Quiz · Easy
A quick check on trophic levels and the 10% rule, symbiosis, population growth, succession and nutrient cycles.
Producers in an ecosystem capture 10,000 kcal of energy. Using the 10% rule, about how much reaches the tertiary consumers?
100 kcal
1,000 kcal
10 kcal
1 kcal
Each step keeps about 10%: producers 10,000 → primary consumers 1,000 → secondary 100 → tertiary 10 kcal. 100 kcal is the secondary consumer level.
Most of the energy that is NOT passed on to the next trophic level is:
Recycled back to the producers
Lost as heat from cellular respiration
Stored permanently in the soil
Converted into new matter
Organisms use most of their energy for respiration, movement and body heat, and it leaves as heat. Nutrients cycle but energy flows one way, which is why food chains are short.
What is the main role of decomposers such as fungi and bacteria?
Capturing light energy to make glucose
Eating primary consumers
Fixing oxygen from the air
Breaking down dead matter and returning nutrients to the soil
Decomposers recycle carbon, nitrogen and phosphorus from dead organisms and waste. Without them, nutrients would stay locked in dead material and producers would run out.
Which relationship is an example of mutualism?
A tapeworm living in a dog's intestine
Barnacles riding on a whale's skin
Bees collecting nectar while pollinating flowers
A lion hunting a zebra
In mutualism both species benefit: the bee gets food and the plant gets pollinated. The tapeworm is parasitism, the barnacles are usually classed as commensalism, and the lion is predation.
Barnacles attach to a whale and get carried to food-rich water, while the whale is neither helped nor harmed. This is:
Mutualism
Parasitism
Competition
Commensalism
Commensalism is +/0: one species benefits and the other is unaffected. If the barnacles harmed the whale, it would be parasitism.
In a logistic growth model, the carrying capacity (K) is:
The maximum rate at which a population can grow
The number of offspring per female
The largest population the environment can support over time
The population size at which growth is fastest
Logistic growth levels off at K as resources run short, giving an S-shaped curve. Growth is actually fastest at K/2, not at K.
A population with unlimited resources grows in a J-shaped curve. This pattern is:
Logistic growth
Exponential growth
Zero population growth
Carrying capacity
With no limits, the population grows by a constant percentage each generation, so the curve gets steeper and steeper. Real populations eventually hit limits and switch to logistic growth.
Which trait is typical of an r-selected species?
Many small offspring with little parental care
Few offspring with extensive parental care
Long lifespan and late maturity
A population that stays near carrying capacity
r-selected species (insects, weeds) bet on numbers and fast reproduction in unstable environments. The other options describe K-selected species such as elephants and humans.
When sea otters are removed, sea urchins multiply and destroy kelp forests. Sea otters are an example of:
An invasive species
A pioneer species
A producer
A keystone species
A keystone species has an effect on its community far larger than its numbers suggest. By eating urchins, otters protect the kelp that many other species depend on.
Succession that starts on bare rock after a lava flow, with lichens as the first colonizers, is:
Primary succession
Secondary succession
Climax community
Eutrophication
Primary succession starts where no soil exists, and pioneer species like lichens help create it. Secondary succession (after a fire or abandoned farm) starts with soil already in place, so it is faster.
Which organisms convert nitrogen gas (N₂) from the air into ammonia that plants can use?
Denitrifying bacteria
Plant root hairs on their own
Nitrogen-fixing bacteria such as Rhizobium
Fungal decomposers
Plants cannot use N₂ directly. Nitrogen-fixing bacteria, many living in root nodules of legumes, convert it to ammonia. Denitrifying bacteria do the reverse, returning nitrogen to the air.
Which process removes carbon dioxide from the atmosphere?
Cellular respiration
Photosynthesis
Burning fossil fuels
Decomposition
Photosynthesis takes in CO₂ and stores the carbon in sugars. Respiration, combustion and decomposition all release CO₂ back into the air.
DDT is found at much higher concentrations in eagles than in the fish they eat. This is explained by:
Eagles absorbing DDT directly from the air
The 10% rule increasing energy at higher levels
Biomagnification of a persistent toxin up the food chain
Eagles being producers
Fat-soluble toxins like DDT are not broken down or excreted, so each predator stores the toxin from all the prey it eats. Concentration rises at each trophic level, even though energy falls.
Which of these is an abiotic factor in an ecosystem?
Fungi in the soil
A population of predators
Competing plant species
Soil pH
Abiotic factors are nonliving: temperature, water, sunlight, soil pH. The other three are biotic factors, meaning living things.
Which limiting factor is density-dependent?
A wildfire
A contagious disease that spreads faster in crowded populations
A hurricane
An unusually cold winter
Density-dependent factors (disease, competition, predation) hit harder as population density rises. Fires, storms and cold snaps affect populations regardless of density.
