Honors Biology: Unit 5 - Photosynthesis Learning Targets
Related State of MI learning standards:
HS-LS1-5 Use a model to illustrate how photosynthesis transforms light energy into stored chemical energy.
HS-LS1-6 Construct and revise an explanation based on evidence for how carbon, hydrogen, and oxygen from sugar molecules may combine with other elements to form amino acids and/or other large carbon-based molecules.
HS-LS2-3 Construct and revise an explanation based on evidence for the cycling of matter and flow of energy in aerobic and anaerobic conditions.
HS-LS2-5 Develop a model to illustrate the role of photosynthesis and cellular respiration in the cycling of carbon among the biosphere, atmosphere, hydrosphere, and geosphere.
Summarize the processes of photosynthesis.
Draw a chloroplast and label the following parts: the inner and outer membrane, stroma, thylakoid, lumen (thylakoid space), granum, thylakoid membrane.
Use the structure of a chloroplast to explain where each stage of photosynthesis occurs.
The first stage of photosynthesis is the light reaction, which occurs in the thylakoid of the chloroplast (they look like pancakes stacked up). The other stage of photosynthesis, the Calvin cycle, occurs in the stroma, or the gray/inner space of the chloroplast.
On your chloroplast drawing, include a second zoomed-in view of the thylakoid membrane. Draw in the necessary photosystems and enzymes of photosynthesis.
Use this diagram to label and summarize ALL the steps of photosynthesis. Include what is needed and what is generated in each stage.
The light reaction occurs when Photosystems I and II, made of chlorophyll and accessory pigments, absorb light energy from the sun. In short, light reactions absorb light energy and convert it into chemical energy, producing oxygen as well; they also must take place during the day because they need the sunlight energy. The light energy is transferred from one molecule/pigment to the next; the final acceptor is chlorophyll a, the reaction center. Chlorophyll a ends up gaining so much energy that some of the electrons jump to the other molecules, creating electron carriers and an Electron Transport Chain across the membrane. Pq, Pc, and Fd shown in the diagram drawn are proteins that help move said electrons across the membrane. Near Photosystem II, there is an enzyme that splits H2O into H+, O2, and e-. Therefore, water is oxidized, as it loses an electron. The lost electrons are added to the Electron Transport Chain, and protons (H+) accumulate in the thylakoid space. Energy is used to move the H+ against the concentration gradient into the thylakoid space. ATP Synthesis then occurs when H+ moves through the ATP synthase, converting ADP + P into ATP in the stroma. The ATP is later used in the Calvin cycle, the other stage of photosynthesis. When the electrons reach Photosystem I, they receive an energy boost from the reaction center, chlorophyll a. This gives the electrons enough energy to reduce NADP+ on the enzyme (NADP+ Reductase); the NADP” combines with H+ to form NADPH. Which provides the protons and electrons needed for the Calvin Cycle. During the Calvin cycle, CO2, ATP, and NADPH (the last two from the light reactions) are needed as the inputs. In short, the Calvin cycle uses the energy of ATP and NADPH to convert carbon dioxide into stable, easily transported sugars that provide energy and carbon skeletons for building new cells. 3 CO2 molecules enter the cycle during the first stage, fixation. An enzyme called Rubisco helps to fixate CO2 into an organic molecule known as PGA; 6 3-PGA molecules form. The second stage of the Calvin cycle is organization. ATP and NADPH from the light reactions help convert the 6 3-PGA molecules into 6 PGAL, the direct product of photosynthesis, by providing the energy and electrons. 6 ATP turned into 6 ADP, which helped convert the 6 3-PGA into 6 BPGA molecules. 6 NADPH, a reducing agent, converted into NADP+, thus helping the 6 PGAL to form. 1 PGAL molecule (also called G3P) is used to make glucose or other organic compounds by leaving the cycle. The remaining 5 PGAL must stay to help reform RUBP, the third stage in the Calvin cycle. 3 ATP turns into 3 ADP, which helps form 3 RuBP, which is recycled.
