I’m going for real I haven’t done this because it was hard didn’t get it but now I know // ANSWER -
Measuring photosynthesis via the production of oxygen. Oxygen can be measured by counting bubbles evolved from pondweed, or by using the Audus apparatus to measure the amount of gas evolved over a period of time.
All you need is to locate an artery. theres one by your neck, on the the far sides of your wrists, between your thighs, or you could just feel your own heart.