Chapter 31: Plant Structure, Reproduction and Development

Angiosperms -Most diverse category of plants. -Flowers provide a highly effective mode for pollination. -Vascular tissue allows for transportation of water. -Subdivided into monocots and dicots.

Monocots/Dicots Represent two branches of angiosperm evolution. Are characterized by different patterns of vascular tissue distribution in leaves and stems, number of seed leaves, flower structure, and root structure.

Plant Structures/Functions Leaf - photosynthesis Stem - transport Root - absorption (and transport…) Flower - reproduction (not shown…)

The Plant Body The body of angiosperms breaks down into roots and shoots. Shoots can be further subdivided into leaves and stems. All plant structures fit into these three categories: most flowers and thorns are modified leaves, runners and tubers are modified stems, etc.

Root Cross Section Pericycle Cortex Xylem Endodermis Phloem Downloaded 4/10/02 from http://www.puc.edu/Faculty/Gilbert_Muth/phot0167.jpg

Water Uptake Epidermis Endodermis Xylem Cortex Pericycle Water must move from the epidermis, through root tissues, and into the xylem. Water may take a cellular route, or the route between the cells...

Water Uptake Epidermis Endodermis Cellular route = symplast Non-cellular route = apoplast The waterproofing in the endodermis is called the Casparian Strip

Tissue Systems Angiosperms contain three tissue systems. The epidermis covers plant surfaces, provides protection for the inner tissues, and helps to regulate the flow of materials into and out of the plant. Ground tissue plays a role in storage, support, and photosynthesis. Vascular tissue…

Vascular tissue: Vascular tissue allowed plants develop in many new terrestrial environments. It carries materials through the plant body. Two types: Xylem and Phloem. Xylem: Carries water up into the plant, composed of dead trachied and vessel element cells. Phloem: Carries food from sugar sources to sugar sinks, compose of living cells.

Transpiration Allows water to be transported through the xylem, up from the roots and to the rest of the plant. Depends on the cohesive and adhesive properties of water. Cohesion: Molecules stick to like molecules. Adhesion: Molecules stick to molecules that are different from them.

Hydrogen Bonding Remember how hydrogen bonding held water molecules to each other.. …and water molecules to the sides of their container (e.g. xylem tubes)

Transpiration Water exists as a continuous column in the xylem vessels. It is pulled up through the xylem as water exits the leaves through openings called stomata (stoma is Latin for mouth). Action is similar to that of a straw. How is the vascular tissue of plants similar to blood vessels in animals? How is it different?

Xylem Tissue Consists of Tracheids & Vessel Elements When matured, these cells are dead (just cell wall). Plant roots pump inorganic ions into xylem. Water moves into xylem via osmosis ( Results in root Pressure) END RESULT – Xylem sap moves upward.

Stomata Openings found throughout the epidermis of the leaf. Allow for exchange of gases with the outside environment. Major contributor to water loss in plants. Guard cells close stoma to minimize loss of water. Usually close stomata at night.

Guard Cells Control opening of stomata: Open during day and Closed @ night Why open during day??? Sunlight stimulates uptake of K+ Decreased of [CO2] Bio Clock (rhythm)

Guard Cells Control opening of stomata: Open during day and Closed @ night Why closed @ night??? No light, therefore no photosynthesis, therefore no need to take up CO2

Figure 32.4 Stoma Open: Gain K+ Water then enters via osmosis Vacuole in guard cells swell – Turgid Cell wall “buckles” away from companion cell

Figure 32.4 Stoma Closed: Lose K+ Water exits via osmosis Vacuole in guard cells shrink –Flaccid Cell wall “returns” towards companion cell

Open/closing of stomate Guard cell Guard cells on the left are full of water Stomate is open

SEM micrograph of stomate

Water Loss Several mechanisms for reducing water loss have evolved in plants. Cuticle: waxy coating outside of epidermis, helps to seal in water. C-4 plants: Separate the photosynthetic process in space using compartmentalization. CAM plants: Separate the steps of photosynthesis in time.

Nitrogen (Macronutrient) Why Nitrogen???? Required for plant growth & normal processes. Deficiencies = changes in plant color

N2 Fixation Plants cannot use Nitrogen from atmosphere (N2). For absorption from soil Nitrogen must be converted to NH4+ or NO3 Need soil bacteria to perform this conversion.