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O4. Organisms obtain energy in a variety of ways.



Student Outcome: O4.1

Explain the importance of photosynthesis in the conversion of light energy into chemical energy, as illustrated by the following equation:

6CO2 + 6H2O -> C6H12O6 + 6O2

carbon dioxide + water -> glucose + oxygen


Photosynthesis in a Chloroplast

Some terms and definitions:


  • H2O is water.
  • O2 is oxygen.
  • CO2 is carbon dioxide.
  • ATP is adenosine triphosophate.
  • Grana are the stacked membranes that contain chlorophyll.


During the process of photosynthesis, light penetrates the cell and passes into the chloroplast. The light energy is intercepted by chlorophyll molecules on the granal stacks. Some of the light energy is converted to chemical energy. During this process, a phosphate is added to a molecule to cause the formation of ATP. The third phosphate chemical bond contains the new chemical energy. The ATP then provides energy to some of the other photosynthetic reactions that are causing the conversion of CO2 into sugars.


Source: http://www.globalchange.umich.edu/globalchange1/current/lectures/kling/energyflow/PSN_primer.html


Good introduction to photosynthesis - nice graphics - but no text or explanation!


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This is a little more informative - if you are an 8 year old!

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Good animation going from a leaf to the chloroplast here - a good way to introduce yourself to photosynthesis.


Here is a quite detailed summary of the process of photosynthesis and the factors affecting it.


Student Outcome: O4.2

Understand that heterotrophs rely on existing organic molecules for their nutrition.


Heterotrophs (from Greek heteros = other or different, trophos = feeder) are organisms that are not able to make their own food. They must ingest or absorb food produced by other organisms. Therefore, the heterotrophs rely on other organisms for their nutrition. Heterotrophic organisms include animals, fungi, and some single-celled protozoa (e.g., ameba, paramecia) and bacteria. While autotrophs make their own food by converting inorganic nutrients into organic forms, heterotrophs cannot do this. Heterotrophs require most nutrients in an already produced, organic form. They use these nutrients both as a source of energy and as building blocks to form cell and body parts. In a food web the heterotrophs are the consumers.


Source: http://www.bookrags.com/Heterotroph



Student Outcome: O4.3

Explain how most autotrophs and heterotrophs transform chemical energy for use through aerobic respiration, as illustrated by the following equation:

C6H12O6 + 6O2 -> 6CO2 + 6H2O + energy

glucose + oxygen -> carbon dioxide + water + energy


Cellular respiration allows organisms to use (release) the energy stored in glucose. The energy in glucose is first used to produce ATP. Cells use ATP to supply their energy needs. Cellular respiration is therefore a process in which the energy in glucose is transferred to ATP.


In respiration, glucose is oxidized (releasing energy) and oxygen is reduced to form water.


The carbon atoms of the sugar molecule are released as carbon dioxide (CO2).


The complete breakdown of glucose to carbon dioxide and water requires two major steps: 1) glycolysis and 2) aerobic respiration. Glycolysis produces two ATP. Thirty-four more ATP are produced by aerobic pathways if oxygen is present.


Source: http://faculty.clintoncc.suny.edu/faculty/Michael.Gregory/files/Bio%20101/Bio%20101%20Lectures/Cellular%20Respiration/cellular.htm


This video is about glycolysis - bit too much chemistry but what can you do!


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Nice animation here showing the breakdown of glucose - too much detail for us, but just look at the big picture!


Another animation showing glycolysis - again, too much detail, just look at the overall picture, particularly the production of ATP at the end.


Wow. Go here (Concord.org) and open an application called "Molecular Workbench".  You will need the latest version of Java.

Then go here to the Cellular Respiration activity.  Especially focus on Part 3 (Enzymes).

The activity will display many of the enzymes involved in Glycolysis. The good thing is that you can rotate and enlarge the enzymes - even the active site!



Student Outcome: O4.4

Explain that fermentation is an anaerobic alternative to aerobic respiration.

In plants and yeast:

C6H12O6 -> 2C2H5OH + 2CO2 + energy

glucose -> ethanol + carbon dioxide + energy

In animals:

C6H12O6 -> 2C3H6O3 + energy

glucose -> lactic acid + energy


Anaerobic respiration in humans may be summarised by the word equation:


glucose --> lactic acid + energy


In yeast anaerobic respiration may be summarised by:


glucose --> ethanol + carbon dioxide + energy


During glycolysis, glucose molecules (six-carbon molecules) are split into two pyruvates (three-carbon molecules) during a sequence of enzyme-controlled reactions. This is the same reaction as occurs in aerobic respiration. Without oxygen, pyruvate is converted to lactic acid in animals or ethanol in plants and yeast. It produces only about 10% of the energy released in the complete oxidation of glucose.

Source: http://www.chemsoc.org/networks/learnnet/cfb/respiration.htm


Nice video on fermentation below:

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For more chemistry, look at the video, otherwise don't bother!

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Student Outcome: O4.5

Know that much more energy is released through aerobic respiration than through fermentation.


Respiration is the release of energy from glucose or another organic chemical. The chemical energy in glucose can be used to provide the energy required for growth, repair and movement. In fact most things you do require energy.


Aerobic Respiration is the normal form of respiration. It requires oxygen and releases the most energy from glucose. 1Mole of Glucose produces 2830 Kilojoules of energy. When we respire like this we have to breathe oxygen in and breathe carbon dioxide out. We also have to excrete (get rid of) the extra water in our urine.


Anaerobic Respiration also releases energy from glucose but not so much I mole of glucose will produce 118 Kilojoules of energy. When yeast respires anaerobically it produces carbon dioxide and alcohol. When we respire we produce lactic acid. Too much lactic acid poisons our muscles (you get cramp).


Source: http://www.sambal.co.uk/respiration.html


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