Science Models are A scientific model is a

Science Models are. . . A scientific model is a conceptual, mathematical or physical representation of a real-world phenomenon. Can represent these in pictures

Microscope Eyes Diagram shows the microscopic.

X-ray Eyes Diagram shows below the surface.

Initial Student Model

Revised Model What are some differences you notice?

Make a model of how a seed becomes a plant

Don’t be scared of the next model. . .

Watch

REVISE model and explanati on of how a seed becomes a plant

Allow a peer to view your model and give you FEEDBACK

Biology Modeling Criteria 1. Did you revise your model based on observations/data? 2. Is your model scientifically accurate? 3. Did you use your “microscope eyes” or “X-ray eyes” or both? 4. Did you show in words and/or pictures how each relevant component interacts with each other? 5. Did you label at least 3 components? Note: Not graded on artist ability

Transport in Plants

Transport in plants writing 24

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Transport Mechanisms 1) Water first enters the roots (higher water potential to lower potential) 2) Then moves to the xylem • Innermost vascular tissue • Water rises through the xylem because of a combination of factors 3) Most of that water exits through the stomata in the leaves 26

• Most of the force is “pulling” created by transpiration • Evaporation from thin films of water in the stomata • Occurs due to cohesion (water molecules stick to each other) and adhesion (stick to walls) 27

Water flow through root • Porous cell wall • water can flow through cell wall route & not enter cells • plant needs to force water into cells Casparian strip

Controlling the route of water in root • Endodermis • cell layer surrounding vascular cylinder of root • lined with impermeable Casparian strip • forces fluid through selective cell membrane • filtered & forced into xylem cells Aaaah… Structure– Function yet!

• Most of the water absorbed by the plant comes in through the region of the root with root hairs • Surface area further increased by mycorrhizal fungi • Once absorbed through root hairs, water and minerals must move across cell layers until they reach the vascular tissues • Water and dissolved ions then enter the xylem and move throughout the plant 30

Mycorrhizae increase absorption • Symbiotic relationship between fungi & plant • symbiotic fungi greatly increases surface area for absorption of water & minerals • increases volume of soil reached by plant • increases transport to host plant

Water Absorption through Roots • STRUCTURE and FUNCTION 32

Transport in plants • H 2 O & minerals • transport in xylem • transpiration • evaporation, adhesion & cohesion • negative pressure • Sugars • transport in phloem • bulk flow • Calvin cycle in leaves loads sucrose into phloem • positive pressure • Gas exchange • photosynthesis • CO 2 in; O 2 out • stomates • respiration • O 2 in; CO 2 out • roots exchange gases within air spaces in soil Why does overwatering kill a plant?

Leaf structures

Control of Stomates Guard cell • Uptake of K+ ions by guard cells • proton pumps • water enters by osmosis • guard cells become turgid Chloroplast s H 2 O K+ • Loss of K+ ions by guard cells • water leaves by osmosis • guard cells become H 2 O K+ flaccid H 2 O K+ Epidermal cell Nucleu s K+ H 2 O Thickened inner cell wall (rigid) H 2 O K+ Stoma open water moves into guard cells H 2 O K+ Stoma closed water moves out of guard cells H 2 O K+

Control of transpiration • Balancing stomate function • always a compromise between photosynthesis & transpiration • leaf may transpire more than its weight in water in a day…this loss must be balanced with plant’s need for CO 2 for photosynthesis

Rate of Transpiration • Over 90% of the water taken in by the plant’s roots is ultimately lost to the atmosphere • At the same time, photosynthesis requires a CO 2 supply from the atmosphere • Closing the stomata can control water loss on a short-term basis • However, the stomata must be open at least part of the time to allow CO 2 entry 37

• Active pumping of sucrose out of guard cells in the evening leads to loss of turgor and closes the guard cell 38

• Guard cells • Only epidermal cells containing chloroplasts • Have thicker cell walls on the inside and thinner cell walls elsewhere • Bulge and bow outward when they become turgid • Causing the stomata to open • Turgor in guard cells results from the active uptake of potassium (K+), chloride (Cl) • Water enters osmotically 39

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Rate of Transpiration • Transpiration rates increase with temperature and wind velocity because water molecules evaporate more quickly • Several pathways regulate stomatal opening and closing • Abscisic acid (ABA) initiates a signaling pathway to close stomata in drought • Opens K+, Cl– channels • Water loss follows 41

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• Other pathways regulating stomata • Close when CO 2 concentrations are high • Close when temperature exceeds 30º– 34ºC and water relations unfavorable • Alternative photosynthetic pathways, such as Crassulacean acid metabolism (CAM), reduce transpiration 43

Water Stress Responses • Many morphological adaptations allow plants to limit water loss in drought conditions • • • Dormancy Loss of leaves – deciduous plants Covering leaves with cuticle and wooly trichomes Reducing the number of stomata Having stomata in pits on the leaf surface 44

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• Plants have adapted to flooding conditions which deplete available oxygen • Flooding may lead to abnormal growth • Oxygen deprivation most significant problem • Plants have also adapted to life in fresh water • Form aerenchyma, which is loose parenchymal tissue with large air spaces • Collect oxygen and transport it to submerged parts of the plant 46

Water & mineral absorption • Water absorption from soil • osmosis • aquaporins • Mineral absorption • active transport • proton pumps • active transport of H+ aquaporin root hair proton H 2 O

Transport of sugars in phloem • Loading of sucrose into phloem • flow through cells via plasmodesmata • proton pumps • cotransport of sucrose into cells down proton gradient

Pressure flow in phloem • Mass flow hypothesis • “source to sink” flow • direction of transport in phloem is dependent on plant’s needs • phloem loading • active transport of sucrose into phloem • increased sucrose concentration decreases H 2 O potential • water flows in from xylem cells • increase in pressure due to increase in H 2 O causes flow On a plant… What’s a source…What’s a sink? can flow 1 m/hr

Maple sugaring