1. 9.1 Transport in the Xylem of Plants

2. Plant Leaves Absorb radiant energy Optimize the rate of photosynthesis
Cross Section of a leaf

3. Leaf Part
Leaf Function
Waxy Cuticle
Water conservation
Stomata
Opening in leaf/gas exchange
Guard cells
Control stomata opening
Vascular Tissue
Xylem: transports water and minerals from the roots to the shoot by passive transport
Phloem: transports nutrients throughout the plant by active transport
Collenchyma cells
Support vascular bundles (xylem and phloem) and give leaf structure
Chloroplasts (mainly in the mesophyll, spongy and pallisade layers)
Carry out photosynthesis
Spongy layer: filled with air spaces to help facilitate gas exchange
Pallisade layer: packed with chloroplasts

4. Transpiration
The passive movement and evaporation of water from the stems and leaves of a plant
Made of two types of cells
Tracheid cells
Vessel elements
Pits in the sides of the cells allow water to flow between the cells of the xylem

5. Cohesive & Adhesive Properties
Cohesive properties: (hydrogen bonding) hold water molecules together as they travel up the xylem
Evaporation creates a “pull” causing them to move up xylem
Water is also entering the plant causing a “push” of water
Adhesive properties: water is attracted to the sides of they xylem cells
Water molecules adhere to sides of vessels and resist gravitation pull downward

7. Stomata and Guard Cells
opening and closing of stomata controlled by guard cells
1. stomata open and close due to changes in turgor pressure
2. gain and loss of water in the guard cells is largely due to the transport of potassium ions
3. A hormone abscicis acid causes potassium ions to rapidly diffuse across guard cells, causing them to close (due to lack of available water)
4. other factors like carbon dioxide levels and circadian rhythms affect opening and closing

8. Stomata & Guard cells

9. Abiotic Factors and Transpiration Rates
Environmental Factor
Effect
Light
Speeds up transpiration by warming leaf and opening stomata
Humidity
Decreasing humidity increases transpiration because of the greater difference in water concentration
Wind
Increases the rate of transpiration because humid air near the stomata is carried away
Temperature
Increasing temperature causes greater transpiration because more water evaporates
Soil water
If the intake of water at the roots doesn’t keep up with transpiration , turgor loss occurs causing the stomata to close decreasing transpiration
Carbon Dioxide
High CO2 levels in the air around the plant usually causes guard cells to lose turgor and stomata close

10. Root System and Water Uptake
Water and mineral uptake
Occurs in the roots which have adapted in several ways:
roots are covered in tiny hairs that increase the surface area for greater water absorption
2. Branching allows roots to cover more area and increase uptake
3. Cortex cell walls are permeable for osmosis

12. Uptake of Mineral Ions 1. Diffusion of mineral ions
a. Requires concentration gradient (not common because ions are usually in low conc. In the soil)
2. Mutualistic relationships with fungal hyphae
a. Fungi have long multinucleated cells called hyphae
b. Form dense networks called mycelium that grow around roots
c. Plant root provides fungi with nitrates in exchange for needed minerals
3. Mass flow of water in the soil carrying ions

13. Active Transport of Minerals
Mineral ions are taken into the plant by active transport
a. root hairs secrete hydrogen ions into soil particles, exchanging them for mineral ions (calcium, magnesium, iron etc.)
b. ATP is hydrolyzed in order to provide the energy for this process

14. Adaptions of Xerophytes
Xerophytes live in arid (dry) environments
They have developed adaptations to help with transpiration
Reduced leaves sometimes spines
Rolled leaves: block the wind from reaching stomata
Deep roots for more surface area
Thickened waxy cuticle
Reduced number of stomata
Hairs to help trap water
Water storage organ
Low growth
CAM and C4 plants: fix CO2 at very low concentrations, stomata open less frequently