Module 3 Unit 8 Lesson 6

EXCRETION IN PLANTS

Credits: http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookplantanat.htmlhttp://en.wikipedia.org/wiki/Autumn_leaf_color and http://life.bio.sunysb.edu/marinebio/mg_06.jpg

IntroductionAnimals 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?

ObjectivesYou 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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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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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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What is Excretion?

Why carry out excretion?

It helps to maintain homeostasis of the internal environment.

It is a characteristic of all living organisms

It involves the removal from the body of waste substances that are formed during cellular

metabolic activities, such as respiration, and which if left in the body could be toxic.

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O2 is excreted from photosynthesis

Photo: http://www.1ststeps.org/Science/Photosynthesis/photosynthesis.htm 7EXCRETION IN PLANTS

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. 8

EXCRETION IN PLANTS

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/Guttation9EXCRETION IN PLANTS

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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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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Water, brought to leaves via veins, is excreted during transpiration

Source: http://iusd.k12.ca.us/uhs/cs2/images/Leaf%20Cross-section.jpg 12EXCRETION IN PLANTS

Functions of stomata1. 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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Excretion of gases by diffusion

On woody stems - openings or pores in the layer of bark which is impervious to gasesor water. Oxygen and Carbon Dioxide can diffuse throughlenticels that develop in the bark.

http://www.tutorvista.com/content/biology/biology-ii/respiration/plants-gaseous-exchange.php

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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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Latex (white) can be excreted from plants

Source: http://www.desert-tropicals.com/Articles/Stem_cuttings/Euphorbias.html

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Gum oozes out of a branch

Gum

Source: http://waynesword.palomar.edu/ecoph13.htm

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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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