Placing celery in colored water demonstrates how water moves through plants. This experiment allows direct observation of internal plant processes, revealing fundamental principles of plant life.
Observing the Changes
When a fresh celery stalk is placed in colored water, changes become visible within hours. The colored water travels upward through the stalk’s veins, which are part of its internal transport system, gradually taking on the color.
Within 2 to 24 hours, the color becomes more pronounced and extends further up the stalk. The leaves at the top of the celery may display the colored water’s hue. Cutting across the stalk reveals distinct colored dots or rings, showing the water’s paths.
The Science of Water Movement
The movement of colored water through celery demonstrates how plants transport water against gravity. This occurs primarily through xylem vessels, tiny, hollow tubes running throughout the plant from roots to leaves. The colored water enters these vessels and is pulled upward.
Capillary action is one mechanism involved in this upward movement. Water molecules are attracted to each other (cohesion) and to the surfaces of the narrow xylem tubes (adhesion). This combined attraction allows water to “climb” up the tubes, like water rising in a thin straw. While capillary action contributes, especially over short distances, it is not strong enough to move water to the top of tall plants.
The primary driving force behind water movement in plants is transpiration. This is the process where water evaporates from tiny pores, called stomata, on the leaves. As water vapor exits the leaves, it creates a negative pressure or “pull” that draws more water up through the xylem from below. This continuous pulling force, combined with the cohesive properties of water molecules that allow them to form an unbroken column, effectively transports water throughout the plant.
How Plants Drink
The principles observed in the celery experiment apply to how all plants absorb and transport water from their environment. Plants absorb water from the soil through their roots, a process largely driven by osmosis, where water moves from an area of higher concentration in the soil into the root cells. Root hairs, which are tiny extensions on the roots, increase the surface area for this absorption.
Once absorbed, water travels through the plant’s vascular system, reaching all parts from roots to leaves. This continuous flow of water is necessary for plant survival and growth. Water transports nutrients from the soil, facilitates photosynthesis (the process by which plants make their own food), and maintains the plant’s rigid structure. Without sufficient water, plants cannot perform these functions, leading to wilting and death.