Limiting Water Loss (Insects/Plants) Flashcards
What is the main conflict in gas exchange fr terrestrial organisms like insects and plants?
The need for efficient gas exchange opposes the requirement to conserve water, as features that increases gas exchange also increase water loss
How do terrestrial organisms balance gas exchange and water conservation?
They limit water loss without compromising gas exchange efficiency by having adaptations like internal gas exchange surfaces and controlling openings (eg. stomata + spiracles)
Why are gas exchange surfaces located inside the body in terrestrial organisms?
It keeps the air at the exchange surface almost 100% saturated with water vapour, reducing evaporation and water loss
Why is water loss a problem for terrestrial insects?
Water can easily evaporate from their body surface, leading to dehydration
Why is there a conflict between gas exchange and water conservation in insects?
Efficient gas exchange requires a thin, permeable surface with a large area, but those features also increase water loss
What adaptations do insects have to reduce water loss?
1/ A small surface area to volume ratio, which minimises areas where water can be lost
2/ Waterproof body covering - rigid chitin exoskeleton with a waterproof cuticle
3/ Spiracles can close, which prevents water loss but limits oxygen intake, so it mainly occurs when the insects are at rest
Why can’t insects use their body surface for gas exchange like single - celled organisms?
Their waterproof exoskeleton and small surface area to volume ratio prevent efficient diffusion, so they rely on an internal tracheal system for gas exchange
Why can’t plants reduce their surface area to limit water loss like insects?
Plants need a large surface area to capture light for photosynthesis and for gas exchange
What are two basic ways terrestrial plants reduce water loss?
1/ Waterproof covering over parts of the leaves
2/ Closing the stomata when necessary to prevent excessive water loss
What are xerophytes?
Xerophytes are plants adapted to living in dry conditions where water supply is restricted
Why do xerophytes need special adaptations?
Without adaptations, they would lose too much water through transpiration, leading to desiccation (drying out) and death
How do xerophytes reduce their water loss?
They have leaf modifications to limit water loss through evaporation, as most water loss occurs through leaves
How does a thick cuticle help reduce water loss in xerophytes?
A waxy cuticle forms a waterproof barrier, reducing evaporation. A thicker cuticle further decreases water loss
How does rolling up leaves help reduce water loss?
It traps a still air region inside the rolled leaf, which becomes saturated with water vapour, preventing a water potential gradient and reducing evaporation
How do hair leaves help reduce water loss?
Hairs trap moist air near the leaf surface, reducing the water potential gradient between inside and outside, thus lowering evaporation
How do stomata in pits or grooves reduce water loss?
Stomata in pits trap moist air, reducing the water potential gradient and slowing evaporation
How does a reduced surface area to volume ratio help xerophytes conserve water?
Smaller, circular leaves reduce diffusion rate and water loss, while still allowing enough photosynthesis
