Populations Questions

Question 1

Define community (1)

Answer 1

Organisms of all species in an ecosystem/habitat

Question 2

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

Answer 2

No migration

No reproduction

Idea of mixing

Marking does not increase vulnerability to predation

Sample large enough

Question 3

What is the formula for estimated population size in mark release recapture methods?

Answer 3

Number of marked individuals recaptured

Question 4

Explain how you would use a quadrat to estimate the number of dandelion plants in a field measuring 100m by 150m (3)

Answer 4

Randomly place quadrants

Done by getting coordinates from random number generator

Calculate mean per quadrat

Multiply to give estimate for total field

Question 5

Two species are thought to have evolved as a result of sympatric speciation. Suggest how this might have occurred (4)

Answer 5

Original population living in one area

Idea of genetic variability

Reproductive isolation

Gene pool becomes increasingly different

Until interbreeding does not produce fertile offspring

Question 6

What is an ecosystem (1)

Answer 6

A self supporting system in which all organisms interact with the physical environment

Question 7

Pygmy weed competes with naturally occurring plants. Suggest how the introduction of Pygmy weed may lead to a reduction in the diversity of the community in a natural pond. (3)

Answer 7

Pygmy weed competes for CO2, light, nutrients

Some of original plants species lost

Loss of food sources

Consumers die

Question 8

Fur seals feed on krill. Many species of whale living in Antarctic seas feed on krill. Explain how an increase in whaling might have resulted in an increase seal population (2)

Answer 8

Fewer whales means more krill

More krill feeding fish

More food for seals

Question 9

Give two advantages of collecting quantitative data about plant distribution as percentage cover (2)

Answer 9

Data can be collected rapidly

Does not require defining individual plants

Question 10

A team of biologists investigated a method for measuring the abundance of shrews. They used plastic tubes called hair tubes. Some of the hairs from a shrew that enters one of these tubes stick to glue in the tube, these can be used to identify the species of shrew.

Funagoo glue remains sticky after wetting and drying. Explain the advantage of using this (1)

Answer 10

Will work in all weather conditions

Question 11

A team of biologists investigated a method for measuring the abundance of shrews. They used plastic tubes called hair tubes. Some of the hairs from a shrew that enters one of these tubes stick to glue in the tube, these can be used to identify the species of shrew.

The biologists partly blocked the entrances to the tube with tape. Suggest why (1)

Answer 11

So shrews come into contact with glue

Question 12

Biologists collected hairs from shrews of each species. Explain why they selected these hairs at random.

Answer 12

Avoids bias

Question 13

Explain why it is important to check the repeatability of measurements (2)

Answer 13

It increases the reliability of the measurements.

If measurements are repeatable differences are less likely to be due to personal error / anomalies unlikely

Question 14

You could use a scatter graph to check the reliability of measurements made by two observers. Describe how. (2)

Answer 14

Plot graph of one set of results against the other

Expect to see points lying close to the line

Question 15

Define population (1)

Answer 15

Organisms of one species in an ecosystem/habitat

Question 16

A team of biologists investigated a method for measuring the abundance of shrews. They used plastic tubes called hair tubes. Some of the hairs from a shrew that enters one of these tubes stick to glue in the tube, these can be used to identify the species of shrew.

Explain why they could not use the hair tubes to find the total number of shrews present (1)

Answer 16

Shrews may enter more than one hair tube

Many hairs from same shrew

Shrews enter without leaving hair

Question 17

Explain why a statistical test was necessary in analysing the results for the common shrew. Use the terms chance and probability in your answer (2)

Answer 17

A statistical test determines the probability of the results being due to chance

Determines wether correlation is significant

Question 18

Describe how you would decide the number of quadrants to use in order to collect representative data (2)

Answer 18

Calculate a running mean

When enough quadrants, this shows little change

A large number to make sure results are reliable

Question 19

In June young birds leave their nests and join adults. Using mark release recapture to estimate the size of the blue tit population in June would not give reliable results. Explain why (2)

Answer 19

Population changes

As young birds leave their nest / join population

Question 20

In March each pair of adult birds forms a separate territory. The pair stays in this territory while breeding. Using mark release recapture to estimate the size of a blue tit population in March would not give reliable results. Explain why (2)

Answer 20

Would be likely to catch all birds again in second sample

Birds in territories and not mixing with population

Territory sample not representative

Question 21

When whales come to the surface to breathe scientists obtain small samples of their skin. The scientists find the base sequence in some of the DNA from these samples. The base sequence is different in each whale.

You could use information about the base sequence to estimate the size of the whale population by using mark release recapture. Explain why (2)

Answer 21

Recording base sequence is like marking the animal

Finding same base sequence would show animal has been recorded before

Question 22

A scientist measured human disturbance by walking firm one end of the beach to the other. He recorded the number of people he encountered.

Site R - 2.2 (+/- 2.1)
Site G - 17.6 (+/- 9.6)
Site U - 34.6 (+/- 11.6)

What conclusions can you draw about the number of people visiting site R compared with the other sites?

