Can't speak for biology but I tutor chemistry for Year 11 and 12 for the past few years so I've got quite a good understanding of things that are tested in Year 11 and 12. A short answer to your question is no the content from Year 11 is not explicitly tested again in chemistry. For instance you are not going to be asked to randomly draw a galvanic cell or write a nuclear decay equation in Year 12 exams.
However, the concepts that came up in Year 11 are utilised in Year 12, so you need that solid foundation of Year 11 knowledge in some of the topics to be able to understand and do well in Year 12 chemistry. The most important things that I see students coming from Year 11 into Year 12 for chemistry lack is the ability to determine chemical formulas for ionic compounds, calculations from module 2 and the section 1 and 3 from module 3.
For module 1 the most important part is where you learn about figuring out the chemical formulas for ionic compounds. You should know how to write formulas for these types of compounds and also when they polyatomic ions like nitrate, sulfate etc. (so you need to memorise the formula for those ions and their charges).
For module 2 this is the most important module from Year 11 that builds skills for Year 12 content. You need to have a good understanding of how to write chemical equations, balance them, do calculations involving moles, molar ratios and utilising formulas such as n=m/MM and C=n/V in questions like "if the mass of X in a chemical reaction to make Y is 5.00g, write a balanced equation and calculate the mass of Y formed"
For module 3 the most important part is the first one where you go through many different classes of chemical reactions like combustion, precipitation, acid-base, acid-metal, acid-metal carbonate, synthesise and decomposition reactions. These few reactions here actually make up a large portion of content in Year 12, the precipitation reactions form the basis for content learnt in Module 5 (the last section) and the acid-base reactions form the basis for all of module 6. So you need to be able to write equations when give only the starting materials and by remembering that it falls into a certain class of reactions be able to predict the products, write their formulas correctly and balance the equation. For instance "write a chemical equation for the combustion of C8H18", you need to know what combustion means in terms of a fuel + o2 --> co2 + h2o to be able to write the equation. Similar things follow for the other reaction types I listed above
If you are lacking in those particular areas, I would strongly encourage you to practice those things and improve them prior to starting Year 12, as from students I've tutored these areas are 90% of the time the things the students are terrible at and it really limits their ability to do well in Year 12 as they have to waste a lot of time trying to relearn these simpler concepts that they neglected during Year 11. Whereas students who did okay in Year 11 but know these things well are able to do quite well in Year 12 with improved study habits and practice
