When a reproductive organ grows in size from young age till the organism attains maturity, Mitosis occurs to increase the number of cells and grow in size. During production of gametes, meiosis occurs because the gametes are haploid. When two haploid gametes fuse a diploid zygote is formed which grows into an adult.

They are capable of amoeboid movement and engulf the invading microbes or can neutralise their harmful effects. Thus they help in defence of the body.

1. Umbilical cord consists of stem cells, They are undifferentiated cells which undergo unlimited divisions and give rise to one or more different types of cells. Embryonic stem cells differentiate into different tissues and organs.
2. Stem cells can be used in the treatment of certain degenerative diseases in future

(i) In mitosis one parent cell divides into two identical daughter cells, each with a nucleus having the same amount of DNA, same number of chromosomes and genes as the parent cells. It is therefore called as equational division.
(ii) Meiosis is called reduction division because the chromosome number is reduced to haploid (n) from diploid (2n) in the daughter cells.

(i) During this stage chromosomes become short and thick and are clearly visible inside the nucleus.
(ii) Centrosome splits into two daughter centrioles, they move apart and occupy opposite poles of the cell.
(iii) Each centriole is surrounded by radiating rays, termed as aster rays. Spindle fibres appear between the two centrioles.
(iv) Nuclear membrane and nucleolus disappear gradually

(i) Dense connective tissue is a fibrous connective tissue densely packed with fibres and fibroblasts. It is the prinicpal component of tendon and ligaments.
(ii) Tendons consist of parallel bundles of collagen fibres between which are present rows of fibroblasts.
(iii) Ligaments are highly elastic structures and contain very little matrix.

Loose connective tissue includes the areolar tissue and adipose tissue. The matrix consists of collagen fibres, elastin fibres and fibroblast cells.

Dense Connective Tissue: It is a fibrous connective tissue densely packed with fibres and fibroblasts. It is the principal component of tendons and ligaments.
a. Tendons: They are cord like, strong, structures that join skeletal muscles to bones. Tendons have great strength and limited flexibility. They consist of parallel bundles of collagen fibres, between which are present rows of fibroblasts.
b. Ligaments: They are highly elastic structures and have great strength which connect bones to bones. They contain very little matrix. They strengthen the joints and allow normal movement

It is a part of primary meristem which is detached due to formation of intermittent permanent tissue.