4.1 The Organism in the Environment

REVISION NOTES

IGCSE Edexcel Biology

4.1.1 Understand the terms population, community, habitat and ecosystem

4.1.2 Practical: investigate the population size of an organism in two different areas using
quadrats

Quadrats:

Square frames that come in different sizes
Can be placed on the ground to collect information regarding organisms in that particular area
Abundance of plant or smaller animal species measured by recording:
- Population size
- Total number of species
- Percentage cover
- Percentage cover is the approximate percentage of an area that the species cover within the mat

Population size practical:

Use a transect to define the area where the practical will take place
Place the quadrat mat along the transect
Quadrat mats can be placed:
1. On two different ends of the quadrat
2. At specific intervals (every 2m)
3. Randomly along the transect
4. A specific coordinate that is computer generated
Count the number of target species found within the quadrat
Repeat this at two other locations
Estimate population using the following equation:

Estimated population size = Total area of survey/Area sampled using quadrat x Total population calculated

4.1.3B Understand the term biodiversity

Biodiversity:

Range and variety of species within an ecosystem
Includes species richness
Considers variation within each species based on distribution and population size
E.g. high biodiversity can be seen in tropical rainforests:
- Contains a lot of different species
- Wide range of variation that is evenly distributed across the ecosystem
High biodiversity reduces the interdependence
- Ensures that the decline in population of one species does not significantly impact the ecosystem
More diverse ecosystems are more resistant to sudden environmental changes or diseases