Plants excrete waste through various methods without a dedicated excretory system. They excrete gases like oxygen and carbon dioxide through diffusion, water and excess salts through structures like stomata and salt glands, and solid crystals and compounds through storage in leaves, bark, and wood that are later shed. Excretion maintains plant homeostasis by regulating salts and removes byproducts of metabolic processes like respiration.

1. Module 3 Unit 8 Lesson 6
EXCRETION IN PLANTS

2. Credits: http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookplantanat.html
http://en.wikipedia.org/wiki/Autumn_leaf_color and http://life.bio.sunysb.edu/marinebio/mg_06.jpg
Introduction
Animals are known to excrete wastes
and usually have a special set of organs
or a system that carries out that
function. Do you think flowering plants
like these also carry out excretion?

3. Objectives
You should be able to:
1. give examples of waste substances and how
they are excreted by plants.
2. state the importance of excretion to plants.
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4. Salt crystals on the leaf surface of the Black Mangrove
http://commons.wikimedia.org/wiki/File:Avicennia_germinans-salt_excretion.jpg
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5. Salt glands on Button mangrove leaf petioles
salt gland
Photo: http://hdl.handle.net/123456789/271 or http://dspace.mona.uwi.edu/handle/123456789/271
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6. What is Excretion?
Why carry out excretion?
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7. O2 is excreted from photosynthesis
Photo: http://www.1ststeps.org/Science/Photosynthesis/photosynthesis.htm
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8. What ‘waste’ from respiration is
excreted?
Glucose + Oxygen  Carbon Dioxide + Water +
Energy released and made available
C6H12O6 + 6O2  6CO2 + 6H2O + Energy
This means that oxygen combines with sugars
present in cells to break molecular bonds, thus
releasing the energy contained in those bonds.
The other products of the respiratory reactions
are carbon dioxide and water, which can be
excreted if not needed then by the plant.
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9. Guttation - The loss of excess water as liquid
drops from the margins of leaves of herbaceous plants,
occurring when root pressure is high and transpiration
is low. The water usually contains sugars and/or salts.
http://www.rosenfreundehannover.de/botanik.php http://en.wikipedia.org/wiki/Guttation9

10. Ornamental plants form Calcium Oxalate
crystals in (leaf) cells for excretion
www.library.okstate.edu/.../red_emerald.jpg
The cells of these plants
contain Calcium oxalate
crystals which are
eliminated when the leaves
die and fall off.
www.flowersgrowing.com/.../12/diefenbachia.jpg
www.dkimages.com/.../previews/917/70024692.JPG
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11. Calcium Oxalate crystals from
Pomegranate leaf (left) and Tilia sp.
Pomegranate Leaf: http://www.botany.org/plantimages/ImageData.asp?IDN=abot92-12
Tilia sp.: http://waynesword.palomar.edu/ww0601c.htm
Development of the calcium oxalate
crystal in pomegranate
Calcium oxalate crystal in Tilia sp.
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12. Water, brought to leaves via veins, is
excreted during transpiration
Source: http://iusd.k12.ca.us/uhs/cs2/images/Leaf%20Cross-section.jpg
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13. Functions of stomata
1. Gas Exchanges and 2. Transpiration
Oxygen, Carbon
dioxide can
diffuse in/out
Water vapour
diffuses out.
Guard
cell
Source: http://www.worldofteaching.com/powerpoints/biology/plantsgeneral.ppt#262,13,
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14. Excretion of gases by diffusion
On woody stems - openings
or pores in the layer of bark
which is impervious to gases
or water. Oxygen and Carbon
Dioxide can diffuse through
lenticels that develop in
the bark.
http://www.tutorvista.com/content/biology/biology-ii/respiration/plants-gaseous-exchange.php
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15. Various wastes are removed during leaf fall
• Waste compounds are often stored in dead
heartwood, bark and leaves which die/fall off.
http://www.na.fs.fed.us/spfo/pubs/misc/leaves/leaves.htm
• When chlorophyll breaks
down, other compounds
in leaves give the
characteristic autumn
colours seen just
before leaf fall.
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16. Latex (white) can be excreted from plants
Source: http://www.desert-tropicals.com/Articles/Stem_cuttings/Euphorbias.html
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17. Gum oozes out of a branch
Gum
Source: http://waynesword.palomar.edu/ecoph13.htm
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18. Summary
• Excretion is the removal from the organism’s
body of waste substances produced during
cellular metabolism.
• Plants do not have any set excretory system,
so, getting rid of wastes often involves storing
the substance (e.g. Calcium Oxalate, tannins)
in some plant tissue, passing it out onto leaf
surfaces (e.g. salts) or diffusion (e.g. O2, CO2).
• Because salts are so removed, excretion also
serves the important function of osmo-
regulation which maintains homeostasis.
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