Describe how energy is transferred and transformed from the Sun to energy-rich molecules during photosynthesis.
Describe the relationship between the various wavelengths of visible light and the different pigments in Photosystems I and II.
There is a relationship between the various wavelengths of visible light and the different pigments in Photosystems I and II. Photosystems I and II are both made of chlorophyll, the pigment that is in charge of capturing light energy, accessory pigments, and absorbing light energy. This is probably because most photosynthesis depends on the chlorophyll, a green pigment found in the thylakoids. The main difference between the two photosystems is that PS I absorbs larger wavelengths of light, while PS II absorbs smaller wavelengths of light. Chlorophylls a & b (there are two types) absorb ROYBIV (not green!) light in the violet/blue & orange/red ranges, but not in the green range because it reflects green wavelengths of light. Meanwhile, accessory pigments absorb other wavelengths and transfer the energy to chlorophyll a; these pigments are seen in the fall as chlorophyll dies off.
Draw a model of the light reaction. Explain what occurs after sunlight hits the surface of a leaf by Illustrating and describing the energy conversions that occur during photosynthesis. Begin with energy from the electromagnetic spectrum and describe all energy conversions. Starting with a water molecule in the thylakoid space, trace the path of 2 e- through the light-dependent and light-independent reactions.
My model of the light reaction can be seen above in the answer to 1c. For the electromagnetic spectrum, the length of the waves determines the light’s color and energy - the shorter the wave, the greater the energy it contains. It basically shows the range of energy for all visible light waves. After sunlight hits the surface of a leaf, the photosystems absorb the light energy, creating the Electron Transport Chain with electrons, ATP is synthesized, which is then used in the Calvin cycle. When the electrons reach photosystem I, they get an energy boost to reduce NADP+ on the enzyme NADP+ Reductase, NADPH is formed and provides the protons and electrons needed for the Calvin cycle. Thus, the light energy has been converted to chemical energy. The Calvin cycle uses the short-lived, unstable, and excited energy from the light reaction to convert carbon dioxide and water into organic compounds like glucose that can be used to fuel the organism. The water molecule in the thylakoid space, near Photosystem II, is split into protons, oxygen, and electrons. As electrons go along the Electron Transport Chain, protons are sent back into the thylakoid; as ATP forms, protons can diffuse back out of the thylakoid. The electrons and protons end up joining with the hydrogen carrier NADP+. NADP+ is reduced into NADPH by the electrons and protons. NADPH and ATP are used in the light-independent reaction (the Calvin cycle) to make sugars from carbon dioxide.
a. Describe how organisms acquire energy directly or indirectly from sunlight. (Autotrophs and heterotrophs).
Autotrophs take energy from nonliving materials and turn inorganic molecules into organic molecules like sugar. There are two types of autotrophs: photoautotrophs get their energy directly from sunlight; some examples include some bacterias, plant, and algae, and chemoautotrophs, which obtain sunlight energy indirectly by oxidizing inorganic substances such as iron, sulfur, or other minerals. This energy is used to form sugars from carbon dioxide. Heterotrophs cannot produce their own food, so they also acquire energy indirectly from sunlight. They take in organic compounds (containing carbon), usually in the form of plants and animals, to get energy for life functions.
Write the equation for photosynthesis, as well as photorespiration in C3, C4, and CAM plants. Be able to describe each in words.
What are the reactants and products of photosynthesis? Be as specific as you can!
The reactants of photosynthesis are carbon dioxide and water. More specifically, there are 6 carbon dioxide molecules and 6 water molecules. The products of photosynthesis include a 3-carbon sugar and oxygen gas. More specifically, there is one 3-carbon sugar molecule and 3 oxygen molecules. The equation for photosynthesis is 3CO2 + 3 H2O → C3H6O3 + 3O2. Light energy and chlorophyll act as the catalysts in photosynthesis. From this equation, you can determine that carbon dioxide has been reduced and water has been oxidized.
Explain photorespiration. Differentiate between C3, C4, and CAM plants and how each manages photorespiration.
