Photosynthesis and Light Energy

Terms:
photoperiod, photosynthesis, autotrophs, Calvin-Benson cycle, C3, C4, and CAM pathways, Rubisco, chlorophyll, stomata, mesophyll and bundle sheath cells, aerobic and anaerobic respiration, Law of the Minimum, turgor pressure, adhesion and cohesion, capillary action, evapotranspiration, water and osmotic potential

adhesion:  Applied to water molecules, they can adhere to most surfaces because they have both positive and negative charges.

aerobic respiration:  The physiological use of chemical energy by using O₂ to synthesize glucose and produce ATP.

anaerobic respiration: The physiological use of chemical energy using ATP to synthesize glucose to produce more ATP, leaving lactic acid or alcohol as a biproduct.

autotrophs: Organisms, largely plants but also some bacteria and fungi, that have the ability to obtain energy via photosynthesis.

bundle sheath cells: Specialized cells in the leaf, located around vascular bundles, where the Calvin-Benson cycle takes place in C4 plants.

C3 pathway: Photosynthetic pathway where a 3-C molecule is passed through the Calvin-Benson cycle to produce a 5-C molecule and glucose. This cycle takes place in the mesophyll cells of the leaf.

C4 pathway: Photosynthetic pathway where CO₂ is initially converted to a 4-C molecule (malic or aspartic acid) in the mesophyll cells, then transported to the bundle sheath cells where it is resynthesized to produce glucose using the C3 pathway

Calvin-Benson cycle:  The chemical cycle of photosynthesis that occurs in the leaf of plants and synthesizes CO₂ to produce glucose.

CAM pathway:  Crassulacean Acid Metabolism, or a photosynthetic pathway similar to the C4 pathway, only the stomates on the leaves are opened only at night to reduce water loss via transpiration.

capillary action:  The process by which water is drawn up a tube through adhesion and cohesion of the molecules.

chlorophyll: A pigment in plants located in chloroplasts that absorbs energy from light.

cohesion: Applied to water molecules, they can attach to each other because each molecule has a positive and negative-charged side.

evapotranspiration:  The movement of water through a plant when the stomates are opened on the leaves causing evaporated water to leave the plant that produces a pressure differential that pulls more water from the roots via capillary action.

glycolysis: the metabolic pathyway to chemically convert glucose to release energy; can be used to form ATP

Law of the Minimum: There is at least one limiting factor (water, temperature, nutrients, gas, or light) that precludes further growth of a plant or animal in a given environment. 

mesophyll: Specialized cells in the leaf, between epidermis layers, that contain chloroplasts to absorb energy from light.

osmotic potential: The movement of water from high to low concentrations across a membrane.

permanent wilting point: point where water potential in soil is too low for a plant to maintain turgor pressure in its cells and wilts.

photoperiod:  Total time each day of sunlight. Varies considerably as you go from the equator to the poles due to orbit and tilt of earth to sun.

photorespiration: respiration in C3 plants where rubisco is drawn away from completing the Calvin-Benson cycle by excess O₂

photosynthesis: The process by which autotrophs convert sunlight to chemical energy using CO₂ and H₂O.

photolysis: splitting of molecules using light energy

rubisco: An enzyme that in photosynthesis allows CO₂ to chemically react with a 5-C sugar (RuBP) to produce two 3-C molecules in the Calvin-Benson cycle.

stomata:  small openings, usually on the underside of leaves, that allow for gas exchange (CO₂, H₂O, and O₂) with the atmosphere.

turgor pressure:  When a plant uses water for structural support by filling its cells to exert pressure on cell walls.

water potential:  The pressure (measured in negative bars) of water movement from the soil into the roots through osmosis, or from the roots to the leaves by evapotranspiration, so that water and dissolved nutrients can enter the plant for photosynthesis.