Plant Reproduction

Sexual Plant Reproduction – SeedAG-BAS-8-b, SB2, SB2 (e)

What is a seed?

• Seeds are containers of new life.– Seeds are formed in the ovaries of flowers, which

become fruit.– Seeds ensure continuing life as well as provide

food and other products

Kinds of Seeds• Monocot– Monocots are plants that have a seed with one seed

leaf known as a cotyledon.• The embryo in the seed will have one leaf.• As the embryo grows, the leaves develop with parallel

venation.– Corn, wheat, rice, all grasses

• Dicot– Dicots are plants that have a seed with two

cotyledons. • The embryo in the seed has two leaves.• Leaves of a dicot have net venation.

– Tomatoes, beans, petunias, trees

Parts of a seed - Dicot

• Outside– Seed coat– Hilum– Micropyle

• Inside– Cotyledons– Radicle– Hypocotyl– Epicotyl– Plumule

Parts of a seed - Monocot• Outside– Seed coat– Seed scar– Silk scar

• Inside– Endosperm– Radicle– Hypocotyl– Epicotyl– Cotyledon– Plumule

Plant Reproduction

How Seeds are Formed: FlowersAG-BAS-8-(c, d), SB2, SB2 (e)

What is a flower?

• A flower is the reproductive part of a flowering plant.

• They are modified leaves.– Some have attractive colors and fragrances– This is to attract pollinators

Types of Flowers

• Flowers are categorized in two ways– Complete or incomplete– Perfect or imperfect

Complete Flower

• Has all 4 parts:– Sepals – protects the developing bud– Petals – attracts pollinators– Stamens – male reproductive structure– Pistil – female reproductive structure

Incomplete Flowers

• They do not have all of the principle parts– Some flowers do not have a sepal and petals. For

example: the flower in wheat and oats.– In some cases the female and male flower parts

are separate on plants.– Both are needed to produce a seed

Perfect vs Imperfect

• Perfect flower: It has the stamen and the pistil in the same flower

• An imperfect flower has the male sex organs or the female sex organs, but not both on the same flower

Monoecious vs Dioecious

• Plants may have both male and female imperfect flowers on them.

• They are called monoecious plants– Corn is a monoecious plant.– Others include: Squash, melons and pumpkins

• Dioecious is when some plants have male flowers and others have female flowers. – Strawberries are dioecious– Also, gourds and bradford pears

Flower combos

• Flowers can be combinations of complete and incomplete and perfect and imperfect– Wheat- incomplete and perfect– Cotton- complete and perfect

Pollination

• The transfer of pollen from an anther to a stigma of a flower of the same species– Pollen may be moved by wind, insects, birds and

other natural means.– Flowers may be cross-pollinated

• Involves two different plants.• Pollen from anther in one plant is moved to the stigma on

another plant.– or self-pollinated

• It involves flowers on the same plant.• Pollen moved from one flower on one plant to another on

the plant.

Fertilization

• It is the union of the pollen cell with the ovule (egg).

• Pollen grain develops two sperm.• One of the sperm unites with the ovule in the

ovary and forms an embryo.• The other sperm forms tissue known as

endosperm in the embryo.

Fertilization• Initiates the growth of the fruit and seed• A flower that is not fertilized will not produce

seed.• An ovary that has been fertilized forms fruit.• In some cases, the ovary grows very large and

has a seed inside.• Some examples are watermelons, cucumbers,

green peppers and tomatoes.• The seeds that are formed are products of the

parents.

Types of Fruits

• All fruit can be classified into two types.– Fleshy• Those that have large fibrous structure surrounding the

seed• Apples, pears, blackberries, oranges, grapes

– Dry• Fruit that develops as a pod or in a hull• Pods can usually be easily divided half.

– Beans, peas, peanuts and cotton have pods• Hull fruits do not have definite seams in the shell

– Pecans, acorns, corn, oats, wheat, dandelions

Seed Scattering

• Some seeds have structures that help them float long distances in the air.

• Some attach to animal coats.• Some are eaten and spread through

defecation. • Some are dropped/buried by animals.• As plants are domesticated, humans develop

systems of dispersing and planting seeds.