Jackie Mereschuk, age 13, of Sarasota, Fla., for her question:
Why do tomatoes turn red?
Autumn in the temperate zones is a time when the plant world competes with the rainbow. The papery leaves and the fat fruit change from green to riotous colors. Peaches turn yellow and tomatoes turn red when they are ripe, and the reason for these changes is a eomplicated story of chemistry.
A tomato begins life as a shy little flower among the rough, fingery foliage of a tomato plant. The flower is replaced by little green fruit that grows bigger with moisture and sunshine. When it reaches its full size, the growing stops and the shiny skin begins to show tinges of yellow. The yellow deepens with patches of orange and finally changes to tomato red. The lush fruit is now ripe and ready to Eat.
The process of this change is related to the vivid coloring of the autumn woods. It is a chemical affair caused by the pigments that Exist in living plant cells. The most common pigment chemicals of the plant world are chlorophylls that reveal themselves in an assortment of greens, b1ue greens and yellow greens. Anthocyanin pigments reveal themselves as reds, blues and vivid purples.
Along with their chlorophyll, most plants also contain carotene pigments. These pigments color th£ sunflower, the goldenrod, the ripe orange and lemon. Carotenes may also show themselves as vivid red. These golden red chemicals in green leaves and unripe fruit are masked by an abundance of chlorophyll. They begin to show when the chlorophyll departs after its summer stint of making plant food. more
A thriving tomato plant is very green, but contains plenty of hidden carotene pigment. It shows in the small yellow blossoms and finally in the glossy red skin of the ripe tomato. During the growing season, plant food is manufactured by chlorophyll in both the green leaves and the little green fruit. When the fruit is grown, plant sugar is no longer needed. The chlorophyll departs, and the carotene that was there all the time shows up as vividly as a stop sign.
The tomato is now ripe and the plant can do no more for it. The seeds in the fleshy pulp are fully developed. If no one picks it, the ripe fruit finally falls, and maybe some of its seeds will start new tomato plants green plants stuffed with chlorophyll and carotene.
Plant pigments are chemical compounds, someahem very complex. All the chlorophylls contain carbon, hydrogen, nitrogen and magnesium. These molecules are the miraculous food manufacturers for the whole plant. The vivid anthocynnins are compounds of carbon, hydrogen and oxygen, and the colorful carotenes are basic compounds of carbon and hydrogen.