A very strong relationship. I'll take the easiest example :the bees. They are so important for our planet. Without them, we and all living creatures on earth would be on track to dispariton. Let me explain why. At first, the bees need the nectar from flowers to make honey ( source of food ). As they pollen from flower to flower, they transport pollen on their tiny little legs and in this way, they help the plants to reproduce themselves. If, for some reason, there will be no more bees. Plants and flowers will not thrive, plants will be eaten without having contribued to the productivity of the species and they will go out. No plants, no more veggies or fruits for herbivorous and humans, no more herbivorous no more food for carnivorous, etc. Also, without plants, there will be less oxygen on our planet. Slowly the fauna and flora will die on earth and then it will be our turn. That is why relationships with plants and insects are so important. Plants produce oxygen for all of us and they are a natural and healthy source of food and insects help plants to survive and thus save the species.
A trilobite. Trilobites became extinct about 250 million years ago while a ammonite became extinct around the same time as dinosaurs(65 million years ago). You wouldn't find a human skull or a dinosaur footprint
Undergo differentiation
become stem cells
turn on all of the genes found in the nucleus
some cells can undergo cell division
