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.

Tank is empty Steam cleaned on the inside, hatch was closed

Initial Student Model

Revised Model What are some differences you notice?

Let's MODEL!

Make a model of how a seed becomes a plant

Don’t be scared of the next model...

Watch

REVISE model and explanation of how a seed becomes a plant

Allow a peer to view your model and give you FEEDBACK

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

Transport in Plants

Transport in plants writing

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

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)

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 The endodermis, with its Casparian strip, ensures that no minerals can reach the vascular tissue of the root without crossing a selectively permeable plasma membrane. If minerals do not enter the symplast of cells in the epidermis or cortex, they must enter endodermal cells or be excluded from the vascular tissue. The endodermis also prevents solutes that have been accumulated in the xylem sap from leaking back into the soil solution. The structure of the endodermis and its strategic location in the root fit its function as sentry of the border between the cortex and the vascular cylinder, a function that contributes to the ability of roots to transport certain minerals preferentially from the soil into the xylem.

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

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

Transport in plants H2O & minerals Sugars Gas exchange 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 CO2 in; O2 out stomates respiration O2 in; CO2 out roots exchange gases within air spaces in soil Why does over-watering kill a plant?

Leaf structures

Control of Stomates Uptake of K+ ions by guard cells Epidermal cell Guard cell Chloroplasts Nucleus Uptake of K+ ions by guard cells proton pumps water enters by osmosis guard cells become turgid Loss of K+ ions by guard cells water leaves by osmosis guard cells become flaccid K+ K+ H2O H2O H2O H2O K+ K+ K+ K+ H2O H2O H2O H2O K+ K+ Thickened inner cell wall (rigid) H2O H2O H2O H2O K+ K+ K+ K+ Stoma open Stoma closed water moves into guard cells water moves out of guard cells

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 CO2 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 CO2 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 CO2 entry

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

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

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

Other pathways regulating stomata Close when CO2 concentrations are high Close when temperature exceeds 30º–34ºC and water relations unfavorable Alternative photosynthetic pathways, such as Crassulacean acid metabolism (CAM), reduce transpiration

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

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

Water & mineral absorption Water absorption from soil osmosis aquaporins Mineral absorption active transport proton pumps active transport of H+ aquaporin root hair proton pumps H2O

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 H2O potential water flows in from xylem cells increase in pressure due to increase in H2O causes flow can flow 1m/hr In contrast to the unidirectional transport of xylem sap from roots to leaves, the direction that phloem sap travels is variable. However, sieve tubes always carry sugars from a sugar source to a sugar sink. A sugar source is a plant organ that is a net producer of sugar, by photosynthesis or by breakdown of starch. Mature leaves are the primary sugar sources. A sugar sink is an organ that is a net consumer or storer of sugar. Growing roots, buds, stems, and fruits are sugar sinks. A storage organ, such as a tuber or a bulb, may be a source or a sink, depending on the season. When stockpiling carbohydrates in the summer, it is a sugar sink. After breaking dormancy in the spring, it is a source as its starch is broken down to sugar, which is carried to the growing tips of the plant. A sugar sink usually receives sugar from the nearest sources. Upper leaves on a branch may send sugar to the growing shoot tip, whereas lower leaves export sugar to roots. A growing fruit may monopolize sugar sources around it. For each sieve tube, the direction of transport depends on the locations of the source and sink connected by that tube. Therefore, neighboring tubes may carry sap in opposite directions. Direction of flow may also vary by season or developmental stage of the plant. On a plant… What’s a source…What’s a sink?

Maple sugaring