HL Bio - Unit #5.2: Flowering Plants

Stamen

Male Plant Structures

Anther - male

Contain the pollen grains

Filament - male

A stalk that support the anther

Pollen Grains - male

Found within the anther (Flower semen)

• A diploid cell that divides via meiosis to produce 4 haploid cells which each develop into pollen grains

  • Each pollen grain divides once more via mitosis to produce three haploid nuclei 

    • 2 of those nuclei are the male gamete

    • The other nuclei expresses itself during fertilization where it develops into a pollen tube that is used to connect the pollen to the ovule

Carpel

Female Plant Structures

Stigma - female

THe part of the plant where pollen is received

Style - female

Connects the stigma to the ovary

Ovaries

A round section of the flower near the base before the stem begins

Ovule

Found within the ovary

On diploid ovule divides via meiosis to produce 4 haploid cells, where only one of the 4 haploid will divide once more via mitosis 3 times to produce 8 haploid nuclei

• Only one of those 8 haploid is the female gamete/egg, the rest are polar bodies that assist in fertilization and embryo development

Pollination

The transfer of pollen from one plants anther to the stigma of another plant

Wind Pollinated

• Method of the plant relying on the winds breeze to spread its pollen and pollinate other plants

Structure: 

1. Smaller in size and do not have scents or produce nectar

2. Anthers have a larger number of pollen grains

3. Longer stamens that protrude out of the flower

4. Less petals or smaller petals

5. Feathery stigma to catch the pollen

Insect/animal Pollinated

Uses pollinators

• A symbiotic relationship where 

  • Pollinators gain food (nectar) and plants are able to transfer their pollen

Structure:

1. Flowers are large and brightly color to attract insects

2. Scents are secreted to advertise the flower

3. Large and spiky pollen grains to stick to insects

4. Large and sticky stigmas for easier pollen collection

5. Nectarie Glands that secrete sugar solutions (nectar) that are energy sources to insects 

   • Deep inside so insect is forced to get pollen on them

Self-Pollination

Pollen from the same plant is transferred to its own stigma (Continuity)

Many plants are hermaphrodites:

hermaphrodites

Meaning they have both male and female structure and produce both pollen and ovules

Cross-Pollination

The transfer of pollen from the anther of one plant to the stigma of another plant (genetic variation and evolution!!)

• Also causes Hybrid Vigor: where the offsprings are stronger and healthier due to different alleles

Promotion of cross Pollination:

1. Anthers and stigma maturing at different stages of the plants life

2. Complete separation of male and female parts of the same plant 

3. Separation of male and female parts on different plants

4. Self-Incompatibility Mechanism

Anthers and stigma maturing at different stages of the plants life

• Protandry: Anthers of the plant develop first

  • Eg, Foxglove

• Protogyny: Stigmas of the plant develop first

  • Eg, Sacred lotus

Separation of male and female parts on different plants

• Hermaphrodites: Both male and female parts in the same place

• Monoecious: Separation of the male and female parts of the plant 

• Dioecious: Complete separation of the male and female parts (2 different plants)

Self-Incompatibility Mechanism

Genetic process that doesn’t allow the pollen to fertilize the ovule by having different alleles that are allowed to fertilize and others that can’t

Essentially the stigma will have “gates” that only allow certain alleles (genetic varieties) to pass while all others can’t

• In this case the alleles of the plant are those that will not be allowed to entered

Fertilization

The process that occurs once the male gamete (Pollen) reaches and enters the ovule within the ovary

• A long tube that goes down the style carries the male gamete down towards the ovary 

Zygote

The development of an embryo which further develops into a seed

• Ovules will develop in the seeds of the plant while the ovaries develop into the fruit/ the flesh 

  • The fruit provides nutrition for the developing embryo within the seed

Radicle

Embryos root

Plumule

Embryos shoot

Testa

Seed coast

Micropyle

Tiny pores close to the scar that allows for water uptake

Cotyledons

The embryonic leaves that store energy for germination

Epicotyl

Embryonic Stem above the point of attachment of the cotyledon

Hypocotyl

Below the attachment on the cotyledon

Seed dispersal

The process of the plants seeds being spread around either by the wind or by animals

• This process occurs to prevent seeds from germinating too close to the parent plant as they will need to fight for resources - dispersal reduces competition 

Methods of dispersal:

1. Animals: By having the animal eat the fruit and drag the seed along with 

2. Wind: Having the wind take the seed along with its current

3. Water: Traveling the seed by the stream of the water

4. Explosion: The plant has evolved to have mechanism that will “explode” the ovary containing the seeds to allow for a larger range of dispersal when the seeds fall

Germination

1. The radicle emerges first to anchor the seedling into the soils water and absorb the water/minerals

2. Embryonic stem emerges as the testa splits away from the cotyledons with the hooked plumule protecting the leaves from damage by particles

3. Stem grows upwards while retaining its hooked shape

4. Foliage leaves begin to show the plumule emerges above the ground and starts to straighten to lift the foliage leaves

   • Furthermore, Amylase breaks down stored starches to maltose 

   • Hydrolysis also breaks maltose into glucose that is used during respiration for the growing tissues of the cotyledon