1. Introduction

Ipkegyn
A spaceship for founding a space colony: crew size depends on your decisions about diet. Image source: https://www.itl.cat/wallview/omTxRJ_space-colony-live-wallpaper-group-outer-space/. Permission Pending.

At the end of the last module, you responded to this scenario:

  1. You’re the director of a mission to colonize a planet in another solar system.
  2. Your spaceship is to carry colonists on a decades-long journey to your new home.
  3. You have to grow your food on the ship.

Decision: to maximize crew size, are you going to direct your crew to eat as vegetarians or carnivores?

There is an answer, and it lies in the principles of ecology. Let’s take a look.

2. The Easy Math of Energy in Trophic Levels

To keep the math easy, let’s set 2000 Calories/day as our average target calorie intake for each crewperson.

Remember that our ship can produce a lot of energy: enough to grow 2,000,000 food calories worth of food each day. What we’re growing, of course, are plants. If we stick to a strict vegetarian diet, then the math is straightforward: 2,000,000 calories of plant food/day, divided by 2000 calories/day/crewperson= 1000 crew people.

Let's feed our grain to the cows and eat as carnivores.
Let’s feed our grain to the cows and eat as carnivores.

But what happens if we wanted to eat as carnivores? We would take the seeds, grain, leaves, and other plant food that we produced on our ship’s farms, and we would feed it to cows  (or other animals, such as chickens). Then, instead of eating plant foods like bread and apples, we’d eat steak. If we measured the amount of chemical energy available to us from the cows, how much energy would be available for the crew?

Make a prediction:

[qwiz style = “border: 3px solid black; “]

[h]What happens to 2,000,000 plant calories ….

[q] If 2,000,000 calories are available if we eat plants, how much calories will be available if we feed those plants to animals, and then eat the animals?

[c]20,000,000

[c]2,000,000

[c*]200,000

[f]No. What you’re suggesting is that 2,000,000 calories in plants will become 20,000,000 calories in animals. Not possible. A key principle in physics is that any time you transform energy from one form to another, you lose energy. A meat based diet will take the 2,000,000 calories you had in plant food, and reduce it to 200,000 calories in meat.

[f]No. What you’re suggesting is that 2,000,000 calories in plants will stay the same after being fed to animals. Not possible. A key principle in physics is that any time you transform energy from one form to another, you lose energy. A meat based diet will take the 2,000,000 calories you had in plant food, and reduce it to 200,000 calories in meat.

[f]Yes. 2,000,000 calories in plants yield about 200,000 calories after being fed to animals. A key principle in physics is that any time you transform energy from one form to another, you lose energy, and you’re seeing this principle in action.

[x]

[restart]

[/qwiz]

As, you’ve just seen, here are the numbers:

1) Harvestable food energy available in plants 2,000,000 calories
2) Harvestable food energy available in animals that eat the plants 200,000 calories

Harvestable energy means exactly what it says. Imagine taking all of the plants that we can grow on the ship, and measuring their energy. That would be the first row: harvestable energy available in plants. The second row is the energy available to us from the meat of the animals that ate the plants.

Note that the total food energy that we could harvest from the cows is only 10% of the energy in the plants that we fed to the cows. Or, using the terms related to trophic levels that we learned in the previous tutorial, the harvestable energy in the producers (plants) is ten times as great as the harvestable energy in primary consumers.

The loss of 90% of the available food energy from producers to consumers is a widely known rule in ecology. The rule is called the 10 Percent Rule. To make sure that you’re getting this, try to label the diagram below. Note that in this ecosystem, the energy available in the producers starts at 600,000 units of energy.

[qwiz qrecord_id=”sciencemusicvideosMeister1961-Trophic Levels, Interactive Diagrams (Ecosystems)”]

[h]Interactive Diagrams: Trophic Levels and Harvestable Energy

[q labels = “top”]

 

[l]producers

[fx] No. Please try again.

[f*] Correct!

[l]primary consumer

[fx] No. Please try again.

[f*] Excellent!

[l]secondary consumer

[fx] No, that’s not correct. Please try again.

[f*] Correct!

[l]Third-level consumer

[fx] No, that’s not correct. Please try again.

[f*] Good!

[l]600,000

[fx] No. Please try again.

[f*] Good!

[l]60,000

[fx] No, that’s not correct. Please try again.

[f*] Excellent!

[l]6,000

[fx] No. Please try again.

[f*] Excellent!

[l]600

[fx] No, that’s not correct. Please try again.

