CHAPTERS 31 + 32
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Transcript of CHAPTERS 31 + 32
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