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What factors affect the rate of photosynthesis in living leaves?

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Sarah Blechacz

on 26 September 2013

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Transcript of What factors affect the rate of photosynthesis in living leaves?

What factors affect the rate of photosynthesis in living leaves?
The general summary equation for photosynthesis is:
2 H2O + CO2 + light → carbohydrate (CH2O) + O2 + H2O
Leaf Anatomy:
normally infused with gasses (would float in water)
Creating "leaf disks"
What would happen if the gases were drawn from the spongy mesophyll layer by using a vacuum and replaced with water?
Procedure:
If the leaf disk is placed in a solution with an alternate source of carbon dioxide in the form of bicarbonate ions, then photosynthesis can occur in a sunken leaf





Oxygen will accumulate in the air spaces of the spongy mesophyll, and the leaf disk will once again become buoyant and rise in a column of water.

So... the rate of photosynthesis can be indirectly measured by the rate of rise of the leaf disks.
Design experiments to test variables that might affect the rate of photosynthesis. Some ideas include the following, but don’t limit yourself to just these:
Environmental variables

Features of the plant leaves
(color, species, shape, texture etc.)
What could you measure to determine the rate of photosynthesis?
Write these out in "if, and, then" format and get them checked by me prior to starting your tests
(today!)
There will be a write up with this lab... like the candle lab
Cells convert incoming energy to forms that they can use using two major organelles:
Mitochondria
Chloroplasts
Chloroplasts
Structure:
Outer Membrane
Inner Membrane
Stroma: liquid inside inner membrane. Contains DNA and Ribosomes & enzymes. Where sugar is made.
Thylakoids: Membranous sacs inside inner membrane. Where ATP is made. Stacked into "Grana"
Function:
Photosynthesis
Building ("anabolism") of sugar from ATP, CO2 & light. Produces O2 as waste
Stomata
Under hot and dry environmental conditions, stomata close to reduce the loss of water vapor
How do plants that normally live in hot, dry climates cope with this!?
This preserves water, but also results in a greatly diminished supply of CO2 for the plant
Plants that normally live in
dry, hot climates have adapted different ways of initially fixing CO2 prior to entering the Calvin cycle
C4 pathway
CAM pathway
Efficiently fixes CO2 at low concentrations
-Fix CO2 into a 4 carbon compound called oxaloacetate
-The enzyme that catalyzes this reaction (PEP carboxylase) fixes CO2 very efficiently so he C4 plants don't need to have their stomata open so often
-3% of all terrestrial plants
-Examples: sugarcane, crab grass, corn
sugarcane!
Live in very dry conditions- like here!
-Open their stomata to fix CO2 only at night
-Like C4 plants, use PEP
carboxylase to fix CO2
-Oxaloacetate is converted to malate (gets stored in cell vacuoles)
-During the day when stomata are closed, CO2 is removed from the stored malate and enters the Calvin cycle
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