OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

Which hormone is primarily responsible for reducing blood sugar levels?

1. Glucagon

2. Insulin

3. Cortisol

4. Adrenaline

The correct answer is: Insulin

The correct answer is insulin. Insulin is a hormone produced by the pancreas that plays a crucial role in the regulation of blood sugar levels. When blood sugar levels rise, such as after eating, the pancreas releases insulin into the bloodstream. Insulin facilitates the uptake of glucose by cells, particularly in the liver, muscle, and adipose (fat) tissues, allowing these cells to use glucose for energy or store it for later use. This action effectively lowers blood sugar levels back to a normal range. In contrast, glucagon, produced by the pancreas as well, has the opposite effect of increasing blood sugar levels by promoting the conversion of stored glycogen in the liver back into glucose. Cortisol, a hormone produced by the adrenal glands, can increase blood sugar levels as well by enhancing gluconeogenesis—the production of glucose from non-carbohydrate sources. Adrenaline (also known as epinephrine) can also raise blood sugar levels in response to stress or a 'fight or flight' situation by promoting the breakdown of glycogen. Each of these hormones plays distinct roles in glucose metabolism, but insulin is specifically responsible for reducing blood sugar levels.