Gaseous exchange and respiration

 

GASEOUS EXCHANGE IN PLANTS AND ANIMALS

Necessity for Gaseous Exchange in Living Organisms

•             Most organisms use oxygen for respiration which is obtained from the environment. The energy comes from breakdown of food in respiration. Living organisms require energy to perform cellular activities.

•             Carbon (IV) oxide is a by-product of respiration and its accumulation in cells is harmful which has to be removed. Photosynthetic cells of green plants use carbon (IV) oxide as a raw material for photosynthesis and produce oxygen as a byproduct.

Gaseous exchange:

•             The movement of these gases between the cells of organisms and the environment comprises gaseous exchange.

•             The process of moving oxygen into the body and carbon (IV) oxide out of the body is called breathing or ventilation.

•             Gaseous exchange involves the passage of oxygen and carbon (IV) oxide through a respiratory surface.

•             Diffusion is the main process involved in gaseous exchange.

 

Gaseous Exchange in Plants

•             Oxygen is required by plants for the production of energy for cellular activities.

•             Carbon (IV) oxide is required as a raw material for the synthesis of complex organic substances.

•             Oxygen and carbon (IV) oxide are obtained from the atmosphere in the case of terrestrial plants and from the surrounding water in the case of aquatic plants.

•             Gaseous exchange takes place mainly through the stomata.

Structure of Guard Cells

•             The stoma (stomata - plural) is surrounded by a pair of guard cells.

•             The structure of the guard cells is such that changes in turgor inside the cell cause changes in their shape. They are joined at the ends and the cell walls facing the pore (inner walls) are thicker and less elastic than the cell walls farther from the pore (outer wall).

•             Guard cells control the opening and closing of stomata.

Mechanism of Opening and Closing of Stomata

•             In general stomata open during daytime (in light) and close during the night (darkness).

•             Stomata open when osmotic pressure in guard cells becomes higher than that in surrounding cells due to increase in solute concentration inside guard cells. Water is then drawn into guard cells by osmosis.

•             Guard cells become turgid and extend. The thinner outer walls extend more than the thicker walls. This causes a bulge and stoma opens.

•             Stomata close when the solute concentration inside guard cells becomes lower than that of surrounding epidermal cells. The water moves out by osmosis, and the guard cells shrink i.e. lose their turgidity and stoma closes.

**Proposed causes of turgor changes in guard cells:  Accumulation of sugar and pH changes in guard cells occur due to photosynthesis.

 

Process of Gaseous Exchange in Root Stem and Leaves of Aquatic and Terrestrial Plants

Gaseous Exchange in leaves of Terrestrial Plants

•             Gaseous exchange takes place by diffusion.

•             The structure of the leaf is adapted for gaseous exchange by having intercellular spaces that are filled (spongy mesophyll).

•             When stomata are open, carbon (IV) oxide from the atmosphere diffuses into the sub-stomatal air chambers. From here, it moves into the intercellular space in the spongy mesophyll layer.

•             The CO2 goes into solution when it comes into contact with the cell surface and diffuses into the cytoplasm. A concentration gradient is maintained between the cytoplasm of the cells and the intercellular spaces. CO2 therefore continues to diffuse into the cells.

•             The oxygen produced during photosynthesis moves out of the cells and into the intercellular spaces. From here it moves to the sub-stomatal air chambers and eventually diffuses out of the leaf through the stomata. At night oxygen enters the cells while CO2 moves out.

 

Gaseous exchange in the leaves of aquatic (floating) plants

•             Aquatic plants such as water lily have stomata only on the upper leaf surface.

•             The intercellular spaces in the leaf mesophyll are large.

•             Gaseous exchange occurs by diffusion just as in terrestrial plants.

Features that can be observed in the leaf of an aquatic plant:

•             Absence of cuticle

•             Palisade mesophyll cells are very close to each other i.e. compact.

•             Air spaces (aerenchyma) in spongy mesophyll are very large.

•             Sclereids (stone cells) are scattered in leaf surface and project into air spaces.

•             They strengthen the leaf making it firm and assist it to float.

 

Gaseous Exchange through stems

Terrestrial Plants

•             Stems of woody plants have narrow openings or slits at intervals called lenticels. They are surrounded by loosely arranged cells where the bark is broken.

•             They have many large air intercellular spaces through which gaseous exchange occurs.

•             Oxygen enters the cells by diffusion while carbon (IV) oxide leaves.

•             Unlike the rest of the bark, lenticels are permeable to gases and water.

