Topic 4: Bacterial Growth

Question 1

Bacteria reproduce asexually by _______ _______.

What are the 4 steps?

Answer 1

binary fission

1. DNA is replicated
2. Cell growth/new cell contents (e.g. ribosomes) are made
3. Mitosis
4. Cytokinesis - new cell membrane and cell wall form down centre of cell - cell is divided into two equal halves/cells

Question 2

Bacterial population growth is _________ - one cell divides into 2, 2 into 4 etc (doubles each time)

Answer 2

exponential

Question 3

Time between a new cell forming and cell division to form new cells = ________ _____ / ____ _____ _____
(depends on conditions)

Answer 3

generation time / cell cycle time

Question 4

In ideal conditions bacteria can divide every 20 minutes.

One bacterial cell is placed in ideal conditions.

Calculate how many bacterial cells would be produced after 4 hours.

Answer 4

4096

Question 5

Key Summary: What are the ideal conditions for bacterial growth?
(5 conditions)

Answer 5

1. optimum concentrations of nutrients
2. optimum temperature
3. Optimum oxygen concentration
4. Optimum pH
5. Moisture/water

Question 6

Key Summary: Explain the ideal conditions for bacterial growth (explain each one of them)
(5 ideal conditions)

Answer 6

1. Optimum concentrations of nutrients
   - as energy source eg. glucose for respiration to release energy
   - nitrogen is needed for making amino acids and to make proteins for growth
2. Optimum temperature
   - varies with species but usually warm/25 degrees C (but 37 degrees C for ones that infect human body)
   - it increases enzyme activity and therefore metabolism
3. Optimum ph
   - for maximum enzyme activity
4. Optimum oxygen concentration (or no oxygen)
   - for aerobic bacteria to respire
   - no oxygen if bacteria only respire anaerobically
5. Moisture/water
   - for cell functions e.g. hydrolysis reactions

Question 7

The growth curve (bacteria growth on a graph) has 4 phases, what are they? (list them in the order they happen)

Answer 7

1. Lag phase
2. Log/exponential phase
3. Stationary phase
4. Death phase

Question 8

Explain what happens in Lag phase (3 points)

Answer 8

1. no increase in cell numbers
2. cells adjusting to conditions
3. enzymes being made

Question 9

Explain what happens in Log/exponential phase (2 points)

Answer 9

1. steep increase in cell numbers

2. cells dividing exponentially at fastest rate for the conditions

Question 10

Explain what happens in Stationary phase (2 points)

Answer 10

1. no increase in cell numbers

2. growth is limited by lack of nutrients, build up of toxic waste products, changing ph

Question 11

Explain what happens in Death phase

2 points

Answer 11

1. cell numbers decrease

2. number of cells dying is greater than new cells formed