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18 Cards in this Set

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Autotroph
Any organism that manufactures its own organic molecules (glucose, amino acids, fats) from inorganic materials (CO2, H2O, mineral salts). Organic molecules contain potential energy in the form of chemical bonds. Some harness the radiant energy of sunlight to form these chemical bonds. This process is called photosynthesis and occurs in algae and multicellular green plants. Other simple autotrophic bacteria use chemosynthesis to obtain energy for the manufacture of organic materials.
Photosynthesis
Used by plants to convert CO2 and water to glucose and oxygen. Glucose can be stored as starch or used as an energy source. In plants, it takes place in a specialized organelle called a chloroplast. Involves the reduction of CO2 to carbohydrate accompanied by release of oxygen from water. The net reaction is the reverse of respiration-reduction occurs instead of oxidation. It can be divided into two distinct reactions, the light reactions and the dark reactions.
Light Reactions
Reactions in photosynthesis that convert solar energy into chemical energy in the form of ATP (by phosphorylation) and NADPH. These reactions must take place in the light and in the chloroplast. These are also called photolysis reactions. They begin with the absorption of a photon of light by a chlorophyll molecule. When light strikes chlorophyll a P700 in photosystem I, it excites electrons to a higher energy level. These high-energy electrons can flow along two pathways giving cyclic electron flow or noncyclic electron flow.
Cyclic Electron Flow
The excited electrons of P700 move along a chain of electron carriers. A series of redox reactions returns the electrons to P700. The reactions are harnessed to produce ATP from ADP and Pi in a process called cyclic photophosphorylation. The coenzyme carrier ferrodoxin (Fd) is one of the early electron carriers in this electron transport chain.
Noncyclic Electron Flow
The key pathway of the light reactions and involves reactions of both photosystems. Photons of light excite the P700 complex in PSI. Instead of returning to P700 along the carrier chain, the high-energy electrons are transferred to the electron acceptor NADP+. NADP+ is very similar to NAD+ which functions in cellular respiration. NADP+ accepts the high-energy electrons and forms NADPH. P700 is left with electron holes and thus is a powerful oxidizing agent. When light strikes P680 in PSII, electrons are excited. These electrons travel down the same electron carrier chain used by cyclic electron flow until they reach P700 and fill the electron holes. This cascade produces ATP by noncyclic photophosphorylation. Now, P680 has electron holes. P680 is a strong enough oxidizing agent to oxidize water and fill its own holes. Water is split into two hydrogen ions and an oxygen atom and the electrons produced reduce P680. Oxygen atoms combine to form O2. The net result is the production of NADPH and ATP, and the ph
Radioactive Isotopes
AKA tagged atoms that determine the nature of photosynthetic reactions. These include oxygen-18 and carbon-14. Using these molecules, it was determined that the O2 produced in photosynthesis comes from the photolysis of water, and not from CO2. The escape of high-energy electrons from chlorophyll molecules is termed photoionization.
Dark Reactions
Reactions that occur in photosynthesis and are coupled with light reactions. They incorporate CO2 into organic molecules in a process called carbon fixation. These reactions are also called reduction synthesis because carbohydrates are produced by reducing CO2. These reactions occur in the chloroplast and use ATP and NADPH produced by the light reactions to reduce CO2 to carbohydrates. They will only occur during the day, when the light reactions are replenishing the supply of ATP and NADPH. CO2 is the source of carbon for carbohydrate production in the Calvin cycle. The product of the cycle is the three-carbon sugar phosphoglyceraldehyde (PGAL). Two molecules of PGAL can be converted to glucose that can then be oxidized to provide usable energy.
The Calvin/Kreb Cycle
1. CO2 is fed into the cycle; in the Krebs cycle it was produced and released; 2. Reducing power is utilized during the cycle (NADPH); in the Krebs cycle NADH was removed; 3. Energy is used in the cycle (conversion of ATP to ADP); in the Krebs cycle, energy was produced when ATP was formed from ADP and Pi.
