Downloadable worksheets for AQA A Level Biology Homeostasis is the maintenance of a stable internal environment (A-level only), with answers included. Worksheets covering Principles of homeostasis and negative feedback (A-level only), Control of blood glucose concentration (A-level only), and Control of blood water potential (A-level only), matched to the AQA A Level Biology (7402) specification and suitable for A Level Biology. Print or work through on screen.