Ecosystems and Biomass

Question 1

What is meant by net and gross primary productivity?

Answer 1

Gross primary productivity (GPP) - the rate of chemical
energy fixture during photosynthesis by all producers in an
ecosystem, measured in kJ m-2 year-1

Net primary productivity (NPP) - the amount of chemical energy that is available to heterotrophs in an ecosystem

Question 2

How is net primary productivity calculated?

Answer 2

NPP=GPP-R
Gross primary productivity minus energy generated in respiration

Question 3

What is a trophic level?

Answer 3

The position that an organism holds in a food chain, food web, pyramid of numbers or pyramid of biomass.

Question 4

What is biomass and how is it transferred? Can we measure this?

Answer 4

The weight of living matter in a certain area, transferred up trophic levels through consumption. It’s measured in terms of mass of carbon, or dry mass of tissue.

Question 5

State the formula for efficiency of biomass transfer

Answer 5

Efficiency = (biomass transferred/biomass intake) x 100

Question 6

Why are biomass transfers not 100% efficient?

Answer 6

Energy is lost through
-Egestion (feces)
-Excretion (waste products like urine)
-Respiration
-The production of inedible bones and shells

Question 7

Why do food chains usually have fewer than five trophic levels?

Answer 7

Biomass transfers are not 100% efficient and so there’s often not enough energy to support 5 trophic levels.

Question 8

Define population

Answer 8

All organisms of the same species living with one another in a habitat at the same time.

Question 9

Define community

Answer 9

All of the populations of different species living together in a habitat.

Question 10

What is a habitat?

Answer 10

The region where an organism usually lives.

Question 11

Define ecosystem

Answer 11

The community of organisms and non-living components of an area and their interactions. Varies from large ones like biomes to very small ones like microhabitats.

Question 12

Describe biotic and abiotic factors, giving examples.

Answer 12

Biotic: living features like predators or disease.
Abiotic: non-living features like light and t°

Question 13

Define niche

Answer 13

Describes how an organism fits into an ecosystem and its role in that environment.

Question 14

What do population numbers depend on?

Answer 14

Birth rate, death rate, immigration and emigration.

Question 15

What is distribution?

Answer 15

The spread of living organisms in an ecosystem.

Question 16

What is sampling?

Answer 16

Selecting a group of individuals that will represent the whole target population. It allows us to measure the distribution and abundance of organisms.

Question 17

Suggest methods of assessing abundance and distribution of organisms

Answer 17

Quadrats and transects

Question 18

Suggest different ways abundance can be qualified

Answer 18

% area cover, % frequency, density

Question 19

What is random sampling?

Answer 19

A sampling technique to avoid bias, like creating a square grid and generating random coordinates

Question 20

What is systematic sampling?

Answer 20

A sampling technique used to determine the abundance and distribution of organisms along an area at periodic intervals. Commonly used in ecosystems where some sort of gradual change occurs.

Question 21

How can the light intensity be measured?

Answer 21

Using a light meter placed near the ground with the photodetector facing the light source.

Question 22

How can the soil pH be measured?

Answer 22

Using a pH probe which is placed in the soil in order to provide a reading on the display for soil pH.