[f*] Great!

[x]

[restart]

[/qwiz]

What the 10% rule says is this: If you gathered up all of the primary producers and measured their chemical energy, and then did the same with the herbivores/primary consumers, the herbivores would have only 10% of the total chemical energy that was available in the producers. And, if you gathered up all of the secondary consumers/carnivores, and compared the energy in that trophic level to the energy in the primary consumers, you’d find that once again, you’d only transferred 10% of the energy.

Let’s apply the 10% rule to the issue of largest possible crew size on our spaceship to Alpha Centauri.

[qwiz style=”width: 700px !important; min-height: 400px !important;” qrecord_id=”sciencemusicvideosMeister1961-10% Rule Interactive Diagram (Ecosystems)”]

[h]The 10% rule and crew size on our trip to Alpha Centauri

[q labels = “top”]

 

[l]producer

[fx] No. Please try again.

[f*] Good!

[l]primary consumer

[fx] No. Please try again.

[f*] Excellent!

[l]secondary consumer

[fx] No. Please try again.

[f*] Great!

[l]2,000,000

[fx] No. Please try again.

[f*] Great!

[l]200,000

[fx] No. Please try again.

[f*] Great!

[l]CARNIVORE CREW

[fx] No, that’s not correct. Please try again.

[f*] Correct!

[l]HERBIVORE CREW

[fx] No, that’s not correct. Please try again.

[f*] Good!

[/qwiz]

To translate what’s above into actual crew numbers, here’s the math.

  • Eating as primary consumers/vegetarians, you’d have 2,000,000 calories available for the crew. At an average of 2,000 calories/crewmember, that would get you a crew of 1,000.
  • Eating as secondary consumers/carnivores, you’ve have 200,000 calories available for the crew. At an average of 2,000 calories/crewmember, your crew size drops to 100.

In terms of founding a colony, more colonists is better. It maximizes genetic diversity, keeping your population more adaptable. The vegetarian strategy is the wiser course of action.

Of course, the actual decision would be much more nuanced. Humans are omnivores: it’s probably wise for the crew to have access to some animal protein. And the energy equation becomes very different if you’re considering animal products (eggs from chicken, dairy from cows) as opposed to meat. But given the limits of size of ship and amount of energy it can produce, it makes sense to have the crew eat primarily as herbivores, instead of primarily as carnivores.

MISCONCEPTION ALERT: Before going further, let’s clear up a possible point of confusion. What we’re discussing does NOT mean that a pound of meat (steak, or chicken, for example) has less energy than a pound of rice or a pound of broccoli. This is NOT a comparison of energy between organisms, or types of food. It’s a comparison of the energy available between trophic levels.

3. Understanding the 10% Rule

Why is so little energy transferred from one trophic level to the next? One reason is that the work that cells do to keep themselves alive is not performed with perfect efficiency. As sugar is transformed to ATP, and as ATP is broken down to ADP and phosphate to perform cellular work, a lot of energy is lost as heat. It’s the same thing that happens in a car. The gasoline in the gas tank is not perfectly transformed into the kinetic energy that moves the car. Rather, much of the energy is lost as heat: heat that you can feel coming off a car’s hood. That heat is wasted energy that dissipates (disperses, diffuses) into the environment.

Similarly, many of the food calories that you feed to a cow, as they are used by the cow to keep itself alive, dissipate as heat into the environment. Add to that the fact that a cow is a mammal with a body temperature similar to yours, and you get an even greater loss of energy to heat. All of the chemical energy lost as heat is not going to be available to the next trophic level: the carnivores who eat the cow.

In my Food Chain Song (embedded below), I refer to the heat loss as “metabolic rent.” But there are more reasons why energy transfer between trophic levels is so inefficient. The diagram below, which shows a caterpillar harvesting energy from a leaf, shows heat loss, and one additional source of energy loss (note that this diagram uses Joules (J) instead of Calories. The proportions would be the same).

The 67 J arrow on the right side (cellular respiration) is the heat loss that we’ve described above: it’s the energy that the caterpillar is burning just to keep itself alive. But note the 100J arrow to the left labeled “feces.” Not everything that an organism ingests goes making more of that organism. Some ingested food is indigestible, and passes right through you. On an ecological level, all of that defecated matter doesn’t become available to the next trophic level.

So, in the diagram above, what’s left to be transferred to the next trophic level? Only the 33J labeled as “growth.”

