Semi permeable means that some things can go in and out of the cell, but some cannot. Permeable means it allows things to pass through it, so semi permeable means only some things pass through.
Because of their resemblance and relationship to prehistoric reptiles and many people think that birds descended from dinosaurs
Spongy bone has trabecular which serve as reinforcing plates against a force. The loss of spongy bones causes weakening of the internal support that the compact bone requires and the entire bone breaks.