Transcript Document 7586678

By Ayana Hazu and Jessica Smit
 It is known that a leaf must have an elastic nature.
 Would it be possible to stretch a leaf?
 How will stretching affect its properties?
 Autotrophs (self-feeding) – convert simple inorganic
molecules into complex organic molecules
 Photosynthesis:
6CO2 + 12H2O  C6H12O6 + 6O2 + 6H2O
 To find out if leaves could be stretched
 Analyse the leaf’s elastic properties
 Leaves can be stretched
 Leaves will stretch less when submerged in water
 Every experiment done 3 times – took average
 Different types of leaves
 A simple, petiolated, entire leaf (8 x 5cm) – in dry
conditions, room temperature
 A compound, petiolated
leaf (5 x 3cm) – in dry
conditions, room
temperature
 A serrate, entire leaf (7 x 3cm), in dry conditions and at
room temperature
 Comparison between a leaf in dry conditions, and one
that is submerged in cold water.
 Simple, entire leaves of same dimensions were used.
 Placed underwater for five minutes before stretching.
 Compared the biological properties of a stretched leaf
to a normal leaf.
 Observation under a microscope .
 Starch test using iodine solution.
 No alteration to the plant cell structures
 No permanent structural abnormalities.
 No difference in
starch test.
 Experiments 1 -3:
 The graphs are similar
 force is almost directly proportional to the extension
 at a certain point there is a sharp curve where the leaf
loses its ductility
 Possibility for Hooke’s Law?
 Calculation of Young’s Modulus
 By calculating using the Young’s modulus equation:
 With A0 (cross-section of the leaf) = 3cm x 0.5mm
= 1.5 x 10-5 m2
 L0 = 8cm = 0.08m
 For F: E = 1.77 x 107 Pa = 1.76 x 10-3 Gpa
 For G: E = 8.83 x 106 Pa = 8.83 x 10-4 Gpa
 two different structures to the leaf with different
properties in its microscopic structure
 Leaf is not ductile
 Leaves in water produced no straight line – no definite
Young’s Modulus
 Ductile due to sudden curve in graph after x=0.15
 Leaf in water could resist more force than when it is
outside the water.
 Accuracy of measurements
 No leaves are of the same dimentions
 Microscope analysis
 Factors affecting leaf’s Young Modulus
 Uses
 http://www.water.tkk.fi/wr/kurssit/Yhd-
12.135/kirja/stomata.htm
 http://www.bcb.uwc.ac.za/ecotree/leaves/Leaf
typeA.htm
 http://en.wikipedia.org/wiki/Young%27s_mod
ulus
 http://en.wikipedia.org/wiki/Elastic_modulus
 http://en.wikipedia.org/wiki/Yield_%28engin
eering%29
 http://en.wikipedia.org/wiki/Tensile_strength