Transport - Structure and function
Why is transport needed? What is transported in plants, from where
to where and why?
Two parallel transport systems:
Structure of stems: location and function of three tissues -
dermal, ground, and vascular
- dicot - primary versus secondary growth
Transport cells - structure
- xylem cells: tracheids, vessel elements
- phloem cells: sieve tube members, companion cells
Transport in phloem:
- Phloem transports the products of photosynthesis (sugar) from
sources to sinks.
- Requires energy but the movement of water and dissolved
solutes is a passive physical process.
- Pressure - flow hypothesis
- Phloem loading at source, unloading at sink.
- Damage control in phloem - "p - protein"
- Aphids and the study of phloem transport.
Transport in the xylem: How does water get to the leaves at the
top of a 100 meter tall tree?
- Transpiration experiments by Strausberger in 1880's.
- Current theory: Evaporation, Adhesion, Cohesion,
- Problems with water under tension - cavitation
- Root pressure
Sample questions from past exams:
Define and explain the contribution of the following plant
attributes to life on land: vascular system
Contrast transport in the xylem and phloem in terms of what is
transported, the direction of transport and the cells and mechanisms