Describe how viruses recognize what cells to attach to.

Ablastocyst is a group of cells that forms after a human egg is fertilized. the blastocyst consists of two types of cells. some of these cells will become the placenta. what do the other cells develop into?

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

Give three examples of plant activities that are affected by circadian rhythms and natural fluctuations in the length of daylight?