Plant Processes — Reading Comprehension Lesson

Reading Passage

Plant Processes

Plants are the foundation of almost all food chains on Earth because they can make their own food using sunlight — a process called photosynthesis. In photosynthesis, chloroplasts in plant cells capture light energy and use it to convert carbon dioxide from the air and water from the soil into glucose (a sugar) and oxygen. The overall equation is: carbon dioxide + water + light energy → glucose + oxygen. The glucose provides the plant with energy for growth and metabolism, while the oxygen is released as a byproduct — providing the oxygen that animals, including humans, breathe.

Water is essential to all plant processes, and plants have sophisticated systems for moving water from roots to leaves. Water enters the plant through tiny root hairs by osmosis — moving from areas of higher water concentration in the soil to lower concentration inside the root. It then travels upward through the plant in tube-like cells called xylem. This movement is driven largely by transpiration — the evaporation of water vapor through tiny pores called stomata on the surfaces of leaves. On a warm, dry day, a large tree can transpire hundreds of gallons of water. Stomata also regulate the exchange of carbon dioxide and oxygen with the atmosphere.

Plants respond to their environment through growth movements called tropisms. Phototropism is the growth of a plant toward light — driven by the plant hormone auxin, which accumulates on the shaded side of a stem and causes those cells to elongate, bending the plant toward the light. Gravitropism causes roots to grow downward in response to gravity and shoots to grow upward. Thigmotropism is the response to touch — the way a vine winds around a support structure. These responses allow plants to optimize their position for light capture, anchor themselves effectively in soil, and climb toward better-lit environments.

Like animals, plants also carry out cellular respiration — the process of breaking down glucose to release energy. Respiration occurs in plant cells around the clock, while photosynthesis only occurs in the light. During daylight, photosynthesis produces far more oxygen than respiration consumes, so plants are net producers of oxygen. At night, only respiration occurs, and plants take in oxygen and release carbon dioxide. Plants also respond to day length — a phenomenon called photoperiodism — which triggers flowering at the right season. These processes make plants not just passive organisms but highly responsive participants in their ecosystems.

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