Photosynthesis and Cellular Respiration

Transcription

1 Photosynthesis and Cellular Respiration Introduction... 2 Photosynthesis and Cellular Respiration are energy conversion processes... 2 Photosynthesis and Cellular Respiration are enzyme pathways... 3 Photosynthesis... 3 TASK 1: LIGHT IS NEEDED FOR PHOTOSYNTHESIS... 3 TASK 2: CHLOROPHYLL IS NEEDED FOR PHOTOSYNTHESIS... 4 Photosynthetic Pigments... 4 TASK 3: PLANTS USE MORE THAN JUST CHLOROPHYLL TO TRAP THE SUNLIGHT... 5 TASK 4: CARBON DIOXIDE IS NEEDED FOR PHOTOSYNTHESIS... 6 Photosynthetic rate and carbon dioxide in Elodea plants... 6 Cellular Respiration... 7 TASK 5: AEROBIC CELLULAR RESPIRATION IN PEAS... 7 TASK 6: FERMENTATION IN YEAST CELLS... 7 TASK 7: PHOTOSYNTHESIS AND CELLULAR RESPIRATION REVIEW... 9 Materials needed to perform this lab General Biology 1 Instructor: Jose Bava, Ph.D

2 Introduction Photosynthesis and Cellular Respiration are energy conversion processes Living things have the ability to obtain energy and manipulate it in order to function properly. Energy is converted from solar (radiant or electromagnetic) energy into chemical energy by means of a process called photosynthesis. Plants, algae, and some bacteria (called cyanobacteria or blue-green algae) convert the solar energy into chemical energy stored in the covalent bonds of glucose by using simple molecules as an input: water (H 2 O)and carbon dioxide (CO 2 ). The process of photosynthesis is described by the following chemical equation, Sunlight + CO 2 + H 2 O Glucose + O 2 Where H 2 O and CO 2 are called reactants because they react and give as a result of many chemical transformations or reactions the final product: glucose. In the same process oxygen is produced as a by product, a good thing for all living things, because most of them need oxygen to stay alive. With the exception of cyanobacteria, photosynthesis takes place in a specific structure or organelle inside the cell: the chloroplast, this factory holds the green chlorophyll and other molecules that catch the sunlight and pass it on to begin with the sequence of reactions involved in photosynthesis. In cyanobacteria, there are no chloroplasts and the chlorophyll is free in the cytoplasm. Photosynthesis has two main stages: the light reactions, where sunlight is needed, O 2 is produced and a lot of ATP molecules are generated; the dark reactions or Calvin cycle is the second stage and the ATP produced in the first stage is used here to convert H 2 O and CO 2 molecules into glucose molecules. Cellular respiration is the name for the process by which all, including those that also make photosynthesis, convert the chemical energy in the covalent bonds of glucose into chemical energy stored in the energy currency of living things: the ATP (Adenosine Triphosphate). Cellular respiration can involve or not the use of oxygen, and based on this two types can be distinguished: aerobic and anaerobic cellular respiration. The first type requires the use of molecular oxygen (O 2 ) and happens inside a specific structure or organelle inside the eukaryotic cells: the mitochondrion. The process of aerobic cellular respiration is described by the following chemical equation, Glucose + O 2 CO 2 + H 2 O + ATP In eukaryotes, there are three stages that happen in three different parts of the cell: Glycolysis is the first stage and happens in the cytoplasm of the cell, is the part where the glucose is used. The second stage is called Krebs cycle and happens in the mitochondrion matrix; here is where the CO 2 is produced. The last stage is called electron transport system and happens in the inner membrane of the mitochondrion, here is where most of the ATP (abut 90%) is produced and where the O 2 is used to form H 2 O molecules at the end of the stage. Bacteria do not have mitochondria, and they rely on a type of cellular respiration that only has, basically, the first stage mentioned before; it is not exactly the same than glycolysis though, and is called fermentation. Bacteria (prokaryotes) produce a few ATP molecules by means of fermentation, which can also be present in some eukaryotes under specific circumstances. General Biology 2 Instructor: Jose Bava, Ph.D

