Chapter 9- Transport In Plants Flashcards
Define source and sink
- source is where the assimilates are loaded into phloem
- sink is where the assimilates are unloaded from phloem
When bark removed from tree, phloem also removed. If complete ring of bark removed, tree trunk swells above the cut. Why?
- sugar cannot pass out
- cut causes infection
- decreased water potential. Water moves into cells
Why lignin is essential in the wall of xylem vessels?
- provides strength to prevent collapse of vessel because transpiration produces tension + water is under tension
- to waterproof the vessel so cells die + contents decay to create hollow tube
- improve adhesion of water molecules to reduce loss of water through wall
- spiral pattern allows flexibility to prevent stem breaking
Why cartilage is essential in trachea?
- to keep trachea open
- provides strength to trachea to prevent collapse as during inhalation vol of lungs increases + lower pressure in thorax
Describe how cells are organised into tissues using xylem + phloem as examples.
- xylem consists of vessels with no end walls + has function in transpiration stream
- phloem has sieve tube elements + companion cells with many plasmodesmata. Important in translocation
Function of pits?
- allow water to move in + out of xylem vessel
- to supply water to other parts of the plant
Parts of the leaf from which water may be lost?
- stomata
- epidermis
How guard cells are adapted to their function?
- unevenly thickened wall. Thick inner + thin outer walls
- able to change shape
- presence of mitochondria to provide ATP
Use cohesion- tension theory to explain how water molecules move from roots to leaves.
- evaporation at top of plant
- creates tension in xylem
- water molecules stick together by H bonds
- column pulled up by tension
H+ ions are moved out of the companion cells by?
Active transport
How do H+ ions + assimilates get cotransported back into companion cell?
Facilitated diffusion
What assimilates can be loaded?
- sucrose
- amino acids
What evidence might scientists expect to see in companion cells to support phloem loading mechanism?
- many mitochondria
- plasmodesmata between companion cells+ sieve tube
Distinguish between transpiration + transpiration stream
- transpiration is the loss of water vapour by evaporation from a leaf
- transpiration stream is the movement of water up xylem vessels from roots to leaves
Do xerophytes have hairs on their leaves?
Yes
Xylem vessels are impregnated with?
Lignin
Gaps in xylem vessel walls are called?
Pits
Gaps in cell walls between companion cells + sieve tube elements are called?
Plasmodesmata
Explain what happens to the air bubble in the capillary tube of a photometer as no. Of leaves increases?
- as no. Of leaves increases, bubble movement increases
- because there is a larger surface area + more stomata which results in more transpiration
- thus, faster uptake of water by plants
-doing potometer investigation + not all leaves same. Why this may affect results + how to improve?
- diff. No of stomata
- choose shoots with similar sized leaves
Assembles potometer underwater + leaves got wet. Why this may affect results + how to improve?
- reduces water potential gradient between inside + outside of leaf
- assemble with wetting leaves
Sun came out + lab warmed up. Why this may affect results + how to improve?
- increased temp will increase transpiration
- carry out in room with controlled temp
How active loading takes place?
- active transport of H+ ions out of companion cells
- this increases H+ ion conc + creates conc gradient
- assimilates move with H+ ions down conc gradient through cotransporter protein by facilitated diffusion
- sugar diffuses into sieve tube element through plasmodesmata
Why as temp increases, the conc. of sugar found in phloem increases?
- at low temp, molecules have little KE thus little ATP made. So less loading of sugars into sieve tube element
- as temp increases, molecules have more KE thus more ATP made. So more loading of sugars into sieve tube element
- at high temperatures, proteins denature
Why rate of transpiration did not increase between light intensities 10 a.u + 20 a.u?
No extra stomata are opened
Why transpiration is unavoidable during the day?
- stomata are open to allow entry of CO2 for photosynthesis
- water vapour leaves the leaf down water vapour potential gradient
How thick, waxy cuticles in a xerophyte reduce loss of water vapour?
