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22 Cards in this Set
- Front
- Back
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What are organisms called when they can create sugars from light energy?
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Autotrophic.
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Generally speaking, what is used to create sugars during photosynthesis? In a metabolic sense, is photosynthesis a catabolic or anabolic reaction?
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Light, water, and carbon dioxide are used to create sugars. Therefore, photosynthesis is an anabolic reaction.
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Give a general overview (i.e. the chemical formula) of photosynthesis. Compare the photosynthetic reaction with that of cellular respiration. How are they similar and different? What byproduct of photosynthesis is essential aerobic life?
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cellular respiration: sugar + oxygen → carbon dioxide + water + energy to do cellular work
photosynthesis: light energy + carbon dioxide + water → oxygen + sugar One is catabolic (cell resp.) and the other is anabolic (photosyn.). The products of one are the reactants of the other. Oxygen is essential for aerobic life. |
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Do photosynthetic organisms have chloroplasts and mitochondria, or just chloroplasts? Why? Do all parts of a plant photosynthesize? Why or why not?
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Photosynthetic organisms have mitochondria and chloroplasts so that they are able to carry out both photosynthesis and cellular respiration. Many plants have cells, tissues, and organs that do not photosynthesize. For example, most roots have no photosynthetic capacity. Typically, sugars are produced in the photosynthetic tissues and transported to other areas of the plant for immediate nutrition and for storage.
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What is light? What special and unusual properties does light energy have?
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Light is the portion of the electromagnetic spectrum that has wavelengths detectable by the human eye. These are wavelengths of about 400-700nm. Light has both wave and particle characteristics.
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Where does visible light fall on the electromagnetic spectrum? Draw the spectrum and label the different areas including wavelengths.
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Visible light has wavelengths of about 400-700nm
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Describe the wave-like and the particulate nature of visible light.
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Light is similar to x-rays, microwaves, and radio waves because they all have a periodic fluctuating character that travels through space (i.e., a wave). They differ because of their wavelength (i.e., the peak-to-peak distance between oscillations). Importantly, electromagnetic waves can transfer energy to objects in their paths.
Light can also act as a particle that bumps into things as it travels. Light travels as "packets" or quanta of energy known as photons. Each photon has a specific amount of energy. |
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What is meant by reflection and absorption? How do these relate to the colors we observe?
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Reflection describes a situation in which photons bounce off an object. Absorption refers to a situation in which the pigments within an object cause photons to be absorbed into the object. The colors we see are the wavelengths of light that are reflected off of an object. The wavelengths of light that are absorbed into an object are not perceived by our eyes. If all visible wavelengths of light are absorbed, our eyes perceive a “black” color.
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What is a pigment? List some common pigments and the colors they absorb and reflect. What color do they appear to be? Explain why leaves and plants appear green.
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Pigments are compounds that absorb light. Different pigments absorb different wavelengths of light. If a structure (e.g., a leaf) lacks pigments that absorb light in a given wavelength range, then that wavelength of light will be reflected. Chlorophyll is a pigment that absorbs green light badly, so it is reflected to our eyes.
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Describe why leaves change colors in the fall.
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The color of fall leaves come from pigments other than chlorophyll (e.g., carotenoids). These pigments exist in the leaf all summer, but it is not until the pigment chlorophyll is depleted that the other colors become obvious.
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Draw a chloroplast and label the different important structures.
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Draw a chloroplast and label the different important structures.
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What is a photosystem? What does it have to do with photosynthesis?
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A photosystem is the light-harvesting unit in photosynthesis, located on the thylakoid membrane of the chloroplast. In a photosystem, a photon strikes a pigment molecule, and the energy is passed from pigment molecule to pigment molecule until it reaches the reaction center at the center of the photosystem.
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Why is it useful to the photosynthetic organism to have different kinds of pigments in its photosystems?
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Different kinds of pigments each absorb light of a different wavelength, and they send this energy to the chlorophyll molecule at the center of the photosystem (i.e., the reaction center). The chlorophyll molecules of photosystem I and photosystem II are different, and thus are able to exploit many different kinds of wavelengths of light for maximum efficiency.
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Describe how the state of a pigment’s electrons is different in the presence and absence of light
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In a non-illuminated pigment (i.e., one in the dark), critical electrons are usually found in a low-energy state. However, the energy from an incoming photon can bump the electron into a higher energy state. If a photon of light resonates with a particular pigment, it has enough energy to raise a particular electron in the pigment to the next state. When this happens, light has been absorbed and energy has been transferred.
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Explain how a chloroplast makes use of photons of energy. Describe the electron transport chain and how an electron would travel through the two photosystems of the chloroplast. Differentiate between photosystem I and II.
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Light is absorbed by pigments and its energy is channeled to chlorophyll, where it excites an electron. This is photosystem II. The electron is transferred to the primary electron acceptor. From there it rolls downhill, energetically speaking. It loses some energy as it is passed from molecule to molecule through the first electron transport chain. The electron ends up at a second type of chlorophyll molecule in photosystem I. Light is absorbed again and the electron is once again excited and transferred along the chain.
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To what does the term “Z-scheme” refer?
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When diagrammed, the two electron transport chains in photosystems I and II have a “Z” shape, on its side. The electron gets excited, comes back down in energy, gets excited again, and comes back down again.
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What is the source of electrons in the electron transport chain of photosynthesis? What is created as “waste” products in the ETC? What useful functions do these “waste” products have?
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Water is the source of electrons in photosynthesis. Protons and oxygen are released as a byproduct of photosynthesis. Free energy is used to create a proton gradient with the generated hydrogen ions. This stores energy in the form of voltage. Oxygen is used in cellular respiration in many types of organisms.
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Where does the ETC of cellular respiration occur in a cell? Where does the ETC of photosynthesis occur?
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The electron transport chain of respiration occurs in the mitochondria, whereas the electron transport chains of photosynthesis are located in the chloroplasts. The thylakoid membrane is home to the many proteins involved.
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What are the two main uses of the free energy generated through the ETC of photosynthesis?
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First, hydrogen ions (protons) are moved across the membrane. The protons are moved into the thylakoid space where they accumulate; energy is required because these protons are being moved against a concentration gradient (in other words, this is not passive diffusion). The second use of free energy is reduction of an ultimate electron acceptor. At the end of the first electron transport chain, the electron is transferred to another molecule of chlorophyll. At the end of the second electron transport chain, the final acceptor of the electron is NADP+, which is reduced to NADPH.
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What accepts the electron at the end of the photosynthesis ETC? What is this electron acceptor reduced to?
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The final acceptor of the electron is NADP+, which is reduced to NADPH.
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Exactly where within the chloroplast does a proton gradient accumulate? How is the proton gradient maintained?
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The accumulation of protons occurs across the thylakoid membrane and into the thylakoid space. (The thylakoid space has a higher concentration of protons than the surrounding areas on the other side of the thylakoid membrane.) The thylakoid membrane prevents protons from moving back across to the other side.
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Compare ATP synthesis in photosynthesis with ATP synthesis in cellular respiration. What is ATP synthesis in photosynthesis called?
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The charge separation across the thylakoid membrane represents stored energy in the form of a voltage (similar to what happens within mitochondria during cellular respiration). Like mitochondria, chloroplasts also make use of the voltage via ATP synthase proteins in the membrane. These are similar to the ATP synthase molecules associated with cellular respiration. In a process called photophosphorylation, they harness the energy from protons moving across the membrane to make ATP from ADP and phosphate
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