Leaves Change Color
1 We all enjoy the beautiful show of colors as leaves change each autumn. Did you ever wonder how and why· this happens? To answer that question, we first have to understand what leaves are and what they do.
2 Leaves are nature's food factories. Plants take water from the ground through their roots. They take a gas called carbon dioxide from the air. Plants use sunlight to turn water and carbon dioxide into glucose. Glucose is a kind of sugar. Plants use glucose as food for energy and as a building block for growing. The way plants turn water and carbon dioxide into sugar is called photosynthesis. That means “putting together with light.” A chemical called chlorophyll helps make photosynthesis happen. Chlorophyll is what gives plants their green color.
3 As summer ends and autumn comes, the days get shorter and shorter. This is how the trees "know" to begin getting ready for winter.
4 During winter, there is not enough light or water for photosynthesis. The trees will rest and live off the food they stored during the summer. They begin to shut down their food-making factories. The green chlorophyll disappears from the leaves. As the bright green fades away, we begin to see yellow and orange colors. Small amounts of these colors have been in the leaves all along. We just can't see them in the summer, because they are covered up by the green chlorophyll.
5 The bright reds and purples we see in leaves are made mostly in the fall. In some trees, like maples, glucose is trapped in leaves after photosynthesis stops. Sunlight and the cool nights of autumn turn this glucose into a red color. The brown color of trees like oaks is made from wastes left in the leaves.
6 It is the combination of all these things that make the beautiful colors we enjoy in the fall.
7 During summer days, leaves make more glucose than the plant needs for energy and growth. The excess is turned into starch and stored until needed. As the daylight gets shorter in the autumn, plants begin to shut down their food production.
8 Many changes occur in the leaves of deciduous trees before they finally fall from the branch. The leaf has actually been preparing for autumn since it started to grow in the spring. At· the base of each leaf is a special layer of cells called the "abscission layer" or separation layer. All summer, small tubes which pass through this layer carry water into the leaf, and food back to the tree. In the fall, the cells of the abscission layer begin to swell and form a cork-like material, reducing and finally cutting off flow between leaf and tree. Glucose and waste products are trapped in the leaf. Without fresh water to renew it, chlorophyll begins to disappear.
9 Other colors, which have been there all along then become visible. The orange colors come from carotene ('kar-uh-teen) and the yellows from xanthophyll ('zan-thuh-fil). They are common pigments, also found in flowers, and foods like carrots, bananas and egg yolk. We do not know their exact role in leaves, but scientists think they may be involved somehow in photosynthesis.
10 The bright red and purple colors come from anthocyanin (an-thuh-'si-uh-nuhn) pigments. These are also common in plants; for example, beets, red apples, and purple grapes, and flowers like violets and hyacinths. In the leaves, these pigments are formed in the autumn from trapped glucose. Brown colors come from tannin, a bitter waste product. Different combinations of these pigments give us a wide range of colors each fall.
11 As the bottom cells in the separation layer form a seal between leaf and tree, the cells in the top of the separation layer begin to disintegrate. They form a tear-line, and eventually the leaf is blown away or simply falls from the tree.
abscission layer | noun phrase /æbˈsɪʃən leɪər/ طبقة الإسقاط
A special layer of cells at the base of each leaf that helps it detach in autumn.
Similar words: separation layer, detachment layer, cell layer
anthocyanin | noun /ˌænθoʊˈsaɪənɪn/ الأنثوسيانين
A pigment responsible for red and purple colors in leaves, formed from trapped glucose.
Similar words: plant pigment, red pigment, purple pigment
autumn | noun /ˈɔːtəm/ الخريف
The season when leaves change color and fall, marking the transition from summer to winter.
Similar words: fall, harvest time, leaf-fall, equinox
carotene | noun /ˈkærəˌtin/ الكاروتين
A pigment that gives leaves their orange color, also found in carrots.
Similar words: orange pigment, beta-carotene, colorant
cells | noun /sɛlz/ خلايا
Basic units of life, forming the structure of leaves and involved in the separation process.
Similar words: building blocks, biological units, tissue cells
chlorophyll | noun /ˈklɔrəfɪl/ الكلوروفيل
The green pigment in leaves that helps with photosynthesis by absorbing sunlight.
Similar words: green pigment, leaf pigment, photosynthetic pigment
combination | noun /ˌkɑmbɪˈneɪʃən/ مزيج
The mixture of various pigments that produce the wide range of leaf colors.
Similar words: mixture, blend, compound, fusion
deciduous trees | noun phrase /dɪˈsɪdʒuəs triːz/ الأشجار النفضية
Trees that shed their leaves annually in preparation for winter.
Similar words: leaf-shedding trees, autumn trees, seasonal trees
disintegrate | verb /dɪˈsɪntɪˌgreɪt/ يتفكك
To break into small pieces, referring to the way cells in the separation layer break apart.
Similar words: crumble, decompose, decay, fragment
dissolved | verb /dɪˈzɑlvd/ ذاب
Broken down into smaller parts, often referring to how chlorophyll disappears in autumn.
Similar words: melted, dispersed, vanished, absorbed
excess | adjective /ˈɛksɛs/ فائض
Extra, more than is needed.
Similar words: surplus, additional, extra, overabundance
factories | noun /ˈfæktəriz/ مصانع
Places where things are manufactured or made, used metaphorically for leaves producing energy.
Similar words: plants, workshops, production units
glucose | noun /ˈgluːkoʊs/ الجلوكوز
A type of sugar produced by plants during photosynthesis for energy and growth.
Similar words: sugar, energy, saccharide, carbohydrate
leaves | noun /livz/ أوراق
Plant structures that perform photosynthesis and change color in autumn.
Similar words: foliage, greenery, leaf blades, fronds
maples | noun /ˈmeɪpəlz/ أشجار القيقب
A type of tree that produces red leaves in autumn due to trapped glucose.
Similar words: red-leaved trees, Acer trees, autumn trees
nutrients | noun /ˈnuːtriənts/ مغذيات
Substances that plants take from the soil to help them grow.
Similar words: minerals, nourishment, fertilizers, sustenance
oxygen | noun /ˈɑksɪdʒən/ الأكسجين
A gas released into the air by plants during photosynthesis.
Similar words: air, gas, vital air, life element
photosynthesis | noun /ˌfoʊtoʊˈsɪnθəsɪs/ التركيب الضوئي
The process by which plants use sunlight to convert water and carbon dioxide into glucose.
Similar words: energy production, plant synthesis, plant respiration
pigments | noun /ˈpɪɡmənts/ أصباغ
Natural substances that give color to plant parts like leaves, flowers, or fruit.
Similar words: dyes, colorants, hues, tints
separation layer | noun phrase /ˌsɛpəˈreɪʃən leɪər/ طبقة الفصل
The layer of cells that helps the leaf detach from the tree in autumn.
Similar words: abscission layer, cell layer, detachment layer
starch | noun /stɑrʧ/ النشا
A type of stored energy in plants produced during photosynthesis.
Similar words: carbohydrate, polysaccharide, energy reserve
sunlight | noun /ˈsʌnˌlaɪt/ ضوء الشمس
The light from the sun that is necessary for photosynthesis.
Similar words: daylight, sunshine, solar rays, radiance
tannin | noun /ˈtænɪn/ التانين
A bitter waste product in leaves that gives them a brown color in autumn.
Similar words: plant compound, astringent, plant tannin
xanthophyll | noun /ˈzænθəˌfɪl/ الزانثوفيل
A pigment that gives leaves their yellow color in autumn.
Similar words: yellow pigment, carotenoid, plant pigment