Dr. Shaista Qadir

Amino Acids

Amino acids are important biochemical molecules. They contain both a carboxyl group (COOH) and an amino group (NH2). The general formula for an amino acid is H2NCHRCOOH where R is the functional group of the amino acid. There are 20 amino acids derived from proteins. Proteins occur in great variety, thousands of different types may be present in a single cell. Moreover, proteins exhibit great diversity in their biological function. Their central role is made evident by the fact that proteins are the most important final products of the information pathways existing in living organisms.

A General Account of Primitive Angiosperms

The angiosperms are the largest group of land plants and one among the five groups – Angiosperms, Cycadales, Coniferales, Gingoales and Gnetales of extant seed plants. Despite their relatively recent origin, this group is extremely diverse morphologically, taxonomically and ecologically. A number of angiosperms living today are characterized by many extremely primitive features. They are which Darwin called “living fossils”. These are invaluable relics of the early stages of the angiosperm evolution.

Plant body architecture – Basic body plan and modular growth

Plant bodies do not have a fixed size. Parts such as leaves, roots, branches, and flowers all vary in size and number from plant to plant—even within a species, although all of them are produced from a simple structure called the embryo. The latter has a limited number of parts-frequently only an axis bearing one or two cotyledons that too with low level of cellular and tissue differentiation. However, the embryo has a potentiality for further growth because of the presence of apical meristems at two opposite ends that form future shoot and root.

SHOOT APICAL MERISTEM

In the early stages of development of the plant embryo all the cells undergo division, but with further growth and development cell division and multiplication become restricted to special parts of the plant which exhibit very little differentiation and in which tissues remain embryonic in character and the cells retain the ability to divide.  These embryonic tissues in the mature plant body are called meristems. Amongst the vascular plants, the meristems first appear in the embryonic shoot and root.

DIVERSITY OF LEAF SIZE AND SHAPE

Leaf is an above-ground, green,flattened, lateral structure attach- ed to a stem and functioning as the principal organ of photosynthesis and transpiration in most plants. Leaves are typically flat (laminar) and thin, which evolved as a means to maximise the surface area directly exposed to  light. All leaves are not photosynthetic as they may be modified wholly to bud scales and spines or partly to form tendrils. Not all plants have true leaves.

EPHEDRA-MORPHOLOGY, AND REPRODUCTION

Ephandra a genus of shrubby perennial gymnosperm, belongs to the family, Ephedraceae and order Ephedrales. Ephedra can be found in the arid and semi arid regions of Asia,Europe,NorthAfricaWertern North America and South America.The plant is branched, with characteristic jointed, fistular and green stems. Leaves are very small,scaly,usually opposite decussate. Each scaly leaf shows a thick midrib within a thin border,which very rarely shows any stoma.

SEED - A UNIT OF GENETIC RECOMBINATION AND REPLINISHMENT

Seeds provide an important role in maintaining continuity between successive generations among spermatophytes, as the new offspring is packaged within it. The seeds of angiosperms develop from the ovule as a result of double fertilization. A mature seed is protected by seed coat and supplied with stored nutrients. Seed formation depends on normal meiosis to produce viable gametes. Seeds are typically produced from sexual reproduction. It is the formation of offsprings by the fusion of gametes, which necessarily involves reduction division called meiosis.

NODAL ANATOMY

The aerial portion of a vascular-plant sporophyte is composed of shoots. A shoot consists of a stem, branches and its attached leaves. The stem is divided into nodes and internodes.The central vascular network of the shoot and the root is called the stele. Stellar pattern at the node is different from that of the internode Nodes are complex anatomically, because it is here that the vascular tissues of the lateral appendages, such as branches and leaves, are connected with those of the stem with the help of leaf traces and leaf gaps.

ADAPTATION OF ROOTS FOR REPRODICTION AND INTERACTION WITH MICROBES

The roots constitute the lower portion of the plant axis that tends to grow downwards, away from light and towards water. As a general rule, they bear neither leaves nor buds. Their main roles are anchorage, absorption and transport of food, water and minerals to and fro from the plants. However, roots have adapted to fulfill a variety of other special functions including storage, support, aeration as well as reproduction. Reproduction by roots is one of the modes of vegetative/asexual reproduction that plants exhibits.

Growth Rings: Characteristics

A growth ring/tree ring/annual ring is a layer of wood (xylem) produced during a tree's growing season. Each tree ring marks a line between the dark late wood that grows at the end of the previous year and the relatively pale early wood that grows at the start of current year. One annual ring is composed of a ring of early wood and a ring of late wood. The early wood and late wood differ distinctly in the cell size and cell types that they are composed of. Both the cell types contribute to tree's growth in diameter.

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