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By Mr. Nyamawi Waa Girls Secondary School

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Definition:  It is t he  pr oces s by which the respiratory gases (oxygen and carbon (iv) oxide are passed across the respiratory surface. In  simple organism oxygen is absorbed by the exposed surface of the     body by  simple diffusion . In  complex organisms, they have special organs  e.g  lungs or gills which absorb oxygen and remove carbon (iv) oxide from the body. Brought  about by  concentration gradient  that exists between the body of living organism and the surrounding medium.

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Importance  of gaseous exchange Provide oxygen for respiration in all organisms. Provide carbon (iv) oxide for autotrophs for photosynthesis ; Facilitate carbon IV oxide removal from the body as a metabolic waste product .

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- Green plants need  oxygen  for  respiration  and  carbon (iv) oxide  for photosynthesis. -During the day they absorb carbon (iv) oxide and give out oxygen while at night they give out  carbon (iv) oxide  and take in oxygen. -During photosynthesis some of the oxygen given out is used for respiration.

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Adaptations  of respiratory surfaces in plants. They  are  moist to dissolve respiratory  gases  in order for them to  diffuse in solution form. They  have large surface areas  to  increase  efficiency of gaseous exchange. They  have increase ventilation due to the presence of stomata and lenticels and the epidermis, which are in contact with the surrounding medium.  Mesophyll  cells near the air spaces have thin walls. The thin membranes allow fast diffusion of gases.

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Examples  of respiratory Surfaces in Plants 	 Stomata   in leaves 	 pneumatophores  e.g.  Roots 	 Lenticels   in woody stems

Lenticel
Cornplementary cell
Epidermis
Phellem(Cork)
Phelloderm
(Sec.ondary cortex)

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Stomata  are tiny pores found on the surface of the leaf. A Stoma is an aperture on leaves surrounded by guard cells. A Guard cell is special Bean shaped epidermal cells surrounding the stoma that regulate opening and closing of the stomata . Functions of the guard cells   Control the  opeing  and closing of the stomata hence regulating movement of gases  e.g   carbon (iv) oxide ,  oxygen  and  water vapour  into and out of the leaf surface.

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Open
—Nucleus
Thid inn
cell wall
Chloreast
Vnulc
Tlin out
cell wall
Guard cell
Epidermal Cf

They  contain chloroplasts and so can  photosynthesize to produce glucose which facilitate closing and opening of the stomata. They are bean shaped/sausage  shaped  to facilitate the opening and closing of stomata. Inner walls are thicker while outer wall is thin to facilitate the opening and closing of stomata. They  have uneven thickness of their cell walls  ie  thicker on the surrounding the pore .

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Answer the following questions What is gaseous exchange? What is the importance of gaseous  exhache ? Name three structures through which gaseous exchange occurs in plants How is a guard cell adapted to its functions?

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The mechanisms of opening and closing of stomata.

There are three theories that try to explain how the stomata open and close. Photosynthetic theory Starch Sugar inter-conversion Theory. (effect of changes in pH of guard cells) Potassium Ion Theory. Photosynthetic  theory. Chloroplast  in guard cells carry out photosynthesis during the day.   The glucose manufactured in the guard cells increases the osmotic pressure    Of the guard cells . The  cells then draw water from the surrounding epidermal cells by osmosis and become turgid.  The  outer thin  wall stretches, puling the inner thick wall outwards hence opening the stoma.    At night, no photosynthesis occurs.  Manufactured  glucose is changed into insoluble starch.  This  lowers osmotic pressure of the guard cells which lose water to the surrounding by osmosis and become flaccid.  This  closes the stoma.

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Summary   of opening and closing of stomata .

During the day      During the night -Presence of light  -No light -Photosynthesis takes place  -Photosynthesis does not take place. -The glucose formed increases the osmotic pressure in guard cells.  -Any glucose present in the guard cell is converted to starch, causing low osmotic pressure in guard cells -Guard cells draw in water from epidermal cells and become turgid -Stoma  opens  -Guard cells lose water to epidermal cells and become flaccid   - Stoma closes..

