AP Biology Transpiration and Stomata
Living things must exchange matter with the environment to survive, Example: Gas Exchange in Plants photosynthesis cellular respiration
1. During which hours does a plant produce a net excess of O 2? Explain why: 2. During which hours does a plant consume more O 2 than it makes? Explain why:
1. Describe the path of H 2 0 through a land plant. 2. Describe and explain the direction of gasexchange in the Plant s a. Roots b. Leaves
1. Where is water entering and where is it exiting the plant? 2. What is the direction of water movement? 3. How is water moved against gravity? 4. What is the direction of sugar movement? 5. What is the mechanism of this movement? 6. What is the role of light energy in both processes?
1. What is the common ancestor to all plants? 2. When did the first terrestrial plants arise? 3. When did vascular plants arise?
Aquatic Plants Diffusion of O 2 and CO 2 from the water directly into and out of cells on the plant s surface Cold water holds more gas (more primary productivity) No water limitation
Early Terrestrial Plants Life emerged onto land ex. Moss Tied in moist areas Very simple vascular tissue to transport water over short distances (restricts plant size) Mobile sperm (require water)
1. Describe the structure of the root-system shown above? 2. What is the function of the plant s root system? 3. How do root hairs affect total surface area of the root system?
Terrestrial Plants: Xylem Xylem cells line up end-toend; ends are porous Water is transported through the xylem (like water through pipes) This allows water to move from roots to leaves over long distances (plants can become tall)
waxy cuticle Terrestrial plants need adaptations to exchange matter with the environment: Roots (H 2 O & minerals) Xylem for watertransport Adaptations to prevent excessive water-loss: Stoma = a pore that allows CO 2 in and O 2 and H 2 O out Thick, waxy cuticle on leaves Stomata
Stomata opening and closing: http://www.youtube.com/watch?v=cfx4jrspaus
Stoma 1. Name & describe two structural features of the leaf that are designed to limit water-loss: 2. As it relates to water, what is the function of a terrestrial plant s roots? 3. When a leaf is in the light and its stomata are open, in which direction are the following moving through the stomata: H 2 O, CO 2, O 2?
Trade-Offs Guard cell Plants must open stomata to obtain CO 2 during photosynthesis But, when stomata are open a plant experiences water-loss Excess water-loss will cause wilting and the stomata will close Photosynthesis stops without continued CO 2
Plant-Reactions to Water-Stress Water stress results in release of ABA, which causes stomata to close Some plants can fold their leaves Ocotillo shed their leaves in response to seasonal drought
Adaptations Sunken stomata further reduce water-loss
Adaptations Cacti only open their stomata at night when it is cooler (they practice a different form of photosynthesis) Cacti also have water-storage capabilities
Driving Speed Homeostasis: Negative Feedback Loop
Stomata Close Plant Water Potential (hydration homeostasis) [CO2] water potential drops Stomata open Water potential [CO 2 ] Water stress: Hormone ABA released Water potential high, light, [CO2)]
Stomata Close Water potential [CO 2 ] Water stress: Hormone ABA released Plant Water Potential (hydration homeostasis) [CO2] water potential drops Water potential high, light, [CO2)] Stomata open
The Story in the Stomata 1. Describe the trade-off involving stomata: 2. Summarize and explain the relationship between stomata density and atmospheric [CO 2 ]: 3. Explain how could plant fossils be used as indicators of past climates and atmospheric conditions:
1. Evidence for communication? Via shoot or root-system? Justify: 2. Why block chemicals in the soil? 3. Why after 1 hr. plants 9-11 similar to 7-8? 4. Why the control?
Match the species # with the description of its environment (justify your match): Submerged (aquatic) plant Tree that grows in the open savannah grasslands Small bush that grows in the tropical rainforest A plant that grows in a lake, but whose leaves float on the surface of the water Species Density of stomata top 1 75 125 2 0 75 3 0 0 5 57 0 Density of stomata bottom
How can you calculate the density of stomata? Diameter = 0.4 mm # stomata 6 stomata = 6 stomata π(r) 2 π(0.2 mm) 2 0.1256 mm 2 X40 objective = 48 stomata/mm 2
For which type of plant would you expect to find: Stomata on both top and bottom leaf surfaces No stomata Stomata only on the top Justify your selection:
For which type of plant would you expect to find: Stomata on both top and bottom leaf surfaces Emergent plant such as the cattails because both surfaces are exposed to air and the stomata are necessary for gas-exchange but also help to limit water-loss due to transpiration. No stomata The aquatic plant will do gas exchange via diffusion of gases from water through the entire leaf surface area. Water is also not limiting because the plant is submerged. Stomata only on the top The water lily only has its upper surface exposed to air. Here it will want to control water-loss via stomata regulation. The bottom surface is exposed to water, plant does not have to control for water loss here.
