Populations

Population: An interbreeding group of organisms of the same species in a particular habitat. 

Carrying capacity: Maximum number around which a population fluctautes in an enviornment. 

Population number will fluctuate depending on various factors: Birthrate, death rate, immigration and emigration 

Populations will increase in size when:

Births + immigrants > deaths + emigrants 

Lag Phase: 

• Cells adjust to new conditions 
• Takes a wile for enzyme production 
• The bacteria adjust to new conditions, synthesising carriers to absorb nutreints and enzymes to digest.
• May involve switching on genes 

Log (exponential) phase:

• As numbers increase, as long as there is not factors limiting growth, more individuals become availble for reproduction. Bacterial cells divide at a constant rate and the population doubles per unit time. The cell numbers increases logarithmically and so the exponential phase is also called the log phase. 

Stationary phase:

• Occurs when birth rate is equal to the death rate. The population has reached its maximum size, which is the carrying capacity for that particular enviornment
• The actual number depends on the resources available 

The death phase:

• Death rate is greater than birth rate
• Waste products such as ethanol kills cells 
• Net decrease of population 
• Nutreints exhausted and waste too toxic 
• Some dead will act as a nutrient source for others 

Environmental resistance 

Environmental resistance relates to any factor that slows down population growth and can cause it to crash 

Examples: 

• Less food available
• Build up of waste products 
• Not enough space 

For bacteria:

• available food 
• Over crowding 
• Competition 
• Buildup of waste 

Biotic

• Predation 
• Parasitism and disease 
• Competition 

Abiotic 

• temperature 
• Light intensity 
• pH
• rainfall

Biotic factors are density dependent - when some factors play a more significant role in population size if the population is higher, they are often biotic factors

Density independent: Abiotic factors effect the population regardless of the population density.