A)Levels of Organization of Life

Hierarchy of units
1)Cell:The "cell" is the fundamental structural and functional unit of living organisms.

2)tissue:A "tissue" is a set of differentiated cells organized into a cooperative assembly.

3)Organ:A grouping of tissues into a distinct structure, as a heart or kidney in animals or a leaf or stamen in plants, that performs a specialized task.

4)Organism:An individual form of life, such as a plant, animal, bacterium, protist, or fungus; a body made up of organs, organelles, or other parts that work together to carry on the various processes of life.

5)Population: a group of interbreeding organisms having a quality or characteristic in common .

6)Communities: an assemblage of interacting populations occupying a given area.

7)Biosphere:the part of the earth's crust, waters, and atmosphere that supports life.

B)The Evolutionary Tree of Life

1)Evolution:change in the gene pool of a population from generation to generation by such processes as mutation, natural selection, and genetic drift.
2)Species:the major subdivision of a genus or subgenus, regarded as the basic category of biological classification, composed of related individuals that resemble one another, are able to breed among themselves, but are not able to breed with members of another species.
3)Genus:A taxonomic category ranking below a family and above a species and generally consisting of a group of species exhibiting similar characteristics.
4)Metabolism:The complex of physical and chemical processes occurring within a living cell or organism that are necessary for the maintenance of life. In metabolism some substances are broken down to yield energy for vital processes while other substances, necessary for life, are synthesized.

C)A Provisional Tree of Life

1)Bacteria:Any of the unicellular prokaryotic microorganisms of the class Schizomycetes, which vary in terms of morphology, oxygen and nutritional requirements, and motility, and may be free-living, saprophytic, or pathogenic in plants or animals.
2)Archaea:Any of various single-celled prokaryotes genetically distinct from bacteria, often thriving in extreme environmental conditions.
3)Eukarya (eukaryotes):any organism having as its fundamental structural unit a cell type that contains specialized organelles in the cytoplasm, a membrane-bound nucleus enclosing genetic material organized into chromosomes, and an elaborate system of division by mitosis or meiosis, characteristic of all life forms except bacteria, blue-green algae, and other primitive microorganisms.

D)Biology branches

1)Cell Biology:the branch of biology dealing with the study of cells, esp. their formation, structure, components, and function.
2)Genetics:the science of heredity, dealing with resemblances and differences of related organisms resulting from the interaction of their genes and the environment.
3)Physiology:the branch of biology dealing with the functions and activities of living organisms and their parts, including all physical and chemical processes.
4)Biochemistry:the science dealing with the chemistry of living matter.
5)Developmental Biology:the branch of biology dealing with the processes of growth and change that transform an organism from a fertilized egg or asexual reproductive unit, as a spore or gemmule, to an adult.
6)Molecular Biology:The branch of biology that deals with the formation, structure, and function of macromolecules essential to life, such as nucleic acids and proteins, and especially with their role in cell replication and the transmission of genetic information.

7)Neurobiology:The biological study of the nervous system or any part of it.
8)Structural Biology:Structural biology is a branch of molecular biology concerned with the study of the architecture and shape of biological macromolecules—proteins and nucleic acids in particular—and what causes them to have the structures they have.

9)Immunology: The branch of biomedicine concerned with the structure and function of the immune system, innate and acquired immunity, the bodily distinction of self from nonself, and laboratory techniques involving the interaction of antigens with specific antibodies.
the branch of biology that studies microorganisms and their effects on humans .

11)Ecology:the branch of biology dealing with the relations and interactions between organisms and their environment, including other organisms.

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