9.1 Transport in the Xylem of Plants
Plant Structure
Label the diagram of the leaf tissue of a plant
1. ……………………………………Vascular bundle 4. ……………………………………Epidermis (lower) 7. ……………………………………Stoma
2. ……………………………………Xylem 5. ……………………………………Waxy cuticle 8. ……………………………………Palisade mesophyll
3. ……………………………………Phloem 6. ……………………………………Guard cell 9. ……………………………………Spongy mesophyll
Explain the location of the mesophyll (palisade and spongy) and vascular bundle within the leaf
On the upper surface of the leaf, the cells are packed tight and rich in chloroplasts Palisade Mesophyll: …………………………………………………………………………………………………………………………
This increases light absorption for photosynthesis …………………………………………………………………………………………………………………………………………………......
Spongy Mesophyll: …………………………………………………………………………………………………………………………..On the lower surface of the leaf, the cells are interspersed by space and near stomata
…………………………………………………………………………………………………………………………………………………...... This increases gas exchange for photosynthesis
Vascular Bundle: ……………………………Vascular bundles exist……………………………………………………………………………………………….. centrally between the two layers (allowing equal access)
…………………………………………………………………………………………………………………………………………………...... Have xylem for water transport to leaf & phloem for food transport from leaf
Identify the following plant tissues (monocot vs dicot ; root vs stem)
Monocot root Monocot stem Dicot root Dicot stem ………………………… ………………………… ………………………… ………………………… Xylem Structure
Describe the structure of the xylem
…………………………………………………………………………………………………………………………………………………...... Inner lining is composed of dead cells that have fused into a continuous tube
…………………………………………………………………………………………………………………………………………………...... These cells lack a cell membrane, allowing water to enter the xylem freely
………………………………………………………………………………………………………………………………………………The cell walls have thickened cellulose and are reinforced with lignin (annular or spiral) …......
…………………………………………………………………………………………………………………………………………………...... The outer layer is perforated (has pores), enabling water movement out of xylem
Draw the structure of primary xylem vessels in stems
MICROSCOPE DRAWING
Xylem Phloem Xylem Phloem
Meta Proto Pit Lignin Cell wall
Transpiration
Define transpiration Transpiration is the loss of water vapour from the leaves and stems of the plant …………………………………………………………………………………………………………………………………………………......
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Differentiate between fibrous and tap root systems
Fibrous: …………………………………………………………………………………………………………………………………………..Fibrous roots are thin and very spread out
Tap: ………………………………………………………………………………………………………………………………………………...Tap roots penetrate deeply (for stability) and have many connected lateral branches Explain the uptake of mineral ions into the root by direct and indirect active transport
Direct Active Transport Protein pumps use ATP to translocate ions against their concentration gradient …………………………………………………………………………………………………………………………………………………......
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Indirect Active Transport
…………………………………………………………………………………………………………………………………………………...... Proton pumps expel H+ ions into the soil, displacing the cationic minerals from clay
………………………………………………………………………………………………………………………………………………….Displaced minerals will passively diffuse into the root (along a concentration gradient) ......
…………………………………………………………………………………………………………………………………………………...... Anionic minerals may bind to the H+ ions and be reabsorbed with the proton
Outline the role of stomata in regulating the level of evaporation from the leaf
…………………………………………………………………………………The transpiration rate can be regulated by the guard cells
…………………………………………………………………………………which flank the stomata
…………………………………………………………………………………Guard cells occlude the opening when flaccid
…………………………………………………………………………………Guard cell turgor is regulated by abscisic acid
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Define cohesion and adhesion Water molecules stick together (by H-bonding) Cohesion: ……………………………………………………………………………………………………………………………………….. Water molecules form polar associations with the wall of the xylem vessel Adhesion: ………………………………………………………………………………………………………………………………………..
Explain how water is transported around the plant via a transpiration stream
…………………………………………………………………………………………………………………………………………………...... Some of the light energy absorbed by leaves changes into heat, converting water to vapour
…………………………………………………………………………………………………………………………………………………...... The vapour diffuses out and is evaporated, creating a negative pressure gradient in leaves
…………………………………………………………………………………………………………………………………………………...... New water is drawn via the xylem from roots (which enters from soil via osmotic uptake)
…………………………………………………………………………………………………………………………………………………...... Water rises up (against gravity) through xylem vessels via mass flow due to cohesion and adhesion
…………………………………………………………………………………………………………………………………………………...... The flow of water from the roots to the leaf (via the xylem) is called the transpiration stream
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…………………………………………………………………………………………………………………………………………………...... Explain how abiotic factors affect the rate of transpiration in a typical terrestrial plant
Light: ………………………………………………………………………………………………………………………………………………Increasing the light intensity to which a plant is exposed increases the rate of transpiration
………………………………………………………………………Increasing light exposure causes more stomata…………………………………………………………………………...... to open to facilitate photosynthetic gas exchange
Temperature: …………………………………………………………………………………………………………………………………Increasing ambient temperature causes an increase in the rate of transpiration .
…………………………………………………………………………………………………………………………………………………...... Higher temperatures lead to an increase in the rate of evaporation within the mesophyll
Wind: ……………………………………………………………………………………………………………………………………………...Increasing the level of wind exposure causes an increase in the rate of transpiration
…………………………………………………………Wind / air circulation removes water………………………………………………………………………………………...... vapour from near the leaf, effectively reducing proximal humidity
Humidity: ………………………………………………………………………………………………………………………………………..Increasing the humidity is predicted to cause a decrease in the rate of transpiration
…………………………………………………………………………………………………………………………………………………...... Less vapour will diffuse from the leaf if there is more vapour in the air
Identify four adaptations in xerophytes and halophytes that help reduce or increase transpiration
Xerophyte Halophyte
Arid / dry and high temperatures Saline (salty soil / water) Conditions ……………………………………………………………. …………………………………………………………….
…………………………………………………………….Increased water loss via evaporation …………………………………………………………….Reduced water uptake due to hypertonic Issue …………………………………………………………….Reduced water uptake via roots …………………………………………………………….soil conditions (+ high levels of salt uptake)
1. ………………………………………………………Reduced leaves (⬇ evaporation) 1. ………………………………………………………Cellular sequestration (salt in vacuoles)
2. ………………………………………………………Thick cuticles (prevents water loss) 2. ………………………………………………………Tissue partitioning (leaf abscission) Adaptations 3. ………………………………………………………Stomata in pits (traps water vapour) 3. ………………………………………………………Salt excretion (active salt removal)
4. ………………………………………………………CAM physiology (open stomata at night) 4. ………………………………………………………Root level exclusion (avoid salt uptake)
List three ways water transport can be modelled in xylem
1. …………………………………………………………………………………………………………………………………………………...Capillary tubing
2. …………………………………………………………………………………………………………………………………………………...Porous pots
3. …………………………………………………………………………………………………………………………………………………...Filter paper
Describe how potometers can be used to measure transpiration rates
…………………………………………………………………………………………………………………………………………………...... Potometers estimate transpiration rate by measuring the rate of water loss or uptake by a plant
…………………………………………………………………………………………………………………………………………………...... They record the distance moved by an air bubble or meniscus to indicate the rate of water uptake