Respiration in Lower Animals




Respiration in Lower Animals


Class :


Term :

First Term

Week :

Week 6

Instructional Teaching Materials :

  • Photos of plants and animals
  • Sample alimentary canal of animal



  • Scheme of Work
  • On-line Information
  • Textbooks
  • Workbooks

Earlier Tutorials 

The pupils have earlier information on


that was beforehand taught as a topic before this specific lesson


Behavioural Objectives :  On the conclusion  of this lesson, the learners will likely be able to

  • Say the types of respiration in lower animals
  • mention the organs of respiration in lower animals
  • explain the mechanism of breathing in lower animals
  • Describe the mechanism of breathing in mammals.
  • Describe the mechanism of breathing in insects.
  • Describe the mechanism of breathing in fish.




Respiration in Insects

The mechanism of breathing in insects is as follows:

  1. An insect breathes through a trachea system. An insect has an impermeable cuticle but, at intervals along the sides of its body, are about ten tiny openings called spiracles, through which air enters and leaves the trachea.
  2. These lead into air-filled tubes called tracheae which end in very hair-like, tiny structures in tissues called tracheoles. Hence, no body cell is far from a tracheole which contains certain fluids.
  3. As the body wall of an insect contracts and expands, oxygen in the air diffuses through the spiracle into the trachea and tracheole. It then diffuses into the body cells where it is used for aerobic respiration.
  4. Carbon (iv) oxide and water (water vapour) produced, diffuse out of the body through the spiracles.
  5. The spiracles have valves and they are opened only when the carbon (iv) oxide concentration in the tissues is above a specific level.
  6. The spiracles are closed for most of the time when an insect is inactive to reduce water loss.

Mechanism of Breathing in Fish

  1. Gaseous exchange or breathing in fishes occurs across the gill surfaces. All the gills possess a very high surface area-to-volume ratio.
  2. The fish opens its mouth, and water passes over the gill surface inside the opercula which are then closed.
  3. As water flows over the gills, the dissolved oxygen in the water diffuses into the thin walled blood capillaries of the gills. At the same time, carbon (iv) oxide in the blood diffuses into the water.
  4. The alternate opening and closing of the mouth and operculum allow a constant flow of water over the gills.
  5. Oxygen is transported by the blood into every living cell where it is used for aerobic respiration. Hence, the gills are used for gas exchange (breathing) and not just for respiration.


Gaseous Exchange in Plants

As you learnt earlier, plants do not breathe like mammals, but like animals, they exchange gases because they do not have thorax and lungs like mammals, we cannot see their breathing movements which are the visible signs of gas exchange. Completely submerged aquatic plants (e.g. algae) or those floating on water surface (e.g. lettuce) exchange gases by diffusion all over their body surface or through the stomata in their leaves, lenticels in their stem, and through the roots (i.e.from the air spaces in the soil particles around the roots).

Anatomy of a Leaf

The leaf provides food for the rest of the plant through the process of photosynthesis. The outermost layer of the leaf is the epidermis, which is protected by the waxy coating of the cuticle. Guard cells implanted in the epidermis form pores, known as stomata, through which water, oxygen, and carbon dioxide pass. Embedded in the inner tissues of the leaf are chloroplasts, where photosynthesis occurs. The plant veins consist of two specialized tissues. Xylem conducts water from the plant to the leaf, while phloem carries food from the leaf to the plant.

They also occur in the stems of young herbaceous plants. A stoma (stomata-plural) is a tiny pore or opening enclosed by two bean-shaped guard cells. Unlike other epidermal cells, guard cells have chloroplasts. Each guard cell has a thick, relatively inelastic wall around the pore and a thin, elastic outer wall. The mechanism of the opening and closing of stomata is believed to be associated with light intensity and the osmotic pressure within the guard cells. When the osmotic pressure in the guard cells is high, they become turgid as a result of which the pore or stoma opens. When the pressure is low, the guard cells become flaccid and the stoma is closed. In general, the movement of gases and water vapour into and out of leaves is controlled by the opening and closing of the stomata.

The Effect of Light on Gas Exchange in the Leaf

Respiration occurs at all times in living things. During sunlight, the rate of photosynthesis is usually greater than that of respiration in green plants. Oxygen given out during photosynthesis in the day is captured by animals and man for respiration. Also, the carbon (iv) oxide produced by respiring cells is used in photosynthesis, while a lot of carbon (iv) oxide diffuses into the leaf mesophyll cells from outside. The diffusion from the inside of the leaf to the outside is short. Hence, gaseous molecules diffuse rapidly in and out of the leaf through the stomata.

However, at night, photosynthesis stops just as the sun stops shining, but respiration continues because animals must live. Then, some oxygen diffuses into the leaf from outside through the stomata and lenticels. The oxygen is used up in the respiring cells, while the carbon (iv) oxide diffuses out of the leaf and lenticels.

It is worthy to note that the vein of leaves contain vascular tissue. Water and mineral salts and some dissolved gases are distributed to the leaf parts through the xylem. Also, the manufactured food in the leaves is conducted through the phloem in the veins to all parts of the leaves and other plant parts.





The topic is obtainable step-by-step


Step 1:

The subject instructor revises the sooner issues


Step 2.

He introduces the topic new topic


Step 3:

The class coach permits the pupils to current their very personal examples and he corrects them when the desires come up



Conclusion :


The class coach wraps up or conclude the lesson by giving out temporary observe to summarize the topic that he or she has merely taught.

The class coach moreover goes spherical to ensure that the notes are correctly copied or correctly written by the pupils.

He or she does the required corrections when and the place  the desires come up.




  1. Describe the mechanism of breathing in mammals.
  2. Describe the mechanism of breathing in insects.
  3. Describe the mechanism of breathing in fish.





The topic wraps up the subject by giving the learners a complete notice and she or he makes certain that the learners copy the notes accurately . She or he marks the notes and he does the mandatory corrections