Photosynthesis
Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy, usually from the sun, into chemical energy stored in glucose. This process occurs primarily in the chloroplasts of plant cells and can be summarized by the following general equation:
\[ 6 \text{CO}_2 + 6 \text{H}_2\text{O} + \text{light energy} \rightarrow \text{C}6\text{H}{12}\text{O}_6 + 6 \text{O}_2 \]
Phases of Photosynthesis:
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Light-dependent Reactions:
- Occur in the thylakoid membranes of chloroplasts.
- Require light to produce ATP and NADPH.
- Water (H₂O) is split, releasing oxygen (O₂) as a byproduct.
-
Calvin Cycle (Light-independent Reactions):
- Occur in the stroma of chloroplasts.
- Use ATP and NADPH from the light-dependent reactions to convert carbon dioxide (CO₂) into glucose (C₆H₁₂O₆).
- Does not directly require light, but is dependent on the products of the light-dependent reactions.
Cellular Respiration
Cellular respiration is the metabolic process by which cells convert glucose and oxygen into energy in the form of ATP, along with carbon dioxide and water as byproducts. The overall equation for cellular respiration is:
\[ \text{C}6\text{H}{12}\text{O}_6 + 6 \text{O}_2 \rightarrow 6 \text{CO}_2 + 6 \text{H}_2\text{O} + \text{ATP} \]
Stages of Cellular Respiration:
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Glycolysis:
- Takes place in the cytoplasm.
- Glucose is broken down into pyruvate, producing a small amount of ATP and NADH.
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Krebs Cycle (Citric Acid Cycle):
- Occurs in the mitochondrial matrix.
- Pyruvate is further broken down, producing ATP, NADH, FADH₂, and releasing CO₂.
-
Electron Transport Chain (ETC):
- Happens in the inner mitochondrial membrane.
- Uses the electrons from NADH and FADH₂ to create a proton gradient that drives the synthesis of a large amount of ATP.
- Oxygen acts as the final electron acceptor, combining with protons to form water.
ATP (Adenosine Triphosphate)
ATP is a nucleotide that serves as the primary energy currency of cells. It consists of three phosphate groups, a ribose sugar, and an adenine base. The energy stored in ATP is released when the terminal phosphate bond is broken, converting ATP into ADP (adenosine diphosphate) and inorganic phosphate (Pi). This release of energy is harnessed by cells to perform various functions, such as:
- Muscle contraction
- Active transport across cell membranes
- Synthesis of macromolecules
- Cellular signaling
In summary, photosynthesis and cellular respiration are interconnected processes: photosynthesis converts light energy into chemical energy stored in glucose, while cellular respiration breaks down glucose to release that stored energy in the form of ATP, sustaining cellular activities.