Module 3.3 - Transport in plants Flashcards
Why do plants need a transport system in an overview?
All living things need to take substances out of and release waste into their environment.
Every plant cell needs a regular supply of water, oxygen, nutrients and minerals.
They need a transport system to overcome the difficulties of large diffusion distances.
What are the 3 main reasons that plants need a transport system?
Metabolic demand.
Size
Surface area to volume ratio
Why does metabolic demand cause plants to need transport systems?
They have a high demand for particular substances (water and sugar) and this can’t be met by simple diffusion into all cells.
Underground parts of plant’s don’t photosythesise so need glucose and oxygen transported to them and waste products remove.
Hormones made in a part of the plant may need transporting to another area.
Water and mineral ions from the roots need transporting to all cells to make proteins required for enzymes and structure of the cell.
Why does size cause plants to need transport systems?
Some plants are small but others can be huge as they continue to grow throughout their lives.
They need effective transport systems to move substances both up and down from the roots to the topmost leaves to reach all the cells they’re needed in.
Why does surface area cause plants to need transport systems?
Leaves are adapted to have a large SA:V ratio for efficient gas exchange.
Taking into account trunks, stems and roots they have a relatively low SA:V ratio.
Means they can’t rely on diffusion for supplying their cells with everything they need.
What are the features of dicotyledonous plants seeds?
They make seeds that contain 2 cotyledons (organs that act as food stores for the developing embryo plant and for the first leaves when the seed germinates.
What are the transport systems in dicotyledonous plants?
Xylem and phloem that are arranged in vascular bundles.
There may be other types of tissue such as collenchyma and schlerenchyma that give the plant some strength and help support the plant.
What is the role of xylem?
To transport water and mineral ions towards the leaf. To support the plant also.
What is the role of phloem?
To transport assimilates (amino acids and sugars) up and down the plant.
What are the features of the vascular bundle in the roots?
Vessels grouped together in the centre of to help the plant withstand tugging strains from wind.
Xylem tissues in the centre bc it’s the strongest.
Phloem in 4 separate sections.
There are multiple vessels in each section.
Around the vascular bundle is a sheath of cells called endodermis, just inside the endodermis is a layer of meristem cells called the pericycle.
What are the features of the vascular bundle in the stem?
Xylem is located on the inside.
Vascular bundle on the edge provides strength and support to the stem as well as flexibility.
Cambium layer contains meristem cells that divide to produce new xylem and phloem.
What is the schlerenchyma?
Support and structure (around vessels). Thickened with cellulose and lignin.
What is the parenchyma?
General tissue (softer eg leaves / fruit pulp)
Relatively unspecialised, photosythesis and storage.
What is the collenchyma?
Found by epidermis and involved in growth.
Flexible support / wind resistance.
What are the features of the vascular bundle in the leaf?
Xylem is located on top of the phloem.
The midrib is the main vein carrying the vascular tissue through the organ. Helps the structure and support of the leaf.