Unit 1's important because it sets the foundation for a lot of the other concepts - learning demand and supply is vital, that's definitely something you'll want to look over - but you can still do well in Unit 2 without it. Unit 2 more or less builds on some of the skills you learn in Unit 1.
I'm not 100% sure on which areas you need to study that will directly tie in with Unit 2, since my memory's a bit fuzzy on it, but these are the key knowledge points for Unit 1 (taken from the study design) that are important for Unit 3/4.
If you at least know the gist of these ideas then you'll be fine, everything you need to know from Unit 1 will be covered in Unit 3 anyway - if you know these well all it means is that you have less work next year. I'd say spend a couple days or so learning these at most - focus on getting ahead in your Unit 2 content if you care more about your SACs.
Hope you find this helpful
- the basic economic problem of relative scarcity and the need for economic decision making
- the concept and applications of opportunity cost
- resources used to meet needs and wants: natural, labour and capital
- the purpose of economic activity and the influence on material and non-material living standards
- the need for trade-offs such as current versus future, short run versus long run, and cost-benefit analyses
- the production possibility model to illustrate the concepts of scarcity, choice, opportunity cost, underutilisation of resources and efficiency
- the two sector circular flow model of the economy
AOS2:
- the law of demand and the demand curve
- the way non-price factors such as changes in disposable income, the prices of substitutes and complements, preferences and tastes, interest rates, changes in population, consumer sentiment and government intervention, affect demand and the position of the demand curve
- the distinction between a movement along the demand curve and a shift of the demand curve
- the law of supply and the supply curve
- the way non-price factors such as changes in the cost of production, technological change, productivity growth, climatic conditions and government intervention affect supply and the position of the supply curve
- the distinction between a movement along the supply curve and a shift of the supply curve
- effects of changes in demand and supply on equilibrium prices and quantities