Cells grown in laboratory culture dishes undergo only a fixed number of division before dying. The number of possible divisions drops depending on the age of the donor organism. This phenomenon is called the

Hayflick limit

Explanation:

The Hayflick limit, or Hayflick phenomenon, is the number of times a normal human cell population will divide before cell division stops. It was postulated by Leonard Hayflick in 1961,

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explanation:

well for one plants are always the producer, so a is the answer. a wolf is more of the consumer(predator) and the deer is the prey so i know those two are out of the question. also mushrooms are fungi/fungus so a is the producer.