{"id":48,"date":"2023-03-29T20:20:01","date_gmt":"2023-03-29T20:20:01","guid":{"rendered":"https:\/\/test-hcc-press-wp-multisite.pantheonsite.io\/bsc2010l\/?post_type=chapter&p=48"},"modified":"2025-10-29T16:37:29","modified_gmt":"2025-10-29T16:37:29","slug":"chapter-7-photosynthesis","status":"publish","type":"chapter","link":"https:\/\/pressbooks.hccfl.edu\/Bio1LabManual\/chapter\/chapter-7-photosynthesis\/","title":{"raw":"Chapter 7 - Photosynthesis","rendered":"Chapter 7 – Photosynthesis"},"content":{"raw":"

Photosynthesis<\/strong><\/h2>\r\n

BACKGROUND<\/strong><\/h3>\r\n[pb_glossary id=\"96\"]Photosynthesis[\/pb_glossary] is the process by which certain organisms convert the sun\u2019s energy into chemical energy to use in the synthesis of glucose for food. Organisms that carry out photosynthesis to make their organic molecules are called autotrophic. Some examples of autotrophic organisms include plants, algae, and blue-green bacteria. In plants, photosynthesis occurs in chloroplasts in stacks of thylakoid membranes containing photosynthetic pigments. The primary photosynthetic pigment that absorbs light in plants is a green pigment called [pb_glossary id=\"146\"]chlorophyll[\/pb_glossary]. Plants have wide varieties of pigments, absorbing different wavelengths of light. Chlorophyll a is the primary plant pigment and makes up about three-fourths of all plant pigments. It absorbs red and blue light. Chlorophyll b is another plant pigment. It absorbs blue-green and orange-red light. [pb_glossary id=\"282\"]Carotenoids[\/pb_glossary] are accessory pigments that absorb blue and blue-green light. These pigments are fat-soluble and usually masked by chlorophyll a.\r\n\r\n[pb_glossary id=\"147\"]Anthocyanin[\/pb_glossary] is another accessory pigment that absorbs bright red colors. There is also chlorophyll c and d that sometimes take the place of chlorophyll b.\r\n\r\nThere are two main parts to photosynthesis: the [pb_glossary id=\"279\"]light-dependent reaction[\/pb_glossary] and the [pb_glossary id=\"277\"]light-independent reaction[\/pb_glossary]. In the light-dependent reaction, pigments such as chlorophyll trap energy from light and use it to split water molecules (photolysis) into hydrogen ions, electrons, and oxygen. The light energy from photons causes electrons in the chlorophyll molecule to move to a higher energy state. This high-energy electron is then transferred to a primary acceptor molecule and passed down a chain of electron acceptors, releasing energy as it does so. The plant uses the released energy to pump hydrogen ions (released from the photolysis process) across the thylakoid membrane, creating an electrical gradient to make ATP. An electron created during photolysis replaces the electron lost from the chlorophyll. Two electrons and hydrogen from the split water molecule are transferred to the final acceptor molecule, reducing NADP+ to NADPH. The oxygen from photolysis is released into the atmosphere. One NADPH and two ATP molecules are produced for every two electrons entering the pathway. The ATP molecules are released into the stroma as protons diffuse down their gradient through the [pb_glossary id=\"261\"]ATP synthase complex[\/pb_glossary].\r\n\r\n[caption id=\"attachment_94\" align=\"aligncenter\" width=\"1893\"]\"Photolysis Reaction for Photolysis[\/caption]\r\n\r\nThe light-independent reaction involves the fixing of carbon dioxide. As a result, glucose and fructose chains are made, and oxygen is released. This oxygen passes through the stomata of the plant. The ATP and NADPH produced by the light-dependent reaction are used to synthesize organic molecules, such as glucose, from carbon dioxide and water. The metabolic pathway called the Calvin cycle first produces ribulose bisphosphate (RuBP). Next, a carbon atom is attached, creating an unstable six-carbon molecule that splits into two phosphoglycerates (PGA). In the next step, phosphate is donated by ATP, and hydrogen plus NADPH donates electrons to form phosphoglyceraldehyde (PGAL). Two combine to create a six-carbon sugar phosphate, while the rest of the PGAL is recycled back to RuBP. This six-carbon sugar phosphate is the building block for glucose, sucrose, fructose, starch, or cellulose. These products are stored in the stroma before being transported to other parts of the plant. Finally, the oxidized ATP and NADPH (now ADP and NADH+) diffuse back into the grana to be used in the light-dependent reaction.<\/span>\r\n\r\n[caption id=\"attachment_92\" align=\"aligncenter\" width=\"1893\"]\"This Light-Independent Reaction[\/caption]\r\n\r\n[caption id=\"attachment_93\" align=\"aligncenter\" width=\"1893\"]\"This Light-Dependent Reaction[\/caption]\r\n\r\nIf the light-dependent reaction fails to produce the hydrogen, electrons, or energy required by the light-independent reaction, the plant will be unable to create its food or any other organic compounds it needs to survive. This experiment will allow you to observe the effect of the intensity of light on the photosynthetic rates of a chloroplast suspension. The process uses a chemical called [pb_glossary id=\"220\"]2, 6-dichlorophenol-indophenol (DPIP)[\/pb_glossary] as a stand-in for NADP+. DPIP is a blue compound capable of being oxidized and reduced. As a result, the DPIP loses color (becomes less blue) as it is reduced. The intensity of the blue color is measured by taking the absorbency using a spectrophotometer. A decrease in absorbance values indicates photosynthesis is taking place, correlating to the reduction of NADP+. <\/span>The photosynthetic rate under different amounts and quality of light will be measured using this method.\r\n

Paper Chromatography and Rf values<\/h3>\r\n[pb_glossary id=\"271\"]Chromatography[\/pb_glossary] is a process used to separate mixtures such as plant pigments. A solution of pigments is applied to the paper strip, adsorbing to the paper fibers. When the paper tip is dipped in a solvent, the solvent moves up through the paper and dissolves the line of pigments. The different pigments have a different solubility in the solvent, so they move up the strip at different rates. Pigments that dissolve easily in the solvent will move further up the strip while the low solubility pigments stay toward the bottom of the strip, thus separating the pigments. Each pigment has a characteristic rate of movement which can be measured by comparing the distance moved by the pigment to the distance moved by the solvent.\r\n\r\nThe Rf value, or retention factor, is a ratio used to describe the distance a component in a mixture travels in relation to the distance the solvent travels. It is calculated by dividing the distance a component travels by the distance the solvent travels. For example, if the component travels 5 cm and the solvent travels 10 cm, the Rf value is 0.5<\/span>\r\n\r\n[caption id=\"attachment_224\" align=\"aligncenter\" width=\"1024\"]\"This Determining Rf Value in Paper Chromatography[\/caption]\r\n\r\nKEY for Rf values for Photosynthesis pigments<\/span>\r\n