Aquatic Plant Stems

•             The water lily, Salvia and Wolfia whose stems remain in water are permeable to air and water.

•             Oxygen dissolved in the water diffuses through the stem into the cells and carbon (IV) oxide diffuses out into the water.

 

 

 

 

Gaseous Exchange in Roots

Terrestrial Plants

•             Gaseous exchange occurs in the root hair of young terrestrial plants.

•             Oxygen in the air spaces in the soil dissolves in the film of moisture surrounding soil particles and diffuses into the root hair along a concentration gradient.

•             It diffuses from root hair cells into the cortex where it is used for respiration.

•             Carbon (IV) oxide diffuses in the opposite direction.

•             In older roots of woody plants, gaseous exchange takes place through lenticels.

Aquatic Plants

•             Roots of aquatic plants e.g. water lily are permeable to water and gases. Oxygen from the water diffuses into roots along a concentration gradient. Carbon (IV) oxide diffuses out of the roots and into the water. The roots have many small lateral branches to increase the surface area for gaseous exchange. They have air spaces that help the plants to float.

•             Mangroove plants grow in permanently waterlogged soils, muddy beaches and at estuaries. They have roots that project above the ground level. These are known as breathing roots or pneumatophores. These have pores through which gaseous exchange takes place e.g. in Avicenia the tips of the roots have pores.

 

Gaseous Exchange in Animals

•             All animals take in oxygen for oxidation of organic compounds to provide energy for cellular activities.

•             The carbon (IV) oxide produced as a by-product is harmful to cells and has to be constantly removed from the body.

•             Most animals have structures that are adapted for taking in oxygen and for removal of carbon (IV) oxide from the body. These are called "respiratory organs".

 

•             The process of taking in oxygen into the body and carbon (IV) oxide out of the body is called breathing or ventilation.

•             Gaseous exchange involves passage of oxygen and carbon (IV) oxide through a respiratory surface by diffusion.

 

 

Types and Characteristics of Respiratory surfaces

Different animals have different respiratory surfaces. The type depends mainly on the habitat of the animal, size, shape and whether body form is complex or simple.

•             Cell Membrane: In unicellular organisms the cell membrane serves as a respiratory surface.

•             Gills: Some aquatic animals have gills which may be external as in the tadpole or internal as in bony fish e.g. tilapia. They are adapted for gaseous exchange in water.

•             Skin: Animals such as earthworm and tapeworm use the skin or body surface for gaseous exchange.

•             The skin of the frog is adapted for gaseous exchange both in water and on land.

•             The frog also uses epithelium lining of the mouth or buccal cavity for gaseous exchange.

•             Lungs: Mammals, birds and reptiles have lungs which are adapted for gaseous exchange.

Characteristics of Respiratory Surfaces

•             They are permeable to allow entry of gases.

•             They have a large surface area in order to increase diffusion.

•             They are usually thin in order to reduce the distance of diffusion.

•             They are moist to allow gases to dissolve.

•             They are well-supplied with blood to transport gases and maintain a concentration gradient.

 

Gaseous Exchange in Amoeba

•             Gaseous exchange occurs across the cell membrane by diffusion.

•             Oxygen diffuses in and carbon (IV) oxide diffuses out.

•             Oxygen is used in the cell for respiration making its concentration lower than that in the surrounding water.

•             Hence oxygen continually enters the cell along a concentration gradient.

•             Carbon (IV) oxide concentration inside the cell is higher than that in the surrounding water thus it continually diffuses out of the cell along a concentration gradient.

 

 

Gaseous Exchange in Insects

•             Gaseous exchange in insects e.g., grasshopper takes place across a system of tubes penetrating into the body known as the tracheal system.

•             The main trachea communicates with atmosphere through tiny pores called spiracles.

•             Spiracles are located at the sides of body segments; two pairs on the thoracic segments and eight pairs on the sides of abdominal segments.

•             Each spiracle lies in a cavity from which the trachea arises. Spiracles are guarded with valves that close and thus prevent excessive loss of water vapor.

•             A filtering apparatus i.e. hairs also traps dust and parasites which would clog the trachea if they gained entry. The valves are operated by action of paired muscles.

 

Mechanism of Gaseous Exchange in Insects

•             The main tracheae in the locust are located laterally along the length of the body on each side and they are interconnected across.

•             Each main trachea divides to form smaller tracheae, each of which branches into tiny tubes called tracheoles. Each tracheole branches further to form a network that penetrates the tissues. Some tracheoles penetrate into cells in active tissue such as flight muscles. These are referred to as intracellular tracheoles.

