2 *Modifications in reproduction were key adaptations enabling plants to spread into a variety of terrestrial habitats.
3 **Our focus in this chapter: * Water has been replaced by wind and animals as a means for spreading gametes.* Embryos are protected in SEEDS.Vegetative (asexual) reproduction is used for propagation of some plantsin a variety of environments.**Our focus in this chapter:SEXUAL REPRODUCTION!
4 GAMETOPHYTE: reproductive structure of plants -where haploid GAMETES (n) are produced (sperm and egg cells)-gametes fuse to form a ZYGOTE (2n) that develops into a multicellular plant
8 FLOWERS: STAMENS and CARPELS (PISTILS) are the reproductive parts of the flower.
9 FLOWERS: Female gametes develop in EMBRYO SACS, which contain the EGG CELLS this occurs at the base of the carpel /pistil, inside the OVARY
10 Male gametes develop in the stamen inside POLLEN GRAINS this occurs at the stamen tips within chambers of the ANTHERS
11 FLOWER VARIATIONS: Complete flower = flower with sepals, petals, stamens, carpels Incomplete flower = flower missing one or more of these parts(e.g. most grasses do not have petals on their flowers)
12 FLOWER VARIATIONS: Perfect flower = flower having both stamens and carpels (a.k.a. bisexual) Imperfect flower = flower that is either STAMINATE (male) or CARPELLATE (female) – a unisex flower. (a.k.a. unisexual)
13 Monoecious = “one house”; plants with either perfect flowers or with both staminate (male) and carpellate (female) flowers on the same plant(ex: star lily, rose, dandelion)Dioecious = “two houses”;plants having staminate andcarpellate flowers on separateplants (ex: willow, juniper)
14 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 topreventbiodegradation
15 At the time of pollination: A pollen gain consists of 2 cells (both haploid):-GENERATIVE CELL: divides to form 2 sperm cells-TUBE CELL: produces the pollen tube; contains the generative cell
26 To prevent self-pollination (and thus ensuring sperm and egg from different plants meet), some plants:-have stamens and carpels that mature at different times;-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)
27 SELF-INCOMPATIBILITY: the rejection of pollen from the same, or closely related, plant by the stigma
28 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 from the pollen grain resulting in fertilization of the egg;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.
30 DOUBLE FERTILIZATION: When a compatible pollen grain lands on a stigma of an angiosperm, double fertilization occurs.DOUBLE FERTILIZATION = the union of two sperm cells with two cells of the embryo sac
31 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 ZYGOTE;5) other sperm combines with the 2 polar nuclei to form a 3n (triploid) nucleus in the large central cell of the embryo sac.
34 this central cell will give rise to the ENDOSPERM (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).
35 ENDOSPERM:• rich in nutrients (which it provides to the developing embryo)
36 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.
45 *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 fruit becomes sweeter as organic acids or starch are converted to sugar;3) these changes produce an edible fruit which entices animals tofeed, thus dispersing the seeds!