Population size and ecosystems.

Question 1

Population definition.

Answer 1

A group of organisms of the same species.

Question 2

Factors affecting population fluctuation.

Answer 2

-Births
-Deaths
-Immigration
-Emigration(decreases).
Birth+immigration=deaths+emigration(in a stable population).

Question 3

Density independent factors.

Answer 3

Abiotic
Affect death rate
Kill members of small and large populations to the same extent
E.g. Wildfires.

Question 4

Density dependent factors.

Answer 4

Biotic
Affect population more greatly(proportionally) if population is larger & denser
E.G. Larger pop=more food comp, more predation, more diseases, higher spreading of parasites etc.

Question 5

Phases of a population growth curve for bacterium/yeast grown in nutrient broth.

Answer 5

Lag- Enzymes synthesised, DNA replicated
Exponential- Population doubles every unit of time, nutrients abundant
Stationary- Competition of nutrients=death and cell reproduction are equal rates
Death/decline- Nutrient depletion, toxin accumulation=death rate higher than cell reproduction.

Question 6

Carrying capacity meaning.

Answer 6

The maximum number of individuals of a species that the environment can support indefinitely.

Question 7

Phases of a population growth curve for a more complex organism e.g. grey squirrel.

Answer 7

Lag- Population limited by the low numbers to reproduce
Exponential- Doubling of numbers with abundant resources and low predation
Stationary phase- Fluctuation as increase in competition for resources, predation= death rate can become higher than birth rate(when pop increases
When pop decreases, competition reduced–> increases again
Continues indefinitely
Set point of fluctuation=carrying capacity of the environment.

Question 8

Ecosystem definition.

Answer 8

An area that has a particular community of plants and animals interacting with their environment.

Question 9

Community definition.

Answer 9

All of the organisms of all species in an ecosystem.

Question 10

Habitat definition.

Answer 10

The place in an ecosystem where an organism lives.

Question 11

Niche definition.

Answer 11

An organism’s role in an ecosystem
Applies particularly to it’s feeding role.

Question 12

Direction of energy flow along food chains in an ecosystem.

Answer 12

Sunlight
Producers (autotrophs)
Primary consumer (herbivores)
Secondary consumers (carnivores)
May be more trophic levels.

Question 13

Photoautotrophs meaning.

Answer 13

Use light energy from the sun
To fix CO2 into organic molecules (via photosynthesis)
Gross Primary Production (GPP)= rate at which this happens.

Question 14

Net Primary Production (NPP).

Answer 14

Some organic molecules made during photosynthesis used in respiration
What is left=NPP
NPP=plant’s biomass that can be consumed by the next trophic level (herbivores).
NPP=GPP-R.

Question 15

Why is not all sunlight used in photosynthesis?

Answer 15

May be wrong wavelength
Transmitted through leaf
Reflected
Energy is lost at every level due to respiration.

Question 16

What do decomposers feed on?

Answer 16

Dead organism
Faeces
Urine.

Question 17

Why is the number of trophic levels limited?

Answer 17

Because of energy losses
Eventually will not be enough left to sustain another level.

Question 18

Efficiency of a transfer calculation.

Answer 18

little number/big number
x100.

Question 19

General efficiency transfers facts.

Answer 19

Sun–>plant=0.2%
Plant–>herbivore=10%

Question 20

Why do herbivores lose a lot of energy as faeces?

Answer 20

High cellulose levels
Relatively indigestible.

Question 21

Why are endotherms less efficient than ectotherms?

Answer 21

Higher respiratory rates to produce heat
So more energy lost because of this
One reason why aquatic food chains tend to be longer.

Question 22

Methods used in agriculture to reduce energy losses.

Answer 22

Keeping animals warm
Reducing movement
High protein feed.

Question 23

Succession definition.

Answer 23

Change in a community and species composition over time.

Question 24

Stages of primary succession.

Answer 24

Starts from bare rock- no organism living
Pioneer species colonise bare rock- blown in as spores
Lichens erode rock
Die then decay
Eroded rock builds up in cracks= mosses colonise (blown in as spores)
Soil accumulates= grasses, herbaceous plants, shrubs, woodlands(climax community) become established.

Question 25

Climax communities.

Answer 25

Stable, end point of succession- no further changes High species diversity.

Question 26

Factors affecting speed of succession.

Answer 26

Temperature Proximity to a source of seeds and spores to be blown in.

Question 27

Sere meaning.

Answer 27

A stage of succession Characterised by particular communities.

Question 28

How can succession be deflected?

Answer 28

Grazing Mowing Burning Maintaining particular sub climax communities.

Question 29

Secondary succession.

