Sexual reproduction and alternation of generations
Answers are for parents and teachers.
1
A filament alga has N = 14. How many chromosomes has the zygote? After meiosis in the zygospore, how many nuclei form, how many survive, and how many chromosomes does each survivor have?
The zygote has 14 + 14 = 28 (2N). Meiosis gives 4 nuclei; 1 survives and 3 degenerate. The survivor has 14 chromosomes.
2
Sexual reproduction costs more time and energy. Give one reason why it still helps a population when the surroundings change.
The young receive new combinations of features from two parents, so the population has more variety and some young may suit the changed surroundings.
3
A gonad cell with 2N = 36 divides by meiosis to make male gametes. How many chromosomes has each gamete? How many male gametes come from 25 such original cells?
36 ÷ 2 = 18 chromosomes. 25 × 4 = 100 male gametes.
4
In the fern life cycle, name the haploid generation, say what it makes, and say what fertilization restores.
The gametophyte is the haploid generation and it makes the gametes (sperm in antheridia, eggs in archegonia). Fertilization restores the diploid number, 2N, in the zygote.
5
Why is the life cycle of Plasmodium an example of alternation of generations? Where in the mosquito do the new sporozoites finally gather?
It has a sexual generation (gametes fusing in the mosquito) and asexual generations (schizogony in humans, sporogony in the mosquito). The sporozoites move to the salivary glands of the mosquito.