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Flashcards in Transport In Plants Deck (25):

Explain how water enters a plant root from the soil and travels through to the endodermis

Water enters root hair cell by osmosis
because active uptake of mineral ions has created a water potential gradient
Water moves through the cortex down a water potential gradient
Through cell vacuoles/symplastic pathway
Through cell walls/apoplastic pathway


Cause of root pressure?

Active transport by endodermis
Salts into xylem
Lowers water potential in xylem
Water enters by osmosis


Why xylem vessels contain lignin walls and are hollow?

Lignin... Resists tension of water column/provides support/strength
maintains column of water
prevent water loss

Hollow because unrestricted water flow/continuous column/maintains transpiration stream


How does the graph support cohesion-tension theory

Movement starts/peaks earlier in branches higher up
Creates tension/negative pressure/pull


Why cut shoot under water

Prevent air entering/continuous column of water


Why water uptake was not equivalent to transpiration rate/ why transpiration rate does not truly measure rate of transpiration

Water used to provide turgidity
Used in photosynthesis
Water produced in respiration
Apparatus not sealed/leaks


Adaptations of plants for living in desert conditions

Shallow roots enable rapid uptake of rainfall (in x or z)
Widespread allow collection of large volume of water
Swollen stem for water storage
Deep roots for accessing deep groundwater
Small/no leaves so little transpiration


Purpose of reservoir (potometer experiment)

Can take repeat measurements- returns bubble to start/ this is done by opening/using tap/add water from reservoir


Give two precautions students should take to get reliable measurements when setting up
Potometer to measure water uptake by plant shoot?

Seal joints/ensure airtight/ensure watertight
Cut shoot under water
Cut shoot at a slant
Dry off leaves
Insert into apparatus under water
Ensure no air bubbles present
Shut tap
Note where bubble is at start/move bubble to the start position


Explain why transpiration increases when temperature increases

Molecules have more kinetic energy
Faster diffusion of water/more evaporation of water as temperature increases in leaf
Diffusion relates to movement of water


Explain how xylem tissue is adapted to its function?

Long cells/tubes with no end walls
Continuous water columns
No cytoplasm/no organelles
To impede/allows easier water flow
Lignin- support/withstand tension/waterproof/keeps water in cells/pits in walls/adhesive
Pits in walls to allow lateral movement m/get round blocked vessels


Why diameter of tree decreases during the day due to cohesion-tension theory?

Adhesion/ attraction of water molecules to the xylem walls
Results in tension as water pulled up stem
Pulling in walls


Describe how a high pressure is produced in the leaves

Water potential becomes more negative as sugars enter the phloem
Water enters phloem by osmosis
Increased volume of water causes increased pressure


Describe the mass flow hypothesis for the mechanism of translocation in plants

In source/ leaf sugars are actively transported into phloem
By companion cells
Lowers water potential of sieve cell/tube and water enters by osmosis
Increase in pressure causes mass movement (towards sink/root)
Sugars used/converted in respiration/ for storage as starch


Adaptations of sieve tube elements

Elongated elements
Joined end to end
Pores in end walls/perforated end plates/sieve pores
Little cytoplasm/thin layer of cytoplasm
No nucleus/ few organelles


Describe how assimilated (sucrose) are loaded in the phloem

Active transport of H+ ions into cell wall spaces of companion cells
Sucrose moves with H+ ions by co-transport
Creates H+ ions diffusion/concentration gradient
H+ move by facilitated diffusion into sieve tube elements
Sucrose moves with the H+ ions by co-transport


What is the apoplast pathway

Pathway from cells along cell walls/ through intercellular spaces and out through stomata
By diffusion
Down a water potential gradient/diffusion


Adaptations of xerophytes

Sunken stomata- reduce air movement/diffusion gradient
Rolled leaves- reduce surface area
Enclose still air around stomata
Thick Waxy cuticle, reduce cuticular evaporation/impermeable to water
Few stomata, to reduce as for diffusion
Small leaves, reduce surface area for diffusion
=shape of leaf/rounded/small surface area
Small surface area to volume ratio means less water is lost


Cohesion-tension theory

Water evaporates/transpires
Reduces water potential/increases osmotic gradient
Moves via apoplast pathway
Water drawn out of xylem
Creates tension/pulling effect/negative pressure
Cohesion between water molecules due to hydrogen bonding/water moves as a column


Features of the endodermis

Has casparian bands
Which are impermeable/waterproof
Lower water potential in the cytoplasm of endodermis cell
Enters symplastic pathway/cytoplasm of the cell
By osmosis


How does water move through the trunk of a tree

In xylem:
Evaporation/transpiration from leaves
Through stomata
Cohesion of water molecules
Leaf cells have a more negative water potential, so water enters from xylem
Water drawn up as continuous column
Adhesion of water to walls pulls in walls
Capillarity due to narrow lumen of xylem (vessels)
Lignified walls keep xylem open
Root pressure forces some water up


Describe how the structure of the xylem relates to its function

Have no end walls/hollow/no cytoplasm/no organelles as it’s dead
Allows unrestricted flow of water
Provides support/strength/impermeability
Pits allow lateral movement


What is root pressure

Involves active transport
Secretion/movement of salts into xylem
Endodermis-water moves along water potential gradient



Solar energy source
Evaporation of water
Water potential gradient across leaf/mesophyll cells
Tension creates in xylem
Cohesion of water maintains column
Due to H bonding/polarity/charges of water molecules
Adhesive force between water and wall


Xerophytic plant adaptations

Sunken/fewer stomata- reduces water potential gradient air movement across stomata/traps air which becomes saturated/moist/humid
Rolled leaves- reduces water potential gradient air
Movement across stomata/traps air which becomes saturated/reduces surface area
Thick cuticle- reduces cuticular transpiration/greater diffusion distance
Spikey leaves
Reduces leaves/spines- less surface area/ fewer stomata for evaporation
Hairs- traps air which becomes saturated/moist/humid