Reproduction in Organisms

The correct sequence of hormones during gametogenesis is as follows :

(B) Gonadotropin-releasing hormone from hypothalamus : This is the first step as the hypothalamus releases gonadotropin-releasing hormone (GnRH).

(E) Gonadotropins from the anterior pituitary gland : GnRH stimulates the anterior pituitary to release gonadotropins, luteinizing hormone (LH), and follicle-stimulating hormone (FSH).

(A) Gonadotropin LH stimulates synthesis and secretion of androgen : LH stimulates the Leydig cells in the testes to produce androgens.

(C) Androgen stimulates spermatogenesis : Androgens, such as testosterone, stimulate the process of spermatogenesis.

(D) Gonadotropin FSH helps in the process of spermiogenesis : FSH stimulates the Sertoli cells in the testes, which help in the process of spermiogenesis, the transformation of spermatids into mature spermatozoa.

So, the correct answer is Option C : (B), (E), (A), (C), (D).

China rose, Tomato, Petunia and Lemon show axile placentation.

Dianthus and Primrose show free central placentation.

Pea, Lupin and Beans show marginal placentation.

Cucumber and mustard show parietal placentation.

Conidia are the asexual reproductive structures produced in Penicillium.

Gemmules are produced in sponge

Buds are produced in Hydra

Zoospores are produced in Chlamydomonas

Plants like Selaginella and Salvinia produce two kinds of spore i.e., microspores and macrospores. They are known as heterosporous.

Most of the pteridophytes produce single type of spores and are called homosporous

Sorus are brownish or yellowish cluster of spore-producing structures located on the lower surface of fern leaves.

$\bullet$ When male and female sex organs are present on same plant body, such plants are said to be monoecious.

$\bullet$ Most of the species of Chara are monoecious as it has oogonium (female organ) and antheridium (male organ) on the same plant.

$\bullet$ When both reproductive structures are present on different plants then this condition is called dioecious. Cycas circinalis, Carica papaya and Marchantia polymorpha are dioecious.

Bamboo species are monocarpic i.e., flower generally only once in its life-time after 50-100 years.

An offset is a small, virtually complete daughter plant that has been naturally and asexually produced on the mother plant. They are clones, meaning that they are genetically identical to the mother plant. Offset is a vegetative part of a plant, formed by mitosis.

Potato, banana and ginger propagate vegetatively by their modified stems. Potato propagates by tuber which has buds over its eyes or nodes. These buds produce new plantlets. Banana and ginger propagate with the help of rhizomes which also have buds on nodes for the formation of new plantlets.

Sexual reproduction involves formation and fusion of male and female gametes. Gamete formation is accomplished through meiotic cell division which involves crossing over between non-sister chromatids of homologous chromosomes leading to new genetic recombination in gametes. Random fusion of these male and female gametes lead to the genetic variability in the offspring which although resemble their parents but also exhibit new traits of their own.

Binary fission usually takes place in Amoeba, Paramoecium and Euglena.

Vegetative propagation takes place through rhizome in ginger.

In oogamy male and female gametes are morphologically as well as physiologically different. Female gametes are large and nonmotile. Male gametes are small but motile.

There are two mechanisms of regeneration: morphallaxis and epimorphosis.
(i) Morphallaxis - It involves the reconstruction of the whole body from a small fragment by reorganising the existing cells. The regenerated organism is smaller than the original one, e.g., Amoeba. However, after the completion of the process it grows and attains normal size after some time.
(ii) Epimorphosis - It replaces a lost organ of the body by proliferating new cells from the surface of the wound or injured part. Regeneration of an appendage in an arthropod, arm in a starfish, and tail in a lizard occurs by the process of epimorphosis.