1. iGCSE Biology Section 1 lesson 3

2. The nature and variety of living organisms
Content
Section 1
The nature and variety of living organisms
Characteristics of living organisms
Variety of living organisms

3. Lesson 3 b) Variety of living organisms Content
Bacteria: These are microscopic single-celled organisms; they have a cell wall, cell membrane, cytoplasm and plasmids; they lack a nucleus but contain a circular chromosome of DNA; some bacteria can carry out photosynthesis but most feed off other living or dead organisms
Examples include Lactobacillus bulgaricus, a rod-shaped bacterium used in the production of yoghurt from milk, and Pneumococcus, a spherical bacterium that acts as the pathogen causing pneumonia
Protoctists: These are microscopic single-celled organisms. Some, like
Amoeba, that live in pond water, have features like an animal cell, while
others, like Chlorella, have chloroplasts and are more like plants. A pathogenic example is Plasmodium, responsible for causing malaria
Viruses: These are small particles, smaller than bacteria; they are parasitic
and can reproduce only inside living cells; they infect every type of living
organism. They have a wide variety of shapes and sizes; they have no cellular
structure but have a protein coat and contain one type of nucleic acid, either
DNA or RNA Examples include the tobacco mosaic virus that causes discolouring of the leaves of tobacco plants by preventing the formation of chloroplasts, the influenza virus that causes ‘flu’ and the HIV virus that causes AIDS
1.3 recall the term ‘pathogen’ and know that pathogens may be fungi, bacteria, protoctists or viruses.

4. Classification Kingdom Monera (Prokaryotes)
Bacteria and Blue-green algae
Protoctista
Amoeba, Paramecium
Fungi
Moulds, Mushrooms, Yeast
Plants
Algae, ferns and mosses, conifers and flowering plants
Animals
Jellyfish, worms, arthropods, molluscs, echinoderms, fish, amphibia, reptiles, birds and mammals.

5. Classification Kingdom Monera (Prokaryotes)
Bacteria and Blue-green algae
Protoctista
Amoeba, Paramecium
Fungi
Moulds, Mushrooms, Yeast
Plants
Algae, ferns and mosses, conifers and flowering plants
Animals
Jellyfish, worms, arthropods, molluscs, echinoderms, fish, amphibia, reptiles, birds and mammals.

6. Bacteria: These are microscopic single-celled organisms; they have a cell wall, cell membrane, cytoplasm and plasmids; they lack a nucleus but contain a circular chromosome of DNA; some bacteria can carry out photosynthesis but most feed off other living or dead organisms
Examples include Lactobacillus bulgaricus, a rod-shaped bacterium used in the production of yoghurt from milk, and Pneumococcus, a spherical bacterium that acts as the pathogen causing pneumonia

7. Examples of bacteria

8. Examples of bacteria
Lactobacillus – rod shaped bacterium used in the production of yoghurt from milk.

9. Pneumococcus – spherical bacterium. A pathogen causing pneumonia
Examples of bacteria
Lactobacillus – rod shaped bacterium used in the production of yoghurt from milk.
Pneumococcus – spherical bacterium. A pathogen causing pneumonia

10. Pneumococcus – spherical bacterium. A pathogen causing pneumonia
Examples of bacteria
Pathogen – a microorganism that causes disease in its host. The host may be an animal, a plant or even another microorganism.
Lactobacillus – rod shaped bacterium used in the production of yoghurt from milk.
Pneumococcus – spherical bacterium. A pathogen causing pneumonia

11. Structure of bacteria
Singular = bacterium

12. Structure of bacteria
Very small organisms, rarely more than 0.01mm in length, so can only be seen with more powerful microscopes.

13. Structure of bacteria
Very small organisms, rarely more than 0.01mm in length, so can only be seen with more powerful microscopes.
Cell wall
- Not made of cellulose but of a complex mixture of proteins, sugars and lipids.

