What organisms are always at the start of any food chains

Sunlight

Explanation:

I don't know how to explain it but I'm gonna try

Food chain

Sunlight is the most crucial thing in a food change because without it producers will not be cable to produce photosynthesis which is a proces in which producers use sunlight light to produce ATP (energy).And if producers are not able to do photosynthesis the herbivores will not be able to eat and eventually died the same thing happens whit the carnivore they will not have anything to eat and eventually dies.

the corpus luteum secretes estrogens and progesterone. the latter hormone causes changes in the uterus that make it more suitable for implantation of the fertilized ovum and the nourishment of the embryo. if the egg is not fertilized, the corpus luteum becomes inactive after 10–14 days, and menstruation occurs.

i hope this : )