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Plant biology (IX) - Coggle Diagram
Plant biology (IX)
Xylem
Made of long, continuous tubes
Its walls are covered in lignin, which
allows them to withstand very low pressures
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Xylem cells are non-living, water movement is passive
Water cohesion and adhesion create a column of water and allow it to climb towards the top of the plant
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When water evaporates, it is pulled upwards
due to the low pressure created
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Water routes
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Once water is in the roots, it enters
the xylem in two different ways
Phloem
Phloem connects sources (leaves, storage organs) to sinks (any developing part of the plant)
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Composed of sieve tubes, made of sieve tube cells
Phloem loading
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Symplast route
Once it reaches the companion cell, it is converted to an oligosaccharide to maintain the sucrose concentration gradient
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Apoplast route
Mesophyll cells --> companion cells --> sieve cells,
sucrose transport protein needed
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Water pressure
At the sink, sucrose is either metabolised or stored as starch, causing a reduction in osmotic pressure (conc. decreases)
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Causes a pressure build-up, causing
water to flow to an area of lower pressure
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Components
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Sieve tube cells: living, no nucleus
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Transpiration
Guard cells, found in pairs around a stoma,
control the opening of the stomata
Stomata also allow water to evaporate,
this evaporation is called transpiration
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Reproduction
Photoperiodism
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PR is more stable than PFR, so in
darkness PFR goes back to PR
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Long day plants: large amounts of PFR remain at the end of the night and bind to receptors, whcih promote flowering gene expression
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Short day plants: when PFR remains, the receptors inhibit gene transcription of flowering. When little PFR remains, transcription occurs
Pollination
This carries the male gametes which fertilise the ovule, which will then develop into the seed
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