14. Structure of bacteria
Very small organisms, rarely more than 0.01mm in length, so can only be seen with more powerful microscopes.
Cell wall
- Not made of cellulose but of a complex mixture of proteins, sugars and lipids.
Some may have a slime capsule outside the cell wall – protects the bacterium

15. Structure of bacteria
Very small organisms, rarely more than 0.01mm in length, so can only be seen with more powerful microscopes.
No nuclear membrane (prokaryotes), but instead have a single chromosome, a strand of DNA
Cell wall
- Not made of cellulose but of a complex mixture of proteins, sugars and lipids.
Some may have a slime capsule outside the cell wall – protects the bacterium

16. Structure of bacteria
Very small organisms, rarely more than 0.01mm in length, so can only be seen with more powerful microscopes.
No nuclear membrane (prokaryotes), but instead have a single chromosome, a strand of DNA
Cytoplasm
Glycogen granules
Cell wall
- Not made of cellulose but of a complex mixture of proteins, sugars and lipids.
Some may have a slime capsule outside the cell wall – protects the bacterium

17. Bacteria may also have flagella
Structure of bacteria
Bacteria may also have flagella
Very small organisms, rarely more than 0.01mm in length, so can only be seen with more powerful microscopes.
No nuclear membrane (prokaryotes), but instead have a single chromosome, a strand of DNA
Cytoplasm
Glycogen granules
Cell wall
- Not made of cellulose but of a complex mixture of proteins, sugars and lipids.
Some may have a slime capsule outside the cell wall – protects the bacterium

18. Bacteria may also have flagella
Structure of bacteria
Bacteria may also have flagella
Very small organisms, rarely more than 0.01mm in length, so can only be seen with more powerful microscopes.
No nuclear membrane (prokaryotes), but instead have a single chromosome, a strand of DNA
Cytoplasm
Glycogen granules
Cell wall
- Not made of cellulose but of a complex mixture of proteins, sugars and lipids.
Plasmid – a small circular piece of DNA. Often carry genes which give the bacterium resistance to antibiotics
Some may have a slime capsule outside the cell wall – protects the bacterium

19. Physiology of bacteria
Streptococcus

20. Physiology of bacteria
Nutrition – a few species of bacteria are able to photosynthesise and make their own food.
The majority live on their food – they release enzymes which digest the food and then they absorb the liquid products back into the cell.
Streptococcus

21. Physiology of bacteria
Reproduction – bacteria reproduce asexually by a process called binary fission. One cell divides into two, then two into four, and so on. This can happen every twenty minutes. If this were to occur, then after 12 hours there would be 34,359,738,368 bacteria formed from a single cell!
Streptococcus

22. Useful and harmful bacteria

23. Useful and harmful bacteria
Making cheese
Making yoghurt
Antibiotics
Sewage treatment
Oil spill clean up
Mining metals
Fuels
Decay
Genetic engineering
Fixing nitrogen

24. Useful and harmful bacteria
Sore throat
Boils
Pneumonia
Anthrax
Typhoid fever
Scarlet fever
Syphilis
Cholera
Food poisoning
Whooping cough

25. Classification Kingdom Monera (Prokaryotes)
Bacteria and Blue-green algae
Protoctista
Amoeba, Paramecium
Fungi
Moulds, Mushrooms, Yeast
Plants
Algae, ferns and mosses, conifers and flowering plants
Animals
Jellyfish, worms, arthropods, molluscs, echinoderms, fish, amphibia, reptiles, birds and mammals.

26. Protoctists: These are microscopic single-celled organisms
Protoctists: These are microscopic single-celled organisms. Some, like Amoeba, that live in pond water, have features like an animal cell, while others, like Chlorella, have chloroplasts and are more like plants. A pathogenic example is Plasmodium, responsible for causing malaria

27. Examples of Protoctists

28. Examples of Protoctists
Amoeba

29. Examples of Protoctists
Amoeba
Chlorella

30. Examples of Protoctists
Amoeba
Chlorella
Plasmodium

31. Examples of Protoctists
Amoeba fact file:
Microscopic, one-celled organism.
Live in fresh water (puddles, ponds)
Amoeba

32. Examples of Protoctists
Amoeba fact file:
Microscopic, one-celled organism.
Live in fresh water (puddles, ponds)
Typical animal cell, porous cell membrane, cytoplasm, nucleus.
Amoeba

33. Examples of Protoctists
Amoeba fact file:
Microscopic, one-celled organism.
Live in fresh water (puddles, ponds)
Typical animal cell, porous cell membrane, cytoplasm, nucleus.
Feed on algae, bacteria, plant cells, protozoa. Cytoplasm surrounds food particles to form a food vacuole where digestion takes place.
Amoeba

