Unit D: Changes in Living Systems

Suggested Answers for Investigations and Activities

Chapter 1: The Biosphere of Life

Try This Activity: Life in a Fishbowl, page 405

The following chart provides some factors that you may identify from your observations of a tropical fish aquarium and a goldfish bowl.

Factor Tropical Fish Aquarium Goldfish Bowl
Non-living
  • water maintained at constant temperature (near room temperature) by using aquarium heater
  • bubbles of air in aquarium (dissolved oxygen)
  • aerating device present to increase amount of dissolved oxygen in water
  • water filter present to remove harmful waste products
  • pH of water neutral or slightly alkaline
  • water temperature—lower than room temperature
  • bubbles of air in aquarium (dissolved oxygen)
  • pH of water slightly acidic
Living
  • water plants present
  • different species of tropical fish present
  • water plants present
  • algae perhaps present

Analysis

1. Answers may include the observations that both types of fish live in aquatic environments, dissolved oxygen is present, water plants are present, and both types of fish require a schedule for feeding and for exchanging the water.

2. Answers may include the observation that the water temperature of a tropical fish aquarium has to be maintained near room temperature, whereas the water temperature of a goldfish bowl may vary. There may be different types of tropical fish in the aquarium compared to a goldfish bowl. The tropical fish aquarium requires a system for oxygenating and filtering the water, while a goldfish bowl does not require such elaborate devices.

3. The movement of tropical fish—such as guppies—into the goldfish bowl would likely result in the death of the tropical fish. These fish need to live in water that tends to be warmer than water found in goldfish bowls. Goldfish produce more nitrogenous waste products that would be deadly to the tropical fish. The goldfish would have a better chance of surviving in the tropical aquarium because goldfish can live in varied environments. Tropical fish need to live in environments that are more fixed.

Investigation: The Effect of Salinity on Seed Germination, page 408

Analysis

1. Note the following sample data.

Concentration of Salt Solution (g/L) Germination Ratio for Beans (%) Germination Ratio for Sunflowers (%)
Distilled Water 100 60
0.25 100 60
0.50 100 60
1.0 80 60
2.0 60 60
4.0 60 40
8.0 10 40

2. Bar graphs are outlined for bean seeds and sunflower seeds. Note that results vary for different seed varieties.

3. The abiotic factor tested was the salinity of water. The responding biotic factor was the seed germination.

4. Although fewer sunflower seeds germinated in most cases, overall the sunflower seeds showed less variance in germination ratio than the bean seeds.

5. The germination of the beans began to be affected by the salt at a concentration of 1.0 g/L. At higher concentrations, the trend was one of decreased levels of germination. The germination of the sunflower seeds was affected at a concentration of 4.0 g/L. Although there may be slight discrepancies between groups, the overall trends should be similar if the same seeds are used.

Extension

6. The major causes of soil salinity in arid countries are dryland salinity and irrigation salinity. Dryland salinity is caused when deep-rooted trees and shrubs are replaced with shallow-rooted annual crops that do not use as much moisture. The trees act like pumps to take up enough rainwater to keep the underground salty water table well below the root level. When the trees are removed, the rainwater leaches through the soil and dissolves salts as it goes. This salty rainwater follows the slope of the land as it flows underground, and it may resurface at a slightly lower altitude many kilometres away. The topsoil at the site where the water comes to the surface becomes increasingly salty with each year that this process continues.

Irrigation salinity occurs when irrigation water soaks through the soil where the plants are growing. The presence of the irrigation water causes the water table to rise closer to the surface. As the underground water table rises, salt is carried to the surface soil. When the area dries out, the underground water drops back down.

This leaves the salt in the soil. Every time the ground is soaked with irrigation water, the cycle repeats with salt being carried to the surface water with the rising underground water. After many years, the soil becomes so salty that the soil can no longer support crops.

Investigation: Take a Stand: Using Fresh Water for Petroleum Extraction, page 410

Identifying Alternatives/Perspectives

Stakeholder Point of View/Perspective
Petroleum Company Oilfield injection is a technique that has been used for years. This process ensures that a higher percentage of the petroleum found in a reserve is actually extracted.
Local Residents Fresh water from streams, rivers, and lakes is needed for municipal drinking water, irrigation, and for use by local, small businesses. Years of drought means there is no fresh water to spare.
Local Government The petroleum company running the wells has been a major employer for years. The economic spinoffs for other local businesses is significant. However, taxpayers and voters are beginning to get vocal about the use of fresh water for oilfield extraction.
Environmentalists Once this fresh water has been contaminated and placed deep underground, it is removed from the hydrological cycle forever. The focus should be on reducing people’s dependence upon petroleum. Trading water for petroleum is not a wise long-term strategy.

