Chemical Reactions in Nature and Living Systems
Big idea: reactions continually rearrange atoms in air, water, soil and living cells. They are not limited to laboratories.
You will identify reactants and products, interpret evidence and energy transfer, and compare photosynthesis, cellular respiration, rusting and decomposition.
1. Reaction, matter and energy
Reactants are starting substances; products are new substances formed. Atoms are rearranged into new combinations rather than disappearing. Energy can enter, leave or change form. Colour change, gas, precipitate, odour or temperature change may be evidence, but one sign alone is not proof: boiling makes bubbles without producing a new substance.
Plants use light energy to transform carbon dioxide and water into glucose and oxygen. Energy becomes stored in glucose.
Word model: carbon dioxide + water → glucose + oxygen, with light.
Cells transform glucose and oxygen into carbon dioxide and water, releasing usable energy. This controlled chemistry is not a flame inside a cell.
Word model: glucose + oxygen → carbon dioxide + water + usable energy.
Iron reacts gradually with oxygen in the presence of moisture, forming reddish-brown hydrated iron oxides with different properties.
Microorganisms and reactions transform dead organic matter into simpler substances. Atoms return to soil, water and air and can enter new living matter.