Each cell is alive even if it is part of a multi celled body, and all living organisms consist of one or more cells. Also, cells reproduce by dividing so it follows that all existing cells must have arisen by division of other cells. As a cell divides it passes it hereditary material- its DNA- to offspring.
Ans.
Heterozygous organisms show presence of two alternatives alleles for same trait. For plant height, a heterozygous tall plant, will show both the T (for tallness) and t (for shortness) alleles, as T allele is dominant over t allele. When a cross is made between heterozygous tall plants (Tt), there are 50% chances that a randomly selected allele will carry allele for shortness (t) as shown below:
Thus, "the probability that a randomly selected gamete will carry 't' allele in a cross between heterozygous tall pea plants, is 1/2."