The fact that 33/200 is 16.5%, as opposed to to 10% might seem confusing. But remember that this an analysis of one animal eating a part of a plant.  If you widen the analysis to thinking about the actual organisms living in an ecosystem, you can find additional reasons for energy loss between trophic levels. We’ll do that in a moment, but first, answer the questions below.

[qwiz qrecord_id=”sciencemusicvideosMeister1961-10% Rule in Action (Ecosystems)”]

[h]Quiz: The 10% rule in action

[q] In the diagram below, what is the amount of energy that passes through the caterpillar, but which can’t be absorbed into the caterpillar.

[c*]100J

[c]33J

[c]67J

[c]200J

[f]Yes. 100 J is labeled as “feces.” That’s food energy that passes through us, but which we can’t absorb.

[f]No. 33J is labeled as “growth.” That means that this energy gets incorporated into building more caterpillar.

[f]No. 67J is labeled as “cellular respiration.” That means that this energy is used to keep the caterpillar alive, or is lost as heat to the environment.

[f]No. 200J is the original amount of food energy in the leaf that was consumed by the caterpillar.

[q] In the diagram below, what is the amount of food energy that the caterpillar consumes.

 

[c]100J

[c]33J

[c]67J

[c*]200J

[f]No. 100 J is labeled as “feces.” That’s food energy that passes through us, but which we can’t absorb.

[f]No. 33J is labeled as “growth.” That means that this energy gets incorporated into building more caterpillar.

[f]No. 67J is labeled as “cellular respiration.” That means that this energy is used to keep the caterpillar alive, or is lost as heat to the environment.

[f]Yes. 200J is the original amount of food energy in the leaf that was consumed by the caterpillar.

[q] In the diagram below, what is the amount of energy that passes through the caterpillar consumes, and which becomes more caterpillar.

 

[c]100J

[c*]33J

[c]67J

[c]200J

[f]No. 100 J is labeled as “feces.” That’s food energy that passes through us, but which we can’t absorb.

[f]Yes. 33J is labeled as “growth.” That means that this energy gets incorporated into building more caterpillar.

[f]No. 67J is labeled as “cellular respiration.” That means that this energy is used to keep the caterpillar alive, or is lost as heat to the environment.

[f]No. 200J is the original amount of food energy in the leaf that was consumed by the caterpillar.

[q] In the diagram below, what is the amount of energy that the caterpillar consumes, but which gets spent supporting the caterpillar’s own life processes, or is lost as heat?

 

[c]100J

[c]33J

[c*]67J

[c]200J

[f]No. 100 J is labeled as “feces.” That’s food energy that passes through us, but which we can’t absorb.

[f]No. 33J is labeled as “growth.” That means that this energy gets incorporated into building more caterpillar.

[f]Yes. 67J is labeled as “cellular respiration.” That means that this energy is used to keep the caterpillar alive, or is lost as heat to the environment.

[f]No. 200J is the original amount of food energy in the leaf that was consumed by the caterpillar.

[x]

[restart]

[/qwiz]

 

 

A food web showing trophic levels
A food web showing trophic levels

The primary consumers are not going to be able to eat every last piece of the plants below them. Just think of yourself as a primary consumer. If you eat rice, for example, you’re eating only a tiny portion of that plant. Or consider eating an apple: there’s the whole rest of the tree that you’re not consuming. Similarly, when you eat as a carnivore, you eat only a tiny portion of the animal that was killed to feed you. When you eat chicken, you mostly eat the muscle tissue around the breasts, back, and legs. All the rest of the chicken (bones, innards, head, feet, etc). doesn’t get transferred to you.

Here’s how I summarize this in my Food Chain Song.

Each level in a food chain yields only ten percent
Of the former level’s energy you might ask where it went
There are bones and leaves you can’t digest that really make a dent
And don’t ignore the weighty cost of metabolic rent.

4. Ecological Pyramids

Ecologists have organized this notion of energy loss in ecosystems into a pyramid of energy. In the pyramid, you can see available energy dropping by 90% from one trophic level to the next. Remember: 90% of the energy is lost. Only 10% is transferred.

