Question

put the steps of fertilization in order, starting with the first event to occur after the sperm reaches the egg in the uterine tube.
instructions
sperm and ovum pronuclei are enclosed within the nuclear envelope.
the sperm cell membrane fuses with the ovum plasma membrane, and the sperm enters the ovum
the sperm penetrates the corona radiata
the zona pellucida becomes the fertilization membrane.
the acrosome of the sperm releases enzymes that break down the zona pellucida

Explanation:

Fertilization begins with the sperm's approach to the egg. The sperm first penetrates the corona radiata (a layer of cells around the egg). Then, the acrosome of the sperm releases enzymes to break down the zona pellucida (a glycoprotein layer). After that, the sperm cell membrane fuses with the ovum plasma membrane, and the sperm enters the ovum. Following this, the zona pellucida becomes the fertilization membrane (to prevent polyspermy). Finally, sperm and ovum pronuclei are enclosed within the nuclear envelope (completing the fertilization process).

Answer:

1. The sperm penetrates the corona radiata.
2. The acrosome of the sperm releases enzymes that break down the zona pellucida.
3. The sperm cell membrane fuses with the ovum plasma membrane, and the sperm enters the ovum.
4. The zona pellucida becomes the fertilization membrane.
5. Sperm and ovum pronuclei are enclosed within the nuclear envelope.