9.1 - 9.2

Identify the manipulated, responding and controlled variables in an experiment to test the effect of an abiotic factor on the rate of transpiration.

Responding V.: Rate of transpiration; % change of mass (dependent—what you choose to measure). Manip. V.: Temp; humidity, light, wind etc. (independent—what you choose to change). Controlled V.: Factors that could affect the responding variable if not held constant.

Define cohesion.​

Cohesion: Water bonding to other water molecules.

Describe the use of a potometer to measure transpiration rates.

A potometer is used to measure transpiration rates by measuring the amount of water taken by a plant. A whole plant can also be used to measure transpiration. The roots are sealed in a bag and the change in mass of the plant is determined. Any loss of mass is due to evaporation of water out of the leaf.

Outline gas exchange that occurs through leaf stomata.

Leaves are the primary plant organ for photosynthesis (CO2 + Water = Glucose + O2). The lower leaf has pores called the stomata which allows for gas exchange in/out of the leaf. During the day, when photosynthesis is happening, there is net H2O and O2 out of leaf and net CO2 into the leaf. Guard cells are on either side of the stomata can open and close the pores to control the loss of water. The loss of water out of the lead through stomata is due to evaporation, when water is exposed to air the molecules break off.

Outline strategies used by xerophytes and halophytes to reduce water loss. ​

1) Thicker wavy cuticle: prevents water loss from the surface as it reduces the number of stomata. 2) Reduced # of stomata/having stomata pits surrounded by hair: moist air is trapped; reduce concentration gradient and water loss. 3) Reduced leaves w/ photosynthetic stem/rolled leaves: reduced surface area exposure from which transpiration can occur. 4) Stomata closes during the day/opens night CAM physiology: water loss is more rapid during the day so CO2 taxation at night means water loss is minimized. 5) Low growth: low growing plants are less exposed to wind and more likely to be shaded. 6) Deep or wide roots: allows plants to tape water sources. 7) Freshly or succulent stem/leaves: water can be stored in tissues for times of low availability. 8) Tissue partioning: plants might concentrate salt in certain leaves which eventually drops off.

Outline structures and mechanisms involved in the flow of water from roots to leaves.

1) Water enters the roots through osmosis. 2) Water is transported through the xylem. 3) Cohesion and adhesion maintain a chain of water in the xylem from roots to leaves. 4) Water evaporates from the leaves through stomata. 5) The rate of water loss depends on abiotic factors.

Outline why sucrose is used for phloem transport, as opposed to glucose.

Glucose is reactive and metabolizes in cellular respiration. Sucrose is less reactive and would not metabolize during transport.

Explain use of models in science.

Model is a representation of an idea/object/process that is used to describe a phenomena that can't be experienced directly. • Predicts and shows relationships among variables betweens system and their component in the natural world.

Compare the symplastic and apoplastic pathways of water transport through the root.

Once water is the the roots, it moves through two paths. Apoplast pathway: water moves from root hairs to xylem between cells, the cell walls. The water doesn't go into a plant. Symplast pathway: water moves from roots hairs to xylem within cells. Cytoplasm through channels between cells called plasmodesmata.

Explain why roots are hypertonic relative to the soil.

Roots are hypertonic to the soil with about 100x the concentration of ion such as Ca2+, Mg2+, K+, Na2+. Roots are hypertonic because they activity transport ions into them. Water then moves from hypotonic (soil) to the hypertonic (roots) passively by osmosis. _Roots has cellular extensions which further increases the surface_

Outline the role of active transport in maintaining root tonicity.

Roots are hypertonic to the soil with about 100x the concentration of ion such as Ca2+, Mg2+, K+, Na2+. Roots are hypertonic because they activity transport ions into them. Water then moves from hypotonic (soil) to the hypertonic (roots) passively by osmosis. _Roots has cellular extensions which further increases the surface_

State that phloem transport is bidirectional.

Sometimes the sink can become the source and vice-versa. The tube in the phloem must be able to transport sap either directions (with gravity; opposite gravity).

List example source and sink tissues.

Source: any plant structures where carbs are produced (carrot's leaves). Sink: any plant structures which carbs are used (carrot).

Describe the active transport of sucrose into the phloem via a co-transport protein.

The active transport of sucrose to the phloem is also known as phloem loading. • Hydrogen ions are ACTIVELY transported out of phloem cells by proton pumps. • Concentration of hydrogen ions consequently builds up outside of the cell creating a proton gradient. •Hydrogen ions passively diffuse back to the phloem cell via a co-transport protein which carries sucrose with it (against gradient concentration of glucose). • This results in a build0up of sucrose within the phloem sieve tube for subsequent transport of the source.

Describe structure of xylem.

The xylem is a set of continuous tubes. These tubes are formed of dead cells. They are hollow (no cytoplasm). There are no end walls, so there is a continuous tube of cells connected end to end. The cell walls are lignified with lignin (impermeable to water.)

Define translocation, phloem sap, source and sink.

Translocation: the transport of organic solutes in a plant. Phloem sap: is a thick, sugary fluid made primary of water and dissolved sugars and amino acids. Source: any plant structures where carbs are produced (carrot's leaves). Sink: any plant structures which carbs are used (carrot).

Explain the decrease in pressure and transpiration-pull that results from evaporation of water from the leaf.

Transpiration Pull: The upward movement of water in the plant is due to the "pull" cause by the evaporation of water at the stomata. Neg. Pressure: • Water resists evaporation due to surface tension. • As water evaporates, the pulls the next water in the chain up due to cohesion. Pos. Pressure: • At the roots, water is pushed via osmosis die to concentration gradient.

State the transpiration is a passive processes.

Transpiration Pull: The upward movement of water in the plant is due to the "pull" cause by the evaporation of water at the stomata. Neg. Pressure: • Water resists evaporation due to surface tension. • As water evaporates, the pulls the next water in the chain up due to cohesion. Pos. Pressure: • At the roots, water is pushed via osmosis die to concentration gradient.

Define transpiration.

Transpiration is the lost of water vapor from the stems and leaves of the plant.

Outline how xylem is able to maintain rigidity even under low pressure or mechanical disturbance.

Walls of the xylem tube are thickened by a polymer called LIGNIN, provide extra rigidity and support so they can withstand very low pressures without collapsing.

Outline polarity of water molecule.

Water is POLAR. Unequal sharing of electrons between oxygen and hydrogen.

Define xerophyte and halophytic.

Xero(day)phyte: plant that is adapted to live in a habitat with little liquid water. They're at risk for high transpiration rates due to high temperatures and low humidity, such as the desert of ice/snow regions. halo(salt)phytes: plants that are adapted to live in a habitat with high salinity. They lose a lot of water due to the surrounding and soil being hypertonic.