CHARACTERISTICS OF THE PHYLUM MOLLUSCA

The name mollusca comes from the Latin word mollusc meaning soft. They are invertebrates with about 110,000 living species. Most are marine but there are few freshwater and terrestrial mollusk. They possess a visceral mass which contains the internal organs, a mantle which is a covering that lies to either side of but does not completely enclose the visceral mass. It also possess a foot which is a muscular organ that may be adapted for locomotion, attachment, food capture or a combination of functions. Another  feature is the radula, an organ that bears many rows of teeth and is used to obtain food. There is a  nervous system consisted of ganglia connected by nerve cords. The coelom is reduced and is largely limited to the region around the heart. Most mollusks have an open circulatory system. Some mollusks are slow moving and have no head, many others undergo marked cephalizatoion.

MYCORRHIZA

DISCOVERY:
Associations of fungi with the roots of plants have been known since at least the mid-19th century. However early observers simply recorded the fact without investigating the relationships between the two organisms. This symbiosis was studied and described by Franciszek Kamieoski in 1879–1882. Further research was
carried out by Albert Bernhard Frank, who introduced the term mycorrhiza in 1885.
 DEFINITION:
Mycorrhizas are symbiotic relationships between fungi and plant roots (the term means literally 'fungus
root'). Perhaps more than 80% of the species of higher plants have these relationships, and so do many
pteridophytes (ferns and their allies) and some mosses (especially liverworts). They are as common on crop plants (cereals, peas, tomatoes, onions, apples, strawberry, etc) as in wild plant communities, and in several cases they have been shown to be important or even essential for plant performance.

PLANT TISSUES

They are the tissues that are responsible for the chemical reactions and metabolisms undertaken by a plant. They are divided into different groups depending their function and origin. Plant tissues are broadly categorized into three 1. Epidermis 2. Vascular 3. Ground tissues.

Epidermis - Cells forming the outer surface of the leaves and of the young plant body.

Vascular tissue - The primary components of vascular tissue are the xylem and phloem. These transport fluid and nutrients internally.

Ground tissue - Ground tissue is less differentiated than other tissues. Ground tissue manufactures nutrients by photosynthesis and stores reserve nutrients.

Plant tissues are further divided into 1. Meristematic tissues and 2. Permanent tissues.

CELL PHYSIOLOGY

Cell physiology (including cellular electrophysiology) is the biological study of the cell's mechanism and interaction in its environment. The term "physiology" refers to all the normal functions that take place in a living organism. Absorption of water by roots, production of food in the leaves, and growth of shoots towards light are examples of plant physiology.  The heterotrophic metabolism of food derived from plants and animals and the use of movement to obtain nutrients (even if the organism itself remains in a relatively stationary position) are characteristic of animal physiology. These are the parts of cell and their functions.

ARTIFICIAL ENVIRONMENTS

They are also known as artificial ecosystems or man made ecosystems.

DEFINITION

They are environment or ecosystem produced, controlled and manipulated by man or human beings. Artificial environments are environments which rely on human efforts to sustain.They don’t have self regulating mechanisms.

  They have almost no diversity and have simple food webs. The cycling of nutrients is negligible. Inputs in these environments or ecosystems are provided by human efforts.

THE HARDY-WEINBERG EQUATION

INTRODUCTION

Godfrey Hardy and Wilhelm Weinberg are credited with independently generating the mathematical

HARDY

relationship behind the Hardy-Weinberg principle in 1908. The principle describes how genetic alleles will be inherited from generation to generation and was the foundation to the study of population genetics. Diploid organisms, all animals and many plants, have two copies of an allele, one from each parent. The Hardy-Weinberg principle calculates the proportion of the population with a given combination of alleles, or genotype.

WEINBERG

THE HISTORY OF VIRUSES

The name virus was coined from the Latin word meaning slimy liquid or poison. It was originally used to describe any infectious agent, including the agent of tobacco mosaic disease, tobacco mosaic virus. In the early years of discovery, viruses were referred to as filterable agents. Only later was the term virus restricted to filterable agents that require a living host for propagation. The history of viruses dates back as far as 2300 BC. These are the major discoveries in the history of viruses in the 18^th and the 21^st century.