Edexcel IGCSE Biology - Organism in the Environment

define habitat

the place where an organism lives

define population

a group of individuals of the same species living in the same place at a certain time

define community

many different populations that interact with each other in the same habitat (all species in a habitat)

define ecosystem

all the organisms living in a particular area and all the non-living (abiotic) conditions

define biodiversity

the variety of different species of organisms on Earth or within an ecosystem

why is high biodiversity important?

• makes sure that ecosystems are stable - different species depend on each other for things like shelter and food

• different species can help to maintain the right physical environment for them

what 2 items may be used to measure population size and distribution?

• quadrats

• transects

what is a quadrat?

a gridded metal square enclosing a known area

what is a transect?

• a defined area where samples will be taken

• a belt transect is a length/line which quadrats are placed along

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

1. place 2 measuring tapes across the length and width of the area at right angles to each other

2. use a random generator to produce coordinates

3. place the quadrat down at the coordinates with the same corner at the coordinates each time

4. count the number of whole organisms of the type you are investigating

5. record data in a table

6. repeat and calculate averages

7. calculate the area of the quadrat and of the sample area, then calculate the scale factor

8. multiply the average number of organisms by the scale factor

9. repeat the whole process in a second sample area

practical: investigate the distribution of organisms in their habitats and measure biodiversity using quadrats

1. mark out a line in the area you want to study

2. collect data along the line by placing quadrats next to each other (or at regular intervals) - count all the organisms of the species you want

3. could also record other data like height of plants or abiotic factors in each quadrat

4. repeat steps 1-3 several times, then find the mean number of organisms per quadrat

5. plot graphs to see if changing abiotic factor has any correlations

list the abiotic factors that can affect organisms in an environment

• light intensity

• temperature

• moisture levels/rainfall

• soil pH/mineral content

• wind intensity

• CO₂ concentration

describe how light intensity can affect population size and distribution of an organism

• light is required for photosynthesis

• rate of photosynthesis affects rate of plant growth

• plants can be a shelter or food source

• plants are more likely to grow and grow bigger in areas with higher light intensity

describe how temperature can affect population size and distribution of an organism

• optimum temperature is required for photosynthesis

• rate of photosynthesis affects rate of plant growth

• plants can be a shelter or food source

• plants are more likely to grow and grow bigger in areas with temperature closer to optimum

• also affects rate of enzyme activity in animals

describe how moisture levels/rainfall can affect population size and distribution of an organism

• both plants and animals need water to survive

• therefore grow bigger and more likely to grow in areas with enough water

describe how soil pH/mineral content can affect population size and distribution of an organism

• soil pH affects rate of plant decay and therefore rate of mineral ions returning soil

• some plants can only grow in certain pH soil

• plants need sufficient mineral ions to grow

• plants will grow in areas with the right pH

describe how wind intensity can affect population size and distribution of an organism

• affects transpiration rate (higher=higher)

• thus affects rate of photosynthesis (higher=higher)

• plants will live in areas that are the right level of windiness

describe how CO₂ concentration can affect population size and distribution of an organism

• CO₂ is required for photosynthesis

• higher rate of photosynthesis means higher rate of plant growth

• plants are more likely to grow and grow bigger in areas of high CO₂ concentration

list the biotic factors that can affect organisms in an environment

• food availability

• new predators

• new pathogens

• competition

describe how food availability can affect population size and distribution of an organism

• more food means organisms have more energy

• this means that they are more likely to survive and can breed more successfully

• population will increase in areas with lots of food

describe how new predators can affect population size and distribution of an organism

• emergence of a new predator can decrease population size

• organisms may try not to live in areas with lots of predators

describe how new pathogens can affect population size and distribution of an organism

when an area has no resistance to a pathogen, organisms in it can be wiped out quickly

describe how competition can affect population size and distribution of an organism

• if one species is better adapted to the environment than another it will outcompete it until the number of the lesser population are insufficient to breed

• competition is for things like food, space, shelter, mates, water, space, light