The first law of thermodynamics states that energy cannot be created or destroyed. The second law of thermodynamics states that energy cannot be converted without the loss of usable energy.
Autotrophs and Heterotrophs
Autotrophs are organisms that make their own food to obtain energy. Chemoautotrophs use inorganic substances as a source of energy, while photoautotrophs convert light energy from the sun into chemical energy. On the other hand, heterotrophs are organisms that need to ingest food to obtain energy.
Metabolism
Metabolism comprises all chemical reactions in an organism. Catabolic pathways release energy by breaking down larger molecules into smaller molecules, while anabolic pathways use energy released by catabolic pathways to build larger molecules from smaller molecules.
Chapter Overview
Photosynthesis
The equation for photosynthesis is 6CO2 + 6H2O -> C6H12O6 + 6O2. This process is anabolic in nature as light energy is converted to chemical energy.
Cellular Respiration
On the other hand, cellular respiration is catabolic, with the equation C6H12O6 + 6O2 -> 6CO2 + 6H2O + energy. Oxygen is used to break down organic molecules, resulting in carbon dioxide and water.
ATP Structure and Function
ATP, or adenosine triphosphate, is the most important biological molecule that provides chemical energy. Its structure comprises a ribose sugar and three phosphates. When one phosphate is removed, it becomes adenosine diphosphate (ADP).
Photosynthesis
Chloroplasts, found in the cells of leaves, capture light energy from the sun. Their structure includes thylakoids, which are saclike membranes arranged in stacks called grana, and the stroma, which is the fluid-filled space outside of the grana.
Pigments, such as chlorophyll and carotenoids, absorb and reflect light, facilitating the light-dependent reactions.
The Calvin Cycle
The Calvin Cycle involves carbon fixation, the joining of carbon dioxide with other organic molecules, and the regeneration of molecules such as G3P. This process combines ATP and NADPH to produce glucose.
Cellular Respiration
The process of cellular respiration begins with glycolysis, the breaking down of glucose in the cytoplasm. This anaerobic process results in a net gain of 2 ATP.
The Krebs cycle, or citric acid cycle, breaks down pyruvate into carbon dioxide in an aerobic process, resulting in a net gain of 6 CO2, 2 ATP, 8 NADH, and 2 FADH.
The Electron Transport Chain (ETC) is the final step in breaking down glucose, producing the most ATP in an aerobic environment.
Fermentation
Fermentation, which occurs in the cytoplasm, regenerates the cell's supply of NAD+ while producing a small amount of ATP. This process is used by animals when the body is not getting enough oxygen to fuel strenuous activity, resulting in either lactic acid fermentation or alcohol fermentation.
In lactic acid fermentation, pyruvate is converted to lactic acid, while in alcohol fermentation, pyruvate is converted to ethyl alcohol and carbon dioxide. These processes serve as alternative energy pathways in the absence of oxygen.
