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Class Notes for Chapter 9 Transport in Plants AS Level Biology A OCR
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- Transport in plants
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- OCR
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Transport in Plants Transport systems in dicotyledonous plants
Water transport in multicellular plants
Transpiration
Translocation
Plant adaptations to water availability
Transport systems in dicotyledonous plants
, Why do plants need a transport system?
- Metabolic demands – oxygen and
glucose need to be transported from
the leaves to non-photosynthesising
parts of the plant, mineral ions need to
be transported from the roots to all
cells to make proteins.
- Size – some plants e.g. giant redwoods,
are very tall. They need to transport
water and minerals etc along distance
between roots and leaves.
- Surface area to volume ratio is too
small – diffusion alone can’t supply all
the cell requirements so a transport
system is required. Giant redwoods can grow n
up to 115m tall!
Dicotyledonous plants
Dicotyledonous plants make seeds that contain
two cotyledons.
Cotyledons are organs that acts as food stores
for the developing embryo and form the first
leaves when the seed germinates.
Dicotyledons include many popular garden
flowers and vegetables, including legumes, the
cabbage family, the aster family (flowers),
apples, broccoli, carrots, cauliflower, daisies, peaches, potatoes, roses, sweet pea and
tomatoes.
Herbaceous dicotyledons have soft tissues and a relatively short life cycle with leaves and
stems that die down to soil level at the end of the growing season, e.g. daisies.
Woody (arborescent) dicotyledons have hard lignified tissues and a long lifecycle, e.g. apple
trees.
Vascular system in dicotyledons
Dicotyledonous plants have a series of transport vessels running through the roots, stem
and leaves known as the vascular system.
This is made up of xylem vessels and phloem tubes which are arranged into vascular
bundles.
Upper Cuticle
Epidermis
Palisade
Mesophyll
, Xylem
Phloem
Spongy
Mesophyll
Air Space
Lower
Epidermis
Guard Cell with Stoma
chloroplasts
Xylem
Largely non-living
tissue that has two
main functions:
- Transport of water
and mineral ions
- Support
The flow of materials
is from the roots to
the shoots and the
leaves.
There are several
types of xylem cells, most of which are dead and hollow and fused together at the ends.
Xylem parenchyma pack around xylem vessels, storing food and containing tannin deposits.
Tannin is a bitter astringent-tasting chemical that protects plants from being eaten.
Xylem fibres are long cells with lignified secondary walls that provide extra support. Non-
lignified pits are called bordered pits and are where water leaves the xylem.
There are 5 different types of xylem in angiosperms: Tracheids, vessel elements, xylem
parenchyma, sclereids (sclerenchyma cells) and fibres.
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