Transport In Plants Flashcards
Describe the structure of the xylem vessels and how it helps with adaptation.
- Made of dead cells, long hollow tube stretching from roots to leaves.
- Continuous empty lumen to reduce resistance to water flowing through xylem.
- Walls thickened with lignin to prevent collapse of vessel.
What are the functions of the xylem tissues?
- Conduct water and dissolved mineral salts from roots to stems and leaves.
- Provide mechanical support for plant.
What are the functions of the phloem tissues?
Conducts sucrose and amino acids from leaves to other plant parts.
Describe the features of the phloem tubes.
- Contains sieve tubes which has cells without nucleus that helps in transportation through tubes by D and AT.
- Each ST cell has companion cell has had many ribosomes and mitochondria to produce energy to keep sieve tube cells alive.
How is phloem adapted for its function?
- Companion cells many mitochondria which provide energy needed for companion cells to load sugars from mesophyll cells into ST by AT.
- Holes in sieve plants allow rapid flow of manufactured food substances through ST.
What the function of cambium cells, the cortex and the pith?
- CC divide and differentiate to form new xylem and phloem tissues, giving rise to thickening of stem.
- Pith and cortex store up food substances like starch.
How does the root adapt to carry out its function?
External: protective cells to protect young cells from injury during elongation, elongate to increase length for SA, many mitochondria for AR for AT, PPM prevent cell sap from leaking out allow diffusion to occur.
Internal: no cuticle, xylem and phloem not bundles together, outgrowth of epidermal cells to increase SA to volume ratio.
What is translocation and how can it be proven?
- Transport of manufactured substances like sugar and amino acids in plants.
- Experiment with aphids, ‘ringing’ experiment, use of C14 isotopes.
Describe how water enters a plant.
- Sap in RH conc with sugars and salts.
- Lower water potential than soil water, water enters by osmosis.
- This dilutes sap in RH.
- High water potential in sap causes water to move into inner cells.
- Cycles continues.
Describe root pressure.
- Pressure generated by uptake of H2O by osmosis in roots.
- As H2O enters, pressure increases in roots.
- This pressure forces water up xylem vessels.
What is capillary action?
- Water moves up xylem vessels due to differences between adhesive and cohesive forces of water molecules and surface of vessels.
What is transpiration?
Loss of water vapour from plant, through leaves’ stomata.
Describe the transpiration pull process.
- Water molecules moves out of mesophyll cells to form thin film of moisture over their surfaces.
- Water evaporates from thin film of moisture into intercellular air spaces. Water vapour accumulates in large air spaces near stomata.
- Water vapour diffuses though stomata to drier air outside leaf. (T)
- As water leaves cell, cell sap increases conc hence more more water drawn from cells deeper by osmosis.
- These cells remove water from xylem.
- Water drawn up to replace water loss in aerial positions in XV.
Explain how light intensity affects transpiration rate.
- During sunlight, stomata opens and become wider, higher TR.
- During darkness, stomata closes and less water loss from leaf hence lower TR.
How does temperature affect transpiration pull?
When all factors constant, higher temperatures causes higher evaporation from cell surfaces hence TR higher.
