Transport in Plants flashcards

Why don't plants need blood vessels like animals?

They use xylem and phloem to transport substances instead.

What are the main transport tissues in plants?

Xylem (for water and minerals) and phloem (for sugars and amino acids).

How does xylem transport substances?

Transports water and mineral ions upward from roots to leaves.

How does phloem transport substances?

Transports sugars and amino acids up and down the plant.

What structural features are found in xylem vessels?

Dead cells, no organelles, continuous tubes, lignin in walls, and pits for lateral flow.

What is the function of lignin in xylem?

Strengthens and supports the plant; prevents collapse of xylem vessels.

What are pits in xylem walls for?

Allow movement of water and minerals between adjacent cells.

What are sieve tube elements?

Living phloem cells that lack nuclei and form tubes for solute transport."

What are companion cells and their function?

Cells with nuclei and mitochondria that support sieve tube elements via plasmodesmata.

Q: What are vascular bundles?

A: Groups of xylem, phloem, and sclerenchyma for transport and structural support.

Q: What is the role of sclerenchyma in vascular bundles?

Sclerenchyma provides structural support to the vascular bundles. The cells are dead, with thickened cell wallsreinforced with lignin, making them strong and rigid.

How are vascular bundles arranged in the stem?

Xylem inside, phloem in the middle, sclerenchyma outside.

How is water absorbed by plant roots?

Through root hair cells by osmosis, down a water potential gradient.

What is transpiration?

The evaporation of water from leaves through stomata.

What is the cohesion-tension theory?

Water molecules stick together (cohesion) and are pulled upward (tension) due to transpiration.

What causes cohesion between water molecules?

Hydrogen bonding between polar water molecules.

What creates the tension in xylem water transport?

Water loss from leaves creates negative pressure, pulling more water upward.

What is translocation in plants?

Movement of sugars and amino acids from source to sink through phloem.

What is a source and sink in phloem transport?

Source: where sugars are made (e.g., leaves). Sink: where sugars are used/stored (e.g., roots, fruits).

Is translocation passive or active?

Active – requires ATP for loading sugars into sieve tubes.

Q: What is the mass flow hypothesis?

Active loading of solutes creates a pressure gradient, causing solutes to flow from source to sink.

How does loading solutes into phloem affect water potential?

Lowers it, causing water to enter by osmosis, increasing pressure.

What connects companion cells and sieve tubes?

Plasmodesmata

What is the function of companion cells?

Support sieve tubes with energy and nutrients.

Where is phloem located in the stem?

Between xylem and sclerenchyma.

What are two main reasons plants need water?

Photosynthesis and mineral transport.

Q: What drives water movement through the xylem?

Transpiration

Explain how the mass flow hypothesis accounts for the movement of sugars from leaves to roots

• Sugars transferred to pholem

• Lower water p so water enters pholem

• Pressure increases in pholem due to moving sugars

• Sugars converted to insoluble starch in root cells

• Increased water p so water moves out

Compare and contrast the stucture of xylem and pholem

Similarities

• Both have cellulose in cell wall

• Both tissues contain tubes

Differences

• Xylem vessels Have lignin pholem do not

• Pholem have companion cells and xylem do not

Cohesion tension

• Water mols are polar

• Cohesion is due to hydrogen bonding between water molecules

• Column of water is under tension as water evaporates

• Evaporation causes pressure to decrease

Describe the differences between the apoplastic and symplastic pathway

Apoplastic

• non-living

• Uses cell walls

• Favours diffusion

• Blocked by casparian strip

Symplastic

• living

• Plasmodesmata

• Osmosis

• Does not have a casparian strip