3.1.3 Transport In Plants Flashcards
Why do large multicellular plants need a transport system?
- larger organisms have a smaller SA:Vol ratio
- rate of diffusion too slow + diffusion distance too long
- molecules and mineral ions need transporting from one part of the plant to the other
Why does a small SA:Vol ratio mean that large multicellular plants require a transport system?
- leaves have a large SA:Vol ratio but stems, trunks + roots have a small SA:Vol
- therefore cannot rely on diffusion across outer surface alone to supply cells with required molecules
Why does a larger size mean that large multicellular plants require a transport system?
- some plants are tall
- diffusion distance is too great
- effective transport system needed to move substances up + down tip to root of leaves and stems
Why do larger metabolic domands mean that large multicellular plants require a transport system?
- underground parts of plant don’t photosynthesise - need glucose transporting to them + remove waste
- hormones need transporting to area of effect
- mineral ions need transporting from root hair cells to cells of plant to make proteins
Where are food stores in Dicots and Monocots?
Dicots: Cotyledons x2
Monocots: Endosperm
What are the roles of the xylem and phloem
Xylem: Tranport water + mineral ion up the plant
Phloem: Transport sugars/sucrose up + own the plant
Both examples of mass flow
What is meristematic tissue and where is it found?
Tissue where cells are able to divide by mitosis and differentiate into other cell types - found at growing points of the plant (root tips and shoot tips)
Name 2 ways you could observe the position of xylem vessels in leaf stalks?
- put leaf in dye or food colouring
- cut transversely
OR - cut a thin transverse cross section
- stain or observe with microscope
How are the xylem and phloem positioned in a leaf?
As a vascular bundle - xylem on top, phloem underneath
What components are phloem tissue made from?
Companion cells + sieve tube elements
How are companion cells and sieve tube elements linked?
Via microscopic channels through their cellulose cell walls called plasmodesmata - links cytoplasm of adjacent cells
What are sieve tube elements?
- elongated cells with little cytoplasm
- joined end to end to form a column so solutes can be transported long distances
- perforated so solutes can pass from cell to cell
- few organelles + no nucleus
What process is the phloem used for and what does it transport?
Translocation - transaports assimilates (sucrose + amino acids)
Explain the sites found in the plant and what happens in them
Source site - assimilates loaded into phloem
Sink site - where assimilates are unloaded from the phloem
Give examples of sources and sinks
Sources
- green leaves
- green stems
- tubers unloading stores
- food stores in seeds when germinating
Sinks
- actively dividing meristems
- developing tubers laying down food stores
- growing roots
- developing seeds laying down food stores
Give evidence for the phloem being used
- Bark/ outer edge of tree removed (including phloem)
- This lowers water potential in bark above cut out
- This swells due to water moving into this area by osmosis
Why is starch not transported in phloem sap?
- too viscous to move
- insoluble
- can’t enter + leave cells
Explain the process of how sucrose is moved from the source
- Sucrose is taken into companion cell from source using ATP
- Sucrose diffuses through plasmodesmata into phloem sieve tube element
- Sucore lowers water potential of sieve tube element
- Water moves in via osmosis
- This increases hydrostatic pressure at source
Explain the process of how sucrose is moved to the sink
- Sucrose leaves sieve tube element and moves into sink cell/companion cell by diffusion or active transport
- Loss of sucore from sieve tube element increases water potential
3.Water moves out via osmosis - This decreases hydrostatic pressure at source
What is mass flow?
Sucrose moveing from an area of high hydrostatic pressure to low hydrostatic pressure
Explain how assimilates are loaded into the phloem and out of it
- H+ ions are actively transported out of companion cells into source cells (creating a concentration gradient)
- H+ ions move back into companion cell with sucrose/amino acids into companion cell through co-transport proteins
- Surcose/amino acids diffuse from companion cell into sieve tube element via plasmodesmata - lowering water potential of sieve tube element
- Water moves into sieve tube element via osmosis creating high hydrostatic pressure
- Water moves from high to low hydrostatic pressure carrying sucrose/ amino acids
- Assimilates moves into companion + sink cell via diffusion or active transport
- Water leaves phloem via osmosis from high to low water potential
Describe and explain pieces of evidence that prove translocation in companion cells?
- companion cells become negatively charged compared to surroundings - H+ ions move out of companion cells
- pH changes don’t occur in companion cells treated with cyanide, which stops aerobic respiration - H+ ions can only move out of companion cells by active transport, which requires ATP
- scientists see mitochondria, plasmodesmata and intrinsic proteins in the cell surface membrane - mitochondria for ATP production, plasmodesmata for assimilate diffusion and proteins for movement of H+ ions + sucrose/ amino acids
Why does translocation require ATP and how do we know it does?
Assimilates move 100,000x faster in phloem faster than with just diffusion - companion cells have many mitochondria to make ATP - if aerobic respiration stops so does translocation
What are xylem vessels and what do they transport?
- Dead hollow cells with lignified cell walls + no organelles
- joined end to end with no end walls forming a continuous tube
- transports water + minerals