The Calvin Cycle
CO2 is fixed to RBP (ribulose bisphosphate), a five-carbon sugar. The resulting unstable six-carbon molecule splits to form 2 molecules of PGA (phosphoglyceric acid). PGA is then phosphorylated and reduced (by ATP and NADPH) to form PGAL. Most of the PGAL is recycled to RBP by a complex series of reactions. In six turns of the Calvin Cycle, 12 PGAL are formed from 6 CO2 and 6 RBP. The 12 PGAL recombine to form 6 RBP and 1 molecule of glucose, the net product.
PGAL
Phosphoglyceraldehyde. It is generally considered the prime end-product of photosynthesis and it can be used as an immediate food nutrient, combined, and rearranged to form monosaccharide sugars (e.g. glucose), which can be transported to other cells, or packaged for storage as insoluble polysaccharides such as starch.
Chloroplast Structure
Photosynthesis takes place here. It is a highly organized plastid containing the chlorophyll pigment. It is bounded by two membranes and contains a network of membranes called thylakoid membranes. Chlorophyll resides within the thylakoid membranes. Thylakoid sacs are stacked into columns called grana. The fluid matrix of the chloroplast is called the stroma.
Chlorophyll
A very complex molecule containing over 100 atoms. It is complexed with the metal magnesium. When it absorbs photons of light, electrons in the ground state are boosted to an excited state and can be harnessed to drive the reactions of photosynthesis. It absorbs light in the red and blue wavelengths, giving it a green appearance. The principle types are chlorophyll a and b. These two types are part of two photosystems.
Photosystem
The light capturing unit of the thylakoid membrane. Each one is composed of a number of chlorophyll molecules. In the center is a single chlorophyll molecule coupled to other proteins that are ultimately excited by the absorbed photon. In photosystem I this chlorophyll a molecule is called P700 because it absorbs best at 700nm. In photosystem II, the special chlorophyll a molecule is P680.
The Leaf
Specialized organs that are the principal sites of photosynthesis. They have several adaptations for carrying on photosynthesis: Waxy cuticle: reduces transpiration and conserves water. There are no openings on their upper surface. Palisade layer: A layer of elongated chloroplast-containing cells spread over a large surface area. They are directly under the upper epidermis and are well exposed to light. Spongy layer: The stomatas open into air spaces that contact an internal moist surface of loosely packed spongy layer cells. The moist surface is necessary for diffusion of gases into and out of cells, for both photosynthesis and respiration. The air spaces also increase the surface area available for gas diffusion by the cells. This layer of cells also contains chloroplast. Guard cells: Surround each of the stomata on the lower surface of the leaves.
Stomata
Openings in the lower epidermis of a leaf that permit diffusion of CO2, water vapor, and oxygen between the leaf and the atmosphere. The size of the opening is regulated by guard cells. Guard cells open these openings during the day to admit CO2 for photosynthesis and close them at night to limit loss of water vapor (transpiration). During the day, the guard cells, which contain chloroplasts, produce glucose. The presence of high glucose content in the cells causes them to swell up by osmosis (a condition known as turgor). Since the inner wall of the guard cell is thickened, the swelling produces a curvature of the opening between the guard cells, and the opening increases. At night, photosynthesis ceases, cell turgor decreases, and the openings close. During a drought, the stomata will close even during the daytime to prevent loss of water by transpiration. Photosynthesis will cease because of a lack of CO2.
Vascular Bundles
Veins containing xylem and phloem bring water to the leaf from the roots (xylem) and carry manufactured food out of the leaf (phloem).
The Root
Contains specialized epidermal cells with thin-walled root hairs. They provide an increased surface for absorption of water and minerals by diffusions and active transport.
Chemosynthesis
Some bacteria form carbohydrates using chemical energy rather than by using the radiant energy of the sun. These bacteria oxidize compounds of nitrogen, sulfur, or iron. The small amount of energy released by this oxidation is sufficient for the formation of glucose. The energy produced is sufficient to support the vital functions of these nitrogen, sulfur, and iron bacteria. Nitrifying bacteria oxidize ammonia and nitrites to nitrates. The plants use these nitrates to make proteins. The bacteria use the energy obtained from this oxidation to make glucose.