7. Transport in plants Flashcards
Adhesion (water movement)
The formation of hydrogen bonds between carbohydrates in
the xylem vessel walls and water molecules. This contributes to the capillarity of water and transpiration pull.
Apoplastic pathway
One of two pathways by which water and minerals move across the root. Water moves through intercellular spaces between cellulose molecules in the cell wall.
Casparian strip
A waterproof strip surrounding the endodermal cells of the root that blocks the apoplast pathway, forcing water through the symplast route.
Cohesion (water movement)
The formation of hydrogen bonds between water molecules. This contributes to the capillarity of water and transpiration pull.
Cohesion-tension theory
The model that explains the movement of water from the soil to the leaves in a continuous stream.
Companion cells
Active cells of the phloem located adjacent to the sieve tube elements which produce ATP for metabolic processes in both themselves and the sieve tube elements. They retain their nucleus and organelles.
Cotransport
A form of secondary active transport. The movement of one substance down its concentration or electrochemical gradient is coupled to the transport of another substance via transmembrane proteins.
Dicotyledonous plants
Plants that produce seeds that contain two cotyledons. They have two primary leaves.
Endodermis
The innermost layer of the cortex of a dicotyledon root. It is impregnated with suberin which forms the Casparian strip. Endodermal cells actively transport mineral ions into the xylem.
Evaporation
A transition from the liquid state to the gaseous state which requires heat energy.
Eyepiece graticule
A scale bar inside the eyepiece of a light microscope which can be calibrated against a ruler to measure structures.
Herbaceous plants
Plants which do not have woody stems.
Hydrostatic pressure
The force which fluid molecules exert on the walls of a vessel.
Lignin
An organic polymer that has a role in the support and impermeability of vascular tissues.
Mass flow
Sugars flow passively from the source to the sink down a hydrostatic pressure gradient.
Phloem
A living plant transport vessel responsible for the transfer of assimilates to all parts of the plant. The phloem consists of sieve tube elements and companion cells.
Potometer
An apparatus used to measure water uptake from a cut shoot.
Root hair cells
Specialised cells responsible for the uptake of water and minerals from the soil. They have long hair-like extensions known as root hairs, which are adapted as exchange surfaces.
Sieve plates
The perforated end walls of sieve tube elements that allow plant assimilates to flow between cells unimpeded.
Sieve tube elements
The main cells of the phloem. They are elongated cells laid end-to-end with sieve plates between. They contain few organelles.
Sinks (plants)
The regions of a plant that remove assimilates e.g. roots, meristem, fruits.
Sources (plants)
The regions of a plant that produce assimilates e.g. leaves, storage organs.
Suberin
A waterproof, waxy material that forms the Casparian strip in the endodermis.
Symplastic pathway
One of two pathways by which water and minerals move across the root. Water enters the cytoplasm through the plasma membrane and moves between adjacent cells via plasmodesmata. Water diffuses down its water potential gradient by osmosis.
Translocation
The bulk movement of organic compounds in plants from sources to sinks via the phloem.
Transpiration
Water loss from plant leaves and stems via diffusion and evaporation. The rate of transpiration is affected by light, temperature, humidity, air movement and soil-water availability.
Water potential
A measure of the tendency of water molecules to move from one area to another measured in kilopascals (kPa) and given the symbol .
Xerophytes
Plants that are adapted to live and reproduce in dry habitats where water availability is low, e.g. cacti and marram grass.
Xylem
A non-living, heavily lignified plant transport vessel responsible for the transfer of water and minerals from the roots to the shoots and leaves.
Why do plants need a transport system (instead of using diffusion and osmosis)?
- Transportation of assimilates from source to sink.
- Transport of water and mineral ions across far distances e.g., the roots to leaves of a very tall tree.
- Plant cannot be supported by only short-distance transport methods (osmosis and diffusion). Would take too long for water, mineral ions and assimilates to reach destinations. Therefore, not efficient enough.
Assimilates
organic products synthesised as a result of photosynthesis.
What are the features of plant transport systems?
- Require vascular tissue made of xylem and phloem.
* Xylem – transports water and mineral ions from roots to stems and leaves.
* Phloem – transports assimilates from source to sink. - Long distance bulk transport systems. (Mass flow theory).
- Transport tissue distributed between roots, stem and leaves so that all cells can receive their required mineral ions and assimilates.
- A transport medium in which to transport dissolved substances. (Xylem or phloem sap).
- Movement of transport medium using pressure differences.
- Gaseous exchange does not occur in transport tissues (unlike mammals).
