Title: IB Biology Review Chapter 36: Plant Transport What
1IB Biology Review
- Chapter 36 Plant Transport
2What substances need to be transported throughout
the plant?
- Water
- Sugars / energy / sap
- Nutrients
- Hormones
3How 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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5Apoplastic 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
6Symplastic Route
- Water is absorbed through the cell membrane of a
root hair cell - Water travels through cells via connecting
structure called a plasmodesmata
7Apoplastic and Symplastic Routes
8How 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
9What 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
10What 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
11What 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
12What 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
13How 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
14Translocation
- 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
15How 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)
161. 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
172. 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
183. 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
194. 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
205. 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