Biology For Dummies
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Plants have roots that stick down into the earth. The roots pull water, which has nutrients dissolved in it, up from the ground, providing fuel. A few special forces cause the water to move up the stem of the plant through the specialized tissue called the xylem.

Water moves through the plant by one of these mechanisms:

  • Osmosis: Osmosis uses the difference in concentrations of nutrients between the soil and the root to move water (and nutrients) into the plant. More minerals and nutrients are in the center of the root, which is an area called the stele or vascular cylinder (higher concentration), than are in the outside of the root (lower concentration).

    The water and nutrients keep moving toward the center of the root to the xylem, which is a tube that then sends the water and nutrients up the root and into the stem. During osmosis, water moves from an area of lower concentration to the area of higher concentration.

  • Capillary action (adhesion): Once the water and nutrients are inside the xylem, adhesion and cohesion continue to move the water up through the plant. Adhesion occurs when the water molecules cling to the xylem tissue. Adhesion provides the force to pull water up the sides of the tube in the xylem.

  • Cohesion-tension: Cohesion occurs when water molecules stick to each other. Cohesion causes the water in the tube of the root and stem to become one long column of fluid and nutrients. As water evaporates from the plant into the atmosphere (called transpiration in plants but respiration in animals), the column of water continues to move up to fill the space left by the water molecules that were “pulled out” of the leaves upon evaporation.

    This force of water evaporating from the leaves is called bulk flow, and it is ultimately caused by the sun’s energy. Why? Because the sun heats the water inside the leaves, causing the water to evaporate. When the sun heats the water in plant leaves, it not only results in transpiration, but it causes photosynthesis to occur as well.

Photosynthesis is the biochemical process of energy from the sun splitting water molecules inside the plant and combining with carbon dioxide molecules so that a hydrolysis reaction occurs, creating molecules of glucose that the plant can consume as fuel and oxygen that animals can use in their bodies.

The energy from the sun is “turned into” energy inside the plant. Then, the energy in the plant is transferred to the animal that eats it, and so on, and so on.

The equation for photosynthesis looks like this:


The process of photosynthesis is such an important process because it is the basis of all food chains. Without plants undergoing photosynthesis, animals would not be able to harness the energy from the universe or obtain oxygen to breathe.

Plants and animals work together: Decaying animals and feces provide the organic matter in the soil that plants need, and plants provide carbohydrates and oxygen that animals need.

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