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SS2: BIOLOGY - 2ND TERM

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  1. Mechanism of the Respiratory System | Week 1
    6 Topics
    |
    2 Quizzes
  2. Mechanism of Gaseous Exchange in Plants | Week 2
    1 Topic
    |
    1 Quiz
  3. Excretory Systems I | Week 3
    5 Topics
    |
    1 Quiz
  4. Excretory Systems II | Week 4
    4 Topics
    |
    3 Quizzes
  5. Nutrient Cycling in Nature I | Week 5
    3 Topics
  6. Nutrient Cycling in Nature II | Week 6
    2 Topics
    |
    1 Quiz
  7. Ecological Management | Week 7
    4 Topics
  8. Ecological Tolerance | Week 8
    2 Topics
    |
    1 Quiz
  9. Adaptation | Week 9
    3 Topics
    |
    1 Quiz
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Topic Content:

  • Types of Respiratory Surface
    • Body Surface
    • Gills
    • Tracheal System
    • Lungs
  • Characteristics of an Efficient Respiratory Surface

The respiratory surface is a special area that is developed in order to satisfy the requirements for gaseous exchange in larger organisms. Examples include external gills, internal gills, lungs, and the insect tracheae.

Body Surface:

1. Cell membrane: In simple unicellular organisms, such as Amoeba and Paramecium, the cell is close to the external environment. These organisms are small, and their surface area to volume ratio is large, literally, gaseous exchange occurs by diffusion across the surface membrane. These organisms do not have specialized structures for gaseous exchange to meet their oxygen demand.

2. Cutaneous respiration: It is a form of respiration in which gaseous exchange occurs through the skin of some animals such as earthworms, frogs, and toads. In these organisms, the surface area to volume ratio is large. In these organisms, their skin is kept moist so that oxygen or carbon dioxide can easily dissolve in the moisture before it diffuses across the body surface, which is richly supplied with blood vessels so that dissolved oxygen diffuses easily into the blood and is transported to all parts of the body.

Gills:

A gill is a respiratory organ found in many aquatic organisms such as fishes, crustaceans, and amphibians which extracts dissolved oxygen from water and excretes carbon dioxide.

In a bony fish, the gills are found inside the gill chambers and protected by the gill cover or operculum.

Each gill consists of a bony framework known as the gill arch, with two rows of numerous filaments attached. These filaments are highly vascularized (i.e. richly supplied with blood vessels). Gaseous exchange occurs in the filaments.

gills

Attached to the gill arch are short bony structures known as gill rakers. They serve as filters and protect the delicate gills.

Each gill filament has several flattened plates which increase its surface area for gaseous exchange, these flattened plates are called lamella.

gills in bony fishes

Tracheal System:

Insects and some other invertebrates exchange gases between their tissues and the air through a system of air-filled tubes called tracheae. The tracheae open to the outside through tiny holes called spiracles.

insects

Air enters and exits the insects via small openings called spiracles which are found in pairs at every segment of the insect’s body, and the oxygen then diffuses into the insect’s body.

The spiracles are guarded by valves controlled by muscles which enable the insect to open and close them. The spiracles open into a network of tubes all over the body.

These are tracheae that branch further into tracheoles and come in contact with the surface of cells in the body of the insects.

trachea system insects
tracheal system in insects

Lungs:

The lungs are the organs for gaseous exchange in all mammals, birds, most reptiles and some amphibians. The lungs are located in the thoracic or chest region of the body and consist of air sacs or alveoli which provide a large surface area for gaseous exchange.

lungs

The lungs are pinky spongy tissues enclosed within a pleural sac that contains pleural fluid which allows the inner and other walls to slide over each other whilst breathing takes place without much friction.  

The pleural sac divides the lungs into sections called lobes. The left lung has two lobes while the right has three (3) strong muscles attached to the rib cage allowing expansion and contraction, resulting in inflation and deflation of the lungs. 

The epithelium of lungs is highly vascularized

Characteristics of an Efficient Respiratory Surface:

i. Thin Walls: Thin walls help to shorten the distance through which gases diffuse. Diffusion is relatively slow, so a thin surface will increase the rate of diffusion.

ii. Large Surface Area: This further increases the rate of gaseous exchange.

iii. Moist Surface: Gases dissolve in the moisture helping them to pass across the gas exchange surface. The Oxygen dissolves before entering the blood or body fluid.

iv. Permeable walls: Permeable walls allow gases to pass through freely.

v. Extensive Blood Supply: Respiratory surfaces are richly supplied with blood capillaries which ensures oxygen-rich blood is taken away from the respiratory surface to the tissues.