Flashcards · 0610 · Topic 19

Organisms and their environment flashcards

21 cards on Topic 19, subtopics 19.1 to 19.4. Pick a subtopic or study them all.

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Principal source of energy input to biological systems: The Sun.
Describe the flow of energy through living organisms: Light energy → chemical energy in organic compounds (by photosynthesis in producers) → passed along by feeding → eventually transferred to the environment as heat.
Energy vs nutrients in an ecosystem: Energy flows in one direction and is not recycled; it is eventually transferred to the environment as heat. Nutrients such as carbon are recycled.

Food chain and food web: Food chain: shows the transfer of energy from one organism to the next, beginning with a producer. Food web: a network of interconnected food chains.
Producer, consumer and decomposer: Producer: makes its own organic nutrients, usually using energy from sunlight, through photosynthesis. Consumer: gets energy by feeding on other organisms. Decomposer: gets energy from dead or waste organic material.
Trophic level, and the order of trophic levels: The position of an organism in a food chain, food web or ecological pyramid. Producers → primary → secondary → tertiary → quaternary consumers.
Why can a pyramid of numbers be inverted, and why is biomass better?: One large organism (e.g. a tree) can support many small ones. A pyramid of biomass accounts for the size of organisms, so it gives a truer picture.
Efficiency of energy transfer between trophic levelsExtended: efficiency (%) = energy at higher level ÷ energy at lower level × 100. E.g. 360 ÷ 4500 × 100 = 8.0%.
Why energy transfer between trophic levels is inefficientExtended: Heat lost in respiration; parts not eaten; parts not digested (faeces); excretion; energy used in movement.
Why is it more efficient for humans to eat crops than livestock?Extended: Eating crops involves one energy transfer; eating livestock fed on crops adds another trophic level, with energy lost as heat, in movement and in faeces. More people can be fed from the same area.

Carbon cycle: processes that remove CO₂ from or add CO₂ to the air: Removes: photosynthesis. Adds: respiration, decomposition (respiration by decomposers) and combustion.
How are fossil fuels formed in the carbon cycle?: From dead organisms that were not fully decomposed, over millions of years.
NitrificationExtended: Ammonium ions → nitrate ions, by nitrifying bacteria.
Nitrogen fixation vs denitrificationExtended: Fixation: nitrogen gas → nitrogen compounds, by lightning or nitrogen-fixing bacteria (in soil and root nodules). Denitrification: nitrate ions → nitrogen gas, by denitrifying bacteria.
Role of decomposers in the nitrogen cycleExtended: They break down protein in dead organisms and waste into ammonium ions.

Population: A group of organisms of one species, living in the same area, at the same time.
Community and ecosystem: Community: all of the populations of different species in an ecosystem. Ecosystem: a unit containing the community of organisms and their environment, interacting together.
Factors affecting the rate of population growth: Food supply, competition, predation and disease.
Phases of a sigmoid population growth curve: Lag (slow rise), exponential or log (steep rise), stationary (level), death (fall).
Explain the stationary phase of a sigmoid curveExtended: Limiting factors such as food or space act, so births equal deaths.
Explain the exponential and death phasesExtended: Exponential: resources are plentiful, so births far exceed deaths. Death: food runs out or toxic waste builds up, so deaths exceed births.