LIFE SCIENCES GRADE 11 - Gaseous Exchange


Click on the link below for the introduction of the lesson :

Lesson Description In this lesson we will:

· Discuss what is gaseous exchange?

· Consider requirements of an efficient gaseous exchange surface.

·  Differentiate between gaseous exchange, cellular respiration and breathing.

· Discuss structure and adaptations of the human gaseous exchange system.

· Discuss gaseous exchange at lung surface







Essay question 

Describe how the gas is required during earobic respiration enters the body and gas exchange in the lungs from the atmosphere along with transportation on oxygen. (20)



What is Gaseous Exchange?

The main function of the respiratory system is to take in oxygen from the atmosphere and make it available to the cells for cellular respiration. Carbon dioxide is produced during respiration and must be removed.

Gas exchange takes place in two places in the body. The lungs, where oxygen is taken up and carbon dioxide is released through the respiratory membranes, and the tissues, where oxygen is released and carbon dioxide is taken up. External respiration is gas exchange with the external environment and takes place in the alveoli of the lungs. Internal respiration is gas exchange with the internal environment and takes place within the tissue. The actual gas exchange takes place by simple diffusion. No energy is required to move oxygen or carbon dioxide through the membrane. Instead, these gases follow a pressure gradient that allows diffusion. Lung anatomy maximizes gas diffusion. Respiratory membranes are highly permeable to gases. Respiratory and capillary membranes are very thin. The entire lung has a large surface area.




Terms that are important that you can differentiate between:

  • Breathing – the mechanical process whereby air moves into and out of the lungs. (inhalation and exhalation)
  • Gaseous exchange – the exchange of oxygen and carbon dioxide across a gaseous exchange surface.
  • Cellular respiration – the release of energy from glucose in the presence of oxygen



Requirements of an Effective Gaseous Exchange Surface

To enable oxygen and carbon dioxide to diffuse through it easily, it must be:

  • Large – to ensure the maximum exchange of gases can take place.
  • Thin and permeable – so that diffusion can take place easily and rapidly.
  • Moist – so that gases can dissolve to form a solution.
  • Well ventilated – good oxygen supply and carbon dioxide removal. (maintain a diffusion gradient)
  • Efficient transport system – for effective transport of gases.
  • Well protected - to prevent desiccation (drying out) and mechanical injury





Phase 1 

  • watch the video inserted in the introduction section.
  • note down what is required for you to do. 
  • read the rubric carefully it will help you complete the task  
  • Study the note to help you write your essay. 

Phase 2

  • open your word document.
  • Read the essay title and find the key words to have an idea what the essay is all about 
  • write an essay that must not be longer than a page. 
  • Write subheadings 
  • write the essay in point form 
  • Make sure you have at 20 points 
  • Other points you will get from how you have structured the essay.  

Phase 3 

  • email your work using your school/ personal email with your name on it. Should you experience challenges with submitting via email, submit using whatsapp. 

Phase 4

  • Work submitted. Keep the submittion prove saved.   

marking criteria 




Relevance (R)


Logical sequence (L)

Comprehensive (C


All information provided is relevant to the question

Ideas are arranged in a logical/cause-effect sequence

All aspects required by the essay have been sufficiently addressed


Only information relevant to the description of gas exchange. There is no irrelevant information.

All the information regarding description of gas exchange, aerobic respiration is given in a logical manner

Correct points as follows: -

 2/4 for gas exchange ,

- 3/5 for  transportation of 0xygen

- 6/8 for aerobic respiration





                                                                                                                                                                                Total = 20 marks 


Re- visit the task and check if everything is correct and well organized. 

re- visit the topic and explain the importance of gaseous exchange in the atmosphere.  


marks are all dependent on your writing and structure. 

thank you all for participating in the lesson. 

Videos can help enhance the students learning process. Be sure to watch YouTube to give you a better understanding of the lesson. 

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