2.2 Energy & Biomass in Ecosystems (DP IB Environmental Systems & Societies (ESS): SL): Flashcards

False.

Matter, such as nutrients and water, cycles through ecosystems and is reused and recycled.

Photosynthesis is the conversion of light energy into chemical energy, stored in the form of glucose, by autotrophs such as plants and algae.

An autotroph is an organism, such as a plant, alga or photosynthetic bacterium, that produces its own food using photosynthesis.

Producers occupy the first trophic level in a food chain.

The inputs to photosynthesis are light energy, carbon dioxide and water.

The two products of photosynthesis are glucose and oxygen.

False.

Photosynthesis takes place inside the chloroplasts of plant cells.

Chlorophyll captures light energy during photosynthesis.

Glucose from photosynthesis also provides the starting material for other organic molecules such as cellulose and starch.

A respiratory substrate is a molecule, such as glucose, that is used in respiration to release energy for growth.

Photosynthesis produces the raw material producers use to build their biomass.

Respiration is the conversion of organic matter into carbon dioxide and water, releasing energy.

The chemical energy released by cellular respiration is used to carry out active processes, such as growth and repair, within living cells.

The two inputs of aerobic respiration are glucose and oxygen.

False.

Aerobic respiration takes place inside the mitochondria of a cell.

During respiration, stored chemical energy is also transformed into heat.

Cellular respiration always releases some heat because it is not 100% efficient at transferring energy from substrates into a usable chemical form.

False.

Heat generated during respiration cannot be transformed back into chemical energy and is ultimately lost from the body.

The heat energy released by respiration increases the entropy in an ecosystem.

Living organisms use the energy released by respiration to maintain relatively low entropy (high organisation).

False.

Respiration takes place in all living organisms, including plants.

A trophic level is the position that an organism occupies in a food chain or food web.

Primary consumers are herbivores that feed on producers and occupy trophic level 2.

A secondary consumer is a predator that feeds on primary consumers, occupying the third trophic level.

False.

Tertiary consumers are predators that feed on secondary consumers, occupying the fourth trophic level.

A detritivore, such as an earthworm, is a consumer that feeds on decomposing organic matter (detritus).

A scavenger, such as a vulture, is a consumer that feeds on dead animal carcasses.

A consumer that depends on a host organism for survival, such as a tapeworm, is called a parasite.

An apex predator is a carnivore or omnivore at the top of a food chain that has no predators of its own.

When an apex predator dies, the chemical energy stored in its body is passed on to decomposers.

False.

Decomposers are traditionally excluded from food chains because they gain carbon compounds from a variety of trophic levels.

Producers are placed at the start of food chains because they make their own carbon compounds through photosynthesis.

A food web is a network of interconnected food chains.

Food webs are more useful than food chains because they reflect that consumers feed on multiple food sources and provide more information about the transfer of energy in an ecosystem.

Interdependence, as shown by a food web, is how a change in one population can affect other populations within the same web.

In food chain and food web diagrams, arrows indicate the direction of energy flow and biomass transfer.

False.

Within a food web, some organisms occupy more than one trophic level, depending on what they consume.

In this food web, the squirrel, fox and eagle each occupy more than one trophic level.

True.

Frogs and mice would decrease significantly if earthworms declined, because earthworms are their only food source.

The grass population would increase because fewer earthworms would mean fewer species feeding on the grass.

The sparrow population would only decrease slightly because sparrows have an alternative food source (caterpillars) besides earthworms.

In this food web, the eagle occupies the apex predator position, the top trophic level shown.

False.

The total organic matter transferred from one trophic level to the next is never 100%.

Not all available food is harvested because there may be too many leaves, not enough caterpillars, or leaves may be in inaccessible locations.

Of the food harvested, not all is consumed because caterpillars may eat only the softer, more nutritious parts of a leaf and leave tougher or toxic portions.

Of the food consumed, not all is absorbed because some parts are indigestible and are egested rather than taken into the body.

Of the energy absorbed, not all is stored because some is lost as heat during cellular respiration.

The four stages that limit the transfer of organic matter between trophic levels are harvesting, consumption, absorption and storage.

