Organisms and their Environment
19. Organisms and Their Environment — Cambridge IGCSE Biology 0610 Revision Notes & Topical Questions
5 min read 10 parts Lesson 1 of 7 2 quizzes
Lesson summary
19. Organisms and their environment — IGCSE BIOLOGY notes: Define the main ecological terms and summarise energy flow, feeding relationships, nutrient cycles, populations and sampling.Habitat — the place where an organism lives.Population = a group of organisms of one species liv…
- Decomposer
- Trophic level
- Primary consumers
- Secondary and tertiary consumers
- Chain shape
- Transect line
Section 1 of 10Ecology terms
Ecology terms
Habitat
- Habitat the place where an organism lives.
Population
Population a group of organisms of one species living in the same area at the same time.
Community
Community all the populations of different species in an ecosystem.
Ecosystem
Ecosystem a unit containing the community of organisms and their environment, interacting together.
Producer
- Producer an organism that makes its own organic nutrients, usually by photosynthesis.
Consumer
- Consumer an organism that gets energy by feeding on other organisms.
Decomposer
- Decomposer an organism that gets energy from dead or waste organic material.
Section 2 of 10Trophic levels
Trophic level
Trophic level the position of an organism in a food chain, food web or ecological pyramid.
Producers
- Producers first level, the plants.
Primary consumers
- Primary consumers herbivores, which eat plants.
Secondary and tertiary consumers
- Secondary and tertiary consumers carnivores, which eat animals.
Omnivores
- Omnivores eat both plants and animals.
Chain shape
- Chain shape producer, then primary, secondary and tertiary consumers.
Section 3 of 10Energy, nutrients and populations
| Topic | Key idea |
|---|---|
| Energy flow | Starts as sunlight, flows one way, most is lost at each level |
| Nutrient cycles | Carbon and nitrogen are recycled by decomposers |
| Food webs | Interlinked food chains showing feeding relationships |
| Populations | Change with food, predators, disease and competition |
Energy, nutrients and populations
Energy transfer is inefficient because organisms use energy in respiration, movement and heat loss, and not all parts are eaten.
This is why food chains rarely have more than five links.
Section 4 of 10Energy pyramids, nitrogen cycling and population growth
Energy pyramids, nitrogen cycling and population growth
Energy and biomass pyramids
An energy pyramid compares the energy transferred at successive trophic levels over a stated time.
- It is upright because only part of the energy entering one level becomes available to the next.
- Respiration transfers energy to the surroundings, and some material is not eaten or is lost in waste.
- A biomass pyramid measures standing dry mass at a particular time.
- It can be inverted, for example when small, rapidly reproducing aquatic producers support a larger standing biomass of consumers.
Nitrification
Nitrifying bacteria convert ammonium ions to nitrite ions and then nitrate ions under aerobic conditions. Plants absorb nitrate ions and use the nitrogen to make amino acids and proteins. Nitrogen fixation converts atmospheric nitrogen into biologically available compounds; denitrification returns nitrogen gas to the atmosphere.
The stationary phase
In a closed population, a roughly constant population size means that births and deaths are approximately balanced. Individuals may still reproduce. Growth slows near the carrying capacity because resources, disease, predation or other limiting factors restrict further increase. If migration occurs, population change also includes immigration and emigration.
For more detail, study nutrient cycles and population growth in the later lessons in this unit.
Sources: OpenStax: energy flow and ecological pyramids; nitrogen transformations; limits to population growth.
Section 5 of 10Sampling ecosystems
Sampling ecosystems
Quadrat
- Quadrat placed at random positions to count plants and calculate mean density.
Transect line
- Transect line samples across a changing environment such as a shore.
Pitfall traps and nets
- Pitfall traps and nets used for animals.
Larger samples
- Larger samples give more reliable results.
Random sampling
- Random sampling random numbers give coordinates for each quadrat.
Population estimate
- Population estimate mean number per quadrat multiplied by total area divided by quadrat area.
Section 6 of 10Competition and adaptation
1
Plants compete for light, water and mineral ions.
2
Animals compete for food, mates and territory.
3Intraspecific competition
- Intraspecific competition between members of the same species, usually the most intense because they need identical resources.
4Interspecific competition
- Interspecific competition between different species.
5Adaptation
- Adaptation suits organisms to their habitat, for example water-saving features in hot deserts and insulation in the Arctic.
6Climate change
- Climate change populations unable to adapt or move may become extinct.
Section 7 of 10Human impact and management
Human impact
- Human impact deforestation, overfishing, pollution and introduced species disturb ecosystems.
Conservation
- Conservation protected areas, quotas, captive breeding and seed banks maintain biodiversity.
Sustainability
- Sustainability using resources so that they remain available for future generations.
Abiotic measurements
- Abiotic measurements ecologists measure light intensity, temperature, pH and soil moisture.
Section 8 of 10More from the specification
Biomass accumulation and trophic efficiency
- Net primary productivity represents biomass available to primary consumers;
- approximately 10% of energy is transferred across successive trophic levels.
Carbon cycle and atmospheric greenhouse gases
- Photosynthesis fixes atmospheric CO2 into plant biomass,
- while cellular respiration, combustion of fossil fuels,
- and decomposition return CO2 to the air.
Ecosystem carrying capacity and population curves
- Population growth in natural ecosystems follows an S-shaped sigmoid curve, plateauing at carrying capacity (K) due to limiting density-dependent factors.
Pyramid of biomass
- Pyramid of biomass represents standing dry mass at each trophic level.
- It is often upright, but can be inverted when producers reproduce rapidly and are consumed quickly.
Carbon dioxide in the carbon cycle
- Carbon dioxide in the carbon cycle photosynthesis removes carbon dioxide from the atmosphere, incorporating carbon into agricultural crops like wheat.
Sigmoid population growth curve
- Sigmoid population growth curve shows initial lag phase, exponential growth, and plateau when environmental resistance limits population size.
Fossil fuel
- Fuel formed from long-dead organisms.
Biomass
- The dry mass of living matter in an organism or trophic level.
Growth
- A permanent increase in size and dry mass.
Microorganism
- A living organism so small that it can only be seen clearly with a microscope.
Bacteria
- Single-celled microorganisms, much smaller than plant or animal cells.
Section 9 of 10Key terms
| Term | Meaning |
|---|---|
| Habitat | The place where an organism lives. |
| Population | A group of organisms of one species in the same area at the same time. |
| Community | All the populations of different species in an ecosystem. |
| Ecosystem | A community and its environment interacting. |
| Trophic level | The feeding position of an organism in a food chain. |
| Quadrat | A square frame used to sample organisms. |
Section 10 of 10Exam technique
1
Confusing a population with a community — a population is one species and a community is all the species.
2
Saying energy is recycled — nutrients cycle but energy flows and is lost as heat.
3
Saying a species will die out when a food source falls — say its population decreases.
4
Taking a non-random sample — random positions avoid bias.
Marked practiceQuizzes for this lesson
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