Robert Lindblom Math & Science Academy



Reflection: Answer the following questions in complete sentences. Use the essays on pages 447-449 and 455-457 to write detailed answers.

First, take some time to see if you can answer these questions without looking at the key. Doing this will help you study!!

1. How are cellular respiration and photosynthesis similar? How are they different?

2. Plants gain mass as they grow, just like you. Why is it incorrect to say that plants get their food from the soil?

3. How does energy flow from the beginning of photosynthesis to the end of cellular respiration? What are the different forms of energy involved?

4. Earth’s early atmosphere had no oxygen. Use your understanding of plant photosynthesis to explain how photosynthetic organisms made the evolution of organisms that use aerobic cellular respiration possible.

5. Imagine the discovery of a new desert plant that has a unique pigment in its leaves. This pigment strongly absorbs all sunlight from green light (wavelength = 500 nanomenters) to red light (wavelength = 700 nanometers). If you observed this plant in the desert, what color would the leaves appear to be? Why?

6. After doing this lab, what questions do you still have about photosynthesis and/or cellular respiration?

The key is on the next page…

Reflection: Answer the following questions in complete sentences. Use the essays on pages 447-449 and 455-457 to write detailed answers.

1. How are cellular respiration and photosynthesis similar? How are they different?

There are a few things you can say here. You may notice that both equations contain the same substances (carbon dioxide, glucose, water, sugar, and energy). You may also notice that the reactants of carbon dioxide are the products of photosynthesis (plants make oxygen and glucose); all other organisms then need to convert glucose into a more usable form of chemical energy (ATP) through cellular respiration. Some stages of cellular respiration in animals (Krebs cycle and electron transport chain) require oxygen. You may also talk about both processes being useful for converting energy from one form to another. In photosynthesis, light energy is transformed to chemical energy (in the bonds between glucose molecules). In CR, chemical energy in glucose is transformed into an even more accessible form, ATP.

2. Plants gain mass as they grow, just like you. Why is it incorrect to say that plants get their food from the soil?

Remember that not all plants grow in soil. While the soil may give plants some nutrients (such as nitrogen or phosphorus), we did not discuss that here in class.

You should focus on the photosynthesis reaction:

light energy + CO2 + H2O ( C6H12O6 + O2

The “mass” of a plant comes from the product of photosynthesis (glucose), which can remain glucose or become starch or other complex carbohydrates. That mass needs to come from other matter, so look at the reactants. Notice that glucose is made of carbon, hydrogen, and oxygen atoms. Carbon dioxide contains the carbon and oxygen atoms glucose needs, while water contains the hydrogen. Some of the water that plants absorb remains water (plants need to store water in their vacuoles) as well. Matter cannot be created or destroyed, but it does move around quite a bit (changing molecules).

3. How does energy flow from the beginning of photosynthesis to the end of cellular respiration? What are the different forms of energy involved?

Remember, energy cannot be created or destroyed. That is the law of conservation of energy. Energy can transfer from one place to another, and it can change form (be converted). So at the beginning of photosynthesis, the sun provides a lot of light and heat. This light energy is used to drive the process of photosynthesis. The end product of photosynthesis is a glucose molecule. Some of the light energy is converted to chemical energy when bonds in CO2 and H2O break and then reform glucose (C6H12O6). Finally, glucose is used as a reactant in cellular respiration. It is broken down into simpler molecules in a series of reactions, and the final product is a net gain of 36 ATP molecules from one glucose molecule. This is a form that can be used by all cells very easily.

Overall, you should have something like this:

Light energy ( Chemical energy (glucose) ( More accessible chemical energy (ATP)

4. Earth’s early atmosphere had no oxygen. Use your understanding of plant photosynthesis to explain how photosynthetic organisms made the evolution of organisms that use aerobic cellular respiration possible.

Long ago, there were very simple organisms. Eventually, some of these organisms gained the ability to do photosynthesis, using sulfuric acid (not CO2) and water as reactants. As more and more photosynthetic organisms were born, they made more and more O2 (oxygen gas) as a product of the photosynthesis reaction. This totally changed the chemical makeup of Earth’s atmosphere, which influenced the evolution of other types of organisms. Next, some other simple organisms gained the ability to use the oxygen in the atmosphere and break down glucose molecules to do aerobic cellular respiration. Remember, not all organisms do aerobic CR. Some organisms (like yeast or bacteria) don’t have access to oxygen and can only get energy from glycolysis (which does not require oxygen) or from anaerobic fermentation.

5. Imagine the discovery of a new desert plant that has a unique pigment in its leaves. This pigment strongly absorbs all sunlight from green light (wavelength = 500 nanomenters) to red light (wavelength = 700 nanometers). If you observed this plant in the desert, what color would the leaves appear to be? Why?

Many of you misread this question. It says that this pigment absorbs all pigments from 500 nm (green) to 700 nm (red). You need to read carefully for science questions. This means that the pigment is going to absorb red, orange, yellow, and green light. If colors are not being absorbed, they are being reflected. That means (if we think of a rainbow or ROYGBIV) that the colors that will be reflected are the only ones left (blue, indigo, and violet), or the ones that have the shortest wavelengths. We see the colors that are reflected (not absorbed), so the plant’s leaves would probably be a purplish blue color. If you get stuck on this, I highly recommend you reread the essay on pages 447-449. Pay close attention to Figure 8.35 and the spectrum of light energy.

6. After doing this lab, what questions do you still have about photosynthesis and/or cellular respiration?

Questions will vary, but it is important that you always try to formulate at least one question. If you don’t, that tells me you know EVERYTHING about photosynthesis and cellular respiration, which is very doubtful (no offense).

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