In this example, the oak tree is the producer and the caterpillar is the primary consumer.

Gross productivity (GP) is the total gain in biomass by an organism or community in a given area and time period.

Net productivity (NP) is the amount of energy or biomass remaining after losses due to cellular respiration.

The plant's net productivity would be 700 kJ (1000 kJ minus 300 kJ).

False.

Respiratory losses are usually greater in consumers than in producers, due to energy-requiring activities such as digestion and movement.

The net productivity of a population represents the maximum sustainable yield that can be harvested without reducing future resource availability.

Harvesting beyond the sustainable yield can lead to overexploitation and depletion of fish stocks.

The dry mass method estimates biomass by drying collected organisms in an oven to remove water, then measuring the dry weight of the sample.

Dry mass can be used to estimate biomass because water makes up most of an organism's mass and is removed during drying.

Calorimetry estimates biomass by burning a known quantity of biological material and measuring the heat produced using a calorimeter.

Extrapolation from samples is particularly useful for large or difficult-to-sample populations.

False.

Measuring dry mass can take a long time, sometimes several days, since the sample must be dried at a low temperature to avoid burning it.

A bomb calorimeter gives a more accurate estimate because it ensures almost all the heat energy from the burning sample is transferred to the water.

A pyramid of numbers is an ecological pyramid in which the width of each bar represents the number of organisms at that trophic level.

A pyramid of numbers becomes inverted when the organisms at a lower trophic level, such as an oak tree, are individually much larger than those above them.

False.

A pyramid of numbers does not account for the size of individual organisms, giving equal weighting to a single oak tree and a single grass plant.

Parasites can make a pyramid of numbers misleading because a single host organism may support many parasites, producing a top-heavy pyramid.

A pyramid of biomass shows the dry mass of organisms at each trophic level, excluding the water contained in their tissues.

Unlike pyramids of numbers, pyramids of biomass are usually pyramid-shaped, regardless of the shape of the corresponding pyramid of numbers.

A pyramid of biomass can appear inverted in marine ecosystems because fast-reproducing phytoplankton are constantly consumed, giving them a low standing crop despite high productivity.

False.

A pyramid of biomass represents a snapshot in time (the standing crop) and does not show the rate of biomass production or turnover.

A pyramid of energy shows the flow of energy through trophic levels, indicating the rate at which that energy is being generated.

Approximately 10% of energy is transferred from one trophic level to the next.

Unlike pyramids of numbers or biomass, pyramids of energy are never inverted, because they always show a decrease in energy along the food chain.

Energy is lost at each trophic level due to reasons such as incomplete digestion or the loss of heat during respiration.

False.

Pyramids of energy are the most difficult and time-consuming to construct, as they require detailed data collected over a full year.

Bioaccumulation is the build-up of persistent or non-biodegradable pollutants within an organism or trophic level because they cannot be broken down.

Biomagnification is the increase in the concentration of persistent or non-biodegradable pollutants along a food chain.

Top predators accumulate higher pollutant concentrations because there is a decrease in total biodegradable biomass at each successive trophic level.

Three examples of persistent, non-biodegradable pollutants that biomagnify along food chains are PCBs, mercury and DDT.

DDT accumulation in birds of prey caused thinning of eggshells and reduced reproductive success.

False.

Mercury can be converted into a highly toxic form called methylmercury, which accumulates in fish and can harm humans who eat them.

A chemical factory released toxic methylmercury into waste water entering Minamata Bay, contaminating fish and shellfish eaten by local people.

Microplastics absorb non-biodegradable pollutants like sponges, increasing their transmission and concentration up the food chain.

False.

Oysters exposed to microplastics containing pollutants showed lower feeding rates, altered growth and reduced reproductive success.

Burning fossil fuels also releases pollutants such as sulfur dioxide, which contributes to acid rain and lowers soil pH, reducing photosynthesis rates.

Deforestation causes habitat loss, disrupts food webs, and reduces the carbon sink capacity of forests.

Urbanisation replaces natural habitats with impervious surfaces, increasing surface runoff and creating urban heat islands that raise local temperatures.

Intensive agriculture can cause soil degradation, water pollution and loss of biodiversity.