6.5 ECOSYSTEMS

Question 1

What are the levels of ecosystems?

Answer 1

Individual - population - community - ecosystem - biome - biosphere

Question 2

What are pyramids of numbers?

Answer 2

Pyramids of numbers:
- food chains and food webs are a useful means of showing what different organisms eat and energy flow
- but do not provide quantitative information - ecological pyramids do

Question 3

What are the issues with pyramids of number?

Answer 3

Issues with pyramids of number:
- no account is taken of size = one tree is given the same value of one aphid
- number of individuals is so great that is is impossible to represent them accurately on the same scale as other species in the food chain = one tree and one million aphids

Question 4

What are pyramids of biomass?

Answer 4

Pyramids of biomass:
- more reliable, quantitative description of a food chain is provided when their biomass is measured
- biomass is the total mass of the plants and/or animals in a particular place = any mass of organisms, dry biomass = no water

Question 5

What is the nitrogen cycle?

Answer 5

The nitrogen cycle:
1. ammonification - the process by which decomposers break down nitrogen containing compounds into dead organisms, faeces and urine into ammonium compounds
2. nitrification - the process by which ammonium compounds in the soil are converted into other organic compounds that can be absorbed by the plants (oxidation reaction so can only occur in well-aerated soil)
3. denitrification - the process by which denitrifying bacteria convert nitrates into nitrogen gas in anaerobic conditions
4. nitrogen fixation - the process by which nitrogen gas is converted into ammonia
5. assimilation - the processes of photosynthesis and the absorption of raw materials by which plants derive their nutrition
6. consumption - the process of animals eating plant proteins, digesting them and using the amino acids to produce their own proteins

Question 6

Why is carbon so important?

Answer 6

Importance of carbon:
- one of the most significant elements = found in carbohydrates, fats, proteins and nucleic acids
- main source of carbon is carbon dioxide in the atmosphere = 0.02%
- constantly cycles between atmosphere and living organisms

Question 7

Why do carbon levels fluctuate in the atmosphere?

Answer 7

Why carbon levels fluctuate:
- localised levels fluctuate seasonally due to photosynthesis rate (lower in summer as more photosynthesis and higher in winter as less photosynthesis)
- photosynthesis only occurs during the day removing co2, whereas respiration occurs 24 hours a day, adding co2 at a steady rate = so co2 levels are higher at night

Question 8

What are carbon sinks?

Answer 8

Carbon sinks are reservoirs that retain carbon and keep it from entering earths atmosphere
- abiotic carbon sinks = sedimentary rocks, fossil fuels, oceans
- biotic carbon sinks = humus and plants

Question 9

How is biomass measured?

Answer 9

Measuring biomass:
- easiest way to measure wet mass as it is fresh
- water content varies so dry mass should be used = dry biomass
- destructive so only small samples can be taken, then is not representative of population
- even if water is removed, gut contents can remains and add to biomass measurement

Question 10

What are the issues with pyramids of biomass?

Answer 10

Issues:
- seasonal changes = plant biomass may vary within season when sample is taken as a single point in time = not accurate representation of a population

Question 11

What are pyramids of energy?

Answer 11

Pyramids of energy:
- most accurate representation of energy flow through ecosystem
- collecting data can be difficult and complex
- data are collected in a given area (eg 1m2) and in a set time (eg 1 year)
- results are more reliable than those for biomass as two organisms of the same biomass may store different amounts of energy
- 1g of fat stores 2x amount of energy of 1g carbohydrate

Question 12

What is energy transfer?

Answer 12

Energy transfer:
- in most living cells ATP is the immediate energy source
- initial entry of energy into the ecosystem by photosynthesis
- however energy is lost at each trophic level = less energy available to higher levels = fewer consumers as you go up food chain

Question 13

Why do plants lose energy?

Answer 13

Plants lose energy through unsuitable wavelengths of light, inefficiency of photosynthesis, light reflected, light absorbed (by non-photosynthetic parts)
- respiration

Question 14

What is gross primary productivity?

Answer 14

GPP is the rate at which plants convert light to chemical energy.

Question 15

What is net primary productivitity?

Answer 15

NPP is the remaining energy left for consumers after energy loss from plant
NPP = GPP - R

Question 16

What is primary productivity?

Answer 16

Primary productivity is the rate at which light is transferred to chemical energy (biomass) in plants.

Question 17

What is secondary productivity?

Answer 17

Secondary productivity is the rate at which an animal gains biomass as a result of eating a plant or an animal.

Question 18

Who carries out primary production and why?

Answer 18

Primary production is carried out by farmers, gardeners and plant growers to increase the yield of the plants and animals they are growing/rearing.

Question 19

How do you improve primary production?

Answer 19

Primary production is improved by:
- light quality and intensity = use artificial light in a greenhouse
- water availability = automated irrigation in a greenhouse
- temperature = greenhouse has higher temperature than outside, thermostat to light/vent the greenhouse
- mineral availability = add fertiliser to crops/soil = NPK
- co2 concentration = alter co2 concentration artificially

Question 20

What is succession?

Answer 20

Succession is a process by which communities of plants and animals colonise an area and then, over time, are replaced by other more varied organisms.

Question 21

What are the types of succession?

Answer 21

The types of succession are primary succession, where the starting point is bare rock, and secondary succession, that occurs following damage to a community leaving soil that plants can colonies

Question 22

What is a pioneer species?

Answer 22

A pioneer species is the first species to colonies a bare substance in primary succession - they are often able to withstand desiccation, extremes of temperatures and low levels of minerals = e.g lichen.

Question 23

What is the process of succession?

Answer 23

Succession:
bare rock - pioneer species - pioneer species break up rock - ps die and decompose and builds up humus - simple plants can now grow - simple plants cast shade to stop ps growth - organic matter gradually increases as bigger plants die - colonised by dominant plant species and a climax community is rescued

Question 24

What is a climax community?

Answer 24

A climax community is an ecological community at which populations of plants or animals remain stable and exist in balance with each other and their environment.

Question 25

What is a sere?

Answer 25

A sere is a stage in the process of succession.

Question 26

What is secondary succession?

Answer 26

Secondary succession:
- similar to primary except occurs when current seral stage is removed abruptly
- may be due to a natural disaster such as a fire or volcanic eruption or by human influence such as deforestation and strip mining.

Question 27

What is deflected succession?

Answer 27

Deflected succession is a community that remains stable only because human activity prevents succession from running its course.

Question 28

What is carrying capacity?

Answer 28

Carrying capacity (limit ‘k’) is the maximum population size an ecosystem can support.

Question 29

What are models of population growth?

Answer 29

Models of population growth:
- each interval of time results in an equivalent addition of new individuals
- natural populations may follow a linear pattern shortly after establishment, but often the number of individuals increases faster once critical density is reached- this is called exponential growth.

Question 30

What is the Sigmoid population growth curve?

Answer 30

Sigmoid population growth curve:
- phase 1 = period of slow growth
- phase 2 = period of rapid growth
- phase 3 = stable state