Transport in Plants M3 Flashcards
Describe the similarities and differences between xylem and phloem
S - both involved in mass flow, both found together in vascular bindles, and both have elongated cells. D - Phloem contains sieve tube elements and companion cells whereas xylem just contains xylem vessels. Phloem transports carbohydrates + other assimilates. Xylem transports water and mineral ions. Xylem cells are dead and hollow, strengthened by lignin. sieve tube cells are alive and contain cytoplasm but few other organelles and are kept alive by companion cells.
Name the six monosaccharides
alpha glucose, beta glucose, ribose, deoxyribose, fructose, galactose
Name some of the adaptations of the Xerophytes
Thick waxy cuticle, reduces water loss. Spine, small SA so less water is lost via transpiration. Hairs, trap moisture in the air. Rolled leaf, water evaporating collects in the trapped area of leaf and reduces water loss. Fewer stomata, so less water lost by transpiration.
Name some of the adaptations of the Hydrophytes
Stomata on upperside enable leaf to take in CO2 from the air through p/s. Aerenchyma, airspaces that make leaf buyout and enables them to float to take in light for p/s. LSA, maximise photosynthesis, water loss is not an issue. Less lignin and stems are more flexible, changing with water weight so they stay on the surface on the water.
Name some sinks in plants.
Meristems/cambium of roots, shoots and leaves
Storage organs when they are being formed…tubers, bulbs.
Flowers, fruits, seeds.
Name some sources in plants.
Leaves and photosynthetic regions of stems
Storage organs when they are being broken down by hydrolysis…..tubers, bulbs, germinating seeds.
Where do aphids place their proboscis
Phloem sieve cell
Explain a possible mechanism for the loading and transport of sugars in the phloem
Loading
• loading into companion cells
• location of companion cells at a source or named
source
• active loading of sucrose (using ATP)
• mitochondria presence in companion cells
• description of mechanism of H+ gradient and
cotransport
• movement via plasmodesmata into sieve tube elements
Movement
• mass flow from source to sink
• ref to high hydrostatic pressure at source
• ref to inflow of water by osmosis at the source (creating the pressure)
• ref to passage through sieve plates or cytoplasmic
connections
• ref to low hydrostatic pressure at the sink
• ref to unloading at the sink
Explain, in terms of water potential how water moves from the soil to the endodermis in a root
Water is absorbed from the soil by the root hairs
By osmosis down the water potential gradient
The water potential is higher in the epidermal cells than in the xylem in the root centre
Water moves from cell to cell through the cytoplasm down the water potential gradient-symplast pathway
Water also moves through the fibres of the cell wall and intercellular spaces-apoplast pathway
But must go through the endodermal cells via symplast due to the Casparian strip
Key points of Plant dissection (e.g. celery)
- Use a SHARP scalpel to cut a THIN CROSS - SECTION. 2. Place the sample to soak in Touldine blue. 3. Add of a microscope slide, with a drop of water to prevent it from drying out, apply a coverslip. 4. View specimen under the microscope and draw a labelled diagram.
Describe transpiration
The loss of water from leaves as a result of evaporation
What is the role of the Casparian strip
forces h20 and ions across the partially permeable membrane out of endodermis cell. prevents the apoplastic pathway. h20 has to move vis symplastic pathway, prevents h20 moving back of xylem by apoplast.
Describe the symplastic pathway.
through the cytoplasm, water enters the root via osmosis and down the water potential gradient, via plasmodesmata.
Describe the apoplast pathway.
through cell wand intercellular space. Cannot pass through endodermis as Caspian strip is impermeable due to waterproof band of suberin. Must pass endodermis via cytoplasm. This is faster and requires no energy.
What is the cohesion/tension theory.
Cohesion occurs between water molecules because they are polar they stick together (hydrogen bonds) - if some are pulled into leaf, more will follow. Adhesion occurs between water molecules and other molecules like cellulose in a xylem wall, a water column in xylem will move upwards.
What is some evidence for translocation?
- If poison inhibits respiration in the mitochondria of companion cells is used, translation stops. Respiration cant produce ATP which is required for respiring tissues so active transport stops.
- Development of microscopy show adaptations of companion cells to active transport. Lots of mitochondria for respiration folds in the plasma membrane suggesting there are carrier proteins.
Describe the process of unloading
sucrose diffuses from phloem to sinks due to pressure being lower at the sink than at the source. The sink pressure is lower as the sink is using and storing sugars. Diffusion gradient between from phloem t surrounding cells. Solutes leave phloem, w/s increase in STE, and H2O moves out by osmosis (to leaves or via xylems transpiration stream,) and pressure decreases.
Describe the process of loading
APOPOPLAST PATHWAY (requires energy). H+ is pumped out of cc, by proton pumps, H+ outside cell increases.H+ wants to diffuse back into cc, gets cotransporter with sucrose into the cc. Sucrose diffuses from cc into STE through plasmodesmata and w/p decrease in STE, so H2O moves into STE via osmosis, which generates the turgor pressure for mass flow.
