Biodiversity in the Sonoran Desert pt.2

unit 2

What is the stomata and what is its primary function?

• gaps in the leaf that open and closed using guard cells

• primary function = gas exchange

What does it mean when the stomata is open? closed?

• open = guard cells are turgid; water is abundant

• closed = guard cells are flaccid; water is scarce

Can the stomata be forced open, if need be? if so, how is it forced open?

• yes; forced by hormones and ion flow 

What will happen to the stomata if there is an unlimited supply of water for a plant? 

• the stomata will stay open all the time

• intercellular spaces will have a high enough water concentration → cells stay turgid and make opening for stomata → gas exchange can happen normally 

What would happen if the stomata never opened?

• no photosynthesis and there would be oxygen toxicity; however, more water will be conserved

• example of plant tradeoffs

Describe the rate of H2O loss

• how fast water transpires increases with the gradient (diff.)

• water doesn’t always escape at the same rate

What are other factors that impact the rate of transpiration?

• temperature

• wind

• humidity

• surface area (# of stomata or leaf area)

What does the total amount of water transpired contingent on?

• the amount of time stomata are open and rate

• ex. on a hot, dry, windy day, a plant with closed stomata won’t lose any water

smaller gradient = ______ diffusion, and larger gradient = ______ diffusion

• slower

• faster

Why do plants in the Sonoran Desert have small leaf areas?

• b/c this is a product of few or small leaves and acts to limit water loss from stomata

How can winter annuals survive living in a place that gets so little rain, so infrequently?

2 strategies:

• when it does rain, grow really fast and hope you don’t dry out before you produce seeds

• limit how much water you lose and try to get through your life cycle slowly, but steadily

• this is why plants grow slower when it’s dry

• tradeoffs (they can risk growing fast w/ lots of gas exchange, but they might run out of water. they can risk growing slow w/ little gas exchange, but might get outcompeted by faster growing plants)

How can we measure the tradeoffs between growth rate and water level in plants?

• relative growth rate (RGR) = biomass gained/time

• water-use-efficiency (WUE) = carbon gained (growth)/water

What does it mean if a plant has high water-use-efficiency? What does it mean if its WUE is low?

• high WUE: conserves water

• low WUE: loses water quickly 

Why can’t a plant have high RGR AND high WUE? 

• b/c a plant cannot grow fast and conserve H2O simultaneously 

• essentially like asking why can’t a car go fast and maintain a high MPG

What can give a plant high RGR?

• having lots of leaves

• as leaf area increases, so does growth rate

• however, having lots of leaves is bad for water conservation

Describe the trade-off between rapid growth and drought tolerance

• negative relationship

• faster growers = water wasters (not drought tolerant)

• slow growers = water conservers (drought tolerant)

True or false: water precipitation is really unpredictable in the Sonoran Desert? 

true