The need of exchange surface

• Most animals and plants consist of different types of cells organised as tissues, organs and systems.
• The human respiratory system is a body system adapted for efficient gas exchange.
• Organisms need to take in food, oxygen, water, and other essential substances from the environment.
• Plants also need carbon dioxide, a gaseous compound of carbon and oxygen, which is a by-product of respiration, and which is needed by plants for photosynthesis.
• Oxygen is produced as a by-product of photosynthesis.
• Algae subsumed within plants and some bacteria are also photosynthetic.
• Organisms need to remove waste substances.
• Small organisms exchange these essential and waste substances between themselves and the environment over their body surface.
• Inside their bodies, in small organisms, substances don’t have to move far.
• The size of their surface, or surface area, defines how quickly they can absorb substances.
• The size of their volume defines how much of these substances they need.
• Multicellular organisms increase in size, they face two problems: their surface area does not increase as fast as the volume and diffusion is not quick enough to move substances to where they’re needed in the organism’s body.
• Body systems that add additional absorbing area to exchange surfaces include the human respiratory system.
• Diffusion is not quick enough to move substances to where they’re needed in the organism’s body.
• A transport system is a solution to the problem of diffusion not being quick enough to move substances to where they’re needed in the organism’s body.