9.1- Transport Systems In Dicotyledonous Plants Flashcards
Explain metabolic demands as a reason why multicellular plants need transport systems.
- internal and underground parts of a plant do not photosynthesise so require oxygen and glucose to be transported to them.
- waste products of cell metabolism to be removed.
- hormones produced in one part need go be transported to the areas where they have an effect.
- mineral ions absorbed by the roots need to be transported to all cells to make proteins required for enzymes and structure.
Explain size as a reason why multicellular plants need transport systems.
- many perennial plants are very large. For example trees.
This means they need effective transport systems to mive substances up/down from the root tips to the top most leaves and stems.
Explain SA:V as a reason why multicellular plants need transport systems.
- although leaves are adapted to have a relatively large sa:v ratio, once the roots and stems are taken into account plants have a small sa:v ratio overall.
- therefore they cannot rely on diffusion alone to supply their cells with everything they need.
What are dicotyledonous plants and the 2 types?
Dicots are plants who make seeds that contain two cotyledons.
- herbaceous dicots: leafy, soft tissued plants with a short life cycle.
- arborescent dicots: woody, hard tissued plants with a long life cycle.
What are cotyledons?
organs that act as food stores for the developing embryo plant and form the first leaves when the seed germinates.
Explain what the vascular system and bundles are in herbaceous dicots.
- vascular system= the series of transport vessels running through the stem, roots and leaves in dicotyledonous plants.
- in herbaceous dicots the vascular system is made up of the xylem and phloem transport vessels.
- these transport tissues are arranged in vascular bundles in the leaves, stems and roots.
What is the xylem?
- a large non-living tissue with two main functions:
1. Transport of water and mineral ions.
2. Support. - the flow of materials is from the roots to the shoots and leaves in one direction.
- made up of several cell types, most are dead when they are functioning. The cells dont contain cytoplasm or nuclei.
What makes up the main structure of the xylem tissue.
- xylem vessels are long hollow structures made by several columns of cells fusing end to end. (are the main structures)
- one way tube so that adhesion and cohesion is not interrupted.
- thick walled xylem parenchyma packs around the vessels, storing food and containing tannin deposits.
Tannin= bitter chemical that protects plants from herbivore attacks.
What are xylem fibres and the role of lignin?
They are long cells with lignified secondary walls that provide extra mechanical strength but do not transport water.
- lignin can be laid down in the walks of the vessels by forming either rings, spirals or solid tubes with lots of small unlignified areas called bordered pits.
- the bordered pits is where the water leaves the xylem and moves into other cells.
- the main role of lignin is to reinforce the vessels so they don’t collapse under the transpiration pull.
- amount of lignin increases as cell gets older.
What is the locations of xylem and phloem in roots?
In the roots, the vascular bundle is in centre.
- there is a central core of xylem in X shape. Phloem located between the arms of the X.
- this provides strength to withstand the pulling forces the roots are exposed to.
- around vascular bundle there is layer of cells called the endodermis which contain a layer of meristem cells called the pericycle.
Locations of xylem and phloem in stems?
- vascular bundles are found near outer edge of the stems. To give strength/support.
- xylem is found towards the inside of the bundle and phloem towards the outside.
- have a layer of cambium in between. These are meristems that divide to form new xylem and phloem.
Locations of xylem and phloem in leafs?
Vascular bundles form the midrib and veins of a leaf.
- within each vein, xylem is located on top of the phloem.
What is the Phloem?
Living tissue that transports food in the form of organic solutes around the plant from the leaves.
- supplies cells with the sugars and amino acids needed for cellular respiration and for the synthesis of needed molecules.
- flow of material can go either direction.
- phloem tubes are not lignified.
What are sieve tube elements?
- sieve tube elements are the main transporting vessels of the phloem.
They are made up of many elongated cells joined end to end to form long hollow structures. - they have no nucleus or tonoplast and very little cytoplasm which leaves space for the phloem sap to flow.
What are sieve plates and their role?
The ends of sieve tube elements have perforated walls called sieve plates which let the phloem contents flow through from one sieve tube element to the next.
- they support the lumen, keeping it open.
- they become blocked if the sieve tube element becomes injured to prevent the sap escaping.
