The document outlines the structure and function of plant tissues, focusing on xylem and phloem, detailing their roles in water and nutrient transport. It discusses meristems, auxins, and cytokinins in growth regulation and tropic responses, alongside the transition from vegetative to reproductive phases in plants. The role of phytochrome in flowering is also highlighted.

1. Plant physiology
Shantal Al Habib
IB Bio
Mrs. Mariam Ohanyan
18 October 2016

2. Plants’ Tissue Structure

5. 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 Source: Britannica.com

6. Water Transport
IB Biology Companion

7. Phloem Structure
● Sieve tube cells
● With sieve plates
● Companion cells (numerous
mitochondria)
● 2-way movement
● Reduced cytoplasm
● No nucleus
Source: Britannica.com

8. Phloem Loading
Apoplast 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
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After sucrose is withdrawn at the sink, amount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

9. 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

10. Auxins
Hormones 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

11. Tropisms
Directional growth response
1.Absorption of light by
phototropins
2.Bind to receptors (PIN 3)
3.Light intensity detection
4.Auxin is transported to the
shady part
5.Growth is in a curve towards
light

12. 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 faster
5.Root bends downward

13. Puberty in plants?
Vegetative -> reproductive
phase
When meristems produce flowers rather than leaves
=> allow sexual reproduction

14. PR
PFR
660 nm
Rapid
730 nm
Slow
Length of dark period:
Phytochrome
Transcription of Flowering time (FT)
FT mRNA => translated to FT protein
Binds to transcription factor => activation of flowering genes

17. Sexual reproduction
Source:

18. THANK YOU FOR YOUR
ATTENTION!