"Proportionality" in biology is called positive correlation: positive correlation only requires the independent variable (x) to grow, and the dependent variable (y) to grow with it, and there is no strict mathematical relationship.

Physical direct ratio (for example); Proportion (example) requires independent variable (X), and dependent variable (Y) conforms to the relationship y=k*x(k is a certain quantity), which has a strict mathematical relationship, so "control variables (this sentence is a bit outrageous, is it from the mouth of the teacher)". The following is an image representation:

Passing through the origin is proportional (for example)

However, the origin is not called direct proportion (for example)

Negative correlation on the left and positive correlation on the right.

Generally speaking, direct ratio can mean positive ratio and positive correlation. Generally, in biology and Chinese, these representations are positively correlated, while mathematics and physics represent positive ratios. I don't know anything else, because I am a science student. (The location of the uploaded map is a bit abnormal, so we can make do with it. )