Photosynthesis SAC Help

[MickyMouse!]

Hey guys, I'm new to atar notes but really need some help with the photosynthesis sac which involved the spinach leave disks in the bicarbonate solution. These are some of the questions that I just need you guys to make sure I'm right. If not please correct me .

Background Info. We cut 20 spinach leave disks and placed them all in a bicarbonate solution, then using a syringe, created a vacuum to remove any air present within the leave disks themselves so they would sink. Then we labeled 2 test tubes and and put 10 disks into each test tube with even amounts of the solution. Test Tube A was then placed in a cupboard and test tube B was placed outside in direct sunlight. Every minute we recorded the number of disks that floated to the top in both test tubes. So we are testing the affect of light on the rate of photosynthesis.


1.In considering this experiment, a student in your class suggests that discs made from carrot pieces should have been easier to cut and therefore should have been used in this experiment instead of spinach leaves. Is the student correct in making this assumption? Explain.
---I said that the student is incorrect because the actual carrots that grow underground are not exposed to light and are not photosynthetic because they don't contain any chloroplasts or chlorophyll, hence can not trap sunlight energy to photosynthesize. However the leaves that grow above ground are the site in which photosynthesis takes place, there for using carrots in this experiment would have given us no results. Could someone double check if I'm right on this one.

2. In the experiment, what measures of control were used? what proof do you have that photosynthesis is occurring.
---I know that photosynthesis is occurring if the leaves float to the top because oxygen is being produced, so does that mean the control measure was the exposure to light?

3.The light-dependent phase of photosynthesis produces loaded carrier molecules. Name this "loaded" molecule and outline its role in photosynthesis.

4.The chemical formula for glucose is C6 H12 02. The glucose molecule contains 6 Carbons. Compare the source of this carbon in this experiment with that of the usual environment for the spinach leave.

5.What is the product of photosynthesis that provides energy that enables plants to live for such long periods in winter without sunlight.

6. The product of photosynthesis must undergo a three-stage process for animals to access the energy in the product . Name and describe each stage.


Thanks in advance for those of you who are able to help .

[Irving4Prez]

1. I am not too sure on this but some species of carrots aren't necessarily grown underground completely. As in, their roots would be within the soil and half their body but not the top half of the carrot. Thus it would be remiss to say that "carrots that grow underground are not exposed to light" as you are generalising. You would be better off avoiding that specificity when answering this question. Secondly, you should avoid writing "give us no results" as the phrase is quite bland. Perhaps change it to something among the lines of, "As the leaves of the carrots won't be used during the experiment, the carrot pieces won't have chlorophyll which harness light energy for photosynthesis to occur".The rest of your response seems to be correct though as the carrot themselves don't contain chlorophyll which are light trapping pigments

2. The control in this case was the spinach leave disks within Test Tube A as the cupboard wouldn't have access to light energy. Test Tube B was placed outside in direct sunlight and thus should undergo photosynthesis which was indicated by the oxygen being produced by the disks. Thus, the spinach leave disks would float to the top of test tube B whereas in test tube A, they would have remained situated within the bottom.

3. The loaded molecules are NADP+ and once they 'combine' with Hydrogen, they form NADPH. They basically carry the hydrogen ions from the light dependent stage to the Calvin's cycle in where they unload the hydrogen ions.

5. My immediate answer would be glucose to be stored as starch within the starch storages but that doesn't seem correct as glucose is constantly being utilised by cellular respiration. 

6. Glycolysis: Occurs in the cytoplasm of the cell where 1 glucose molecule is converted to 2 pyruvate molecules. 2 NAD+ are reduced to 2 NADH and a net output of 2 ATP is produced via substrate level phosphorylation.
Krebs Cycle: Occurs in the matrix of the mitochondria. Prior to this stage, a link reaction converts 2 pyruvate molecules into 2 acetyl co enzyme A molecules. In both the link reaction and Krebs cycle, 8 NADH, 2 FADH2 and net output of 2 AT via substrate level phosphorylation are produced.
Electron Transport Chain: Occurs in the cristae of mitochondria and the carrier molecules formed in the 2 prior stages unload the hydrogen ions and their respective electrons. The electrons pass from cytochrome to cytochrome, generating energy for the hydrogen protons to cross into the inter membrane space. Upon coming back down, the hydrogen protons cross through ATP synthase producing 32 ATP. Excess hydrogen protons and electrons combine with oxygen to form water.

