Biology Test 220

Parietal:

This type of placentation is found in the unilocular syncarpous ovary. In it, the ovule develops on the inner wall of the ovary or on the peripheral part.

Ovary becomes bi or multilocular due to the formation a false septum.

For example, Cucurbita, Argemone and Cruciferae family (Mustard). 

Axile:

It is found in multicarpellary syncarpous gynoecium. The fusion margin of carpels grows inward and meets in the centre of the ovary.

Thus, an axis forms in the centre of the ovary and the ovary becomes multi-chambered. The ovules are borne at the central axis.

A number of these chambers are equal to the number of the carpel.

For example,  Potato, China rose, Onion, Lemon, Orange, Tomato.

Bhojpatra  is derived from Betula utilis.

The para rubber tree is originated in Brazil. Its latex extracted from the tree’s trunk is a major source of natural rubber, which is obtained from vessel

Tunica-Corpus Theory: Schmidt in 1924 postulated tunica- corpus theory on the basis of studies of shoot apices of angiosperm. This theory is concerned with planes of cell division in the apex. In contrast to apical cell theory and histogen theory tunica-corpus theory is applicable only to shoot apex and not to root.

A fourth histogen, the calyptrogen, produces the root cap. The histogens have been thought to lie in linear order in the apex, with the initial cells of the vascular system toward the older part of the root, and those of the cap toward the tip.

Some roots, called adventitious roots, arise from an organ other than the root—usually a stem, sometimes a leaf. They are especially numerous on underground stems, such as rhizomes, corms, and tubers, and make it possible to vegetatively propagate many plants from stem or leaf cuttings.

Here only utricularia is angiosperm

Dryopterris is pteridophyte

Gnetum and taxus are gymnosperms

The xylem formed during the spring season contains numerous large vessels with wider lumen and possess less amount fibres. So, it acquires a greater radial width than the summer wood. The xylem formed during the summer and autumn season is very less amount since the activity of the cambium is highly reduced.

All cells are surrounded by a plasma membrane. The membrane is composed of a phospholipid bilayer arranged back-to-back. The membrane is also covered in places with cholesterol molecules and proteins. The plasma membrane is selectively permeable and regulates which molecules are allowed to enter and exit the cell.

Desmosomes (macula adherens) consists of intercellular thrckening matedals, disc-shaped intracellular thickening adjacent to each membrane with tonofibrils. These act as intercellular cementing material, adhere cells together at places like spot welding.