Biology 102 Chapter 38

By Charlotte Howard,2014-11-21 23:03
6 views 0
Biology 102 Chapter 38

    Biology 102 Chapter 39

    Reproduction in Flowering Plants

1. Describe the life cycle of an angiosperm.

    ---pollen from anther lands on sticky stigma at carpel’s


     --can self-pollinate but not the rule

    ---pollen grain germinates = pollen tube growth down

     through the style

    ---when tube reaches the ovary, pollen tube grows through

     micropyle and discharges 2 sperm cells into embryo sac ---double fertilization occurs as 1 sperm nucleus unites

     with egg = diploid zygote; other sperm nucleus fuses

     with 2 nuclei in embryo sac’s central cell = triploid

     (3n) endosperm

    ---after double fertilization, ovule matures into a seed ---embryo is 2n; has rudimentary root and 1 or 2 cotyledons

     (seed leaves)

    ---endosperm is 3n, (triploid), divides repeatedly forming

     endosperm which is rich is starch/other food reserves ---seed coat is 2n

    ---seed germinates into new sporophyte generation ---produces spores that germinate into gametophyte generation ---megagametophyte and microgametophyte


    2. Identify by which generation, structure, and process spores are produced.

    ---sporophyte generation produces spores

    ---produced by megasporangium and microsporangium ---diploid to haploid...only way to do that is MEIOSIS 3. Identify by which generation, structure, and process gametes are produced.

    ---gametophyte generation produces gametes

    ---female gametophytes (megagametophytes) which are called

     embryo sacs develop in megasporangia

     --will eventually produce an egg along with other cells ---male gametophytes (microgametophytes) which are called pollen

     grains develop in microsporangia

    ---gametophyte (N) produces gametes (N)takes MITOSIS to do that 4. Describe the formation of pollen.

    ---pollen grain is the immature male gametophyte that

     develops within the anthers of stamens in angiosperms ---in sporangial chamber of anther, diploid microsporocytes

     undergo meiosis to form 4 haploid microspores

    ---haploid microspore nucleus undergoes mitotic division to

     give rise to a generative cell and a tube cell

    ---wall of microspore thickens and becomes sculptured into

     species-specific pattern

    ---these 2 cells and thickened wall are the pollen grain;

     an immature male gametophyte

    5. Explain the relationship between pollen and microgametophyte. ---pollen grain (microgametophyte/male gametophyte) develop in microsporangia

    ---can be viewed as synonymous, botanist would object 6. With reference to the mature microgametophyte (germinating pollen grain), distinguish among generative nucleus, tube nucleus, and sperm nucleus.

    ---pollen grain becomes mature male gametophyte when the

     generative cell (nucleus) divides to form two sperm


    ---both sperm formed have haploid nuclei

    ---tube cell (with its nucleus) responsible for pollen

     tube growth

    7. Describe the development of an embryo sac, and explain what happens to the egg and polar nuclei.

    ---ovule is structure which forms within chambers of plant

     ovary and contains the female gametophyte

    ---female gametophyte is the embryo sac

    ---megasporocyte in sporangium of each ovule grows & goes

     through meiosis to form 4 haploid megaspores

     --only 1 usually survives

    ---remaining megaspore grows and its nucleus undergoes

     three mitotic divisions, forming one large cell with

     8 haploid nuclei

    ---membranes partition this into multicellular embryo sac

    ---within the embryo sac

     --egg cell is located at one end, flanked by 2 other

     cells (synergids)

