Reproduction in Flowers

Hermaphrodite

A flower that has both male and female reproductive systems.

Monoecious plant

A plant that has both male and female reproductive organs. Similar to hermaphrodites but monoecious is more specific to plant biology

Dioecious plant

A plant that has an only male or only female reproductive system

Sepal

The part of a flower that protects it when in bloom.

Receptacle

The part of a flower that bears the stamen and carpel.

Stamen

The male reproductive organ of a flower, consisting of the filament and anther.

Carpel

The female reproductive organ of a flower, consists of the style, stigma, ovary, and ovule.

Nectary

A gland found at the base of a flower that produces nectar to attract insects.

Petals

The brightly colored and scented part of a flower that attracts insects.

Ovary

The part of a flower that produces and stores the female gametes called ovules and becomes a fruit after fertilization.

Ovules

Structures within the ovary that contain eggs (ova) and become seeds after fertilization.

Ovum

An female gamete waiting to be fertilized by a pollen grain.

Style

The part of a flower that holds the stigma in place for optimal pollination, and facilitates internal fertilization

Stigma

The surface of a flower that collects pollen for fertilization, and stimulates the germination of the pollen grains to create a pollen tube.

Filament

The part of a flower that holds the anther in the optimal position for pollen delivery, allows materials to pass to the anther.

Anther

The part of a flower that produces pollen grains and delivers them to the stigma.

Pollination

The transfer of pollen from the anther to the stigma of a plant of the SAME species/compatible plant

Requirements for pollination

1. Stigma and anther at same level of maturity

2. Anther must be above stigma

Cross pollination

The transfer of pollen from the anther of one plant to the stigma of another plant of the same species.

What causes a flower to cross pollinate

1. Self incompatibility

2. Anther and stigma at different levels of maturity

3. If the plant is dioecious

Advantages of cross pollination

1. Genetic variation

2. Dispersal of seeds, preventing overpopulation and competition

3. Organisms are more vigorous, able to survive and adapt in changing environments

Disadvantage of cross pollination

1. Dependent on external factors such as wind and insects

2. Thus in adverse conditions where these external factors are limited, so is pollination

3. Requires more energy to produce more gametes since the release of gametes does not guarantee fertilization

Self-pollination

The transfer of pollen from the anther of a plant to the stigma of the same flower or a different flower on the same plant.

Advantages of self-pollination

1. Not dependent on external factors (wind, insects)

2. Can occur despite adverse circumstances

3. Time-efficient as mates do not have to be found

4. Desirable traits are kept

Disadvantages of self-pollination

1. Produces seeds with less vigor

2. Less variation

3. Less dispersal, leading to overpopulation and competition for resources

Wind-pollinated flowers

Flowers with small, dull, and unscented petals,

long style and stigma

long. branched, feathery anther and filament

feathery stigma and style

No nectaries or honey guides

produce more pollen

small, light pollen grains.

Insect-pollinated flowers

Flowers with large, brightly colored, and scented petals

Honey guides

Nectaries!!

style and stigma firmly inside the flower

anther and filament firmly inside the flower

lobed or flat, sticky stigma

produce less pollen

large, sticky, pollen grains.

Fertilization

The process in which the male and female gamete fuse to form a zygote.

Steps of fertilization

1. The pollen grain (male gamete) lands on the stigma (female gamete)

2. The stigma influences the pollen grains to release water and enzymes necessary to create a pollen tube

3. The pollen grains release two sperm nuclei that travel in this pollen tube to the ovary through the micropyle

4. The first sperm nuclei fertilizes the ovum, and the second fertilizes the polar nuclei, forming the endosperm. This is called double fertilization

5. The resulting zygote divides by mitosis to form an embryonic seed — consisting of an embryonic root (radicle), an embryonic shoot (plumule).

6. In endospermic seeds, the endosperm remains, and in non-endospermic seeds, the endosperm is absorbed into the cotyledon

7. The integuments dry up to form the seed coat

8. The ovary wall develops into a fruit, the ovules develop into seed coats

Similarities between human and plant fertilization

• Both involve the male gamete traveling to the female gamete

• Both occur internally, within the parent

• Both form a zygote and an embryo

Differences between human and plant fertilization

• Fertilization happens outside of the ovary in humans, happens within the ovary in plants

• In humans only the ovum is fertilized in plants the ovary ovule and ovum are fertilized

• In humans the parent nourishes the embryo, in plants the parent does not — the resulting seed must survive on its own

• Plants have double fertilization, meaning two sperm nuclei are needed for fertilization. Humans have single fertilization

Seeds contain

• embryonic root

• Embryonic shoot

• cotyledon/endosperm

• testa

Fruit development

The process in which the ovary develops into a fruit after fertilization.

Fruits scars

1. from the style

2. from the receptacle

Pericarp

The three layers of a fruit, including the exocarp (outside layer), mesocarp (middle layer), and endocarp (inner layer).

Seed dispersal

The mechanisms by which seeds are spread away from the parent plant.

Importance of seed dispersal

1. Reduces overpopulation and thus competition

2. Promotes colonization of new areas

3. Increases variation within a species when they are brought to new areas

Animal dispersal

Seed dispersal through animals eating fruits and either spitting out or excreting the seeds.

e.g tomato, castor oil seed,

Wind dispersal

Seed dispersal through lightweight seeds with wing-like features or feathery extensions.

e.g. poui seed, silk cotton seeds

Water dispersal

Seed dispersal through seeds with a waterproof exocarp that allows them to float downstream.

e.g. coconut

Mechanical dispersal

Seed dispersal through dry plants automatically opening along points of weakness to eject seeds.

e.g. pride of Barbados

Lateral meristem

a meristem that is responsible for the growth in width of the plant (e.g. cambium p)

Apical meristem

A meristem that is responsible for the growth in height of the plant