Question

Describe the three main reasons why multicellular organisms need their cells to divide. Which of
these are accomplished by mitosis and which are accomplished by meiosis? In which types of cells
do mitosis and meiosis each take place? Does either mitosis or meiosis change the number of
chromosomes in a cell?

Describe the structure of chromosomes. Define and distinguish the following terms: unduplicated
(single-stranded) chromosome, duplicated (double-stranded) chromosome, chromatid, and
centromere. What process needs to occur before any cell division takes place?

Answer 1

1. multicellular organism use cell division for growth and the maintanance ,repair of cells and tissues, reprooduction.
2. mitosis helps in growth of multicellular organisms., it also useful in replacement of lost cells,meiotic division results in 4 haploid gamates,it avoid unnecessary duplication of chromosomes in fertilization, produce genetic variation.
3. Mitosis takes place in somatic cells (vegetative cells). Meiosis takes place in reproductive cells (germ cells ).
4. In meosis reduction of chromosome no takes place . chromosome number changed to half.
5. structure of chromosomes- structure consists of chromatid , centromere, telomere, secondary constriction and satellite, chromomere.

• chromatids-each metaphase chromosomes appears to be longitudinally divided into two identical part each ot it known as chromatids.
• centromere- the point where the chromatids are joined or fused together are called centromere.
• telomere- the two ends of chromosomes are called telomere
• secondary constriction and satellite- constriction inaddition to centromere. the region between secondary constriction and telomere is called satellite.
• chromomere-in some species during pachytene stages small bead like structures are formed called chromomere.

6.unduplicated chromosome- chromosomes with single linear strands

duplicated chromosomes- contain two identical copies joined by centromere.

7.before cell division the cell grows and prepare for cell division.the nucleus and cytoplasm are metabolically very active and the amount of DNA become doubled.