Researching the Issue

The following sample responses represent a concise, point-form sampling of the detailed work your research could uncover.

Stakeholder Sampling of Key Arguments Made by Each Stakeholder
Oil Company
  • The petroleum industry is being unfairly singled out as a user of fresh surface water—irrigation accounts for 47% of provincial water use and cooling for power plants totals 27%. The petroleum industry currently only uses 1% of fresh surface water for oilfield injection and another 3% for the processing of industrial oil and gas.
  • The petroleum industry is already reducing its use of fresh surface water by using deep underground sources of saline (salt) water unfit for human consumption or use in agriculture. This is particularly noticeable in areas affected by drought.
Local Residents
  • Although reducing personal water use is an important component of water conservation, only 11% of water used in the province passes through municipal systems. Leaving it up to local residents to carry all the burden of reduced water use will not work. Everyone has to conserve, even the petroleum industry.
  • Local farmers and ranchers have noticed that in areas where the petroleum industry is using fresh water, water wells have shown a marked decrease in capacity. It appears the use of water by the petroleum industry has an effect on the water available for agriculture.
  • Local streams and lakes are popular sources of recreational activities, such as fishing, swimming, and boating, and will be adversely affected if water levels drop.
Local Government
  • The economic health of the entire province, as well as many small Alberta communities, is directly tied to the petroleum industry. Any decision that could have an adverse effect on the economy has to be considered very carefully.
  • The issues surrounding legislation that enforces reduced water use are controversial. Although the petroleum industry represents a large piece of Alberta’s economy, the agricultural industry represents a large number of voters. The unpopularity of this issue makes wait and see a very attractive strategy.
  • Canada is second only to the United States in terms of per capita use of water. Citizens of most other countries use much less water. Charging for water used will likely be necessary.
Environmentalists
  • Once water has been removed from the hydrological cycle for oilfield injection, it is gone forever.
  • A process needs to be put in place to track the actual amount of water used by each stakeholder group in the province.
  • The best way to provide an incentive for water conservation is to charge for the amount of water used. The largest users of fresh, surface water in the province are farmers, who use 47% for irrigation. All farmers should be charged for their water use.
  • Injecting carbon dioxide from power plant smokestacks into oil wells instead of water would also reduce greenhouse gas emissions.

Analyzing the Issue

The following sample responses indicate how the sample arguments presented earlier could be sorted into two columns.

Arguments for Using Fresh Water for Oilfield Injection Arguments Against Using Fresh Water for Oilfield Injection
  • The petroleum industry is being unfairly singled out as a user of fresh surface water—irrigation accounts for 47% of provincial water use and cooling for power plants totals 27%. The petroleum industry currently only uses 1% of fresh surface water for oilfield injection and another 3% for processing.
  • The petroleum industry is already reducing its use of fresh surface water by using deep underground sources of saline (salt) water unfit for human consumption or use in agriculture. This is particularly noticeable in areas affected by drought.
  • The economic health of the entire province, as well as many small Alberta communities, is directly tied to the petroleum industry. Any decision that could have an adverse effect on the economy has to be considered very carefully.
  • Although reducing personal water use is an important component of water conservation, only 11% of water used in the province passes through municipal systems. Leaving it up to local residents to carry all the burden of reduced water use will not work. Everyone has to conserve, even the petroleum industry.
  • Local farmers and ranchers have noticed that in areas where the petroleum industry is using fresh water, water wells have shown a marked decrease in capacity. It appears the use of water has an effect on the water available for agriculture.
  • Local streams and lakes are popular sources of recreational activities, such as fishing, swimming, and boating, and will be adversely affected if water levels drop too far.
  • Once water has been removed from the hydrological cycle for oilfield injection, it is gone forever.
  • A process needs to be put in place to track the actual amount of water used by each stakeholder group in the province.
  • The best way to provide an incentive for water conservation is to charge for the amount of water used. The largest users of fresh, surface water in the province are farmers, who use 47% for irrigation. They should also be charged for their water use.

