Only mitochondrion, chloroplast, and cytoplasm needed in drawing (see my drawings below).
Please use the "Talk to Ed and Mike" forum in Moodle if you wish to discuss the assignment further.
See Take-Home Assignment #3 for the original questions.
a. Photosynthesis, Respiration and Plant Growth
This question illustrates the two parts of the energy and matter equation for the plant (energy and matter gain by photosynthesis and energy and matter loss by respiration). This is all part of that energy flow and nutrient cycling deal.
Light energy is taken in by photosynthesis with an increase of biomass as CO2 is fixed (taken up) in the Calvin cycle. Energy is lost as heat from respiration and biomass is reduced as CO2 is released. As long as CO2 uptake by photosynthesis is greater than CO2 loss by respiration, the plant will continue to grow. This is the concept of Net Primary Production - the amount of energy (light) and CO2 that is taken in minus the amount of energy (heat) and CO2 that is given off.
Plants do photosynthesis only when light is available. Plants do respiration ALL the time, light or dark. A plant has to "make hay while the sun shines" because they are loosing matter and energy by respiration all the time.
It is a little more complicated when you consider the concept of biosynthesis. That is just the idea that the simple sugars that plants make by photosynthesis are used as the raw materials in the enzyme reactions that produce more complex compounds like complex carbohydrates (starches and cellulose, etc.), proteins, fats and lipids, and nucleic acids. All these enzyme reactions require energy in the form of the ATP that is produced by the plant's mitochondria in aerobic respiration. All the chemical compounds that are produced by biosynthesis, or anabolism (and that are retained in the plant) make up the biomass of the plant.
In the dark, the plants are using the organic chemicals stored in the seeds as fuel for respiration. The young seedlings still need ATP to stay alive. As a result, they are releasing mass in the form of CO2 and energy in the form of heat. Because there is no light, they are not increasing biomass and energy content by doing photosynthesis, so they loose weight in the form of CO2 released from the plant.
This is how you loose weight too. You will always be loosing CO2, but at different rates, depending on your level of exercise. The more you exercise, the more ATP you need to work your muscles, and the more CO2 your mitochondria release as they make that ATP. The other side of the equation is controlled by your intake of organic molecules. If you eat more carbon than you give off as CO2, you will gain weight.
The plants grown in 24 hour/day light were able to take in more light energy and CO2 than the plants grown in 8 hours light/16 hours dark so they gained the most weight.
b. Energy Flow and Nutrient Cycles
The example in part a. above illustrates both of these concepts. Energy enters the living ecosystem as sunlight, which is converted into chemical bond energy by photosynthesis as plants produce simple organic compounds (sugars) from carbon dioxide. The energy that was once sunlight, exists in the bonds of the complex organic compounds produced by biosynthesis using the simple sugars as the raw material. Plants absorb minerals from the soil and incorporate them into the organic compounds they produce. All this biosynthesis takes energy in the form of ATP, which is produced by respiration in plants (and most other organisms). About 90% of the sugar produced by the plant must be broken down to produce the ATP needed for biosynthesis and other plant life functions. About 90% of the energy originally captured as light by the plant during photosynthesis is lost as heat. 90% if the CO2 taken up by photosynthesis is lost as CO2 produced by respiration.
The energy and matter, including minerals, are passed from one trophic level to the next in organic compounds as one organism eats another. Each organism uses the organic compounds (products of biosynthesis) in its food as the raw materials to produce its own complex organic compounds. This takes energy in the form of ATP which is produced by respiration. In the process, respiration releases energy in the form of heat and mass in the form of CO2.
Each organism releases energy in the form of heat, equal to approximately 90% of the energy it absorbs as sunlight or eats in the form of plants and animals. Each organism looses mass in the form of CO2, equal to approximately 90% of the mass it fixes during photosynthesis or that it eats as a heterotroph.
Only about 10% of the matter and energy acquired by an organism over its lifetime is available to the next trophic level. All the rest has been lost as heat (energy) and CO2 (matter).
The heat energy lost from an organism can never be retrieved by plants. The heat energy eventually is lost to space as the heat radiates out of the atmosphere. Energy in the ecosystem must be continually replenished from the sun. This is why we talk about the flow of energy through an ecosystem. Energy flows into the ecosystem as sunlight and flows out of the ecosystem as heat.
The carbon, oxygen, and minerals that are part of an organism's body can be recycled back to plants. Eventually, everything dies and when a body decays by the digestive action of the decomposing organisms the minerals bound in the organic compounds of the body will eventually be released back into the soil in an inorganic form which plants may absorb again. The CO2 that is produced by the respiration of decomposers is released to the air and can be returned to plants through photosynthesis. The organisms that do this decomposition are actually using the dead bodies as a source of energy and raw materials for their own growth and reproduction. They will temporarily incorporate part of the energy and the raw materials into their own cells. As they live, they release CO2 and heat as do all organisms. When they die something else will "eat" them and eventually the matter is returned to the ecosystem to be taken up by plants again. When we are talking about matter (carbon, hydrogen, oxygen, and minerals) we can talk about cycling.
Drawings required!!
Only mitochondrion,
chloroplast, and cytoplasm needed in drawing (see my drawings below).
Note that I have included only materials that are actual inputs or outputs in each of the five processes below. You might have included specific enzymes (like rubisco or ATPase) or other intermediates (like RuBP or Coenzyme A). That is just fine and not wrong. I left them out because they are integral parts of the cycles or reactions and assumed to be there as participants in the reactions. You should have included at least the items in these lists.
We should also realize that each of the enzyme reactions is not 100% efficient in energy transfer and there is loss of energy (in the form of heat) in all of these reactions. (I did not expect you to include heat in your list of outputs.)
Components listed
in RED font and noted by "$"
indicate
energy content. Follow the flow of energy through Photosynthesis and
Respiration.
Components
listed in GREEN font and
noted by "#" indicate carbon, originally from carbon dioxide.
One might note that any of the
organic molecules involved in the process contain C that was once CO2,
but I am just following the main path of carbon compounds from CO2 up
take in photosynthesis to CO2 release in respiration.
| Light dependent reaction occurs in the thylakoid membrane of the chloroplast
Calvin Cycle
|
 |
Glycolysis
occurs in the cytoplasm
| requires | produces |
| $ # glucose --> $ ATP --> ADP & P --> NAD --> |
$ # pyruvic
acid ADP $ ATP $ NADH |
| Krebs Cycle occurs in the mitochondrial matrix
Electron Transport Chain
|
 |