1. Modern Biology Chapter 32
Plant Life Cycles
Modern Biology Chapter 32

2. Alternation of Generations: the overview

3. Mosses: Structures involved
What you associate with mosses is a gametophyte
Gametophytes are haploid

5. …Because repetition is the spice of life!

6. 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

7. Mosses: The next generation…
Diploid sporophyte produces cells that undergo meiosis; this produces haploid organisms, or gametophytes.

8. Ferns

9. Ferns: Structures involved
What you associate with ferns is the sporophyte
Sporophyte grows from gametophyte
Gametophytes are tiny (10 mm)
Antheridium
Archegonium

11. Ferns: Development/ Growth
Mitosis occurs producing a diploid sporophyte with fronds
Sporophyte remains attached to the gametophyte, crushing it as it increases in size

12. Ferns: The next generation…
Specialized cells, usually on the underside of the fronds, undergo meiosis and produce spores.

13. Conifers

15. 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

16. Flowering Plant Life Cycles
Modern Biology Chapter 32

17. Flowering plants: Structures involved

22. Ovule: female sex cell
Consists of a mega sporangium surrounded by two integuments

23. Ovule: female sex cell
One large diploid megaspore mother cell undergoes meiosis and produces 4 haploid megaspores

24. Ovule: female sex cell
One megaspore enlarges and the other three wither away….

25. Ovule: female sex cell
Remaining mega spore undergoes three mitotic divisions to produce 8 haploid nuclei

26. 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

27. 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

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

30. Pollen: male sex cell
Wall develops around microspores and the two celled structure is a pollen grain- this is the mature male gametophyte

31. 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

32. Flowering plants: Fertilization (Double Fertilization)
Pollen tube grows from pollen (takes about a day)

33. 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

34. 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

35. Video!!

37. Flowering plants: Seed structure

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

39. Flowering plants: Seed germination
Typically roots come before leaves

42. Flowering plants: fruit