Why do many terrestrial plants have stomata only on the bottom of their leaves (or more on the bottom than top)?
Why do many terrestrial plants have stomata only on the bottom of their leaves (or more on the bottom than top)? The top of the leaves are exposed to more sunlight, which would speed evaporation from stomata. Concentrating stomata on the leaf bottoms helps to slow water loss via transpiration.
There are trees over 330 ft. (100 m) tall. They don t have hearts to pump fluids, yet they move water this great distance against the force of gravity. Which acronym can help you remember the mechanism?
Water is a Polar Molecule Oxygen is more electronegative than Hydrogen - it exerts a stronger pull on the electrons
partial- partial+ partial+ Water is a polar molecule. Oxygen has a partial negative (δ-) charge. Hydrogen has a partial (δ+) charge.
Emergent Properties of Water Molecules Hydrogen bonds are electrostatic attraction between δ + and δ Hydrogen bonds are weaker than covalent bonds In liquid water they constantly break and reform Hydrogen bonds are responsible for water s special properties such as cohesion and adhesion δ+ δ + δ- δ + δ- Hydrogen bond δ+ δ-
1. Describe the role of adhesion: H 2 O H- bonds with the xylem walls; opposes downward pull of gravity 2. Describe the role of cohesion: H 2 O H- bonds with each other, exerting a pull on the watercolumn as each H 2 O molecule exits a stomata
1. What is the pattern in Ψ from the soil to the roots? 2. Why does water move from the soil into the roots? 3. What is the pattern in Ψ from the roots to the shoots? 4. What is the pattern in Ψ from the leaves to the outside air? 5. Why does water exit the stomata into the air?
1. What is the pattern in Ψ from the soil to the roots? Ψ decreases 2. Why does water move from the soil into the roots? Ψ decreases 3. What is the pattern in Ψ from the roots to the shoots? Ψ decreases 4. What is the pattern in Ψ from the leaves to the outside air? Ψ decreases 5. Why does water exit the stomata into the air? H 2 O from Ψ Ψ
Transpiration Water diffuses through plant tissues, entering through the roots and exiting via leaf-pores called stomata Adhesion Cohesion Tension Water molecules adhere to xylem vessels due to H-bonding Water molecules stick to each other due to H-bonding As H 2 O molecules evaporate from the stomata, they create a pull on the molecules below, creating a tension that pulls water up against gravity
An acre of actively growing corn can transpire 3,000 4,000 gallons (11,000 15,000 liters) of water a day
Describe & explain the relationship between the variables from 0 60% open stomata. Do the same for >60% open stomata.
As % open stomata from 0 to 60, so does the rate of transpiration because with more stomata open there is diffusion between the leaf and the environment. Above 60%, there is no change in the rate of transpiration because another factor becomes limiting (i.e. rate of water movement, humidity, etc.).
1. Calculate the average rate of transpiration for species A. 2. Calculate the average rate of transpiration for species B. 3. Which species had the higher rate of transpiration? Justify: 4. List and discuss three structural or physiological adaptations that could account for the differences:
Because the slope of line A is steeper than B and 0.24 ml H 2 O/100g/min is higher than 0.14 H 2 O/100g/min
b.
1. Show a graph of the relationship between temperature and the rate of transpiration (make sure you label your axes) 2. Discuss the mechanism by which temperature effects the rate of transpiration:
As temp., kinetic energy of molecules, thus the speed of diffusion (evaporation of water from stomata openings) will increase. At a certain temp. the rate will level off because other factors now limit the rate of transpiration.
1. Show a graph of the relationship between relative humidity and the rate of transpiration (make sure you label your axes and note that relative humidity runs on a scale from 0 to 100%) 2. Discuss the mechanism by which humidity effects the rate of transpiration:
As relative humidity, transpiration rate, because as humidity, the gradient in Ψ between the leaf and the air, thus water loss.
Boundary layer of high humidity, difference in Ψ inside and outside the leaf is, so transpiration rate Wind blows away boundary layer Difference in Ψ (or osmotic potential) inside and outside the leaf, so transpiration rate
The effect of light on the rate of transpiration
See video on potometer set-up https://www.youtube.com/watch?v=ce-4q2nxine
Which condition would result in a higher rate of transpiration? Explain: 1. Full sunlight or shady environment 2. Humid or dry environment 3. Still or breezy environment Go and inspect your lab station: Discuss methods Discuss how to measure ml using the pipette