3 Photosynthesis and Cellular Respiration are enzyme pathways Both photosynthesis and cellular respiration do not happen in just one reaction. It is impossible for living things to get the products for every process in only one step. A series of chemical reactions happens instead, and every reaction involves the participation of a specific enzyme that speeds up that reaction. Overall, more than a couple dozens enzymes are need for each process. You may recall from the enzymes lab that enzymes are proteins that speed up reaction millions of times, and they are not actually used in the reaction, a reason why enzymes can be reused millions of times before the get old. The series of chemical reactions that are part of the same process are called enzyme pathways or biochemical pathways. Photosynthesis and cellular respiration are two typical examples of enzyme pathways, where each product resulting from one chemical reaction is the substrate for the enzyme that speeds up the next chemical reaction. Keep in mind that most processes in living things involve enzyme pathways of different length. If an enzyme that participates in a given pathway is missing because of a mutation in the gene coding for that enzyme, then the entire pathway is disrupted! Photosynthesis TASK 1: LIGHT IS NEEDED FOR PHOTOSYNTHESIS By means of this experiment, we will investigate what happens of light is not available for photosynthesis. We know at this point that photosynthesis should not occur after a given period if the plant was not exposed to light energy. In the photosynthesis equation, this can be notice observing what happens when the light reactant is or not present SUNLIGHT + CO 2 + H 2 O > C 6 H 12 O 6 (glucose) + O 2 CHLOROPHYLL, ENZYMES 1) Check the equation for photosynthesis, which product would you most likely test for? Well, even if the equation says plants convert the oxygen and carbon dioxide into glucose, plants do not store energy in the form of glucose in the leaves but in the form of starch, a complex molecule made of many joined glucose molecules. During this experiment, we will determine whether or not light is important for photosynthesis by qualitatively testing the amount of starch rather than glucose. 1. A plant with normal exposure to sunlight has parts of their leaves masked with black paper to prevent light reaching the cells. 2. Get a leaf and make a drawing of it, indicating the part of the leaf that has been covered with the paper mask. 3. Fill about 300ml of a big beaker with water in hot plate and wait until the water boils 4. Remove the paper mask from the leaf Testing a leaf for starch 5. Drop the leaf in the beaker of boiling water. Boil for 5 minutes to break the granules that contain the starch 6. Transfer the leaf to a small beaker containing about 2 cm of isopropyl alcohol. 7. Float the small beaker in the larger beaker containing the boiling water. Leave the leaves in the hot alcohol for 5 minutes to dissolve out most of the chlorophyll 8. Remove the leaf from the small beaker and place it in one lid of a petri dish 9. Flood the leaf with Lugol s iodine solution. The iodine has a light brown color and will turn dark blue/black in the presence of starch. The resulting darkness in the leaves is then proportional to the amount of starch present in them. 2) What are the independent (X) and dependent (Y) variables we used in this experiment? X=... Y=... General Biology 3 Instructor: Jose Bava, Ph.D

4 3) What part of leaf has more starch stored?... 4) What part of the equation does the starch correspond to?... 5) Based on the previous, was this experiment a direct or indirect way to assess photosynthesis? (DIRECT / INDIRECT). 6) What general conclusion for photosynthesis can you make from these results?. TASK 2: CHLOROPHYLL IS NEEDED FOR PHOTOSYNTHESIS Plants have chlorophyll, a molecule that is able to trap the sunlight in order to begin with the process of photosynthesis. Chlorophyll is also responsible for the green color in plants because mainly absorbs the red and blue colors of light but almost completely reflects the green color, the reason why parts of plants having chlorophyll look green. Sometimes, parts of the leaves lack chlorophyll and they appear white or with a different color. We will compare starch concentrations between white and green parts of the leaves as a measure of the amount of photosynthesis that happens in each part. In the photosynthesis equation, this can also be noticed in the light reactant, because the white areas will not be able to trap the sunlight SUNLIGHT + CO 2 + H 2 O > C 6 H 12 O 6 (glucose) + O 2 CHLOROPHYLL, ENZYMES 1. Remove a green and white variegated leaf from the plant A, which has the normal conditions. 2. Test the leaf for starch in the way explained for procedure 1 7) What are the independent (X) and dependent (Y) variables we used in this experiment? X=... Y=... 8) What part of the leaf has more starch stored?.... 9) What part of the equation does the starch correspond to?... 10) What general conclusion for photosynthesis can you make from these results?... Photosynthetic Pigments In the introduction of the previous task we mentioned that chlorophyll traps mostly blue and red light but reflects green. These colors are three of the several colors we can distinguish with our eyes; the full spectrum of light includes many different types of energy that we used in different ways nowadays, check the picture below and you will surely recognize the names of several of them. The comparative size of some familiar things is also provided General Biology 4 Instructor: Jose Bava, Ph.D

