1. Populations

Question 1

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

Answer 1

• 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

Question 2

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

Answer 2

Narrow based population pyramid

Question 3

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

Answer 3

• Better food supply so fewer deaths by starvation

- Cleaner water supply so less disease transmission.

Question 4

Give two possible reasons for fluctuating death rate

Answer 4

• Epidemics/ outbreaks of disease

- Limited/changing food supply

Question 5

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

Answer 5

• 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

Question 6

Give examples of abiotic and biotic factors.

Answer 6

Abiotic:

• temperature
• rainfall

Biotic:

• Competition
• Predation

Question 7

Define an ecosystem.

Answer 7

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

Question 8

Define biome.

Answer 8

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

Question 9

Define a population.

Answer 9

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

Question 10

Define a community.

Answer 10

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

Question 11

Define a habitat.

Answer 11

The place where a community of organisms lives

Question 12

What is a microhabitat?

Answer 12

A smaller unit within a habitat with its own microclimate.

Question 13

What is an ecological niche?

Answer 13

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

Question 14

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

Answer 14

• 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.

Question 15

Why is random sampling important?

Answer 15

• Avoids bias

- Ensures data obtained are valid

Question 16

How do we make sampling random?

Answer 16

• 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

Question 17

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

Answer 17

-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.

Question 18

What are the two ways abundance can be measured?

Answer 18

• 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

Question 19

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

Answer 19

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)

Question 20

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

Answer 20

• 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

Question 21

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

Answer 21

• 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

Question 22

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

Answer 22

• 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

Question 23

Describe intra-specific competition

Answer 23

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

Question 24

Describe inter-specific competition.

What happens when two species occupy a similar/ the same niche?

Answer 24

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.

Question 25

Describe the stages of a predator-prey cycle.

Answer 25

- 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

Question 26

Give 3 reasons for cyclic fluctuations in populations

Answer 26

- Predator prey cycles - Disease - Climatic factors

Question 27

What is selection pressure?

Answer 27

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

Question 28

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

Answer 28

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

Question 29

Which factors may temporarily reduce the human population?

Answer 29

- War - Disease - Famine

Question 30

What is the equation for population growth?

Answer 30

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

Question 31

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

Answer 31

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

Question 32

What factors affect birth rate?

Answer 32

- 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

Question 33

Give the equation for birth/ rate.

Answer 33

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

Question 34

What factors affect death rate?

Answer 34

- 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

Question 35

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

Answer 35

- 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)

Question 36

What is the definition of the average life expectancy?

Answer 36

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

Question 37

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

Answer 37

-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

Question 38

(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.

Answer 38

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 quadrat/section); 5. Valid method of calculating total number of bluebells/plants. e.g. mean number of plants per quadrat/section/m2 multiplied by number of quadrats/sections/m2 in wood;

Question 39

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

Answer 39

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

Question 40

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

Answer 40

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

Question 41

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

Answer 41

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

Question 42

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

Answer 42

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

Question 43

(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.

Answer 43

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

Question 44

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

Answer 44

``` 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; ```

Question 45

(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 %.

Answer 45

``` 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 respiration; ```

Question 46

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

Answer 46

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