There are other ecological pyramids that show other aspects of ecosystem structure. One is a pyramid of numbers. This pyramid shows the actual number of organisms at each trophic level. In the pyramid of numbers below, you see that 1,500,000 producers support 200,000 herbivores. These herbivores support 90,000 secondary consumers, who in turn support one top-level carnivore.

pyramid of numbers
A pyramid of numbers for a grassland ecosystem

But unlike a pyramid of energy, which is always widest at its base, the pyramid of numbers can have a base that’s narrower than the levels above. Consider a forest ecosystem where one tree might support thousands of insects, which are preyed upon by birds. That pyramid would look like this:

Another pyramid of numbers
A pyramid of numbers for a forest ecosystem

Ecosystems can also be represented through a pyramid of biomass. Biomass is living matter, and a biomass pyramid shows the amount of living matter in each trophic level. Here’s a typical biomass pyramid.

Like a pyramid of numbers, there are biomass pyramids that are inverted, with the base more narrow than the layers above. But that goes beyond the scope of our efforts here. If you want to read more about pyramids of biomass, you can follow this link to Wikipedia.

Let’s check your understanding of ecological pyramids with this quiz.

[qwiz random = “true” qrecord_id=”sciencemusicvideosMeister1961-Ecological Pyramids (Ecosystems)”]

[h]Quiz: Ecological Pyramids: Checking Understanding

[q] The diagram below shows a

[c]pyramid of energy

[c]pyramid of biomass

[c*]pyramid of numbers

[f]No. A pyramid of energy differences at each trophic level. You could identify this by energy-related units such as “joules,” “calories,” etc.

[f]No. Biomass is living matter. A pyramid of biomass shows differences in biomass at each trophic level. You could identify it by units such as grams or kilograms.

[f]Yes. This is a pyramid of numbers, and shows the number of organisms at each trophic level.

[!!]question 2[/!!!]

[q] The diagram below shows a

[c*]pyramid of energy

[c]pyramid of biomass

[c]pyramid of numbers

[f]Yes. A pyramid of energy differences at each trophic level. You could identify this by energy-related units such as “joules,” “calories,” etc.

[f]No. Biomass is living matter. A pyramid of biomass shows differences in biomass at each trophic level. You could identify it by units such as grams or kilograms.

[f]No. A pyramid of numbers shows the number of organisms at each trophic level.

[!!]question 3[/!!!]

[q] The diagram below shows a

 

[c]pyramid of energy

[c*]pyramid of biomass

[c]pyramid of numbers

[f]No. A pyramid of energy differences at each trophic level. You could identify this by energy-related units such as “joules,” “calories,” etc.

[f]Yes. Biomass is living matter. A pyramid of biomass shows differences in biomass at each trophic level.

[f]No. A pyramid of numbers shows the number of organisms at each trophic level.

[!!]question 4[/!!!]

[q] The diagram below shows a

[c]pyramid of energy

[c]pyramid of biomass

[c*]pyramid of numbers

[f]No. A pyramid of energy differences at each trophic level. You could identify this by energy-related units such as “joules,” “calories,” etc.

[f]No. Biomass is living matter. A pyramid of biomass shows differences in biomass at each trophic level.

[f]Yes. A pyramid of numbers shows the number of organisms at each trophic level.

[!!]question 5[/!!!]

[q] In the diagram below, the secondary consumers are the

[c]shrimp

[c*]bleak

[c]perch

[f]No. This is a terribly tricky question. The shrimp are shown at the bottom of this pyramid, but you know enough about biology and ecology to know that shrimp are animals, and can’t be producers. Therefore, they have to be the primary consumers in this system.

[f]Yes. The bleak are eating the shrimp. Since the shrimp have to be the primary consumers, the bleak have to be secondary consumers.

[f]No. This is a terribly tricky question. Even though the perch are the 3rd level up, you know that the shrimp are animals, and can’t be producers. Therefore, they have to be the primary consumers in this system. That would make the perch a third level consumer. Who’s the secondary consumer?

[q] Which type of ecological pyramid HAS to be widest at its base?

[c]Pyramid of numbers

[c]Pyramid of biomass

[c*]Pyramid of energy

[f]No. In an ecosystem where a few very large producers support many consumers (a tree supporting thousands of insects), it’s possible for the pyramid of numbers to be narrower at its base.

[f]No. There are some aquatic ecosystems where, at any point in time, there is more mass at the level of primary consumers than there is at the level of producers.

[f]Yes. A pyramid of energy, based on the laws of physics, has to be widest at its base. No exceptions.

[q]If the amount of chemical energy in the giraffes is 150,000 units, how much energy would be in the lions?

[c*]15,000

[c]150,000

[c]1,500,000

[f]Yes. Following the 10% rule, there’d be 10% of the energy available in the lions as there is in the giraffes.