•             Tracheoles in between the cells are known as intercellular tracheoles. The main tracheae are strengthened with rings of cuticle. This helps them to remain open during expiration when air pressure is low.

Adaptation of Insect tracheole for Gaseous Exchange

•             The fine tracheoles are very thin about one micron in diameter in order to permeate tissue.

•             They are made up of a single epithelial layer and have no spiral thickening to allow diffusion of gases.

•             Terminal ends of the fine tracheoles are filled with a fluid in which gases dissolve to allow diffusion of oxygen into the cells.

•             Amount of fluid at the ends of fine tracheoles varies according to activity i.e. oxygen demand of the insect.

•             During flight, some of the fluid is withdrawn from the tracheoles such that oxygen reaches muscle cells faster and the rate of respiration is increased.

 

Gaseous Exchange in Bony Fish (e.g. Tilapia)

•             Gaseous exchange in fish takes place between the gills and the surrounding water.

•             The gills are located in an opercular cavity covered by a flap of skin called the operculum.

 

Adaptation of Gills for Gaseous Exchange

•             Gill filaments are thin walled.

•             Gill filaments are very many (about seventy pairs on each gill), to increase surface area.

•             Each gill filament has very many gill lamellae that further increase surface area.

•             The gill filaments are served by a dense network of blood vessels that ensure efficient transport of gases.

•             It also ensures that a favorable diffusion gradient is maintained.

•             The direction of flow of blood in the gill lamellae is in the opposite direction to that of the water (counter current flow) to ensure maximum diffusion of gases.

 

Gaseous Exchange in an Amphibian - Frog

•             A frog uses three different respiratory surfaces. These are the skin, buccal cavity and lungs.

Skin

•             The skin is used both in water and on land.

•             It is quite efficient and accounts for 60% of the oxygen taken in while on land.

 

Adaptations of a frog's skin for gaseous exchange

•             The skin is a thin epithelium to allow fast diffusion.

•             The skin between the digits in the limbs (i.e. webbed feet) increases the surface area for gaseous exchange.

•             It is richly supplied with blood vessels for transport of respiratory gases.

•             The skin is kept moist by secretions from mucus glands.

•             This allows for respiratory gases to dissolve. Oxygen dissolved in the film of moisture diffuses across the thin epithelium and into the blood which has a lower concentration of oxygen.

•             Carbon (IV) oxide diffuses from the blood across the skin to the atmosphere along the concentration gradient.

 

Buccal (Mouth) Cavity

•             Gaseous exchange takes place all the time across thin epithelium lining the mouth cavity.

 

Adaptations of Buccal Cavity for Gaseous Exchange

•             It has a thin epithelium lining the walls of the mouth cavity allowing fast diffusion of gases.

•             It is kept moist by secretions from the epithelium for dissolving respiratory gases.

•             It has a rich supply of blood vessels for efficient transport of respiratory gases.

•             The concentration of oxygen in the air within the mouth cavity is higher than that of the blood inside the blood vessels.

•             Oxygen, therefore dissolves in the moisture lining the mouth cavity and then diffuses into the blood through the thin epithelium.

•             On the other hand, carbon (IV) oxide diffuses in the opposite direction along a concentration gradient.

Lungs

•             There is a pair of small lungs used for gaseous exchange.

Adaptation of Lungs

•             The lungs are thin walled for fast diffusion of gases.

•             Have internal foldings to increase surface area for gaseous exchange.

•             A rich supply of blood capillaries for efficient transport of gases.

•             Moisture lining for gases to dissolve.

Gaseous Exchange in a Mammal

Human

•             The breathing system of a mammal consists of a pair of lungs which are thin-walled elastic sacs lying in the thoracic cavity.

•             The thoracic cavity consists of vertebrae, sternum, ribs and intercostal muscles. The thoracic cavity is separated from the abdominal cavity by the diaphragm. The lungs lie within the thoracic cavity. They are enclosed and protected by the ribs which are attached to the sternum and the thoracic vertebrae.

•             There are twelve pairs of ribs; the last two pairs are called 'floating ribs' because they are only attached to the vertebral column. The ribs are attached to and covered by internal and external intercostals muscles. The diaphragm at the floor of thoracic cavity consists of a muscle sheet at the periphery and a central circular fibrous tissue. The muscles of the diaphragm are attached to the thorax wall.

