Exercise 05

Principle: In flowering plants, female gametophyte (embryo sac) is a microscopic structure situated deep inside the ovule. An ovule generally has one female gametophyte. Development of female gametophyte begins with megaspore mother cell. Most common type of female gametophyte is the monosporic, 8-nucleate, 7-celled type.

Requirements: Permanent slides of V.S. of ovary, photographs/chart or models showing stages of female gametophyte development and microscope

Procedure:

(i) In a V.S. of ovary we generally find several ovules. Carefully observe each ovule and locate as many stages of female gametophyte development as possible.

(ii) Draw the diagrams as observed under microscope.

Observation:

(i) Record the features of ovule like number of integuments, nucellus and micropylar and chalazal poles. Fig 5.1 shows the female gametophyte (embryo sac) as seen in a V.S. of an ovule. Different stages of development of female gametophyte are shown in Fig. 5.2.

(ii) Observe the placement of embryo sac close to the micropylar pole.

(iii) Note the contents of embryo sac, namely, an egg apparatus (2 synergids and egg) at micropylar end, secondary nucleus in the center and three antipodal cells at the chalazal end (Fig. 5.2).

Questions:

1. Explain the difference between gamete and a gametophyte.

2. Name two differences between synergids and egg.

3. What is the function of polar nuclei?