topic 9 plant physiology
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Plant physiologyShantal Al HabibIB BioMrs. Mariam Ohanyan18 October 2016
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Xylem Structure
● Elongated lignin tubes● Arranged end-to-end● Non-living cells● Rigid structures which
withstands low pressure● Pressure lower than
atmospheric ● One way movement
Transport of
water-> passive transport
Source: Britannica.com
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Water Transport
IB Biology Companion
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Phloem Structure
● Sieve tube cells● With sieve plates● Companion cells (numerous
mitochondria)● 2-way movement● Reduced cytoplasm● No nucleus
Transport of organic
compounds
-> active transport-
Translocation
Source: Britannica.com
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Phloem LoadingApoplast route
Through cell walls (mesophyll cells to companion or sieve cells)
Active transport:H+ ions transported out of companion cells
=> sucrose concentration gradient
Co-transport protein:H+ flow down the gradient
=> energy is released
=> used to carry sucrose into the companion-sieve complex
Symplast route
Through connections called plasmodesmata in the cytoplasm Sucrose -> oligosaccharide in companion cells
Build up of carbohydrate=> water enters companion cells by osmosis
Pressure build up:=> water moves from high to low
After sucrose is withdrawn at the sink, amount of solute decreases=> decrease in osmotic pressure -> water drawn back into transpiration stream
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Meristems
Undifferentiated cells undergoing cell division. Primary meristems are at the tips of the plant parts and are known as apical. They have the following 2 types:
1- Root apical meristems: growth of root
2-Shoot apical meristems: growth of stem
Source: url
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AuxinsHormones that:
❏Control and initiate growth
❏Influence and regulate leaf and fruit development
❏Inhibit the growth of auxillary buds Cytokinins Produced in the root
❏ Promotes auxillary bud growth
Ratio determines whether the bud will develop or not
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TropismsDirectional growth response
1.Absorption of light by phototropins
2.Bind to receptors (PIN 3)3.Light intensity detection4.Auxin is transported to
the shady part5.Growth is in a curve
towards light
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Root and Statoliths
If the root is placed on its side:
1.Statoliths form on the lower side because of gravity
2.PIN 3 directs auxin to the bottom
3.High auxin conc. Inhibits elongation
4.Top cells elongate faster5.Root bends downward
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Puberty in plants?
Vegetative -> reproductive phase When meristems produce flowers rather than leaves
=> allow sexual reproduction
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PR PFR
660 nmRapid
730 nmSlow
Length of dark period:PhytochromeTranscription of Flowering time (FT)FT mRNA => translated to FT proteinBinds to transcription factor => activation of flowering genes
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Sexual reproduction
Source:
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