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.

• Leaf - photosynthesis

• Stem - transport

• Root - absorption (and transport…)

• Flower - reproduction (not shown…)

Plant Structures/Functions

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 SectionCortex

Endodermis

Pericycle

Xylem

Phloem

Downloaded 4/10/02 from http://www.puc.edu/Faculty/Gilbert_Muth/phot0167.jpg

• 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

Xylem

Epidermis Endodermis

Cortex Pericycle

• Cellular route = symplast• Non-cellular route = apoplast• The waterproofing in the endodermis is called the

Casparian Strip

Water UptakeEpidermis Endodermis

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.

Remember how hydrogen bonding held water molecules to each other..

Hydrogen Bonding

…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 cells on the left are full of water• Stomate is open

Guard cell

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.