Take a Stand and Defend Your Position

The letter to the editor of a local newspaper represents a sample response.

Dear Editor,

I am writing in response to the question of whether petroleum companies should be allowed to use fresh water to help extract petroleum from the ground. It is my opinion that this practice should be stopped, and that the petroleum industry should be told to find alternative technologies. Despite the arguments in support of this practice, the long-term health of the environment and Alberta’s communities outweigh these concerns.

The petroleum companies claim they are only using about 1% of the available fresh surface water, while irrigation accounts for 47%. The key point that these numbers do not reveal is that the 1% is permanently removed from the water cycle and can never be used again because it is contaminated and sealed deep underground. Although irrigation uses much more water, this water is still available to the environment through run-off, evaporation, and other natural processes.

The petroleum companies claim that they use saline water from deep underground sources for oilfield injection. To my knowledge, this only occurs in areas in the southern part of the province that have been designated as drought sensitive—freshwater resources are already at critically low levels. In other areas where this practice has not been made a requirement, petroleum companies continue to use the least-expensive water available. This is the surface water from lakes, streams, and rivers. It seems to me that the option of using surface water for oilfield injection should be banned across the province.

What will be the long-term effects of removing fresh surface water from our environment? The fact that no one really knows the answer to this question should be reason enough for caution. However, here is what we do know:

  • Water is a finite resource—there is only so much of it to go around. Many experts feel that it will be a resource in great demand by the end of the twenty-first century.

  • Canadians are second only to United States citizens in their per capita use of water. We must start to find ways to reduce our water use. Why would we be wasteful today of something that we know we will be in short supply of later?

  • The best way to ensure conservation is to meter the use of water and to charge accordingly. Why do the citizens of Calgary use more water per capita than the citizens of Edmonton? Every house in Edmonton has a water meter and people are charged for their water use—that is not the case in Calgary. The petroleum industry should also be charged for its water use.

  • Alberta’s environment is a jewel that will still be here long after both the petroleum and the petroleum companies are gone. Why should we allow industry to trade the long-term health of our environmental heritage for the sake of their economic bottom line?

The United Nations estimates that more than one billion people on the planet do not have access to fresh drinking water. This should remind us that we can live without petroleum, but we can’t live without water.

Yours sincerely,

A concerned student

Evaluation

1. Answers will vary. People in farming communities may have a more negative view of petroleum companies using local fresh water to extract petroleum since this source of water is also the supply of drinking water for the rural community. People in urban settings may not consider the use of fresh water for petroleum extraction to be a significant problem because of the perceived abundance of water in the urban setting.

2. A short-term effect of using local fresh water is a lower cost for petroleum extraction. Long-term effects of using fresh water are the reduction of available drinking water and negative environmental consequences.

Extension

3. a. Note the following calculation.

Vpetroleum = 500 000 barrels
Vwater lost = ?

Each day, 10 000 barrels or 1.59 × 106 L of water are removed from the water cycle.

b. The answers to this question will vary as new information becomes available. One of the environmental impacts of the oil-sands developments north of Fort McMurray is the possible link to the drop in water level at the mouth of the Athabasca River as it flows into Lake Athabasca. In the Cold Lake area, the use of water for oil-sands extraction has been linked to troubles that local residents are having with their water wells. The water wells have to be dug deeper to maintain the same flow, but the water quality from the deeper wells has deteriorated.

Investigation: Predator-Prey Population Dynamics, pages 419 to 421

Analysis

(Note that all answers that depend upon interpreting the graph should be treated as ± 2 years as the graph is challenging to interpret.)

1. a. The population of snowshoe hares peaked in the following years: 1853, 1856, 1863, 1875, 1885, 1895, 1904, 1912, 1923, and 1932.

b. The overall trend is that the population peaks every 8 to 12 years. The average time between these peaks is close to 10 years.

2. a.

The lynx population peaked in the following years: 1845, 1856, 1865, 1875, 1885, 1894, 1904, 1913, and 1925.
b. The overall trend is that the population peaks every 9 to 12 years. The average time between these peaks is close to 10 years.