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During  the day photosynthesis takes place in the guard cell using carbon (iv)oxide The pH in the guard cells tends to rise as the conditions becomes less acidic as carbon(iv)oxide is continuously used up.  The  increasing pH  favours  the conversion of starch into glucose . This increases the osmotic pressure of the guard cells.    The guard cells  draw water from epidermal cells and become turgid. This opens the stomata.    At night, there is no sunlight so photosynthesis does not take place . Plants  take in oxygen releasing carbon(iv)oxide.    Carbon(iv)oxide from respiration accumulates in the guard cells lowering the pH  which  favours   the conversion of glucose to starch.  Starch is osmotically inactive. This  reduce osmotic pressure in the guard cells which lose water to the surround cells and become flaccid.  This close the stomata.

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In day time (light) adenosine triphosphate (ATP) is produced which causes potassium ions to move into guard cells by active transport.  These ions cause an increase in solute concentration in guard cells that has been shown to cause movement of water into guard cells by osmosis.  Guard cells become turgid and the stoma opens.  At night potassium and chloride ions move out of the guard cells by diffusion and level of organic acid also decreases.  This causes a drop in solute concentration that leads to movement of water out of guard cells by osmosis.  Guard cells lose turgor and the stoma closes.

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Gaseous exchange takes place by diffusion.  The structure of the leaf is adapted for gaseous exchange by having intercellular spaces that are filled. These are many and large in the spongy mesophyll. When stomata are open, during the day, carbon(IV)oxide from the atmosphere diffuses into the  substomatal  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  substomatal  air chambers and eventually diffuses out of the leaf through the stomata. At night  Oxygen  diffuses from the atmosphere where it is more concentrated into the  plant through the respiratory surfaces. Similarly carbon (IV) oxide  diffuses out as a metabolic waste product along a concentration gradient into the atmosphere.

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Stomata are modified in number of ways depending on the habitat of the plant. Depending on the habitat where a plant leaves, there are three categories of plants i.e. Xerophytes Hydrophytes Mesophytes

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Distribution of stomata in  aquatic(floating) plants Hydrophytes Aquatic plants such as water lily have  numerous  stomata on  the upper leaf surface. The intercellular spaces in the leaf mesophyll are large. Gaseous exchange occurs by diffusion just as in terrestrial plants. Observation  of internal structure of leaves of aquatic plants Transverse section of leaves of an aquatic plant such as Nymphaea differs from that of terrestrial plant.  The following are some of the features that can be observed in the leave of an aquatic plant; Absence of cuticle Palisade mesophyll cells are very close to each other  ie.compact .  Air spaces ( aerenchyma ) in spongy mesophyll are very  large to facilitate gaseous exchange and for  bouyancy .  Sclereids   (stone cells) are scattered in leaf surface and project into air  spaces for  bouyancy .  They strengthen the leaf making it firm and assist it to float.

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These are plants adapted to life in dry areas. They have less number of stomata that are small in size. Stomata may be sunken, hairy and in some they open during the night and close during the day.

upper
Cuticle Vein
Bundle-sheath Palisade
multiple
extension parenchyma
epidermis
Spongy
multiple
Guard cell bundle sheath
epidermis

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They are plants growing in areas with adequate amounts of water. They have a fairly large number of stomata found on both leaf surfaces.

Leaf Cross Section
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They  are openings found on woody stems and they are made of loosely packed cells. They allow gaseous exchange between the inside of the plant and the outside by diffusion. Actual gaseous exchange occurs on some moist cells under the lenticels.

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Plants  like the mangroves growing in muddy salty waters have specialized aerial breathing roots called  pneumatophores .   These are roots  that project above the ground level.  Pneumatophores  rise above the salty water to facilitate gaseous exchange.

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All animals take in oxygen for oxidation of organic  compounds (respiration)  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.