     --at opposite end are 3 antipodal cells

     --other 2 nuclei (polar nuclei) share cytoplasm of

     large central cell

     --at end containing egg is micropyle (opening through

     integuments surrounding embryo sac

    8. Outline the process of double fertilization and describe the function of endosperm.

    ---double fertilization is the union of two sperm cells

     with two cells of the embryo sac

    ---after adhering to a stigma, pollen grain germinates &

     extends pollen tube between cells of style toward ovary ---generative cell divides (mitosis) to form two sperm ---pollen grain with a tube enclosing 2 sperm = mature

     male gametophyte

    ---directed by chemical attractant, usually calcium, tip of

     pollen tube enters through micropyle and discharges 2

     sperm nuclei into embryo sac

    ---one sperm unites with egg to form zygote

    ---other sperm combines with two polar nuclei to form a

     3n nucleus in large central cell of embryo sac ---this central cell will give rise to endosperm which is

     a food storing tissue

    9. Describe the relationship between the ovary in a flower of a plant and the fruit produced by the plant. Do the same for the ovule and seed.

    ---after fertilization, ovary wall of flowering plant, together

     with its seeds, develop into a fruit

    ---fruit may consist of only mature ovary and its seeds, or may

     include other parts of the flower or structures closely

     related to it

    ---a fruit protects the seeds and aids in their dispersal

     by wind or animals

    ---a fruit develops from the ovary of the flower while

     seeds are developing from the ovules

    ---a true fruit is a ripened ovary

     --pollination triggers hormonal changes that cause ovary

     to grow

     --wall of ovary thickens to become the pericarp

     --transformation of flower into fruit parallels seed


     --in most plants, fruit does NOT develop without

     fertilization of the ovules

     -parthenocarpic plants are an exception

    ---in some angiosperms, other floral parts also contribute

     to formation of what we call fruit

    ---simple fruit derived from single ovary;

     --cherries (fleshy); soybeans (dry)

    ---aggregate fruit derived from single flower with several

     separate carpels


    ---multiple fruit derived from an inflorescence or separate

     tightly clustered flowers


    ---OVULE develops into seed containing an embryo and supply of


    ---protective seed coat is formed from integuments of ovule 10. Compare and contrast the parts of a seed of a monocot and that of eudicot.

    ---monocot seed has only one cotyledon whereas a dicot seed

     has two cotyledons

    ---some dicot seeds have fleshy cotyledons because they

     have absorbed food from the endosperm

    ---others (castor bean) retain food supply as endosperm

     and have cotyledons that are very thin

     --cotyledons will absorb food from endosperm & transfer

     to embryo when seed germinates

    ---seed of monocot has only one cotyledon

    ---members of grass family (including corn & wheat) have

     specialized type of cotyledon called scutellum (small


     --scutellum very thin with large surface area pressed

     against endosperm for absorbing nutrients during


    ---embryo of grass seed enclosed by sheath consisting of

     a coleorhiza (covers the root) and a coleoptile (covers

     the embryonic shoot

    11. Explain how fruits help disperse seed.

    ---fruits may be fleshy and edible or dry and inedible ---dry, winged fruits (ash, elm, maple) blown by wind ---water disperses some fruits (coconuts)

    ---some “hitch” rides on animals

    ---some travel through animals (birds and berries) ---some “carried” by animals

    12. Define photoperiodism and using this phenomenon, explain how an integrated control system can regulate a plant process such as flowering.

    ---defined as regulation of processes (flowering, etc.) by the

     changing length of day (or of night)

    ---numerous genes participate in process




     --products are transcription factors that mediate expression

     of still further genes

    ---only requires one leaf for plant to detect photoperiod

     and for floral buds to develop

    ---if all leaves are removed, no photoperiod detection


    ---is believed unidentified hormone is produced in leaves

     --moves to buds

     --or a change in relative []s of 2 more hormones ---this hormone (or mixture) appears to be same in

     both long-day and short-day plants

    ---combination of environmental cues (photoperiod) and

     internal signals (hormones) induces the transition

     of bud’s meristem from vegetal state into flowering


    13. Distinguish among annual, biennial, and perennial plants.

    ---annual completes entire life cycle (seed to flower) in less

     than one year

    ---biennial grows for all or part of one year, live on into a

     second year during which it flower, form seeds, and die ---perennial lives for a few to many years during which both

