Syllabus Point:
In vascular plants, transport of water and mineral nutrients from the roots occurs via xylem through root pressure, capillary action (adhesion and cohesion of water molecules), transpiration; transport of the products of photosynthesis and some mineral nutrients occurs by translocation in the phloem.
Learning Objectives
- To understand the structure and function of plants in terms of transporting substances.
- To be able to identify key parts of plant anatomy from diagrams
- To be able to explain how water is transported in plants
- To be able to explain how nutrients are transported in plants.
Plants need water and minerals...
Plants need water for the same reasons that all living things do:
Getting their water...
Getting their minerals...
- To perform metabolic reactions
- To use as a medium for transporting substances
Getting their water...
- Almost all of the water used by land plants is absorbed from soil by roots.
- A root system consists of a complex network of individual roots.
- Roots grow from their tips.
- Finer roots have the greatest ability to absorb water,
- Fine roots can be covered by root hairs.
- Root hairs are important because:
- they significantly increase the absorptive surface area
- they improve contact between roots and the soil.
- Some plants establish symbiotic relationships with fungi, further increasing the total absorptive surface area.
Getting their minerals...
- Minerals are acquired in much the same was as water -via absorption by the root system
- Active transport and diffusion are the two major processes by which minerals move into the plant
How does water travel?
- Upon absorption by the root via osmosis, water first crosses the epidermis
- Makes its way toward the center of the root, crossing the cortex and endodermis.
- Arrives at the xylem.
- The force of more water being "pushed" into cells creates pressure helping drive the water on.
- Once in the xylem tissue, water moves easily over long distances in these open tubes. (Xylem begin as a series of living cells but as they mature the cells die, lose their cellular contents and form hollow tubes).
- Water eventually is evaporated through stomata
So what is Xylem?
There are no muscles to pump it! So how does it move up?
This continuous flow from roots to leaves is referred to as TRANSPIRATION or the "transpiration stream".
Maintaining water levels:
Water Loss > Water Gain
Water Gain > Water Loss
- Xylem is plant vascular tissue that sends water and dissolved minerals from the roots to the rest of the plant.
- It also provides physical support.
- Xylem tissue:
- Xylem cells undergo programmed death, following which they lose their contents and end walls, become hollow tubes.
- Xylem cell walls have lignin to create rigidity.
There are no muscles to pump it! So how does it move up?
- Root Pressure (explained above under "How does water travel?")
- Adhesion: The force of attraction between water molecules and the sides of the vessels.
- Cohesion: The force of attraction among the water molecules pull eachother along.
This continuous flow from roots to leaves is referred to as TRANSPIRATION or the "transpiration stream".
Maintaining water levels:
Water Loss > Water Gain
- Raises the tension of the water columns in the xylem.
- Water potential increases.
- Roots pull water more quickly from the soil.
- Stomata close due to flaccid guard cells.
- cells loose their turgidity and become flaccid.
- plant wilts and cells eventually die do to inability to metabolise.
Water Gain > Water Loss
- Lowers the tension of the water columns in the xylem
- water potential decreases
- Roots pull water more slowly from soil
- Guard cells are very turgid and stomata are open allowing transpiration.
- Not typically a problem and turgidity actually helps with support.
Plants need to transport sucrose (from photosynthesis)
Phloem tissue is responsible for transporting glucose produced from photosynthesis.
- Movement: bidirectional (goes up or down plant to wheerever it is needed). referred to as "Translocation".
- Location: alongside xylem in "vascular bundles"
- Form: Elongated, tubular shape, living cells, thin walled sieve tubes which have pores at each end allowing longitudinal flow of material, some cells have horizontally placed pores to allow for horizontal flow.
- Materials: Sucrose from photosynthesis. Also some hormones and amino acids.
- Energy: Active transport. However the nutrients are dissolved in sap, so osmotic pressure also plays a role (passive).
Plant Leaf Structure
Now You Should:
Go back and revise gas exchange in plants.
Read all of Chapter 13
Complete all Question Sets from Chapter 13
Complete WACE Study Guide Transport in Vascular Plants Q 1 - 9 (starts on p. 137)
Read all of Chapter 13
Complete all Question Sets from Chapter 13
Complete WACE Study Guide Transport in Vascular Plants Q 1 - 9 (starts on p. 137)
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