Unit 3: Life on Earth

• Ecosystem


  An ecosystem is a biological unit.

  
  

  It consists of all the organisms (the community) living in a particular habitat and the non-living components with which they interact.
• Habitat


  A habitat is the place where an organism lives.
• Species


  A species is a group of organisms capable of interbreeding with each other to produce fertile offspring.
• Population


  A population is a group of organisms of the same species.
• Community


  A community is all the organisms, of every species (plant and animal) living in an ecosystem.
• Examples of ecosystems


  Marine

  Polar

  Tundra

  Forest (tiaga)

  Forest (tropical)

  Grasslands

  Desert

  Freshwater
• Producers


  Producers are green plants that make their own food using photosynthesis.

  They convert light energy from the sun into chemical energy (food). They are always thefirstorganism in a food chain.
• Consumers


  Consumers are organisms which obtain their food from other organisms.
• Primary consumer (herbivores)


  Herbivoresfeed only onplantmaterial, also known as primary consumers.
• Secondary consumer (carnivores)


  Carnivoresfeed only onanimalmaterial also known as secondary consumers.
• Omnivores


  Omnivores feed on both plant and animal material.
• Decomposers


  Decomposers include fungi and bacteria.

  Decomposers break down organic matter (dead organisms and waste) to gain energy.

  Decomposers have a vital role in recycling nutrients.
• Predator


  Predators are animals that hunt and kill their prey.
• Prey


  An animal that is eaten by another animal is called the prey.
• Biotic (living factors) that affect the distribution of life


  - Competition

  - Predation

  - Disease
• Abiotic (non-living) factors that affect the distribution of life


  - Temperature

  - Rainfall

  - pH
• Niche


  Niche is the role an organism plays within a community.

  It relates to:

  - the resources it requires in its ecosystem such as light and nutrient availability.- its interactions with other organisms in the community such as competition, predation and disease.- the conditions it can tolerate such as temperature, pH, salinity or pollution.
• Competition


  Competition in ecosystems occurs when resources are in short supply.
• Intraspecific competition between members of thesamespecies.

  Intraspecific competition ismore intensebecause individuals are competing forALL the same resourcesas the individual's niches are IDENTICAL.
• Inter


  specific competitionCompetition between members oftwo differentspecies.

  Interspecific competition isless intenseas theniches are not identicalso they will only compete for SOME of the same resources.
• Plants compete for...


  Water

  Space

  Sunlight

  Nutrients such as nitrates and phosphates etc.
• Animals compete for...


  Water

  Food

  Shelter

  Mates

  Territory
• Biodiversity


  Biodiversity is the variety of different species that live in an ecosystem.
• Purpose of a food chain

  To show the interactions between the organisms in an ecosystem.
• Food chains process


  1. When a plant is eaten by an animal, energy is transferred from the plant to the animal (the primary consumer).

  
  

  2. When the primary consumer is eaten by a second animal (the secondary consumer), energy is transferred.
• Food chain


  A relationship where one organism feeds on the previous one and in turn provides food for the next one in the series is called a FOOD CHAIN.
• What do the arrows represent in a food chain?

  The arrows in the food chain showthe direction of the energy flow.
• Distribution meaning


  The word 'distribution' refers tothe way in which the organisms are spread out in a given area.

  eg. where on earth do we find a particular species and how widespread are they? Are they localised or spread over a large area?
• Biotic components


  Food availability

  Competition

  Disease

  Parasites

  Plants
• Abiotic components


  Temperature

  Climate

  Sunlight

  Oxygen availability

  pH

  Salinity
• Measurement of abiotic factor

  
  

  Light Meter


  Possible sources of error + solution

  Light sensitive panel shaded by user= hold light meter away from body

  Position of the sun changes= take readings at the same time of day

  Weather conditions affect readings= take many samples over a long period of time
• Measurement of abiotic factor

  
  

  Thermometer


  Possible sources of error + solution

  Temperature reading not stabilised= allow time for the reading to stabilise.

  Probe not inserted deeply into the soil= push probe into soil to half its depth

  Reading affected by warmth of hand= don't handle the probe.
• Measurement of abiotic factor

  
  

  pH meter


  Possible sources of error + solution

  pH reading not stabilised= allow time for the reading to stabilise

  Probe not inserted deeply in soil= push probe into soil to half its depth

  Probe contaminated by previous sample= wipe probe clean after every reading
• Measurement of abiotic factor

  
  

  Moisture meter

  Possible sources of error + solution

  Moisture reading not stabilised= allow time for the reading to stabilise

  Probe not inserted deeply in soil= push probe into soil to half its depth

  Probe contaminated by previous sample= wipe probe clean after every reading
• All sampling techniques used for living organisms

  Possible sources of error + solution

  The number and types of organisms are not representative of the ecosystem as a whole= sample repeated and random to increase reliability

  Misidentification of organisms= use identification keys and guide books or seek expert advice.
• Quadrats


  Quadrats are used to sample plants and very slow moving animals.

  
• Method for using a quadrat

  1. Quadrats should be placed randomly so that a representative sample is taken.2. To record anabundancescore for the organism, the number of squares in the grid of the quadrat frame where the organism is present is counted.3. Sampling is alsoreplicated (repeated)randomly across the area to ensurerepresentativesampling of the area.
• Quadrats

  
  

  Possible sources of error + solution

  Plants miscounted= set clear rules on whether a plant is in or out of the quadrat

  Quadrats not placed randomly= place quadrats randomly
• Pitfall traps


  Pitfall traps can be used for sampling small invertebrate animals which move cross the soil surface or in leaf litter.

  
• Method for use of pitfall trap

  1. The trap must be sunk in a hole which fits it exactly, and the top edge of the trap needs to be level with the soil surface for it to work properly.

  
  

  2. The sides of the trap should be steep and smooth to ensure that invertebrates which fall in cannot climb out again.

  
  

  3. A raised lid should be placed completely across the top of the trap to prevent the entry of rain water and any birds/predators feeding on the contents of the trap.

  
  

  4. Several or many traps are often distributed randomly in a habitat to ensure representative sampling of the area.

  
  

  5. Traps need to be checked regularly to avoid organisms already in the trap removing others by feeding on them.