Hello,
So the independent variable is what is changed during the experiment. In this case it seams to be the temperature from a quick glance.
The dependent variable is what you are measuring in the experiment. This is the bubbles that are produced from the CO2 being generated. So you could say bubbles, or you can also use bubbles generated by carbon dioxide.
Controlled variables are what remain constant/ the same throughout the experiment. In the one you have attached.
- The amount of sugar
- The amount of yeast
- The amount of water
- Same size equipment e.g 1000mL beaker
Limitation are generally things that can affect the result. In this instance it could be that the experiment needs to be repeated a few times to make it more precise. The yeast may not be active/fresh (yeast can not work properly if stored incorrectly, some active yeasts in stores need to be refrigerated after opening) which could affect how well it ferments sugars so less CO2. Bubbles aren't a supper reliable way of measuring, due to human error you may misread the results etc.
I am a tad rusty on my bio knowledge but I hope this helps.
When it comes to general tips to help in bio, I don't really have much to say. However, make sure you know your content inside and out, even just the basic concepts. Look at how things link together over the year. I would advise doing practice questions, and if you ever get stuck, always ask for help. Experimental design always has a question on the exam, so make sure you know these by the end of the year, and for your poster SAC in unit 4.
Good luck.