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What is Plant Physiology? - Definition & Experiments

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  • 0:01 What Is Plant Physiology?
  • 0:25 Water Transport
  • 1:28 Nutrient Production &…
  • 2:18 Phototropism & Other Tropisms
  • 4:01 Fruit Ripening
  • 4:44 Lesson Summary
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Lesson Transcript
Instructor: Amanda Robb
Plants are enjoyed by many people - in our homes, on our tables as foods, and in hundreds of products we use every day. In this lesson, we will explore how plant physiology helps us to understand the many functions and behaviors of plants.

What Is Plant Physiology?

Plants have many different uses. But how do plants develop from seeds, and how do they grow? This is where plant physiology comes into play. Plant physiology is the study of how different parts of plants function. It includes many aspects of plant life, including nutrition, movement, and growth.

Water Transport

Water is an essential requirement for plant growth. Plants have a complex xylem system that moves water from the soil all the way up to the leaves, where it is used to make energy. The xylem moves water absorbed in the roots to the top of the plant through a process called transpiration. Water evaporates from the leaves, causing more water to flow upward to fill the gap. Think of it like a blood vessel system for the plant: The leaves act like the heart - a driving force moving water through the plant - and the xylem acts like the blood vessels. Properties of water, like adhesion and cohesion, where water sticks to itself and the xylem walls, helps the water to climb upward as well.

To really investigate the xylem, you can try this cool experiment at home. Mix some blue food coloring with water and place a stalk of celery (with leaves) in the solution. Within half an hour, the blue dye will climb through the xylem with the water and turn the leaves of the celery completely blue! That's the xylem in action.

Nutrient Production and Transportation

Plants also require nutrients to grow and develop, but unlike people, plants produce their own nutrients. All plant cells contain chlorophyll, a chemical which allows plants to harvest energy from the sun and create glucose (or sugar). The process by which plants make glucose is called photosynthesis. Glucose is the same sugar that is in foods like candy or bread. The entire plant needs this sugar, not just the green leaves, so plants have evolved a system called phloem to move the sugar and other nutrients to the entire plant. Phloem is similar to xylem in that it is a network of tubes within the plant designed to transport nutrients, but there is one big difference: Xylem flows in only one direction, like our blood, but phloem is more like our digestive system, distributing nutrients throughout the entire plant.

Phototropism and Other Tropisms

Scientist Charles Darwin and his son were the first to investigate phototropism in plants using the following experiment with grass seedlings. First, they cut off the tips of the shoots, and the plants did not grow towards the light. An opaque cap on the shoot also prevented light-directed growth, but a clear cap did not. In their conclusion, they reasoned that the indicator that causes phototropism was inside the tip of the shoot of the plant and was stimulated by light.

Later, other scientists realized that the trigger for phototropism was a chemical called auxin. Frits Went was the first to discover it in 1926. First, Went cut the tips off of the shoots of several plants. This removed the natural chemical signal for the plant to bend towards light. Then, he tried adding chemicals in the form of agar blocks to the tips of the shoots to make them bend. The chemical that caused them to bend towards light again - auxin - had to be the one produced by the plant!

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