     growth and flowering occur

    14. Distinguish among short-day, long-day, and day-neutral plants.

    ---short-day plants require a light period shorter than a

     critical length and generally flower in late summer,

     fall, and winter

     --chrysanthemums, poinsettias, some soybeans

    ---long-day plants flower only when light period is longer

     than a certain number of hours, generally in late spring

     and summer

     --spinach, radish, lettuce, iris, many cereals ---day-neutral plants are unaffected by photoperiod and

     flower whey reach a certain stage of maturity

     --tomatoes, rice, dandelions

    ---was discovered in 1940s that night length, not day

     length actually controlled flowering & other responses

     to photoperiod

     --if daytime period broken by brief exposure to darkness

     there is no effect on flowering

     --if nighttime period is interrupted by short exposure

     to light, plants do NOT flower

     --short-day plants flower if night is longer than a

     critical length

     --long-day plants need a night shorter than critical


    15. Distinguish between phytochrome and florigen. ---phytochrome is regulatory plant pigment existing in either

     active or inactive form

     --different wavelengths of light can drive it from one form

     to the other

    ---florigen name given suspected “flowering hormone”

     --photoperiodic induction of leaf induces it to start and

     continue production of florigen

     --transported to other parts of plant switching target parts

     to reproductive mode

    16. Define circadian rhythm and explain what happens when an organism is artificially maintained in constant environment. ---circadian rhythm is a physiological cycle with a frequency of

     about 24 hours

    ---when organism is sheltered from environmental cues,

     rhythm may deviate from 24 hours (called free-running

     periods) and can vary from 21 to 27 hours

    ---the clock may take days to reset once the cues change ---“period” is length of one cycle

    ---“amplitude” is magnitude of change over course of a cycle

    ---period remarkably insensitive to temperature ---periods are highly persistent

     --continue in environment in which there is NO alternation

     of light and dark

    ---periods can be “entrained” (within limits) by light-dark

     cycles that differ from 24 hours

    ---brief exposure to light can shift the rhythm causing a


    17. Distinguish among sexual reproduction, vegetative reproduction, and apomixis.

    ---sexual reproduction involves the formation of some type of

     gametes (sperm/egg; +/- reproductive cell)

     --how those gametes are gotten together is a real hoot ---asexual reproduction does not involve the production of


    ---text defines as “production of offspring from a single

     parent; occurs without genetic recombination, resulting

     in a clone

    ---vegetative reproduction occurs when meristemic tissues

     composed of dividing, undifferentiated cells can sustain

     or renew growth indefinitely

     --parenchyma cells can also divide and differentiate

     into various types of specialized cells

    ---two major natural mechanisms of vegetative reproduction ---fragmentation is separation of parent plant into parts that

     reform whole plants

     --is most common type of vegetative reproduction ---apomixis is the production of seeds without meiosis

     and fertilization

     --diploid cell in ovule gives rise to embryo

     --ovules mature into seeds which are dispersed

     --example: dandelion

    18. Compare sexual and asexual reproduction in plants and state under what conditions asexual reproduction is advantageous. ---sexual reproduction benefits include the generation

     of variation, an asset when environment (biotic and

     abiotic) changes

     --produces seeds for dispersal to new locations and

     which can wait until environments become favorable

---asexual reproduction benefits: in stable environment,

     plants can clone many copies of themselves in a short


     --progeny are mature fragments of parent plant

     -not as fragile as seedlings produced by sexual


    19. Explain the role of tissue culture in plant propagation. ---many plant cells are “totipotent”

     --condition of possessing all the genetic information and

     other capacities necessary to form an entire individual ---cultures of undifferentiated tissues can give rise to

     entire plants

    ---even have way to “de-differentiate” tissues (Fig. 16.3)

    ---can use small pieces of tissue from a parent plant

     --orchids, rhodendendrons

    ---culturing tiny bits of apical meristem can produce plants

     free of viruses

     --lacks developed vascular tissue and viruses tend NOT

     to enter

Report this document

For any questions or suggestions please email