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 plantsThe 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?

Angiosperms

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

Reproductive Organs In AngiospermsReproductive Organs In Angiosperms

Stigma: Sticky tip of the pistil that captures pollen grains

Style: Stalk that supports the stigma and pollen tube growth

Ovary: Swollen base of the pistil containing the ovules

Ovule: Sac containing female gamete

Pistil: female reproductive organ

Anther: Where pollen is produced and stored

Pollen grains: Cases containing male gametes

Filament: Stalk that supports the anther

Stamen: male reproductive organ

Insect-pollinated flowerInsect-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 - SelfPollination - Self

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 - CrossPollination - Cross

Pollination Pollination

What do all these flowers have in common?

Pollination Pollination

What do all these flowers have in common?

Pollination movies

Development of a Pollen Tube

Fertilization in Angiosperms

Once the pollen tube reaches the ovule the sperm fertilizes the female gamete forming the zygote

Pollen tube grows down the style to reach the ovule

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)

SeedFleshy 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 fruitsSome need help from outside agents

Wind, animals, water

Seed Dispersal in Angiosperms

Seed Dispersal in Angiosperms

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.