Many plant cells have green chloroplasts. Chloroplasts make food. Animal cells do not have chloroplasts. A tissue is a group of cells that are alike. Heart tissue is made of heart cells.
Brain tissue is made of brain cells.
Heart tissue is different from brain tissue. An organ is a group of tissues that work together to do a job. The heart, liver, brain, and stomach are organs. Some organs work together in body systems. Body systems include the digestive system and the nervous system.