Human Cell Definitions

cell membrane

This protects the cell and helps it communicate with its environment through receptor proteins on its surface. These proteins allow certain substances to pass into and out of the cell, while blocking others. This selective permeability supports proper nutrition, removal of waste, and overall cell function.

Cytoplasm

This provides both storage space and work areas for the cell. It contains the cell's internal structures, known as organelles, including ribosomes, endoplasmic reticulum, Golgi apparatus, mitochondria, lysosomes, and centrioles. Many essential cell activities occur within the …….

Ribosomes

These are responsible for making enzymes and other proteins. Because of this role, they are often referred to as the cell's "protein factories."

Endoplasmic Reticulum (ER)

This is involved in the transport of proteins and other substances through the cytoplasm. It acts as an internal passageway that helps move materials within the cell.

Golgi Apparatus

This chemically processes molecules received from the endoplasmic reticulum and then packages them into vesicles. For this reason, it is often called the cell's "chemical processing and packaging center."

Mitochondira

These are involved in cellular metabolism and respiration. They provide the principal source of cellular energy, where complex chemical reactions continuously release energy needed for cell activity. They are commonly known as the cell's "power plants.

Lysosomes

These contain enzymes capable of digesting compounds within the cell. Because they break down waste materials and other substances, they are often called "digestive bags."

Centrioles

These play an important role in cell reproduction, particularly during cell division, helping ensure proper organization of the cell's components.

Cilia

These are hairlike structures that project from epithelial cells. Their function is to move mucus, dust particles, and other foreign substances away from areas such as the respiratory tract.

Flagellum

This is the tail-like structure of the sperm cell. It enables the sperm to move or "swim" toward the ovum.

Nucleus (Nuclei)

This is the control mechanism of the cell, governing growth, repair, reproduction, metabolism, and other vital activities. It contains the genetic blueprint, DNA, which is organized into genes that determine individual characteristics. Inside ……. is the nucleolus, which assists in cell metabolism and reproduction. If the …….. is damaged or destroyed, the cell usually dies; however, mature red blood cells lose their …. and continue to function for a limited time.

Chromosomes

are threadlike structures made of nucleic acids and proteins located in the nucleus. They carry genetic information in the form of genes. Normal human cells contain 46 ………, each providing instructions that influence cell structure and function.