algae

Algae are simple, plant-like living organisms that usually live in water (and sometimes in damp soil) and make their own food using sunlight.

• Key feature: most algae contain chlorophyll, the green pigment that helps them do photosynthesis (using sunlight, water, and carbon dioxide to make food).
• Size and body: algae can be microscopic (single-celled, seen only under a microscope) or larger (like seaweeds). In your chapter context, it mainly refers to tiny algae found in pond water or soil.
• Where they live: common in ponds, lakes, rivers, and on wet surfaces. In soil, they may form a thin green layer on damp ground.
• Why they matter: algae are important producers—they form the base of many food chains in water and also release oxygen during photosynthesis.
• Everyday example: the green, slippery layer on the side of a pond or on a water tank is often due to algae growing where there is sunlight + water.
• Helpful nuance: algae are not “dirty” by themselves—small amounts are normal in nature, but when they grow too fast (an algal bloom), they can reduce oxygen in water and harm aquatic life.