MODELS

models (def). a simplified version of a real life situation that can be used to understand how something works and predict how it will respond to change

STRENGTHS

• allow people to make predictions

• can simplify complex/inaccessible situations

• inputs and factors can be manipulated

• can be shared with others

• accessible

WEAKNESSES

• approximation and simplification can be overdone - meaning information can be misleading or missing

• leave some room for differing interpretations

• rely on the knowledge and information of those making them

• also often rely on technology - what happens when that technology fails?

TOK : As models are simplified constructions of reality, how do we know which factors of the world to include and which to ignore?

SYSTEMS

systems (def). a model designed to simplify an intertwined set of interactions or moving parts, comprised of storages, flows, inputs and outputs

• open systems (def). an open system is one that transfers both energy and matter over its boundaries and with its surroundings

• closed systems (def). a closed system is one that only transfers energy across its boundaries, but not matter - e.g. the nitrogen cycle, hydrological cycle and carbon cycle, but only on a global scale

• isolated systems (def). an isolated system is hypothetical concept of a system that does not transfer either matter or energy with its surroundings

  • you can only really think of the entire universe as an isolated system - but even that is hard to prove

TRANSFERS AND TRANSFORMATIONS

transfers (def). when energy or matter only changes location (storage)

• e.g. water moving from river to ocean, movement of heat energy from one organism to another, sugar moving from one organism to another when its eaten

transformations (def). when energy or matter changes location and state or chemical nature

• matter to matter - e.g. glucose to starch, water to ice

• energy to energy - e.g. light energy to heat energy

• matter to energy - e.g. combustion of fuels

• energy to matter - e.g. photosynthesis

FLOWS AND STORAGES

flows (def). how matter and energy travels between different stores or in and out of the system

• e.g. photosynthesis, respiration, absorption and combustion

• represented through arrows within system diagrams

storages (def). places within systems that matter or energy is stored

• e.g. the atmosphere, water, within plants or animals and within soil

• can be short term or long term - e.g. stored within a plant vs. stored within fossil fuels

• represented by boxes within system diagrams

short term storages long term storages flows