Plant Adaptations and Transport Mechanisms in Vascular Plants

What adaptations did early algae have for resource acquisition?

Leafless shoots with waxy cuticles and some stomata, anchored by rhizoids.

How did competition among plants influence their evolution?

Taller plants dominated, leading to the evolution of larger shoots and roots for better anchorage and resource acquisition.

What is the significance of vascular tissue in plants?

Vascular tissue (xylem and phloem) allows for the transport of water, nutrients, and sugars, enabling complex root and shoot systems.

What is phyllotaxy and why is it important?

Phyllotaxy refers to the arrangement of leaves on a stem, which is crucial for maximizing light capture.

What are the three types of phyllotaxy?

1. Alternate phyllotaxy (one leaf per node), 2. Opposite phyllotaxy (two leaves per node), 3. Whorled phyllotaxy (more than two leaves per node).

How does leaf orientation affect light capture?

Horizontal leaves capture more light, while vertical leaves protect from excessive light exposure.

What is the leaf area index?

The ratio of total upper leaf area to the ground area, influencing light capture efficiency.

What is the compromise between photosynthesis and water loss in plants?

Stomata facilitate gas exchange for photosynthesis but can also lead to dehydration.

How do plants adjust their root architecture for nutrient acquisition?

Roots can extend straight through soil or branch towards nutrient pockets, optimizing absorption efficiency.

What are the two major pathways for transport in plants?

The apoplast (external to plasma membranes) and the symplast (cytosol of cells).

What is the apoplastic route?

A pathway for water and minerals that does not pass through cell membranes but travels above cells.

What is the symplastic route?

A pathway where water and solutes move through the cytoplasm of cells, bypassing cell walls.

What role do aquaporins play in plant cells?

Aquaporins facilitate the transport of water across plant cell plasma membranes.

What is osmosis?

The diffusion of water through a semipermeable membrane from an area of high water potential to low water potential.

What is water potential and how is it measured?

Water potential (Ψ) is the capacity to do work, measured in megapascals (MPa). Pure water at sea level has a potential of 0 MPa.

What is the water potential equation?

Ψ = Ψs + Ψp, where Ψs is solute potential and Ψp is pressure potential.

What happens during plasmolysis?

The cell membrane pulls away from the cell wall due to water loss, causing the cell to shrink.

What is turgor pressure?

The pressure exerted by the protoplast against the cell wall, resulting from water entering the cell.

What is the cohesion-tension hypothesis?

It explains how water is pulled up through the xylem due to evaporation from leaves creating a negative pressure.

What is the role of the endodermis in root cells?

The endodermis acts as a security checkpoint, regulating the entry of water and minerals into the vascular cylinder.

What is the Casparian strip?

A waxy barrier in the endodermis that forces water and minerals to pass through cell membranes rather than between cells.

What is bulk flow in plants?

The movement of liquid in response to a pressure gradient, allowing for long-distance transport of water and nutrients.

How do xylem and phloem facilitate transport?

Xylem conducts water and minerals, while phloem transports sugars; both utilize specialized cells for efficient bulk flow.

What is the significance of root hairs in plants?

Root hairs increase surface area for absorption of water and nutrients from the soil.

What is the impact of soil solution on root absorption?

Soil solution, containing water and dissolved minerals, enhances the exposure of root cells for better absorption.

What is the difference between short-distance and long-distance transport in plants?

Short-distance transport occurs across plasma membranes, while long-distance transport utilizes bulk flow through vascular tissues.

What is the function of the endodermis in plant roots?

Acts as a security checkpoint for minerals and water entering the vascular cylinder.

What is xylem sap?

A solution of water and dissolved minerals that passes through the endodermis into the stele.

How is xylem sap transported?

By bulk flow, which is very fast and relies on transpiration.

What is root pressure?

A pressure from xylem sap that accumulates minerals and can lead to guttation.

What does the cohesion-tension hypothesis explain?

Transpiration provides the pull for the ascent of xylem sap due to the cohesion of water molecules.

What happens during transpiration?

Water vapor escapes from the stomata, creating negative pressure that pulls water up from the roots.

What role do stomata play in water loss?

They are the major pathways for water loss in plants.

What is the function of guard cells?

They control the diameter of the stomata by changing shape, regulating water loss.

What stimuli cause stomatal opening?

Light, depletion of CO2, and an internal circadian clock.

What is the effect of drought on stomata?

Abscisic acid signals guard cells to close stomata to reduce water loss.

What adaptations do xerophytes have?

They have fleshy stems to store water and may use CAM photosynthesis.

What is translocation in plants?

The transport of sugars from sources (mature leaves) to sinks (growing parts).

What are sieve tube elements?

Phloem cells that facilitate the flow of sap in angiosperms.

What is phloem sap?

An aqueous solution that contains sugars, amino acids, hormones, and minerals.

How does sugar move from sources to sinks?

Through active transport and osmotic movement, driven by pressure differences.

What is the role of companion cells?

They assist in loading sugars into sieve tube elements and enhance solute transfer.

What is the significance of plasmodesmata?

They allow communication and transport between plant cells.

What is cavitation in the xylem?

The formation of air bubbles that can interrupt the flow of water.

How does transpiration affect leaf temperature?

It cools the leaf through evaporation, preventing enzyme denaturation.

What happens when stomata close?

Guard cells release K+, causing water to exit and the cells to become flaccid.

What is the rate of phloem sap flow?

Phloem sap flows at approximately 1 meter per hour.

What is the role of electrical signaling in phloem?

It triggers responses that can change gene transcription and transport processes.

What happens to leaves during prolonged drought?

They become wilted and injured due to lack of water.

What is the relationship between stomatal density and CO2 levels?

Low CO2 levels can lead to increased stomatal densities during leaf development.

What is guttation?

The discharge of water droplets from plants, often due to root pressure.

What is the significance of the negative pressure in leaves?

It pulls water up from the roots through the xylem.

How do guard cells regulate stomatal opening?

They become turgid by taking up water, which increases the pore size.