Life Sciences for Grade 11, dealing with Micro organisms by focusing on the virus and bacteria. how they their reproduce and their importance

1. Micro-organisms:
virus and bacterius
Grade 11
By Obey Maduna

2. MICRO ORGANISMS
 Microorganisms are very small life
forms (ultramicroscopic)
 Microscope examination
 Microbiology: The study of micro-
organisms and their interactions with
the environment and other life forms.

3. IMPORTANT MICROORGANISMS:
 Groups:
 VIRUSES
 BACTERIA
 FUNGI
 PROTISTA

4. VIRUSES
 Are “substances” that cause diseases
and can be transmitted between
organisms.
 Acellular?????
 Obligated intracellular parasites??
 Outside the host – virus metabolically
inert.

5. All virus particles consist of two
parts :
 a central core of a nucleic acid strand
(DNA/RNA)
 surrounded by a protein covering called
a capsid.
nucleocapsid

6.  Some viruses - additional covering
external to the capsid – called the
envelope
 Virus with envelope - enveloped viruses
and those without it = naked viruses.
 Envelope can have accessory structures.

7.  The capsid consist of sub-units called
capsomeres.
 The capsomeres have perfect geometric
shapes.
 Depending on the shape and
arrangement of these capsomeres, two
types of capsids may be identified,
namely helical and Icosahedral capsids

8.  Helical and Icosahedral capsids

9. What criteria are used to classify a
virus?
geometry of the virus,
whether they have envelopes
the identity of the organism they infect
transmission mode
the disease they cause
the type of nucleic acid.

10. Patterns of viral replication
1. The lytic cycle.
Viruses enter a cell, replicate, and then
cause the cell to burst, releasing new
viruses.
2. The lysogenic cycle.
Viruses enter a long term relationship with
their host cells. Their nucleic acid replicates
as the host cells multiply.
D:Chapter_19A_PowerPoint_Lectures19_Lecture_Presentation1906LysogenicLyticCyclesA.ht
ml

12. DIFFERENCE BETWEEN LYTIC AND LYSOGENIC
CYCLES

13. The replication cycle of a
bacteriophage (T4)
• Bacteriophage: A virus that attacks bacteria cells.

14. HIV
• Retroviruses use reverse transcriptase to copy
their RNA genome into DNA
• HIV (human immunodeficiency virus) is the
retrovirus that causes AIDS (acquired
immunodeficiency syndrome)

15. HIV REPRODUCTION

16. BACTERIA
• Microscopic, unicellular prokaryote????.
• Most are heterotrophic but some are capable
to photosynthesize.
• With respect to their oxygen requirement –
3 types:
 aerobic ( need oxygen to survive)
 facultative (can survive with or without
oxygen)
 anaerobic (oxygen will kill these bacteria).

17. Structure of a bacterial cell
• Flagellum: motility of cell
• Pilli: help with conjugation
• Cell envelope: consist of the glycocalyx, cell wall and
plasma membrane – protection
• Slime capsule: protect against loss of water and
stomach/soil acids.
• Cell wall: consist of peptidoglycan – maintain shape of cell.
• Plasma membrane: selective barrier that allows oxygen,
nutrients and wastes through cell.
• Nucleoid: consist of DNA - form chromatic bodies/plasmids.
Genetic information for reproduction.
• Ribosomes: complexes that make proteins (rRNA)

19. Bacteria are classified according to
their shape and arrangement

20. Reproduction and life cycle of
bacteria
• They reproduce asexually by :
budding and/or
simple binary fission
• There is no mitosis.
• They generally gave a single chromosome.
• Genetic exchange may occur through
conjugation.

21. Budding of bacteria.
• Cell's genetic information is duplicated,
creating an identical copy or clone of the
original cell.
• As the new cell pinches off or buds from the
surface, a bud scar is produced.

22. Binary fission of bacteria

23. IMPORTANCE OF BACTERIA
ECONOMICALLY
• Sulphur oxidizing bacteria can break down
copper sulphide into copper sulphate for
copper oar mining.
• Fermentation bacteria is used to produce
cheese, yogurt, buttermilk…..
• Lactobacillus is used to make cheese.
• Vinegar is made when wine/cider is
fermented by acetic acid bacteria.

24. IMPORTANCE OF BACTERIA
AS PATHOGENS CAUSE DISEASES SUCH AS:
• Diphtheria: Bacteria affecting the pharynx –
transmitted through coughing or sneezing.
• Tuberculosis: Bacteria that attack the lungs –
transmitted through saliva
• Plague: Bacteria that infects the lymph nodes
– transmitted to man from flee bites (flees
come from rodents).

25. IMPORTANCE OF BACTERIA
ECOLOGICALLY
• Bacteria form part of the nitrogen cycle
(denitrifying -, nitrifying – and nitrogen-fixed
bacteria)
• Bacteria are also involved in the sulfur and
phosphorous cycles.
• Bacteria act as saprophytes – break down
complex organic molecules into simple inorganic
molecules.
• In rural areas bacteria is used in septic tanks to
help to dispose of sewage.