•             The lungs communicate with the outside atmosphere through the bronchi, trachea, mouth and nasal cavities. The trachea opens into the mouth cavity through the larynx.

•             A flap of muscles, the epiglottis, covers the opening into the trachea during swallowing. This prevents entry of food into the trachea.

•             Nasal cavities are connected to the atmosphere through the external nares (or nostrils) which are lined with hairs and mucus that trap dust particles and bacteria, preventing them from entering into the lungs.

•             Nasal cavities are lined with cilia. The mucus traps dust particles,

•             The cilia move the mucus up and out of the nasal cavities.

•             The mucus moistens air as it enters the nostrils. Nasal cavities are winding and have many blood capillaries to increase surface area to ensure that the air is warmed as it passes along.

•             Each lung is surrounded by a space called the pleural cavity.

•             It allows for the changes in lung volume during breathing.

•             An internal pleural membrane covers the outside of each lung while an external pleural membrane lines the thoracic wall.

•             The pleural membranes secrete pleural fluid into the pleural cavity.

•             This fluid prevents friction between the lungs and the thoracic wall during breathing.

•             The trachea divides into two bronchi, each of which enters into each lung.

•             Trachea and bronchi are lined with rings of cartilage that prevent them from collapsing when air pressure is low. Each bronchus divides into smaller tubes, the bronchioles.

•             Each bronchiole subdivides repeatedly into smaller tubes ending with fine bronchioles.

•             The fine bronchioles end in alveolar sacs, each of which gives rise to many alveoli.

•             Epithelium lining the inside of the trachea, bronchi and bronchioles has cilia and secretes mucus.

Adaptations of Alveolus to Gaseous Exchange

•             Each alveolus is surrounded by very many blood capillaries for efficient transport of respiratory gases.

•             There are very many alveoli that greatly increase the surface area for gaseous exchange.

•             The alveolus is thin walled for faster diffusion of respiratory gases.

•             The epithelium is moist for gases to dissolve.

 

Gaseous Exchange between the Alveoli and the Capillaries

•             The walls of the alveoli and the capillaries are very thin and very close to each other.

•             Blood from the tissues has a high concentration of carbon (IV) oxide and very little oxygen compared to alveolar air.

•             The concentration gradient favors diffusion of carbon (IV) oxide into the alveolus and oxygen into the capillaries.

•             No gaseous exchange takes place in the trachea and bronchi.

•             These are referred to as dead space.

Ventilation

•             Exchange of air between the lungs and the outside is made possible by changes in the volumes of the thoracic cavity.

•             This volume is altered by the movement of the intercostal muscles and the diaphragm.

Inspiration

•             The ribs are raised upwards and outwards by the contraction of the external intercostal muscles, accompanied by the relaxation of internal intercostal muscles.

•             The diaphragm muscles contract and diaphragm moves downwards.

•             The volume of thoracic cavity increases, thus reducing the pressure.

•             Air rushes into the lungs from outside through the nostrils.

Expiration

•             The internal intercostal muscles contract while external ones relax and the ribs move downwards and inwards.

•             The diaphragm muscles relaxes and it is pushed upwards by the abdominal organs. It thus assumes a dome shape.

•             The volume of the thoracic cavity decreases, thus increasing the pressure.

•             Air is forced out of the lungs.

•             As a result of gaseous exchange in the alveolus, expired air has different volumes of atmospheric gases as compared to inspired air.

 

 

Lung Capacity

•             The amount of air that human lungs can hold is known as lung capacity.

•             The lungs of an adult human are capable of holding 5,000 cm3 of air when fully inflated. However, during normal breathing only about 500 cm3 of air is exchanged. This is known as the tidal volume.

•             A small amount of air always remains in the lungs even after a forced expiration. This is known as the residual volume.

•             The volume of air inspired or expired during forced breathing is called vital capacity.

 

Control of Rate of Breathing

•             The rate of breathing is controlled by the respiratory center in the medulla of the brain.

•             This center sends impulses to the diaphragm through the phrenic nerve.

•             Impulses are also sent to the intercostal muscles.

•             The respiratory center responds to the amount of carbon (IV) oxide in the blood.

•             If the amount of carbon (IV) oxide rises, the respiratory center sends impulses to the diaphragm and the intercostal muscles which respond by contracting in order to increase the ventilation rate.

•             Carbon (IV) oxide is therefore removed at a faster rate.

Factors Affecting Rate of Breathing in Humans

•             Factors that cause a decrease or increase in energy demand directly affect rate of breathing.

•             Exercise, any muscular activity like digging.

