Plant transportation and adaptations

What is transpiration?

Evaporation of water from spongy mesophyll and diffusion through stomata.

Why must water be transported from roots to leaves?

To replace water lost by transpiration.

Which tissue transports water in plants?

Xylem vessels.

What is xylem sap composed of?

Mostly water with low concentrations of ions.

Where does water evaporate from in leaves?

Cell wall spaces of mesophyll cells and xylem vessels.

What forces cause transpiration?

Cohesion and adhesion.

What is the transpiration pull?

Tension created by evaporation drawing water up xylem.

Why does transpiration generate tension?

Pressure differences between roots and leaves.

What happens to pressure when water leaves xylem in leaves?

Pressure decreases.

What is negative pressure potential?

Reduced pressure in the water column causing upward pull.

Name three pathways water takes through roots.

Apoplast, symplast, and transmembrane pathways.

What is the apoplast pathway?

Movement of water through cell walls and intercellular spaces.

Why is the apoplast pathway efficient?

It avoids living cell contents.

What is the symplast pathway?

Diffusion through cytoplasm via plasmodesmata.

Why is the symplast pathway less significant?

Organelles create resistance to water flow.

What is the transmembrane pathway?

Osmosis from vacuole to vacuole driven by osmotic gradients.

What is the Casparian strip?

A waxy barrier impermeable to water in the endodermis.

Why does the Casparian strip force symplastic movement?

It blocks passive apoplast flow.

What are the two types of xylem cells?

Tracheids and vessel elements.

How are tracheids adapted for water transport?

They are long and narrow with thin walls.

How are vessel elements adapted for water transport?

They are short with perforated end walls and wide lumens.

What are pits in xylem walls?

Gaps allowing water to enter and exit.

Why is lignin important in xylem vessels?

It strengthens walls and prevents collapse.

Why are mature xylem vessels dead?

Cell contents dissolve leaving hollow tubes.

How are vascular bundles arranged in dicot stems?

In a ring around the stem.

How are vascular bundles arranged in monocot stems?

Scattered throughout the stem.

How do xylem and phloem appear in stem cross sections?

Xylem has large openings, phloem smaller.

Describe xylem arrangement in dicot roots.

Large xylem vessels arranged in a cross.

Describe phloem arrangement in dicot roots.

Arranged around the xylem.

How are vascular bundles arranged in monocot roots?

Xylem arranged in a ring with phloem between.

What tissue surrounds vascular bundles in dicot roots?

A ring of endodermal tissue.