Transport in plantsTransport in plants

Xylem: Evapo-transpirationXylem: Evapo-transpiration

ObjectivesObjectives

Describe the structure of xylem vessels & Describe the structure of xylem vessels & sieve tubes.sieve tubes.

Discuss how the structure of the xylem vessels Discuss how the structure of the xylem vessels suited for its functionsuited for its function

Describe the process involved in transpiration.Describe the process involved in transpiration. Discuss the external factors that affect Discuss the external factors that affect

transpiration transpiration

Why do plants need a transport Why do plants need a transport system?system?

To transport food and water throughout the To transport food and water throughout the plant from roots to leaves at the top of the plant.plant from roots to leaves at the top of the plant.

These substances are used by the plant to aid in These substances are used by the plant to aid in photosynthesis.photosynthesis.

There are two structures used to transport There are two structures used to transport material, the xylem vessels and phloem tubes.material, the xylem vessels and phloem tubes.

Vascular bundles are xylem and phloem tubes in Vascular bundles are xylem and phloem tubes in close proximity to each other.close proximity to each other.

The position and orientation of vascular The position and orientation of vascular bundles vary throughout the plant.bundles vary throughout the plant.

The phloem however is always found on the The phloem however is always found on the outer part of the bundleouter part of the bundle

XylemXylem

Xylem vessels transport water and dissolved Xylem vessels transport water and dissolved minerals from the root to the shoot of plants.minerals from the root to the shoot of plants.

Xylem adaptationsXylem adaptations

These are well adapted with:These are well adapted with: Long & Tubular cellsLong & Tubular cells Hollow (no cell contents)Hollow (no cell contents) Thick bands of cellulose and ligninThick bands of cellulose and lignin Water-resistant wallsWater-resistant walls

Direction of movement of Direction of movement of substances in vascular tissue.substances in vascular tissue.

Xylem tissueXylem tissue

MONOCOTSMONOCOTS

Root pattern (xylem and phloem) – ring

DICOTSDICOTS

Stem pattern – Ring-shaped xylem and phloem.

LARGE CELLS ARE XYLEM

SMALL CELLS ON OUTSIDE ARE PHLOEM

DICOTSDICOTS

Root pattern (xylem and phloem) – X-shape

Mineral and water uptake in rootMineral and water uptake in root*osmosis*osmosis

Casparian StripCasparian Strip

The Casparian strip The Casparian strip controls water controls water movement into the movement into the vascular cylinder of vascular cylinder of the root.the root.

Water cannot move Water cannot move between cells. It must between cells. It must move through the cells move through the cells by osmosis. Why is by osmosis. Why is this important?this important?

Thinking question:Thinking question:

What would happen in a root that had no What would happen in a root that had no Casparian strip? Why would this be a Casparian strip? Why would this be a problem?problem?

Water movement up the xylemWater movement up the xylem Step Step

1:Capillary 1:Capillary actionaction

Cohesion and Cohesion and adhesion cause adhesion cause water to “crawl” water to “crawl” up narrow tubes. up narrow tubes. The narrower the The narrower the tube the higher the tube the higher the same mass of same mass of water can climb.water can climb.

Maximum height: Maximum height: 32 feet.32 feet.

Capillary actionCapillary action

Cohesion: polar Cohesion: polar water molecules water molecules tend to stick tend to stick together with together with hydrogen bonds.hydrogen bonds.

Adhesion: water Adhesion: water molecules tend molecules tend to stick to polar to stick to polar surfaces. surfaces.

Cohesion-tension theoryCohesion-tension theory

Cohesion between water molecules creates a Cohesion between water molecules creates a “water chain” effect.“water chain” effect.

As molecules are removed from the column by As molecules are removed from the column by evaporation in the leaf, more are drawn up.evaporation in the leaf, more are drawn up.

Part 2: Root pressure

There is a higher pressure in roots due to the higher conc. of water molecules being absorbed from soil.

Water moves form area of high pressure (in roots) to low pressure (in leaves)

Part 3: Transpiration pull due to Part 3: Transpiration pull due to evaporationevaporation

Evaporation at the surface of the leaf keeps the Evaporation at the surface of the leaf keeps the water column moving. water column moving.

This is the strongest force involved in transpiration.This is the strongest force involved in transpiration.

Factors affecting transpiration rateFactors affecting transpiration rate

Temperature: temp = TRTemperature: temp = TR Humidity: Humidity = TRHumidity: Humidity = TR Wind velocity: Wind velocity = TRWind velocity: Wind velocity = TR Light intensity: affects stomatal openingLight intensity: affects stomatal opening Water content in soil : Less water in soil lead Water content in soil : Less water in soil lead

to less available for plants. The cellss get to less available for plants. The cellss get flaccid and in turn, plant wilts. Long term flaccid and in turn, plant wilts. Long term deprivation leads to death of plant.deprivation leads to death of plant.

Stomata controlStomata control Guard cells around Guard cells around

the stomata are the stomata are sensitive to light, sensitive to light, CO2, and water CO2, and water loss.loss.

Cells expand in Cells expand in response to light response to light and low CO2 and low CO2 levels, and collapse levels, and collapse in response to in response to

water losswater loss..

StomataStomata

When stomata are open, evaporation draws When stomata are open, evaporation draws water out of the leaf. Gas exchange can also water out of the leaf. Gas exchange can also occur to keep photosynthesis and respiration occur to keep photosynthesis and respiration running.running.

When stomata are closed, evaporation cannot When stomata are closed, evaporation cannot occur, nor can gas exchange. What happens occur, nor can gas exchange. What happens to photosynthesis and transpiration?to photosynthesis and transpiration?