Habitats and ecosystemsIB MYP Biology: Revision notes
Section 1
Living things and where they live
All living things share common features: they are made of cells, they contain DNA (the genetic material), and they carry out life processes such as respiration, growth and reproduction. Yet life shows huge diversity: from tiny bacteria to blue whales, organisms come in many different forms because each has features suited to where it lives.
Ecologists use four key terms:
- Habitat: the place where an organism lives, e.g. a rock pool.
- Population: all the organisms of one species living in a habitat.
- Community: all the populations of different species living in the same habitat.
- Ecosystem: a community of living organisms together with the non-living parts of their environment.
A population is only ONE species. Several species together make a community.
Section 2
Biotic and abiotic factors
The environment has two kinds of factor:
- Biotic factors are the living parts: food supply, predators, disease, competition and pollinators.
- Abiotic factors are the non-living parts: temperature, light intensity, water or moisture, soil pH and wind.
Both kinds affect where an organism can live and how many individuals survive. For example, woodlice are found in damp places because they lose water quickly in dry air (an abiotic factor), and their numbers can also fall if a predator such as a shrew moves in (a biotic factor).
Quick check: if it is alive or was once alive, it is biotic. Temperature, rain and light are always abiotic.
Section 3
Adaptations to habitats
An adaptation is a feature that helps an organism survive in its habitat. There are three types:
- Structural: a body feature, e.g. a camel's wide feet or a polar bear's thick fur and blubber.
- Behavioural: a way of acting, e.g. emperor penguins huddling together or desert animals being active at night.
- Physiological: a process inside the body, e.g. the icefish's antifreeze blood or a camel producing very little urine.
Desert: small leaves or spines (less water lost), roots that spread wide, large ears that lose heat, pale fur that reflects sunlight.
Polar: thick fur or blubber for insulation, small ears, white fur for camouflage, a large body to reduce heat loss.
Always explain HOW the adaptation helps: 'large ears lose heat so the fox stays cool', not just 'the fox has large ears'.
Section 4
Interdependence
Organisms in an ecosystem depend on each other for food, shelter, pollination and seed dispersal. This is interdependence. Feeding relationships are shown in food chains, and the feeding links in a whole ecosystem form a food web.
Because the links are connected, removing one species affects others. In a kelp forest, if sea otters are removed:
- Sea urchins (eaten by otters) increase.
- More urchins eat the kelp, so kelp decreases.
- Fish that shelter in the kelp decrease.
The effects spread through the web, so removing one species can unbalance the whole community.
Must know
- Habitat, population, community and ecosystem have different meanings.
- Biotic factors are living; abiotic factors are non-living.
- Adaptations are structural, behavioural or physiological, and must be linked to survival.
- All living things are made of cells and contain DNA, but show great diversity.
- Removing one species can change the numbers of many others.
That's the notes covered.
Carry on to the next subtopic.
Exam questions on Habitats and ecosystems
- In the dunes of the Sahara Desert, a group of about forty fennec foxes lives alongside desert plants, beetles, lizards and other animals. Daytime temperatures reach over 40 °C, the sand is dry, and rain is rare. Fennec foxes have very large ears and pale fur, and they hunt mainly at night.Explain how the fennec fox's large ears help it to survive in the desert.2 marks
- Scientists studying the Antarctic coast describe a range of organisms: an icefish whose blood contains a natural antifreeze, an emperor penguin that huddles with others through the winter, and a lichen that grows on bare rock.The icefish has natural antifreeze in its blood. State the type of adaptation this is and explain how it helps the icefish to survive.2 marks
- A student investigates whether woodlice prefer damp or dry conditions. She uses a choice chamber with a damp side and a dry side, separated by a mesh floor. She places ten woodlice in the centre, covers the chamber with a lid and counts how many are on the damp side after ten minutes. She repeats this four times with the same ten woodlice, and finds 8, 7, 9 and 8 woodlice on the damp side.Identify the independent variable, the dependent variable and one control variable in this investigation.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).