3. a. Most of the time, there are more snowshoe hares than lynx. This is due to the fact that an individual lynx will feed on many snowshoe hares during a winter season. So, in order for the situation to sustain itself, there needs to be plenty of prey for the lynx.

b. When the snowshoe hare population increases there is more prey available for the lynx, so more lynx survive and have offspring. This causes an increase in the lynx population a few years later. When the snowshoe hare population crashes after reaching the peak, the growing numbers of lynx face increased competition for the limited number of snowshoe hares. As a result, there is a decline in the lynx population following the crash in the snowshoe hare population.

4. If the snowshoe hare population disappeared, the lynx population would likely disappear as well because the snowshoe hare is the lynx’s main food source.

5. The size of the hare population could be affected by the availability of vegetation that forms the bulk of its diet. If another species of herbivore overbrowsed this same vegetation, then the limited food supply would weaken the hares and make them more susceptible to starvation and predators. Weather could also play a significant role, as years of drought could have an impact on the vegetation available to the hares.

The size of the lynx population could be affected by diseases that affect the lynx but not the hares. Both populations can be affected by the humans who trap them. If the trappers preferred to trap one species over the other, this would tend to upset the rhythm of the rise and fall of the populations.

Extension

6. Predation ensures that sufficient resources will be available for prey that survives predators. The prey that tends to be killed are the individuals that are less fit—sick, injured, or old. Predation keeps the prey population healthy. The number of prey will limit the number of predators.

Utilizing Technology: Purple Loosestrife—An Invasive Species, page 460

Procedure, step 2

Evaluation

1. In some cases, bulletins could be improved if the answers were more complete and contained more essential information that would have completely addressed all aspects of the question. In other cases, information might have been complete but the communication of this information may not have made an effective use of the chosen medium.

2. This is a great opportunity for students to learn from their fellow students. The purpose of the bulletin is to effectively convey essential information about purple loosestrife. In some cases, other groups may have found new and surprising information. In other situations, they may have found novel ways to present this information to create an effective bulletin.

Chapter 2: Changing Populations

Try This Activity: Coloured Toothpicks, page 469

Discussion

1. The collected toothpicks represent members of species that have become prey for predators.

2. In the short term, predation causes the prey population to decrease. The fact that red and yellow members of the species are most susceptible to predation could have a long-term effect on the population because colour is a heritable trait. In the long term, the population could become dominated by green members with very few toothpicks left with red or yellow colouring.

3. Some colours are easier for the predators to see in that environment. Colour can harm the prey species, as in the case with yellow and red toothpicks. Colour can help by supplying camouflage, as in the case of green and blue toothpicks.

4. The red and yellow members were the least able to cope with the predator’s arrival.

5. Given that colour is a heritable trait, more green members of the population would tend to survive predation and leave offspring with the inherited trait for being green. To a lesser extent, blue members of the population may also have a superior survival rate relative to red and yellow members. This means that over time a greater percentage of the population may be coloured green and blue, with few left having the trait for yellow or red.

Investigation: Succession on Land, page 471

Prediction

1. The variables—other than the amount of potting material and water—that should be controlled for this experiment include the temperature, amount of light, depth of planting, location within the room, time of day for observations, as well as any other reasonable controls.

2. The potting mix that should produce the best results should be the garden soil because this substrate is the most advanced. Humus is a key ingredient.

Observations

You should create an observation table with a column for the date, as well as columns for each of the potting materials. The columns should have enough space for you to write short statements about any changes you observe.

SAMPLE OBSERVATION TABLE
Date Sand Clay Garden Soil Rock Chips
May 8 three seeds planted three seeds planted three seeds planted three seeds planted
May 10 two seeds sprouted one seed sprouted three seeds sprouted one seed sprouted
May 11 three seeds sprouted three seeds sprouted three seeds sprouted—two tiny open leaves showing on one seedling two seeds sprouted
May 15 seedlings seem to be shrivelling up two tiny open leaves showing on all seedlings two tiny open leaves showing on all seedlings—seedlings taller than in other mediums two seedlings not growing—one seed still not sprouted

Keep in mind that germination only requires water and warm temperatures, so the seeds will most likely sprout in all potting conditions within a few days. Observations and the analysis will be comparative in nature in terms of seedling height and apparent health. It is not important that students actually measure the height or diameter of the seedlings with a ruler, but rather that they compare them to the other seedlings in the experiment. The procedure indicates that two visible and completely open leaves on the seedling will be considered positive germination. Tomatoes are dicots and produce two embryonic seed leaves. If using monocots, such as bean seeds, for the experiment, a completely open, single seed leaf will be a positive germination.

