Difference Between Spermatids and Sperm Cells

Main Difference – Spermatids vs Sperm Cells

Sperm cells are the male gametes of both animals and plants. The sperm cells of higher organisms are a type of highly structurally and functionally differentiated cells. Most of them have flagella; hence, they are motile. Sperm cells are smaller types of gametes when compared to female gametes. Spermatids and sperm cells are two stages formed during the formation of male gametes. The main difference between spermatids and sperm cells is that spermatids are the undifferentiated cells produced by meiosis whereas sperm cells are the morphologically differentiated cells formed by a process known as spermiogenesis in animals. The whole process of formation of sperm cells from the germ cells in the male gonads is known as spermatogenesis in animals.

Key Areas Covered

1. What are Spermatids
     – Definition, Formation, Structure, Function
2. What are Sperm Cells
     – Definition, Formation, Structure, Function
3. What are the Similarities Between Spermatids and Sperm Cells
     – Outline of Common Features
4. What is the Difference Between Spermatids and Sperm Cells
     – Comparison of Key Differences

Key Terms: Animals, Fertilization, Sperm Cells, Spermatids, Spermatogenesis, Spermiogenesis, Spermatozoa

What are Spermatids

Spermatids refer to the immature male gametes formed from spermatogonia during meiosis. Spermatogonia are diploid cells that undergo mitosis to form primary spermatocytes. The primary spermatocytes undergo meiosis 1 to form secondary spermatocytes, which are haploid. Secondary spermatocytes undergo meiosis 2 to form spermatids. A single, primary spermatocyte may produce four spermatids. These spermatids then undergo spermiogenesis, differentiating into mature sperm cells. Hence, spermatids can be considered as the precursors of sperm cells. Spermatogenesis is shown in figure 1.

Figure 1: Spermatogenesis

A spermatid is a rounded-shape cell with regular types of organelles. It has scattered mitochondria throughout the cell. Spermatids can be found near the wall of the seminiferous tubules. Since spermatids have completed meiosis, they are considered as cells that have completed the nuclear maturation. However, they must undergo cytoplasmic maturation to become a mature sperm cell that can fertilize an egg cell.

What are Sperm Cells

Sperm cells refer to mature, male reproductive cells that are capable of fertilizing an egg cell. They are also known as spermatozoa. The formation of a mature sperm cell from the gem cells known as spermatogonia inside the seminiferous tubules of animals is known as spermatogenesis. Spermatogenesis is composed of two steps: meiosis and spermiogenesis. The germ cells known as spermatogonia undergo meiosis to produce haploid spermatids. Spermatids undergo differentiation to become sperm cells during spermiogenesis. Males continuously produce sperm cells throughout their lifetime, starting at puberty. Sperm cells come out of the seminiferous tubules along with the semen or seminiferous fluid. The structure of a sperm cell in humans is shown in figure 2.

Figure 2: Sperm Cell

Sperm cells are small, compact, and elongated cells that are highly adapted to their function, i.e., fertilization of the female egg cell. A typical sperm cell has three sections: head, middle region, and the tail. The head consists of the nucleus, a pair of centrioles, and an acrosome cap. The haploid nucleus contains a single set of chromosomes of the species. The acrosome cap is a differentiated Golgi apparatus that contains the hydrolytic enzymes that help the penetration of the jelly coat of the egg cell during fertilization. A large number of mitochondria are concentrated in the middle part of the sperm. They produce the energy required by the mobility of the tail. The tail is made up of a single flagellum in humans. In plants, algae and other seedless plants produce motile sperm cells while flowering plants produce non-motile sperm cells.

Similarities Between Spermatids and Sperm Cells

• Spermatids and sperm cells are two types of cell stages formed during the formation of male gametes in a process known as spermatogenesis.
• Both spermatids and sperm cells are formed in the seminiferous tubules of the testes.
• Both spermatids and sperm cells are haploid.
• Both spermatids and sperm cells have organelles.
• Both spermatids and sperm cells are incapable of dividing further.

Difference Between Spermatids and Sperm Cells

Definition

Spermatids: Spermatids are immature male gametes, formed from spermatogonia during meiosis.

Sperm Cells: Sperm cells are mature male reproductive cells that are capable of fertilizing an egg cell.

Formation

Spermatids: Spermatids are formed during meiosis of germ cells.

Sperm Cells: Sperm cells are formed from spermatids in a process known as spermiogenesis.

Found in

Spermatids: Spermatids can be found near the walls of the seminiferous tubules.

Sperm Cells: Sperm cells can be found in the middle of the seminiferous tubules.

Differentiation

Spermatids: Spermatids are undifferentiated cells.

Sperm Cells: Sperm cells are differentiated cells.

Maturity

Spermatids: Spermatids are immature forms of male gametes.

Sperm Cells: Sperm cells are mature forms of male gametes.

Structure

Spermatids: Spermatids are large cells with a rounded-shape.

Sperm Cells: Sperm cells have mostly an elongated shape with flagella.

Nucleus

Spermatids: Spermatids have a large, rounded nucleus.

Sperm Cells: Sperm cells have a small, elongated nucleus.

Arrangement of Mitochondria

Spermatids: Mitochondria are scattered throughout the spermatid.

Sperm Cells: Mitochondria are concentrated near the flagellum in sperm cells.

Golgi Apparatus

Spermatids: Spermatids have Golgi apparatus.

Sperm Cells: Sperm cells lack Golgi apparatus.

Centrioles

Spermatids: The centrioles of the spermatids occur near the nucleus.

Sperm Cells: The centrioles of sperm cells serve as the basal body of the flagellum.

Mobility

Spermatids: Spermatids are immotile as they lack flagella.

Sperm Cells: Sperm cells are motile as they have flagella.

Capacity to Fertilize

Spermatids: Spermatids are incapable of fertilizing an egg cell.

Sperm Cells: Sperm cells have the capacity to fertilize an egg cell.

Conclusion

Spermatids and sperm cells are two stages of the male gametes. Both spermatids and sperm cells are haploid. Sperm cells are the morphologically and functionally differentiated cells that are mature. They are capable of fertilizing an egg cell. Spermatids are immature forms of sperm cells formed during the meiosis. Spermatids differentiate into sperm cells during spermiogenesis. The main difference between spermatids and sperm cells is the structure and the ability to fertilize an egg.

Reference:

1. Gilbert, Scott F. “Spermatogenesis.” Developmental Biology. 6th edition., U.S. National Library of Medicine, 1 Jan. 1970, Available here.

Image Courtesy:

1. “Figure 28 01 04” By OpenStax College – Anatomy & Physiology, Connexions Web site, Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia
2. “Simplified spermatozoon diagram” By Mariana Ruiz – based on “Gray’s Anatomy” 36th edit Williams and Warwick, 1980 (Public Domain) via Commons Wikimedia