Unit 9 - Transport in Plants Flashcards
Why do plants need transport systems?
- metabolic demands
- large size
- low surface area to volume ratio
Define cotyledon.
Organ found in seeds that acts as a food store for the developing embryo and forms the first leaves when the seed germinates.
Define dicotyledonous plant.
A plant which produces seeds with two cotyledons.
Define herbaceous dicot.
A plant with soft tissues and a short life cycle.
Define arborescent dicot.
A plant with hard lignified tissues and a long life cycle.
Define vascular bundle in plants.
The arrangement of the transport tissues in a plant. In herbaceous dicots, the xylem and phloem form vascular bundles, with cambium tissue in between them (the cells in this tissue can differentiate into xylem or phloem).
Where are the xylem and phloem found in the roots of a plant?
In the middle - this helps withstand the pressure from the stems and leaves being blown by the wind.
Where are the xylem and phloem found in the stem of a plant?
Around the edge with the phloem on the outside and the xylem facing inwards, surrounded by parenchyma tissue. This gives strength and support.
Where are the xylem and phloem found in the leaves of the plant?
The main vein (midrib), which supports the leaf’s structure. Branching veins spread throughout the leaf.
What is the role of xylem in the plant?
To transport water and mineral ions from the roots of the plant to the rest of the plant.
What is the structure of xylem?
Xylem is a non-living tissue. The vessels are made of long cells fused together into a hollow column (the cells have died and the contents and end walls decayed). Extra mechanical strength is given by xylem fibres which don’t transport water - they are long cells with lignified secondary walls. Lignin is a polymer which is laid in the xylem walls as rings, spirals or as tubes with bordered pits and gives strength to the vessels.
What is parenchyma?
A tissue which packs around the xylem vessels. It stores food and contains tannin - a bitter tasting chemical protecting the xylem from being eaten by herbivores.
What is the role of phloem in the plant?
To transport sugars and amino acids made in photosynthesis from the leaves around the plant (both up and down).
What are the sieve tube elements of the phloem?
Unlignified cells joined to form a long hollow vessel. As the plant grows, pores appear in the walls between the cells to form sieve plates and the tonoplast, nucleus and other organelles break down.
What are the companion cells of the phloem?
Cells which form with the sieve tube elements and are linked to them by plasmodesmata. They function to provide energy for the sieve tube elements.
