OCR (A) Biology A-level - Transport in Plants

Comprehensive vocabulary flashcards covering the transport systems (xylem and phloem), transpiration, xerophyte/hydrophyte adaptations, and the mechanisms of water and sugar movement in plants.

Xylem

A tissue that enables water and dissolved minerals to travel up the plant in a passive process known as transpiration, while also providing structural support.

Phloem

A tissue that enables sugars to reach all parts of the plant in an active process known as translocation.

Vascular bundle

A unit containing xylem and phloem components which serves to enable the transport of substances and provide structural support.

Endodermis

An outer layer of cells surrounding the X-shaped xylem arrangement in the root that supplies the xylem vessels with water.

Pericycle

An inner layer of meristem cells located within the vascular bundle of the root.

Cambium

A layer of meristem cells found between the xylem and phloem in the stem involved in the production of new xylem and phloem tissue.

Lignin

A tough substance deposited in spiral patterns in xylem vessels to thicken them and enable the plant to remain flexible.

Pits

Structures in xylem vessels that enable water to move sideways between the vessels.

Sieve tube elements

Living cells in the phloem that form a tube to transport sugars such as sucrose in the dissolved form of sap.

Companion cells

Cells in the phloem involved in $ATP$ production for active processes like loading sucrose into sieve tubes.

Plasmodesmata

Gaps between cell walls that link the cytoplasm of sieve tube elements and companion cells, allowing communication and the flow of substances.

Transpiration

The process where plants absorb water through the roots, which moves up the plant and is released into the atmosphere as water vapour through stomata.

Transpiration stream

The movement of water up the stem that enables photosynthesis, growth, and elongation while supplying minerals and controlling temperature.

Potometer

A device used to investigate the rate of transpiration by measuring the movement of the meniscus as water vapour lost by the leaf is replaced.

Xerophytes

Plants adapted to living in dry conditions through features like thick waxy cuticles, smaller leaves, and hairs or pits that trap moist air.

Hydrophytes

Plants adapted to live in water, featuring thin or absent waxy cuticles, air sacs for buoyancy, and stomata on the upper surfaces of leaves.

Symplast pathway

A route for water movement where water enters the cytoplasm through the plasma membrane and passes between cells through plasmodesmata.

Apoplast pathway

A route for water movement through water-filled spaces between cellulose molecules in cell walls, which does not involves passing through plasma membranes.

Casparian strip

A layer of suberin in the endodermis that is impenetrable to water, forcing water in the apoplast pathway to enter the symplast pathway.

Root pressure

The upward push of water caused by the endodermis actively moving minerals into the xylem, which drives water in by osmosis.

Tension-cohesion theory

The theory explaining water flow maintained by surface tension and the attractive forces (cohesion) between water molecules.

Capillary action

The process where forces of cohesion cause water molecules to adhere to the walls of the xylem, pulling the water up.

Assimilates

Substances such as sucrose that are transported during translocation from sources to sinks.

Active loading

An energy-requiring process where companion cells use $ATP$ to transport hydrogen ions to create a gradient for sucrose to enter via cotransporter proteins.

Mass flow

The movement of water and assimilates like sucrose from the source to the sink down a hydrostatic pressure gradient.