3.3.4.2 Mass Transport in plants Flashcards

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1
Q

Describe one piece of evidence that supports the root pressure theory and explain how it supports the theory

A
  • sap discharged from a cut stem

- only upward force could make this happen

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2
Q

The diameter of a tree is less during the day than it is at night.

Explain how this supports cohesion tension theory?

A
  • evaporation of water through leaves mainly during daytime
  • so tension in xylem creates an inward pull
  • so xylem vessels become narrower due to the adhesion of water molecules to walls of xylem vessels
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3
Q

The diameter of a tree is less during the day than it is at night.

Explain how this does NOT support root pressure theory

A
  • root pressure gives OUTWARD force pushing on walls of xylem
  • so trees would become wider not narrower as xylem should = wider
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4
Q

Using the cohesion tension theory explain the changes in the circumference of a tree throughout the day?

A
  • inc of light, at the start of the day, causes stomata to open
  • so water evaporates out of stomata causing water to move across the leaf by OSMOSIS
  • evaporation exerts force causing tension in water columns
  • cohesion holds water column together
  • adhesion between walls of xylem and water mol results in pulling force which causes water columns to decrease in volume
  • hence xylem vessels and tree trunk both = narrower
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5
Q

Which part of the cortex forms the apoplast pathway?

A

The cell walls

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6
Q

use your knowledge of transpiration to explain changes in rate of flow in xylem?

A
  • stomata open
  • transpiration highest around midday as middle of day warmer
  • increased tension
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7
Q

explain why values for pressure in xylem are negative?

A
  • inside xylem lower than atmospheric pressure

- water under tension

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8
Q

describe how high pressure is produced in leaves?

A
  • wp becomes lower
  • water enters phloem by osmosis
  • increase volume of water increases pressure
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9
Q

explain one way in which sieve cells are adapted for mass transport?

A
  • few organelles

- so easier flow

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10
Q

explain one way in which companion cells are adapted for mass transport?

A
  • many mitochondria
  • to release ATP
  • for active transport
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11
Q

in an investigation where a translocation inhibitor is used, why is it important that the rate of photosynthesis is kept constant?

A
  • rate of photosynthesis related to rate of sucrose production
  • rate of translocation higher when sucrose concentration higher
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12
Q

a student investigated the rate of transpiration from a leafy shoot.

she used a potometer to measure the rate of water uptake by the shoot.

suggest one environmental factor the student should keep constant during the investigation?

A

temperature

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13
Q

a student investigated the rate of transpiration from a leafy shoot.

she used a potometer to measure the rate of water uptake by the shoot.

the student cut the shoot and put it into the potometer under water. explain why?

A

prevent air entering

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14
Q

a student investigated the rate of transpiration from a leafy shoot.

she used a potometer to measure the rate of water uptake by the shoot.

the student wanted to calculate the rate of water uptake by the shoot in cm3 per minute.

what measurements did she need to make?

A
  • distance and time

- diameter of capillary tube

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15
Q

a student investigated the rate of transpiration from a leafy shoot.

she used a potometer to measure the rate of water uptake by the shoot.

the student assumed that water uptake was equivalent to rate of transpiration.

give 2 reasons why this might NOT be valid assumption?

A
  • used in photosynthesis

- used to provide turgidity

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16
Q

a student investigated the rate of transpiration from a leafy shoot.

she used a potometer to measure the rate of water uptake by the shoot.

the student measured the rate of water uptake 3 times.

suggest how the reservoir allows repeat measurements to be made?

A

returns bubble to start

17
Q

describe how CO2 in air outside leaf reaches mesophyll cells inside leaf?

A
  • via stomata
  • controlled by guard cells
  • down diffusion gradient
  • through spongey mesophyll
18
Q

phloem

A
  • transports glucose and amino acids
  • direction UP and DOWN
  • made of living cells (sieve cells and companion cells)
19
Q

companion cells

A
  • support sieve cells

- provide ATP (sieve cells have no mitochondrion)

20
Q

sieve tube cell

A
  • living with little cytoplasm
  • few organelles
  • hollow
21
Q

sieve plates

A

thin pores between sieve tube cells

22
Q

evidence for mass flow / translocation

RADIOACTIVE LABELLING

A
  • use radioactive c14 label
  • grow plants in c14 atmosphere
  • measure c14 as it moves down stem / trunk
23
Q

evidence for mass flow / translocation

RINGING EXPERIMENT

A
  • remove bark in ring from tree trunk (contains phloem not xylem)
  • solutes can move up or down
  • bulge forms above ring
  • fluid above ring has more solute e.g. sugars than below

EVIDENCE SOLUTES ARE MOVING DOWN

24
Q

problems with ringing experiment

A
  • not fully understood

- not a perfect theory

25
Q

define cohesion

A

water molecules stick together because they are polar

26
Q

xylem

A
  • transports water and minerals
  • direction = UP only
  • hollow tube made of dead cells
  • no cell walls between cells
27
Q

cohesion tension theory

A
  • transpiration of water through stomata
  • creates low pressure at top of xylem
  • water in xylem pulled up creating tension
  • because water mol stick together = cohesion
  • water molecules brought up as single column
28
Q

factors affecting transpiration

A
  • TEMP - higher temp, inc rate of transpiration
  • LIGHT - more stomata open when more light, inc transpiration
  • HUMIDITY and WIND affect water vapour gradient
  • steeper gradient (more humid / windy) higher transpiration
29
Q

mass flow hypothesis / translocation

A
  • at SOURCE - high conc of solute (sucrose)
  • active transport of solute from companion cell into sieve tube cell
  • dec WP
  • water moves in by osmosis from companion cell and xylem
  • creates high hydrostatic pressure in phloem
  • mass movement from source to sink
  • where solute stored/removed
30
Q

sink

A
  • uses / breaks down/ converts solute into something else
  • creates low conc of solute (solute to starch)
  • inc WP - water moves out by osmosis
  • decreases pressure in phloem