This document defines the soil-plant-atmospheric continuum (SPAC) as the pathway for moving water from soil through plants to the atmosphere. It describes the three pathways - symplast, apoplast, and cellular - by which water travels from the soil into the root and then through the xylem up into the leaves. The document also lists factors like soil water holding capacity, diffusion pressure, and humidity that affect the SPAC and provides a flow chart illustrating how water moves through the different parts of a plant from the soil into the atmosphere.
4. Presented to : Dr.Muhammad Kabir
Presented by : Farhana Sheikh
Roll No : BS-Bot-F17-R03
Class : BS Botany6th(Regular)
Subject : Botany
Course title : Plant Ecology-1
Department of Biological Sciences
UOS Sub Campus Bhakkar
5. Contents:
Definition
Water
Functions of water in plants
How water reach the leaf of plant.
Symplast pathway
Apoplast pathway
Cellular pathway
Pathway of water
Fectors affecting SPAC
Movenent of water in plant
7. Explanation
The low water potential of the atmosphere, and relatively
higher (i.e. less negative) water potential inside leaves,
leads to a diffusion gradient across the stomatal pores of
leaves, drawing water out of the leaves as vapour.
As water vapour transpires out of the leaf, further
water molecules evaporate off the surface of
mesophyll cells to replace the lost molecules since
water in the air inside leaves is maintained at
saturation vapour pressure.
8. Conti………..
Water lost at the surface of cells is replaced by water
from the xylem, which due to the cohesion-tension
properties of water in the xylem of plants pulls
additional water molecules through the xylem from
the roots toward the leaf.
10. Functions of water within a plant:
1. Most of plant fresh weight comes from water (up
to 90%)
2. Provide structure and support
3. Source of oxygen release form photosynthesis
4. Medium for transporting nutrients, metabolites,
and plant hormones
5. Lost by transpiration through stomata
6. Inevitable consequence of photosynthesis
11.
12. How water reaches from roots to leaves?
Pathway for water movement from roots to leaves.
Water can travel from the soil to the root
xylem by three distinct pathways
1. symplastpathways
2. apoplast pathways
3. Cellular pathway
13. Symplat pathway:
If water move from one cell to another cell
through plasmodesmata is called symplast
pathway.
The endodermis has barrier and only one pathway
can work which is symplast pathway.
17. Factors affecting the SPAC:
1. Soil water holding capacity
2. Soil particle.
3. Diffusion pressure
4. Osmotic pressure
5. Humidity in atmosphere.
18. Pathway of water through plant:
(Flow chart)
soil water root hair epidermis cortex endodermis
pericycleRoot xylemStem xylemleafatmosphere
19. Movement of water through plant:
The water is present in soil is absorbed by the root
hairs through diffusion.
The water move through concentration gradient.
Then water first enters the epidermis of root and
move toward the xylem of the leaf.
For this the water enter the xylem of stem then in
the xylem of leaf and reach the spongy and palisade
mesophyll.
20. Conti………
Palisade perform more photosynthesis due to
high conc. of chloroplast in them.
The palisade take water for photosynthesis.
If water evaporates in high conc.the wilting of
plant occurs.
