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Cell Biology
Chapter Nine: The MicroscopicWorld
• 9.1 Protozoans
• 9.2 Bacteria
• 9.3 Viruses
Investigation 9B
• Which microscopic organisms are found in pond water?
Investigating Pond Water
9.2 Bacteria
• Bacteria are organisms that consist of a single, prokaryotic cell.
• Bacterial cells have a cell membrane that is surrounded by a tough cell wall.
Bacteria can live in soil, water or air.
9.2 Size and shape of bacteria
• Bacteria are not easy to measure using meters, centimeters, or even millimeters.
• Micrometers (μm) are used to measure them.
Bacteria are much smaller than most other cells.
9.2 Size and shape of bacteria
• Bacteria are identified based on the shape of their cells.
• Rod-shaped bacteria are called bacilli.
• Ball-shaped bacteria are called cocci.
• Spirilla are spiral-shaped bacteria.
Bacilli in your intestine help with digestion.
9.2 Movement and feeding
• Bacteria get around in many ways. – Some bacteria move
using flagella.– Others have a slimy
layer to grip surfaces.– Some are carried by the
movement of air or liquids. .
9.2 Movement and feeding
• Photosynthetic bacteria can make their own food from sunlight and carbon dioxide, just like plants.
• Bacteria that break down dead organisms get their food by absorbing it.
These blue green bacteria use sunlight to make food.
9.2 Bacteria and the beginning of life
• Scientists believe that bacteria were the first organisms on Earth.
9.2 The importance of bacteria• Bacteria are useful in many areas of industry.
– Yogurt and cheese are made with certain types of bacteria.
– Bacteria break down waste products in sewage.– Bacteria can help clean up oil spills.
• Bacteria also cause diseases:– strep throat– respiratory infections– infected wounds
9.2 The importance of bacteria
• Bacteria are an important part of the nutrient cycles that all life depends upon.
9.2 The importance of bacteria
• Bacteria are “nature’s recyclers.”