Gas Exchange in Plants (Edexcel IGCSE Biology (Modular)): Revision Note

Exam code: 4XBI1

Lára Marie McIvor

Last updated

Diffusion in Gas Exchange

  • Diffusion is the movement of molecules from a region of its higher concentration to a region of its lower concentration

  • Molecules move down a concentration gradient, as a result of their random movement

Diffusion across the cell membrane, IGCSE & GCSE Biology revision notes

Diffusion across the cell membrane

Diffusion in organisms

  • Diffusion drives the process of gas exchange 

  • Single-celled organisms, such as amoeba, can exchange gases sufficiently by simple diffusion through the cell membrane

  • Multicellular organisms (such as plants and animals), however, have exchange surfaces and organ systems that maximise the exchange of materials

    • Gills are the gas exchange organs in fish, lungs in humans and leaves or roots in plants

  • These organs increase the efficiency of exchange in several ways:

  • Having a large surface area to increase the rate of transport

  • A short diffusion distance for substances to move across. This short distance is created because the barrier that separates two regions is as thin as possible

  • In addition, animals have:

    • Gas exchange surfaces that are well-ventilated to maintain steep concentration gradients

Gas exchange in amoeba, downloadable IGCSE & GCSE Biology revision notes

Gas exchange in single-celled organisms (such as amoeba) occurs through diffusion

Gas Exchange: Photosynthesis & Respiration

  • The processes of respiration and photosynthesis both rely on the exchange of oxygen and carbon dioxide

Gas exchange during respiration

  • All living cells respire

  • The process requires the uptake of oxygen and the release of carbon dioxide

  • Oxygen diffuses down the concentration gradient from a high concentration (outside the leaf) to a low concentration (inside the leaf)

    • The cells use oxygen in respiration so the concentration is always low inside the respiring cells

  • The carbon dioxide diffuses down the concentration gradient from a high concentration (inside the leaf) to a low concentration (outside the leaf)

Gas exchange in respiration, downloadable IGCSE & GCSE Biology revision notes

In respiration, carbon dioxide diffuses out of the leaf and oxygen diffuses into the leaf

Gas exchange during photosynthesis

  • Plant cells photosynthesize when there is enough sunlight

  • The process requires the uptake of carbon dioxide and the release of oxygen

  • The carbon dioxide diffuses down the concentration gradient from a region of high concentration (outside the leaf) to a region of low concentration (inside the leaf)

    • The cells use carbon dioxide in photosynthesis so the concentration is always low inside the photosynthesizing cells

  • The oxygen diffuses down the concentration gradient from a high concentration (inside the leaf) to a low concentration (outside the leaf)

Gas exchange in photosynthesis, downloadable IGCSE & GCSE Biology revision notes

In photosynthesis, carbon dioxide diffuses into the leaf and oxygen diffuses out of the leaf

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Lára Marie McIvor

Author: Lára Marie McIvor

Expertise: Biology, Psychology & Sociology Subject Lead

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.

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