5 The part of this spectrum our eyes are able to see is a tiny part as you may realize, and the same happens for plants when it comes to their ability to trap the sunlight and pass it on during photosynthesis. Still, the amount of organic material added by plants every year by means of photosynthesis is a huge number around 160,000,000,000 tons per year! In order to trap sunlight in the visible spectrum more efficiently, plants also have some other pigments apart of the chlorophyll that are able to catch sunlight in a different wavelength, thus maximizing the amount of energy captured for the photosynthesis process. Chloroplasts in plants have different photosynthetic pigments, the green chlorophylls a and b being the most common ones. The photosynthetic efficiency is increased by yellow-orange carotenes and red-brown xanthophylls. These pigments are responsible for the change of color in leaves of many plants during autumn. The following graph shows the approximate absorption (% of light captured) for each type of pigment and the type of light absorbed. As a rule, whatever is not absorbed is reflected, and you can see then that there no pigments that really absorb green light in plants. 11) Consider the graph above, why is better to have more than just chlorophyll for photosynthesis?... TASK 3: PLANTS USE MORE THAN JUST CHLOROPHYLL TO TRAP THE SUNLIGHT General Biology 5 Instructor: Jose Bava, Ph.D

6 The different pigments present in plants constitute different molecules, each one having a different structure and hence a different molecular weight. During this experiment, we will use a technique called paper chromatography that allows separating various pigments in characteristics bands depending on their solubility in a developing solution. The solubility of molecules depends on their molecular size: the heavier the molecule the less it will move up in the paper strip, the lighter the molecule is the greater the distance it will move in the paper. Chlorophylls a and b are heavier than xanthophylls and these are heavier than carotenes, so you should observe three characteristic bands at different distances corresponding to the three types of pigments. 1. Obtain a large test tube and a cork stopper. Add chromatography solvent as to fill the tube no more than 2 cm 2. Get a strip of chromatography paper long enough so the bottom of the strip is immersed just below the solvent line 3. Use a micropipette to spot the chromatography strip with concentrated chlorophyll extract. Spot the paper about 2-3 from the pointed bottom end. Let the spot dry, and spot it again. Repeat until you have a small, concentrated green spot on the paper 4. Attach the chromatography strip to the cork clip leaving the chlorophyll spot as the bottom end and place the paper strip into the test tube. Be sure that the end of the paper is immersed in the solvent but the chlorophyll spot stays above the level of the solvent 5. Place the test tube in a rack, and let the solvent move up the paper until it is a centimeter from the top 6. As the solvent touches the pigment extract, each pigment within the extract moves at a different rate. In the end there should be four spots on the paper, each representing one of the four pigments. (chlorophyll a, chlorophyll b, xanthophylls, and carotenoids). Measure the distances each pigment has moved considering the original green spot as the origin and record your observations in the following table. Pigment Distance traveled (cm) Chlorophyll a Chlorophyll b Xanthophylls Carotenoids 12) Considering the solubility of the different pigments, which pigments may be more similar regarding their structure? TASK 4: CARBON DIOXIDE IS NEEDED FOR PHOTOSYNTHESIS Photosynthetic rate and carbon dioxide in Elodea plants For this experiment, we will use a chemical called Phenol red, which has a red color when the ph is 7 (neutral) or higher (basic), and turns yellow when the ph is less than 7 (acid). When CO 2 dissolves in water, it is converted to carbonic acid, which causes a decrease in the ph. In the photosynthesis equation, this can be noticed observing the carbon dioxide reactant being used by a change in color from yellow to red in the phenol red solution SUNLIGHT + CO 2 + H 2 O > C 6 H 12 O 6 (glucose) + O 2 CHLOROPHYLL, ENZYMES General Biology 6 Instructor: Jose Bava, Ph.D

7 1. Obtain a large test tube and fill 90% of it with phenol red 2. Carefully blow bubbles in the phenol red until it turns yellow 3. Empty half of the phenol red solution into another test tube, and put a healthy sprig of elodea one of the test tubes 4. Place both test tubes in bright light for minutes, occasionally agitating the tubes 13) Did any of the tubes show a color change?. 14) Consider the behavior of the phenol red, check the equation for photosynthesis, and explain the previous answer... Cellular Respiration TASK 5: AEROBIC CELLULAR RESPIRATION IN PEAS Here we will use again Phenol red to investigate the process of aerobic cellular respiration in peas; recall from the exercise above that phenol red has a red color when the ph is 7 (neutral) or higher (basic), and turns yellow when the ph is less than 7 (acid). When CO 2 dissolves in water, it is converted to carbonic acid, which causes a decrease in the ph. Aerobic cellular respiration requires oxygen as the final electron acceptor and the equation that describes the process is below. In the cellular respiration equation, this can be noticed observing the production of the carbon dioxide product by a change in color from red to yellow in the phenol red solution C 6 H 12 O 6 (glucose) + 6O > 6 CO H 2 O + 36 ATP ENZYMES 1. Obtain a small test, fill it with phenol red and carefully place 6 peas into the test tube 2. Allow the peas respire for minutes 15) What color did the phenol red change to? 16) Explain why (hint: check the equation for aerobic cellular respiration above) TASK 6: FERMENTATION IN YEAST CELLS Yeasts are fungi! Believe or not, yeasts are the only unicellular fungi that so far biologists know exist on earth. Fungi are normally multicellular and more closely related to animals than to plants. During this exercise, we will analyze the process of anaerobic cellular respiration in yeast cells in different environments. This process does not require oxygen and is called fermentation. The rate of cellular respiration is proportional to the amount of CO 2 produced, and this can be seen as the yeast rising as a consequence of the carbon dioxide gas being produced. The equation for fermentation is, C 6 H 12 O 6 (glucose) > 2 CO C 2 H 5 OH + 2 ATP ENZYMES General Biology 7 Instructor: Jose Bava, Ph.D