The following is a partial observation table based on the segment “Succession on Land.”

Day Sand Clay Garden Soil Rock Chips Compost
1 three seeds planted three seeds planted three seeds planted three seeds planted three seeds planted
2 no plants no plants no plants no plants no plants
3 no plants no plants no plants no plants no plants
4 no plants no plants two seeds sprouted no plants one seed sprouted
5 no plants no plants two plants about 1.5 cm no plants three plants—one plant about 2 cm and two plants about 1 cm
7 no plants no plants two plants about 2 cm and one plant just showing no plants three plants—one plant about 4.5 cm and two plants about 2.5 cm
10 one plant about 1 cm no plants two plants about 4.5 cm and one plant about 0.5 cm no plants little change from day 9
13 one plant about 2 cm no plants little change from day 12 no plants little change from day 12
14 little change from day 13 no plants little change from day 13 one plant about 1 cm little change from day 13
16 one plant about 3 cm no plants one plant about 5 cm, one plant about 4.5 cm, and one plant died one plant about 2 cm little change from day 15
21 little change from day 20 one plant about 2.5 cm and one plant just showing one plant about 6.5 cm and one plant about 6 cm one plant about 4 cm three plants—one plant about 5 cm and two plants about 4 cm
23 little change from day 22 one plant about 3 cm and one plant about 0.5 cm
 one plant about 7 cm and one plant about 6.5 cm one plant about 4 cm and one plant about 1 cm little change from day 22
26 little change from day 25 little change from day 25 little change from day 25 little change from day 25 little change from day 25

Keep in mind that germination only requires water and warm temperatures, so seeds have sprouted in all soil conditions, including the rock chips. Your observations and analysis should be comparative in nature in terms of height and apparent health.

Analysis

3. The garden soil produced the seedlings with the fastest germination.

4. The garden soil produced the seedlings with the greatest height and vigour.

Evaluation

5. Improvements would depend on design methods for a new experiment, but should include a larger sample with more pots and more seeds.

Utilizing Technology: Researching Primary Succession on Mars, page 473

Research Activity

Numerous sites provide information on the conditions on Mars and colonization constraints.

1. Even without the aid of research, students may state the vast distance and costs of this project to be major obstacles for beginning succession on another planet—even a relatively close one such as Mars. From the information provided in the textbook, students may point out that the process of succession takes so long—even for organisms perfectly adapted to Earth’s environment—that the benefits of this project wouldn’t be seen for several lifetimes.

2. Your research may provide these and other challenges for pioneer species.

(a) Extremely low pressure damages organisms and impairs DNA repair.

(b) The temperature only rises above freezing at certain latitudes during the Martian summer. The low temperature would freeze organisms. The formation of ice crystals in the body would cause cell damage.

(c) Liquid water is a prerequisite for Earth life and appears to be only found on Mars in solid form at its coldest poles. Some scientists predict that liquid water may be found in subsurface aquifers. The extremely dry conditions on the surface would cause dehydration.

(d) In the absence of a protective ozone layer, like Earth’s, the surface of Mars receives a large amount of ultraviolet (UV) radiation. This radiation causes mutations and is lethal to most organisms over long periods of time.

(e)

The atmosphere on Mars is much thinner than Earth’s and is composed mostly of carbon dioxide. Many pioneer species need at least some oxygen for their life processes.

Some scientists have proposed ideas to prepare the Martian atmosphere and landscape for primary succession. These include

  • covering the polar icecaps with a dark material, such as a pulverized asteroid, to melt the caps and restore liquid water to the surface

  • building large mirrors and lenses in space to reflect sunlight onto the icecaps

  • releasing chlorofluorocarbons (CFCs) and other greenhouse gases to trap heat

  • adding microbes that have been genetically engineered or selectively bred to withstand Martian conditions

  • using nanotechnology (miniature robots) to release carbon dioxide from carbonate rocks
3. Societal, ethical, and scientific concerns include the following.
  • The immense financial cost of the project alone would be a societal concern. A project of this magnitude would cost many billions of dollars. One could argue that this money could/should be spent on many other causes and societal problems on Earth.

  • There would be societal concerns that the problems people have created on Earth would simply be transferred to another location.

