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Flashcards in 1. Populations Deck (46):

Suggest an explanation for the change in the percentage of deaths due to cancer shown in the diagram

-Decrease in percentage of population dying from infectious diseases
-Therefore greater proportion of those remaining die of cancer
-Greater survival to old age so cancer more likely
-Because of accumulated genetic error/ exposure to mutagens/ reduced immune response


What would an age pyramid look like for a population that had a life expectancy at birth of 70 years

Narrow based population pyramid


Explain how two changes in social conditions could have reduced the death rate

-Better food supply so fewer deaths by starvation
-Cleaner water supply so less disease transmission.


Give two possible reasons for fluctuating death rate

-Epidemics/ outbreaks of disease
-Limited/changing food supply


Suggest three reasons why the rapid increase in human population has resulted in the reduction of populations of many other species

-Predation of other species/ eat more of other species
-Interspecific competition/ disruption of food chain
-Destruction of habitat/damage by pollution
-Niche not present
-Competition for named abiotic resource


Give examples of abiotic and biotic factors.




Define an ecosystem.

-Made up of all the interacting biotic and abiotic factors in a specific area. Very often a self contained, self functioning unit


Define biome.

a large naturally occurring community of flora and fauna occupying a major habitat, e.g. forest or tundra.


Define a population.

A group of interbreeding organisms of a particular species in a habitat.


Define a community.

All the populations of different organisms living and interacting in a particular place at the same time.


Define a habitat.

The place where a community of organisms lives


What is a microhabitat?

A smaller unit within a habitat with its own microclimate.


What is an ecological niche?

A niche describes how an organism fits into the environment- where it lives and what it does there.


What are the three factors to consider when using quadrats to sample an area?

-SIZE of quadrats to use- depends on size of species being counted and how they are distributed
-NUMBER of sample quadrats to record within the study area- larger numbers means more reliable results
-POSITION of quadrats within the study area- random sampling must be used to produce statistically significant results.


Why is random sampling important?

-Avoids bias
-Ensures data obtained are valid


How do we make sampling random?

-Make a grid by laying out two tape measures perpendicular to eachother
-Obtain coordinates using a random number generator (generated by a computer or using a random number table)
-Place a quadrat at the intersections of coordinates and sample at that point


Why would systematic sampling along a transect be used instead of using a quadrat to randomly sample?

-When you want to measure the abundance and distribution systematically when some form of transition in the organisms takes place- for example, measuring the stages of zonation.


What are the two ways abundance can be measured?

-FREQUENCY- counting whether a species is present in a quadrat or not
-PERCENTAGE COVER- estimate of area within a quadrat that a particular plant species covers


What is the equation to work out the estimate of a population size using the mark-release-recapture method?

Estimated population size= (total number of individuals in the first sample) X (total number of individuals in the second sample) / (number of marked individuals recaptured)


What are the assumptions we make in the mark-release-recapture technique?

-Proportion of marked:unmarked in the second sample is the same as marked:unmarked in the total population
-Marked individuals distribute homogeneously
-No immigration or emigration
-No births and deaths within the population
-Marking is not toxic or makes it more liable to predation
-Mark is not rubbed off


Describe the graph of the phases of the usual pattern of growth for a natural populations.

-STAGE 1 period of slow growth-small number of individuals reproduce to slowly build up their numbers
-STAGE 2 Log phase- exponential growth where increasing number of individuals continue to reproduce
-STAGE 3 stable phase where rate of growth declines until the size of the population is more or less stable with small fluctuations


What are the abiotic factors that influence the size of a population?

-Temperature- species have an optimum temperature, above it enzymes may denature and below it enzymes will not function fast enough
-Light- the ultimate source of energy in an ecosystem
-pH- affects the action of enzymes
-Water and humidity- affects transpiration in plants and evaporation in animals


Describe intra-specific competition

Competition between individuals of the same species for:
-Breeding sites


Describe inter-specific competition.
What happens when two species occupy a similar/ the same niche?

When individuals of different species compete for food, light, water etc.

The species better adapted will effectively eliminate the other species as no two species can occupy the same niche.


Describe the stages of a predator-prey cycle.

-Predators eat prey, thereby reducing the population of prey
-Predators in greater competition due to reduced prey
-Predator population is reduced as some individuals not able to obtain sufficient food for survival
-With fewer predators, fewer prey are eaten
-Prey population therefore increases
-More prey available means the predator population increases


Give 3 reasons for cyclic fluctuations in populations

-Predator prey cycles
-Climatic factors


What is selection pressure?

The well adapted individuals are more likely to survive to reproduce (withstand disease, escape predators etc...)


What are the two major reasons why there has been a major explosion in the human population size?

-The development of agriculture
-The development of manufacturing and trade which created the industrial revolution


Which factors may temporarily reduce the human population?