-reduces evaporation through leaf epidermis
How curled leaves in a xerophyte reduce loss of water vapour?
-traps water vapour + this reduces water potential gradient between inside + outside leaf
How hairs in a xerophyte reduce loss of water vapour?
-traps water vapour. This reduces water potential gradient between inside + outside leaf
Sugar most commonly translocated?
Sucrose
Adaptations of sieve tubes?
- elongated sieve tube elements
- elements joined end to end to form column
- sieve plates
- little cytoplasm
- few organelles
- no nucleus
Features of xylem that enable steam to pass from heated end of stem to cut end?
- cells joined end to end with no end walls
- pits in walls
- hollow as no organelles
Define transpiration
The loss of water vapour by evaporation from the leaf
How transpiration contributes to the mechanism of water transport up the stem?
- in leaf, water loss is replaced via apoplast pathway down water potential gradient by water from xylem in xylem vessel
- loss of water causes low hydrostatic pressure at the top
- water moves down pressure gradient under tension by mass flow which is due to the cohesion between water molecules
Why bunch of flowers may survive longer if ends of stems removed immediately before flowers placed in water?
- air in xylem removed
- restore continuous column of water in xylem
Explain transpiration stream?
- water vapour loss by evaporation at top of plant
- water replaced via apoplast pathway from xylem down water potential gradient
- this creates low hydrostatic pressure at top of xylem
- high hydrostatic pressure at bottom of xylem
- water, under tension, pulled up in continuous stream by mass flow
- due to cohesion between water molecules bonded by H bonds
- adhesion of water molecules to xylem
Steps you should take when setting up potometer to ensure apparatus works properly?
- apparatus should be air tight
- leaves dry
- shoot is healthy
- assemble apparatus under water
- cut end of shoot
Why repeat experiment?
- to help identify anomalies
- to make results more reliable
Factors that decrease rate of transpiration?
- lower temp
- less light
- more humid
- less wind
Why potometer only gives an estimate of the rate of transpiration?
- potometer measures water uptake
- not all water taken up is lost by evaporation
- some water used in photosynthesis + making cells turgid
Type of plant adapted to reduce water loss from leaves?
Xerophytes
Adaptations of leaves that reduce evaporation?
- hairy leaves: traps water vapour
- sunken stomata: traps water vapour
- rolled leaves: traps water vapour + reduces SA
- thick waxy cuticle: reduces evaporation from epidermis
- fewer stomata: less diffusion
How water enters the endodermis?
- ions enter against conc. gradient by active transport
- this reduces water potential of endodermal cell
- water moves by osmosis down water potential gradient
Why leaf described as an organ?
- organ is a collection of tissues working together to carry out a particular fucnction
- leaves have epidermis, xylem, phloem
-for photsynthesis, gaseous exchange
One molecule absorbed, how may be transported ot fruits?
- in xylem by transpiration/ cohesion tension
- in phloem by translocation/ mass flow
despite x being similar to nicotine, approved for use?
have little effect on humans
Why both plants and animals need to be able to respond to changes in environment?
- to avoid stress
- to access resources
- to avoid being eaten
Describe the features of xylem that enable steam to pass from heated to cut end.
- continuous as cells joined end to end
- no organelles
Transpiration?
Transpiration is the loss of water vapour from a leaf via stomata
How transpiration contributes to mechanism of water transport up stem?
- in the leaf water loss is replaced via the symplast pathway down the water potential gradient by water from the xylem
- in the xylem, this causes low hydrostatic pressure at top. Water moves from high pressure to low pressure down pressure gradient under tension by mass flow
Why flowers may survive longer of ends of stems are removed immediately before placed in water?
- to remove any air bubbles
- restore continuous column of water
Why plant cells do not burst when they are in pure water?
-cell wall provides strength
Why meristematic tissue need to be stained?
- provide contrast between cell structures
- diff structures take up diff amounts of stain
Where meristematic tissue can be found ?
Cambium
Tip of shoot
Tip of root
