Chapter 9 Energy in a Cell

9.1 Energy for Organisms All organisms require energy All organisms require energy –The energy source for everything on earth is the sun  Producers obtain energy directly from the sun through photosynthesis  Consumers obtain energy by consuming it from producers, either directly (herbivores) or indirectly (carnivores)

9.1 Energy molecules The primary energy molecule in organisms is ATP, or adenosine triphosphate The primary energy molecule in organisms is ATP, or adenosine triphosphate –ATP is made up of an adenosine molecule with 3 phosphate groups  ADP is similar to ATP, but with only 2 phosphate molecules  As the ATP molecule breaks down, it releases energy (and a phosphate group) to the cell and turns into ADP

9.1 ATP Binds to proteins The energy from ATP is released by binding to an active site on a protein The energy from ATP is released by binding to an active site on a protein –The site on the protein is a specific shape that fits with the ATP molecule –When the energy and phosphate group is released to produce ADP, the shape of ADP no longer fits on the site and is released from the protein, allowing another ATP molecule to bind

9.1 Cell Uses of Energy Cells use energy for a variety of processes, including: Cells use energy for a variety of processes, including: –Metabolism –Making new molecules –Building membranes and organelles –Maintaining homeostasis

9.2 Photosynthesis Photosynthesis is the process that uses the sun’s energy to make simple sugars Photosynthesis is the process that uses the sun’s energy to make simple sugars 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2 –These simple sugars are converted into carbohydrates, which are energy storage molecules –Photosynthesis occurs in 2 stages  The light dependent reactions convert light energy into chemical energy (produce ATP)  The light independent reactions convert the ATP into simple sugars

9.2 Plant Pigments Photosynthesis occurs in the plant organelles called the chloroplasts Photosynthesis occurs in the plant organelles called the chloroplasts –Chloroplasts contain thylakoid disks containing pigments  The specific pigment leading to the green color is chlorophyll, which absorbs every wavelength of light except green –The color change of leaves in the fall occurs because the leaves stop producing chlorophyll and the other pigments become visible

9.2 Light Dependent Reactions The first phase of photosynthesis requires sunlight The first phase of photosynthesis requires sunlight –The sunlight strikes the chlorophyll molecules and release electrons –The electrons go into a series of 2 electron transport chains, releasing small amounts of energy as they travel –The energy released helps to form ATP from ADP –The energy remaining goes into NADP + to form NADPH, which is used in the light independent reactions

9.2 Light Independent Reactions The second phase of photosynthesis does not need light and is commonly referred to as the Calvin Cycle The second phase of photosynthesis does not need light and is commonly referred to as the Calvin Cycle –The Calvin cycle uses carbon dioxide to form sugars –It takes place inside the chloroplasts in a section called the stroma

9.2 The Calvin Cycle

9.3 Cellular Respiration Cellular respiration is the process by which mitochondria break down food molecules to produce ATP Cellular respiration is the process by which mitochondria break down food molecules to produce ATP –It has 3 stages:  Glycolysis  Citric acid cycle  Electron transport chain –Glycolysis is anaerobic (needing no oxygen) –Citric acid cycle and electron transport chain are aerobic (requiring oxygen)

9.3 Glycolysis Glycolysis is a series of chemical reactions in the cytoplasm that break down glucose into pyruvic acid Glycolysis is a series of chemical reactions in the cytoplasm that break down glucose into pyruvic acid –Glucose has 6 carbons and pyruvic acid has 3, so each glucose makes 2 pyruvic acid  Glycolysis requires 2 ATP molecules to start and ends with 4 ATP molecules, so 2 new molecules of ATP are produced  2 molecules of PGAL are also produced

9.3 Citric Acid Cycle In the citric acid cycle, one molecule of ATP and 2 molecules of CO 2 are produced for each molecule of acetyl-CoA broken down In the citric acid cycle, one molecule of ATP and 2 molecules of CO 2 are produced for each molecule of acetyl-CoA broken down –It is also called the Kreb’s Cycle

9.3 Citric Acid Cycle Diagram

9.3 Electron Transport Chain The electron transport chain in cellular respiration is similar to the one in photosynthesis The electron transport chain in cellular respiration is similar to the one in photosynthesis –It passes electrons along using NADH and FADH 2 losing small amounts of energy along the way  The lost energy goes to form ATP or to move hydrogen ions into the mitochondria  At the end of the chain, the remaining energy goes into oxygen and produces 2 molecules of water

9.3 Fermentation There are 2 types of fermentation, both of which occur when there is no oxygen available for ATP production There are 2 types of fermentation, both of which occur when there is no oxygen available for ATP production –Lactic acid fermentation reverses the pyruvic acid production and releases lactic acid which builds up in muscles and causes fatigue –Alcoholic fermentation is used by yeast and some bacterial cells to produce CO 2 and ethyl alcohol.  The CO 2 bubbles are what causes bread to rise and the ethyl alcohol cooks off when it is baked

9.3 Comparing Photosynthesis & Cellular Respiration PhotosynthesisRespiration Food synthesized Food broken down Energy from the sun stored in glucose Energy in glucose released Carbon dioxide taken in Carbon dioxide given off Oxygen given off Oxygen taken in Produces sugars from PGAL Produces CO 2 and H 2 O Requires light Does not require light Occurs only in the presence of chlorophyll Occurs in all living cells