- Transport system is unidirectional, as in, it is not a circular flow (like mammal circulatory system). However, the phloem can transport assimilates both up and down.
Herbaceous plants
plants that have a soft and non-woody stem, ALSO, plants that have a life cycle of only one year.
The difference between dicotyledonous and monocotyledonous plants?
Dicotyledonous plants – flowering plants developed from seeds that have two embryonic leaves/cotyledons. Their leaves are in multiples of 4 or 5 and have a reticulated vein network. In stems, vascular tissues arranged in bundles in a ring pattern.
VS
Monocotyledonous plants – herbaceous flowering plants developed from seed with only one embryonic leaf. Leaves are in multiples of 3 and have parallel veins. In stems, vascular tissues is arranges in bundles scattered around stem.
Why should plants be structured to maximise SA:V?
Plant leaves and root systems need to maximise their SA:V as much as possible in order to facilitate the uptake of water and mineral ions, as well as the absorption of sunlight and carbon dioxide.
How do herbaceous vs woody plants facilitate gaseous exchange differently?
In herbaceous plants, the stems (and leaves) contain stomata which facilitate gaseous exchange.
In woody plants, there are lenticels to facilitate gas exchange.
How are the stem and roots structured?
Stem and roots are both organs containing different tissues. Above soil, plant is structured to withstand different mechanical stresses, such as wind. Plants are supported by sclerenchyma, parenchyma and collenchyma tissues. Vascular bundle arrangement differs to perform particular function.
Epidermis
outermost layer of stem and roots. Protective layer of cells that is covered by wax cuticle.
Describe structure and function of parenchyma tissues?
living undifferentiated cells in stem and roots functioning as packing tissue (fill empty spaces) AND a storage tissue.
* Spherical cells.
* Thin cellulose cell walls.
* Large vacuoles.
* Some have chloroplasts.
* Can be found in cortex of stem sand roots and pith of stems.
* Turgid parenchyma cells provide hydrostatic support.
Describe structure and function of collenchyma tissue?
living tissue specialised for support and found commonly as a layer directly beneath epidermis.
* Cellulose cell walls with uneven thickening.
* Cell walls also contain pectin.
* Adapted for areas of growth as cell walls able to stretch.
Describe structure and function of sclerenchyma tissues?
dead cells compose tissue; specialised for support and strength in areas that are no longer elongating.
* Two distinct groups: sclereids and fibres.
* Cellulose walls very thick, some walls contain lignin.
* Fibres are long.
* Sclereids are shorter and of varying shapes.
How is vascular tissue distributed in a dicotyledonous stem?
- Vascular bundles close to outside of stem.
- Lateral forces acting on plant are best resisted by a cylindrical non-continuous circle arrangement of vascular bundle (especially for herbaceous stems).
- Because the stem is non-continuous the stem is still flexible.
- Xylem inside, phloem outside.
- Between xylem and phloem is cambium.
Cambium
meristematic tissue containing stem cells for division that can specialise into either xylem or phloem cells.
How is vascular tissue distributed in a dicotyledonous root?
- Situated centrally because roots are subject to pulling forces.
- Central column of supporting tissue.
- Xylem arranged in star (4 point) shaped block of tissue surrounded by separate phloem groups.
- Around both is the pericycle and endodermis.
How is the structure of root hair cells adapted to their function?
- Epidermis in area with plentiful root hair cells known as piliferous layer.
- Root hair cell is a modified epidermal cell.
- Cell has a large vacuole.
- Long cytoplasmic extension projecting.
- Large surface area for water and mineral uptake.
- Root hair delicate - does not live for long.
- As root grows, new root hair cells nearer to tip replace old ones.
- No waxy cuticle.
- Thin cellulose cell wall.
- Many aquaporins (channel proteins for water uptake) in cell surface membrane.
- Many mitochondria to provide ATP for active uptake.
What to include in plan diagram?
- Individual cells not drawn.
- Cells not drawn but tissues labelled.
- Shows proportions of different tissues.
- Annotations should be added if required, and include description of shape, size and colour. (E.g., differences in staining).
- Lines should be clear and continuous.
- Make proportions shown realistic.
- Use all available space.
- Do not shade or colour.
- Label lines should not have arrowheads or be crossed.
How is vascular tissue distributed in a leaf?
- Vascular tissue is situated in reticulated vein network in lamina (blade of leaf) form side veins.
- Side veins merge into central main vein or midrib.
- Xylem on top, phloem on the underside.
- Veins often surrounded by ring of parenchyma cells.
