Reading Essentials for Biology Glencoe (794133), страница 67
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Infer How might a plantbenefit from producingseeds that can remaindormant for long periods?________________________________________________________________________animal’s wastes. Animals that gather nuts such as squirrels andsome birds may drop and lose a few seeds. An animal may buryseeds only to forget where.Plants that grow in or near water, such as coconut palms andwater lilies, produce fruit or seeds that float. Air pockets makethem able to float and drift away from the parent plant. Someseeds stick to animal fur. Orchid seeds are so small that they canbecome airborne.
Poppy fruit forms a seed-filled capsule thatsprinkles its tiny seeds like a salt shaker in the wind. Tumbleweedseeds scatter as the plant is blown along the ground.What is dormancy?The seed coat is hard and dry, so the seed can survive conditions that are unfavorable to the parent plant. Some seeds mustgerminate quickly or they will die. Other seeds can remain in thesoil until conditions are again favorable for plant growth.
Thisperiod of inactivity is called dormancy. The length of time a seedcan remain dormant varies from one species to another. Someseeds, such as willow and maple, can remain dormant for only afew weeks. These seeds cannot survive harsh conditions for longperiods of time. The seeds of desert wildflowers and someconifers can survive dormant periods of 15 to 20 years. Scientistsdiscovered ancient seeds that were more than a thousand yearsold. Imagine their amazement when these seeds began to develop.What is necessary for germination?Dormancy ends when the seed is ready to germinate.Germination is the beginning of the development of the embryointo a new plant.
Dormancy usually ends when water softens theseed coat, oxygen is present, and temperatures are favorable.Water starts the chemical reaction process in the embryo. Thechemical reaction process in living things is called metabolism.Once metabolism has begun, the seed must continue to receivewater or it will die.Many seeds germinate best at temperatures between 25˚C and30˚C. Most seeds won’t germinate if the temperature is below 0˚Cor above 45˚C.Some seeds need specific conditions for germination. The seedsof some conifers and wildflowers, such as lupines and gentians,will not germinate unless they have been exposed to fire. Appleseeds need a period of freezing temperatures.
Coconut seeds haveto soak in salt water. Some seeds germinate better if they passthrough the acid environment in an animal’s digestive system.292Chapter 24READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.24.3NameDateClassSection24.3The Life Cycle of a Flowering Plant, continuedOnce the seed coat has been softened by water, the embryostarts to come out of the seed.
The first part of the embryo toappear is the embryonic root called the radicle (RA dih kul). Theradicle grows down into the soil and develops into a root. Thepart closest to the seed is called the hypocotyl (HI poh kah tul).The part of the plant that first appears above the soil is oftenan arched portion of the hypocotyl. As the hypocotyl grows, itstraightens upward. As it straightens, it brings the cotyledons (if itis a dicot), and the plant’s first leaves with it. In monocots, thecotyledon remains below the soil surface. As the plant grows theleaves turn green, and produce food through photosynthesis.6.
When does photosynthesis begin in a new plant?________________________________________________________________________HypocotylA The radiclewill becomethe primaryroot.RadicleB The hypocotylCotyledonSeed coatis the first partof the stemto appear.Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Primary rootEpicotylWithered cotyledonsHypocotylCotyledonD As new leavesmature, thecotyledonswither andfall away.C As thehypocotylstraightens,the plant’sfirst leavesare exposedto sunlight.READING ESSENTIALSSecondaryrootsChapter 24293NameDateClassSection24.3The Life Cycle of a Flowering Plant, continuedHow do plants reproduce without seeds?7.
Producing a new plantfrom part of anotherplant is called (Circle yourchoice.)a. photoperiodism.b. vegetativereproduction.c. germination.The roots, stems, and leaves of plants are called vegetativestructures. When these structures are used to produce a new plant,it is called vegetative reproduction. Vegetative reproduction iscommon among anthophytes. For example, potatoes are actuallymodified stems called tubers. Each bud or “eye” on a potato canproduce a new plant. Farmers cut potato tubers into pieces andthen plant them.Using vegetative reproduction to grow many plants from oneplant is called vegetative propagation.
Some plants, such as begonias, can be propagated by planting cuttings. Cuttings are piecesof stem or leaf that have been cut off a plant.Plants can be grown from plant tissue. Pieces of plant tissuefrom meristems are placed on nutrients in test tubes or petridishes.
Plants grown from cuttings and tissue culture have thesame genetic makeup as the plants from which they came. Theyare botanical clones.◗ After You Readdormancy: period of inactivity in a mature seedprior to germinationgermination: beginning of the development ofan embryo into a new plantdouble fertilization: anthophyte fertilization inwhich one sperm fertilizes the egg and theother sperm joins with the central cell;results in the formation of a diploid (2n)zygote and a triploid (3n) endospermhypocotyl (HI poh kah tul): portion of the stemnearest the seed in a young plantendosperm: food storage tissue in an anthophyte seed that supports development ofthe growing embryopolar nuclei: two nuclei in the center of the eggsac of a flowering plant that become thetriploid (3n) endosperm when joined with asperm in double fertilizationradicle: embryonic root of an anthophyteembryo; the first part of the young sporophyte to emerge during germination1.
Read the terms and definitions in the Mini Glossary above. Circle two terms that are relatedto each other. On the lines below, tell how these terms are related.________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________294Chapter 24READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Mini GlossaryNameDateClassSection24.3The Life Cycle of a Flowering Plant, continued2.
Place a check mark to indicate whether the organ or structure is involved in the variousactivities. You may place a check mark in more than one column.PollinationFruit Formation Seed Production Seed DispersalOvaryPollen grainNectarEndospermSeed coatFleshy fruitsCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Visit the Glencoe Science Web site at science.glencoe.com to find yourbiology book and learn more about the life cycle of a flowering plant.READING ESSENTIALSChapter 24295NameDateClassSection25.1 Typical Animal CharacteristicsSC.G.1.4.1 The student knows of the great diversity and interdependence of living things.◗ Before You ReadThink about all the animals you are familiar with.
They may be pets, animals in nature, or captiveanimals such as in a circus or zoo. This section explains what all animals have in common. On thelines below, list the characteristics you know about that all animals share.______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________◗ Read to LearnCharacteristics of Animals1. Analyze What is onecharacteristic all animalsshare? (Circle your choice.)a. They are autotrophs.b.
They spend the sameamount of energy toobtain food.c. They are heterotrophs.296Chapter 25How do animals obtain food?One characteristic animals share is that they are heterotrophic.That means that they must consume or eat other organisms to gettheir energy and nutrients.
All animals depend either directly orindirectly on autotrophs for food. Remember autotrophs areorganisms that make their own food.Scientists hypothesize that animals first evolved in water.Although water is denser and contains less oxygen than air, it usually has more food suspended, or floating in it. Some animals thatlive in water, such as barnacles and oysters, do not move fromplace to place. They have adaptations that allow them to capturefood from their environment.
Organisms that permanently attachto a surface are called sessile (SE sul). They do not use muchenergy to obtain their food. Some animals that live in water, suchas corals and sponges, move only during the early stages of theirlives. They hatch from fertilized eggs into free-swimming larvalforms. As adults, most of them are sessile and attach to rocks orother objects.There is very little suspended food in the air.
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