6.5 Limiting water loss

Question 1

Why must terrestrial organisms balance water loss and gas exchange?

Answer 1

Water easily evaporates from their body surfaces, making them dehydrated. many of the adaptations for efficient gas exchange increase evaporation of water.

Question 2

What are the adaptations in insects to limit water loss?

Answer 2

• SMALL SURFACE AREA TO VOLUME RATIO: minimizes the area over which water is lost.
• WATERPROOF COVERINGS: rigid outer skeleton of chitin covered with a waterproof cuticle.
• SPIRACLES: can be opened and closed to prevent water loss, conflicting the need for oxygen

Question 3

What are the similarities between limiting water loss in plants and insects?

Answer 3

• plants also have a waterproof covering (waxy cuticle)
• plants can open and close the stomata
• *plants cannot have a large SA to volume ratio as it would limit photosynthesis**

Question 4

What are xerophytes?

Answer 4

Plants adapted to living in areas with a short supply of water.

Question 5

how are xerophytes adapted to living with a limited water supply?

Answer 5

• THICKER CUTICLE: less water can escape
• ROLLING UP OF LEAVES: protects the lower epidermis, and the stomata. traps some air which becomes saturated with water so there is no water potential gradient.
• HAIRY LEAVES: Traps moist air next to the epidermis, reducing the water potential gradient
• STOMATA PITS/GROOVES: traps moist air to reduce water potential gradient.
• REDUCED LEAF SA TO VOLUME RATIO: makes a more efficient exchange surface. Must be balanced against the need for photosynthesis.