IGCSE Biology Theory Unit 4 Full Class Notes

ECOLOGY AND THE ENVIRONMENT

 Ecology – scientific study of interactions btwn organisms and surroundings
 Population – group of organisms from same species, in same area at same time
 Community – populations of different species living together in same area
 Habitat – place where organisms live
 Ecosystem – self-sustaining system of organisms interacting w each other + physical
environment
 Biodiversity – measure of range and variety of living organisms w/in ecosystem

COMPONENTS OF ECOSYSTEM

 Ecosystem consists of:
o Biotic components (living)
o Abiotic components (non-living, physical, and chemical) – soil composition, temp, pH
etc.
 Components of ecosystem
o Producers – plants which photosynthesize
o Consumers – animals that eat plants or other animals
o Decomposers – organisms that break down organic matter + recycle nutrients
o Physical environment – all non-biological components of ecosystem

FACTORS AFFECTING POPULATION SIZES

BIOTIC FACTORS

 Biotic factors – living factors that can affect size and distribution of populations
o Availability of food
 Rich + diverse food supplies = significantly ^ animal species vs. ones that don’t
o Predators
 Prevent prey populations ^ out of control
 Introducing new predators in area can affect balance and have significant effects
on number
o Pathogens
 Introducing new pathogens can cause widespread disease
o Competition for food, water, shelter
 Well-est. ecosystem – can coexist fairly well
 New species introduced can rapidly outcompete existing populations
 Causes significant decrease in populations
 Abiotic factors – nonliving factors that affect size and distribution of populations
o Light intensity
 Some require bright light, others shade
 Affects distribution of plant species
o Moisture levels
 Most can’t survive in water-logged soil cos O2 deficiency
 Some grow in boggy conditions not drought tolerant

, o Temperature
 Both animals and plants grow optimally at specific temp
o Oxygen level
 Aquatic organisms require certain dissolved O2 levels
o pH of soil or water
 some plants grow in alkaline soil, other acidic, others can’t
 aquatic organisms can cope w acidic waters
 affects distribution
o Availability of minerals
 w/out minerals – growth and reproduction low
o CO2 levels
 Areas w ^CO2 levels = healthier plants cos photosynthesis

BIODIVERSITY

 Measure of range and variety of living organisms w/in ecosystem
 Biodiversity due to:
o Genetic diversity
o Species diversity
o Ecosystem diversity
 Ecosystem’s biodiversity combination of:
o Species richness – no. of different species present
o Relative abundance of each species
 Biodiversity is good for ecosystem
 More stable w ^ biodiversity
o Ecosystem dominated by one species - ^likely to be affected by ecological disaster
 Disease could wipe out dominant species
 Impact on other species that rely on them for food + shelter
o W ^ biodiversity resources can be supplied w help of other species

INVESTIGATING POPULATION SIZE

 Sample – small representative part of population
 Quadrat – square frame of wood or metal divided into smaller squares inside
o Placed on ground and plants found inside can be counted
o Placement of quadrat = random to avoid biased results
 When using quadrat:
o Place randomly so representative sample is taken
o Validity + reliability of results ^ w ^quadrat samples taken

TRANSECTS

 Method used when there is a transition across an area
 Transect – line across habitat/part of habitat
 No. of organisms of each species observed + recorded at regular intervals along transect
 Line transect only records organisms that actually touch line