Compare and contrast the processes of photosynthesis; aerobic respiration; and the two types of fermentation. Give examples of organisms that make use of each of these processes.
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To compare and contrast the processes of photosynthesis, aerobic respiration, and the two types of fermentation, we need to understand what each process involves and the organisms that utilize them.
1. Photosynthesis:
- Photosynthesis is the process by which green plants, algae, and some bacteria convert sunlight into chemical energy (glucose) and release oxygen.
- It takes place in the chloroplasts of plant cells and involves two main stages: the light-dependent reactions and the light-independent reactions (also known as the Calvin cycle).
- During the light-dependent reactions, sunlight is absorbed by pigment molecules, which excite electrons that initiate a flow of electrons generating ATP (adenosine triphosphate) and NADPH (reduced nicotinamide adenine dinucleotide phosphate).
- The light-independent reactions, or the Calvin cycle, use ATP and NADPH energy to convert carbon dioxide into glucose.
Example organisms that perform photosynthesis: Plants, algae, and some bacteria (such as cyanobacteria), all possess chlorophyll pigments that enable them to carry out photosynthesis.
2. Aerobic Respiration:
- Aerobic respiration is the process by which cells convert glucose and oxygen into carbon dioxide, water, and ATP.
- It occurs in the mitochondria of eukaryotic cells and is the primary source of energy production.
- Aerobic respiration follows three main stages: glycolysis, the citric acid cycle (also known as the Krebs cycle), and the electron transport chain.
- Glycolysis occurs in the cytoplasm, and it breaks glucose down into two molecules of pyruvate and produces a small amount of ATP and NADH.
- The citric acid cycle takes place in the mitochondria and further breaks down pyruvate to generate high-energy electron carriers (NADH and FADH2) and some ATP.
- Finally, the electron transport chain, occurring in the inner mitochondrial membrane, transfers electrons from NADH and FADH2 to generate ATP.
Example organisms that undergo aerobic respiration: Plants, animals, fungi, and most bacteria carry out aerobic respiration to generate ATP for cellular activities.
3. Fermentation:
Fermentation is an anaerobic process that occurs when an organism lacks oxygen or cannot proceed with aerobic respiration. There are two types of fermentation:
- Alcoholic Fermentation:
- Alcoholic fermentation is performed by some yeasts and bacteria.
- It involves the conversion of pyruvate, produced during glycolysis, into ethanol (alcohol) and carbon dioxide.
- This process regenerates NAD+ so that glycolysis can continue, albeit with a limited ATP production.
- Lactic Acid Fermentation:
- Lactic acid fermentation is common in certain bacteria, fungi, and animal muscle cells.
- Pyruvate from glycolysis is converted directly into lactate (lactic acid), which regenerates NAD+.
- This process allows glycolysis to continue, producing limited ATP.
Example organisms that undergo fermentation:
- Alcoholic Fermentation: Yeasts (e.g., Saccharomyces cerevisiae) used in baking and brewing, as well as bacteria (e.g., Zymomonas mobilis) used in alcohol production.
- Lactic Acid Fermentation: Some bacteria (e.g., Lactobacillus) used in yogurt production, and our own muscle cells during intense exercise when oxygen is limited.
In summary, photosynthesis is the process used by plants, algae, and bacteria to convert sunlight into glucose and oxygen, while aerobic respiration is the process in which cells produce ATP using glucose and oxygen. Fermentation occurs when there is no oxygen, with alcoholic fermentation generating ethanol and carbon dioxide, and lactic acid fermentation producing lactic acid.