STT1. Explain how the energy we get from food originally came from the sun. STT2. What is the Law of Conservation of Energy?

### STT1: Energy from Food and the Sun The energy we obtain from food ultimately originates from the sun through a process called photosynthesis. Here’s how it works step by step: 1. **Photosynthesis**: Plants, algae, and some bacteria capture sunlight using a pigment called chlorophyll. This process occurs mainly in the leaves of plants. 2. **Conversion of Light Energy**: During photosynthesis, plants convert solar energy into chemical energy. They take in carbon dioxide from the air and water from the soil, and using sunlight, they transform these into glucose (a type of sugar) and oxygen. The overall chemical reaction can be summarized as: \[ 6 \text{CO}_2 + 6 \text{H}_2\text{O} + \text{light energy} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6 \text{O}_2 \] 3. **Energy Storage**: The glucose produced is a form of stored energy. Plants use some of this energy for their own growth and metabolism, but they also serve as a food source for other organisms. 4. **Consumption by Animals and Humans**: When animals (including humans) eat plants or other animals that have consumed plants, they obtain the stored energy in the form of carbohydrates, fats, and proteins. The body then metabolizes these nutrients to release energy for cellular processes. 5. **Energy Transfer**: This process illustrates the flow of energy from the sun to plants and then to animals and humans, demonstrating the interconnectedness of ecosystems. ### STT2: Law of Conservation of Energy The Law of Conservation of Energy states that energy cannot be created or destroyed; it can only be transformed from one form to another. Here are the key points: 1. **Energy Transformation**: Energy can change forms, such as from kinetic energy (energy of motion) to potential energy (stored energy), or from chemical energy (in food) to thermal energy (heat) during metabolism. 2. **Total Energy Remains Constant**: In a closed system, the total amount of energy remains constant over time. For example, when you eat food, the chemical energy in the food is converted into kinetic energy (movement) and thermal energy (heat) in your body, but the total energy before and after the transformation remains the same. 3. **Applications**: This principle is fundamental in physics and helps us understand various processes, including mechanical systems, thermodynamics, and even biological systems like metabolism. In summary, the energy we derive from food is a result of the sun's energy being captured by plants and transformed into chemical energy, while the Law of Conservation of Energy emphasizes that energy can only change forms but cannot be created or destroyed.