34. Examples of Protoctists
Amoeba fact file:
Microscopic, one-celled organism.
Live in fresh water (puddles, ponds)
Typical animal cell, porous cell membrane, cytoplasm, nucleus.
Feed on algae, bacteria, plant cells, protozoa. Cytoplasm surrounds food particles to form a food vacuole where digestion takes place.
Pseudopodia = “false feet”. Amoebas move by changing the shape of their body, forming pseudopods.
Amoeba

35. Examples of Protoctists
Chlorella fact file:
Single-celled green algae. Spherical in shape.
Chlorella

36. Examples of Protoctists
Chlorella fact file:
Single-celled green algae. Spherical in shape.
Contains chlorophyll which enables it to photosynthesise.
Chlorella

37. Examples of Protoctists
Plasmodium fact file:
A single-celled Protozoan that causes the disease known as malaria.
Spread from person to person by the female mosquito as they suck blood.
Plasmodium

38. Examples of Protoctists
Plasmodium fact file:
A single-celled Protozoan that causes the disease known as malaria.
Spread from person to person by the female mosquito as they suck blood.
Plasmodium invades the red blood cells of the host and feeds on the cytoplasm.
Plasmodium

39. Examples of Protoctists
Plasmodium fact file:
A single-celled Protozoan that causes the disease known as malaria.
Spread from person to person by the female mosquito as they suck blood.
Plasmodium invades the red blood cells of the host and feeds on the cytoplasm.
Nearly 3 million people each year die from malaria.
Plasmodium

40. Viruses: These are small particles, smaller than bacteria; they are parasitic and can reproduce only inside living cells; they infect every type of living organism. They have a wide variety of shapes and sizes; they have no cellular structure but have a protein coat and contain one type of nucleic acid, either DNA or RNA. Examples include the tobacco mosaic virus that causes discolouring of the leaves of tobacco plants by preventing the formation of chloroplasts, the influenza virus that causes ‘flu’ and the HIV virus that causes AIDS

41. Examples of viruses
Tobacco Mosaic Virus
(virology.wisc.edu)

42. Examples of viruses Tobacco Mosaic Virus (virology.wisc.edu)
InfluenzaVirus
(medimoon.com)

43. Examples of viruses Tobacco Mosaic Virus (virology.wisc.edu) HIV Virus
(123rf.com)
InfluenzaVirus
(medimoon.com)

44. Examples of viruses TMV was the first virus to be discovered in 1930.
Causes mottling and discoloration of tobacco leaves.
Rod-like appearance, surrounded by a resistant protein coat
Tobacco Mosaic Virus
(virology.wisc.edu)
HIV Virus
(123rf.com)
InfluenzaVirus
(medimoon.com)

45. Examples of viruses Highly contagious, infects the respiratory tract.
It affects all ages, but children tend to get it more than adults
Spread by droplets that are coughed or sneezed.
Tobacco Mosaic Virus
(virology.wisc.edu)
HIV Virus
(123rf.com)
InfluenzaVirus
(medimoon.com)

46. Examples of viruses
Tobacco Mosaic Virus
(virology.wisc.edu)
A slowly-replicating retrovirus that causes acquired immunodeficiency syndrome (AIDS), which causes the immune system to fail. Infection through body fluids.
HIV Virus
(123rf.com)
InfluenzaVirus
(medimoon.com)

47. Retrovirus - a virus that replicates in a host cell
Examples of viruses
Retrovirus - a virus that replicates in a host cell
Tobacco Mosaic Virus
(virology.wisc.edu)
A slowly-replicating retrovirus that causes acquired immunodeficiency syndrome (AIDS), which causes the immune system to fail. Infection through body fluids.
HIV Virus
(123rf.com)
InfluenzaVirus
(medimoon.com)

48. Structure of viruses

49. Structure of viruses Protein Coat Injection Tube Genetic Material
Tail Plate

50. Structure of viruses
Much smaller than a bacterium, can only be seen with electron microscopes

51. Structure of viruses
All viruses have a central core of RNA or DNA surrounded by a protein coat.
Much smaller than a bacterium, can only be seen with electron microscopes

52. No nucleus, cytoplasm, cell organelles or cell membrane
Structure of viruses
All viruses have a central core of RNA or DNA surrounded by a protein coat.
No nucleus, cytoplasm, cell organelles or cell membrane
Much smaller than a bacterium, can only be seen with electron microscopes

53. Structure of viruses
All viruses have a central core of RNA or DNA surrounded by a protein coat.
No nucleus, cytoplasm, cell organelles or cell membrane
Much smaller than a bacterium, can only be seen with electron microscopes
So, are they really cells at all?