Answer 22

Fewest people at site R as mean is lowest

Standard deviations do not overlap so significant / not due to chance

Question 23

A scientist reported that the difference between the number of people visiting site R and the number visiting the other two sites differed significantly (p

Answer 23

There was a probability of less than 0.05

That the difference was due to chance

Question 24

A scientist measured the dry biomass of seaweeds at sites R, G and U. He collected all the organisms of a particular species in a quadrat and incubated them in an oven at 80 degrees Celsius.

Suggest why incubating them at a higher temperature would not produce valid results (1)

Answer 24

Combustion would cause loss of dry mass

Question 25

The ratio of the dry biomass of animals to the dry biomass of seaweeds is always a lot less than one. Explain why (2)

Answer 25

Seaweeds are producers

Loss of energy between tropic levels

As a result of respiration

Question 26

Use the letters B (birth rate), D (death rate), E (emigration rate) and I (immigration rate) to show a population that stays the same size (1)

Answer 26

B + I = D + E

Question 27

Use the letters B (birth rate), D (death rate), E (emigration rate) and I (immigration rate) to show a population that is increasing in size (1)

Answer 27

B + I > D + E

Question 28

Suggest one reason for the increase in life expectancy since 1990 (1)

Answer 28

Improved medical care

Improved nutrition

Improved sanitation

Less disease

Question 29

In 2007 the population was 107million
The birth rate was 20 per 1000
The death rate was 5 per 1000

Calculate the size of the population in 2008 (2)

Answer 29

107,000,000
————— x 15 = 1605000
1000

107,000,000 + 1605000 =108605000

Question 30

If maximum life expectancy is 95. How could a graph be used to find average life expectancy (2)

Answer 30

Find value when 50% still alive

Use to calculate as a percentage of 95

Question 31

In a demographic transition give one factor that might cause an increase in birth rate (1)

Answer 31

Better prenatal care

More people survive to reproductive age

Better nutrition of mother

Question 32

In a demographic transition, give one factor that might cause a decrease in death rate (1)

Answer 32

Better nutrition

Better sanitation

Introduction of healthcare

Vaccination programmes

Question 33

The population in 1851 was 18 million
The birth rate was 34.3 per 1000
The death rate was 22.0 per 1000

Calculate the size of the population in 1852 (2)

Answer 33

18,000,000
————– x 12.3 = 221400
1000

221400 + 18,000,000 = 18221400

Question 34

One reason for the decrease in death rate between 1931 and 1951 was the introduction of mass vaccination. Explain how this would reduce death rate (2)

Answer 34

Creates herd immunity

Any individual has lower chance of meeting infected individual

Prevents spread of disease

Question 35

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

Answer 35

Birth rate and death rate

Immigration and emigration

In a given time period

Question 36

Ecologists could use the mark release recapture method to o estimate the number of one species of fish in a lake. Describe how (3)

Answer 36

Capture sample, mark, release

E.g. Mark with paint

Take second sample and count marked organisms

Population = (number in S1 x number in S2) divided by number marked in S2

Question 37

A species of fish breeds at certain times during the year. During this season the mark release recapture method might not give a reliable estimate. Suggest why (1)

Answer 37

Population changes

Question 38

Ecologists found that each species of fish had adaptations to its niche. One of these was the shape of its mouth. Suggest how this is an adaptation to its niche (2)

Answer 38

Specific mouth shape for specific food

Competition between species is reduced

Question 39

What is interspecific competition (1)

Answer 39

Competition between species

Question 40

What is intraspecific competition (1)

Answer 40

Competition within a species

Question 41

Describe how you would place quadrats at random (2)

Answer 41

Split area into squares

Generate numbers from a computerised random number generator

Question 42

Explain the importance of collecting lizards from a large number of sites when studying them (1)

Answer 42

Representative / identify anomalies

Question 43

The population number of two species of lizard varied at different times of the year. Suggest two reasons why (2)

Answer 43

Temperature variation

Breeding

Food source

Question 44

Scientists investigated the percentage of two lizard species infected with malaria at different sites on an island. They used the percentage of lizards infected at each site rather then the number. Explain why (2)

Answer 44

Number in sample varies

Allows a valid comparison

Question 45

Newts are predators of the tadpoles of the spade foot toad. In a pond, suggest an explanation for the increased number of newts resulting in an increased percentage survival of the tadpoles of spring pepper frogs (2)

Answer 45

Newts feed on toad

Less competition for frogs

Question 46

Feather mites are parasites found on the wings of many birds, they feed on the oil that the birds produce. This oil keeps the feathers in good condition. Birds unable to oil their feathers properly use more energy in maintaining body temperature. Suggest how feather mites could affect breeding in great tits (2)

Answer 46

Breeding less successful

Feathers in poor condition

So less energy for reproduction

Question 47

Scientists located a large number of great tit nests. They sampled these at random, explain why they sampled the nests at random (2)

Answer 47

Avoids bias

Data representative

Allows use of a statistical test

Question 48

Different fish species occupy different depths in a lake, suggest and explain one advantage of this to the fish (2)

Answer 48

Less competition

For food/prey/oxygen