Lesson 8 GRQs PDF

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Photosynthesis Guided Reading Questions (Do these before the Mastering Assignment.) (Reading 7.5-7.10, 37.19 and 38.4) Reading objectives  Describe the two parts of photosynthesis and the inputs and outputs of both parts.  Explain what kind of sunlight is used by the plant and why sunlight is necessary.  Explain photophosphorylation in the light reactions of photosynthesis, and describe how photophosphorylation is similar and different from the oxidative phosphorylation in aerobic respiration.

Before reading 7.5, draw a picture of the chloroplast and its membranes (see figure 7.2). the “anatomy” of the chloroplast is important to the process.

1. Describe in words what happens in the light reaction of photosynthesis: -

Light reaction = photo, Calvin cycle = synthesis The light reaction occurs in thylakoids It is the conversion of light energy to chemical energy Release O2 Water is split  provides source of electrons and gives off O2, light energy is absorbed by the chlorophyll molecules in the thylakoid membranes, light energy is used to drive the transfer of electrons and H+ from water to NADP+  reduced to NADPH, NADPH temporarily stores electrons and provides “reducing power” to the Calvin cycle, generate ATP from substrate level phosphorylation 2. How is the Calvin cycle linked to the light reaction?

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Occurs in the stroma and assembles sugar molecules using CO2 and the energy-rich products of the light reactions

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Carbon fixation  incorporation of carbon from CO2 into organic compounds  carbon compounds are reduced to sugars with electrons from NADPH created in light reactions ATP from light reactions provides chemical energy to power several steps of Calvin Cycle 3. Examine figure 7.5B and describe it aloud. Try to then look away and replicate similar drawing here in pencil. Correct it until you have all the inputs and outputs of both parts.

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Chlorophyll a absorbs blue-violet and red light Chlorophyll b absorbs blue and orange light and broadens the range of light a plant can use by conveying absorbable energy to chlorophyll a which can then use the energy in light reactions Carotenoids absorb yellow and orange light and photoprotection some carotenoids absorb and dissipate excessive light energy that could damage chlorophyll or cell molecules

4. What kind of visible light do plants NOT absorb well? Why do plants have various pigments in the chloroplast? Plants do not absorb green light, which is why plants are green. The other colors are absorbed by the plants, but the green wavelengths are transmitted and reflected by the pigments in the thylakoid membranes. Pigments are light-absorbing molecules which allow the thylakoid membranes to absorb the light necessary for the light reactions of photosynthesis. 5. Describe what light does in a photosystem by writing a detailed legend for fig 7.7B. First, a pigment molecule of a light-harvesting complex absorbs a photon. Then, the lightharvesting complex transfers the energy from molecule to molecule until it reaches the reactioncenter complex. This energy (photon) is used to boost an electron from reaction – center chlorophyll a to its excited state. The electron is immediately captured by the primary electron acceptor, which is reduced. (There are 2 types of photosystems  photosystem 1 and photosystem II, photosystem II functions first) 6. Before looking at the details of electron transport and chemiosmosis of module 7.9, describe Figure 7.8—a mechanical analogy. What is the big picture relative to electrons? The yellow photon “mallet” provides the energy to boost an electron from photosystem II to a higher energy level where it is caught by the primary electron acceptor. The electron is loaded onto an electron transport chain “ramp” that leads it to photosystem I  as the electrons roll 2

down the ramp, they release energy that is used to produce ATP. When an electron reaches photosynthesis I, it is pumped to a higher energy level where it is caught by the primary electron acceptor of photosystem I  these electrons are then used to reduce NAADP+ to NADPH.

Electrons flow from ___water______ ultimately to ____NADP+_________, which is reduced to ______NADPH______. 7. Just like in aerobic respiration the electrons lose small amounts of energy as they “bounce” from one electron carrier to the next. That released energy is used to do what cellular work? This energy is used to pump H+ across a membrane against the concentration gradient. In this case, the H+ is pumped across the thylakoid membrane into the thylakoid space. 8. Similar to mitochondria during aerobic respiration, a H+ gradient is generated across membranes (meaning there are more H+ on one side than the other). In the chloroplast, in what compartment do more H+ build up in? ___________thykaloid space___________. These H+ then flow through what protein? _______ATP synthase_____ as they follow their concentration gradient (from high to low). What product of the light reaction has just been made as a result of the H+ gradient? ATP 9. Electrons in photosystem II would eventually be used up if not replaced. Water plays a role in replacing electrons. How? What part of the water molecule is used in the process and what part diffuses away?

10. Look at your overview fig 7.5B again. Have you learned all the inputs and outputs of the light dependent reaction yet? Be sure to review. Let’s consider the last output: NADPH. After electrons bounce through the electron transfer chain following photosystem II, they have lost considerable energy. They get re-excited at photosystem I and get passed to another electron transfer chain. What is the terminal electron acceptor in this reaction? ______NADP+_____ 3

What is it called once it is reduced? _______NADPH__________. Is it useful to the cell? Why? It is useful to the cell because it is used to provide high-energy electrons to the Calvin cycle for reducing CO2 to sugar.

11. The Calvin cycle takes place where in the chloroplast? _______stroma______What is the chemical formula for glucose? _______C6H12O6______ So, how many carbons are in the molecule? ___6___ Therefore, how many carbon dioxide molecules will be needed from the atmosphere? ___6____

12. Taking carbon from the carbon dioxide in the air (called an inorganic molecule) and attaching the carbon to an organic molecule is called _______carbon fixation________. In the chloroplast, the name of the enzyme that performs this process is called ______rubisco_______

For the purpose of intro biology, we want to take away the major points of the Calvin cycle: How many ATP total are needed to make one glucose? ____9____ How many NADPH are needed to convert total to make one glucose? ____6____ How can the chloroplast get more ATP and NADPH? Can get it from the light reactions Readings: Section 37.19 and 38.4 13. Look at your finger nail. Think about the protein keratin that makes it up. Keratin is an organic molecule consisting of many carbon atoms. Where did those carbon atoms originally come from? CO2 in the atmosphere 14. How does photosynthesis remove carbon dioxide from the air? Carbon in CO2 becomes part of the plant. The cO2 enters a leaf cell and then moves into the chloroplast where it is used in the Calvin cycle. In this cycle, it is broken down and the carbon is incorporated into organic molecules, which are part of the plant. What happens to carbon in the wood of a tree when it is burned? It releases CO2 into the atmosphere List things that increase CO2 in the atmosphere. - Consumers  releasee of CO2 in cellular respiration - Decomposition  through decomposers like fungi and soil microbes - Burning of fossil fuels and wood List things that remove CO2 from the atmosphere.

-Plants, algae, cyanobacteria

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15. What is the global consequence for the atmosphere if CO2 output by respiration exceeds its intake by photosynthesis and absorption into the ocean? The atmosphere will continue to heat up  global warming. The ocean’s chemistry will be affected and absorb more CO2. 16. What happens to the oceans as they absorb more and more CO2? Affects ocean chemistry -CO2 dissolves in water to form carbonic acid -Increased amounts of carbonic acid = decreased ocean pH -Affects organisms who construct shells of exoskeletons from calcium carbonate (CaCO3) -Lower pH = lower concentration of CO3 ions

a)Light energy, b) light reactions c) Calvin cycle, d) ATP is synthesized, e) the electron transport chain, f) NADPH, g) ATP, h) reduced

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