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Various types of respiratory surfaces have been developed by different animals to facilitate gaseous exchange depending on animals size, activity, environment/medium of operation. A continuous supply of oxygen is important for the survival of animals. Oxygen is necessary for  respiration . Unicellular  and simple organisms have a large surface area to volume ratio . The  exchange of oxygen and carbon (iv) oxide is by simple diffusion  through  the cell membrane. Examples  of unicellular organisms :    .  Amoeba    .  Paramecium     .Earth worm In  large  multicelullar  organism  e.g  humans, elephants  etc.       They have a small surface area to volume ratio . They  have specialized   structures for gaseous exchange   e.g  lungs, gills etc.

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Type of Respiratory surface  Environment or medium of operation         Example of                                            organism.   Cell  membrane       water  Amoeba. Cell  membrane       water  Paramecium. Tracheole       Air  Insects. Gill  filaments       water  Fish. Gills       water  Tadpole. Buccal  cavity/skin       water/air  Adult frog. Lungs       Air  Bird/reptiles. Lungs       Air  Human beings. Skin       water  Frog

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CHARACTERISTICS OF RESPIRATORY SURFACES .

1.They are moist to  dissolve respiratory  gases during diffusion-gases diffuse faster in solution form. 2. They are thin to create a shorter distance for rapid diffusion of  respiratory gases . 3. They  have  a large surface area in order to  ensure  maximum gaseous    exchange.  4. They are highly  vascularized ( well-supplied with  blood vessels)   to transport absorbed gases rapidly and to create a high diffusion gradient. 5. Have a high concentration gradient (High diffusion pressure deficit) to permit rapid diffusion of respiratory gases.

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MECHANISMS OF GASEOUS EXCHANGE IN PROTOZOA

Protozoa  e.g  amoeba carry out respiration inside the cell.  It uses oxygen and releases carbon (iv) oxide. There is a high concentration of oxygen in the surrounding water than in the cell.  Oxygen therefore diffuses across the cell membrane from the surrounding into the cell.  The carbon (iv) oxide in the cell is at a higher  concentration.  Than in the surrounding and it diffuses out across the cell membrane.

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MECHANISMS OF GASEOUS EXCHANGE IN INSECTS.

The respiratory system in insects is called  Tracheal system. Components  of Tracheal system Spiracles. Trachea. Tracheoles .                  Spiracles These are tiny pores on the abdomen and thorax. Are closed and opened by valves. Are surrounded by hair, which traps dust particles in the air.

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Trachea Forms two branches one on each side of the body. They are strengthened by  chitinous  ring.               Tracheoles . They branch from the trachea. They are sites for gaseous exchange. They have thin walls and moist ends located in the tissues.

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Inhalation (Inspiration)      Exhalation ( Epiration ) Abdominal muscles relax Abdominal muscle contract Pressure in the Abdomen and trachea reduces compared to atmospheric pressure Pressure in the trachea increase compared to the atmospheric pressure Thoracic spiracles open Abdominal spiracles opens; Air enters in them into the trachea , then into the  tracheoles  Carbon (iv) oxide  is forced out through the spiracles; Gaseous exchange Oxygen being highly concentrated   in the air  in the tracheoles dissolve  in the moisture in the tracheoles then diffuses into the tissues Carbon (iv) oxide  being highly concentrated in  the tissue cells  diffuse  out of the tissue into the tracheoles  NB. Respiratory gases in insects are not transported by the blood.

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Fish uses gills for gaseous exchange; Fish live in water that contains oxygen and other gases are dissolved in it.   Components of breathing system of a bony  fish. Operculum, Opercular   cavity/Gill  chamber; Mouth  cavity/buccal  cavity) A gills comprising of; Gill bar. Gill filaments. Gill  rakers .

