Plant Science - Exam 4

what is hydrogen bonding

attraction between molecules to a hydrogen atom

what does hydrogen bonding result in

adhesion and cohesion

what are the main properties of water

adhesion and cohesion

what is adhesion

the attraction of molecules to other molecules of a different kind

what is cohesion

the attraction of molecules for other molecules of the same kind

what are the three main processes that water flows through

• bulk flow:

• diffusion

• osmosis

what is bulk flow

• one of the three movements of water (also known as mass flow)

• all molecules move together

• based on differences in potential energy

what is potential energy of water known as

water potential (lots of water = high potential / little water = low potential)

what is diffusion

• one of the three movements of water

• random movement of particles (solutes) in a solution from areas of high concentration to low

• movement of any other molecule other than water

what is active transport

to move molecules against their gradient that requires energy

what transport type is diffusion

passive

what direction will water always flow in

regions of high water potential to regions of low water potential

how does water move across during osmosis

through a semipermeable membrane

in a concentration of high solutes and low water concentrations what type of water potential would this be

low water potential

in a concentration of low solutes and high water concentrations what type of water potential would this be

high water potential

how do water molecules travel in osmosis

they travel from areas of high water molecules to areas of low water molecules

plants use the different properties in water to maintain what

turgor pressure (wall pressure)

what does turgor pressure mean

hydrostatic pressure in a cell (the vacuole pushing out and against the cell wall

what kind of solution does the inside of a plant cells vacuole consist of

hypertonic solution

what does wall pressure mean

force of cell wall opposing hydrostatic pressure

why does turgor pressure occur

because plant cells concentrate strong solutions of salts, sugars, and organic acids in their vacuoles creating a hypertonic solution. water then moves into the vacuole and the vacuole pushes against the cell wall

what does it mean for a plant to be turgid

the plant is rigid with the ability to stand upright on its own

what is plasmolysis

separation of the plasma membrane from the cell wall due to a lack of water

what type of solution do plant cells prefer to be in

hypotonic solution

wha would occur if a plant cell was placed into a hypertonic solution

the cell would experience plasmolysis

What is the difference between turgid, flaccid and plasmolyzed

• turgid means that the plant cell is in a hypotonic solution allowing for the plant to maintain turgid pressure and wall pressure through osmosis.

• flaccid means that the plant cell is in the beginning stages of exposure to a hypertonic solution and the cell is no longer able to maintain turgid pressure and wall pressure through osmosis as a result. The plasma membrane of the plant cell has begun to separate from the cell wall but the plant could still recover if exposed to a hypotonic solution to restore turgid pressure and wall pressure through osmosis.

• plasmolyzed means that the plant cell has been subjected to a hypertonic solution for a long enough duration that the plasma membrane has almost completed separated from the cell wall and turgid pressure and wall pressure are no longer present. At this point the plant cell cannot recover due to a lack of water.

what does imbibe mean

when plants take up water or absorb water

how do plants lose large quantities of water

through transpiration due to their open stomata on the leaves

how much water do plants lose from the water the uptake

plants lose 99% of the water they uptake to the atmosphere and trees can loose between 50 to 100 gallons a day

what is the absorption of water and the loss of water vapor through the stomata known as

transpiration

what is transpiration

the loss of water and absorption of water through the stomata of a plant and can occur from any above ground organ with leaves being the main culprit

why do plants need transportation

in order to photosynthesize

how is CO2 related to transpiration

the uptake of CO2 for photosynthesis is bound to transpiration

why is transpiration necessary for plants

the chief function of the leaf is photosynthesis and cell membranes are impervious to CO2 gas. As a result to pass into the protoplast, CO2 must go into solution requiring a moist cell surface

where does transpiration first occur

in the stomata

what is stomatal transpiration

the first type of transpiration to occur in a plant and occurs in two stages

what are the two stages that stomatal transpiration occurs in

• first evaporation of water from cell wall surfaces bordering the extracellular space