  • There are ethical and safety issues if genetically modified microbes are used for terraforming. Microbes would have to be cultured on Earth (and then transported) and there would be a risk of release on Earth with unknown consequences.

  • A scientific concern is that no ozone layer on Mars means that the planet receives a large amount of UV rays. The high amount of UV rays would cause many mutations among any pioneer species. If there is much travel between Earth and Mars there would be a concern that the mutants could be accidentally transported back to Earth. This could possibly cause problems associated with introduced species or even with the species becoming pathogenic (disease causing).

  • An ethical concern is that Mars may have its own life forms, as some evidence has indicated, and introducing new species may interfere with the natural role of Martian life and the process of evolution on the planet. What about the rights of Martians? Or as Mark Lupisella wrote in his 1997 paper on space policy: “Could we forgive ourselves if we caused the extinction of the first extraterrestrial species we came into contact with?”
4.

For the risk-benefit analysis, you may come up with many positive reasons to complement the many negative ones described.

  • Exploring and living on Mars to pursue exploration has great scientific value in determining the development of Earth and the solar system. Having another well-studied planet to compare with would not only give scientists a better understanding of mechanisms at work on Earth, but would serve as a stage for further space exploration.

  • Mars may hold valuable resources that Earth lacks in significant quantities. Comfortably living there would allow humans to take advantage of these resources.

  • Mars may provide a solution, or at least temporary relief, to Earth’s human population problems.
5.

You may feel that the scientific value of pursuing exploration on Mars and other parts of space may be of great value. The resources and the possible benefit of relief to Earth’s human population problem may also be of great value.

You may decide that terraforming Mars is just too expensive and too risky. The societal concerns and ethical and safety issues may not be worth the benefits of attempting to colonize a planet like Mars.

Investigation: Aquatic Succession, pages 474 and 475

Prediction

1. Many will predict that the control flask will have no evidence of succession if accidental contamination can be avoided. Predictions on the succession flask will vary because many people will be surprised at the growth that occurs there.

Analysis

Answers to numbered analysis questions will vary depending on the results. It is not important for you to identify the organisms sighted, but you should make generalizations about changes in the relative numbers and types of species at each time interval as compared to the control.

Even if the control becomes contaminated and you begin to see succession where it wasn’t intended, this is a good opportunity to discuss how life always finds a way in nature.

The following is an observation table based on the segment “Aquatic Succession.”

Day Control Flask Succession Flask
Physical
Changes		 Number of Types
of Organisms Observed		 Physical
Changes		 Number of Types
of Organisms Observed
1 Water is clear, and no life is present. none Water is murky and has particles floating in it. none
2 Water is clear, and no life is present. none Water is murky, and there is condensation on the inside of the flask. 4
3 Water is clear, and no life is present. none Water is clearer, and the particles are settling to the bottom. 3
4 Water is clear, and no life is present. none Water is clearer, and the particles are settling to the bottom. 3
5 Water is clear, and no life is present. none Water is clearer, and the particles are settling to the bottom. 3
6 Water is clear, and no life is present. none Water is clearer, and the particles are settling to the bottom. 4
7 Water is clear, and no life is present. none Water is clearer, and the particles are settling to the bottom. 4

The following answers are based on the “Aquatic Succession” segment.

Analysis

2. You should see no change in the control flask. In the flask containing vegetation, you should see that particles settled out over the 7 days of observations.

3. The numbers of each organism was not indicated in the multimedia segment.

4. The types of species changed over the observation period. Nematodes appeared to dominate by the end of the observation period.

5. No organisms entered the control flask. The control flask could have become contaminated and then would have shown some limited succession.

Investigation: Observing Primary and Secondary Succession, page 477

Analysis

1. and 2. The construction of buildings, roads, sidewalks, and parks impact on the process of succession. Other ways in which people impact the process of construction are through farming, logging, and oil and gas exploration. You personally may impact succession when you cut the lawn or ride a bike through a ditch.

3. This question is meant to guide you toward thinking that many of the building materials used for homes and schools may be considered by pioneer plants to be primary environments. For example, in Europe most old stone churches and buildings have lichens, mosses, and even ferns growing between cracks or seams in the stone.

