What type of atom is at the center of the chlorophyll porphyrin ring?

Which type of air has a relative humidity of 100 percent?

Antigens are Multiple Choice something made by a white blood cell to destroy a pathogen. membrane receptors on B-lymphocytes. disorders involving overactive immune systems. something that an antibody or T-lymphocyte binds to.

Which of the following sentences are correct? (1) for millions of years dinosaurs ruled the earth; they roamed freely over the land and through the oceans.

A third-world country village gets a monthly air drop of white rice. The amount of rice is enough so that every villager never has a hungry stomach. Which of the following is a concern related to nutrition? The rice may be poisoned.

On the earth, "down" means toward the earth's ...

All living things are made of cells. What might be a major difference between cells that are found in human skin and human nerve cells?

I live in wet land, I respire through roots

What do scientist think causes the movement of earth's plate?

If a normal human cell has 46 chromosomes how many chromosomes will it's daughter cell have?

Differentiate between sexual and asexual reproduction