Transport systems in dicotyledonous plants Flashcards
(16 cards)
What is the pressure in the phloem?
2000kPa
What are the 3 main reasons why multicellular plants need transport systems?
- Metabolic demands => internal and underground parts of the plant do not photosynthesise so they need oxygen and glucose transported to them and waste products removed. Hormones also need to be transported within the plant. Mineral ions absorbed by the roots need to be transported to all cells to make proteins (for enzymes and cell structure)
- Size => specifically large plants need very effective trnsport systems to move substaces both up and down from the tip of the roots to the topmost leaves and stems
- Surface area:volume ratio (SA:V) => leaves are adapted to have a relatively large SA:V ratio for the exchnage of gases with the air. The size and complexity of multicellular plants means that when the stems, trunks and roots are taken into account they still have a relatively small SA:V ratio meaning they cannot rely solely on diffusion to supply their cells with what they need
What is the vascular system?
A system of transport vessels in animals or plants
What is a vascular bundle?
The vascular system of herbaceous dicots, made up of xylem and phloem tissue
Where are the vascular bundles located in the stem? And draw it.
In the stem, the vascular bundles are found around the edge to give strength and support
Answer on revision card
Where are the vascular bundles located in the roots? And draw it.
In the roots, the vascular bundles are in the middle to withstand the tugging strains that result as the stems and leaves are blown in the wind
Answer on revision card
Where are the vascular bundles located in the leaf? And draw it.
- In the leaves, the midrib of a dicot leaf is the main vein carrying the vascular tissue through the organ
- It also helps to support the structure of the leaf
- Many small branching veins spread through the leaf functioning both in transport and support
Answer on revision card
What are the two types of vessels in vascular bundles? And what are their functions?
- Xylem => responsible for transport of water and minerals, and support
- Phloem => transports food in the form of organic solutes (e.g. amino acids and sucrose)
What is the structure of the xylem?
- It is made up of several types of cells, most of which are dead
- The xylem vessels are the main structures made by several columns od cells fusing together end to end
- Thickened walls
- Large lumen
- Hollow tube
What are the two other tissues associated with the xylem? What is their structure and function?
Thick-walled xylem parenchyma:
- It packs around the xylem vessels, storing food, and containing tannin deposits
- Tannin is a bitter, astringent-tasting chemical that protects plant tissues from attack by herbivores
Xylem fibres:
- They are long cells with lignified secondary walls that provide extra mechanical strength but do not transport water
What is the function of lignin? And what are the different patterns of lignification in xylem?
- Lignin helps reinforce the xylem vessels so that they do not collapse under the transpiration pull
- It can form rings, spirals or relatively solid tubes with lots of small unlignified areas called boreded pits
- Lignin provides mechanical strngth to the vessel and allows flexibility of movement
What is the function of the non-lignified bordered pits in the xylem vessel?
The are found on the side of some xylem vessels to allow sideways movement of water to supply water to all the living cells in the stem
What does herbaceous and dictoyledonous mean?
- Herbaceous - plant with no woody tissue
- Dicotyledonous - plants with two cotyledons in the seed
What is the structure of the phloem?
- The main transporting vessels of the phloem are the sieve tube elements
- The phloem sieve tubes are made up of many cells joined end to end to form a long, hollow structure
- The phloem tubes are not lignified
- In the areas between the
cells, the walls become perforated to form sieve plates, which look like sieves and let the phloem contents flow through - As the large pores appear in these cell walls, the tonoplast (vacuole membrane), the nucleus and some of the other organelles break down - The phloem becomes a tube filled with phloem sap and the mature phloem cells have no nucleus
- Closely linked to the sieve tube elements are companion cells (have many mitochondria to produce ATP for active transport)
What are sieve plates?
Areas betwen the cells of the phloem where the walls become perforated giving many gaps where a sieve like appearance allows the phloem contents to flow through
What are sieve tube elements?
The main cells of the phloem that have a greatly reduced living content (little cytoplasms and no organelles) and sieve plates between the cells
