Plant Phys Exam 1

Cellular characteristics can have a strong influence on the function of a cell. Discuss how the cellular characteristics of a representative parenchyma, collenchyma, and sclerenchyma cell influences function in these cell types. You should include detailed diagrams as part of your answer. 

Parenchyma - thin, flexible, primary walls, large central vacuole, functions - photosynthesis, storage, wound repair

example - chlorenchyma in leaves, aids in photosynthesis due to abundant of chloroplasts

Collenchyma - uneven, thick cell walls, flexible and structural support, found in growing tissue (petioles and young stems)

Sclerenchyma - thick, lignified, secondary walls, rigid support, dead at maturity, forming fibers and sclereids

2. You have created a mutant plant in which the guard cells are not as permeable to solutes as the wild type. How will this mutation influence guard cell function, transpiration rates, and whole plant water transport? Which other plant processes might be affected by this mutation?

Effect on Guard cells - reduced permeability to solutes means slower osmotic changes which affects stomatal opening and closing

Transpiration rates - decreased transpiration due to less efficient stomatal function

Whole other plant processes - reduced CO2 uptake which means decreases in photosynthesis and potential growth reduction

3. Detail and describe the anatomy of a typical leaf and how that relates to function. 

Epidermis - protection, regulation of water loss via cuticle and stomata

Mesophyll - Palisade = primary site of photosynthesis, Spongy Mesophyll = Gas exchange

Vascular Bundles - Xylem: transports water and minerals Phloem: Transports Sugars and Nutrients

4. Water has certain physicochemical properties. Three of these include high surface tension, cohesion, and adhesion. Describe, in detail, the significance of these three properties of water in the soil-plant-air continuum.

Surface Tension - Helps form menisci in leaf cell walls, generating negative pressure for water movement

Cohesion - Water Molecules stick together via hydrogen bonds, allowing for continuous water columns in xylem

adhesion - water adheres to xylem walls, counteracting gravity and supporting capillary action

5. Using Fick’s first law, describe why long-distance water movement through plants cannot be due to diffusion but is sufficient for cellular level transport. What force is responsible for long distance water transport? 

Fick’s First Law: Describes diffusion efficiency, which is too slow for long-distance transport in plants

Long-distance Transport Force: Driven by negative pressure (tension generated by transpiration in leaves, pulling water up through the xylem - cohesion-tension theory)

6. Tracheids and vessel elements are both water-conducting cells. Tracheids are considered “safe”, but vessel elements are considered “fast”. Using detailed diagrams and associated text, discuss how the structure of these cells relates to their function. Be sure to discuss relative cell diameter, cell wall characteristics, and cell length. 

Tracheids - narrower, overlap with pit pairs, slower transport, found in gymnosperms and ferns, more resistant to embolisms

Vessel Elements - Wider, stacked end-to-end, forming efficient pipelines, found in angiosperms, more susceptible to cavitation (air bubbles)

7. Discuss the significance (to the plant) of the Casparian strip.

Located in the endodermis of roots, made of suberin, forcing water and solutes to pass through the symplast rather than the apoplast, regulates nutrient uptake and prevents harmful substances from entering the vascular system

8. Plants face two main challenges with respect to water transport. Explain, in detail, what these two challenges are and how anatomical features of plants can help plants withstand these challenges

-Water Scarcity

-High Evaporation Demand

adaptations: thick cuticle reduces evaporation, sunken stomata reduce water loss, xerophytes have CAM metabolism, storing CO2 at night to reduce water loss

9. Discuss the origins of land plants and the challenges and opportunities they faced as they colonized land.

-Challenges: water availability, structural support, reproduction without water

-Adaptations: Waxy Cuticle, stomata, vascular tissues, lignified cell walls for structural support, pollen and seeds for reproduction without water

10. Track the path of a water molecule through the soil-plant-air continuum. What forces influence its movement along this pathway?

-Soil, Root hairs, cortex, endodermis (casparian strip forces symplastic movement), xylem, leaf mesophyll, stomata, atmosphere

Driving Forces: Water Potential gradient, transpiration pull, cohesion and adhesion

11. Provide a detailed description of why plants can use the energy from the sun to drive the flow of water through the plant.

-Sunlight increases transpiration

-Creates negative pressure in the leaf, pulling water from the roots (cohesion-tension theory)

-Stomatal Regulation allows water loss control while enabling CO2 uptake

12. Water loss at the leaf level is influenced by boundary layer and stomatal resistance. Define both of these terms. Then, describe how leaf size and morphology as well as wind speed influence these processes.

-Boundary Layer Resistance: Thin layer of still air around the leaf, thicker boundary layer slows transpiration

-Stomatal Resistance: Regulated by guard cells, determines the rate of gas exchange

-Effects of leaf size, morphology, and wind speed: Larger leaves have higher transpiration but thicker boundary layers, wind reduces the boundary layer, increasing transpiration, needle-like leaves reduce water loss

13. Below is a Hofler diagram. Explain what information can be gleaned from this diagram. How would the pressure component differ for a cell with a more rigid cell wall? For a cell with a more elastic cell wall? How would this affect the cell’s ability to maintain turgor under drying conditions? How do these cell wall properties influence equilibration with the environment and why?

-Interpretation: Shows the relationship between cell turgor pressure and relative cell volume

-Rigid Cell Wall: Steeper Slope; maintains structure but loses turgor under drought stress

-Elastic Cell Wall: Flatter Slope can shrink more but retains some turgor

-Significance: Elastic walls allow plants to tolerate water loss better, turgor maintenance is key for cell expansion and Function