1. Algae
Reproduction of ulva

2. Alternation of Generations
Plants reproduce by switching back and forth between haploid and diploid generations.
This is called alternation of generations.

3. Alternation of Generations
Diploid plants (sporophytes):
They always have a complete set of chromosomes; one from each parent.

4. Alternation of Generations
Haploid plants (gametophytes):
These plants only have one set of chromosomes from one parent only.
In ulva, the sporophyte
and gametophyte
generations look the same!

5. Reproduction of the Ulva
Note:
Isogamy:
Iso = same, gamy = gametes, so gametes of the same size and appearance.
Heterogamy:
Hetero = different, so gametes that are of different sizes.
Syngamy:
The fusion of gametes.

6. Reproduction of the Ulva
Step 1:
The sporophyte develops into a diploid (2N) plant that is identical to the haploid plant.
Step 2:
Specialized cells in the sporophyte undergo meiosis to produce haploid zoospores.
This is asexual.

7. Reproduction of the Ulva
Step 3:
The zoospores do not fuse, instead they divide by mitosis and form different (male /female ) gametophytes.
Step 4:
Gametophytes grow into haploid gametophyte plants.

8. Reproduction of the Ulva
Step 5:
The gametophyte plants produce haploid female and male gametes.
The gametes are not the same size (heterogamy)
Step 6:
The gametes fuse (syngamy) and fertilization occurs.
This is the sexual stage.

9. Reproduction of the Ulva
Step 7:
A diploid (2N) zygote is formed.
Step 8:
The zygote develops into a sporophyte.

10. Reproduction of the Ulva
Asexual stage:
This allows for quick population growth when the conditions are good.
Sexual stage:
This might help algae survive sudden changes in the environment.