The heart is a muscular organ that pumps blood. blood that contains waste materials is brought to the heart by blood vessels. this blood enters the and then moves down. the presence of the prevents the backflow of blood inside the heart

Some birds look for food near cattle and other livestock. the movement of the cattle churns up the ground, making insects available to the birds. the cattle appear to be unaffected by the presence of the birds. what kind of relationship exists between the birds and the cattle? o a. parasitism o b. commensalism o c. predation o d. mutualism

The breakdown of food is accomplished by enzymes. a. physical b. chemical c. mechanical d. none of the above

Which is a genetic engineering advancement directly related to a career in biotechnology? 1) improving solar energy collection 2) transporting textiles at higher rates 3)creating crop foods that resist insect pests 4)repairing historical sites with quality materials