Plant physiologyShantal Al HabibIB BioMrs. Mariam Ohanyan18 October 2016

Plants’ Tissue Structure

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

Water Transport

IB Biology Companion

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

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After sucrose is withdrawn at the sink, amount of solute decreases=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

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

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

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

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

Puberty in plants?

Vegetative -> reproductive phase When meristems produce flowers rather than leaves

=> allow sexual reproduction

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

Sexual reproduction

Source:

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