54. Structure of viruses MRS GREN
All viruses have a central core of RNA or DNA surrounded by a protein coat.
No nucleus, cytoplasm, cell organelles or cell membrane
Much smaller than a bacterium, can only be seen with electron microscopes
So, are they really cells at all?
MRS GREN

55. Structure of viruses MRS GREN
All viruses have a central core of RNA or DNA surrounded by a protein coat.
Viruses do reproduce, but only inside the cells of living organisms, using materials obtained from the host cell.
No nucleus, cytoplasm, cell organelles or cell membrane
Much smaller than a bacterium, can only be seen with electron microscopes
So, are they really cells at all?
MRS GREN

56. Structure of viruses MRS GREN
All viruses have a central core of RNA or DNA surrounded by a protein coat.
Viruses do reproduce, but only inside the cells of living organisms, using materials obtained from the host cell.
No nucleus, cytoplasm, cell organelles or cell membrane
Much smaller than a bacterium, can only be seen with electron microscopes
The protein coat is called a capsid, and is made up of regularly packed protein units called capsomeres.
So, are they really cells at all?
MRS GREN

57. Multiplication of viruses

58. Multiplication of viruses
Viruses are able to survive outside the host cell, but they must penetrate into a host in order to reproduce.

59. Multiplication of viruses
1. The virus sticks to the cell membrane of a suitable host cell.

60. Multiplication of viruses
1. The virus sticks to the cell membrane of a suitable host cell.
2. An ‘injection’ tube ‘injects’ the DNA or RNA into the host cell.

61. Multiplication of viruses
1. The virus sticks to the cell membrane of a suitable host cell.
2. An ‘injection’ tube ‘injects’ the DNA or RNA into the host cell.

62. Multiplication of viruses
3. The viral DNA uses the cell’s contents to make new strands and capsomeres

63. Multiplication of viruses
3. The viral DNA uses the cell’s contents to make new strands and capsomeres
4. The DNA and capsomeres make new virus particles which escape from the cell

64. Diseases caused by viruses
Common cold
Poliomyelitis
Measles
Mumps
Chickenpox
Herpes
Rubella
Influenza
AIDS

65. Pathogen – a microorganism that causes disease in its host
Pathogen – a microorganism that causes disease in its host. The host may be an animal, a plant or even another microorganism.

66. Pneumococcus – causes pneumonia
Pathogen – a microorganism that causes disease in its host. The host may be an animal, a plant or even another microorganism.
Bacterium
Pneumococcus – causes pneumonia

67. Pneumococcus – causes pneumonia
Pathogen – a microorganism that causes disease in its host. The host may be an animal, a plant or even another microorganism.
Bacterium
Virus
Pneumococcus – causes pneumonia
InfluenzaVirus
(medimoon.com)

68. Pathogen – a microorganism that causes disease in its host
Pathogen – a microorganism that causes disease in its host. The host may be an animal, a plant or even another microorganism.
Bacterium
Virus
Protoctist
Pneumococcus – causes pneumonia
InfluenzaVirus
(medimoon.com)
Plasmodium – causes malaria

69. Pathogen – a microorganism that causes disease in its host
Pathogen – a microorganism that causes disease in its host. The host may be an animal, a plant or even another microorganism.
Fungus
Fusarium – fungal pathogen that infects wheat crops
(bbsrc.ac.uk)
Bacterium
Virus
Protoctist
Pneumococcus – causes pneumonia
InfluenzaVirus
(medimoon.com)
Plasmodium – causes malaria

70. End of Section 1 Lesson 3 In this lesson we have covered:
Outline of the monera kingdom
Outline of the protoctist kingdom
Outline of viruses
Examples of pathogens