Gaseous Exchange in Plants and Animals

Contents Exchange of materials Gaseous exchange in Flowering Plants Adaptations of leaf for rapid diffusion of gasses Gaseous exchange in Humans Functions of the various parts Pathway of the air An efficient respiratory surface How do we breathe? Inspiration Expiration Gaseous Exchange in the Alveoli How does the blood carry O2? How does the blood carry CO2? Composition of inhaled and exhaled air Asthma Chronic Bronchitis Other Respiratory Disorders

Exchange of materials Necessary between the cells of an organism and its environment. Oxygen, carbon dioxide, nutrients, wastes and ATP all move by diffusion.

Exchange of materials is necessary To allow oxygen combine with food to release energy (ATP) = respiration. To ensure that the fluid balance of cells (= homeostasis) and their temperature is kept constant. To remove waste materials produced in cells = excretion.

Gaseous exchange in Flowering Plants O2 and CO2 exchanged through stomata. Stomata are tiny openings in the upper or lower epidermis of a leaf through which gases pass - surrounded by two guard cells. In woody stems gaseous exchange occurs through lenticels. Lenticels are raised openings (pores) in the bark of a woody stem formed by loosely arranged cells with air spaces between them to facilitate gaseous exchange

Lenticel

During the day CO2 diffuses into the leaf through the stomata Moves to the chloroplasts Used in photosynthesis to make glucose O2 produced as waste Diffuses out of leaf through stomata

Adaptations of leaf for rapid diffusion of gases are flattened have stomata have air spaces between the cells mesophyll cells (ground tissue) are loosely arranged and their surfaces are moist

T.S. of a leaf showing diffusion of gases

T.S. of leaf

Gaseous exchange in Humans Occurs at a special site called the respiratory surface = the lungs. The lungs are part of the breathing system. They lie in the thoracic (chest) cavity above the diaphragm. Enclosed and protected by the rib cage.

The parts of the human breathing system

The parts of the human breathing system

Functions of the various parts (1/2) Nostrils Allow air to enter the nose Nose Warms, filters and moistens air Pharynx (throat) Connects nose and mouth to larynx Glottis Opening to the larynx Epiglottis Prevents food passing into the windpipe when you swallow Larynx (voice box) Makes sounds

Functions of the various parts (2/2) Trachea (windpipe) Allows air to pass to lungs Cartilage Keeps trachea and bronchi open Bronchus Transports air into lung Bronchiole Transports air into alveoli Alveoli (air sacs) Site of gas exchange Pleural membranes Allow friction-free movement of lungs

Pathway of the air Air enters the nostrils and passes through the nose, nasal passages, pharynx, larynx, bronchi, bronchioles and finally reaches the alveoli. Some air enters through the mouth, buccal cavity, pharynx, larynx … alveoli. Gaseous exchange occurs in the alveoli.

An efficient respiratory surface (1/2) Must have the following: A large surface area It must be moist - O2 and CO2 can only diffuse in solution It must be very thin – for rapid diffusion

An efficient respiratory surface (2/2) It must have a large blood capillary network – to allow gaseous exchange between air and blood stream – capillary walls only one cell thick – increase rate of diffusion. It must receive a constant supply of air – the breathing movements provide good ventilation.

How do we breathe? Occurs in two stages: - Inhaling (Inspiration) and Exhaling (Expiration) One breath = one inhalation + one exhalation At rest approx 16 breaths per minute. Breathing not under conscious control. Controlled by brain.

Inspiration - Active i.e. requires energy This is taking air into the lungs. The intercostal muscles between the ribs contract causing the ribs to move upwards and outwards. The circular muscles of the diaphragm contract and cause it to flatten. These actions result in an increased volume of the thorax and a decrease in the air pressure in the lungs - consequently air is drawn into the lungs.

Inhaling

Expiration - Passive i.e. requires no energy. This is expelling air from the lungs. The diaphragm and intercostal muscles relax causing the ribs and diaphragm to return to their original position. These actions result in a decreased volume of the thorax and an increase in the air pressure in the lungs - consequently air is expelled from the lungs

Exhaling

The bell jar model of the lungs

Control of breathing Breathing is controlled by the 'respiratory centre' in the medulla oblongata connected by nerves to the diaphragm and intercostal muscles. A rise in the amount of carbon dioxide in the blood passing through the respiratory centre stimulates impulses to be sent to the diaphragm and intercostal muscles, causing an increase in the depth and rate of breathing.

Gaseous Exchange in Alveoli Occurs by diffusion. Air in alveoli is rich in O2 Blood in capillary is O2 poor O2 diffuses from the alveoli into the blood capillaries. CO2 is plentiful in blood capillaries CO2 low in the alveoli  CO2 diffuses out of the capillaries into the alveoli

Rapid diffusion is possible because There are millions of alveoli (350,000,000 per lung) Alveolus wall one cell thick and surrounded by a thin layer of fluid Large blood capillary network surrounding each alveolus Capillaries narrow and walls are only one cell thick also

Gas exchange at an alveolus

How does the blood carry O2? O2 dissolves in moist lining of alveolus. Diffuses through walls of alveolus and capillary. And into red blood cells. Joins with haemoglobin to form oxyhaemoglobin. Carried to every cell in the body. O2 released and passes from the capillary into the cells.

How does the blood carry CO2? (1/2) CO2 produced by cells during respiration. Diffuses from cells into the blood. Some dissolves in blood plasma. Most of it diffuses into the red blood cells. Here an enzyme joins it to water to form carbonic acid: CO2 + H2O --> H2CO3

How does the blood carry CO2? (2/2) The carbonic acid (H2CO3) is split into hydrogen ions (H+) and bicarbonate ions (HCO3-). HCO3- ions diffuse out of red blood cells and are transported in the plasma. H+ ions remain in the red blood cells. Removing CO2 from lungs ensures pH of blood remains constant.

Composition of inhaled and exhaled air Gas Inhaled Exhaled Nitrogen (N2) 79% Oxygen (O2) 20.9% 16.4% Carbon dioxide (CO2) 0.03% 4.1% Water vapour (H2O) Variable Saturated

One of the following Breathing Disorders Asthma Chronic Bronchitis

Asthma

What is it? Asthma results in the narrowing of the bronchioles which prevents air reaching the alveoli.

Symptoms Breathlessness and wheezing

Causes Can be triggered by a number of different things: - Pollen, house dust, vigorous exercise, cat and dog dander (scaly pieces of skin), infection, tobacco smoke and other air pollutants.

Prevention If a specific cause is known to trigger the asthma then steps can be taken to avoid it. e.g. if pet dander is responsible, then the person should not keep a pet or hold or play with one if possible. A person with asthma should not smoke. A person without asthma should not smoke either.

Treatment Inhaling a bronchodilator which widens the bronchioles is common. The inhalation technique is very important. Inhalers should only be used on medical advice.

Chronic Bronchitis

What is it? an inflammatory condition affecting the bronchi causing them to become narrower.

Symptoms Persistent cough, Breathlessness, Production of a lot of mucus (phlegm).

Causes Smoking and other air pollutants.

Prevention Never smoke, Why not? When you smoke tiny particles get trapped on the mucus lining the bronchi. This is an irritant and causes more mucus to be produced. Excess mucus collects in the bronchi, And causes the familiar ‘smoker’s cough’.

Treatment A bronchodilator (e.g. ventilin) to open the bronchi may be prescribed to relieve the breathlessness. In severe cases the patient may need to inhale pure oxygen.

Other Respiratory Disorders Not examinable for information only

Lung cancer

Spread of lung cancer

How smoking damages the lungs 1

How smoking damages the lungs 2

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