1. Nutrients: They require a constant supply of nutrients, including proteins, carbohydrates, fats, vitamins, and minerals. These nutrients are essential for building cells, tissues, and organs, and for providing energy for growth and development.

2. Oxygen: Embryos need oxygen for cellular respiration, the process by which cells convert nutrients into energy. Oxygen is also essential for the development of many organs and tissues.

These are fundamental needs that ensure the embryo can grow and develop properly.