Topic 3.3

• What is active loading?

  The process by which hydrogen ions are actively pumped out of companion cells using ATP, before diffusing down a concentration gradient, back into the cells via

  co-transporter proteins, whilst carrying sucrose.
• What is adhesion?

  The formation of hydrogen bonds between carbohydrates in

  the xylem vessel walls and water molecules. This contributes to the capillarity of water and transpiration pull.
• What is the apoplast route?

  One of two pathways by which water and minerals move across the root. Water moves through intercellular spaces between cellulose molecules in the cell wall.
• What is a casparian strip?

  A waterproof strip surrounding the endodermal cells of the root that blocks the apoplast pathway, forcing water through the symplast route
• What is cohesion?

  The formation of hydrogen bonds between water molecules.

  This contributes to the capillarity of water and transpiration pull
• What is the cohesion-tension theory?

  The model that explains the movement of water from the soil to

  the leaves, in a continuous stream
• What are companion cells?

  The active cells of the phloem located adjacent to the sieve tube

  elements. They retain their nucleus and organelles, producing ATP for metabolic processes in both themselves and the sieve tube elements
• What are dicotyledonous plants?

  Plants that produce seeds that contain two cotyledons. They have

  two primary leaves
• What are hydrophytes?

  Plant that are adapted to live and reproduce in very wet habitats,
• What is phloem?

  A living plant transport vessel responsible for the transfer of assimilates to all parts

  of the plant. The phloem consists of sieve tube elements and companion cells.
• What is plasmodesmata?

  Small pores between adjacent sieve tube elements and

  companion cells that allow communication and the exchange of materials
• What is a potometer?

  An apparatus used to measuer water uptake from a cut root
• What are root hair cells?

  Specialised cells responsible for the uptake of water and minerals from the soil. They have long hair-like extensions known as root hairs, which are adapted as exchange surfaces.
• What are sieve plates?

  The perforated end walls of sieve tube elements that allow plant assimilates to flow between cells unimpeded
• What are sieve tube elements?

  The main cells of the phloem. They are elongated cells laid end-to-end with sieve plates between. They contain few organelles.
• In plants, what are sinks?

  The regions of a plant that remove assimilates
• in plants what are sources ?

  The regions of a plant that produce assimilates
• What is a symplast route?

  One of two pathways by which water and minerals move across the root. Water enters the cytoplasm through the plasma membrane and moves between adjacent cells via plasmodesmata. Water diffuses down its water potential gradient by osmosis
• What is translocation?

  The movement of organic compounds in the phloem, from sources to sinks.
• What is transpiration?

  Water loss from plant leaves and stems via diffusion and evaporation. The rate of transpiration is affected by light, temperature, humidity, air movement and soil-water availability
• What is a transpiration stream?

  The flow of water from the roots to the leaves in plants, where it is

  lost by evaporation to the environment
• What is a vascular bundle?

  The vascular system in herbaceous dicotyledonous plants. It consists of

  two transport vessels, the xylem and the phloem.
• What is a vascular system?

  A network of transport vessels in animals and plants
• What are xerophytes?

  Plant that are adapted to live and reproduce in dry habitats where water availability is low
• What are the xylem?

  A non-living plant transport vessel responsible for the transfer of water and minerals from the roots to the shoots and leaves