[MickyMouse!]

Thanks so much  Irving4Prez. For question 4, I was thinking maybe the answer could be that in the experiment, the source of carbon could be the bicarbonate soda or the carbon produced as a result of cellular respiration, while in the environment of the spinach, the source of carbon is atmospheric Carbon dioxide.  Could someone please see if that makes sense?

[Irving4Prez]

Thanks so much  Irving4Prez. For question 4, I was thinking maybe the answer could be that in the experiment, the source of carbon could be the bicarbonate soda or the carbon produced as a result of cellular respiration, while in the environment of the spinach, the source of carbon is atmospheric Carbon dioxide.  Could someone please see if that makes sense?

When you place a bicarbonate solution within a test tube, due to the pH of water, carbon dioxide will form amongst other products. Essentially, the carbon dioxide formed from the bicarbonate solution and possibly the carbon dioxide formed through cellular respiration will be the source of carbon. In terms of the environment of the spinach, your explanation sounds logical

[Yacoubb]

1) Spinach leaf cells contain many chloroplasts. These chloroplasts contain the green-pigment chlorophyll that captures & converts the radiant energy of sunlight to chemical energy, stored in sugars. Carrot leaves contain chloroplasts that allow the carrot to photosynthesise and obtain its organic food. However, the carrot cells (i.e. discs that would be used) do not contain any chloroplasts and thus do not contain chlorophyll, the pigment that captures and converts the radiant energy of sunlight to chemical energy. Thus, the carrot cells would not enable the experimenter to effectively observe the effects of light on photosynthetic rate.

2) The controlled variables would be water and CO₂ concentration. This is because the pre-treatment for the spinach leafs were the same, and the independent variable was light exposure. The product of photosynthesis is oxygen; the production of this oxygen would cause the leaf discs to float upwards in test tube B. Because the leaves in test tube A were not exposed to light, they could not photosynthesise, and therefore no discs would have risen. This provides proof that photosynthesis has occured.

3) NADPH ~ Nicotinamide Adenine Dinucleotide Phosphate is an acceptor carrier molecule that accepts the H+ ion produced from the photolysis of water. This 'loaded' carrier provides the H+ ion involved in the formation of glucose, and enables the synthesis of this organic compound to take place.

4) The Carbon in the environment of the leaf discs would be as CO₂, a carbon form in its highly-oxidised state. This carbon is however, reduced in the Carbon-reduction stage of the light-independent stage, for a Carbon form useable to create C₆H₁₂O₆, where the carbon is in a less oxidised, more pure form.

5) Glucose - any excess glucose that is produced is stored in long, branched chains as starch, which in turn is stored in starch granules in the cytosol. In periods where photosynthetic rate is low, this glucose can be obtained through hydrolysis of the starch polysaccharide, and then used to produce ATP that is required by these organisms to carry out endergonic requirements of metabolism.

6) The process of aerobic cellular respiration involves:
(a) Glycolysis; occuring in the cytosol of cells, the glucose molecule is converted to a pyruvate molecule, producing 4 ATP molecules; however, there is only a net output of 2 ATP molecules/glucose molecuke.
(b) Kreb's Citric Acid Cycle; occuring in the matrices of the mitochondria, the pyruvate molecules are converted into loaded carriers NADH and FADH₂, and carbon dioxide is produced. 2 ATP molecules/glucose molecule are produced in this stage.
(c) Electron Transport Chain: the cytochromes carry electrons within loaded carriers NADH and FADH2 through the electron transport chain, releasing 32-34 ATP molecules/glucose molecule.

Overall, the energy yield of aerobic cellular respiration is 36-38 ATP molecules/glucose molecule.

I know this was already answered, but perhaps you can take some note of the differences in answers

[LucySanderson6]

Were these questions from the QATs SAC?