3FlowersMost people appreciate flowers for their appearance or their fragrance.Why do plants have flowers? Think about it!Flowers are the reproductive organs of certain plants. They are specialized to carry out sexual reproduction and to begin the development of fruit and seeds.Let’s look closely at the structure of a typical flower.
4Flower StructureThe receptacle is the structure at the tip of the twig. All the flower parts are attached to the receptacle.The most visible parts of many flowers are the petals.All the petals together form the corolla of the flower.The petals usually are scented and brightly colored. This helps attract insects and animals, such as butterflies, bees and birds.
5Flower StructureThe centrally located pistil is the female organ of the flower.The pistil consists of the following parts:Stigma – The sticky top.Style – The slender stalk that supports the stigma.Ovary – The swollen base that contains the ovules (immature seeds).
6Flower Structure Each stamen consists of the following parts: Anther – The sac-like structure at the top of the stamen that produces and stores pollen.Filament – The slender stalk that supports the anther.Sepals are the outermost circle of leaves that serve to protect the other parts of the flower while it is still a bud.All the sepals together form the calyx of the flower.Sepals are usually green in color, but they may be the same color as the petals.
7Information A complete flower contains these parts: PistilStamensCorolla (petals)Calyx (sepals)A flower that lacks any of these parts is an incomplete flower.An incomplete flower that lacks a pistil is a staminate (male) flower.An incomplete flower that lacks stamens is a pistillate (female) flower.
8ReviewIn addition to a receptacle, complete flowers have these structures:Pistil (female organ)Stamens (male organs)Corolla (petals)Calyx (sepals)An incomplete flower lacks one of the listed structures.Staminate (male) flowers are incomplete because they lack pistils.Pistillate (female) flowers are incomplete because they lack stamens.
9Select The Best Matching Choice: Staminate:Answer Column:A female flower organLacking pistilsFlower petalsLacking stamensA male flower organFlower sepalsLacking a receptacleLacking sepalsCorrect Answer: BPistillate:Correct Answer: DStamen:Correct Answer: EPistil:Correct Answer: ACalyx:Correct Answer: FCorolla:Correct Answer: C
10Gametophytes and Pollination Section TwoGametophytes and Pollination
11InformationFlowering plants reproduce sexually through the union of male and female gametophytes (gametes) during fertilization.The male gametophyte is in the pollen (located in the anther).The female gametophyte is the ovule (located in the ovary).Pollination includes the transfer of pollen from an anther to a stigma. Before fertilization can take place in the ovary, pollination must occur.
12Anthers The anther produces pollen. The anther is located in an exposed position, making it easy for the wind or visiting animals to disperse the pollen.
13Flowering Plant Gametophytes Each anther has four pollen chambers, or sacs.Within the pollen sac, diploid cells develop (change) into pollen grains.A diploid cell contains 2N chromosomes (N pairs). The value of N is different for almost every species.Each diploid cell divides twice by meiosis, forming four haploid microspores.
14Flowering Plant Gametophytes Haploid microspores contain half the chromosomes that the diploid cell contained.Therefore, each microspore has 1N chromosomes.Meiosis produces cells that each have a haploid (N) number of chromosomes.Each microspore becomes a pollen grain.
15Flowering Plant Gametophytes A thick cell wall forms. This protects the grain and prevents it from drying out.The nucleus divides by mitosis, producing two nuclei within each pollen grain.One nucleus in the pollen grain is the tube nucleus.The other nucleus is the generative nucleus.Each pollen nucleus has 1N chromosomes. Mitosis produces two haploid (N) nuclei from the original haploid nucleus.
16Flowering Plant Gametophytes When the pollen sac matures and splits open, it releases thousands of pollen grains.After being released from the anther, pollen is carried by the wind or animals and can find its way to the sticky stigma of the same or another flower.
17Flowering Plant Gametophytes The ovary produces ovules.There can be several ovules within an ovary.Each ovule is attached to the wall of the ovary by a short stalk.Meiosis occurs twice in each ovule, forming four haploid cells, three of which disintegrate.The haploid cell in the ovule has 1N chromosomes. Haploid cells contain half the number of chromosomes found in diploid cells.
18Flowering Plant Gametophytes The remaining haploid cell divides several times by mitosis to produce the embryo sac (female gametophyte).The embryo sac contains seven cells, one much larger than the others, and two polar nuclei.The polar nuclei can be fertilized by the pollen to form the endosperm (food) in the seed.One of the smaller cells is the egg cell, which can be fertilized by the pollen to form a zygote.Each nucleus in the embryo sac has 1N chromosomes. Mitosis preserves the chromosome number in each haploid nucleus.
