2.1C Transport in plants & transpiration

Epidermis

The outermost layer of cells covering the plant.​

• PROTECTION - It serves as a barrier against desiccation (drying out) and infection.

• WATER LOSS REDUCTION - Waxy cuticle that is waterproof, thereby reducing water loss through evaporation.

• LIGHT TRANSMISSION - Cell walls are transparent, allowing light to pass through to underlying photosynthetic tissues.​

• WATER & MINERAL UPTAKE - Large surface area.

Endodermis

Cells located in the root, which contain deposits of suberin in their cell walls.

• Controls uptake into the stele.

• Interrupts the apoplast pathway.

• Ensures the symplast pathway​.

Xylem vessel

Xylem is non-living tissue is responsible for the one-way transport of water and inorganic ions from the roots to the aerial parts of the plant.

• No cytoplasm or cell contents so less resistance to water movement.

• When cells die, cell walls break down creating a continuous tube allowing large amounts of water to flow.

• PROTOXYLEM - Found in the zone of elongation.

  • Annular or spiral lignification patterns, which provide flexibility and allow for continued growth.

  • Narrow lumens to facilitate water transport during early development.​

• METAXYLEM - Mature vessels.

  • Reticulate or pitted lignification patterns, offering greater strength and support.

  • Wider lumens to accommodate increased water transport needs.​

What is lignin?

Within the cell wall providing structural support and waterproofing, and essential in preventing leakage of water & tubing collapsing under negative pressure as a result of transpiration.

What are pits?

They allow lateral movement of water transport of cells a reduces resistance to flow.

Phloem tissue

Phloem is living tissue responsible for the translocation (two way transport) of organic solutes, such as sucrose and amino acids, throughout the plant.

• SIEVE-TUBE ELEMENTS - These are elongated, living cells that align end-to-end to form continuous tubes.

  • Sieve plates at their end walls, which are perforated with pores to allow for the flow of phloem sap.

  • Lack of a nucleus and minimal organelles at maturity, maximising space for translocation.​

• COMPANION CELLS - Nucleated with dense cytoplasm.

  • Undertake metabolism for sieve tubes.

  • Loading and unloading of solutes into and out of the phloem.

  • Providing ATP for active transport processes, facilitated by numerous mitochondria

What is the casparian strip?

Suberin which forms a waterproof component, blocking the apoplast way in the endodermis.