Ecosystems, Watersheds & Conservation — Problem set, Grade 6
What can resource pathways and comparable records reveal about an ecosystem? Does the supplied buffer model change runoff and sediment under matched conditions, and what does that imply for a real watershed?
Review the key ideas
Ecosystems, Habitats & Biomes
An ecosystem is every living thing in an area together with the non-living conditions they depend on, and the two cannot be separated. Which organisms live where is decided mostly by temperature and rainfall, which is why the same kind of biome appears on continents that have never been connected.
Food Chains, Food Webs & Energy Flow
Energy enters an ecosystem only through producers and leaves it as heat at every step, with roughly a tenth passing from one feeding level to the next. That single fraction explains why food chains are short and why large predators are rare.
Cycling Matter Through Organisms & Environment
The atoms in your body have all been used before, many times. Matter cycles endlessly between organisms and their surroundings because it cannot be created or destroyed, and the limit on life in most places is not the amount of an element present but whether it is in a form anything can use.
Human Impacts, Conservation & Tradeoffs
The largest cause of species loss is not hunting or pollution but habitat being taken for other uses, and the largest water pollution problem comes from fertiliser doing exactly what it was designed to do in the wrong place. Every conservation decision is a trade-off, and saying so honestly is part of doing it well.
Watersheds, Water Quality & Sampling Limits
A watershed is all the land that drains to one point, so everything done upstream arrives downstream. Judging the health of the water means measuring the right things, reading what lives there, and being honest that a single sample cannot establish very much on its own.
Problem 1
Answer and explanation
The shaded patch has greater recorded species richness, while the sunny patch has more recorded individuals. Neither measure alone proves a universally better habitat. Species identity, seasonal changes, detection, and the needs of a particular organism matter. These are illustrative patch records, not a survey of every forest.
Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.
Problem 2
Answer and explanation
No. Habitat use can span several features and locations. The study boundary should match the question rather than assume the organism never moves.
Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.
Problem 3
Answer and explanation
The arrows show receiving organisms obtaining matter and energy from resources. 80 ÷ 800 = 10% in the stated biomass-transfer model, not a universal percentage. The second fish provides another feeding route, and the web lacks population sizes and rates; it cannot specify an exact future bird count.
Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.
Problem 4
Answer and explanation
Draw fish → bird, showing the direction of matter and energy transferred through feeding. State the convention so the arrow can be interpreted.
Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.
Problem 5
Answer and explanation
Soil: 20 − 5 + 3 = 18 units. Plants: 8 + 5 − 2 = 11. Animals: 2 + 2 − 3 = 1. The total remains 30 units. These are simplified nutrient-account units, not a complete real decomposition pathway or energy total; actual stores and processes would be more detailed.
Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.
Problem 6
Answer and explanation
Decomposition can return matter to usable nutrient pathways, but energy spreads through processes and thermal transfers. Plants still require an energy source such as sunlight.
Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.
Problem 7
Answer and explanation
Mean sediment is 20 g bare and 12 g buffered, a reduction of 8 g or 40% relative to the bare mean. The buffer fits the stated budget and merits a bounded further test. Tray records do not guarantee a 40% field reduction in all storms; scale, plant establishment, maintenance, and other outcomes need study.
Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.
Problem 8
Answer and explanation
No. Evaluate scientific accuracy, evidence, and tradeoffs rather than agreement with a preferred policy or personal belief.
Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.
Problem 9
Answer and explanation
A’s mean dissolved oxygen is 8 mg/L; B’s is 5 mg/L. A has lower recorded turbidity under the stated method. These indicators support different physical/ecological comparisons, but the small record does not identify every cause, represent all seasons, or certify either water as safe to drink.
Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.
Problem 10
Answer and explanation
No. Missing measurement is not measured zero. Preserve the absent entry and obtain a comparable record if the question requires it.
Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.