Chapter 38 Plant Reproduction p. 783

 

Read the intro…Check out the century plant… p. 783

 

Sporophyte and gametophyte generations alternate in the life cycle of plant p. 783

• Life cycle of angiosperms
• Alternation of generations
• Sporophyte
• Gametophyte
• p. 784 Figure 38.1  Overview of angiosperm life cycle
• Note the reduced gametophyte…now found inside the flower.

 

• The reduced gametophyte in angiosperms is completely dependent of the dominant sporophyte

 

• The male gametophyte develops within the anthers

 

• Female gametophyte develops within the ovary (the ovary eventually becomes the fruit)

 

Flowers are specialized shoots bearing the reproductive organs of the angiosperms sporophyte p. 784

• p. 785 Figure 38.2 Review of an idealized flower  Flower anatomy
• Flower parts: starting from outside to inside

 

• Sepals: enclose and protect bud

 

• Petals:

 

• Stamens: male reproductive organ
• Filament
• Anther: contain pollen chambers; pollen production

 

• Carpels: female reproductive organ
• Ovary: the base; contains one or more ovules (ovules will become the seeds)
• Style:  neck
• Stigma: sticky top

 

• Receptacle :site attachment to stem

 

 

Alternation of Generations: a closer look

• Stamen and Carpels
• Both contain sporangia (structures that produce spores)
• Within sporangia the gametophyte develops
• Pollen grains: Male gametophyte
• Sperm producing
• Formed within pollen sacs (within anthers)

 

 

• Embryo sacs: Female gametophyte
• Egg producing
• Formed within ovules (within ovaries)

 

• Pollination
• Pollen grains land on stigma
• Each producing pollen tubes to the ovary
• Discharges sperm
• Fertilization
• Zygoteàembryo
• Ovules develops into a seed
• Ovary into a fruit

 

 

Complete Flowers: have all four organs (sepals, petals, carpels and stamen)

Incomplete Flowers: lack one or more (ex. Grass…lack petals)

 

 

 

Development of the male gametophyte p. 786

• Pollen Sacs (sporangia) Figure 38.4a p. 787
• Contains diploid cells (microsporocytes) that undergo meiosis...producing 4 haploid microspores
• Microspores divides once by mitosis: producing two cells
• A generative cell (becomes sperm)  and a tube cell (forms tube)
• Two-celled structure encased within distinctive walls Figure 38.5 p. 787

 

 

 

 

 

 

 

 

 

 

Development of the female gametophyte p. 786

• Figure 38.4b p. 787
• Within ovary chambers
• Ovules
• Each contain one sporangium
• A diploid cell (megasporocyte) undergoes meiosis…producing 4 haploid megaspores
• Only one megaspores; continues to divide (mitosis) until it contains 8 haploid nuclei (becomes the embryo sac)
• 3 nuclei are grouped together...one is the egg, the other two help  guide the pollen tube to the egg
• 3 have unknown use
• 2 are called polar cells

 

 

 

 

Double Fertilization gives rise to the zygote and endosperm p. 789

• Pollen grains germinate once on the stigma
• The generative cell divides (mitosis) forming 2 sperm
• The germinated pollen grain is the mature male gametophyte
• The 2 sperm will be released into the embryo sac
• One sperm fertilizes egg (2n); One fuses with the 2 polar cells (3n)
• The triploid cell becomes the endosperm (food storage tissues)
• Stock pile proteins, oils and starches…nutrient sink
• Provides nutrients to the developing embryo...eventually to the seedling.
• Some plants export endosperm to the cotyledon (seed leaves)
•   Double fertilization: Figure 38.9 p. 790

 

 

Structure of the mature seed p. 791

§         SEED STRUCTURE

§         Contains Embryo

·        Consists of the following parts Figure 38.11 p. 792

o       Epicotyl- becomes the shoot tip

o       Plumule- young leaves attached to epicotyl

o       Hypocotyl- becomes young shoot

o       Radicle- becomes the root

o       Coleoptile- in monocots, surrounds embryo, appear as the first leaves (though not true leaves)

o       Seed coat- protective outer coat

o       ENDOSPERM (aka Cotyledon) fleshy part of seed. Nourishment for developing embryo.

The ovary develops into a fruit adapted for seed dispersal p. 792

Read

 

Seed Dormancy p. 793

Seed Germination (Emergence from Dormancy)

§         condition of low metabolic activity; no growth and development

§         Factors

·        Uptake of water (imbibe)

·        Suitable temperature

·        Availability of oxygen

·        Exposure to freezing temperatures

·        Fire

·        Exposure to light

·        Abrasion

·        Exposure to digestive enzymes

·        Note: not all seeds need all of the above

·        Germination begins with the imbibition (absorption) of water

 

 

Vegetative propagation of plants is common in agriculture p. 795

Vegetative Propagation

·        Asexual form of reproduction

·        Parts of parent plant (roots, stems or leaves) produce another plant.

§        Grafting- a cutting that is attached to a similar plants…seedless oranges

§        Bulbs- short stems underground...onions

§        Runners- horizontal stems above ground… strawberries

§         Tubers- underground stems…potatoes

§         Stolons (above ground)

§         Rhizomes (below ground)