This question relates to Topic 8 (Part 1). a.The organiser is responsible for the formation of which tissue during vertebrate embryonic development? (2 marks) b.Name four signalling molecules that are secreted by the organiser. What feature do these molecules have in common? (3 marks) c.Explain how these molecules generate gradients of other signalling molecules that mediate the function of the organiser and determine the fate of cells during vertebrate embryonic development