Ecosystems

Question 1

Ecosystem

Answer 1

-group of living and non living things and the interrelationship between them

Question 2

Components of an ecosystem

Answer 2

1.habitat- where an organism lives
2.population- all of the organisms of the same species that live in the same place at the same time
3.community- all of the populations of different species that live in the same place at the same time

Question 3

Niche

Answer 3

-role of each species in the ecosystem
-difficult to fully define as each organism interacts with living and non living parts

Question 4

Biotic factors effecting ecosystems

Answer 4

-producers eg.plants that supply chemical energy
-consumers eg. primary, secondary, tertiary
-decomposers eg. fungi that feeds on waste material

Question 5

Abiotic factors affecting ecosystems

Answer 5

-pH
-humidity
temperature
-concentration of pollutants

-at extreme values, species may perform better or worse or may die

Question 6

Types of changes in ecosystems that affect population size

Answer 6

-cyclic- repeating rhythm eg. predator and prey fluctuations
-directional- not cyclic, one direction eg. erosion
-unpredictable/erratic- no rhythm and no constant direction eg. effects of hurricanes

Question 7

Biomass

Answer 7

-organic (glucose) and inorganic (mineral ions) components of a plant

Question 8

Trophic level

Answer 8

-level at which an organism feeds in a food chain

Question 9

Biomass transfers

Answer 9

-each trophic level, some biomass is lost (either through respiration and heat or dead organisms and waste material)
-biomass is less at higher levels of the food chain
-represented as a pyramid of numbers
-producers at bottom with biggest bar, consumers above, bars smaller

Question 10

Calculating efficiency of biomass transfer

Answer 10

=biomass at higher trophic level/ biomass at lower trophic level x100
or
=biomass of primary consumer/ biomass of producer x100

Question 11

Productivity

Answer 11

rate of production of new biomass by producers

Question 12

Gross primary productivity

Answer 12

rate which plants convert light energy into chemical energy through photosynthesis

Question 13

Net primary productivity

Answer 13

proportion of energy from the sun available to enter the food chain

Question 14

How farmers increase primary productivity (plants)

Answer 14

-plant crops early in the season so they get a lot of light
-breed drought resistant strains
-greenhouse so plants kept warm
-crop rotation which stops reduction in soil level of in organic materials
-pesticides, fungicides, herbicides

Question 15

How farmers increase secondary productivity (livestock)

Answer 15

-harvest animals just before adulthood to minimise loss of energy
-selective breeding, animals with faster growth rates
-antibiotics to reduce loss of energy fighting pathogens
-stopping grazing which prevents loss of energy

Question 16

Steps in saprophytic decomposition

Answer 16

-secrete enzymes onto waste material
-digest the material into small molecules and the absorb them into their body
-molecules are then stored or respired

Question 17

Nitrogen cycle

Answer 17

-nitrogen fixation
-ammonification
-nitrification
-denitrification

Question 18

Nitrogen fixation

Answer 18

-plants can’t use N2 directly due to triple bond
-has to be fixed by lightning, haber process or nitrogen fixing bacteria
-bacteria live in root nodules and have mutualistic relationship- supplies plant with fixed nitrogen in exchange for glucose
-proteins in nodules absorb O2, making conditions anaerobic which is optimum for nitrogen reductase

Question 19

Ammonification

Answer 19

-NH4+ is released from ammonification by bacteria involved in putrefaction of proteins found in waste matter

Question 20

Nitrification

Answer 20

-oxidising NH4+ to NO2-
or
-oxidising NO2- to NO3-

Question 21

Denitrification

Answer 21

-some bacteria convert NO3- to N2 gas
-they do this in anaerobic conditions as they use NO3- as a source of O2

Question 22

Carbon cycle

Answer 22

-driven by photosynthesis and respiration
-animals and plants respire producing CO2
-plants use CO2 in photosynthesis
-carbon is exchanged between air and water, forming carbonic acid when dissolved in water or hydrogen carbonate

Question 23

Succession

Answer 23

progressive change in a community of organisms over time

Question 24

Primary succession

Answer 24

development of a community from bare ground

Question 25

Secondary succession

Answer 25

take solace in a previously colonised but disturbed or damaged habitat

Question 26

How primary succession occurs

Answer 26

-algae and lichens live on bare rock= pioneer community
-erosion of rock and build up of waste material creates enough soil for larger plants to grow
-larger plants succeed the smaller plants until a stable community is reached= climax community

Question 27

Succession on sand dunes

Answer 27

-pioneer species eg sea rocket colonise sand just above high water mark
-sand builds up around plants due to wind. Plants die and decay, nutrients accumulate so larger plants can colonise it
-with more stability and nutrients, plants like marram grass start to grow
-as nutrients build up other plants colonise the sand

Question 28

Deflected succession

Answer 28

-when succession is stopped or interfered with eg. cutting the grass, using herbicide/fertiliser

Question 29

2 types of data quadrants can collect

Answer 29

-Distribution- presence or absence of each species
-Abundance- number of individuals of each species

Question 30

Where to place a quadrat
(sampling)

Answer 30

Random sampling- use random numbers and plot coordinates
Systematic sampling- take samples at regular distances

Question 31

Population size of species=

Answer 31

mean no. individuals of species in each quadrant/ fraction of total habitat area covered by single quadrat

Question 32

2 types transects

Answer 32

-Line- regular intervals, count the species touching the tape
-Belt- regular intervals, place quadrat next to the line

Question 33

Using pilot study to determine how many samples to take

Answer 33

-take random samples across the habitat and create a cumulative frequency table
-plot cumulative frequency against quadrat number
-where the curve levels off is how many quadrats to use