Transport systems in dicotyledonous plants 9.1 Flashcards
what is the pressure in the phloem
It is around 2000 kPa
What 3 main reasons are there for why multicellular plants need transport systems
Metabolic demands
size
surface area (SA:V)
What about metabolic demands means that plants need transport systems
The cells of the green parts of the plant make their own glucose and oxygen by photosynthesis - but many internal and underground parts of the plant do not.
They need oxygen and glucose transported to them and the waste products of cell metabolism removed.
Hormones made in one part of a plant need transporting to the areas where they have an effect.
Mineral ions absorbed by the roots need to be transported to all cells to make the proteins required for enzymes and the structure of the cell
what about the size of the plants means that they need transport systems
some plants are very small but because plants continue to grow throughout their lives, many perennial plants (plants that live a long time and reproduced year after year) are large and some of them are enormous.
This means plants need very effective transport systems to move substances both up and down from the tup of the roots to the topmost leaves and stems
What about the surface area : volume ratio of plants means that they need transport systems
Leaves are adapted to have a relatively large SA:V ratio for the exchange of gases with the air.
However, 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.
This means they cannot rely on diffusion alone to supply their cells with everything they need
what are dicotyledonous plants
Dicotyledonous plants (dicots) make seeds that contain 2 cotyledons, organs that act as food stores for the developing embryo plant and form the first leaves when the seed germinates
what are the 2 types of dicotyledonous plants
There are herbaceous dicots & woody dicots
what are the characteristics of hebaceous dicots
Herbaceous dicots, with soft tissues and a relatively short life cycle (leaves and stems that die down at the end of the growing season to the soil level)
What are the characteristics of woody dicots
woody dicots have hard lignified tissues and a long life cycle (in some cases 100s of years)
what part of the plants are known as the vascular system
Dicotyledonous plants have a series of transport vessels running through the stem, roots and leaves. This is known as the vascular system
What 2 types of vessels make up the vascular system
The vascular system is made up of the xylem and the phloem
How are the xylem and phloem arranged in the vascular system
The transport tissues are arranged together in vascular bundles in the leaves, stems and root of herbaceous dicots
How are the vascular bundles arranged in the stems of herbaceous plants
How are the vascular bundles arranged in the roots of herbaceous plants
How are the vascular bundles arrange in the stems of herbaceous plants
what is the function of the xylem
The transport of water and mineral ions, and support.
What is the structure and composition of the xylem
They are long, hollow structures made by several columns of cells fusing together end to end.
Lignin in the xylem can for springs, spirals or relatively solid tubes with lots of small unlignified areas called bordered pits.
what is the composition of the xylem
- largely non-living tissue.
- made up of several types of cells
^most of which are dead when they are functioning in the plant. - xylem contains
^Thick-walled xylem parenchyma
^Xylem fibres - Lignin can be laid down in the walls of the xylem vessels
why is there tannin deposits in the xylem tissue
Tannin is a bitter, astringent-tasting chemical that protects plant tissues from attack by herbivores
What is the function of xylem parenchyma
it packs around the xylem vessels, storing food and containing tanninin deposits
What is the structure and function of 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 bordered pits in the lignin with in the xylem
This is where water leaves the xylem and moves into other cells of the plant
what is the function of the phloem
Phloem is a living tissue that transports food in the form of organic solutes around the plant from the leaves where they are made by photosynthesis.
The phloem supplies the cells with sugars and amino acids needed for cellular respiration and for the synthesis of all other useful molecules.
The flow of materials in the phloem can go both up and down the plant
what is the main transporting vessel in the phloem
The main transporting vessel of the phloem are the sieve tube elements
what are the sieve tubes made up of
like the xylem, they are made up of many cells joined end to end to from a long, hollow structure, unlike the xylem they are not lignified
what are sieve plates and what is there function
In the areas between the cells, the walls become perforated to from sieve plates, which look like sieves and let the phloem contents low through
as phloem cells become perforated to form sieve plates what occurs
- the tonoplast, nucleus and some of the other organelles break down
- phloem becomes a tube filled with phloem sap
- mature phloem cells have no nucleus
what are the similarties and differences in the structure of the xylem and mature phloem cells
Neither xylem vessels nor mature sieve tubes have nuclei, but xylem vessels are dead and phloem vessels are living tissue
what cells form with the sieve tube elements
companion cells
How are the companion cells and sieve tube elements linked
These cells are linked to the sieve tube elements by many plasmodesmata
what are plasmodesmata
microscopic channels through the cellulose cell walls linking the cytoplasm of adjacent cells
what is the function of companion cells
They maintain their nucleus and all their organelles.
The companion cells are very active cells and it is thought that they function as a ‘life support system’ for the sieve tube cells, which have lost most of their normal cell functions
what supporting tissues are also found in the phloem tissue
Phloem tissue also contains supporting tissues including fibres and sclereids, cells with extremely thick cell walls
