3A.1 Size & Surface Area

3A.1 Size & Surface Area

Exchange of Substances with the Environment

• Every organism needs to exchange substances with it's environment, no matter what size it is.
• Every organism needs oxygen and nutrients for respiration and create waste products such as carbon dioxide and urea, that need to be removed.
• Most organisms need to remain at the same temperature, so heat is exchanged as well.

Surface Area : Volume Ratio

• Surface area : volume ratio affects how quickly substances are exchanged.
• Smaller organisms have a higher surface are : volume ratio than larger organisms.

Exchange Organs in Single-celled Organisms

• All organisms need to be supplied with substances for respiration and have waste substances removed.
• These substances can diffuse directly into & out of the cell across the cell membrane.
• Diffusion rate is quick because of a short diffusion pathway (distance needed to travel).

Energy Organs in Multicellular Organisms

• Diffusion across the outer membranes is too slow  because:
• 1. Cells are too deep in the body, there is a large distance between them and…