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k.c.s.e biology reference notes Form 1-4


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1/1/2018

GASEOUS EXCHANGE IN PLANTS AND ANIMALS - KCSE BIOLOGY NOTES, AUDIOVISUALS, SCHEMES OF WORK, QUESTIONS AND ANSWERS

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COURTESY OF ATIKA SCHOOL

TOPIC 7: INTRODUCTION TO GASEOUS EXCHANGE IN PLANTS AND ANIMALS - KCSE BIOLOGY NOTES, AUDIOVISUALS, SCHEMES OF WORK, QUESTIONS AND ANSWERS

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SPECIFIC OBJECTIVES

GASEOUS EXCHANGE IN PLANTS AND ANIMALS
GASEOUS EXCHANGE IN PLANTS AND ANIMALS
By the end of the topic, the learner should be able to:
  1. Explain the need for gaseous exchange in living organisms
  2. Explain the mechanism of gaseous exchange in plants
  3. Compare the internal structures of aquatic and terrestrial roots, stems and leaves
  4. Examine various types of respiratory structures in animals and relate them to their functions
  5. State the characteristics of respiratory surfaces
  6. Describe the mechanisms of gaseous exchange in protozoa, insects, fish, frog and mammal
  7. Describe the factors which control the rate of breathing in humans
  8. State the causes, symptoms and prevention of respiratory diseases.

TOPIC/SUBTOPICS OUTLINE

​GASEOUS EXCHANGE (36 LESSONS)
Gaseous exchange in living organisms (necessity)
Gaseous Exchange in Plants
  • Mechanisms of opening and closing of stomata
  • The process of gaseous exchange in root, stem and leaves of both aquatic (floating) and terrestrial plants
Gaseous Exchange in Animals
  • Types and Characteristics of Respiratory Surfaces - cell membrane, gills, buccal cavity, skin and lungs
  • Mechanism of gaseous exchange in
    •    Protozoa - amoeba
    •    Insect – grasshopper
    •    Fish – bonyfish
    •    Amphibia – frog
    •    Mammal - human
Factors affecting rate of breathing in humans
Respiratory diseases: Asthma, Bronchitis, Pulmonary tuberculosis, Pneumonia and whooping cough
Practical Activities
Observe permanent slides of cross- sections of aerial and aquatic leaves and stems
Examine the distribution of spiracles on grasshopper or locust
Examine the gills of a bony fish
Dissect a small mammal and identify the structures of the respiratory system (demonstration) Construct and use models to demonstrate breathing mechanisms in a mammal (human) Demonstrate the effect of exercise on the rate of breathing

INTRODUCTION TO GASEOUS EXCHANGE IN PLANTS AND ANIMALS

Necessity for Gaseous Exchange in Living Organisms

  • Living organisms require energy to perform cellular activities.
  • The energy comes from breakdown of food in respiration.
  • Carbon (IV) oxide is a byproduct of respiration and its accumulation in cells is harmful which has to be removed.
  • Most organisms use oxygen for respiration which is obtained from the environment.
  • Photosynthetic cells of green plants use carbon (IV) oxide as a raw material for photosynthesis and produce oxygen as a byproduct.
  • 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 

FIGURE 1: STRUCTURE OF GUARD CELL
FIGURE 1: STRUCTURE OF GUARD CELL
  • 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 become 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.
  • Guard cells have chloroplasts while other epidermal cells do not.
  • Photosynthesis takes place during daytime and sugar produced raises the solute concentration of guard cells.
  • Water is drawn into guard cells by osmosis from surrounding cells.
  • Guard cells become turgid and stoma opens.
  • At night no photosynthesis occurs hence no sugar is produced.
  • The solute concentration of guard cells falls and water moves out of the guard cells by osmosis.
  • Guard cells lose turgidity and the stoma closes.
pH changes in guard cells occur due to photosynthesis.
  • In day time carbon (IV) oxide is used for photosynthesis. This reduces acidity while the oxygen produced increases alkalinity.
  • Alkaline pH favours conversion of starch to sugar.
  • Solute concentration increases inside guard cells, water is drawn into the cells by osmosis. Guard cells become turgid and the stoma opens.
  • At night when no photosynthesis, Respiration produces carbon (IV) oxide which raises acidity. This favours conversion of sugar to starch. Low sugar concentration lead to loss of turgidity in guard cells and stoma closes.

