Plant Reproduction
Biology H
Alternation of generations
Plants alternate between a haploid form—the gametophyte—and a diploid form—the sporophyte
The gametophyte produces haploid gametes than fuse to form the zygote
The zygote grows up into the sporophyte plant
Meiosis occurs in regions of the plant producing spores
Spores grow into the gametophyte plant
Non-vascular plants
Mosses
Have very few adaptations to life on land
Thallus: main structure of plant
Rhizoids: anchor the plant to the ground
Need to live in moist places
Water moves by osmosis into all parts of the plant
Needs water for fertilization
Ferns
Ferns are the oldest vascular plants
Have true roots, stems and leaves
Stems grow horizontally underground (rhizome)
Roots branch off rhizome into soil
Leaves (fronds) grow up from the rhizome
Underneath the fronds are sori—clusters of sporangia containing many spores
Cuticle helps retain water
Water is necessary for reproduction—the sperm has to swim to the egg
Seed producing vascular plants
The seed is better adapted to dispersal and survival than spores since thy are multicellular and come
with their own food source
They can be dispersed by wind, water, animals, etc
2 types: gymnosperms and angiosperms
Gymnosperms
Seeds form in cones
Sperm is transferred to the egg by wind
Ex: conifers
Male cone produces pollen and is carried to the female cone by the wind
The seed is also carried away from the tree by the wind
Sporophyte is the tree; gametophyte is the cones
Flower structure
Flowers are modified leaves that are produced to attract pollinators
Sepals: leaflike structures that enclose the bud
Petals: brightly colored modified leaves that attract pollinators
Stamen: male reproductive structure; filament and anther—produces pollen
Carpel: female reproductive structure; stigma—receives pollen, style, ovary—contains the ovules
Alternation of generations
The plant is the sporophyte (diploid) structure
Within the plant are cells that undergo meiosis to become haploid
The gametophyte is the pollen grain or embryo sac; both are totally dependent on the sporophyte plant
On fertilization, the diploid number is regained; zygote grows up into the plant
Seed structure
After fertilization the seed dehydrates and forms the seed coat
The embryo: the developing plant
Epicotyl: becomes the shoot
Plumule: becomes the 1st leaves
Radicle: becomes the root, grows 1st
Hypocotyl: connects the epicotyl to the radicle
Cotyledons: structures that contain or absorb endosperm, digest it and give it to the embryo
Fruits
Form from the pericarp (ovary walls)
Surrounds and protects the seeds; aids in dispersal
Can be dry or fleshy
Dry fruits: sunflower seeds, peas, beans, wheat, corn, rice, nuts, etc
Fruits ripen in response to hormones at about the same time the seeds are fully developed
Changes in ripening fruit (color, softening, sweetening) entice animals to eat the fruit to disperse the
seeds