Which protein serves as a chemical messenger?
hemoglobin
actin
myosin
insulin

Previous pagenext pagepage 3 of 10question 3 (1 point)which of the following consist of cells that do not have a nucleus? of the above

Compare and contrast the adaptations of free-living flatworms and parasitic flatworms

When does the circulatory system work with the respiratory system? a. during blood cell formation b. during cellular respiration c. during intestinal digestion d. during a viral infection