Exchange Organs And Mass Transport Systems

Question 1

Single-Celled Organisms

Answer 1

• substances diffuse directly into the cell across cell-surface membrane
• diffusion rate is quick because small distances substances have to travel

Question 2

Multicellular organisms

Answer 2

• diffusion across outer membrane is too slow
• as cells deep within body have big distance between outside
• large animals have a low surface area to volume ratio
• need specialised exchange organs rather than using straight forward diffusion to absorb and excrete substances

Question 3

Mass Transport

Answer 3

• efficient system to carry substances to and from their individual cells
• mammals = circulatory system and blood carrying hormones, anti-bodies and waste like CO2
• plants=transport of water solutes in xylem and phloem

Question 4

Heat Exchange - Body Size

Answer 4

• rate of heat loss depends on SA
• large = difficult to lose heat
• small = lost more easily
• smaller organisms have a high metabolic rate so generate enough heat

Question 5

Heat Exchange - Body Shape

Answer 5

• Compact shape = small SA relative to volume so minimising heat loss
• less compact shape = large SA relative to volume so increases heat loss