Bioenergetics: Energy in Living Systems
Ever wondered how plants create their own food or why you get out of breath during exercise? Photosynthesis is the process where plants convert carbon dioxide and water into glucose using light energy. The equation is: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.
This amazing process happens in chloroplasts, which contain chlorophyll - the green pigment that captures light energy. Photosynthesis is endothermic, meaning it takes in energy from light to work.
Plants don't just make glucose for fun - they use it cleverly! Glucose gets converted into starch for storage, turned into cellulose to strengthen cell walls, or broken down during respiration to release energy. Plants can even make amino acids from glucose (with help from soil nitrates) to build proteins.
Limiting factors control how fast photosynthesis occurs. These include light intensity, CO₂ concentration, temperature, and chlorophyll amount. When one factor is in short supply, it becomes the bottleneck that stops the rate increasing - even if everything else is perfect.
Quick Tip: Remember that when a graph plateaus, the limiting factor has changed from the one you're investigating to something else!
Respiration releases energy from glucose in two ways. Aerobic respiration uses oxygen and happens in mitochondria, producing lots of energy. Anaerobic respiration occurs without oxygen during intense exercise, creating lactic acid in muscles or ethanol in yeast - which is why we can make bread and beer!
When you exercise hard, your body responds brilliantly. Your breathing rate increases to get more oxygen, your heart rate speeds up to pump oxygenated blood faster, and your breath volume increases. After exercise, you need extra oxygen to deal with lactic acid - this is called oxygen debt.
All these chemical reactions together make up your metabolism - the sum of every reaction keeping you alive. From converting glucose to different storage molecules to breaking down proteins into urea, metabolism never stops working.