Summary Life Sciences (Biology) - Life at a molecular, cellular, and tissue level

LIFE AT MOLECULAR, CELLULAR AND TISSUE LEVEL:


THE DIVERSITY OF LIFE:
 The viruses, bacteria, protists, and fungi are considered to have evolved very
early in history before animals and plants.
 This is because they:
- Are a hugely diverse group.
- Found in all the planet’s environments.
- Occur is vast numbers.
- Vary in size, micro-organisms (invisible to eye), macro-organisms (visible to
eye)
- Either acellular or eukaryotes.
- Can for colonies.


PATHOGENIC AND NON-PATHOGENIC MICRO-ORGANISMS:
 Pathogenic = disease causing.
 Non-pathogenic = harmless.
 Pathogens are often called germs.

, VIRUSES:


CHARACTERISTICS OF VIRUSES:
 Viruses are extremely small (microscopic)
 Either active (virus) or dormant (virion)
 Not really living organisms as they do not exhibit the seven life processes.
 Viruses are obligate intracellular organisms as they only survive in other cells.
 Viruses can only reproduce inside a living cell.
 Always associated with diseases.
 They can remain in a dormant state.
 Can be different shapes.


SHAPES OF VIRUSES:
 Polyhedral (cubical)
- The capsid has twenty triangular
sides.
- E.g., adenovirus

 Helical (spiral)
- The capsid resembles a coiled spiral.
- E.g., tobacco virus.

 Complex (tadpole like)
- Has a head, sheath, and tail fibers.
- E.g., bacteriophage.




STRUCTURE OF VIRUSES:
 A virus is acellular, it does not have a nucleus, cytoplasm, or organelles.
 Consists of a core of DNA or RNA.
 The nucleic acid is surrounded by a protein
coat called a capsid.
 In some viruses it is enclosed by an envelope
of a lipid bilayer that protects the host from




BACTERIA:

, CHARACTERISTICS OF BACTERIA:
 Bacteria is the most diverse and abundant group of organisms on earth.
 Bacteria practically inhabit all environments, they are found in water, soil, air
and in animals’ gastrointestinal tracts.
 Most of them are useful but some can cause diseases.
 Bacteria are unicellular and are of the smallest organisms, they can be
observed through a light microscope and range in size from one to ten
micrometers.
 Bacteria can exist singly, in chains (streptococcus) or in clumps
(staphylococcus)
 They reproduce by binary fission. (a process whereby bacteria asexually
reproduce by dividing into two with identical DNA)
 In unfavorable conditions they can become dormant.




SHAPES OF BACTERIA:
 Cocci:
- Spherical bacteria

 Bacilli:
- Rod-shaped bacteria

 Spiralla:
- Spiral shaped bacteria

 Vibrios:
- Comma-shaped bacteria




STRUCTURE OF BACTERIA:
 Bacteria are unicellular and carry out living functions.