[f]No. Following the 10% rule, there’d be 10% of the energy available in the lions as there is in the giraffes.

[f]No. Following the 10% rule, there’d be 10% of the energy available in the lions as there is in the giraffes.

[q]If the amount of chemical energy in the giraffes is 150,000 units, how much energy would be in the plants that support the giraffes?

[c]15,000

[c]150,000

[c*]1,500,000

[f]No. Following the 10% rule, have to be 10 times as much energy in the trophic level supporting the giraffes than in the giraffes themselves.

[f]No. Following the 10% rule, have to be 10 times as much energy in the trophic level supporting the giraffes than in the giraffes themselves.

[f]Yes. Following the 10% rule, have to be 10 times as much energy in the trophic level supporting the giraffes than in the giraffes themselves.

[x]

[restart]

[/qwiz]

5. Biological Magnification: Interactive Reading

[qwiz style=”width: 760px” qrecord_id=”sciencemusicvideosMeister1961-Biological Magnification (I.R., Ecosystems)”]

[h]Interactive Reading: Biological Magnification

[q labels = “top”]

Biomagnification. Source: http://www.brainkart.com/article/Biomagnification_38169/. Permission pending

An environmental consequence of the way that __________ and energy flow through ecosystems is biological magnification, frequently shortened to biomagnification. In biological magnification, pollutants that are released into the environment become increasingly concentrated at higher _________ levels. In the diagram to the left, for example, shows the effect of the pesticide DDT(formerly used for controlling insect pests, and now banned in many parts of the world).

Here’s what happened in the United States in the 1950s and 1960s. DDT was sprayed on crops to control ________. Through runoff after rainstorms, DDT  entered the water supply at a ______ concentration (one part/trillion). The producers in aquatic ecosystems absorbed the DDT into their body tissues. Because the DDT is not easily broken down, it persisted in the producers’ bodies. When these __________ were eaten by consumers (zooplankton in the diagram) the pesticide became further ____________. This continued from trophic level to trophic level, until the DDT reached 10,000,000 parts/trillion in the fish eating birds (ospreys, eagles) at the top of this ___________. Because DDT interfered with processes related to depositing calcium in eggshells, these fish-eating birds started laying eggs with thin ________, which broke under the weight of the birds sitting on them during incubation. This led to significant declines in the birds’ reproduction rates, and overall ___________ decline.

Biologist Rachel Carson identified this problem in the late 1950s, and wrote the environmental classic The Silent Spring in 1962. Her work led to a national _____ on DDT in 1971, and was influential in sparking the modern environmental movement. Problems with ________________ continue, however, with many other pollutants.

[l]ban

[fx] No. Please try again.

[f*] Excellent!

[l]biomagnification

[fx] No, that’s not correct. Please try again.

[f*] Correct!

[l]concentrated

[fx] No, that’s not correct. Please try again.

[f*] Good!

[l]food web

[fx] No, that’s not correct. Please try again.

[f*] Correct!

[l]insects

[fx] No. Please try again.

[f*] Great!

[l]low

[fx] No, that’s not correct. Please try again.

[f*] Great!

[l]matter

[fx] No, that’s not correct. Please try again.

[f*] Good!

[l]population

[fx] No. Please try again.

[f*] Good!

[l]producers

[fx] No, that’s not correct. Please try again.

[f*] Excellent!

[l]shells

[fx] No. Please try again.

[f*] Good!

[l]trophic

[fx] No. Please try again.

[f*] Good!

[x]

[restart]

[/qwiz]

 

 

6. Concluding Thoughts

The key idea from this module is that while matter in ecosystems is endlessly recycled, energy dissipates as it flows from one trophic level to the next.  Here’s a haiku that captures this:

In ecosystems
Energy will dissipate
But matter cycles

The energy doesn’t disappear. It just becomes less useful. In almost every ecosystem on Earth, energy starts as sunlight. If the sun stopped shining, energy would stop flowing, and life would cease. Producers transform this light energy into chemical bond energy through photosynthesis, capturing it as carbohydrates. As this chemical energy moves from trophic level to trophic level, most of the energy diffuses away as heat. Consequently, fewer and fewer organisms can be supported at higher trophic levels.

I’ve tried to capture a lot of these ideas in my Food Chain song. If you are watching it in a classroom setting, please use headphones or earbuds so as not to disturb the students around you.

If you feel confident that you’ve mastered the ideas in this module, take this quiz.

