Ecosystems

Question 1

What is a species?

Answer 1

A group of similar organisms that can interbreed to produce live, fertile offspring

Question 2

What is a population?

Answer 2

A group of individuals of 1 species that occupy the same habitat at the same time and can interbreed

Question 3

What is a community?

Answer 3

All of the populations of different species living and interacting in a place at the same time

Question 4

What is a habitat?

Answer 4

Where an organism lives, which is characterised by physical conditions and the other organisms present

Question 5

What is an ecosystem?

Answer 5

The dynamic interaction between all biotic and abiotic factors in a given area

Question 6

What is a niche?

Answer 6

How an organism fits into the environment and their role in the ecosystem

Question 7

What is included in a niche?

Answer 7

Habitat, species behaviour, interactions with other species and the environment

Question 8

What are biotic factors?

Answer 8

Living organisms that affect the ecosystem conditions.

Other species (predator, pathogen, competitor)
Producers, consumers and decomposers

Question 9

What are abiotic factors?

Answer 9

Non living components that affect the ecosystem conditions.

Temperature, pH, humidity, pollutant levels, water, light etc.
Influenced by biotic factors

Question 10

What determines how well a species survives?

Answer 10

How well they are adapted to its niche - overlapping leads to competition.
The greater the number of niches, the greater the number of organisms present.

Question 11

What are the 3 kinds of ecosystem dynamics?

Answer 11

Cyclic - repeat periodically
Directional - factors continue in either direction and may last longer that the organism’s lifetime
Erratic - no periodicity or direction

Question 12

How is energy from photosynthesis stored?

Answer 12

Chemical energy is stored as organic molecules in plant biomass, so when it is eaten, the energy stored is transferred along the food chain.

Question 13

What are ways of illustrating food chains?

Answer 13

Food webs, trophic levels within webs, pyramid of numbers (how many organisms at each level) and pyramids of biomass (how much dry biomass is at each level).

Question 14

What are disadvantages of pyramids of biomass?

Answer 14

• Dry biomass calculations are time consuming
• Samples are used to estimate - unrepresentative
• Only show data at one point in time, so not accurate reflection of habitat sampled

Question 15

What is biomass?

Answer 15

The total mass of living material in a specific area at a given time

Question 16

What are the different types of biomass?

Answer 16

1. Dry is more accurate, as it gives the chemical energy stored.
2. Wet has varied water content, so is inaccurate. But is less destructive.

Question 17

How is dry biomass measured?

Answer 17

Kill the organism then put it in an oven at 80’C and measure mass periodically.

Question 18

What are sources of biomass loss?

Answer 18

• Some parts of organisms are inedible or cannot be digested/consumed
• Energy is lost is excretion and respiration
• Some is lost due to heat loss which is transferred to the environment

Question 19

What are ways of reducing biomass losses?

Answer 19

• Simplifying food chains
• Reducing energy loss as heat during respiration

Warm environment for livestock reduce movement, exclude competitors/predators, control food intake, selective breeding, antibiotics

Question 20

What is carrying capacity?

Answer 20

The maximum population size which can be maintained over a period in a certain habitat.

Question 21

What are examples of limiting factors?

Answer 21

Temperature, pH, light, water

Disease, predation. competition

Question 22

What is interspecific competition?

Answer 22

Competition between individual of different species.

This happens when niches overlap and they are competing for resources.

Question 23

What is intraspecific competition?

Answer 23

Competition between individuals of the same species.

If a community has limited resources. It slows population growth and keeps the population size relatively stable.

Question 24

What is succession?

Answer 24

A process by which different species comprising a community change over time.

Gradual, directional change that occurs in stages. Changes biodiversity of the area.

Question 25

What is primary succession?

Answer 25

The colonisation of lifeless areas by living organisms eg. algae.

Question 26

What are the stages of primary succession?

Answer 26

1. Inhospitable area is colonised by a pioneer species
2. They alter the abiotic factors by releasing nutrients and forming soil by decomposition. New plant species outcompete the pioneer
3. Organic matter available increases through the cycle, creating more soil.
4. Other species grow and change the abiotic environment more. The cycle repeats
5. This process continues until an equilibrium is reached = climax community

Question 27

Where does secondary succession take place?

Answer 27

On land which has been previously colonised by was damaged eg. wildfires
Not start from bare ground.

Question 28

What is deflected succession?

Answer 28

When natural ecological succession is stopped/interfered with by humans.
eg. grazing, burning, fertiliser

Question 29

What is a plagioclimax community?

Answer 29

An area/habitat with a sub-climax community in which the influences of humans has prevented the ecosystem developing further.

Question 30

Why are nutrient cycles necessary?

Answer 30

There is a finite supply, so resources must be recycled to keep habitats stable.

Question 31

What are saprotrophs?

Answer 31

They secrete enzymes onto the dead/waste, digesting the material and absorbing it. It is then stored/respired to release energy.

Question 32

What are the steps of the carbon cycle?

Answer 32

1. Organisms respire to release CO2
2. Photosynthesing organisms take up CO2 for use, increasing their biomass
3. Plants are eaten, and the C trapped in their biomass is transferred along the food chain
4. The dead organisms/waste are decomposed by decomposers which respire and release CO2

Question 33

How can carbon re-enter the cycle if not eaten by animals?

Answer 33

• Decomposition of fossil fuels releases CO2
• Release of CO2 reacts with H2O vapour in the air to form acid rain
• CO2 enters water bodies as hydrogen carbonate

Question 34

Why is the nitrogen cycle needed?

Answer 34

Nitrogen is very unreactive, so must be converted so plants can take it up.

Plant roots absorb nitrates to make organic N-containing compounds. Plants eaten so they pass along the food chain.

Question 35

What are the 4 stages of the nitrogen cycle?

Answer 35

Nitrogen fixation, ammonification, nitrification, denitrification.

Question 36

What is nitrogen fixation?

Answer 36

N gas is converted to inorganic N-containing compounds.
Natural (lightning) or unnatural (Haber process).

Question 37

What is needed for nitrogen fixation?

Answer 37

Free living bacteria = azotobacter. Reduces N gas to NH3 - make amino acids

Mutualistic bacteria = Rhizobium. Use N gas to make amino acids for the plant, which gives carbs from photosynthesis.

Question 38

What is ammonification?

Answer 38

Breaking down organic N-containing compounds into NH3 or NH4+. By saprotrophs.

Question 39

What is nitrification?

Answer 39

Ammonium is converted into nitrites and then nitrates by nitrifying bacteria in oxidation reactions.

Into nitrites by Nitrosomonas bacteria. Into nitrates by Nitrobacter bacteria. Both are chemoautotrophic as they gain energy from oxidation reactions.

Question 40

What is denitrification?

Answer 40

Nitrates are converted into N gas in anaerobic environments by denitrifying bacteria which make N gas and nitrous oxide.

Reduces availability of N-containing compounds for plants, so must prevent build up.