Explanation:

- Option 1: Zygote

- A zygote is a fertilized egg formed by the fusion of sperm and egg cells.

- It is found in the ovule, not in the middle of a flower.

- Option 2: Pollen

- Pollen is the yellow dust found in the flower's center.

- Produced by the anthers, it's crucial for plant reproduction.

- Option 3: Stomata

- These are tiny pores on leaves for gas exchange.

- They aren't present in the flower's center.

- Option 4: Sperm

- Plant sperm are within pollen but not seen as yellow dust.

- They contribute to fertilization after pollination.