I find that biology can be hard for some, easy for others. The difficulty in biology comes form the mixture of chapters. People tend to find chapters on the digestive system, the heart, the lungs and the kidneys 'relatively' easy. This is because we can all relate to these chapters, we're doing them all the time. You may never have done biology before but still have a good idea about how your lungs work or how food passes through your body. When it comes to the cell, and cellular processes, students tend to have no real analogy in their life. So things like respiration can be very difficult to understand. The same can go for plant biology.
While biology can be hard, there are videos online for almost every subject in biology, that explain things with nice imagery. The problem there is that sometimes these videos include extra info that you may not need (though its no harm to know it and put it down in the exam, show the examiners you know EVERYTHING about it!).
Biology is a really fascinating subject, as it tells us about ourselves and the natural world around us. Just don't forget, no matter how hard or daunting it may seem, there are alternative ways to learn that DO NOT involve you reading whole pages of text, or writing out paragraphs 100 times to learn by heart. Try videos online or powerpoint presentations. Learn the diagrams by heart and fit the words in an essay around it. Then you can test your knowledge with online quizzes or even the app I suggested above. This can go for all subjects btw. Not just Biology.
Hope this has helped...