Interactions and ecosystems

Ten questions of mixed difficulty, covering Interactions and ecosystems. Print it, or work through it on screen — the answer key starts on its own page.

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Interactions and ecosystems

Science 7 · maddyhelps.com

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A robin builds its nest in a spruce tree. The robin gets a safe place to raise its young, and the tree is neither helped nor harmed. This relationship is
1. a) commensalism
2. b) parasitism
3. c) mutualism
4. d) competition
In a pond, water fleas eat algae, small fish eat water fleas, and herons eat small fish. Which of these is the producer?
1. a) The herons
2. b) The water fleas
3. c) The small fish
4. d) The algae
In a boreal forest, snowshoe hares eat willow shrubs, and lynx eat snowshoe hares. If a disease kills most of the lynx, what will most likely happen next?
1. a) The willows are not affected, since lynx never eat them
2. b) More willow grows, since the hares have less to eat
3. c) More hares survive, and more willow gets eaten
4. d) Fewer hares survive, since their predator is gone
In a meadow, grasses capture 10 000 kJ of energy from sunlight. Mice eat the grasses, snakes eat the mice, and hawks eat the snakes. If roughly 10% passes on at each step, about how much reaches the hawks?
1. a) 7290 kJ
2. b) 10 kJ
3. c) 1000 kJ
4. d) 100 kJ
Winter ticks live on a moose through the winter, feeding on its blood. The ticks benefit, and the moose is weakened. This relationship is
1. a) parasitism
2. b) predation
3. c) commensalism
4. d) mutualism
A sealed jar holds pond water, a water plant and a snail, and sits near a window. Both stay alive for weeks. Which best explains why the snail does not run out of oxygen?
1. a) The snail gives off oxygen when it breathes, and the plant takes it in
2. b) The plant's photosynthesis gives off oxygen and uses the snail's carbon dioxide
3. c) The water held enough oxygen at the start to last for many weeks
4. d) The plant gives off oxygen through respiration, both day and night
A wildfire burns a forest in the foothills, but the soil and many roots survive. Within a year or two, fireweed and young aspen are growing there. This is
1. a) primary succession, because the first plants were small
2. b) secondary succession, because the soil was left behind
3. c) primary succession, because the forest had to start over
4. d) secondary succession, because a wildfire is a natural event
Students list what they find in a patch of forest. Which of these is an abiotic factor?
1. a) The insects living under bark
2. b) The fungi growing in the soil
3. c) The amount of rain that falls
4. d) The seeds on the forest floor
Students count the dandelions in five 1 m² quadrats in a 200 m² field. They find 3, 5, 2, 4 and 6. About how many dandelions grow in the whole field?
1. a) 1200
2. b) 20
3. c) 4000
4. d) 800
Mushrooms and other fungi growing on a fallen log slowly break it down and return its nutrients to the soil. They are acting as
1. a) scavengers
2. b) herbivores
3. c) producers
4. d) decomposers

Answer key · Interactions and ecosystems

Science 7 · maddyhelps.com

a) commensalism — In commensalism one partner benefits and the other is not affected, which fits the robin and the tree. Calling it parasitism is the usual mistake: the tree gets nothing back, but parasitism needs the host to be harmed.
d) The algae — A producer makes its own food using energy from sunlight, and in this chain only the algae can do that. The water fleas are the first animals in the chain, but they are consumers: they get their energy by eating the algae.
c) More hares survive, and more willow gets eaten — With fewer lynx hunting them, more hares survive, and more hares eat more willow. A change at one level of a food web passes along the chain, so it reaches the willows even though a lynx never eats a plant.
b) 10 kJ — Each step passes on roughly a tenth: 10 000 kJ in the grasses, 1000 kJ to the mice, 100 kJ to the snakes and 10 kJ to the hawks. Taking away 10% at each step gives 7290 kJ, but it is the other way round: about 90% is used for living or lost as heat at every level.
a) parasitism — In parasitism, one partner lives on or in a host and benefits while the host is harmed. It is not predation, because the ticks do not kill and eat the moose; they feed on it while it stays alive.
b) The plant's photosynthesis gives off oxygen and uses the snail's carbon dioxide — In light, photosynthesis takes in carbon dioxide and gives off oxygen, while the snail's respiration does the reverse, so the two keep recycling the same gases. Plants respire too, and respiration always uses oxygen, so the plant only gives off oxygen while it has light.
b) secondary succession, because the soil was left behind — Succession is secondary when soil survives the disturbance, with seeds and roots in it, so plants return quickly. Primary succession starts where there is no soil at all, such as bare rock left by a melting glacier; whether the cause was natural makes no difference.
c) The amount of rain that falls — Abiotic means non-living: rain, sunlight, temperature and the minerals in soil. Seeds are the usual trap, because they look lifeless, but each one is a living plant waiting for the right conditions to grow.
d) 800 — Find the average for one square metre first, (3 + 5 + 2 + 4 + 6) ÷ 5 = 4, then multiply by the 200 m² of field: 4 × 200 = 800. Multiplying the total of 20 by 200 gives 4000, which treats all 20 dandelions as if they grew in a single square metre.
d) decomposers — Decomposers break dead matter down into nutrients that plants can take up again, which is how matter gets recycled. A scavenger, such as a raven, eats dead animals but leaves the final breakdown to decomposers, and fungi are not producers, because they cannot make food from sunlight.