•             Sickness

•             Emotions like anger, flight

•             Sleep.

Effects of Exercise on Rate of Breathing

•             Students to work in pairs.

•             One student stands still while the other counts (his/her) the number of breaths per minute.

•             The student whose breath has been taken runs on the sport vigorously for 10 minutes.

•             At the end of 10 minutes the number of breaths per minute is immediately counted and recorded.

 

 Respiration

•             Respiration is the process by which energy is liberated from organic compounds such as glucose. The energy is used in the cells and much of it is also lost as heat. In humans it is used to maintain a constant body temperature.

Tissue Respiration

•             Respiration takes place inside cells in all tissues.

•             Most organisms require oxygen of the air for respiration and this takes place in the mitochondria.

Mitochondrion Structure and Function

Structure

•             Mitochondria are rod-shaped organelles found in the cytoplasm of cells.

•             A mitochondrion has a smooth outer membrane and a folded inner membrane.

•             The folding of the inner membrane is called cristae and the inner compartment is called the matrix.

Adaptations of Mitochondrion to its Function

•             The matrix contains DNA ribosomes for making proteins and has enzymes for the breakdown of pyruvate to carbon (IV) oxide, hydrogen ions and electrons.

•             Cristae increase surface area of mitochondrial inner membranes where attachment of enzymes needed for the transport of hydrogen ions and electrons are found.

•             There are two types of respiration:

a)      Aerobic Respiration

•             This involves breakdown of organic substances in tissue cells in the presence of oxygen.

•             All multicellular organisms and most unicellular organisms e.g. some bacteria respire aerobically.

•             In the process, glucose is fully broken down to carbon (IV) oxide and hydrogen which forms water when it combines with the oxygen.

•             Energy produced is used to make an energy rich compound known as adenosine triphosphate (ATP). It consists of adenine, an organic base, five carbon ribose-sugar and three phosphate groups.

•             ATP is synthesized from adenosine-diphosphate (ADP) and inorganic phosphate.

•             The last bond connecting the phosphate group is a high-energy bond.

•             Cellular activities depend directly on ATP as an energy source.

•             When an ATP molecule is broken down, it yields energy.

Process of Respiration

•             The breakdown of glucose takes place in many steps. Each step is catalyzed by a specific enzyme. Energy is released in some of these steps and as a result molecules of ATP are synthesized.

•             All the steps can be grouped into three main stages:

Glycolysis:

•             The initial steps in the breakdown of glucose are referred to as glycolysis and they take place in the cytoplasm.

•             Glycolysis consists of reactions in which glucose is gradually broken down into molecules of a carbon compound called pyruvic acid or pyruvate.

•             Before glucose can be broken, it is first activated through addition of energy from ATP and phosphate groups.

•             This is referred to as phosphorylation.

•             The phosphorylated sugar is broken down into two molecules of a 3-carbon sugar (triose sugar) each of which is then converted into pyruvic acid.

•             If oxygen is present, pyruvic acid is converted into a 2-carbon compound called acetyl coenzyme A (acetyl Co A).

•             Glycolysis results in the net production of two molecules of ATP.

 TCA/Kreb’s cycle

•             The next series of reactions involve decarboxylation i.e. removal of carbon as carbon

(IV) Oxide and dehydrogenation, removal of hydrogen as hydrogen ions and electrons.

•             These reactions occur in the mitochondria and constitute the Tri-carboxylic Acid Cycle (T.C.A.) or Kreb's citric acid cycle.

•             The acetyl Co A combines with 4-carbon compound with oxalo-acetic acid to form citric acid - a 6 carbon compound.

•             The citric acid is incorporated into a cyclical series of reactions that result in removal of carbon (IV) oxide molecules, four pairs of hydrogen, ions and electrons.

Electron Transport Chain

•             Hydrogen ions and electrons are taken to the inner mitochondria membrane where enzymes and electron carriers affect release of a lot of energy.

•             Hydrogen finally combines with oxygen to form water, and 36 molecules of ATP are synthesized.

 

b)      Anaerobic Respiration

•             Anaerobic respiration involves breakdown of organic substances in the absence of oxygen. It takes place in some bacteria and some fungi.

•             Organisms which obtain energy by anaerobic respiration are referred to as anaerobes.

•             Obligate anaerobes are those organisms which do not require oxygen at all and may even die if oxygen is present. Facultative anaerobes are those organisms which survive either in the absence or in the presence of oxygen.

•             Such organisms tend to thrive better when oxygen is present e.g. yeast.

