IB Biology Review Chapter 36: Plant Transport What

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IB Biology Review

• Chapter 36 Plant Transport

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What substances need to be transported throughout
the plant?

• Water
• Sugars / energy / sap
• Nutrients
• Hormones

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How does water get into the plant?

• Through the roots
• Apoplastic route
• Symplastic route
• What adaptation do roots have to increase surface
  area?
• Root hairs
• Mycorrhizae fungus

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Apoplastic Route

• Water enters the route between cells
• Infiltrates around cells
• Hits Casparian strip (waxy buffer)
• Water is forced to be absorbed through a cell
  membrane
• Why should all water be forced through a cell
  membrane?
• Prevents contaminants from being absorbed into
  the plant

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Symplastic Route

• Water is absorbed through the cell membrane of a
  root hair cell
• Water travels through cells via connecting
  structure called a plasmodesmata

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Apoplastic and Symplastic Routes
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How is water delivered to the stem and leaf
cells?

• Via xylem
• What helps water move up the xylem?
• Transpiration
• Cohesion / Adhesion(capillary action)
• Root pressure

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What is transpiration?

• When evaporating water pulls up other water
  molecules through the xylem
• Occurs via cohesion (hydrogen bonding) and
  adhesion
• Where does the water leave the leaf?
• Stoma / Stomata

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What are stomata?

• Small pores on the surface of the leaf
• Functions
• Allows excess water to escape
• Allows oxygen to escape
• Allows carbon dioxide to enter the leaf
• What controls if the stomata are open or closed?
• Guard cells

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What can affect the rate of transpiration?

• Temperature
• more transpiration as temperature rises
• water molecules move more / have more kinetic
  energy
• faster evaporation (due to more latent heat
  available)
• If it gets too hot, guard cells close to save
  water
• Light Intensity
• more transpiration in the light
• light causes stomata to open for photosynthesis
• the brighter it is, the more the stomata open,
  speeding up transpiration

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What can affect the rate of transpiration?

• Humidity
• less transpiration as (atmospheric) humidity
  rises
• smaller concentration gradient, so water cant
  leave the leaf as easily
• Wind Intensity
• more transpiration as wind (speed) increases
• water vapor blown away from the leaf
• increases the concentration gradient, so water
  wants to leave the leaf

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How is sap (containing sugar) moved around the
plant?

• Through translocation in phloem
• Which direction does the sap flow?
• From sugar sources to sugar sinks
• Spring roots -gt growing leaves
• Fall sugar-producing leaves -gt roots

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Translocation

• Occurs in the phloem
• Living tissue that is composed of companion cells
  / sieve tube members
• Products of photosynthesis moved either from
  sugar source to sink
• Movement of water causes flow

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How are nutrients absorbed into the roots?

• Transport proteins in root cells use active
  transport and voltage differences
• Electrochemical gradient established so that
  inside the root cell is negative
• Cations (positively charged) diffuse down the
  gradient
• Anions (negatively charged) are cotransported by
  hydrogen ions ()
• Mixture is neutral ( and is neutral)

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1. Describe how water is transported in a plant.
(4
marks)
IB Exam Question

• transported in xylem (vessels)
• passive / no energy used by plants
• evaporation / transpiration causes low pressure /
  suction / pull
• transpiration stream / continuous column of water
  from roots to leaves
• water molecules are cohesive (so transmit the
  pull) / hydrogen bonding
• root pressure can move water up the plant
• apoplastic pathway is through cell walls

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2. Explain the process of water uptake and
transport by a plant.
(8 marks)
IB Exam Question

• roots have a large / increased surface area
• root hairs increase the surface area
• water is absorbed by osmosis
• solute concentration inside the root is higher
  than in the soil / outside
• due to active transport of ion into the root
• apoplastic and symplastic transport across root
• apoplastic route is through the cell walls (and
  intercellular spaces)
• symplastic route is through the cytoplasm (and
  plasmodesmata)
• carried up stem by xylem
• water has to pass through cytoplasm of endodermis
  / Casparian strip blocks water
• water movement in xylem due to pulling force /
  transpiration pull from leaves
• cohesion between water molecules

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3. Explain how roots absorb water and then
transport it to the xylem, noting any special
adaptations that help these processes to occur.

(9 marks)
IB Exam Question

• roots have a large/increased surface area (in
  relation to their volume)
• root hairs increase the surface area
• water is absorbed by osmosis
• solute concentration inside the root is higher
  than in the soil / outside
• due to active transport of ions into the root
• apoplastic and symplastic transport across the
  root
• apoplastic route is through the cell walls (and
  intercellular spaces)
• symplastic route is through the cytoplasm (and
  plasmodesmata)
• water has to pass through cytoplasm of endodermis
  / Casparian strip blocks walls
• water movement in xylem due to pulling force /
  transpiration pull
• cohesion between water molecules

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4. Explain how abiotic factors affect the rate of
transpiration in a terrestrial plant.
(8 marks)
IB Exam Question

• less transpiration as (atmospheric) humidity
  rises
• smaller concentration gradient (of water vapour)
• more transpiration as temperature rises
• faster diffusion / more kinetic energy (of water
  molecules)
• faster evaporation (due to more latent heat
  available)
• more transpiration as wind (speed) increases
• humid air / water vapour blown away from the
  leaf
• increasing the concentration gradient (of water
  vapour)
• more transpiration in the light
• due to light causing stomata to open
• wider opening with brighter light hence more
  transpiration

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5. Outline the role of the phloem in the active
translocation of biochemicals.


(5 marks)
IB Exam Question

• living tissue
• composed of companion cells / sieve tube members
• companion cells involved in ATP production
• sucrose / amino acids / assimilate / products of
  photosynthesis transported
• bi-directional transport
• source / leaves to sink / fruits / roots /
  storage organs / named storage organ
• pressure flow hypothesis / movement of water into
  phloem causes transport