Ecology...

Front 1

Describe the consequences of overpopulation of a species. (6)

Back 1

a. members of a species tend to produce more offspring than can survive;
b. competition for available resources occurs;
c. habitat has a carrying capacity/limit to the population it can support;
d. overpopulation is when carrying capacity is exceeded;
e. the habitat may be destroyed by exploitation by the species;
f. food web may be interrupted;
g. an example (e.g. greater abundance of predators may be stimulated by overpopulation of prey / prey may be reduced because of over-abundance of predators)
h. invasion of new habitats by the overpopulating species/migration;
i. natural selection (of successful variations);
j. evolution of a species (with new characteristics);
k. mortality will exceed natality / death of individuals will reduce population (to carrying capacity);
l. example of effect of limiting factor; (e.g. spread of disease)

Front 2

what is an autotroph

Back 2

synthesize their organic molecules from simple inorganic substances

Front 3

heterotrophs

Back 3

organisms that obtain organic molecules from other organisms

Front 4

Detritivore

Back 4

an organism that ingests non-living organic matter

Front 5

Saprotroph

Back 5

an organism that lives on or in non-living organic matter, secreting digestive enzymes into it and absorbing the products of digestion.

Front 6

Explain how the flow of energy in the food web differs from the movement of nutrients. (2)

Back 6

nutrients are recycled in a food web and energy enters and leaves/is not recycled;
nutrients are recycled by saprotrophs/returned to environment and reused;
while energy (enters as light and) is dispersed as heat;

Front 7

Discuss reasons why the levels of a pyramid of energy differ in size. (2)

Back 7

(the shape of pyramid) shows energy lost from base to top of pyramid/80 to 90 % lost at each trophic level;
(because) energy is used/released through cell respiration/heat/metabolism/
movement (at each trophic level);
not all tissues are eaten i.e. bone/hair/cellulose/excretion/undigested/die (so energy is not available for next trophic level);

Front 8

Describe the relationship between the rise in the concentration of atmospheric carbon dioxide and the enhanced greenhouse effect. (5)

Back 8

CO2 is a greenhouse gas;
increases in CO2 increase/enhance the greenhouse effect;
greenhouse effect is a natural phenomenon but not its increase;
Earth receives short wave radiation from the sun;
reradiated from Earth as longer wave radiation/infra red/heat;
CO2 /greenhouse gases trap/absorb longer wave radiation/infra red/heat;
global warming happened during same time/period as CO2 rise;
CO2 concentration correlated (positively) with global temperature / global temperature
increases as CO2 concentration increases;
(causal) link accepted by most scientists;
no proof that man-made increases in CO2 have caused global warming;

Front 9

Outline the precautionary principle. (5)

Back 9

those proposing something must prove that it causes no harm;
before they start to do it;
objectors do not have to prove that there will be harm;
activities that risk/threaten/may cause harm are banned;
trials/tests must be done first;
precautionary principle is applied when possible consequences are severe;
precautionary principle should be used in the case of global warming;
action should be taken to reduce CO2 emissions before proved it is the cause;
another example of implementation of the precautionary principle;

Front 10

Antibiotic resistance in bacteria is an example of evolution in response to environmental change. Using another example, explain how an environmental change can lead to evolution. (8)

Back 10

natural selection (in correct context);
better-adapted individuals survive/more likely to survive;
more reproduction/genes passed on by better adapted individuals;
name of species;
description of original/decreasing phenotype;
type of environmental change that led to evolution;
consequence of environmental change description of new/increasing phenotype;
genetic basis of phenotypes;
reason for new phenotype being better adapted;
detail of reason for adaptedness of new phenotype; [8 max]
The following has been provided as an example answer.
great tit;
bird that lays its eggs in spring;
global warming/climate change;
more caterpillars (on trees) in early spring;
laying eggs earlier in spring;
time of egg laying is (partly) genetically controlled;
eggs laid early hatch at start of period of greatest food abundance;
more young can be fed/young grow faster/fewer deaths;

Front 11

Name one nitrogenous waste product of birds.

Suggest an adaptive advantage of this waste product in relation to their habitat.