 

Products of Anaerobic Respiration

•             The products of anaerobic respiration differ according to whether the process is occurring in plants or animals.

Anaerobic Respiration in Plants

•             Glucose is broken down to an alcohol, (ethanol) and carbon (IV) oxide.

•             The breakdown is incomplete.

•             Ethanol is an organic compound, which can be broken down further in the presence of oxygen to provide energy, carbon (IV) oxide and water.

C6HI206 _ 2C2H50H + 2C02 + Energy

(Glucose) (Ethanol) (Carbon (IV) oxide)

Fermentation-

•             Is the term used to describe formation of ethanol and carbon (IV) oxide from grains.

•             Yeast cells have enzymes that bring about anaerobic respiration.

Lactate Fermentation

•             Is the term given to anaerobic respiration in certain bacteria that results in formation of lactic acid.

Anaerobic Respiration in Animals

•             Anaerobic respiration in animals produces lactic acid and energy.

C6H1P6 _ 2CH3CHOH.COOH + energy

(Glucose) (Lactic acid) +  energy

•             When human muscles are involved in very vigorous activity, oxygen cannot be delivered as rapidly as it is required. The muscles respire anaerobically and lactic acid accumulates.

•             A high level of lactic acid is toxic. During the period of exercise, the body builds up an oxygen debt.

•             After vigorous activity, one has to breathe faster and deeper to take in more oxygen. Rapid breathing occurs in order to breakdown lactic acid into carbon (IV) oxide and water and release more energy. Oxygen debt therefore refers to the extra oxygen the body takes in after vigorous exercise.

 

Comparison between Aerobic and Anaerobic Respiration

Aerobic Respiration                                                                        Anaerobic Respiration

1. Site                    In the mitochondria.                                                                       In the cytoplasm

2. Products         Carbon dioxide and water.                                                          Ethanol in plants and lactic acid

3. Energy yield   38 molecules of A TP (2880 KJ)                                                   2 molecules of ATP 210KJ

(From each glucose molecule)

4. Further reaction No further reactions on carbon dioxide and water     Ethanol and lactic acid can be broken down further in the presence of oxygen.

Comparison between Energy Output in Aerobic and Anaerobic Respiration

•             Aerobic respiration results in the formation of simple inorganic molecules, water and carbon (Iv) oxide as the byproducts.These cannot be broken down further. A lot of energy is produced. When a molecule of glucose is broken down in the presence of oxygen, 2880 KJ of energy are produced (38 molecules of ATP).

•             In anaerobic respiration the by products are organic compounds. These can be broken down further in the presence of oxygen to give more energy. Far less energy is thus produced. The process is not economical as far as energy production is concerned. When a molecule of glucose is broken down in the absence of oxygen in plants, 210 KJ are produced (2 molecule ATP). In animals, anaerobic respiration yields 150 kJ of energy.

Substrates for Respiration

•             Carbohydrate, mainly glucose is the main substrate inside cells.

•             Lipids i.e. fatty acids and glycerol are also used. Fatty acids are used when the carbohydrates are exhausted. A molecule of lipid yields much more energy than a molecule of glucose.

•             Proteins are not normally used for respiration. However during starvation they are hydrolyzed to amino acids, deamination follows and the products enter Kreb's cycle as urea is formed. Used by the body protein in respiration results to body wasting, as observed during prolonged sickness or starvation.

 

Respiratory quotient

•             The ratio of the amount of carbon (IV) oxide produced to the amount of oxygen used for each substrate is referred to as Respiratory Quotient (RQ) and is calculated as follows:

R.Q. = Amount of carbon (IV) oxide produced Amount of oxygen used

•             Carbohydrates have a respiratory quotient of 1.0, lipids 0.7 and proteins 0.8. Respiratory quotient value can thus give an indication of types of substrate used. Values higher than one indicate that some anaerobic respiration is taking place.

 

Application of Anaerobic Respiration in Industry and at Home

Industry

•             Making of beer and wines.

•             Ethanol in beer comes from fermentation of sugar (maltose) in germinating barley seeds.

•             Sugar in fruits is broken down anaerobically to produce ethanol in wines.

•             In the dairy industry, bacterial fermentation occurs in the production of several dairy products such as cheese, butter and yoghurt.

•             In production of organic acids e.g., acetic acid, that are used in industry e.g., in preservation of foods.

•             Fermentation of grains is used to produce all kinds of beverages e.g., traditional beer and sour porridge.

•             Fermentation of milk.