Photorespiration occurs when the enzyme RuBisCO oxygenates RuBP, which wastes some of the energy photosynthesis produces. The equation RuBP (5C) + O2 → 1 PGA (3C) + Phosphoglycolate (2C). Usually, when carbon dioxide binds to rubisco and combines with RuBP, two molecules of PGA form. But, if oxygen replaces carbon dioxide in this reaction, then there is only one molecule of PGA produced and another molecule of 2-carbon acid glycolate. The glycolate is transported out of the chloroplast and partially broken down to carbon dioxide, so the organism loses fixed carbon atoms. Photorespiration also enables organisms to recover some carbon in the glycolate, and may help reduce photoinhibition by providing a way for chlorophyll to release the excess light energy that causes it. Overall, the result is that photosynthesis and glucose production slows because some carbon is unused.
Explain how living organisms gain mass through the process of photosynthesis.
What is carbon fixation? When does it occur? What enzyme controls this process?
Carbon fixation is when carbon dioxide is fixed into an organic molecule (PGA). Energy is used to convert carbon dioxide and water into organic compounds that the organism can actually use. It occurs in the light independent reaction of photosynthesis, or the Calvin cycle. The enzyme that controls this process is Rubisco. This process produces 6 molecules of 3-PGA.
How is carbon fixation related to plant growth?
Carbon fixation is related to plant growth because it eventually helps to produce 6 molecules of PGAL, one of which is used to make glucose and other organic compounds that can help the plant grow. The 6 PGA are reduced to PGAL, with the help of an ATP molecule and NADPH (reducing agent). Three turns of the cycle, incorporating one more carbon dioxide molecule with each turn, form 6 molecules of PGAL. One is used to help make fuel for the organism, while the other 5 are needed to regenerate RuBP.
Photosynthesis occurs in plants but is also related to the growth of animals. How?
Photosynthesis occurs in plants, but is also related to the growth of animals. This is because animals need to eat plants in order to survive; their bodies need to get energy from other living things. Photosynthesis also means oxygen is produced for animals to breathe. With this energy from photosynthesis, animals can grow and survive. In conclusion, animals indirectly get energy from photosynthesis.
Describe the various factors that impact the rate of photosynthesis. Explain each of the 5 factors that can impact the rate of photosynthesis, and include a sketched graph for each.
The first factor that can impact the rate of photosynthesis is light intensity. When light intensity is increased, the rate of photosynthesis also increases. At full saturation, photosynthesis is going as fast as possible (shown on the sketched graph). The second factor that can impact the rate of photosynthesis is temperature. When temperature is increased, so is the rate of photosynthesis. However, when the temperature reaches too high, photosynthetic enzymes denature, stomata close to conserve water, oxygen is increased while carbon dioxide is decreased, photorespiration is increased and photosynthesis is decreased. Another factor that can impact the rate of photosynthesis is CO2 concentration. When you increase CO2, the rate of photosynthesis increases. However, after saturation, there’s no effect anymore. O2 concentration also affects the rate of photosynthesis. Increasing oxygen decreases photosynthesis, while increasing photorespiration (O2 starts to replace carbon dioxide and bond with rubisco, causing problems). Other factors that can impact the rate of photosynthesis are humidity & nutrients.
Summarise chemoautotrophs get their energy and matter.
Chemoautotrophs get their energy and matter from the oxidation of inorganic substances, such as iron, sulfur, nitrogen, etc because they are found in the deep earth or deep ocean and grow where sunlight is limited. Chemoautotrophs fix their own carbon dioxide and require less energy than photosynthesis. They cannot compete with complex organisms very well, so they have to grow where other organisms cannot survive, in harsh environments. Chemoautotrophs usually fixate carbon dioxide using the Calvin cycle. The more reduced the electron source is, the more energy is released when it is oxidized. So, the ones who oxidize the most reduced substances such as hydrogen or sulfur are able to produce more energy and grow faster than those with partly oxidized electron donors like ferrous iron and nitrite ions. In fact, many chemoautotrophs can adapt to changing environments by switching electron donors or becoming a heterotroph when food is plentiful.