Question

Today you'll have the opportunity to apply what you know about oxidation/reduction reactions to a familiar biological process. Please feel free to reference your Unit 4 Oxidation Guided Notes to support you on this question set. First let's review the most general concepts of electron exchange. Please complete the paragraph below with the correct terms. (5 points)
Redox reactions are all about moving electrons. When an atom loses electrons we say it is
and so a neighboring atom must gain electrons and be
. The atom that loses electrons, loses "negative charges" and becomes more
overall and the atom that gains electrons, gains 'negative charges' and becomes more
overall. What ends up happening is electrons get shifted and stored. A compound that stores electrons can work like a
if those electrons are removed and replaced.
Today's redox reaction we'll look at will be photosynthesis. We'll probably look at it differently than you ever have before but as a reminder, carbon dioxide enters plant leaves through stoma on the under side of the leaf and the roots bring water up from the soil. The whole process requires the catalyst of sunlight to begin knocking electrons loose. The light has to be the right frequency to get the job done.

In this sentence the word catalyst could best be defined as ___________________.

(1 point)

something needed to speed up a reaction that isn't itself used up during the reaction

a portion of the reaction that slows down the transfer of electrons

something that could be present or absent and the reaction would carry on fine

a portion of the reaction that joins carbon dioxide to water
Sunlight is the source of energy used to trigger photosynthesis in which plants convert that energy into stored energy in sugars and other molecules. The law of conservation of energy is fully honored in that energy isn't created or destroyed but light energy is converted into chemical potential energy stored in plant-derived molecules like sugar. A process that requires the input of energy from an outside source is ___________________.(1 point)

automatic

exergonic

exothermic

endergonic




In the image above, we can see the waste product or result of photosynthesis forming bubbles. From the simplified reaction, identify the product we see escaping the maple leaf seen here.

CO2 + H2O → [CH2O] +O2


(1 point)

carbon dioxide

oxygen

water

sugar
Study the image seen here very closely you'll be able to see how the atoms recombine based on the colors of the elemental symbols. Look at the labeled oxidation states for each atom. Use what you know about how these must balance to complete the image with the single missing oxidation number.(1 point)
Use the image again and determine which elements have been oxidized, reduced, or unchanged.



(4 points)
Oxidized Reduced Unchanged
The (green) hydrogen atom



The (red) carbon atom



The (red) oxygen atom



The (blue) oxygen atom



Think about how the oxidation states changed and complete the following sentence with the best terms. (2 points)
In the process of photosynthesis, the oxygen originally in water becomes more positive. This makes it the . The carbon atoms found in carbon dioxide become less positive, this means carbon is the in the process of photosynthesis.

Answer 1

Redox reactions are all about moving electrons. When an atom loses electrons we say it is oxidized and so a neighboring atom must gain electrons and be reduced. The atom that loses electrons, loses "negative charges" and becomes more positive overall and the atom that gains electrons, gains 'negative charges' and becomes more negative overall. What ends up happening is electrons get shifted and stored. A compound that stores electrons can work like a battery if those electrons are removed and replaced.

In this sentence the word catalyst could best be defined as
- something needed to speed up a reaction that isn't itself used up during the reaction.

A process that requires the input of energy from an outside source is
- endergonic.

From CO2 + H2O → [CH2O] + O2 the product we see escaping the leaf is
- oxygen (O2).

Missing oxidation number (for C in CH2O):
- 0

Which elements have been oxidized, reduced, or unchanged:
- The (green) hydrogen atom: Unchanged
- The (red) carbon atom: Reduced
- The (red) oxygen atom: Unchanged
- The (blue) oxygen atom: Oxidized

Final sentence:
- In the process of photosynthesis, the oxygen originally in water becomes more positive. This makes it the reducing agent. The carbon atoms found in carbon dioxide become less positive, this means carbon is the oxidizing agent.