Plant Life Cycles Modern Biology Chapter 32. Alternation of Generations: the overview.

Plant Life Cycles

Modern Biology Chapter 32

Alternation of Generations: the overview

Mosses: Structures involved

• What you associate with mosses is a gametophyte

• Gametophytes are haploid

…Because repetition is the spice of life!

Mosses: Development/ Growth

• Mitosis occurs producing a diploid sporophyte• Sporophyte remains attached to the

gametophyte– Diploid – Sporophyte cannot feed itself, but is genetically

different than the gametophyte

Mosses: The next generation…

• Diploid sporophyte produces cells that undergo meiosis; this produces haploid organisms, or gametophytes.

FernsFerns

Ferns: Structures involved

• What you associate with ferns is the sporophyte• Sporophyte grows from gametophyte• Gametophytes are tiny (10 mm)

– Antheridium– Archegonium

Ferns: Development/ Growth

• Mitosis occurs producing a diploid sporophyte with fronds

• Sporophyte remains attached to the gametophyte, crushing it as it increases in size

Ferns: The next generation…

• Specialized cells, usually on the underside of the fronds, undergo meiosis and produce spores.

ConifersConifers

Conifers: Fertilization

• Typically the conifers much reach maturity before they can reproduce sometimes up to 30 years.

• Conifers can reproduce without water for the sperm to swim in.

• Sexual reproduction can actually take years

Flowering Plant Life Cycles

Modern Biology Chapter 32

Flowering plants: Structures involved

Ovule: female sex cell

– Consists of a mega sporangium surrounded by two integuments

Ovule: female sex cell

– One large diploid megaspore mother cell undergoes meiosis and produces 4 haploid megaspores

Ovule: female sex cell

– One megaspore enlarges and the other three wither away….

Ovule: female sex cell

– Remaining mega spore undergoes three mitotic divisions to produce 8 haploid nuclei

Ovule: female sex cell

– Two nuclei move to the center of the cell while the remaining 6 move to the polar ends- three to each side

Ovule: female sex cell

– Cell walls form around the 6 nuclei at the ends

– One of these 6 cells becomes the egg, (the others die at fertilization)

– Embryo sac consists of 7 cells and 8 nuclei- this is the mature female gametophyte

Pollen: male sex cell– Microspore mother cells undergo meiosis and produces 4 haploid microspores, each of which undergoes mitosis to form two haploid cells

Pollen: male sex cell

– Wall develops around microspores and the two celled structure is a pollen grain- this is the mature male gametophyte

Pollen: male sex cell

– The larger cell will produce the tube cell containing the tube nucleus.• When attached, the tube nucleus will make a pollen tube

– The smaller cell is the generative cell• It will undergo yet another mitotic division to produce

two sperm

Flowering plants: Fertilization (Double

Fertilization)• Pollen tube grows from pollen (takes about a day)

Flowering plants: Fertilization (Double Fertilization)

• The two cells produced from the generative cell enter the ovule through the pollen tube– One of the sperm fuses with the egg to

form a diploid zygote• This will be the embryo

Flowering plants: Fertilization (Double Fertilization)

• The two cells produced from the generative cell enter the ovule through the pollen tube– The other sperm fuses with the two nuclei in the megaspore to produce a triploid nucleus.

• This will be the endosperm- the nutrients contained within a seed so that the embryo has energy to remain alive and begin the growth process

Video!!

Flowering

plants:

Seed structure

Flowering plants: Seed germination• Seeds can remain dormant for many years• When the conditions are right, the seed will

germinate

Flowering plants: Seed germination• Typically roots come before leaves

Flowering plants: fruit