Photosynthesis Basics and Limiting Factors
Photosynthesis happens inside chloroplasts and is an endothermic reaction - meaning it takes in energy from the environment (sunlight). The simple equation you need to remember is: carbon dioxide + water → glucose + oxygen.
The rate of photosynthesis depends on three main limiting factors: light intensity, CO₂ concentration, and temperature. Whichever one is in shortest supply becomes the limiting factor - like having the slowest person in a relay race holding everyone back.
During different conditions, different factors limit the process. At night, it's obviously light intensity that's the problem. In winter, temperature becomes the limiting factor. On a warm, bright day, CO₂ concentration might be what's holding things back.
Quick Tip: Remember that chlorophyll can also be a limiting factor if the plant is diseased or lacks nutrients - damaged chloroplasts can't absorb light properly!
Plants don't just make glucose for fun - they use it for respiration, making cellulose for cell walls, creating amino acids (which become proteins), and storing energy as starch or oils. Starch is brilliant for storage because it's insoluble, unlike glucose which would make cells swell up with water.
When you're interpreting photosynthesis graphs, look for the plateau - that flat bit shows you've reached the maximum rate for that limiting factor. Temperature graphs are trickier because the rate increases up to about 45°C, then crashes as enzymes get denatured.
For the practical experiment with pondweed, you're measuring oxygen bubbles in a capillary tube to work out the rate of photosynthesis. Remember to control temperature and time, repeat for reliability, and vary the distance of your light source to test how light intensity affects the rate.