Transport in plantsTransport in plants

Xylem: Evapo-transpirationXylem: Evapo-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.

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 uptakeMineral and water uptake

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?

Capillary actionCapillary action

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.

Step 2: Capillary actionStep 2: Capillary 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 3: EvaporationPart 3: Evaporation

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.

Stomata controlStomata control

Guard cells around Guard cells around the stomata are the stomata are sensitive to light, sensitive to light, COCO22, and water , and water loss.loss.

Cells expand in Cells expand in response to light response to light and low COand low CO22 levels, and collapse levels, and collapse in response to in response to water loss.water 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?

HOW DOES XYLEM WORK?HOW DOES XYLEM WORK?

Cohesion of water molecules – Water is “sticky”