Searching for comprehensive textbook
Try Campbell biology.....it covers almost all the topics under biology in a lucid way...also the book has packed quite a volume of info in it ranging from a beginner level to a fairly advanced level....excellent book also in matters of presentation &amp; writing style so that one won't feel bored....


Pros:

Genetics ( both classical and modern)
Ecology (including ethology)
Evolutionary biology
Animal classification
Immunology

Cons:

Biochemistry ( it somewhat feels short)
Plant anatomy ( not adequately covered)
Plant classification ( same as above)



&amp; the rest of the chapters are like animal physiology etc. they are mixed...like some 
principles they have gone thoroughly...some others not...but it's acceptable as they have to cover everything in one book...

But of course it's my personal opinion...so before considering it I would rather recommend downloading the book in pdf format &amp; have a look at it yourself...but I feel you won't be disappointed....