organ in the fish. Enclosed in the gill chamber and about three to four in numbers. Each gill is made up of a gill filament (where gaseous exchange takes place) and the gill raker (that prevents food particles from entering the gill chamber) and the gill arch (in which the filaments are built). The gills are concealed by the operculum.The fish initiates breathing by closing the operculum and opening the mouth and lowering the floor of the mouth. Water which contains dissolved oxygen rushes into the mouth of the fish. The fish then closes its mouth and water rushes into the gill chamber and moves across the gill filaments. Oxygen in the water then diffuses into the gill filaments while CO₂ diffuse out of the body expelled through water as the fish opens its operculum.

TOAD

Tadpole: This is a larval toad or frog that hatch from eggs and can only survive in water. Tadpoles have tiny external gill flaps that extract oxygen from water as it passes over them. Tadpoles open their mouths as they swim and take in water. As the mouth closes, muscles transfer the water to the gills. These consist of thin membranes called lamellae, which take oxygen from the water where it enters the blood stream through the process of diffusion. Tadpoles can also rise to the surface and gulp oxygen from the air. As tadpoles mature the gills are absorbed by the body as other respiratory systems develop.

Adult Toad:

The adult toad respire in three difference ways namely: the skin, mouth, and lungs

BUCCAL (MOUTH) GASEOUS EXCHANGE

The toad is able to utilize its mouth as a respiratory organ because of the following: 

• It is very large i.e. has a large surface area.
• It has a thin mucus membrane for easy diffusion
• It is well supplied with blood capillaries

To initiate breathing, the toad closes its mouth, the nostrils are opened and the floor of the buccal cavity is lowered, air is drawn through the nostrils into the buccal cavity. After this, the capillaries and the glottis close and gaseous exchange takes place between the blood and the inhaled air. To get rid of air, the floor of the buccal cavity is raised increasing the air pressure, and hereby forcing the nostrils to open and air in the buccal cavity containing carbon dioxide flows out.

EVALUATION

1. State the structure involved in respiration in fishes.
2. Differentiate between the mechanism of respiration in fish and that of toad.     

SKIN /CUTANEOUS RESPIRATION IN TOAD

This is possible because of the large surface area of the skin. The skin is moist because of continuous secretion form the mucus gland, there is adequate supply of blood capillaries and finally, the membrane serving as the skin is thin. simple diffusion of gases takes place through it both on land and water.

LUNGS /PULMONARY RESPIRATION IN TOAD

This is similar to what is obtainable in the buccal respiration but with a slight difference. In order to draw air into its mouth the toad lowers the floor of its mouth, which causes the throat to expand. Then the nostrils open allowing air to enter the enlarged mouth. The nostrils then close and the air in the mouth is forced into the lungs by contraction of the floor of the mouth. To elimate the carbon dioxide in the lungs the floor of the mouth moves down, drawing the air out of the lungs and into the mouth. Finally the nostrils are opened and the floor of the mouth moved up pushing the air out of the nostrils.

RESPIRATORY SYSTEM IN MAMMALS

The respiratory system of mammals is the most complex of all respiratory systems. It comprises of a pair of lungs enclosed in the thorax and connected to the outside by series of branched air tube.

In human beings air can be drawn in through the mouth or nose. Both lead into the pharynx a short passage way which branches at the end into two directions. One leads to the digestive tract while the other leads to the larynx (voice box) and the lower air pathway. The entrance of the larynx is called the glottis and it is covered by cartilagenous flap (epiglottis) which prevents food from entering the wind pipe. For air to enter larynx, the glottis must remain open.

The trachea (wind pipe) branches into two bronchi. The presence of cartilagenous rings in the trachea and bronchi prevents them from collapsing when the air pressure in them is low. Each bronchus leads to the lung where it branches into small tubes called bronchioles. The alveoli are richly supplied with blood capillaries and are sited or surface where gaseous exchange takes place.

As oxygen follows this pathway from the outside to the lungs, C0₂ is released out from the lungs to the outside via same pathway.

MECHANISM OF RESPIRATION IN MAMMALS

This entails two phases namely external and internal respiration

External Respiration (Breathing) This is the taking in of oxygen (inspiration or inhalation) and giving out of C0₂ and water vapour (expiration or exhalation).

EVALUATION

1. List the two phases of respiration in a named mammal
2. Discuss briefly the process of external respiration

MECHANISM OF INSPIRATION OR INHALATION IN MAN

• The intercostals muscle contract     
• The rib are moved upward and outward
• The diaphragm becomes flattened
• There is an increase in the volume of thoracic cavity
• Consequently air is drawn from the nostril to the trachea, bronchi, bronchioles, and finally to the alveoli.

MECHANISM OF EXPIRATION OR EXHALATION IN MAN        

• The intercostals muscle relax
• The ribs are moved downward and inward
• The diaphragm becomes dome shape
• There is decrease in the volume of thoracic cavity.
• Consequently air is drawn from the alveoli, bronchioles, bronchi, and trachea.
• Consequently air containing waste products like CO₂ and water vapour from inside the alveoli or lungs are forced out through bronchioles, bronchi, trachea, and finally to the exterior through the nose.