Explanation is based on accumulation of potassium

Ions
  • 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.

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.
These are many and large in the spongy mesophyll.
When stomata are open, 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 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.
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 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.
Others have respiratory roots with large air spaces.
Continue Reading ...

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TOPICAL QUESTIONS

These questions are good for group discussions in and out of a classroom environment they can also be used in a question and answer brainstorming sessions

  1. What is gaseous exchange?
  2. Why is gaseous exchange important to organisms?
  3. Name the structure used for gaseous exchange by plants
  4. Briefly describe the structure of stomata
  5. State the factors which affect stomatal opening
  6. Name the theories suggesting the mechanism of opening and closing of stomata
  7. Describe the mechanism of opening and closing of stomata
  8. What is the advantage of having stomata open during daytime and having them closed at night?
  9. State the ways in which leaves of plants are adapted to gaseous exchange
  10. Describe how gaseous exchange takes place in terrestrial plants
  11. State the ways in which floating leaves of aquatic plants are adapted to gaseous exchange
  12. How is aerenchyma tissue adapted to its function?
  13. Explain stomatal distribution in plants of different habitats
  14. List the types of respiratory surfaces of animals
  15. State the characteristics of respiratory surfaces in animals
  16. Describe gaseous exchange in protozoa
  17. Make a labeled drawing of a fish gill
  18. How is a fish gill adapted to its function?
  19. Discuss gaseous exchange in bony fish example is tilapia
  20. What is counter-flow system?
  21. What is the advantage of counter-flow system?
  22. Describe the mechanism of gaseous exchange in terrestrial insects
  23. State how traceholes are adapted to gaseous
  24. What is breathing?
  25. Name the structures in humans that are used in gaseous exchange
  26. Describe the mechanism of gaseous exchange in a mammal
  27. Explain how mammalian lungs are adapted to gaseous exchange
  28. Name the features of alveoli that adapt them to their function
  29. How is the trachea of a mammal suited to its function?
  30. State the advantages of breathing through the nose rather than through the mouth
  31. Give the conditions under which the carbon iv oxide level rises above normal in mammalian blood
  32. Explain the physiological changes that occur in the body to lower the carbon iv oxide level back to normal when it rises
  33. Describe the factors which control the rate of breathing in humans
  34. Name the respirator diseases
  35. Define respiration
  36. Explain the significance of respiration in living organisms
  37. Draw and label a mitochondrion
  38. Explain the roles of enzymes in respiration
  39. What is aerobic respiration?
  40. Give a word equation for aerobic respiration
  41. What are the end products of aerobic respiration?
  42. What is anaerobic respiration?
  43. What are obligate anaerobes?
  44. What are facultative anaerobes?
  45. State the word equation representing anaerobic respiration in plants
  46. Name the end products of anaerobic respiration in plants alcohol/ethanol carbon iv oxide
  47. Give a word equation of anaerobic respiration in animals
  48. Name the end products of respiration in animals when there is insufficient oxygen supply
  49. Why is there a high rate of lactic acid production during exercise?
  50. Why does lactic acid level reduce after exercise?
  51. State why accumulation of lactic acid during vigorous exercise lead to an increase in heartbeat
  52. State the economic importance of anaerobic respiration
  53. What is oxygen debt?
  54. What is respiratory quotient(RQ)?
  55. Why are respiratory quotient important?
  56. Name the respiratory substrates 
  57. Why does anaerobic respiration of a given substrate yield a smaller amount of energy than aerobic respiration?
  58. Mention the types of experiments carried out for respiration

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