Why reproduce? Asexual reproduction
Answers are for parents and teachers.
1
A fish lays 6000 eggs and 1 egg in every 1500 grows into an adult. How many adults is that? Compare with a bird that lays 3 eggs and cares for them, and say what the comparison shows.
6000 ÷ 1500 = 4 adults. The bird has far fewer eggs, but its care means most of its young survive. Where the young are protected, a small number is enough; where most are lost, many are needed.
2
A bacterium divides by binary fission every 30 minutes. How many bacteria come from one after 2.5 hours, if none die?
2.5 hours = 150 minutes, and 150 ÷ 30 = 5 divisions. 2 × 2 × 2 × 2 × 2 = 32 bacteria.
3
A cell with 2N = 20 reproduces by binary fission. How many chromosomes does each new individual receive, and how many individuals are there after three rounds of division?
Each receives 20 chromosomes, a complete set, because mitosis copies the set. After three rounds there are 2 × 2 × 2 = 8 individuals.
4
A queen lays 90 eggs and 20 are not fertilized. How many drones can develop? If a worker has 24 chromosomes, how many has a drone?
20 drones develop from the unfertilized eggs. A drone is haploid, so it has 24 ÷ 2 = 12 chromosomes.
5
Why is tissue culture useful for a rare plant that is hard to grow from seed?
Each piece or isolated cell carries all the genetic information, so a piece grown in a nutrient medium with plant hormones can become a whole plant. Many identical plants can be made from one.