31 January Science 8 (view eclipse from sunset on) Beginning Photosynthesis

  1. Review DSN entry from previous class. http://rfrazier.msblogs.aes.ac.in/2018/01/28/29-january-science-8/
  2. Read today’s blogpost.
  3. Prepare DSN entry for today’s class.
  4. Check out the lunar eclipse today (will have already started by moonrise / sunset). Take some pictures! Imagine where the earth, sun, and moon are in relation to one another. Remember the classroom-sized model we made in December: https://www.timeanddate.com/eclipse/in/india/new-delhi
  5. Reading “difficult” things. Please assemble in Carbon jigsaw groups–send notes/DSN entries to those students (from your group) who are absent today. Break the piece into parts. Focus first on what you do know and understand. Summarize. Discuss. Then go and look up what you think are the most important words/phrases. Then revise your summary and discuss again. Make note of the new and important ideas:
  • Sucrose and Saccharomyces cerevisiae: a relationship most sweet
  • sugarandyeast
  • The abstract:

A. Sucrose is an abundant, readily available and inexpensive substrate for industrial biotechnology processes and its use is demonstrated with much success in the production of fuel ethanol in Brazil.

B. Saccharomyces cerevisiae, which naturally evolved to efficiently consume sugars such as sucrose, is one of the most important cell factories due to its robustness, stress tolerance, genetic accessibility, simple nutrient requirements and long history as an industrial workhorse.

C. This minireview is focused on sucrose metabolism in S. cerevisiae, a rather unexplored subject in the scientific literature.

D. An analysis of sucrose availability in nature and yeast sugar metabolism was performed, in order to understand the molecular background that makes S. cerevisiae consume this sugar efficiently.

E. A historical overview on the use of sucrose and S. cerevisiae by humans is also presented considering sugarcane and sugar beet as the main sources of this carbohydrate.

F. Physiological aspects of sucrose consumption are compared with those concerning other economically relevant sugars.

G. Also, metabolic engineering efforts to alter sucrose catabolism are presented in a chronological manner.

H. In spite of its extensive use in yeast-based industries, a lot of basic and applied research on sucrose metabolism is imperative, mainly in fields such as genetics, physiology and metabolic engineering.

6. Beginning Photosynthesis. What are the claims? What is the evidence? How do we know?

How do you think scientists have come to the conclusions they have about photosynthesis? How do they know?

What do you think constitutes the evidence for the following simplified versions of photosynthesis? (What is the difference between the two versions?)





The overall equation for Photosynthesis is

6 CO2+ 12 H2O + light–>C6H12O6 + 6 O2 + 6 H2O

The equation in words says that six molecules of carbon dioxide plus twelve molecules of water in the presence of light will make one molecule of glucose, six molecules of oxygen gas, and six molecules of water.

Where do you think the released oxygen comes from–the carbon dioxide or water? See if this animation helps you figure out the answer. Notice that the equation in this animation includes 6 more water molecules. Why do you think this is the case? Try the experiments, take the quiz.


See how this teacher has tried to explain photosynthesis to his students:


  • What is the point?
  • How well does it work? What questions do you have?
  • What confusions might arise? How? Why?
  • What misconceptions might develop? How? Why?

Historical timeline of photosynthesis histphoto

  • How many scientists and how many years did it take to arrive at the claim of photosynthesis?
  • 6CO+ 12H2O ——> C6H12O+ 6O+ 6H2O
  • Many intermediate reactions and reaction cycles–one set decomposes water and one set builds simple carbon compounds–energy driving these reactions comes from sunlight


Photosynthesis from Botany: A Blooming History

Notice the structure of the documentary. The narrator, botanist Timothy Walker, 


begins by stating the “claim” of photosynthesis. He then describes how the video will follow the discoveries and logic of investigators as evidence accumulates over 400 years(!) to support the claim. Remember, scientists DID NOT know the claim in advance. In fact, there were many alternative ideas and misconceptions about plants. It is important to consider how ideas are tested and how knowledge is constructed in the history of scientific ideas.

We will pause at certain points in the video to “process” the progress in the historical development of the claim (the fact of photosynthesis and the explanation of how it works) and acquiring the evidence (empirical results and logic) that supports the claim.



  • Notes, names, new words, evidence and argument, questions you have
  • Names: van Helmont, Ingenhousz, Sachs, Benson, Calvin
  • Important findings, analysis, conclusions:
  • Words:
  • Reference: From Peter Raven’s Biology of Plants raven06b_10

Examine the online textbook E.O. Wilson’s Life on Earth. Download  and examine those sections that you think are relevant to photosynthesis and understanding the flow of matter and energy involving life on earth. (Add what you think are the important words to your word list. Read short passages. Do not read so much that you feel overwhelmed. Summarize in writing what you get from a passage. Write down the questions that you have.)




How does “knowing that” something is the case compare to “knowing how” to do something? Are some kinds of knowing preferred to others? By you? In school? In life?


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