Transcript Biology of Plants

Transportation of Water in Plants
By Arsalaan Muhammad
8a
E-portfolio Project
So what basically happens:
• In every plant, water moves from the ground, through the roots, up the stem, enters
the leaves, and finally exits from the plant through the leaves and repeats. In the
following slide show, you will find out what how water is transported through a plant.
This is fun waiting to be seen!
It all starts at the roots
• The water and any other Soluble nutrients disseminate in through the roots to
the xylem and then are distributed where needed in the plant. Root hairs help
absorb the water and others nutrients in the soil. From here, there is a
process called osmosis, which is when water moves from a region of higher
concentration to one of lower concentration.
Parts of the roots
• The outer layer of the root is the epidermis. This region
produces root hairs which project into the soil increasing
surface area for uptake of water.
• Below the epidermis is the cortex. Cortical cells are highly
permeable to water and dissolved solutes.
• Below the cortex is a thin layer called the endodermis. The
endodermis controls flow of water and minerals within the
plant.
• At the centre of the root is the stele. This region contains the
vascular tissues (the xylem and phloem) surrounded by a
layer of cells called the pericycle. The remainder of the stele
is the vascular cambium. These cells are able to divide to
form new xylem and phloem increasing the size of the roots.
So what are the Xylem and Phloem?
What causes the water to go up the plant?
• The answer to this is the Root Pressure and Capillary Action.
• Root Pressure: Water moves up through a plant because of root pressure and capillary action.
Root pressure occurs during times when transpiration is low but the soil is very moist, and the
roots absorb too much water. Because the water accumulates in the plant, a slight root pressure
is created that pushes the xylem sap to the tips or edges of leaves, where it forms drops (the
process is called guttation).
• Capillary action: During capillary action, water rises up the walls of the thin, porous xylem tube as
a result of the forces of adhesion, cohesion and surface tension. Xylem tubes are made of
cellulose, to which water molecules stick.
Next Part of the Journey- Reaching the Xylem
• The water moves across the root from the hair cell to the xylem by three
different pathways:
• apoplast pathway - water passes through the cell walls and from the wall of
one cell to the wall of an adjacent cell
• symplast pathway - water moves through the cytoplasm and from the
cytoplasm of one cell into the cytoplasm of the next cell via the
plasmodesmata- (a narrow thread of cytoplasm that passes through the cell
walls of adjacent plant cells and allows communication between them.)
• vacuolar pathway - water passes from the vacuole of one cell into the
vacuole of the next cell
• Water is not completely free to move from the root hair cell to the xylem.
• The apoplastic pathway is blocked when it reaches the endodermis because
the endodermal cells have a waxy, waterproof layer which prevents the
further passage of water through the wall. This waxy layer is called the
Casparian strip and is shown in the diagram below.
In the xylem
• Once in the xylem, water with the minerals that have been deposited in it (as well as occasional organic
molecules supplied by the root tissue) move up in the vessels and tracheids. At any level, the water can leave the
xylem and pass to supply the needs of other tissues. At the leaves, the xylem passes into the petiole and then
into the veins of the leaf. Water leaves the finest veins and enters the cells of the spongy (temporarily stores the
sugars and amino acids synthesized in the palisade mesophyll) and palisade layers. Here some of the water may
be used in metabolism, but most is lost in transpiration.
Cohesion and Adhesion Theory
• Cohesion: The cohesion theory is when water molecules
are strongly attracted to each. Cohesion is whereby the
driving force of transport is transpiration, that is, the
evaporation of water from the leaf surfaces. Water
molecules cohere (stick together), and are pulled up the
plant by the tension, or pulling force, exerted by
evaporation at the leaf surface.
• Adhesion is when water molecules adhere or stick to the
walls of the xylem. When unequal distribution of ions go
across the membrane, solutes move along the
concentration gradient. when unequal distribution of ions
go across the membrane, solutes move along the
concentration gradient. This is called diffusion.
The leaves (main parts)
•
Leaves have xylem and phloem tubes.
•
The epidermis is on the outside to protect the leaf. The epidermal layer of a leaf
protects the tissues which lie between them and also help in the process of
gaseous exchange.
•
The palisade mesophyll (photosynthesis cell) have chloroplast which have green
substance called chlorophyl.
•
Spongy mesophyll protects the epidermis. They are more rounded and are not as
tightly packed as palisades. They contain less chlorophyll.
•
Stomata's connect to air spaces between mesophyll. Carbon dioxide travels
through stomata at the bottom of the leaf.
