Population Size & Ecosystems

Question 1

What factors:

a) increase population size?
b) decrease population size?

Answer 1

a) Birth and immigration

b) Death and emigration

Question 2

In the carbon cycle, what removes carbon dioxide from the atmosphere?

Answer 2

Photosynthesis in plants and algae

Question 3

In the carbon cycle, what contributes to the amount of carbon dioxide in the atmosphere?

Answer 3

• Respiration in animals and plants
• Decay organisms respiring
• Combustion of fossil fuels

Question 4

What is global warming, and what are the consequences of it?

Answer 4

• Global warming is the increase in average global temperature, caused by the greenhouse effect
• Consequences include: rising sea levels, increased frequency of droughts and hurricanes, more forest fires etc

Question 5

What are the four main biological processes in the nitrogen cycle?

Answer 5

• Nitrogen fixing
• Nitrification
• Ammonification
• Denitrification

Question 6

What is nitrogen fixing? And what are examples of organisms that account for it?

Answer 6

• The reduction of nitrogen atoms in nitrogen molecules to ammonium ions by prokaryotic organisms
• Azotobacter (in soil), and Rhizobium (in root nodules of legumes)

Question 7

What is nitrification?

Answer 7

• The addition of nitrogen to the soil, most commonly as nitrate and nitrite ions
• The bacteria Nitrosomonas oxidises ammonium to nitrite
• Nitrite is then oxidised to nitrate by Nitrobacter

Question 8

What is ammonification?

Answer 8

-When decomposing bacteria and fungi decompose nitrogen compounds in dead plants and animals into simpler molecules, such as ammonium ions

Question 9

What is denitrification? And what organisms carry this out?

Answer 9

• When denitrifying bacteria convert nitrates and ammonium ions in the soil into nitrogen gas
• The anaerobic bacteria Psuedomonas carry this out

Question 10

How can human activities improve the nitrogen cycle?

Answer 10

• Farmers ploughing and draining land, improving soil aeration
• Farmers using crop rotation and planting legumes
• Using fertilisers
• Using manure and compost

Question 11

What are the four sections of population growth curves, and what is happening at each section?

Answer 11

• Lag phase, which is a period of adjustment to new conditions
• Exponential growth phase, when conditions for growth are ideal and there are no limiting factors
• Stationary phase, when birth rate is equal to death rate, and the carrying capacity is reached
• Death phase, when the factors which caused population growth to slow become more significant

Question 12

Name some biotic/density dependent factors affecting populations

Answer 12

• Food availability
• Overcrowding
• Competition for scarce resources
• Predators
• Disease and parasites

Question 13

Name some abiotic/density independent factors affecting population size

Answer 13

• Climatic factors (droughts, floods, storms)
• Lack of shelter
• Plants need light of correct intensity and wavelength
• Shortage of oxygen
• Water quality
• Pollution

Question 14

What is the difference between intraspecific and interspecific competition?

Answer 14

• Intraspecific competition is between individuals of the same species
• Interspecific competition is between individuals of different species

Question 15

What is the difference between gross primary productivity (GPP) and net primary productivity (NPP)?

Answer 15

• GPP is the rate of production of chemical energy in organic molecules by photosynthesis in a given area over a given time
• NPP is the energy in the plants biomass which is available to the primary consumers

Question 16

What is secondary productivity?

Answer 16

-The rate at which consumers convert the chemical energy in their food into biomass