19PollinationPollination is the transfer of pollen from an anther to a stigma.Self-pollination is the transfer of pollen from the anther to the stigma of the same flower or to the stigma of another flower on the same plant. Self-pollination requires both male (stamen) and female (pistil) parts on the same plant.Only complete flowers, having both stamens and a pistil, can pollinate themselves.Incomplete flowers on the same plant can pollinate each other only if one flower is pistillate and the other is staminate.Cross-pollination is the transfer of pollen from an anther on one plant to a stigma on another plant of the same species.
20InformationMany plants can fertilize themselves through self-pollination, but this is not an effective means of reshuffling genes within a species and increasing variety.Cross-pollination is most effective in creating new combinations of genes within plants.Cross-pollination is the transfer of pollen from an another to a stigma on another plant.
21ReviewThe anthers of flowering plants produce male gametophytes called pollen.Each pollen grain contains one tube nucleus and one generative nucleus. Both nuclei are haploid.The ovary produces female gametophytes called embryo sacs.An embryo sac contains seven cells (including one egg cell) and eight haploid nuclei.Pollination is the transfer of pollen from an anther to a stigma and is an essential step in sexual reproduction among flowering plants.
22Select The Letter Of The Correct Answer From The List Below: A. diploid D. pollinationB. haploid E. ovaryC. seven F. pollenThe male gametophyte, ____________________, is formed in the anther.The __________________ produces the female embryo sac.Mature pollen and mature egg cells contain _________________ nuclei.An essential step in sexual reproduction in flowering plants is ________________.
23Answers: pollen ovary haploid pollination The male gametophyte, ____________________, is formed in the anther.The __________________ produces the female embryo sac.Mature pollen and mature egg cells contain _________________ nuclei.An essential step in sexual reproduction in flowering plants is ________________.ovaryhaploidpollination
24Fertilization and Embryos Section ThreeFertilization and Embryos
25What Happens After A Pollen Grain Lands On The Surface Of A Stigma? Sticky fluid, hairs or rough projections often cover the stigma and hold the pollen grain.Chemicals from the pistil cause the pollen grain to grow and form a pollen tube.The generative nucleus divides by mitosis to form two haploid sperm nuclei.The haploid tube nucleus controls the growth of the pollen tube.
26What Happens After A Pollen Grain Lands On The Surface Of A Stigma? The pollen tube continues to grow down through the pistil for several hours until it reaches the embryo sac in the ovary.When the pollen tube reaches the ovule within the ovary, it digests a hole in the embryo sac wall.Then, the tube nucleus disintegrates.One sperm nucleus enters the embryo sac and fuses (unites) with the egg nucleus to form a zygote (fertilized egg).This process is called fertilization.
27What Happens After A Pollen Grain Lands On The Surface Of A Stigma? The zygote is a diploid cell containing 2N chromosomes; N from the sperm and N from the egg.The two haploid polar nuclei fuse to form a diploid fusion nucleus which, in turn, fuses with the other sperm nucleus.This second fertilization results in an endosperm nucleus.The endosperm nucleus has triploid (3N) chromosomes, three times the chromosome number of an egg or a sperm.
28InformationThe ovules of flowering plants undergo double fertilization:One sperm nucleus from the pollen grain fertilizes the egg to form the zygote.The other sperm nucleus fertilizes the polar nuclei to form the endosperm nucleus.The zygote develops into an embryo, and the endosperm nucleus becomes the stored food that nourishes the embryo.A seed is a matured ovule consisting of the embryo and its stored food.
29Fertilization Summarized The sperm and the egg are haploid cells, each containing N chromosomes.Fusion occurs when the sperm and the egg nuclei combine to form a zygote.The zygote nucleus is diploid and contains 2N chromosomes.In flowering plants, a second fertilization takes place.The two haploid polar nuclei (inside the embryo sac) combine to form a fusion nucleus.The fusion nucleus is diploid and contains 2N chromosomes.The second sperm nucleus then fuses with the fusion nucleus to form the endosperm nucleus.The endosperm nucleus is triploid and contains 3N chromosomes.
30Cell DivisionThe seed develops from the ovule as the zygote and endosperm nucleus undergo many cell divisions during the process of mitosis.During mitosis, the nucleus divides and forms two nuclei identical to the original.After the nucleus divides, the entire cell divides and two identical cells form.
31What Happens To A Flower After Fertilization? The flower’s job is done after fertilization. Much of the plant’s energy is used to develop the ovary and the ovules.In several weeks, the fertilized ovule ripens and becomes a seed.The ovary also ripens and becomes a fruit.If an ovary contains several ovules, each ovule can form a seed.The petals and stamens of the flower are no longer necessary, and they often wither.In many plants, however, the receptacle and the calyx become part of the fruit.
