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
tip
--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
---OVERHEAD TIME
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
(mitosis)
---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
development
--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
--strawberries
---multiple fruit derived from an inflorescence or separate
tightly clustered flowers
--pineapple
---OVULE develops into seed containing an embryo and supply of
nutrients
---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
shield)
--scutellum very thin with large surface area pressed
against endosperm for absorbing nutrients during
germination
---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
---FLORAL MERISTEM IDENTITY GENES
---PATTERN FORMATION GENES
---ORGAN IDENTITY GENES
--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
occurs
---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
state
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
length
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
a PHASE SHIFT
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
gametes
---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
period
--progeny are mature fragments of parent plant
-not as fragile as seedlings produced by sexual
reproduction
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