Answer 29

Starts from cleared land Where communities have lived before Faster due to seeds, roots and soil to support the plants After forest fires.

Question 30

Random sampling method.

Answer 30

Used on a uniform area Grid area Generate random numbers to select co-ords Place quadrats at co-ords Use to asses cover %/number of organisms.

Question 31

What to measure in fieldwork?

Answer 31

Abiotic factors that may affect results E.g. pH, light intensity, soil, water Use Simpson's diversity index (counted species/organisms).

Question 32

Method w/ transects.

Answer 32

Use when there is a change in conditions Place quadrats at regular intervals along a line Count/use % cover Present data as a kite diagram.

Question 33

Practical work- risks.

Answer 33

Biting/stinging insects Slippery conditions Sunburn Hypothermia.

Question 34

Methods to insure fairness/ accuracy of fieldwork.

Answer 34

Use correct sized grid preliminary investigation to determine this Carry out enough repeats Different times of year Successive years?

Question 35

What recycles nutrients in a nutrient cycle?

Answer 35

Decomposers- bacteria/fungi Use organic molecules and convert them to inorganic compounds.

Question 36

Autotrophs function.

Answer 36

Use energy from sunlight/chemicals Convert inorganic compounds to organic ones Then passed along food chain.

Question 37

Carbon cycle steps.

Answer 37

1) Plants take in CO2, use it in photosynthesis, make organic molecules, passed through food chain 2) Plants and animals respire and secrete CO2 3) Combustion releases CO2 4) Decomposers respire= releases CO2.

Question 38

Carbon footprint definition.

Answer 38

Total amount of CO2 released attributable to an individual, product or service over the course of a year.

Question 39

Human impacts on the carbon cycle.

Answer 39

Deforestation- less CO2 absorbed Combustion of fossil fuels- releases 'locked in' CO2 to atmosphere.

Question 40

Effect of CO2.

Answer 40

Traps heat Raises global temperatures Global warming.

Question 41

Effects of global warming.

Answer 41

Species distribution- species pushed further north and south as equator gets warmer Agricultural practices- may need to have drought resistant crops, may need crops that can survive w/ excess rain.

Question 42

Factors affecting rate of decomposition.

Answer 42

Colder= slower pH, more acidic= slower O2 availability: slower when less oxygen available.

Question 43

Nitrifying bacteria.

Answer 43

Nitrosomonas-converts ammonium to nitrite Nitrobacter-convert nitrite to nitrate.

Question 44

Nitrogen fixing bacteria.

Answer 44

Convert nitrogen gas to ammonium: Azotobacter-free living in soil Rhizobium-in root nodules of legumes, symbiotic.

Question 45

Dentrifying bacteria.

Answer 45

Convert nitrate to nitrogen gas Pseudomonas-thrive in water logged soils.

Question 46

Rhizobium.

Answer 46

-Symbiotic relationship w/ legumes -Fixes N gases to ammonium ions -Makes amino acids -Exports them to legumes -Legume makes root nodule for Rhiz -Gives it carbs, micro-anaerobic conditions(for nitrogen fixation).

Question 47

Dentrification.

Answer 47

Nitrogen released back into atmosphere From dentrifying bacteria Nitrate to N gas Anaerobic conditions, water-logged soils Slows nitrification=nitrate poor soil.

Question 48

Insectivorous plants.

Answer 48

Water-logged areas Insect proteins-->amino acids.

Question 49

Ploughing in agriculture.

Answer 49

Introduces air to soil Encourages nitrification.

Question 50

Drainage in agriculture.

Answer 50

Reduces water logging Reduces dentrification.

Question 51

Leaching meaning.

Answer 51

Soluble ammonium, nitrite and nitrate ions dissolve in ground water and drain away Loss in nitrites.

Question 52

Eutrophication.

Answer 52

Excess nutrients in lakes and rivers from leaching.

Question 53

Algal bloom.

Answer 53

Microscopic algae undergoing a population bloom As a result of eutrophication Blocks light from bottom-dwelling plants=die Algae die=decomposer increase=use more oxygen in water=increased biological oxygen demand Fish and invertebrates die and are decomposed.

Question 54

What do plants do with nitrates and ammonium ions?

Answer 54

Absorb them and use to synthesise nitrogen containing compounds Key components in amino acids, proteins, nucleic acids, chlorophyll=photosynthesis(CO2+water).

Question 55

Negatives of draining land.

Answer 55

Loss in species rich wetlands Reduces species diversity.

Question 56

Benefit of using wide borders around fields.

Answer 56

Support wild flowers(favour poor soil), pest predators, pollinators Fertiliser=reduction in wild flowers&pollinators-->reduce species diversity.