32ReviewUnder the control of the tube nucleus, the pollen tube grows down through the pistil until it reaches the ovule. Then, the two sperm nuclei enter the embryo sac.Within the embryo sac, the haploid sperm nuclei carry out two separate fertilizations. One forms a diploid zygote (fertilized egg) and the other forms a triploid endosperm nucleus.The zygote develops into an embryo (immature plant). The endosperm nucleus provides food (endosperm) for the growing embryo.A seed is a mature ovule made up of an embryo and an endosperm.
33Quiz: Fill In The Blanks… After pollination, the tube nucleus directs the growth of the _____________ through the pistil to the ovule. The two haploid ___________ nuclei then enter the embryo sac. There, one nucleus combines with the egg nucleus to form the diploid ____________. The other nucleus combines with the fusion nucleus to form the triploid _____________ nucleus. Eventually, the cells that contain these nuclei, and the surrounding ovule, become a seed.pollen tubespermzygoteendosperm
35FruitsA fruit is a ripened ovary that can include other parts of the flower, such as the calyx and the receptacle.Most fruits can be classified as either fleshy or dry.Fleshy fruits are soft and pulpy at maturity.Let’s learn more about these types of fleshy fruits:AppleGrapePeach
36AppleAn apple is a pome type of fleshy fruit. Its outer fleshy layer is derived from the calyx and receptacle of the flower (blossom).The soft core, formed from the ovary, contains several seeds.A pear is another example of a pome.
37GrapeA grape is a berry type of fleshy fruit. The fleshy layer, often juicy, is derived entirely from the ovary and contains numerous seeds.Other examples of berry type fleshy fruits include the following:WatermelonTomatoBanana
38PeachA peach is a drupe type of fleshy fruit. It consists of an outer fleshy layer and an inner hard and stony layer.Both layers are formed from the ovary. The inner layer (pit) contains one or more seeds.Other examples of drupe type of fleshy fruits include the following:PlumCherryOlive
39Dry FruitDry fruits are another kind of fruit with which you are probably familiar.Dry fruits are dry and hard or papery at maturity.Let’s learn more about these types of dry fruits:Bean podCorn kernelAcorn
40Bean PodA lima bean plant produces a pod type of dry fruit. The fruit consists of a single chamber (pod) containing many seeds.The pod splits when ripe and releases the seeds (beans).Other examples of plants that produce pod type dry fruits include:Pea plantMilkweed plantLily plant
41Corn KernelA corn kernel is a grain type of dry fruit. Each kernel (grain) of corn is a complete fruit.A corn kernel contains one seed. The seed coat is permanently attached to the ovary wall.Other examples of plants that produce grain type dry fruits include:WheatOatBarley
42AcornAn acorn is a nut type of dry fruit. It consists of one seed surrounded by a hard ovary wall.Other examples of nut type dry fruits include the following:HazelnutPecanChestnut
43InformationA seed is the mature ovule of a flower, consisting of the following parts:Seed coatEmbryoEndospermThe seed coat (outer layer) develops from the wall of the ovule and protects the embryo against injury, parasites and dehydration.The embryo is a tiny plant that develops from the zygote.The endosperm develops from the endosperm nucleus of the embryo sac. It provides the embryo with nutrients.
44Monocot Seed Structure A kernel of corn is a complete fruit.Let’s examine the following parts of a corn kernel:CotyledonHypocotylEpicotylEndosperm
45Monocot Seed Structure Corn is a monocot plant. Each kernel has one cotyledon that contains stored nutrients (starch and sugar).The cotyledon absorbs food from the endosperm when the kernel germinates.The hypocotyl is the embryonic stem and root of the corn plant.The rolled-up leaves of the epicotyl are true leaves that become permanent leaves in the adult plant.
46Monocot Seed Structure The endosperm fills most of the corn grain and contains starch and sugar.The plant uses the endosperm as a source of food for growth.
47Dicot Seed Structure Each lima bean is a separate seed. Let’s examine the following parts of the bean seed embryo:CotyledonsHypocotylEpicotyl
48Dicot Seed StructureThe bean is a dicot plant. Bean seeds have two cotyledons.The cotyledons completely digest and absorb the endosperm and make up most of the bean structure.The cotyledons store a large amount of protein and starch. This provides food for the growing embryo as well as for humans and other animals that eat the bean.The hypocotyl is the embryonic stem and root of the plant.The epicotyl consists of two tiny leaves that grow quickly when the seed germinates (sprouts).The leaves of the epicotyl are true leaves that become permanent leaves in the adult plant.
49Information Seeds can be dispersed by the following means: MechanicalWindAnimalsWaterEach plant’s seeds are specialized to take advantage of one method of seed dispersal.
50InformationMechanical dispersal occurs when a pod dries out and bursts. Seeds within the pod can be thrown several feet.The wind carries dandelion and maple seeds, which contain wisps of hair or wings.Animals help disperse seeds by eating fleshy fruits and eliminating the seeds in their feces. Seeds with burrs can stick to animal fur and be carried several miles.Water helps disperse floating seeds or fruit, such as the coconut.