Caudal Fin
pectoral Fin
Dorsal fins
pelvic

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1.Operculum – These are gill covers on both sides of the head  .  They open into the  opercular  cavity by an operculum flap. 2.Opercular cavity – They are located on either side of the head, beneath the gills; 3.Gill bar – They are curved bony structures that holds the gill filaments on one  Side  and gill  rakers  on the other  side. They  are used for support of  gill filaments and gill  rakers . 4.Gill filaments – They are sites for gaseous exchange . Are  membraneous   projectionson  the gill bar.  They have a dense  carpilary  network. 5. Gill  rakers  – They are bony teeth-like structures /pointed  facing the mouth cavity. -  They filter solid material in incoming water preventing them  from  damaging the delicate gill  filaments. They  are attached to the gill bar.

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Gill  filaments are thin  walled  to create a shorter distance for rapid diffusion of respiratory gases .  Gill filaments are very many  (about seventy  pairs on each gill), to increase surface  area for  diffusion of respiratory gases .  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.  The curved shape of the gill bar allows more  fillaments  to fit on it. Gill  rakers  prevent solid particles in water from reaching the delicate gill  fillaments .

A Carp with the Operculum
removed to show tty
Gills
Gill.a.mertts
Gill-takers
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Mechanisms of gaseous exchange in bony fish .

Inhalation        Exhalation Mouth opens The floor of the mouth is lowered Volume in the mouth cavity increases  Pressure  reduces  causing water to be drawn into the buccal cavity.  Operculum cavity bulges out but  opercular  flap presses on the body remaining closed  preventing water from entering or leaving through the opening.  Volume  in the gill chambers increases Pressure decreases allowing in the water from the mouth  cavity to flow in to the gill chamber over the gill  filaments. Mouth closes. Mouth floor is raised; Volume reduces in mouth cavity Pressure increases, forcing the water into the gill chambers. Operculum press inwards. Volume of the gill cavity reduce  Water is forced out of the gill chamber Pressure  increases                            Gaseous exchange in the gills As water passes over the gills  Oxygen  diffuses from water through the gill filaments into the  capillaries alongside concentration  gradient. Co 2  diffuses of the capillaries into the  water  alongside concentration  gradient.

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NB – In order to have maximum gaseous exchange  faster diffusion between the blood in the gill filaments and the flowing water, a steep concentration gradient must be maintained across the respiratory surface. This is achieved by the flow of water and blood in opposite directions. This system in  which blood flows over the gills in the opposite direction with   incoming water  is called  counter current flow .  Importance – for maximum gaseous exchange /faster diffusion due to steep  Concentration  gradient.

Water flow
over
lamellae
showing
% 02
2
Blood flow
through
lamellae
showing
% 02

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When water flows over the gill filaments in one direction and blood in the opposite direction, the concentration of oxygen in blood and water may be 0% and 15% respectively at the beginning. As more oxygen diffuses from water into the blood, the concentration of oxygen in the blood becomes higher. In addition, as blood flows in vessels, it continues to be in contact with water that has a higher concentration of oxygen. At all the pts, the concentration of oxygen is higher in the water than in the blood.     In  parallel flow blood and water flow in the same direction. Oxygen in the water can diffuse into the blood rapidly at the beginning. This is because of the large difference in concentration of oxygen between blood (100% oxygen).

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Mechanisms of gaseous Exchange in amphibians (frog )

An adult frog lives on land but goes back into the water during the breeding season.  A frog uses three different respiratory surfaces.  These are the  skin, buccal cavity and lungs.

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The skin of the frog has some important features to allow effective gaseous exchange with its environment. These are : Has a large network of  capillaries;to  transport respiratory gases to and from it. Its kept moist  by secretions from mucus  glands  to dissolve respiratory gases. Have a thinner skin to permit rapid diffusion; Gaseous exchange through the skin takes place when the frog is on land and in  Water ;

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When the frog is submerged in water, oxygen dissolved in water diffused through the skin into blood capillaries;  This  is because the concentration of oxygen is higher in the water than in the  blood capillaries, carbon (iv) oxide from the blood capillaries below the  When  on land, oxygen from air  dissolves and diffuses  blood capillaries below it, carbon (iv) oxide from the blood diffuses in the opposite directions. Toads  do not use the skin surface for gaseous exchange  normally  except when they are hibernating.

