3.1.3 - Transport in plants Flashcards
Why do plants need a specialised transport system ?
- To move products of photosynthesis, water, and oxygen around from their place of origin to where they are needed
- Most plants have to transport substances over large distances
- SA: V ratio is small in plants (even though for leaves SA:V high)
Define dicotyledonous
Plants that produce two seed leaves
How do you tell if a plant is mono- or di- cotyledonous from its leaves ?
- Monocots have vessels parallel to the leave
- Dicots have vessels which branch out from a central vessel
What are dicotyledonous plants (dicots) ?
They make seeds that contain two cotyledons
What are cotyledons ?
They are organs that act as food stores for the developing embryo plant
What do cotyledons form ?
They form the first leaves when the seed germinates
What are herbaceous dicots ?
- They have soft tissues and a relatively short life cycle
- They die down at the end of the growing season to the soil level
What are arborescent dicots ?
They are woody dicots, which have hard lignified tissues and a long life cycle
Define vascular system
A system of transport vessels in plants
What are the two main types of transport vessels in herbaceous dicots ?
Xylem and phloem
Define vascular bundle
- The vascular system made up of xylem and phloem tissue
- The transport tissues are arranged together packed in vascular bundles
What is the function of the xylem ?
- The transport of water and mineral ions
- Support
What does the xylem carry ?
Water and mineral ions
What is the flow of the xylem like ?
Up from the roots to the shoots and leaves
What is the xylem made up of ?
- It is made up of dead cells
- Long hollow structures made by several columns of cells fusing together end to end
What are the two tissues associated with the xylem in herbaceous dicots ?
- Thick walled parenchyma
- Tannin
What is the role of the parenchyma ?
It packs around the xylem vessels, storing food and containing tannin deposits
What is the role of tannin ?
It is a bitter astringent tasting chemical that protects plant tissues from attacks by herbivores
What is the role of lignin in the xylem ?
To provide extra mechanical strength
How can the lignin be laid in the walls of the xylem ?
- Rings
- Spirals
- Solid tubes with lots of small unlignified areas called bordered pits
What is the function of the phloem ?
To transport food in the form of organic solutes around the plant from the leaves where they are made by photosynthesis
What does translocation supply the cell with ?
It supplies the cells with the sugars and amino acids needed for cellular respiration and for the synthesis of other molecules
What is the flow of the phloem like ?
It can go both up and down the plant
What is the main transporting vessel of the phloem ?
Sieve tube elements
What is the structure of the phloem like ?
- Many cells joined end to end to form a long hollow structure
- Not lignified
- Sieve plates
- Companion cells
What is the role of the sieve plates ?
To allow the contents of the phloem to flow both ways
What is the result of the pores in the cell wall, caused by the sieve plates ?
The pores in the cell walls cause the tonoplast, the nucleus and some other organelles to break down
What does the phloem become, overall ?
A tube filled with phloem sap and the mature phloem cells have no nucleus
What are companion cells ?
They are cells that are closely linked to the sieve tube elements by plasmodesmata
What are plasmodesmata ?
Microscopic channels through the cellulose cell walls linking the cytoplasm of adjacent cells
Why are the companion cells active ?
They act as a life support system for the sieve tube cells, which have lost most of their normal cell functions
Why is water key in plants ?
- Turgor pressure as a result of osmosis in plant cells provides a hydrostatic skeleton to support the stems and leaves.
- The loss of water by evaporation helps the plant keep cool
- Mineral ions are transported in water
- It is a raw material for photosynthesis
What are root hair cells ?
An exchange surface in plants where water is taken into the plant from the soil
In which part of the root is water taken up ?
Root hairs