Inhaled and exhaled air are made up of the following

Air Component            Inhaled Air                   Exhaled Air

Oxygen                         21%                              16%

Carbon dioxide              0.03%                           4%

Nitrogen                        78%                              78%

Water vapour                 variable             saturated (higher)

EVALUATION

1. Differentiate between inhalation and exhalation in mammals.
2. Write a short note on ‘gaseous exchange in man’.

CELLULAR (INTERNAL) RESPIRATION

The oxidation of glucose to release energy is known as cellular respiration and it occurs in the mitochondria (power house) of all living cells.

Within the cytoplasm of the cells, one molecule of 6-carbon sugar is broken down into two molecules of 3-carbon pyruvate catalysed by the enzymes in the cytoplasm. This process does not require oxygen. Each pyruvic acid is further oxidized completely to carbon dioxide and water in the mitochondria. The breakdown of glucose to pyruvic acid is termed glycolysis whileseries of chemical reactions occurring within the mitochondrion, responsible for the final breakdown of food molecules to form carbon dioxide, water, and energy carried out by seven enzymes is known as the Krebs cycle (citric acid cycle). Most of the ATPs are generated in the Krebcycle (36 ATP). A total of 38 ATP molecules are formed when one molecule of glucose is completely oxidized.

AEROBIC AND ANAEROBIC RESPIRATION

In most cells, cellular respiration takes place in the presence of oxygen and this is known as aerobic respiration. The largest amount of ATP possible is generated through it from one molecule of glucose (38 ATP).

In some other organisms, the cells gets energy from breaking down glucose in the absence of oxygen, this is known as anaerobic respiration. Only two ATPs are produced. Lactic acid often results from anaerobic respiration instead of pyruvic acid in animals which make it useful in the production of yoghurt. In plants, alcohol and carbon(IV)oxide are produced.

EVALUATION

1. What is internal respiration?

2. Differentiate between aerobic and anaerobic respiration

RESPIRATION IN PLANT

There is no special respiratory organ in plant. Gases move in and out the plant through the stomata and lenticels

• Stomata:They are tiny pores in the lower epidermis of leaves. Each stoma is enclosed within two bean shaped cells known as guard cells. It regulates the opening  and closing of the stomata,
• Lenticels: These are breathing pores or tiny opening found in the bark of older stems. Lenticels consist of a loose mass of small thin-walled cells which permits easy diffusion of gasses in and out of the plant.

MECHANISM OF GASEOUS EXCHANGE IN PLANTS

Oxygen, carbon dioxide, and water vapour are released by simple diffusion process in plants. Oxygen diffuses into plants through the stomata and lenticels while CO₂ and water vapour diffuses out of the plant through the same opening. This is facilitated by the difference in the concentration gradient of these gases. The plant takes in oxygen mostly during the night and gives out carbon dioxide and water vapour during the day due to photosynthetic activities of the plant. Oxygen is the by-product of photosynthesis.

The opening and closing of the stomata is regulated by the guard cells. When the guard cell is turgid, the stomata open but when the cells become flaccid the stomata are closed.

GENERAL EVALUATION

1. State the organs of respiration in plant
2. Describe the gaseous exchange in plants.
3. What is (a) glycolysis (b) Krebs’s cycle?
4. Define photosynthesis.
5. Explain the process that leads to the production of yoghurt

Reading Assignment

College Biology, Chapter 8, Page 170 – 185       

WEEKEND ASSIGNMENT

SECTION A

• During anaerobic respiration, how many ATP are produced?

A. 2 ATP B. 3 ATP C. 4 ATP D. 5 ATP

• The cartilaginous flap which prevents food from entering the wind pipe is 

A. glottis B. epiglottis C. larynx D. oesophagus

• The gaseous exchange in mammals takes place in the

A. trachea B. bronchus C. alveolus D. lungs

• When the guard cell is turgid, the stomata A. opens B. closes C. shrinks D. breaks
• In strenuous activities in the absence of oxygen, glucose is broken down into

A. pyruvic acid B. carbon dioxide C. lactic acid D. alcohol

SECTION B

1. Explain  fermentation.
2. Differentiate between internal and external respiration.

GENERAL EVALUATION

1. Write short note on cutaneous respiration.
2. Differentiate between the cutaneous respiration and pulmonary respiration in toad.
3. Explain why toads have a lot of alternatives to respiration.
4. Describe the process of gaseous exchange in fish.
5. What is diffusion?   

Reading Assignment

College Biology, Chapter 8, Page 170 – 185       

Weekend Assignment

                                            SECTION A

• The following gases except one is not exchanged during respiration.

A. Oxygen B. Hydrogen C. carbon dioxide D. None of the above.

• Inhalation and exhalation constitute the 

A. internal respiration B. cellular respiration C. external respiration D. pulmonary respiration.

• For easier and faster diffusion of gases during respiration, the respiratory surface must by …… walled.

A. thin B. fat D. fluid D. rigid

• Lung is an organ for respiration in the following organisms except 

A. man B. toad C scorpion D. cattle

• The cartilaginous flap which prevents food from entering the wind

A. glottis B. epiglottis C. larynx D. oesophagus

                                        SECTION B

1. Discuss the mechanism of respiration in Tilapia fish.
2. State the organ of respiration in (a) iroko tree (b) scorpion (c) snake (d) housefly (e) bat