Extension

4. There probably would not be many examples of succession on a well-tended lawn, but after five years of neglect it would be overrun by weeds and wild grasses. If you are located in a part of the province where boreal forest is the climax community, shrubs and small deciduous trees would be growing after ten years. At 50 years, you could expect a full deciduous forest with a canopy that would be ideal for conifers to start growing. At 100 years, there would most likely be a climax community of conifers.

5. a. The Mayans would have had to remove trees to make room for buildings, and they would need to plant farms to grow crops for food and clothing. The courtyards and public areas would have been paved over with stone. The Mayans probably would have brought irrigation into the area for their crops.

b. The jungle has reclaimed the site. The process of succession has returned the area to a climax community.

6. The final product will vary depending on the climax community (prairie, boreal forest, aspen parkland, or other climax community) where you live.

Utilizing Technology: Forest Harvesting, page 479

Procedure

Forest Harvesting Method Description of Method Advantages of Method Disadvantages of Method
selection cut A predetermined percentage of a stand’s merchantable timber is harvested. The trees selected are the ones that are larger, older, and less healthy. This method has a very low visual impact on the landscape. Enough vegetation is left remaining to act as cover for watersheds and wildlife. The remaining forest includes trees of a variety of ages. Some of the residual trees can get scuffed, broken, or damaged as the selected trees are removed. This could lead to diseases and sites of decay on the remaining trees.
clearcutting All of a stand’s merchantable timber is harvested. This method is cost effective—harvesting the most timber for the lowest cost. The area that remains after clearcutting is unsightly. Since all of the trees have been removed, reforestation with a single species reduces biodiversity.
shelterwood cut This technique is similar to clearcutting, with clumps of trees retained in the cut-over area. Some seed-bearing trees are left to help with reforestation efforts. Some trees are left for wildlife. This method is still unsightly, but it is somewhat better than clearcutting.
seed tree cut This method leaves mature trees spread throughout the cut-over area if these tree species—like white spruce—have seeds spread by the wind. This method attempts to let the natural process of secondary succession unfold. The spruce is a shallow-rooted tree, so the remaining trees are susceptible to blowing down. Even if seeding occurs, complete reforestation must be initiated within two years.

Analysis

1. The selection-cut method does the least amount of damage in terms of habitat fragmentation and habitat destruction because a significant portion of the forest is still standing.

2. Clearcutting does the most damage in terms of habitat fragmentation and habitat destruction because all trees are removed as the area is cleared.

Utilizing Technology: Graphing Populations, page 483

Suggestions for Using the Microsoft® Excel Program to Graph Data

step 1: Enter the data to be graphed into two columns. Titles are not necessary at this point.

step 2: Highlight both columns, and open the Chart Wizard.

step 3: The Chart Wizard will guide you through the graphing procedure. There are four steps.

(1) First, you will be asked to choose the type/format of graph that best suits the data. A line graph will work well for population statistics. (After you make each choice, press the Next button to move on.)

(2) Second, you will be asked how you would like the data displayed.

(3) In the third step, you will be asked to give the graph a title and label the x and y axes.

(4) Last, you will be asked where you want to save and display the chart you have created. (Click the Finish button to complete the procedure.)

The graph can be printed separately, with the original data, or it can be copied and pasted into any Microsoft® Word document.

Suggestions for Using the TI-84 Plus Calculator to Graph Data

* Make sure there are no equations entered in the equation editor. Press the Y= button; move your cursor with the arrow buttons; and clear the equations. Then follow these steps:

step 1: Press the STAT button.

step 2: Select “1: Edit” from the EDIT menu.

step 3: In list L1, enter all the years to be graphed. In list L2, enter the corresponding number of people in the population.

step 4: Press the 2nd button and then the Y= button (STAT PLOT).

step 5: Select “Plot 1,” and press the ENTER button.

step 6: Move the cursor over “ON” and press the ENTER button.

step 7: Move the cursor over the line graph image and press the ENTER button.

step 8: Press the WINDOW button and adjust the scale of both axes as necessary.

step 9: Press the GRAPH button to view the graph.

Sample Graphs

Analysis

1. The data for Canada is in terms of millions of people, while the data for Alberta is in terms of thousands of people.

2. The overall population trend for both the province and the country is a continual increase.

3. The two population graphs are similar because they are both increasing and show a slight curving trend in the data. Comparing the populations from 1901 to 2001, the Alberta population has shown the greatest increase—by a factor of 40.8—while the population of Canada increased by a factor of 5.6.