•
Light energy which chloroplast creates turns carbon dioxide and water to create
glucose and oxygen
•
Photosynthesis takes place in chloroplasts in leaves which absorbs sunlight.
Photosynthesis is the process by which plants convert energy from the sun.
•
Plants use sugar to make starch, fats and proteins.
Transpiration
• Once the water reaches the xylem it moves upwards as a
result of transpiration. So basically, transpiration is kind of
evaporation. Leaves have openings called stomata which are
guard cells which open and close. They only respond to light,
meaning that the plant doesn’t transpire as much at night.
Stomata's circulate carbon dioxide from the air for
photosynthesis to enter the leaf as well as regulate the
amount of water in the leaf. In the process, water evaporates
from the leaf. Transpiration cools plants and allows large
amounts of nutrients and water to shoots.
• The formula for photosynthesis:
• carbon dioxide + water (+ light energy) → glucose + oxygen
=
• 6 CO2 + 6 H2O → C6H12O6 + 6 O2
Bibliography
•
Walker Keenan. "Gymnosperms." 2009. Web. 20 Mar. 2011. <http://sharon-taxonomy2009-p2.wikispaces.com/Gymnosperms>.
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"Transport of Water and Minerals in Plants." 16 Dec. 2010. Web. 18 Mar. 2011. <http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/X/Xylem.html>.
•
Ridwan. "TRANSPORTATION IN PLANTS." Scribd. Web. 23 Mar. 2011. <http://www.scribd.com/doc/4801010/TRANSPORTATION-IN-PLANTS>.
•
Water Transport in Plants. "Water Transport in Plants." Nick's Pages - Mostly Biology. Web. 23 Mar. 2011.
<http://www.nicksnowden.net/Module_2_Biology_pages/water_transport_in_plants.htm>.
•
"SparkNotes: Plants: Essential Processes: Water Transport." SparkNotes: Today's Most Popular Study Guides. Web. 23 Mar. 2011.
<http://www.sparknotes.com/biology/plants/essentialprocesses/section1.html>.
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Holbrook, N. M., M. J. Burns, and C. B. Field. "Negative Xylem Pressures in Plants: A Test of the Balancing Pressure Technique." Science 270 (1995): 1183–
1192.
•
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Raven, Peter H., Ray F. Evert, and Susan E. Eichhorn. Biology of Plants, 6th ed. New York: W. H. Freeman and Company, 1999.
Taiz, Lincoln, and Eduardo Zeiger. Plant Physiology, 2nd ed. Sunderland, MA: Sinauer Associates, 1998.
•
"Water Movement in Plants - Biology Encyclopedia - Cells, Body, Function, Process, Used, Structure, Molecules, Energy." Biology Reference. Web. 23 Mar.
2011. <http://www.biologyreference.com/Ve-Z/Water-Movement-in-Plants.html>.
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"Water in Plants - Biology Online." Life Science Reference - Biology Online. Web. 23 Mar. 2011. <http://www.biologyonline.org/11/8_water_in_plants.htm>.http://www.youtube.com/watch?v=DpFU-NkKUqg
•
Scully, Lizzy. "How Water Moves Through Plants | EHow.com." EHow | How To Do Just About Everything! | How To Videos & Articles | EHow.com. Web. 23
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Glossary
•
Abscisic Acid - The best known of the inhibitor hormones; inhibits growth and prolongs dormancy.
•
Acid Growth Hypothesis - Explains phototropism by suggesting that increased acidity in the walls of certain cells (stimulated by the hormone auxin) increases their flexibility and expandability, so that more water can diffuse
into the cells and cause cell elongation.
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Active Transport - Movement of substances across cell membranes that requires energy expenditure on the part of the cell; contrasts with passive diffusion, or osmosis.
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Apoplast - The pathway from the root surface to the core by which water moves along cell walls and through intercellular spaces, bypassing the cells themselves.
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Auxin - One in a class of plant hormones that stimulates (among other things) cell elongation, secondary tissue growth, and fruit development.
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Cytokinin - One in a class of plant hormones that promotes cell division and tissue growth.
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Day-Neutral Plant - Plant in which blooming is not affected by photoperiod, so that flowering occurs independently of the duration of day and night.
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Ethylene - A plant hormone that controls fruit ripening and promotes senescence (aging).
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Florigen - Name given to the hypothetical hormone that might control flowering in plants.
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Gibberellin - One of a class of plant hormones that stimulates stem elongation, germination, and conversion of the embryonic food source into usable sugars.