Adaptations For transport in Plants Flashcards
Describe the structure of a root in a plant
OUTSIDE
- Epidermis
- exodermis
- cortex
- phloem (middle)
- xylem (middle)
- endodermis
INSIDE
Structure of a stem
OUTSIDE
- epidermis
- collenchyma (cortex)
- parenchyma (cortex)
- vascular bundle
- interfascicular cambium
-pith
What is the xylem made up of
- vessels
- tracheids
- fibres
- parenchyma
Describe structure and function of the xylem
Xylem are dead cells that transport water and minerals up the plant and provide mechanical strength and support as they are strengthened by water proof lignin
What is the structure and function of the phloem
Phloem sieve tubes carry sucrose and amino acids. Sieve elements end in sieve plates containing pores through which cytoplasmic filaments extend linking cells. No other organelles are in the sieve elements. Companion cells contain many mitochondria for ATP and the organelles for protein synthesis. Protein and ATP are passed to the sieve elements through plasmodesmata
What is the casparian strip and what’s it’s effects
The endodermis is impregnated with areas of suberin (casparian strip) this blocks the apoplast pathway, forming water into the symplast pathway. Minerals are selected to move into the symplast by active transport. This sets a water potential gradient with lower water potential in the xylem, so water moves in by osmosis resulting in a force called root pressure
Describe pathway of apoplast through root cortex
From cell wall to cell wall
Describe pathway of symplast through root cortex.
From cytoplasm to cytoplasm through plasmodesmata
Describe the pathway of vacuolar through the root cortex
From vacuole to vacuole
What is transpiration
The loss of water vapour, by evaporation and diffusion out of the open stomata, from leaves of plants. it leads to the transpiration stream
What is the transpiration stream ( describe cohesion- tension theory)
Water moves into the root and enters the xylem (root pressure) cohesive forces between water molecules and adhesive forces between water molecules and the hydrophilic lining if the xylem creates a transpiration pull as the water leaving the xylem into the leaf cells pulls on molecules below
What are factors effecting transpiration
- humidity - air contains more WV decreasing conc gradient
- temperature - KE inc therefore molecules diffuse and evaporate faster
- wind speed - higher rate of diffusion as water vapor blown away
- light intensity - stomata open due to more photosynthesis
What is a hydrophyte
Plants that live in water (e.g water lilies)
What are adaptations of hydrophytes
- little/no waxy cuticle as don’t need to conserve water
- stomata on upper surface as lower surface submerged
- poorly developed xylem as no need to transport water
- large air spaces (aerenchyma) provide buoyancy and act as reservoirs of gas
What is a mesophyte
Live with adequate water
How have mesophyte adapted to it’s environment
-close stomata at night to decrease water loss
-shed leaves in unfavorable conditions (winter)
- underground organs and dormant seeds survive winter
What is a xerophyte
Water is scarce
How did xerophytes adapt to it’s environment
-thick waxy cuticle reducing water loss by evaporation from epidermal tissue
- sunken stomata increasing humidity in an air chamber above stomata, reducing diffusion gradient and therefore water loss
- rolled leaves reduces area of leaf exposed directly to air
- stiff interlocking hairs trap water vapour inside rolled leaf, reducing water potential gradient and therefore water loss
What is translocation
The phloem transports the products of photosynthesis from the source (the leaf) to the sink (area of use or storage)there is evidence to show that this is bidirectional through the phloem
Describe how removal of phloem proves translocation
- Ringing experiments (removal of phloem) show accumulation of sucrose products on leaf side of the ring but none on the root side. Movement of sucrose was blocked by removal of phloem. Therefore, phloem is the route if transport
Describe how use of aphids to sample sap from the phloem proves translocation
An aphid stylus extends into sieve tube elements. If a laser is used to remove the stylus from the body, the stylus then becomes a micropipette and sao drips out. This can be analysed to shown that sucrose and amino acids are carried in the phloem, both above and below leaves
Describe how radioactive labelling of CO2 is used to prove translocation
Radioactive labelling of carbon dioxide which will become incorporated into sucrose can be used in conjunction with aphid stylus to determine rate of transport in phloem. Allows us to determine source and sink by autoradiography
Evidence and describe theory of mass flow
Sucrose made at source lowers water potential. Water enters cells and sucrose is forces into phloem (loading) this increases hydrostatic pressure and therefore mass flow occurs along the phloem to the root where sucrose is stored as starch, water potential is less negative and water moves into the xylem
What is evidence against theory of mass flow
- sieve plates impede flow
- translocation is faster than expected with diffusion
- this theory does not explain bidirectional flow or different rates of flow of sucrose and amino acids
- does not explain companion cell mitochondria, high O2 intake or stopping of translocation by cyanide
