Chapter 5 - Population Size & Ecosystems.

Question 1

What is a populations size determined by?

Answer 1

• Birth rate (Or any other way that an organism increases their numbers).
• Death rate.
• Immigration.
• Emigration.

Question 2

What are the 4 phases of a growth curve?

Answer 2

• Lag phase.
• Log (Exponential) phase.
• Stationary Phase (Birth rate = Death rate).
• Death phase (Birth rate < Death rate).

Question 3

Why can’t the rate of increase in the log phase be maintained?

Answer 3

Because environmental resistance sets in.

• There is less food available.
• Concentration of waste products become increasingly toxic.
• Not enough space/nesting sites.

Question 4

What is environmental resistance?

Answer 4

Refers to environmental factors that slow down population growth.

Question 5

What are the two types of factors that will affect a population size?

Answer 5

Density-dependent factors and Density-independent factors.

Question 6

What are examples of Density Dependent/Independent factors?

Answer 6

Density Dependent - Depletion of food supply, parasitism.

Density Independent - Flood, Fire.

Question 7

What is an Ecosystem?

Answer 7

A characteristic community of interdependent species interacting with the abiotic components of their habitat.

Question 8

What is the carrying capacity of a species?

Answer 8

The maximum population size that can be maintained over a period of time by an environment.

Question 9

What is the abundance of a species?

Answer 9

The number of individuals in a species in a given area or volume.

Question 10

How can animal/plant abundance be assessed?

Answer 10

• Mark-Release-Recapture.
• Kick sampling.
• Using a quadrat (Mean number of individuals/%age cover/%age frequency).

Question 11

What is the most significant energy source for ecosystems?

Answer 11

The sun.

Question 12

What is a trophic level?

Answer 12

A feeding level; the number of times that energy has been transferred between the sun and successive organisms along a food chain.

Question 13

What is the difference between a Detritivore and a Decomposer?

Answer 13

Detritivore - Organisms (worms, woodlice etc.) that feed on small fragments of organic debris (Detritus).
Decomposers - Microbes (Fungi, Bacteria etc.) that obtain nutrients from dead organisms and animal waste.

Question 14

What is the difference between Primary productivity and Secondary productivity?

Answer 14

Primary - Rate at which energy is converted by producers into biomass.
Secondary - Rate at which consumers convert the chemical energy of their food into biomass.

Question 15

Why is it that about 60% of the sunlight that falls on a plant isn’t absorbed by photosynthetic pigments?

Answer 15

• The light may may be the wrong wavelength.
• Reflected.
• Absorbed by non-photosynthetic parts of the plant.
• Transmitted through the leaf.

Question 16

What is Gross Primary Productivity?

Answer 16

The rate of production of chemical energy in organic molecules by photosynthesis.

Question 17

What is Net Primary Productivity?

Answer 17

What is left of GPP after some is released by the respiration of the plant.

Question 18

Why is energy lost at each trophic level of a food chain?

Answer 18

• Energy in molecules that are egested.
• Some energy lost as heat.
• Energy remains in molecules in parts that aren’t eaten.

Question 19

Why are Carnivores more efficient at energy conversion compared to herbivores?

Answer 19

Carnivores food is more easily digested as they produce the correct enzymes to digest it. Herbivores need a separate gut bacteria in order to digest the cellulose cell wall in their food.

Question 20

What are the problems with a pyramid of numbers?

Answer 20

• Doesn’t take into account size of the organism.
• Doesn’t differentiate between Juvenile and adult forms.
• Range of number may be so large, drawing to scale may be difficult.
• Pyramid may be inverted.

Question 21

What Ecological Pyramid is the most accurate way of representing feeding relationships?

Answer 21

A pyramid of energy.

Question 22

When may a pyramid of biomass be inverted?

Answer 22

In an aquatic ecosystem when the standing crop of phytoplankton is larger than the zooplankton.

Question 23

What is the difference between primary succession and secondary succession?

Answer 23

Primary - Change in structure and species composition of a community over time in an area that has not been previously colonized.
Secondary - The changes follow the disturbance/damage to a colonised habitat.

Question 24

What is a climax community?

Answer 24

A stable, self-perpetuating community that has reached equilibrium with its environment, and no further change occurs.

Question 25

What is the sequence of communities, with different species and structures called? and what can it be divided up into?

Answer 25

Sere.

Seral stage.

Question 26

What is a pioneer species?

Answer 26

The first species to colonise a new area in an ecological succession e.g. lichen.

Question 27

What factors will affect succession?

Answer 27

• Migration.
• Competition.
• Inter-species relationships.

Question 28

What is the difference between Inter-specific Competition and Intra-specific competition?

Answer 28

Inter - Competition between individuals of different species.
Intra - Competition between individuals of the same species.

Question 29

What is a niche?

Answer 29

The role and position a species has in it’s environment, including all interactions with the biotic and abiotic factors of its environment.

Question 30

What is the difference between Commensalism and Mutualism?

Answer 30

Commensalism - An interaction between organisms of two species from which one benefits but the other is un-affected.
Mutualism - Interaction between organisms of two species from which both derive benefit.

Question 31

What human activities have caused the levels of CO2 in the atmosphere to rise?

Answer 31

• Burning fossil fuels.

- Deforestation.

Question 32

What 3 main biological processes contribute to the Carbon cycle?

Answer 32

• Respiration.
• Photosynthesis.
• Decomposition.

Question 33

What are the 2 ways that deforestation releases CO2 back into the atmosphere?

Answer 33

• Trees remove CO2 from the atmosphere through photosynthesis.
• Their burning/Decomposition releases CO2 into the atmosphere.

Question 34

What is Global Warming?

Answer 34

The increase of average global temperature, in excess of the greenhouse effect caused by the atmosphere’s historical concentration of CO2.

Question 35

What are some of the consequences of global warming?

Answer 35

• Melting of polar ice/
• Increased frequency of extreme weather conditions.
• Increased frequency of forest fires.
• Expansion of deserts.
• Extinction of species.
• World food production may decrease.

Question 36

What is a carbon footprint?

Answer 36

The equivalent amount of Carbon Dioxide generated by an individual, a product or a service in a year.

Question 37

How can we reduce the production of greenhouse gases?

Answer 37

• Recycle.
• Drive less.
• Use less air conditioning/heating.
• Reduce meat consumption (especially red).
• Avoid food waste.
• Plant trees (Afforestation).

Question 38

What are the 5 main bacteria involved in the Nitrogen cycle and what do they do?

Answer 38

• Rhizobium (In root nodules of Legumes); Nitrogen Fixation.
• Azozotobacter (Free in soil); Nitrogen fixation.
• Nitrosomonas; Ammonium to Nitrites.
• Nitrobacter; Nitrites to Nitrates.
• Pseudomonas; Denitrifying bacteria.

Question 39

What is the process that converts Detritus into Ammonium?

Answer 39

Ammonification.

Question 40

What human activities can improve the circulation of nitrogen in agricultural soils?

Answer 40

• Ploughing fields.
• Draining land.
• Artificial Nitrogen fixation (e.g. Haber process).
• Using ‘brown’ manure.
• planting field of legumes and then plough back into the soil as ‘green’ manure.

Question 41

What can excessive use of fertilizers cause in nearby streams?

Answer 41

Eutrophication - The artificial enrichment of aquatic habitats by excess nutrients, often caused by run-off fertilisers.

Question 42

What measures can be taken to reduce the likelihood of eutrophication?

Answer 42

• Restrict the amount of fertilizer applied to the soil.
• Only apply when crops are actively growing.
• Leave at least 10m strip next to watercourses.
• Dig draining ditches.