Transpiration Module 10

Question 1

Leaf gas exchange

Answer 1

Control of gas exchange through the stomata
90% occurs through the stomata, 5-10% occurs through the cuticle, this can vary depending on the size of the cuticle

Question 2

How does the stomata regulate gas exchange

Answer 2

When they are open water evaporates and CO2 is able to enter for photosynthesis and calvin cycle
When they close water is conserved but CO2 cannot enter

Question 3

Transpiration is what?

Answer 3

The loss of water through the leaf(its a process)

Question 4

What is the best control for water loss?

Answer 4

Having less stomatas and closing the stomata

Question 5

Carbon Dioxide Exchange

Answer 5

approximately 0.04% of air is CO2
CO2 enters through the stomata which drives PS
increasing CO2 entry is accomplished by opening the stomata or increasing number of stomata

Question 6

When does the atmosphere have more CO2?

Answer 6

In north America it is in December and January because the plants drop their leaves and don’t use CO2

Question 7

Cost/benefit of Gas Exchange

Answer 7

for every gram of CO2 fixed, the plant loses 250-600g of water
plants are constantly balancing water loss with CO2 entry by controlling the stomatal openings

Question 8

Function of Transpiration

Answer 8

beneficial, keeps water column intact and moving
cools the leaf by 10-15 degrees celcius
moves nutrients (and herbicides) in transpiration streams from soil to leaf
no energy is required
enables capture of nutrients from a volume of soil

Question 9

Transpiration Processes

Answer 9

Evaporation and Diffusion

Question 10

Evaporation

Answer 10

takes place in the sub-stomal chambers
Inside the leaf, water is taken from surrounding cells
this creates a chain reaction, takes from the stem, from the roots, from the soil

Question 11

Diffusion

Answer 11

the movement of molecules from a region of high to low concentration (dye in water)
as water is diffusing out, CO2 molecules are diffusing into the leaf

Question 12

Environmental factors that affect transpiration

Answer 12

Temperature
Humidity
Wind
Light

Question 13

Temperature Factor

Answer 13

very important
evaporation rate doubles per 10C rise in temp, up until a point
transpiration increases with air temperature (until 30 to 35C)
if moisture is available leaf temperature probably does not exceed 30-35C due to evaporative cooling
if restricted, leaf temp will rise

Question 14

Humidity Factor

Answer 14

refers to the amount of water in the air
transpiration is higher if air in stomates is moist and outside air is dry

Question 15

Wind Factor

Answer 15

transpiration increases on windy days
air currents move water vapour away from the leaf
affected by the leaf shape, pubescence (little tiny hairs that can block wind, a boundary layer)

Question 16

Light Factor

Answer 16

light striking a leaf tends to increase leaf temperature, this increasing transpiration rates
light increases PS, which decreases CO2, which causes stomates to open

Question 17

Daily cycle of transpiration for most plants

Answer 17

early in the morning the day is cooler (low transpiration rate)
midday the stomates close to avoid excessive water loss
later in the day, it is cooler, stomates open
dark period stomates are closed, plants can’t use CO2 at night

Question 18

Hanging Laundry

Answer 18

think about how quickly clothes dry when they hang outside
sunny quickly
cold wet slowly
transpiration is low at night

Question 19

When do cacti transpire?

Answer 19

at night
it’s very hot and sunny during the day so they save water and then transpire at night

Question 20

Midday wilting

Answer 20

transpiration in plants is greatest on moist soils on hot, sunny, windy days
transpiration may exceed the plant’s ability to take up water, and midday wilt occurs
leaves wilt but they may still photosynthesize
overnight the plant moisture is replenished (water is taken up by roots)
if a plant remains wilted overnight, then the plant has severe water deficits (heat stress)

Question 21

What features do plants have to regulate water loss? (8)

Answer 21

1.reduce stomate numbers (reduces CO2)
2.stomates on the lower leaf surface
3.sunken stomata
4.epidermal hairs (reduces wind velocity against the opening)
5.bulliform cells (plant can roll to reduce SA and light interception)
6.thickened cuticle
7.lower SA surface:volume ratio (pines)
8.C3 vs C4 vs CAM

Question 22

C3 vs C4 bs CAM

Answer 22

C3 is plant like wheat and cereals
C4 is tropical plants, can withstand drought
CAM is cacti

Question 23

How does water move through plant parts?

Answer 23

Water pull, root pressure, and capillary action

Question 24

What is water pull?

Answer 24

as each water molecule evaporates into the substomatal chamber, it pulls another water molecule from below
water is sucked through the plant
possible because of the cohesive properties of water
no energy is required
water columns of cut twigs recede quickly
tree trunk is smaller during the day

Question 25

What is the chain reaction of water movement?

Answer 25

water will be replaced from close by cells
if there is a break in the link this process will not occur
think of when you put a flower in a vase, you cut the end so water flows

Question 26

Root pressure (push)

Answer 26

a pump priming device
at night no transpiration but there is continued uptake of water into the xylem (in response to the high concentration of minerals)
will push water and nutrients up xylem in small herbaceous plants (guttation)

Question 27

What is guttation?

Answer 27

Guttation is the exudation of drops of xylem sap on the tips or edges of leaves of some vascular plants

Question 28

Capillary Action

Answer 28

Capillary action is when liquid flows through narrow spaces without external forces, such as gravity
the liquid’s movement is aided by intermolecular forces present in between the liquid and solid surface