7. Trophic Levels and Energy Pyramids Quiz

[qwiz random = “true” qrecord_id=”sciencemusicvideosMeister1961-Trophic Levels, Ecological Pyramids Quiz (Ecosystems)”]

[h]Quiz: Trophic levels and Energy pyramids

[!!!!!!] question 1 +++++++++[/!!!!!!]
[q topic= “trophic_levels_and_energy”]A feeding level, such as primary consumer or secondary consumer, is also known as a(n)

[c*] trophic level

[c] ecological level

[c] Habitat

[c] ecological niche

[f] Correct. A feeding level is more formally known as a trophic level.

[f] No. You’re looking for a term that relates to an organism’s feeding level. If you know the term ‘autotroph,’ (an organism that feeds itself) you can use word roots to figure out the answer.

[f] No. A habitat is an organism’s address, or where it lives. You’re looking for a term that relates to an organism’s feeding level. If you know the term ‘autotroph,’ (an organism that feeds itself) you can use word roots to figure out the answer.

[f] No. A ‘niche’ is an organism’s profession, or how it makes its living. You’re looking for a term that relates to an organism’s feeding level. If you know the term ‘autotroph,’ (an organism that feeds itself) you can use word roots to figure out the answer.

[!!!!!!] question 2 +++++++++[/!!!!!!]
[q topic= “trophic_levels_and_energy”]As energy is transferred between trophic levels, _________ percent of energy will be lost.

[c] 10

[c] 40

[c] 60

[c*] 90

[f] No. The rule about energy transfer is the 10% rule, which says that only 10% of the energy is transferred between one trophic level and the next. If 10% is transferred, then how much will be lost?

[f] No. The rule about energy transfer is the 10% rule, which says that only 10% of the energy is transferred between one trophic level and the next. If 10% is transferred, then how much will be lost?

[f] No. The rule about energy transfer is the 10% rule, which says that only 10% of the energy is transferred between one trophic level and the next. If 10% is transferred, then how much will be lost?

[f] Yes. The rule about energy transfer is the 10% rule, which says that only 10% of the energy is transferred between one trophic level and the next. If 10% is transferred, then 90% will be lost.

[!!!!!!] question 3 +++++++++[/!!!!!!]
[q topic= “trophic_levels_and_energy”]If there are 700,000 Calories of harvestable energy in an ecosystem’s primary consumers, then you would expect there to be __________ Calories of harvestable energy in the secondary consumers.

[c] 7,000,000

[c] 700,000

[c*] 70,000

[c] 7,000

[f] No. The rule about energy transfer is the 10% rule, which says that only 10% of the energy is transferred between one trophic level and the next. If there are 700,000 Calories of harvestable energy in the primary consumers, then there will be 10% of 700,000 in the secondary consumers. What’s 10% of 700,000?

[f] No. The rule about energy transfer is the 10% rule, which says that only 10% of the energy is transferred between one trophic level and the next. If there are 700,000 Calories of harvestable energy in the primary consumers, then there will be 10% of 700,000 in the secondary consumers. What’s 10% of 700,000?

[f] Yes. The rule about energy transfer is the 10% rule, which says that only 10% of the energy is transferred between one trophic level and the next. If there are 700,000 Calories of harvestable energy in the primary consumers, then there will be 10% of 700,000, or 70,000 in the secondary consumers.

[f] No. The rule about energy transfer is the 10% rule, which says that only 10% of the energy is transferred between one trophic level and the next. If there are 700,000 Calories of harvestable energy in the primary consumers, then there will be 10% of 700,000 in the secondary consumers. What’s 10% of 700,000?

[!!!!!!] question 4 +++++++++[/!!!!!!]
[q topic= “trophic_levels_and_energy”]Analysis of a an island ecosystem shows that there are 6,000 Calories of harvestable energy available in an ecosystem’s secondary consumers. The amount of harvestable energy available in the producers must be _________ Calories

[c] 600

[c] 6,000

[c] 60,000

[c*] 600,000

[f] No. The rule about energy transfer is the 10% rule, which says that only 10% of the energy is transferred between one trophic level and the next. If there are 6,000 Calories of harvestable energy in the secondary consumers, then there would have to be ten times as much energy in the primary consumers, and another ten times as much in the producers. What’s 6,000 times 10 times 10?

[f] No. The rule about energy transfer is the 10% rule, which says that only 10% of the energy is transferred between one trophic level and the next. If there are 6,000 Calories of harvestable energy in the secondary consumers, then there would have to be ten times as much energy in the primary consumers, and another ten times as much in the producers. What’s 6,000 times 10 times 10?

