Chapter 24 Reproduction in Plants

Alternation of Generations• All plants have a life cycle in which a diploid sporophyte

generation alternates with a haploid gametophyte generation- Sperm and eggs represent the haploid gametophyte - zygotes produced from fertilization create diploid

sporophyte• In seed plants we recognize the sporophyte as the plant• Where are the gametophytes found?

Gymnosperms• Cones are the where we find the gametophytes for

seed plantsTwo cone types:

1. Pollen cones – contain pollen grains and represent the male gametophyte (sperm)

2. Seed cones – contain 2 ovules that develop into large egg cells or the female gametophyte (egg)• Pollination – cycle begins in the spring when male

cone releases large amounts of pollen grains; female is fertilized when pollen is caught and contacts ovule– Mainly wind blown to reach other plants

Pollen vs Seed Cones

Alterations of Generations

Structure of Flowers• Angiosperms or flowering plants contain the gametophytes

within the structures of the flower4 kinds of specialized parts of flower:

1. Sepals – outer leaf-like covering for the bud2. Petals – attract pollinators with bright colors3. Stamen – contains male gametophyte anther- oval sac where meiosis takes place for

production of pollen grainsfilament –supports anther4. Carpels – contains female gametophyteOvary – produces eggsStigma – female receptacle surface where pollen is caught Style – narrow stalk that supports stigma

Flower Anatomy

Angiosperms

• Pollination with angiosperms is mainly by animals - bees, birds, bats, and other insects carry pollen

to each flowersome is wind-blown, but less efficient

• Fertilization – pollen grain lands on stigma forms pollen tube fusing one sperm with an egg– Second fertilization takes place that forms an endosperm

(3n) food rich cell that nourishes seedling during development

– Double fertilization is believed to explain the evolutionary success of angiosperms

Alterations of Generations

Seed and Fruit Development

• Seeds provide a protective and nutritional covering for embryos

- as they mature ovary walls thicken to form fruit around seeds

Ex: apple

• Seed dispersal is necessary for continuation of species

- can occur by eliminated waste from animals- can be spread by wind and water

Seed and Fruit Development• Seed dormancy – period when the embryo is alive but

not growing- occurs in order to grow during optimal

conditions- can allow for long distance dispersal- environmental conditions like temperature and

moisture can end dormancy • Seed Germination – early growth stage of embryo

- absorbs water, swells food storing tissues- cracks open seed coat- young root emerges and grows