[OLD] Populations - Ecosystems: Exam Questions

Question 1

What is an ecosystem?

Answer 1

All the living and non-living components of a particular area

Question 2

New Zealand Pygmy weed has been introduced into many garden ponds and has spread to some natural ponds. Here, it 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 2

1) Pygmy weed competes for CO2, light, or nutrients
2) This causes a reduction in numbers of original plants
3) Some original plants species are lost
4) This loss or habitats, niches, shelter or food sources
5) causes the consumers to die

Question 3

Give one advantage of calculating the index of dives

rainy rather than just recording the number of species present. (1)

Answer 3

It also takes abundance of each species into account as biodiversity is also affected by population sizes.

Question 4

Explain what is meant by the ecological term community (1)

Answer 4

All the living organisms in an ecosystem at a given time.

Question 5

Suggest and explain one advantages to different species of fish occupying different depths in a lake (2)

Answer 5

1) They will occupy different niches (food, prey or oxygen)

2) So there will be less competition

Question 6

What is meant by an abiotic factor?

Answer 6

An ecological factor making up part of the non-biological environment of an organism.

Question 7

Other than temperature, suggest one abiotic factor that is likely to affect the position of the tree line on a mountain (1)

Answer 7

pH of the soil, water, light, CO2, incline, wind (speed)

NOTE: don’t talk about oxygen in relation to limiting photosynthesis/growth of a plant

Question 8

The population of trees in a forest evolved adaptations to a mountain environment. Use your knowledge of selection to explain how. (3)

Answer 8

There is variation in all organisms.
The trees with advantageous characteristics are more likely to survive in the mountain environment.
So are more likely to reproduce and pass on their genes that allow them to survive.
4) Allele frequencies change.

Question 9

Ecologists studied a community of fish in a lake.
The ecologists could have used the mark-release-recapture method to estimate the number of one species of fish in the lake. Describe how. (3)

Answer 9

1) Capture fish and release them back in the same place
2) Before releasing them, mark them by e.g attaching a tag
3) Recapture fish and count the number that had been marked
4) Use the Lincoln Index to estimate total population size: population = (no in sample 1 X no in sample 2)/(no marked in sample 2)

Question 10

A species of fish breeds at a certain time of the year. During this fish-breeding season, the mark-release-recapture technique might not give a reliable estimate. Suggest one reason why. (1)

Answer 10

(If there is a large amount of births between the first and second sample) the proportion of marked to unmarked animals would not be the same in the second sample as in the population as a whole.

Question 11

Ecologists found that different 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. (2)

Answer 11

1) The shape of its mouth may allow it to feed on things that the other species of fish cannot.
2) Interspecific competition is reduced.

Question 12

Explain the meaning of the ecological term population. (1)

Answer 12

A group of individuals of the same species that occupy the same habitat at the same time.

Question 13

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

Answer 13

1) The mark is not lost or rubbed off.
2) The marked individuals have sufficient time to redistribute themselves evenly.
3) No immigration.
4) No reproduction.
5) Sample large enough.

Question 14

Two similar species of birds feed of slightly different side insects and have slightly different temperature preferences.
These two species are thought to have evolved as a result of sympatric speciation. Suggest how this might have occurred.

Answer 14

!!!

Question 15

Describe a practical technique which you could use to find the mean population density of daisies on a lawn. (3)

Answer 15

1) Use 2 tape measures to create a study area on the lawn. Use a random number generator to find a point in the area to place a quadrat. Identify which plants are daisies using a field guide.
2) Repeat until the running mean no longer changes from quadrat to quadrat.
3) Count the abundance of daisies in each quadrat and divide by area.

Question 16

Describe how you would investigate the distribution of marram grass from one side of a sand dune to the other. (3)

Answer 16

1) Create a transect by placing a tape measure from one side of the dune to the other.
2) Use systematic sampling by placing a quadrat down next to the tape measure every metre for example.
3) Measure the percentage cover of marram grass in each quadrat.

Question 17

Marram grass is a pioneer species that grows on sand dunes. It has long roots and a vertically growing stem that grows up through the sand.
Sand dunes are easily damaged by visitors and are blown by the wind. Planting marram grass is useful in helping sand dune ecosystems to recover from damage.
Use your knowledge of succession to explain why.

Answer 17

1) As a pioneer species, marram grass changes the abiotic conditions of the environment and makes it less hostile.
2) With its long roots and stem growing through the sand, it will secure the sand dunes in place.

Question 18

Farmland was left for 30 years and developed into a woodland.
Name the process that resulted in the development of woodland from farmland. (1)

Answer 18

(secondary) succession

Question 19

Farmland was left for 30 years and developed into a woodland.
During this period, ecologists recorded an increase in the diversity of birds in the area.
Explain the increase in the diversity of birds as the woodland developed. (3)

Answer 19

1) Greater variety of plants/insects
2) Mean more food sources
3) So more available niches

Question 20

The species that are present change during succession. Explain why. (2)

Answer 20

1) Pioneer species change the environmental conditions and make it less hostile, so other species can move in.
2) These continue to change the environment and outcompete the pioneer species.

Question 21

Pine trees in a forest have leaves all year. Explain how this results in a low species diversity of plants in the forest. (1)

Answer 21

Only plants which can photosynthesise with less light remain.

Question 22

Give two factors which could limit the rate of photosynthesis (1)

Answer 22

Carbon dioxide concentration

Temperature

Question 23

Suggest appropriate units for gross productivity. (1)

Answer 23

Unit of energy/mass, per area, per year.

Question 24

Explain the increase in biomass during succession. (3)

Answer 24

1) Pioneer species
2) Change abiotic conditions
3) Increase number/amount/diversity of species of plants/animals

Question 25

Explain a decrease in gross productivity as a woodland matures. (2)

Answer 25

1) Less light / more competition for light

2) Reduced photosynthesis

Question 26

Suggest one reason for conserving woodlands. (1)

Answer 26

To protect endangered species that live there.