4. Responses will vary depending on your knowledge of world history. The baby boom (high birth rates after World War II) has been attributed to the return of soldiers and a greater sense of security after the end of the Second World War. In Canada, people born from 1947 to 1964 are considered to be of the baby boom generation. The baby boomers represent a larger proportion of the Canadian population than other groups.

5. This question is designed to get you thinking about global population issues in anticipation of topics yet to be studied. The answer to this question will be subject to opinion, experience, and prior knowledge about the concerns of overpopulation.

Investigation: Investigating the Fossil Record: Plotting Changes Over Time, pages 490 and 491

Note: The finished chart that shows the organization of the fossils will vary between groups. One of the many possible charts is shown on this page.

Analysis

1. Layer 2 is 6000 years old, layer 3 is 9000 years old, and layer 4 is 12 000 years old.

2. The vertical axis on this chart represents time, since the chart progresses from the oldest layers at the bottom to the youngest layers at the top. The horizontal axis on this chart represents morphology, since the greater the difference in form and shape from the shell below, the greater the amount of shifting left or right between layers.

3. In layer 3, shell a did not lead to a similar-looking shell in the next layers. It appears that this species of land snail became extirpated from the Grand Bahama Island at this time.

4. An example of a long, nearly vertical line is that shell e in layer 5 leads to shell c in layer 4, which leads to shell a in layer 3. This species of snail apparently changed very little in the 6000 years of sedimentation between layers 5 and 3.

5. The sample chart provided does not show a dotted line. This answer describes another possible chart that is not shown. Shell b in layer 4 does not lead to a similar shell in layer 3, but it does seem to match shell c in layer 2. Since layer 3 was skipped, a dotted line is drawn from shell b in layer 4 to shell c in layer 2. It appears that the fossil record is incomplete and that a shell is missing to connect the 6000 years between layers 4 and 2.

6. If there is 3000 years between layers, the word suddenly only makes sense in terms of geological time. If you consider that Earth is 4.5 billion years old, a change in 3000 years is fairly sudden by Earth’s standards. If you consider that a human being can live to be 80 years old, 3000 years is not sudden at all.

Communication and Teamwork

7. Most charts will show shell a from layer 3 stopping. This suggests that this type of snail became extirpated from the area. Most charts will also likely show shell f from layer 3 leading to both shells b and d in layer 2, which in turn lead to shells a and e in layer 1. Beyond these similarities, there is a long list of potential differences.

8.

It is interesting to hear what specific shell details the other groups focused upon when they were making their decisions about positioning the shells. It is typical for many students to say that they would have used a more extensive list of defining characteristics to classify the shells.
9. Yes, it is entirely possible for two people, or two groups of people, to start with the same data and come to different conclusions. In this case, the differences are likely due to the fact that each group decided upon its own criteria for classifying the shells. If a common criteria was first established and agreed upon by all groups, then the results may have been more similar.

Investigation: Investigating Natural Selection: A Simulation, pages 498 and 499

Analysis

1. Answers will vary according to the results.

2. There is usually competition at the feeding bowl as students representing parent birds crowd to gather the food. If the parent birds are not quick, the food may be gone before they have a chance to get more for the chicks. Competition may also occur at the nest between chicks as one chick (or more than one chick) may be louder, more aggressive, or steal from other chicks. Some may share the food among themselves. The practice of altruism is also an adaptation that can benefit the overall success of a group or species.

3. It is important that the feeding bowl is placed centrally to make sure that all groups have equal access to the food. In this way, distance is controlled in the simulation.

4. Larger mouths (cups) and longer-reaching necks would be an advantage. Another advantage would be aggression through stealing food from other chicks.

5. The most successful beak types would live to reproduce while others disappeared. If there were two or three successful types of beaks, they might eventually become a separate species.

Evaluation

6. The distance to the food source and offspring numbers would not be controlled. The presence of a predator would be likely. There would be several food sources in different locations.

Extension

7. The activity is similar to the toothpick activity because both are simulating natural selection. Both populations would change dominant characteristics over time. The difference is the selective pressure. In this activity the pressure is the limited food source, while in the toothpick activity the pressure is the presence of a predator who selects more brightly coloured prey.

Science 20 © 2006, Alberta Education