How does a tiny seed grow into a massive tree? Photosynthesis Where did all of that mass come from? Visible light is a small band within a very broad electromagnetic spectrum. Chloroplasts capture sunlight energy for photosynthesis. . In the 1600s, a Flemish scientist named • Later experiments carried out by other Jan Van Helmont (1580–1644) scientists showed that plants use carbon conducted an experiment to find out. dioxide (from the air) and water to make a simple carbohydrate (glucose) and oxygen. • He grew a willow tree in a carefully weighed amount of soil. • So the tree’s mass comes from air and water! t ! • He noticed that the mass of the soil barely H i d h h f h il b l changed while the mass of the tree • This chemical reaction (photosynthesis) greatly increased. takes place only in the presence of light. • He concluded that the extra mass came from water, not from the soil. The Sun provides Earth with a steady Visible light is part of a collection of waves source of light. known as the electromagnetic spectrum. 1
Your eyes see sunlight as white light, Light is a wave, like a ripple on a pond. but it is really made up of different colors of light. Waves can be described by their wavelength (the length from peak to peak), and their energy. • A clear prism can split white light into a white light into a rainbow of color Color is how we experience the energy Light waves have very short wavelengths. of light. • They range from 800 nm (red light) to 400 • All of the colors of visible light nm (violet light). have different – One nanometer (nm) is equal to one- energies. billionth of a meter! billionth of a meter! • Red light has the lowest energy and violet light has the highest energy. • As we move through the rainbow from red to violet, the energy of the light increases. A plant cell has chloroplasts that work How is a plant cell similar to solar cells much like solar cells found in calculators. found in calculators? • Chloroplasts also • A solar calculator has convert energy in a solar cells that convert process called process called light energy into li h i photosynthesis. electrical energy. • Plant cells then store • The electrical energy this energy from the powers the calculator. sun in the form of molecules. 2
Photosynthesis is a chemical reaction Photosynthesis that takes place in the chloroplasts of plant cells. During photosynthesis, plants use the energy of sunlight to produce energy-rich molecules of sunlight to produce energy rich molecules called carbohydrates (ex. glucose). In photosynthesis, plants take in carbon dioxide and water and release glucose and oxygen wastes. Why most plants are green? Chlorophyll is found inside the Plants need red and blue light to grow. chloroplasts of plant cells. • Chlorophyll absorbs • Chlorophyll is the main mostly blue and red pigment used in light, and reflects green photosynthesis. light. light. – A pigment is a • This is why most plants molecule that absorbs look green. some colors of light and reflects others. 3
Also, certain colors of visible light have Why don’t plants absorb all colors of just the right amount of energy to make light? photosynthesis occur. • The reason is the same reason you wear light-colored clothes when it’s hot outside. Infrared light has too Ultraviolet light has • Like you, plants must reflect some light to little energy to make more energy but avoid absorbing too much energy and photosynthesis would cause other overheating. occur. chemical reactions. Chlorophyll masks other plant pigments Why do leaves during the spring and summer. change color? • In the autumn In some parts of photosynthesis slows the world, the down down. l leaves of some f • Chlorophyll breaks plants, such as down; and red, orange, sugar maple trees, and yellow pigments in turn brilliant red or the leaves are revealed! gold in the autumn. 4
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