Explain the structure of a mature egg-M2
A mature egg at the metaphase II (M2) stage is the final stage of oocyte maturation, and is ready for fertilization by a sperm. The structure of a mature egg at M2 can be divided into several parts:

1. Zona pellucida: The zona pellucida is the glycoprotein layer that surrounds the egg cell. This layer is responsible for protecting the egg and regulating the interaction between the egg and the sperm during fertilization.
2. Cell membrane: The cell membrane is the outermost layer of the egg cell, and is made up of lipids and proteins. This layer controls the transport of molecules into and out of the cell, and is the site of many signaling pathways that are important for fertilization and early embryonic development.
3. Cytoplasm: The cytoplasm is the region of the egg cell between the cell membrane and the nucleus, and contains many organelles, including mitochondria and ribosomes, which are responsible for producing the energy and proteins required for fertilization and early embryonic development.
4. Nucleus: The nucleus is the central region of the egg cell, and contains the genetic material (DNA) required for fertilization and embryonic development.
5. Polar body: During oocyte maturation, the cytoplasm of the oocyte is divided unevenly, resulting in the formation of one large egg and one or more smaller polar bodies. The polar body is a small, non-functional cell that is eventually discarded by the body.

Overall, the structure of a mature egg at M2 is adapted to allow for successful fertilization and embryonic development. The zona pellucida and cell membrane protect the egg and regulate the interaction between the egg and the sperm, while the cytoplasm and nucleus provide the necessary energy and genetic material required for fertilization and early embryonic development.

Explain the structure of a sperm
Sperm, also known as spermatozoa, are the male reproductive cells responsible for fertilizing the female egg. The structure of a sperm can be divided into three main parts: the head, the midpiece, and the tail.

1. Head: The head is the front part of the sperm and contains the genetic material (DNA) required for fertilization. The head is covered by a cap-like structure called the acrosome, which contains enzymes that help the sperm penetrate the outer layer of the egg during fertilization.
2. Midpiece: The midpiece is the region of the sperm that contains the energy-producing organelles called mitochondria. These organelles provide the energy required for the sperm to swim and move towards the egg.
3. Tail: The tail is the long, whip-like structure that propels the sperm forward through the female reproductive tract towards the egg. The tail is made up of a central axoneme surrounded by a sheath of fibers and proteins that provide structure and support.

In addition to these three main parts, there are also other structures present in the sperm, including the neck, which connects the head to the midpiece, and the basal body, which anchors the tail to the sperm cell. The entire structure of a sperm is adapted to enable it to move rapidly through the female reproductive tract towards the egg, and to penetrate the egg’s outer layer during fertilization.

Explain the structure of an embryo on day 2, day 3 and day 5 ( blastocyst stage)
During the early stages of embryonic development, the fertilized egg undergoes several rounds of cell division and differentiation to form a structure called a blastocyst. Here’s a brief overview of what happens during days 2, 3, and the blastocyst stage of embryonic development:

Day 2: At this stage, the fertilized egg has divided into two cells, which are called blastomeres. These blastomeres are still contained within the zona pellucida, a protective layer surrounding the developing embryo.

Day 3: By day 3, the fertilized egg has undergone several rounds of cell division, resulting in a ball of about 8 to 16 cells called a morula. The morula is still surrounded by the zona pellucida, but it will soon be shed as the morula develops into a blastocyst.

Blastocyst stage: At this stage, which occurs around 5 to 6 days after fertilization, the developing embryo has differentiated into two distinct cell populations. The inner cell mass (ICM) is a group of cells that will go on to form the embryo proper, while the outer layer of cells, called the trophoblast, will eventually form the placenta. The blastocyst has also shed the zona pellucida and has begun to implant in the uterine wall.
In summary, during the first few days of embryonic development, the fertilized egg undergoes several rounds of cell division and differentiation to form a blastocyst, which consists of an outer layer of cells that will form the placenta and an inner cell mass that will go on to form the embryo itself.