Textbook Notes: Bacteria

Question 1

What are bacteria?

Answer 1

Single celled microorganisms. They are prokaryotes (no nucleus).

Question 2

Describe the structure of a bacterial cell.

Answer 2

Gelatinous sheath (capsule) - protects bacteria against viruses and allows it to stick to surfaces. Fluid filled outer layer.

Cell wall - provides stuctural support. Stops cell from becoming damaged. Rigid outer layer.

Cell membrane - controls what enters the cell. Semi permeable layer.

Chromosome (nuclear material) - holds genetic information. Threadlike structure.

Flagellum - aids movement.

Ribosomes - make proteins.

Question 3

What are autotrophs?

Answer 3

Bacteria that build up their own food from carbon dioxide and water.

Question 4

What are heterotrophs?

Answer 4

Bacteria that use food produced by other organisms. May feed on dead organic matter (decomposers).

Question 5

Describe waste products and excretion in bacteria.

Answer 5

• Some wastes can be toxins that kill living cells.
• Some wastes can change the pH when they dissolve in water, causing other microbes (not suited to change) to die
• some can be helpful, such as the bacteria in soil - they excrete nitrates that help plant growth.

Question 6

Describe fermentation.

Answer 6

Fermentation is a process in which a carbohydrate is converted into an alcohol or an acid.

Question 7

Why can’t the exponential population growth of bacteria continue indefinitely?

Answer 7

because:

Food is used up.
Waste products accumulate – toxins.
Bacteria are eaten by other organisms. (competition)

Question 8

How are bacterial growth and reproduction related?

Answer 8

Bacterial cells grow before they reproduce. They use the water and nutrients. Once they have doubled in size, they undergo binary fission.

Question 9

Describe the different phases of bacterial growth.

Answer 9

Phase 1 - each individual bacterium is reproducing at a constant rate, very fast. Resources are plentiful.

Phase 2 - There is increasing competition for food, and accumulation of waste products. However, the no. of bacteria per unit time is still increasing rapidly.

Phase 3 - population growth rate is decreasing, resources being used up. More competition.

Phase 4 - Population growth rate is zero – division has ceased altogether.

Question 10

Describe the relationship between bacterial growth rate and temperature.

Answer 10

At higher temperatures, bacteria are killed. For most bacteria, death occurs above 55–60 °C.

Bacterial growth rate doubles for every 10 °C rise. Above a certain optimum temperature, further increase slows growth rate.

Question 11

Why do we put food in the fridge?

Answer 11

Enzymes involved in the life processes of bacteria are slowed down by low temperatures and will speed up again if warmed. Most domestic refrigerators operate at about 5 °C.

Question 12

What is antibiotic resistance and how does it occur?

Answer 12

Antibiotic resistance is when an antibiotic has lost its ability to control/kill bacterial growth. This can happen due to mutations occuring during reproduction, forming new bacteria that are able to become resistant.

Question 13

What are optimum conditions?

Answer 13

1. Agar - sterile, provides all O.C
2. Nutrients - pH, slightly alkline, 7.2 - 7.4
3. Moisture
4. Dark places (temperature)
5. Oxygen (for those that carry out anaerobic respiration)

If conditions are not favourable, bacterial colonies either perish, or form a protective cover: spores. These remain dormant until conditions become favourable again.

Question 14

How do bacteria contribute to the carbon cycle?

Answer 14

The decomposers in the cycle (bacteria and fungi) feed on dead organic matter and release CO2 into the atmosphere as they respire.

Question 15

How do bacteria contribute to the nitrogen cycle?

Answer 15

• Decomposers (bacteria and fungi) break down dead plants and animals to release the nitrogen trapped inside.
• denitrifying bacteria convert nitrate to nitrogen gas. They are in the soil.

When plants and animals die, their proteins are converted into ammonia. Conversion of ammonia to nitrates can only be done by the bacteria.

Question 16

Give 2 examples of how decomposers help dispose of organic wastes.

Answer 16

Sewage treatment

• Wastes settle, so solids sink to the bottom of the tank. The weight of the solids means there is no oxygen present, so the waste is digested by anaerobic bacteria.
• Warm temperatures needed are provided by the respiration of the bacteria.
• The liquid part of the wastes is pumped into large open tanks or ponds that are aerated regularly so aerobic bacteria can digest any remaining wastes.

Question 17

Why is sewage treatment important?

Answer 17

• Prevents the spread of diseases. Bacteria that cause these diseases leave the body via the faeces and must be prevented from getting into food or water.
• If sewage gets into rivers, its decay can cause fish and other aquatic life harm.
• Sewage has an unpleasant smell.

Question 18

What are the advantages of sewage treatment?

Answer 18

Once all pathogens are removed from the waste…

• solid material can be used as fertiliser, returning nutrients to the soil.
• liquid can be safely released into the ground or the sea.

Question 19

What is composting and why is it important?

Answer 19

Composting is a way the remains of plants are recycled.
When leaves and dead plants fall to the ground, they are digested by decomposers living in the soil, releasing carbon and nitrogen (nutrients).

Question 20

What conditions are required for composting to occur effectively?

Answer 20

Oxygen - aerobic decomposers produce an almost odour-free, nutrient- rich compost.

Warmth – decomposers need warm temperatures to be active. They produce a lot of heat through their own respiration.

Water – too much water will produce anaerobic conditions, too little and the decomposers will die.

A suitable pH, and a mixture of nutrients.

Question 21

How do antibiotics work?

Answer 21

They interfere with the cell walls of bacteria and prevent them growing and reproducing.

Question 22

What are the causes of food poisoning?

Answer 22

• Growth of microbes in the digestive system.
• Build up of toxins produced by bacteria present.
  These interfere with the functioning of the digestive system, causing symptoms of food poisoning (vomiting, fever, diarrhoea).

Question 23

How do microbes cause disease and how is disease spread?

Answer 23

Transmission of mircobes through insects biting/sucking.
Transmitted through bodily fluids. (eg mucous, semen, saliva).
Microbes can be carried in contaminated water.
Transmitted by direct contact.
Some microbes carried in contaminated food.
Some microbes carried in the air in mucous droplets.

Question 24

How do bacteria respire?

Answer 24

Aerobic bacteria:

glucose + oxygen → Carbon dioxide + Energy + Water

Anaerobic bacteria:

glucose → Carbon dioxide + Energy + Ethanol