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NOTES Plant Reproduction and Development Ch

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					                                          NOTES: CH 38 - Plant Reproduction

*Modifications in reproduction were key adaptations enabling plants to spread into a variety of
        .

* Water has been replaced by               and                       as a means for spreading gametes.
* Embryos are protected in SEEDS.
* Vegetative (asexual) reproduction for propagation of some plants in a variety of environments.
Our focus in this chapter will be…SEXUAL REPRODUCTION

ALTERNATION OF GENERATIONS
 the angiosperm (                                  ) life cycle includes ALTERNATION OF GENERATIONS –



                                                        alternate with


 SPOROPHYTE (2n):
-the recognizable plant most familiar to us
-produces haploid spores by
-spores undergo mitosis and develop into a multicellular male or female
 GAMETOPHPYTES (n):
-
-gametes fuse to form a                             (    ) that develops into a multicellular sporophyte…
                                         …ALTERNATION OF GENERATIONS!
FLOWERS:
-the reproductive structure of angiosperm sporophytes
-four sets of modified leaves:
         1)                                                 3)
         2)                                                 4)
 STAMENS and CARPELS (PISTILS) contain the sporangia and are the reproductive parts of the flower.
 Female gametophytes develop in carpel sporangia as                                , which contain the
 this occurs inside the                   (at the base of the carpel, surrounded by                               )
 Male gametophytes develop in the stamen sporangia as
 this occurs at the stamen tips within chambers of the

POLLINATION:
-occurs when wind- or animal-born pollen released from the anthers lands on the STIGMA at the tip of the carpel
-this is followed by this sequence:
1) a pollen tube grows from the pollen grain, down the carpel, into the embryo sac;
2) sperm are discharged resulting in fertilization of the eggs;
3) the zygote develops into an embryo;
4) as the embryo grows, the ovule surrounding it develops into a SEED;
5) while seed formation is taking place, the entire ovary is developing into a FRUIT, which will contain one or more
seeds.
        *Seeds are dispersed from the source plant when fruits are moved about by the wind or animals.
             *Seeds deposited in soil of the proper conditions (moisture, nutrients), will GERMINATE.
*the embryo starts to grow and develops into a new                                        .
*after flowers are produced by the sporophyte, a new generation of GAMETOPHYTES develop and the life cycle
continues!

FLOWER VARIATIONS:
 Complete flower =
 Incomplete flower =
(e.g. most grasses do not have petals on their flowers)
 Perfect flower =
 Imperfect flower =
 Monoecious = plants with both staminate and carpellate flowers on the same plant (ex:                          )
 Dioecious = plants having staminate and carpellate flowers on separate plants (ex:                             )

Development of the Male Gametophyte (POLLEN):
 POLLEN GRAIN = the immature male gametophyte; develops within the anthers of stamens in an angiosperm
         extremely durable; tough coat to prevent biodegradation
 Steps in pollen grain formation:
1) diploid microsporocytes undergo meiosis to form 4 haploid MICROSPORES;
2) haploid microspore nucleus undergoes mitosis, giving rise to a GENERATIVE CELL and a TUBE CELL;
3) microspore wall thickens and becomes sculptured into a species-specific pattern.

Development of the Female Gametophyte (EMBRYO SAC)
 OVULE = structure that forms within the plant ovary
 Steps in embryo sac formation:
1) a diploid megasporocyte in each ovule grows and goes through meiosis to form 4 haploid MEGASPORES (only
one survives)
2) the remaining megaspore grows and its nucleus undergoes three mitotic divisions, forming one large cell with eight
haploid nuclei.
3) membranes partition this into a multicellular EMBRYO SAC.

Embryo Sac:                                                              (diagram of embryo sac below):
 egg cell at one end; flanked by two other cells
 at opposite end are three antipodal cells
 the other two nuclei (“polar nuclei”) share the cytoplasm of the
large central cell
POLLINATION =
Methods of Pollination / spread of pollen:
•
•
•                                   (most plants cross-pollinate)


To prevent self-pollination (and thus ensuring sperm and egg from different plants meet), some plants:
-have stamens and carpels that                                                     ;
-have structural arrangement of flower parts that reduces the chance of pollen getting transferred from stamen to
carpel;
-are SELF-INCOMPATIBLE (a biochemical block that prevents the pollen grain from developing and fertilizing the
egg)


SELF-INCOMPATIBILITY:

DOUBLE FERTILIZATION:
When a compatible pollen grain lands on a stigma of an angiosperm, double fertilization occurs.

DOUBLE FERTILIZATION =



Steps:
1) pollen grain adheres to stigma, germinates, and extends a pollen tube toward the ovary;
2) generative cell divides (mitosis) to form 2 sperm;
3) directed by a chemical attractant, pollen tube enters and discharges its 2 sperm nuclei into the embryo sac;
4) 1 sperm unites with the egg                                     ;
5) other sperm combines with the 2 polar nuclei to form a 3n nucleus in the large central cell of the embryo sac.
 this central cell will give rise to the                           (a food storing tissue for the seed/embryo)

**after double fertilization, each ovule develops into a seed and the ovary into a fruit surrounding the seed(s).



ENDOSPERM:
• rich in nutrients (which it provides to the developing embryo)
• in monocots, stores nutrients that can be used b y the seedling after germination
• in dicots, food reserves of the endosperm are exported to the cotyledons, thus mature seeds have no endosperm


Structure of the mature seed:
in mature seeds, the embryo is quiescent (dormant) until germination
• the seed dehydrates until its water content is only 5-15% by weight.
• the embryo is surrounded by endosperm, enlarged cotyledons, or both.
• the seed coat is formed from the integuments of the ovule.
Dicot seed structures:                                           (diagram of mature dicot seed):

-cotyledons =

-hypocotyl = embryonic axis below cotyledons

-radicle =

-epicotyl = embryonic axis above cotyledons




FRUITS:
-ovary develops into fruit (adapted for                                              )
-fruits can be classified as:

• SIMPLE FRUITS: derived from a single ovary (ex:                                    )

• AGGREGATE FRUITS: derived from a single flower with several separate carpels (ex:                       )

• MULTIPLE FRUITS: derived from separate tightly clustered flowers (ex:                                   )

*Fruits ripen about the time seeds are becoming fully developed
Ripening fruits are characterized by:
1) fruit becomes softer as a result of enzymes digesting the cell wall components;
2) colors usually change and                                      as organic acids or starch are converted to sugar;
3) these changes produce an edible fruit which entices animals to feed, thus                                      !

				
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