Energy Losses in Producers

Energy enters an ecosystem when producers trap light energy in photosynthesis and convert it into chemical energy in organic molecules such as glucose. Yet only a small percentage, typically around 1 to 3%, of the light energy falling on a plant is converted in this way. The rest is lost at the very first step of the food chain.Reasons why most light energy is not captured:
- Some light misses the leaves altogether and hits the ground or other surfaces.
- Some light is reflected from the leaf surface.
- Some light passes straight through the leaf without hitting a chloroplast; it is transmitted.
- Chlorophyll absorbs mainly red and blue light. Much of the green light is reflected, and other wavelengths cannot be used.
- Photosynthesis may be restricted by a limiting factor such as low carbon dioxide concentration, low temperature or shortage of water, so not all absorbed light can be used.
- Energy is lost as heat during the reactions of photosynthesis, because no energy conversion is 100% efficient.Worked example: 1 000 000 kJ m⁻² year⁻¹ of light falls on a field of wheat, and the crop converts 20 000 kJ m⁻² year⁻¹ into chemical energy.efficiency = 20 000 ÷ 1 000 000 × 100 = 2%Because so little light energy is captured, the amount of energy available to the whole food chain is limited from the start. Farmers can increase the efficiency of crops by reducing limiting factors, for example by irrigating fields or growing crops in glasshouses with extra carbon dioxide and heating.