Back 11

Uric acid

excreted with little water/as a paste advantage because flight means cannot carry much water

Front 12

Explain the energy flow in a food chain as exemplified by a pyramid of energy. (8)

Back 12

a food chain includes a producer and consumers;
represents the direction of energy flow;
energy loss occurs between trophic levels;
due to material not consumed/assimilated;
and from heat loss due to cell respiration;
energy passed on from one level to next is 10−20%;
which limits length of food chain;
photosynthesis / producers convert solar energy to chemical energy (in organic molecules);
consumers obtain necessary energy from eating organisms of previous trophic level;
an energy pyramid shows the flow of energy from one tropic level to the next (in a community);
units are energy per unit area per unit time / Jm−2 yr−1 ;
Pyramid of energy – properly drawn, each level no more than one fifth the width of the level below it, with three correctly labelled trophic levels
e.g. producer, primary consumer;

Front 13

Outline the effects of factors that increase or decrease the size of a population. (4)

Back 13

natality/immigration causes increased population size;
mortality/emigration causes decreased population size;
predation / disease / any other limiting factor decreases population size;
population change =(natality + immigration) −(mortality + emigration);
natural disasters / density independent factors;

Front 14

Define the term random sample.

Back 14

sample where all members of a population equally likely to be selected / sample selected without bias

Front 15

Explain the usefulness of standard deviation when comparing the means of two sets of data. (2)

Back 15

standard deviation is a measure of variability / measure of spread of data around mean;
high value (of standard deviation) indicates highly variable data / low value indicates low variability;
(high standard deviation leading to) overlap of two sets of data suggests no difference between the two;

Front 16

Outline the role of variation in evolution. (3)

Back 16

members of a population show variation;
variation has its origins in sexual reproduction / meiosis / mutation;
some variations allow an individual to be better adapted;
(better adapted varieties) survive to reproductive age;
frequency of advantageous alleles increases (over time);

Front 17

Explain how polygenic inheritance leads to continuous variation. (2)

Back 17

polygenic inheritance is when a characteristic/phenotype is determined by more
than one gene;
as the number of genes involved increases, the number of intermediate phenotypes
increases;
discrete groups become more difficult to recognize / phenotypes become continuous;

Front 18

Explain the significance to organisms of water as a habitat. (4)

Back 18

is transparent so it allows photosynthesis / capture of prey;
aquatic food chains can exist;
resists changes in temperature / has a high specific heat capacity;
provides a stable thermal environment;
water contains dissolved gases needed for life;
hydrogen bonding/surface tension enables water surface to be used as a habitat;
high boiling point means natural water habitats rarely boil;
when water cools/freezes it becomes less dense so ice forms at surface, providing insulation to water below, in which living organisms can survive;

Front 19

Define the term community as it relates to ecosystems.

Back 19

group of populations living (and interacting with each other) in an area

Front 20

Outline the causes and consequences of the enhanced greenhouse effect. (5)

Back 20

a. burning of (fossil) fuels/coal/oil/gas releases carbon dioxide;
b. deforestation/loss of ecosystems reduces carbon dioxide uptake;
c. methane emitted from cattle/livestock/melting permafrost/waste dumps;
d. heating of the atmosphere/global warming/climate change;
e. melting of ice caps/glaciers/permafrost / sea level rise / floods / droughts /
changes in ocean currents / more powerful hurricanes / extreme weather events
/ other abiotic consequence;
f. changes in species distributions/migration patterns / increased decomposition
rates / increases in pest/pathogen species / loss of ice habitats / other biotic
consequence;

Front 21

All organisms in an ecosystem are involved in the carbon cycle. Outline the roles of living organisms in the carbon cycle. (8)

Back 21

plants/producers fix carbon (dioxide)/use carbon (dioxide) in photosynthesis;
sugars/carbon compounds (produced) in plants/producers from photosynthesis;
(carbon compounds in) plants/producers eaten by animals/primary consumers/herbivores;
(carbon compounds in) primary consumers eaten by secondary consumers/ passed along food chain;
carbon compounds/sugars/organic molecules digested and absorbed by consumers;
carbon dioxide released by cell respiration (in plants/animals/consumers);
plants/animals die and are decomposed by (saprotrophic) bacteria/fungi;
carbon dioxide released by cell respiration in bacteria/fungi/decomposers;
enzymes released to digest/hydrolyse carbon compounds in organic matter;
forest fires/combustion releases carbon dioxide;
humans burn fossil fuels adding carbon dioxide to the atmosphere;