CHAPTERS 31 + 32

Plant Structure and Function

31.3 Three Basic Parts of a Plant:Roots, Stems, and Leaves

Roots

• Anchors the plant in the soil• Absorbs an transports minerals and water• Stores food

Stem

• Above the ground• Supports and

separates the leaves• Flowers for

reproduction• Leaves for

photosynthesis

Leaf

-“the blade”-Usually flat to receivesunlight-Veins contain water andfood-conducting tubes

Some Leaf Vocabulary

• Parenchyma = non-woody, functioning part of the plant

• Chlorenchyma= photosynthesizing non-woody, functioning part of the plant

Leaf

• Blade = usually the flat, broad organ above ground – the leaf

• Midrib= central or main vein

Xylem Tissue

• Contains two water-conducting cells:• Dead, only cell walls• Water moves only up the plant.

Phloem

• Food conducting tubes (up and down)• Cells remain alive

Transpiration

• Evaporation of water from mostly leaves (could also be stems).

• Transpiration You Tube

How does the water get from the roots to the leaves?

• 1. Root pressure – water absorbed in roots• 2. Mass flow of liquid water from the roots to

the leaves is driven in part by capillary action up the xylem tubes.

• 3. Transpiration evaporation pulls the water up.

Capillary Action in Xylem

• Adhesion of water to sides of xylem tubes (hydrophilic cellulose molecules via H-bonds) and cohesion of water to water molecules (H-bonds) to make a column.

TranspirationPulling force of water by evaporation

Guard cells control transpiration.

How Guard Cells Work

• A stoma opens when its guard cells gain K+ ions and water by osmosis

• The water vacuoles become turgid and the guard cells become bowed (inner membrane is thicker) as they fill and open the stoma

How the Guard Cells Work (2)

• When the guard cells lose K+, they also lose water by osmosis

• The water vacuoles become flaccid and less bowed

• The stomata close

Usually

• Guard cells keep stomata open during the day• CO2 enters for photosynthesis

• Guard cells keep stomata closed at night• No sunlight-no photosynthesis-save water

3 clues to stomatal opening at dawn

• 1. SUNLIGHT-stimulates guard cells to accumulate K+

• 2. LOW LEVEL OF CO2 in the leaf• 3. BIOLOGICAL CLOCK of some sort (even if

put in a dark closet, they will still open)

If it is a drought, WHAT HAPPENS?

• The stomata will close to reduce water loss and prevent wilting. This also slows down CO2 intake and photosynthesis.

Root PressurePushes water up xylem a few meters

Fig. 31.2 Comparison of monocots and eudicots

Fig. 31.13A Bean Germination(a Eudicot)

Fig. 31.13B Corn Germination (a monocot)

Leaf Texture

• Waxy Hairy

• Rough

Leaf Shape

Leaf Arrangement on Stem

Leaf Venation