Bio Lab Wksht & HW Questions 73

Bio Lab Wksht & HW Questions 73 - at the end of the...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
68 F. The Female Gametophyte Examine a cross-section of a Lilium (lily) ovary and identify the ovules. Each ovule is attached to the ovary by a stalk called the funiculus, which may be visible. Label the ovule below to indicate the funiculus, integuments, nucellus (modified megasporangium wall), micropyle and the megaspore mother cell . In typical angiosperms, the megaspore mother cell inside the nucellus divides meiotically to produce four haploid nuclei. Three degenerate, and one undergoes mitosis three times to result in eight haploid nuclei (cell membranes develop around them later). These nuclei comprise the female gametophyte, or embryo sac. Examine the prepared slide of a Lilium embryo sac at the eight nucleate stage on demonstration. Although it is unlikely that all eight nuclei will be visible, you should look for the some of the following: three antipodal cells
Background image of page 1
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: at the end of the embryo sac (opposite the micropyle); two nuclei in the central region of the embryo sac, termed the polar nuclei ; and three nuclei at the micropylar end of the embryo sac, consisting of two synergids surrounding an egg. During the process of double fertilization , one sperm nucleus fuses with the egg to form a zygote (2n), which eventually divides by mitosis to become the embryo. The second sperm nucleus does not degenerate (unlike fertilization in conifers), but instead fuses with the two polar nuclei to form the endosperm nucleus (3n) . The endosperm nucleus then divides to form endosperm tissue, which provides nutrition for the developing embryo. The fertilized ovule is termed a seed. Seeds remain inside the ovary, which develops into the fruit (see Section H). Draw an embryo sac and label all of the nuclei visible....
View Full Document

{[ snackBarMessage ]}

Ask a homework question - tutors are online