Explanation:
Homologous chromosomes are 2 physically different chromosomes that have the same genes but are not genetically identical. Sister chromatids are 2 copies of a single chromosome and so are genetically identical (they also are physically attached to one another).
Lichens are typically the first organisms to colonize bare rock. They are therefore the pioneer species in primary succession. Many organisms require soil before they can colonize an area. Lichens that colonize bare rock secrete acids that break down the rock and start the soil-production process.
Answer/Explanation:
We are not told if the plant has 20 chromosomes in total or 20 pairs of chromosomes. E.g. a human has 23 chromosomes, but we are diploid, so there are 46 chromosomes present in most cells.
An exception to the rule is the gametes, or the sex cells, where we are haploid. We have 23 chromosomes in these cells.
Pollen cells in plants are the sex cells. Therefore, they are haploid. If we assume that 20 chromosomes is the haploid number (and there are therefore 20 pairs of chromosomes) then the pollen will have 20 chromosomes.
If we assume that 20 chromosomes is the diploid number (and therefore there are 10 pairs of chromosomes), then the pollen will have 10 chromosomes.