What is the equation for population growth?

Population growth= (births + immigration) - (deaths + emigration)


What is the equation for percentage population growth rate in a given period?

Percentage population growth rate (in a given period)= (population change during the period)/(population at the start of the period) x100


What factors affect birth rate?

-Economic conditions- low income usually results in higher birthrates
-Cultural and religious backgrounds- some may be opposed to birth control etc, some countries encourage larger families
-Social pressures and conditions- in some countries large families improves social standing
-Birth control- the extent to which abortion and birth control are used massively affects birth rate
-Political factors- government influence birth rate through education and taxation policies


Give the equation for birth/ rate.

Birth/death rate= (number of births/deaths per year)/ (total population the same year) X1000


What factors affect death rate?

-Age profile- more elderly people means a higher death rate
-Life expectancy at birth- MEDCs usually live longer
-Food supply- adequate and balanced diet reduces death rate
-Safe drinking water and effective sanitation- reduces water borne diseases
-Natural disasters- more prone to drought, famine or disease increases the death rate
-War- immediate drop in the population and a longer term fall as a result of fewer fertile adults


Describe the population pyramids for a:
-Stable population
-Increasing population
-Decreasing population

-STABLE- typical pyramid shape- birth and death rate are in balance
-INCREASING- wider base pyramid due to a high birth rate and a narrow apex due to fewer older people.
-DECREASING- narrow base of pyramid due to low birth rates and a lower mortality rate, leading to more older people (wider apex to pyramid)


What is the definition of the average life expectancy?

The age at which 50% of the individuals of a population are still alive


(2 marks)
What information is required in order to calculate the growth rate of a population?

-Birth rate and death rate= 2 marks
Or -Population at the start of the time period and population at the end of the time period


(5 marks)
The bluebell is a flowering plant found in woodlands. Global warming has been
associated with a change in the population of bluebells. Describe how you could
estimate the number of bluebells in a small woodland.

1. Use a grid / split area into squares/sections;
2. Method of obtaining random coordinates /
numbers, e.g. calculator/computer/random
numbers table/random number generator;
3. Count number/frequency of plants in a quadrat;
4. Calculate mean/average number (per
5. Valid method of calculating total number of
bluebells/plants. e.g. mean number of plants per
quadrat/section/m2 multiplied by number of
in wood;


(1 mark)
Explain what is meant by the term population

Organisms/individuals of one
species in a habitat / same place;


(1 mark)
Give two factors which could lead to a decrease in the death rate in a human

Improved medical care, improved
nutrition, more food, improved
sanitation, less disease, improved
living conditions, improved economy,
war ends;


(2 marks)
How might a survival curve for a human population in 1751 vs 2007 show that the country had undergone a demographic transition?

1. Increase in (average) life
2. Low death rate / decrease in
death rate / few(er) deaths / more
survivors / fewer babies/infants
die / more old(er) people;


(2 marks)
Give two conditions for results from mark-release-recapture investigations to be valid.

1. Marking is not removed / marking
does not affect survival/predation;
2. Limited/no
3. Sufficient time for (marked)
individuals to mix (within the
4. No/little births/deaths/breeding;
5. Sampling method is the same;


(5 marks)
Changes in ecosystems can lead to speciation. A high concentration of copper in soil
is toxic to most plants. In some areas where the soil is polluted with copper,
populations of grasses are found to be growing. These populations of grass belong to
a species also found growing on unpolluted soils.
It has been suggested that a new species of grass may evolve on soil that has been
polluted with copper. Explain how this new species might evolve.

1. Variation/variety;
2. Mutation;
3. Some plants have allele to
survive/grow/live in high
concentration of copper/polluted
4. (Differential) reproductive
success / adapted organisms
5. Increase in frequency of allele;
6. No interbreeding (with other
populations) / separate gene
pool / gene pool differs (from
other populations);


The ecologists found that each species of fish had adaptations to its niche. One of
these adaptations was the shape of its mouth.
Suggest how the shape of mouth is an adaptation to its niche

1. With different mouth eats
different food / has different way
of feeding / specific mouth shape
for specific food;
2. Competition between
species/interspecific competition
is reduced;


(2 marks)
The average efficiency of energy transfer between producers and primary consumers
in pyramids of energy is around 10 %.
Suggest why the efficiency of energy transfer from producers to primary consumers in
this food web is higher than 10 %.

1. Single-celled producers are
more digestible / contain less
cellulose (than plants) / less
energy lost in faeces;
2. All of producer eaten/parts of
plant not eaten;
3. Less heat/energy lost / less


(2 marks)
Energy from the sun may ultimately end up in dead plant matter. Describe how

1. Photosynthesis/light
dependent reaction/light
independent reaction;
2. Carbon-containing