Observe and measure prepared sea urchin embryos and chick embryos. Conduct an experiment using chick embryos. Determine the effect of a stimulant and depressant on a chick embryo's heart rate.

Increase with a stimulant and decrease with a depressant

Explanation:

Stimulants and depressants are observed using various organisms. The way a stimulant works is by increasing the dopamine levels in the body. This in turn causes increased heart rate as would be seen in the chick embryo heart. On the other hand a depressant would lower dopamine levels. This would reduce the neurotransmitter and cause the heart rate to slow down.

any abiotic or biotic factor in an ecosystem that causes a population's size to slow or decrease is a limiting factor.