[f] No. The rule about energy transfer is the 10% rule, which says that only 10% of the energy is transferred between one trophic level and the next. If there are 6,000 Calories of harvestable energy in the secondary consumers, then there would have to be ten times as much energy in the primary consumers, and another ten times as much in the producers. What’s 6,000 times 10 times 10?

[f] Yes. There would have to be 600,000 Calories in the producers to support 6,000 Calories in the secondary consumers. The rule about energy transfer is the 10% rule, which says that only 10% of the energy is transferred between one trophic level and the next. If there are 6,000 Calories of harvestable energy in the secondary consumers, then there would have to be ten times as much energy in the primary consumers, and another ten times as much in the producers. 6,000 times 10 times 10 = 600,000

[!!!!!!] question 5 +++++++++[/!!!!!!]
[q topic= “trophic_levels_and_energy”]In a series of trophic levels, the level farthest from the producers usually

[c] has the most biomass.

[c] has the most individuals.

[c] receives the most energy.

[c*] receives the least energy.

[f] No. In the same way that energy declines from one trophic level to the next, biomass will also decline as you move to the trophic levels furthest from the producers. Note that for a variety of reasons, this might not happen between producers and primary consumers. However, biomass decline will happen at higher trophic levels.

[f] No. In the same way that energy declines from one trophic level to the next, numbers of individuals will also decline as you move to the trophic levels furthest from the producers. Note that for a variety of reasons, this might not happen between producers and primary consumers. However, decline in number of individuals will happen at higher trophic levels.

[f] No. Energy declines from one trophic level to the next.

[f] Yes. The trophic levels furthest from the produces receives the least energy.

[!!!!!!] question 6 +++++++++[/!!!!!!]
[q topic= “trophic_levels_and_energy”]The amount of organic matter at each trophic level is called the

[c] organic mass.

[c*] biomass.

[c] energy pyramid.

[c] trophic mass.

[f] No. Here’s a hint about the answer: it’s the mass of biological material.

[f] Yes. The amount of organic matter at each trophic level is called the biomass.

[f] No. An energy pyramid represents energy flow between trophic levels. Here’s a hint about the answer: It’s the mass of biological material.

[f] No. Here’s a hint about the answer: it’s the mass of biological material.

[!!!!!!] question 7 +++++++++[/!!!!!!]
[q topic= “trophic_levels_and_energy”]The organisms at the bottom of an ecological pyramid are

[c] consumers.

[c*] producers.

[c] decomposers.

[c] heterotrophic.

[f] No. Think about the Food Chain song. ‘At the bottom of a food chain are ______________ like green plants.’ Ecologically, green plants are ….

[f] Yes. As the Food Chain Song goes, ‘At the bottom of a food chain are producers like green plants.’

[f] No. At the bottom of the food chain are the organisms that make the food. Think of a synonym for ‘make’ and you’ll have the answer.

[f] No. Heterotrophic organisms are consumers. What’s needed here is an organism that can make food. Think of a synonym for ‘make’ and you’ll have the answer.

[!!!!!!] question 8 +++++++++[/!!!!!!]
[q topic= “trophic_levels_and_energy”]A basic law of ecology is that 10 percent of

[c] a species can be hunted during a given season.

[c*] the energy in one trophic level becomes available in the next trophic level.

[c] the carbon in the atmosphere enters the carbon cycle.

[c] the oxygen an animal breathes is absorbed into the blood.

[f] No. Here’s a hint. The 10% rule relates to the flow of energy in an ecosystem.

[f] Yes. The 10% rule states that only 10% of the energy in one trophic level is transferred to the next trophic level.

[f] No. Here’s a hint. The 10% rule relates to the flow of energy in an ecosystem.

[f] No. Here’s a hint. The 10% rule relates to the flow of energy in an ecosystem.

[!!!!!!] question 9 +++++++++[/!!!!!!]
[q topic= “trophic_levels_and_energy”]The image shown below is a

[c] pyramid of energy

[c] pyramid of biomass

[c*] pyramid of numbers

[c] food web

[f] No. A pyramid of energy would show the change from one trophic level to the next in terms of an energy unit like joules or calories. What does this pyramid show?

[f] No. A pyramid of biomass would show the change from one trophic level to the next in terms of a unit such as kilograms/square meter. What does this pyramid show?

[f] Yes. This is a pyramid of numbers.

