Lab 5: Transpiration

Transpiration =

the loss of water vapor by plant parts (usually the leaves)

Stomata =

epidermal openings on the undersides of the leaves

From what openings does water vapor exit plants?

the stomata

What is the purpose of transpiration?

gas exchange for photosynthesis, cools the plant, capillary: water from the roots and stems is pulled into the leaves

What is the problem?

plants are not well adjusted to retain water, so they lose a significant amount of water daily

Guard cells =

open and close the stomata to regulate water losee

How many guard cells are there per stomatal opening?

2

Thickened cuticle =

waxy covering on the leaves

What are all the adaptations that help prevent water loss?

guard cells, thickened cuticle, reduced leaves, and modified photosynthetic pathway

What kind of photosynthesis allows the plant to keep the stomata closed during the day?

C4 and CAM

What can be used to measure rate of transpiration?

a potometer

How is the transpiration rate calculated?

by measuring the distance traveled by water over time

What does the speed of the water movement mean for transpiration rate?

the faster the water moves, the greater the rate of water uptake & the greater the transpiration rate

What happens to transpiration rate if you increase the temperature?

it increases because evaporation & diffusion are faster at higher temps

What happens to transpiration rate if you decrease the humidity?

it will increase

Humidity decreases:

the concentration gradient between the inside and outside of the leaf

What happens to transpiration rate if you increase the wind speed?

it will increase since it’ll also increase the rate of diffusion of water vapor from the leaf

What happens to transpiration rate if you increase the light intensity?

it will increase

Why does increasing the light intensity increase transpiration rate?

the stomata open wider to allow more carbon dioxide into the leaf for photosynthesis

What is the key difference between C3, C4, and CAM photosynthesis?

the initial carbon compound produced during carbon fixation

What are the differences in the initial carbon compound produced during carbon fixation?

C3 plants creating a 3-carbon compound, C4 plants producing a 4-carbon intermediate, and CAM plants storing carbon dioxide at night to fix it during the day

What is the most common photosynthetic pathway?

C3

What are C4 and CAM photosynthetic pathways adaptations to?

they are adaptations to hot, dry climates

C3 plants often go dormant during:

dry season

C3 plants are often plants of:

moist forests, winter annual weeds, or spring ephemerals

What is C3 plants?

single reaction, occurs in mesophyll

Where do the reactions occur in C4 plants?

light dependent reaction occurs in mesophyll, but light independent reaction occurs in bundle sheath cells

What does C4 allow for?

partial closing of stomata in hot/dry conditions

C4 is often:

fire-adapted; dominate in grasslands and open woodlands

When do the reactions occur in CAM plants?

light independent reaction occurs at night and the stomata remain closed during the day

What are the pros and cons of CAM?

inefficient, but virtually no water loss via stomata

Where is CAM found?

dominate in extreme environments — ex. thin-soiled glades, deep xeric sands, hypersaline soils, and the most arid deserts

How does light affect the stomata in transpiration?

causes them to open, which significantly increases the rate of transpiration

How does temperature affect the stomata in transpiration?

the stomata on a plant leaf tend to open wider, leading to an increased rate of transpiration

How does air flow affect the stomata in transpiration?

increases the rate of transpiration by removing the humid air layer around a leaf

How does humidity affect the stomata in transpiration?

High humidity causes stomata to close, reducing the rate of transpiration, while low humidity stimulates stomata to open, increasing the rate of transpiration

Why might a plant keep its stomata closed under dry conditions?

to prevent excessive water loss through transpiration

What would be problematic with keeping the stomata closed?

it significantly limits a plant's ability to take in carbon dioxide necessary for photosynthesis