8 In aerobic respiration, glucose is completely broken down to CO 2 + H 2 O but during fermentation, it is only partially broken down. Much of the energy originally available in glucose remains in the products produced. Plant and fungal cells produce alcohol as a result of fermentation and animal cells produce lactic acid. Notice from the above equations that aerobic respiration produces much more ATP per glucose molecule than fermentation 1. Obtain four (4) fermentation tubes and fill each one as indicated in the table below Tube 1: warm yeast solution Tube 2: warm yeast solution + sucrose Tube 3: warm yeast solution + protein Tube 4: refrigerated yeast solution + sucrose 2. Cover the opening of each tube with your thumb and invert it to remove all the air in the upright end of the tube 3. Let the tubes stand for 30 minutes, after which you will measure with a ruler how far the water has been displaced from the upright end of the tube. 17) Record the results in the following table Tube 1: warm yeast solution Tube 2: warm yeast solution + sugar Tube 3: warm yeast solution + protein Tube 4: refrigerated yeast solution + sugar Amount of bubbles produced (mm) 18) Which tube would be used as a control here?. 19) Which tube actually had the greatest gas production?.. 20) Explain why tube two had more gas production than tube 1 (hint: what part of the equation is being helped by the sugar in tube two?)... 21) Explain why the tube three had less cellular respiration than tube one 22) Explain why the tube four had less cellular respiration than tube one 23) Explain why tube two had more gas production than tube three 24) Check the equation for cellular respiration, what is the gas being collected?.. General Biology 8 Instructor: Jose Bava, Ph.D

9 TASK 7: PHOTOSYNTHESIS AND CELLULAR RESPIRATION REVIEW Based on the introduction provided above, complete the following sentences related to both photosynthesis and cellular respiration. 25) In all the equations used in this lab, what is the reason why enzymes and/or chlorophyll are presented in between both sides of the equation under the arrow? 26) O 2 is needed for....., but is produced during.. 27) CO 2 is needed for....., but is produced during.. 28) Sunlight is a type of....energy that is converted into energy by means of photosynthesis. The chemical energy is stored in the.. bonds of the.. molecule 29) Plants, algae, and some bacteria called cyanobacteria are able to trap the sunlight because of what component of photosynthesis?. 30) Plants realize photosynthesis in a specific organelle in the cell called This organelle is also present in ( ALGAE / CYANOBACTERIA / EUKARYOTES / ALL) 31) Photosynthesis has two main stages called... and.. O 2 is produced during..., glucose is produced during. CO 2 is used during. and H 2 O is used during.. 32) Aerobic cellular respiration happens in a specific organelle in the cell called. This organelle is present in.. (PLANTS / ANIMALS / ALL EUKARYOTES / ALL ORGANISMS) 33) The two types of cellular respiration are called and Fermentation is a type of respiration that happens mostly in. and produces.. (THE SAME / MORE / LESS) ATP molecules per molecule of glucose used 34) There are three stages for aerobic cellular respiration, during the glucose is broken down, during.. in the mitochondrion matrix the CO 2 is released, and during the O 2 is used, H 2 O is produced, and most of the ATP is generated General Biology 9 Instructor: Jose Bava, Ph.D

10 Materials needed to perform this lab Elodea sprigs 2 Geranium plants: one exposed to normal light and the other deprived of light for 48 hours Lugol s iodine Isopropyl alcohol Green pigment extract for chromatography Developing solution for chromatography (300 ml) Flood lamps (8) Phenol red indicator Beakers of 250 ml (8) Beakers of 600 ml (8) Chromatography tubes, corks, and paper (8) Hot plates (4) Pincers (8) Fermentation tubes (4) Green peas Warm yeast solution (300 ml) Sucrose solution (100 ml) Albumin solution (100 ml) General Biology 10 Instructor: Jose Bava, Ph.D