[f] No. A food web would show all of the possible food chains in a ecosystem. This image is an ecological pyramid. What’s changing from one trophic level to the next?

[!!!!!!] question 10 +++++++++[/!!!!!!]
[q topic= “trophic_levels_and_energy”]The image shown below is a

[c] pyramid of energy

[c*] pyramid of biomass

[c] pyramid of numbers

[c] food web

[f] No. A pyramid of energy would show the change from one trophic level to the next in terms of an energy unit like joules or calories. What does this pyramid show?

[f] Yes. This is a pyramid of biomass.

[f] No. A pyramid of numbers would show the change from one trophic level to the next in terms of numbers of individuals at each trophic level. What does this pyramid show?

[f] No. A food web would show all of the possible food chains in a ecosystem. This image is an ecological pyramid. What’s changing from one trophic level to the next?

[!!!!!!] question 11 +++++++++[/!!!!!!]
[q topic= “trophic_levels_and_energy”]The image shown below is a

[c*] pyramid of energy

[c] pyramid of biomass

[c] pyramid of numbers

[c] food web

[f] Yes. A pyramid of energy shows the change from one trophic level to the next in terms of an energy unit like joules or calories.

[f] No. A pyramid of biomass would show the change from one trophic level to the next in terms of a unit such as kilograms/square meter. What does this pyramid show?.

[f] No. A pyramid of numbers would show the change from one trophic level to the next in terms of numbers of individuals at each trophic level. What does this pyramid show?

[f] No. A food web would show all of the possible food chains in a ecosystem. This image is an ecological pyramid. What’s changing from one trophic level to the next?

[!!!!!!] question 12 +++++++++[/!!!!!!]
[q topic= “trophic_levels_and_energy”]The image shown below could NOT be a

[c*] pyramid of energy

[c] pyramid of biomass

[c] pyramid of numbers

[f] Yes. A pyramid of energy shows the change from one trophic level to the next in terms of energy. Based on the laws of physics, it HAS to be widest at its base. This diagram is a pyramid of numbers.

[f] No. A pyramid of biomass shows the change from one trophic level to the next in terms of a unit such as kilograms/square meter. It’s possible for a pyramid of numbers to be wider at the level of primary consumers than it is at the level of producers. What ecological pyramid MUST be widest at its base?

[f] No. A pyramid of numbers shows the change from one trophic level to the next in terms of numbers of individuals at each trophic level. A pyramid of numbers can be narrower at the level of producers than the level of primary consumers (think of a single tree that supports thousands of insects). What type of ecological pyramid MUST be widest at its base?

[!!!!!!] question 13 +++++++++[/!!!!!!]
[q topic= “trophic_levels_and_energy”]As energy moves from one trophic level to the next, a significant amount of energy will be lost in the form of

[c] herbivores consumed by carnivores

[c*] heat dissipating into the environment

[c] plants consumed by herbivores

[f] No. Consumption itself isn’t a major source of energy loss between trophic levels. The greater loss occurs as energy in the trophic level below dissipates into the environment. This dissipation of energy occurs in what form?

[f] Yes. As energy is transferred between trophic levels, a significant amount of energy is lost in the form of heat that dissipates into the environment.

[f] No. Consumption itself isn’t a major source of energy loss between trophic levels. The greater loss occurs as energy in the trophic level below dissipates into the environment. This dissipation of energy occurs in what form?

[!!!!!!] question 14 +++++++++[/!!!!!!]
[q topic= “trophic_levels_and_energy”]As energy moves from trophic level to trophic level it will

[c] increase

[c] accumulate

[c*] dissipate

[f] No. Total harvestable energy decreases from one trophic level to the next. What happens to it?

[f] No. Total harvestable energy decreases from one trophic level to the next. What happens to it?

[f] Yes. Total harvestable energy decreases from one trophic level to the next as it dissipates into the environment.

[!!!!!!] question 15 +++++++++[/!!!!!!]
[q topic= “trophic_levels_and_energy”]As matter moves through an ecosystem it

[c] increases

[c] dissipates

[c] accumulates

[c*] cycles and circulates

[f] No. The matter in an ecosystem is a fixed quantity.

[f] No. The matter in an ecosystem is a fixed quantity.

[f] No. The matter in an ecosystem is a fixed quantity.

[f] Yes. Matter is recycled over and over again as it moves through ecosystems. Matter is recycled. Energy dissipates.

[x]
[restart]

[/qwiz]

Next steps

This ends this series of tutorials about energy and ecology.

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