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Biology contentExchange and transport systems
Genetic information, variation and relationships between organisms
,Exchange and transport systems
Size and surface
area
• Every organism needs to exchange things with the
environment.
• Cells need to take in oxygen for aerobic respiration.
• Cells need to excrete waste products like carbon dioxide
and urea.
• Most organisms need to stay at the same temperature, so
heat needs to be exchanged.
Surface area: volume ratio
• Surface area= top and bottom surfaces of cube + four
sides of cube.
• Volume= length x width x height.
,Exchange and transport systems
Respiration
• Glucose + oxygen -> carbon dioxide + water.
• Uses for the energy released by respiration:
Working your muscles
Growth and repair of cells
Building larger molecules from smaller ones e.g., proteins from amino acids
Chemical reactions to take place
Absorbing molecules in active transport
, Exchange and transport systems
Smaller organisms
• Chlamydomonas are single-celled organisms that live in freshwater ponds.
• They contain flagella and a chloroplast.
• Oxygen for respiration and carbon dioxide for photosynthesis are dissolved in the
surrounding water and diffuse into the cell.
• The short diffusion pathway means diffusion can occur for the gas exchange they n
o As an organism’s size increases, the time taken for oxygen to diffuse from the cell s
membrane to the tissues become too great.
The surface area : volume ratio decreases.
It is too slow to provide oxygen for multicellular organisms.
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