Transcript Plant Reproduction

Plant Reproduction
Sexual Plant Reproduction – Seed
AG-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: Flowers
AG-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.