Plant Transport Systems

What is the role of xylem in plants?

Xylem transports water and minerals from roots to shoots.

What does phloem transport?

Phloem transports photosynthetic products from source to sink.

What adaptations do plants have for resource acquisition?

Plants have adaptations to acquire water, minerals, and light.

How do shoot architecture and light capture relate?

Shoot length and branching affect light capture, with a trade-off between height and branching.

What is phyllotaxy and why is it important?

Phyllotaxy is the arrangement of leaves on a stem, which is species-specific and important for maximizing light capture.

What is self-pruning in plants?

Self-pruning occurs when respiration exceeds photosynthesis, leading to the shedding of lower leaves.

How do stomata function in plants?

Stomata allow gas diffusion into photosynthetic tissues but also lead to significant water loss through evaporation.

What is the role of mycorrhizae in plant root systems?

Mycorrhizae are fungi that form mutualistic relationships with plant roots, increasing surface area for water and mineral absorption.

What are the two major transport pathways in plants?

The two major transport pathways are apoplast (external to plasma membrane) and symplast (cytosol of living cells).

What is the difference between apoplastic and symplastic transport?

Apoplastic transport occurs through cell walls and extracellular spaces, while symplastic transport involves crossing a plasma membrane once and then moving through the cytosol.

What is osmosis in the context of plant cells?

Osmosis is the diffusion of water affected by solute concentration and pressure.

What is water potential and how is it measured?

Water potential (Ψ) is measured in megapascals (MPa) and includes effects of solute concentration and physical pressure.

What is turgor pressure?

Turgor pressure is the positive pressure exerted by the plasma membrane against the cell wall.

What happens during plasmolysis?

Plasmolysis occurs when the protoplast shrinks and pulls away from the cell wall in a hypertonic environment.

What is the function of aquaporins in plants?

Aquaporins are transport proteins that facilitate the passage of water across cell membranes.

What drives bulk flow in plants?

Bulk flow is driven by a pressure gradient, allowing water and solutes to move together through xylem and phloem.

How does transpiration contribute to water transport in plants?

Transpiration drives water and mineral transport from roots to shoots via xylem.

Where does most water and mineral absorption occur in plants?

Most absorption occurs near root tips where root hairs increase surface area.

What is the endodermis in plant roots?

The endodermis is the innermost layer of the root cortex that regulates the flow of water and minerals into the xylem.

What is the endodermis?

The innermost layer of the root cortex that regulates mineral transport into the xylem.

What is the function of the Casparian strip?

It is a waxy wall of endodermal cells that blocks apoplastic transfer to the vascular cylinder.

How does xylem sap move from roots to leaves?

By bulk flow driven by transpiration.

What is transpiration?

The evaporation of water from a plant's surface.

What generates root pressure?

Root cells pump mineral ions into the xylem at night, lowering water potential and causing water to flow in.

What is guttation?

The exudation of water droplets on leaf tips.

What is the cohesion-tension hypothesis?

It explains how transpiration and water cohesion pull water from shoots to roots.

What role does surface tension play in water transport?

It creates negative pressure potential, lowering water potential and pulling water from hydrated areas.

How do cohesion and adhesion assist in the ascent of xylem sap?

Cohesion attracts water molecules to each other, while adhesion helps water stick to xylem cell walls, offsetting gravity.

What is cavitation in the context of xylem transport?

The formation of a water vapor pocket that breaks the water chain, though transport can continue through pits.

What drives bulk flow in xylem?

A water potential difference at opposite ends of xylem tissue, driven by transpiration.

How does bulk flow differ from diffusion?

Bulk flow is driven by pressure potential and occurs in dead cells, moving the entire solution quickly.

What regulates the rate of transpiration?

Stomata, which are controlled by guard cells that balance photosynthesis and water conservation.

What percentage of water loss occurs through stomata?

About 95%.

What happens to guard cells when they become turgid?

They bow outward, opening the stoma.

What triggers stomatal opening at dawn?

Light, depletion, and an internal circadian clock.

What is the effect of drought stress on stomata?

It causes stomata to close during the daytime.

What is abscisic acid (ABA) and its role in plants?

A hormone produced in response to water deficiency that causes stomatal closure.

What adaptations do xerophytes have to reduce water loss?

They may have fleshy stems for storage or modified leaves to minimize transpiration.

What is translocation in plants?

The transport of sugars from sources to sinks via the phloem.

What are sieve-tube elements?

Conduits for translocation in the phloem.

What is the difference between a source and a sink in plant transport?

A source is a net producer of sugar (e.g., mature leaves), while a sink is a net consumer or depository (e.g., roots, buds).

How is sugar loaded into sieve-tube elements?

It may move by symplastic or apoplastic pathways and often requires active transport.

What drives the movement of phloem sap?

Bulk flow driven by positive pressure from sources to sinks.

What is the symplast?

A living tissue responsible for dynamic changes in plant transport, connected by plasmodesmata.

How does phloem function as an information superhighway?

It allows for systemic transport of macromolecules and rapid electrical communication throughout the plant.