This preview shows page 1. Sign up to view the full content.
Unformatted text preview: ophytes
- Made of only FOUR cells!
- 1 tube cell (pollen tube)
- 1 generative cell (sperm)
- 2 prothallial cells (sterile; ? function) - Does NOT have an antheridium
- sperm form from generative cell Prothallial cells 41 Pollen tube formation
• After pollen grain arrives near ovule
it begins to develop.
• Tube cell divides into pollen tube
which grows toward developing egg
in archegonium of ♀ gametophyte
• Generative cell moves to tip of tube
and divides into 2 sperm (mitosis)
TAKES ONE YEAR
While this happening… Sperm
nucleus Female cone 42 At time of pollination ovule is immature
(and so is ♂ gametophyte in pollen)
Megasporophyll Ovule =
+ integument (2n) Pollen grain reaches ovule
& pollen tubule burrows through
ovule wall to megaspore inside.
Pollen near ovule Figure 30.6 (4) (Campbell et al.) Megaspore (2n) 43 Ovule maturation
Megaspore (n) TAKES
YEAR female gametophyte (n)
(in archegonium) Megaspore (n) in megasporangium
develops into female gametophyte (n)
which produces egg (gamete)(n)
in archegonium (gametangium) Figure 30.3 and 30.6 (Campbell et al.) 44 Fertilization
pollination POLLINATION FERTILIZATION
Figure 30.6 (Campbell et al.) 45 From Ovule to Seed
Seed = Sporophyte Embryo (2n) + food supply (n) + seed coat After fertilization, seed takes ONE more YEAR to complete development • Fertilized egg (zygote)(2n) develops into embryo (multicellular 2n)
(embryo = new sporophyte)
• Female gametophyte tissue becomes food for embryo Figure 30.3 (Campbell et al) 46 Seed dispersal
occurs a minimum of: POLLINATION • One year
• Two years
after pollination DISPERSAL...
View Full Document