Download NOTES: Plant Reproduction and Development

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* Water has been replaced by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
 GAMETOPHPYTES: reproductive structure of plants
-.
(sperm and egg cells)
-gametes fuse to form a
(2n) that develops
into a multicellular plant
…ALTERNATION OF GENERATIONS!
FLOWERS:
-the reproductive structure of angiosperm sporophytes
-four sets of modified leaves:
1)
2)
3)
: -anther, filament
4)
: stigma, style, ovary
 STAMENS and CARPELS (PISTILS) are the reproductive parts of the flower.
 Female gametes develop in
, which contain the
 this occurs at the base of the carpel /pistil, inside the
 Male gametes develop in the stamen inside
 this occurs at the stamen tips within chambers of the
FLOWER VARIATIONS:
 Complete flower = flower with
 Incomplete flower = flower missing one or more of these parts (e.g. most grasses do not have petals on their
flowers)
 Perfect flower = flower having both
(a.k.a. bisexual)
 Imperfect flower = flower that is either
(a.k.a. unisexual)
 Monoecious = “one house”; plants with both staminate and carpellate flowers on the same plant (ex:
)
 Dioecious = “two houses”; 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
 at the time of pollination:
A pollen gain consists of 2 cells (both haploid):
-GENERATIVE CELL:
-TUBE CELL:
; contains the generative cell
Development of the Female Gametophyte (EMBRYO SAC)
● Female gametes are contained in the EMBRYO SAC
(diagram of embryo sac below):
Embryo Sac:
egg cell (OVUM) at one end
ovum flanked by 2 syngerids (help to attract sperm cells)
 two nuclei in center (“polar nuclei”)
POLLINATION:
-occurs when wind- or animal-born pollen released from the anthers lands on the STIGMA at the tip of the carpel
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:
from the same, or closely related, plant by the stigma
after POLLINATION…
-pollination 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
5) while seed formation is taking place, the entire ovary is developing into a
more seeds.
;
, which will contain one or
DOUBLE FERTILIZATION:
When a compatible pollen grain lands on a stigma of an angiosperm, double fertilization occurs.
DOUBLE FERTILIZATION =
with two cells of the embryo sac
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 (triploid) 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:
•
(which it provides to the developing embryo)
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 outer layers / integuments of the ovule.
Dicot seed structures:
(diagram of mature dicot seed):
-cotyledons =
-hypocotyl = embryonic axis
-radicle =
-epicotyl = embryonic axis
*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.
FRUITS:
-ovary develops into fruit (adapted for
)
*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
!