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Sexual Reproduction In Plants. Meeting the Challenge. Making New Plants. Many plants reproduce successfully through asexual reproduction. Others use sexual reproduction to pass on their genetic material. Why is this challenging? This is challenging because most plants do not move.
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Sexual Reproduction In Plants Meeting the Challenge
Making New Plants • Many plants reproduce successfully through asexual reproduction. • Others use sexual reproduction to pass on their genetic material. • Why is this challenging? • This is challenging because most plants do not move.
Meeting the Challenge • In animals the product of sexual reproduction is the zygote. • In plants the product of sexual reproduction is the seed. • The seed contains an embryo, a food supply and a seed coat (protects seed from dehydration). • Plants can be classified into two groups based on their seed type.
Angiosperms • Flowering plants • The seeds form inside the flowers. • When mature the seeds are enclosed in a case, such as a pod or a shell. • Can you think of examples of angiosperms?
Gymnosperms • Gymnosperms do not produce flowers. • Seeds are produced inside cones. • Their seeds have a coat but they are not enclosed in a case. • Can you think of examples of gymnosperms? • Can you name any others?
Gymnosperms Cycad Cypress Gynkgo
Others ?? • Not all plants fall into these two categories. • Ferns and mosses are neither angiospem nor gymnosperm. • They reproduce sexually without seeds.
Sexual Reproduction in Angiosperms • More than one half of all known plants are angiosperms. • Some produce large, showy flowers (lily, tulip,etc,) • Some have very small, easily missed flowers (grasses) • Big or small, all flowers have the same function.
Purpose of Flowers • All of the plant’s reproductive organs are contained in the flower. • Female reproductive organ is called the pistil. • Male reproductive organ is called the stamen
Anther: Where pollen is produced and stored Stigma: Sticky tip of the pistil that captures pollen grains Pollen grains: Cases containing male gametes Style: Stalk that supports the stigma and pollen tube growth Filament: Stalk that supports the anther Ovary: Swollen base of the pistil containing the ovules Ovule: Sac containing female gamete Stamen: male reproductive organ Pistil: female reproductive organ Reproductive Organs In Angiosperms Insect-pollinated flower
Pollination and Fertilization • Pollination is not the same as fertilization! • Pollination takes place when pollen grains are transferred from the anther to the stigma (same flower or different ones). • Who transfers the pollen? • Wind, insects, birds, bats
Pollination and Fertilization • Fertilization is the process by which the male gamete (sperm) fuses with the female gamete (egg) • Where is the sperm? • The sperm is transported by the pollen tube down the style to the ovules in the ovary. • Where is the egg cell? • Is inside the ovule in a structure called the megagametophyte.
Pollination in Angiosperms • Before seeds can develop inside the flower pollen grains from the anther must reach the stigma of the pistil. • Some plants self-pollinate - both male and female gametes come from the same plant. • What might be some of the advantages to this type of sexual reproduction?
Pollination in Angiosperms • Most angiosperms cross-pollinate. • Pollen from one plant is transferred to another plant. • Most common way to cross pollinate is to use the wind or insects. • Which type of pollination would produce the most seeds?
Pollination What do all these flowers have in common?
Pollination What do all these flowers have in common? Pollination movies
Fertilization in Angiosperms Development of a Pollen Tube
Pollen tube grows down the style to reach the ovule Once the pollen tube reaches the ovule the sperm fertilizes the female gamete forming the zygote Fertilization in Angiosperms • While the pollen tube is growing, cells inside the ovule prepare for its arrival. • Once the sperm cell meets the egg, a zygote is formed.
Seed and fruit development in Angiosperms • Other cells in the ovule develop into the seed coat and others into the endosperm which contains food. • Zygote now goes through mitosis to form an embryo. Mature bean seed Seed coat
In Angiosperm the developing seed is surrounded by the walls of the ovary. • As the ovary matures it becomes the fruit. Fleshy Dry
Watch a flower develop into a fruit with seeds! Apple animation! http://www.youtube.com/watch?v=bwCpQflmQG4
Can you tell which is which? Fruit Fruit (dry fruit) Seed Fleshy receptacle
If the ovules are not fertilized the ovary does not grow into a fruit. • Can you think of a fruit that you normally eat in which the last statement might not be true? Parthenocarpic (seedless) fruits
Seed Dispersal in Angiosperms • The fruit of an angiosperm aids in its dispersal. • Dispersal is the transport of the seed away from the parent. • Some launch their own fruits • Some need help from outside agents • Wind, animals, water
Seed Dispersal in Angiosperms Can you think of other seed dispersers?q Watch Seed dispersal Video!
Seed Dispersal in Angiosperms But why is seed dispersal important? Brainstorm activity: Form teams of three and discuss with your teammates why is seed dispersal important. Make a list with all the fruits that you know and their mechanisms for seed dispersal. Can you name at least 4 seed dispersal methods? Why do you think that some fruits that are red and tasty when ripe, are toxic (poisonous) when green?
Germination and Growth • Germination - the process in which a seed begins to grow, • Some seeds can lay dormant for years. • What process is going on at the cellular level?
Sexual Reproduction of Gymnosperms • The life cycle is similar to angiosperms. • Gymnosperms do not bear flowers. • These plants are called conifers. • Usually male and female cones are produced in the same trees. • Seeds contain an embryo, food supply, and a coat - but no fruit.
