Step-by-step explanation:
balance between plants & animals is essential because plants are autotrophs , they can make their own food but animals are heterotrophs , they cannot prepare their own food so they have to depend on plants ( autotrophs) for their food.
moreover, to prepare their food plants need C02 , WHICH IS RELEASED IN THE ENVIRONMENT BY ANIMALS ( BY RESPIRATION) & IN TURN THEY RELEASE Oxygen which is essential for the life of animals & also to maintain balance in nature , the number of plants should be equal to the number of animals.