• then diffusion of resulting water vapor into the atmosphere via the stomata

how can the stomata prevent water loss

the opening and closing of the stomata prevents water loss through the leaf

what is the opening and closing of the stomata a result of

changes in turgor pressure

• high turgor pressure = turgid = open

• low turgor pressure = flacid = closed

what is radial micellation

radial orientation of cellulose microfibrils in the guard cell walls is required for pore opening

what does radial micellation prevent

it prevents lateral expansion of guard cells

what does radial micellation promote

it promotes longitudinal expansion

what type of transport requires energy to move molecules against their gradient

active transport

how are guard cells attached to each other

at their ends to each other

how does temperature affect the rate of transpiration

rate of water evaporation doubles for every 10° C increase in temperature

how does humidity affect the rate of transpiration

high humidity lessens the concentration gradient of water between a leaf and the environment

what is the affect of humid environments on leaf size

leaves are bigger in humid environments because there is no “fear” of losing water

how does air currents affect the rate of transpiration

air currents will change the concentration of water concentration outside of a leaf and as a result with increase the rate of transpiration

it lowers the “local” humidity at the leaf surface

is water pushed from the bottom or pulled from the top

its pulled from the top

what is the cohesion-tension theory

the theory that water is “pulled” up the plant through a series of water potential changes across cells

how does water travel through the plant

via the xylem

how does water travel through the xylem

through vessels and tracheids

what is surface tension

cohesion of water molecules

how do bubbles effect water flow through the xylem

it can break the continuity of water

what prevent embolisms in tracheary elements of the xylem

surface tension in bordered pit pair

what prevents an embolism from spreading in conifers

the torus prevents embolism from spreading

what is the maximum height for a tree

130 m or 427 ft

why can trees only grow a certain height

• tensile strength of water has a breaking point

• water stress on leaves due to gravity and increasing path-length resistance leads to poor photosynthesis

what did the study of redwoods indicate

the maximum tension is close to the point of embolism

what is primarily responsible for water absorption

root hairs

where are root hairs located

several mm above root tip

what are root hairs

young roots

how do root hairs increase absorption

by increasing surface area

how does water enter the root hairs

through the epidermis → cortex → endodermis → vascular cylinder

what is root pressure

positive pressure generated by roots in the absence of transpiration

whats the driving force in water uptake by the roots

the difference in water potential in soil and xylem

how can root pressure be enhanced

by secretion of ions/solutes into the xylem

what prevents the movement of ions out of the xylem

casparian strips in the endodermis

what is transpiration caused by

adhesion and cohesion

what is translocation

movement through the phloem also called assimilate transport

how do metabolites move through the phloem

through translocation

what direction does translocation move in

forwards and backwards from source to sink

what is a source

photosynthetic/storage tissue and producers of metabolites

what is a sink

tissue that cannot meet their own nutritional needs like fruit

what is the pressure-flow hypothesis

assimilates are transported from source to sink along a gradient of turgor pressure developed osmotically

what is the transpiration stream and what does it carry

the transpiration stream flows through the xylem and contains water and inorganic ions taken up by roots

what is the assimilate stream and what does it carry

the assimilate stream flows through the phloem and contains sucrose generated by the leaves

where do growing plant parts get more water and ions from

the assimilate stream

what is the definition of a hormone

a chemical signal (internal signal)

what does the greek word horman mean

to stimulate

what do hormones allow for within plants

communication among cells, tissues, and organs

what do hormones control within plants

shape growth, development and differentiation

where do hormones act in plants

in the cells around where they are produced or the location they are transported to

where are hormones synthesized in plants

many different regions

how do hormones control pants

through the expression of specific genes

why do hormones have to act to express specific genes from DNA

because all plant cells are genetically identical meaning function comes from expression

what are the five classic plant hormones

auxins, cytokinins, ethylene, abscisic acid, and gibberellins

what was the first plant hormone discovered

auxin

who discovered the plant hormone auxin

charles and francis darwin

what does auxin do

promotes growth on the dark side of a plant to extend toward light (phototropism)

what was concluded from the experiment with auxins and collars

the signal for light comes from the tip and influences the region of bending

what is the full name for Auxins

indoleacetic acid

where does the name indoleacetic acid come from

the indole ring and the acetic acid side chain

where is auxin primarily synthesized

in root and shoot meristems, leaf primordia, young leaves, and developing fruits and seeds (developing tissues)

when auxin can travel in both directions what type of transport is that called

non-polar transport

what are the characteristics of non-polar transport in the hormone auxin

• can go both directions

• usually carried in phloem

• based on sink/source movement

• most hormones can utilize this transport method

when auxin can travel in only one direction what type of transport is that called

polar transport

what are the characteristics of polar transport in the hormone auxin

• one direction

• carried in vascular parenchyma

• allows for movement independent of phloem transport based on changing sinks and sources

• basipetal transport (away from apex) and acropetal transport (toward the apex)

• only auxin can transport polarly

what is basipetal transport

transport away from apex

what is acropetal transport

transport toward the apex