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Biology IB HL - 9.2 Phloem Transport Part 1

Biology20 CardsCreated about 1 month ago

This deck covers key concepts of phloem transport, including translocation, the structure and function of phloem components, and the relationship between xylem and phloem in vascular plants.

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What is translocation?

Translocation is the movement of organic compounds (e.g. sugars, amino acids) from sources to sinks
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Key Terms

Term
Definition
What is translocation?
Translocation is the movement of organic compounds (e.g. sugars, amino acids) from sources to sinks
What is the source?
The source is where the organic compounds are synthesised – this is the photosynthetic tissues (leaves)
What is the sink?
The sink is where the compounds are delivered to for use or storage – this includes roots, fruits and seeds
Where does translocation occur?
Organic compounds are transported from sources to sinks via a vascular tube system called the phloem
How are sugars transported?
Sugars are principally transported as sucrose (disaccharide), because it is soluble but metabolically inert
What liquid is found in the phloem?
The nutrient-rich, viscous fluid of the phloem is called plant sap
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Biology IB HL - 9.2 Phloem Transport Part 1
TermDefinition
What is translocation?
Translocation is the movement of organic compounds (e.g. sugars, amino acids) from sources to sinks
What is the source?
The source is where the organic compounds are synthesised – this is the photosynthetic tissues (leaves)
What is the sink?
The sink is where the compounds are delivered to for use or storage – this includes roots, fruits and seeds
Where does translocation occur?
Organic compounds are transported from sources to sinks via a vascular tube system called the phloem
How are sugars transported?
Sugars are principally transported as sucrose (disaccharide), because it is soluble but metabolically inert
What liquid is found in the phloem?
The nutrient-rich, viscous fluid of the phloem is called plant sap
What are the phloem sieve tubes mainly composed of?
Phloem sieve tubes are primarily composed of two main types of cells – sieve element cells and companion cells
What other cells apart from the main 2 may be found in the phloem and for what purpose?
The phloem also contains schlerenchymal and parenchymal cells which fill additional spaces and provide support
What are sieve elements?
Sieve elements are long and narrow cells that are connected together to form the sieve tube
How are sieve elements connected?
Sieve elements are connected by sieve plates at their transverse ends, which are porous to enable flow between cells
Do sieve elements have nuclei?
NO Sieve elements have no nuclei and reduced numbers of organelles to maximise space for the translocation of materials
Describe the cell walls in sieve elements
The sieve elements also have thick and rigid cell walls to withstand the hydrostatic pressures which facilitate flow
What are companion cells?
Provide metabolic support for sieve element cells and facilitate the loading and unloading of materials at source and sink
How do companion cells increase SA:VOL ratio?
Possess an infolding plasma membrane which increases SA:Vol ratio to allow for more material exchange
What type of organelles do companion cells have a large amount of?
Have many mitochondria to fuel the active transport of materials between the sieve tube and the source or sink
What type of proteins do companion cells have many of?
Contain appropriate transport proteins within the plasma membrane to move materials into or out of the sieve tube
Can sieve elements “survive” without companion cells? Why/not?
NO Sieve elements are unable to sustain independent metabolic activity without the support of a companion cell This is because the sieve element cells have no nuclei and fewer organelles (to maximise flow rate)
How do companion cells deliver necessary substances to the sieve elements?
Plasmodesmata exist between sieve elements and companion cells in relatively large numbers These connect the cytoplasm of the two cells and mediate the symplastic exchange of metabolites
How are the xylem and phloem grouped?
Xylem and phloem vessels are grouped into bundles that extend from the roots to the shoots in vascular plants
What does the arrangement of vascular bundles depend on?
Differences in distribution and arrangement exist between plant types (e.g. monocotyledons vs dicotyledons) whether in root or stem