B2.3.10 Adaptations of sperm and egg cells (HL) Notes

Sperm and Egg Cells Are Adapted for Fertilization and Zygote Formation

1. Sperm and egg cells, known as gametes, are specialized reproductive cells in humans designed to combine during fertilization, leading to the formation of a zygote.
2. These cells have unique structural adaptations that help them fulfill their specific roles in reproduction.

Adaptations of Sperm Cells

1. Many Mitochondria for Energy Production

1. Sperm cells have a midpiece that is packed with mitochondria.
2. Mitochondria are the "powerhouses" of the cell and are responsible for generating energy (ATP).

2. Streamlined Shape for Efficient Movement

1. Sperm cells have a streamlined shape, with a head that contains the genetic material (DNA) and a tail (flagellum) for propulsion.
2. The streamlined shape minimizes resistance and allows the sperm to move efficiently towards the egg.
3. The tail's whip-like motion propels the sperm through the female reproductive system, increasing the likelihood of encountering an egg for fertilization.

3. Acrosome for Penetration

1. The head of the sperm contains an organelle called the acrosome, which is a vesicle that holds digestive enzymes.
2. These enzymes are crucial for breaking down the outer layers of the egg (the zona pellucida) during fertilization.
3. The acrosome releases its enzymes once the sperm contacts the egg, allowing the sperm to penetrate and fuse with the egg's membrane.

Adaptations of Egg Cells

1. Large Size for Nutrient Storage

1. Egg cells are significantly larger than sperm cells and contain large amounts of cytoplasmic material, including yolk, which is rich in nutrients.
2. The large size and nutrient-rich yolk enable the egg to provide all the necessary materials for the early development of the embryo after fertilization.
3. The nutrients stored in the egg support the growing embryo until it can implant in the uterine wall and receive nutrients from the mother.

2. Protective Layers for Protection and Selectivity

1. The egg is surrounded by protective layers, including the zona pellucida (a glycoprotein layer) and the corona radiata (a layer of follicular cells).
2. The zona pellucida helps prevent the entry of multiple sperm, ensuring that only one sperm fertilizes the egg.
3. Additionally, the egg’s protective layers act as a barrier against harmful substances and protect the egg from physical damage until fertilization occurs.

3. Capability for Cellular Division Post-Fertilization

1. Upon fertilization, the egg contains the necessary machinery for cell division (mitosis), including centrioles and other organelles that help the zygote divide and develop into a multicellular organism.
2. The egg’s ability to divide and undergo mitosis is critical for the development of the embryo.
3. After fertilization, the egg begins dividing rapidly to form the tissues and organs of the developing organism.

Key Differences Between Sperm and Egg Cells

1. Size and Shape: Sperm are small and streamlined for mobility, while eggs are large and nutrient-rich for supporting early development.
2. Mitochondria: Sperm have many mitochondria in their midpiece to provide energy for movement, while eggs have a few mitochondria for basic cellular functions.
3. Genetic Material: Sperm carry half of the genetic information required to form a zygote, while the egg provides the other half, along with essential nutrients for early development.
4. Specialization: Sperm are specialized for mobility and fertilization, while eggs are specialized for nutrient storage and supporting early development after fertilization.