51Seed GerminationUnder favorable conditions, a seed can germinate (sprout) and form a new plant.Let’s compare the germination of a monocot grain of corn and a dicot bean seed.
52Monocot (Corn) Seed Germination The embryo absorbs water, and the root pushes through the softened fruit to form a temporary primary root.Growth occurs as cells divide mitotically in the embryo’s meristematic tissue.The tightly rolled leaves of the epicotyl push through the soil and secondary branch roots develop.Meristematic tissue continues to produce cells that become roots, stems and leaves.Once above ground, the leaves unroll and the stem grows to form the cornstalk.The hypocotyl and cotyledon of the corn grain never appear above ground.
53Dicot (Bean) Seed Germination Water softens the seed coat, and the hypocotyl grows out. Mitotic division of the cells making up the embryo’s meristematic tissue provide new cells for growth.The root grows downward and the hypocotyl forms an arch that pushes up through the soil.Above ground, the hypocotyl straightens and lifts up the two cotyledons and becomes the shoot.The tiny leaves of the epicotyl unfold and grow into adult plant leaves.A dicot’s hypocotyl and cotyledon appear above ground. A monocot’s hypocotyl and cotyledon remain below ground.
54Information Several factors influence the germination of seeds: WaterAirTemperatureLightWater is needed to soften the seed coat (allowing the embryo to grow) and aid in the life processes during growth. Too much water can cause rotting.Seeds must have oxygen to convert food into the energy required for rapid cell division and growth.The two most important factors that affect seed germination are moisture and warmth.
55ReviewA fruit is a mature (ripened) ovary that contains one or more seeds.A seed is a mature ovule consisting of the following parts:Seed coat (for protection)Embryo (immature plant)Endosperm (for food)An embryo can consist of the following parts:One cotyledon (monocot plants)Two cotyledons (dicot plants)Epicotyl that forms leavesHypocotyl that forms stem and rootSeeds can germinate (sprout) under favorable conditions, the most important of which are warmth and moisture.
56Quiz: Fill In The Blanks… After an ovule is fertilized, it develops into a seed. The ovary, meanwhile, becomes the ____________. The ____________ within a seed consists of an epicotyl, a hypocotyl and one or more cotyledons. Monocot seeds, such as corn, have one cotyledon, and _____________ seeds, such as beans, have two cotyledons. The two most important factors that affect seed germination are moisture and ____________.fruitembryodicotwarmth
57Testing Your Knowledge Section FiveTesting Your Knowledge
58This Is A Test of What You Have Learned… There are 10 questions on this test.Try to correctly answer all of the questions.If you miss a question, watch the screen for an explanation of the correct answer.
59Select The Best Matching Choice: Cotyledon:Answer Column:Immature seedSpread far and wideSprout stem and rootsImmature fruitDiploid cellMale plant gametePlant embryo partTrue plant leafCorrect Answer: GThe cotyledon is the part of a plant embryo that often provides food during germination. Monocot plant embryos have one cotyledon, and dicot plant embryos have two cotyledons.Germinate:Correct Answer: CWhen a seed germinates, it sprouts roots and a stem. Germination occurs under various conditions that depend on the type of seed.
60Select The Best Matching Choice: Pollen:Answer Column:Immature seedSpread far and wideSprout stem and rootsImmature fruitDiploid cellMale plant gametePlant embryo partTrue plant leafCorrect Answer: FPollen is the male gamete of plants produced in the anthers of plants that have stamens. Female plants that lack stamens cannot produce pollen.Ovule:Correct Answer: AAn ovule is the immature seed of a plant that develops from the embryo sac within the ovary.
61Select The Best Choice To Complete Each Analogy: seedA fruit is to a flower ovary as a(n) ________ is to an ovule.A. sepalB. seedC. calyxD. gameteE. pistilSince a fruit is a ripened flower ovary, it is most like a seed, which is a ripened flower ovule.
62Select The Best Choice To Complete Each Analogy: ovaryAn anther is to a stamen as a(n) ______________ is to a pistil.A. ovuleB. styleC. filamentD. ovaryE. petalSince the anther is the gamete producing structure of a stamen, it is most like the ovary, which is the gamete producing structure of a pistil.
63Fill In The Blanks… flowers fertilization fruit germinate Many higher plants are equipped with specialized reproductive structures, called ______________, which allow them to reproduce sexually. During the process of ______________, male and female gametes combine to form a zygote. The ovary matures into a structure called a(n) ______________, and the ovules within it mature into seeds. Seeds are dispersed by several means and can ______________ (begin to grow) to form new plants.flowersfertilizationfruitgerminate
64Pollination & Fertilization Biology BasicsReview!You Have Completed...Pollination & Fertilization~Seeds, Fruits and Embryos~