Reading Essentials for Biology Glencoe (794133), страница 62
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It is similar to primarygrowth in a root. The increase in length is due to the productionof cells by the apical meristem at the tip of the stem. Meristemslocated along the stem, called nodes, are where leaves andbranches develop.________________________LeavesThe primary function of the leaves is photosynthesis. Most leaveshave a relatively large surface area that receives sunlight. Sunlightpasses into the photosynthetic tissues just beneath the leaf surface.The flat, broad, green surface of a leaf is called the leaf blade.Sizes, shapes, and types of leaves vary a great deal.
Some leaves,such as those of the Victoria water lily, can be more than twometers in diameter. Other leaves, such as duckweed, are measuredin millimeters. Some plants produce different forms of leaves onthe same plant.A blade of grass is joined directly to the stem, but in otherleaves, a stalk joins the leaf blade to the stem. The stalk is called apetiole (PE tee ohl) and is actually part of the leaf.
The petiolecontains vascular tissues that stretch out from the stem into theleaf and form veins. You can often see the veins if you look closelyat a leaf. They look like lines or ridges.Leaves vary in shape. A simple leaf is one with a blade that isnot divided.
Maple leaves and tulip poplar leaves are examples ofsimple leaves. When a leaf blade is divided into leaflets it is calleda compound leaf. The leaves of the walnut are an example ofcompound leaves.A The leaves of thewalnut are compoundwith many leaflets.268Chapter 23B The needlelike leaves of theevergreen yew can receivesunlight year round.C The tulip poplar is a deciduoustree with broad, distinctive,simple leaves.READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.________________________NameDateClassSection23.2Roots, Stems, and Leaves, continuedNot all leaves grow on a stem in the same way. When twoleaves grow directly opposite each other on a stem, the arrangement is called opposite.
If the leaves are on opposite sides of thestem, but one is higher than the other, the arrangement is calledalternate. When three or more leaves grow around a stem at thesame position, the arrangement is called whorled.Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.What is the structure of a leaf?Use the illustration at right as youstudy the internal structure of a typicalleaf. Notice the cuticle and the upper andlower epidermis. Between the epidermallayers are two layers of mesophyll.Mesophyll (MEH zuh fihl) is the photosynthetic tissue of a leaf.
It is usually madeup of two types of parenchyma cells—palisade mesophyll and spongy mesophyll.Most photosynthesis takes place in thepalisade mesophyll. These cells receivemaximum exposure to sunlight and havemany chloroplasts. The spongy mesophyllcells are surrounded by many air spacesthat allow carbon dioxide, oxygen, andwater vapor to flow freely. Gases also canmove in and out of the stomata.CuticleUpperepidermisPalisademesophyllVascularbundleXylemPhloemLower epidermisStomataSpongy mesophyllGuard cellWhat is transpiration?The waxy cuticle and stomata help reduce water loss.
Guardcells control the size of a stoma. The loss of water through thestomata is called transpiration. The opening and closing of guardcells regulates transpiration. The proper functioning of guardcells is important because plants lose up to 90 percent of all thewater they transport from the roots by transpiration.3.
What regulatestranspiration?________________________________________________________________________What are some modifications in leaves?The pattern of veins in leaves is one way to distinguish different groups of plants. Veins are vascular tissues that run throughthe mesophyll of a leaf. The patterns can be parallel or netlike asshown on page 270. Parallel veins are found in many monocots.Many dicots have netlike veins.
The leaves of ginkgoes aredichotomously veined.READING ESSENTIALSChapter 23269NameDateClassSection23.2Roots, Stems, and Leaves, continuedLeaf venationParallelMany plants have leaves that have functions besides photosynthesis. Some leaves, when crushed or broken, release substancesthat cause pain or swelling. Animals and humans learn to avoidsuch leaves. Cactus spines are modified leaves that help reducewater loss and provide protection from plant-eaters.Carnivorous plants have leaves with adaptations that can trapinsects or other small animals.
Other leaf modifications includethe curling tendrils in sweet peas, the colorful bracts on poinsettias, and the overlapping scales that enclose and protect buds.Leaves often act as water or food storage sites. The leaves ofAloe vera, for instance, store water. A bulb, on the other hand,provides an example of leaves storing food. A bulb consists of ashortened stem, a flower bud, and thick immature leaves.
Foodis stored in the base of the immature leaves. Onions, tulips, andnarcissus grow from bulbs.◗ After You ReadMini Glossarycortex: layer of ground tissue in the root that isinvolved in the transport of water and dissolved minerals into the vascular tissue ofthe rootpetiole (PE tee ohl): in plants, the stalk that joinsthe leaf blade to the stemendodermis: single layer of cells that forms awaterproof seal around a root’s vascular tissue; controls the flow of water and dissolved minerals into the rootsink: any part of a plant that stores sugars produced during photosynthesismesophyll (MEH zuh fihl): photosynthetic tissueof a leafpericycle: in plants, the layer of cells just withinthe endodermis that gives rise to lateral roots270Chapter 23root cap: tough, protective layer of parenchymacells that covers the tip of a roottranslocation (trans loh KAY shun): movementof sugars in the phloem of a planttranspiration: in plants, the loss of waterthrough stomataREADING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.NetlikeNameDateClassSection23.2Roots, Stems, and Leaves, continued1.
Read the key terms and definitions in the Mini Glossary on page 270. Circle any three of theterms that describe the structure or function of leaves. In the space provided explain in yourown words how those three terms relate to leaves.________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________2. For each plant part listed in the first column, write the name of one related structure in thesecond column and one function in the third column.StructureFunctionRootsStemsCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.LeavesVisit the Glencoe Science Web site at science.glencoe.com to findyour biology book and learn more about roots, stems, and leaves.READING ESSENTIALSChapter 23271NameDateClassSection23.3 Plant ResponsesSC.F.1.4.7 The student knows that organisms respond to internal and external stimuli.◗ Before You ReadPlants respond to light and touch.
Have you ever noticed a houseplant growing toward the light?Have you ever pulled weeds for a long time and noticed that your hands felt itchy or that you developed a mild rash? Use the lines below to write how you think plants respond to light and touch andwhy this happens.____________________________________________________________________________________________________________________________________________________________________________________________________________________________________◗ Read to LearnIdentifyDetails As you read this section, highlight the hormone orgroup of hormones discussedin one color.
Underline theaction of the hormone in adifferent color.APlants, like animals, have hormones that regulate growth anddevelopment. A hormone is a chemical that is produced in one partof an organism and transported to another part, where it causes achange. Only a small amount of the hormone is needed to makethis change. In this section, you will learn about different groupsof hormones and some individual hormones that affect plants.Are auxins responsible for stem growth?The group of plant hormones called auxins (AWK sunz) causecells to lengthen or elongate.
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