Question

The tenuninucellate ovule has
(A) Large amount of nucellus
(B) Small amount of nucellus
(C) Micropylar nucellus
(D) Chalazal nucellus

Answer 1

Hint: Ovule has either one layer or no layer of cells found between megasporophyte and epidermal cells during megasporophyte development.

Complete answer: In the early development of megasporophyte, the existence of no cells or a single cell layer seen between megasporophyte and the epidermal cells is termed as tenuinucellate.
The mega sporophyte grows into the embryo sac containing an egg which will develop into an embryo if fertilized and the parameters are appropriate. In tenuinucellate ovules, the nucellus gets degenerated before the maturation of the embryo sac; it does not expand through cell division and forms an enlarged nucellus. Therefore the tenuninucellate ovule has a small amount of nucellus.

Now lets us find the solution from the given options:
1. Large amount of nucellate is found in crassinucellate ovules, in this the nucellus gets expanded through division of cell during development of embryo sac.
2. Next, a small amount of nucellate is found in the tenuinucellate ovule as the nucellus before the development of embryo sac gets degenerated and embryo sac does not get matured.
3. In micropylar nucellus the egg and embryo are also separated from the integuments at the micropyle.
4. Chalazal nucellus degenerates the ovule at the end of the division. Three antipodal cells formed on the chalazal end. The central cell is large and consists of two polar nuclei.

Hence, the correct option is (B) i.e., Small amount of nucellus.

Note: The megasporophyte develops into the embryo sac that consists of the egg which if fertilized form the embryo, this function contains a large amount of nucellus and takes place in a crassinucellate ovule.