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The inner surface of the lungs is thin, moist and is richly supplied with blood capillaries; it has tiny folds which increase the surface area: -Used when the frog is very active i.e. when swimming /leaping -There valves in each nostril. - Lungs lie in the body cavity of the amphibian.  Inspiration When  the nostril are closed ,the air can be forced into the lungs by the pumping action of the flow of the mouth and the air reaches the alveoli which are moist and supplied with large network of capillaries, oxygen combines with  haemoglobin  and is transported to all parts of the body and Co 2  diffuses out.  Expiration The  nares and glottis open. The air in the mouth and the lungs passes out, helped by the natural elasticity of the lungs .

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Adaptation The  lining of the buccal cavity is  thin to reduce the distance travelled by the respiratory gases It  is also richly supplied with blood  capillaries to facilitate transport of the respiratory gases. It’s kept moist; by the mucous  membrane to dissolve the respiratory gases. Inspiration and Expiration Air is taken or expelled from the mouth cavity by raising and lowering the floor of the mouth .

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Gaseous exchange. 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.

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Mechanisms of  Ventilation  in  Amphibians (frog ) in the buccal cavity

Inspiration During  breathing hyoid muscles contract and are pulled down and the floor is lowered. The volume inside the mouth increases, the pressure decreases thus causes the atmospheric air to enter the mouth through nostril (nares ). Expiration When  the  transverse muscles  contract, the floor of the mouth is raised and the volume in the mouth decreases so that air rushes out of the mouth through the nostrils

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Part 				 Brief Description and function   Nostrils			-lined with ciliated epithelial cells; 				-Have goblet cells that secrete mucus; 				-Have hairs to trap dust particles; 				-Have capillaries that warm up incoming air; Glottis			-Opening of trachea; Epiglottis		-Open sand closes the glottis to prevent Solid particles ; 		from entering the trachea	;

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Larynx/voice box		-uses vibrations of air flow to create sound;	 Trachea		-C-shaped cartilaginous rings keep it open; -Passage of air; -Has mucus and cilia; to remove dust and harmful bodies -Strengthened by rings of cartilage to prevent it from Collapsing; Bronchi			-two branches of trachea;-one for each lung 				 -have rings of cartilage to strengthen it; Bronchioles			-branches of bronchi; 				-many branches ending with sac like alveoli;

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Pleural membrane		-two membranes surrounding the outer surface of lungs; -tightly attached to lungs; the other covers the inside the thoracic cavity; -secrete pleural fluids which lubricate the pleural membrane allowing easy movement of the lungs during breathing; Pleural cavity		-found between the two pleural membranes; -filled with pleural fluid and reduces friction; therefore makes lungs move freely in chest cavity during breathing;

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Thoracic cavity/ Chest cavity 	-surrounded by the rib cage and sternum, thoracic vertebra 				-air tight; 				-protects lungs and heart; -any changes in its volume affect the lungs in the same way; Intercostal  muscles		-surround the ribs 				-cause movement of ribs that cause breathing; Diaphragm	-muscular sheet which separates thoracic cavity from abdominal cavity; 	-floor of the thoracic cavity enhances breathing by changing the volume in the thoracic cavity;

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Gaseous Exchange

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 Definition:  It is t he  pr oces s by which the respiratory gases (oxygen and carbon (iv) oxide are passed across the respiratory surface. In  simple organism oxygen is absorbed by the exposed surface of the     body by  simple diffusion . In  complex organisms, they have special organs  e.g  lungs or gills which absorb oxygen and remove carbon (iv) oxide from the body. Brought  about by  concentration gradient  that exists between the body of living organism and the surrounding medium.

Gaseous Exchange

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