Question

Ovules occur along the ventral suture over a ridge in two rows in _____________ placentation.
A. Marginal
B. Parietal
C. Axile
D. Free central

Answer 1

Hint: Placentation relates to the formation, type, and structure, or arrangement of the placenta. The placentation transfers the nutrients, gases, and water to the growing embryo from maternal tissue.

Complete answer:
The arrangement of the ovules on the placenta in the ovary within the ovary wall is called placentation. In the placenta, placenta links to the ovule in the ovary. The placenta is usually found at the margins of a leaf. Placentation is usually sub marginal in position in a simple pistil.
There are various types of placentation as observed as the arrangement of ovules can be different. Five basic types of placentation have been observed which are, a) marginal placentation, b) parietal placentation, c) axile placentation, d) free central placentation, and e) basal placentation.
Marginal placentation is found in Leguminosae plants such as pea plants. In this type of placentation, a lengthy placenta found in the side of the unilocular ovary, the placenta forms a ridge along the ventral suture of the ovary and ovules generate two separate rows. Here the ovules are connected at the carpel’s margin
When the ovules generate on the inner walls of the ovary, the ovary is said to be of parietal placentation. Though it is single-chambered, when a false septum is formed, it becomes two-chambered. This is noticed in the cucumber plant.
In the case of axile placentation, the placenta is axial in position and ovules are attached to the axial. In this case, the carpels are folded. This type of placentation looks into lemon and tomato etc. In the free central placentation, the ovules formed on the central axis and septum are absent. This type of placentation is noticed in Dianthus and primrose. In this type of placenta, the placenta develops from its base and a single ovule is found connected to the base. In sunflower and marigold, this type of placentation is found.

Therefore, the correct and appropriate option is option A.

Note:
Placentation refers to the arrangement of ovules on the placenta in the ovary. According to the arrangement of ovules there are five basic types of placentation. Among them, in marginal placentation, ovules develop on the placenta that are found on the ventral suture and form a ridge. It takes place in the margin of the ovary wall.