Cell Structure and Functions: CBSE Class 8 Science Chapter Notes

What is a Cell? The Building Block of Life

A cell is the smallest structural and functional unit of a living organism. Just as bricks are the building blocks of a house, cells are the building blocks of all life. The study of cells is called cell biology. The discovery of the cell was made possible by the invention of the microscope. In 1665, Robert Hooke, an English scientist, observed thin slices of cork under his self-made microscope. He noticed small, box-like compartments, which he named 'cells'. However, these were dead cells. The first living cells were observed by Antonie van Leeuwenhoek using an improved microscope. Later, the Cell Theory was proposed by Matthias Schleiden and Theodor Schwann, and later expanded by Rudolf Virchow. It states that:

1. All living organisms are composed of one or more cells.
2. The cell is the basic unit of structure and organization in organisms.
3. Cells arise from pre-existing cells.

Key Terms in Cell Biology

Cell

The basic structural, functional, and biological unit of all known living organisms.

Organelle

A specialized subunit within a cell that has a specific function, e.g., Mitochondria, Nucleus.

Cytoplasm

The jelly-like substance filling the cell, enclosed by the cell membrane, where most metabolic activities occur.

Nucleus

The 'control center' of a eukaryotic cell, containing the cell's genetic material (DNA) in the form of chromosomes.

Prokaryotic Cell

A type of cell that lacks a true, membrane-bound nucleus and other membrane-bound organelles. Example: Bacteria.

Eukaryotic Cell

A type of cell that has a true nucleus enclosed within a nuclear membrane and contains other membrane-bound organelles. Examples: Plant and Animal cells.

Cell Membrane

Also called the Plasma Membrane, it is a semi-permeable barrier that controls the entry and exit of substances into and out of the cell.

Cell Wall

A rigid outer layer found in plant cells, fungi, and bacteria that provides structural support and protection.

Gene

A segment of DNA located on a chromosome that is the basic unit of heredity.

Plant Cell vs. Animal Cell: Key Differences

Major Cell Organelles and Their Functions

Must-Remember Facts about Cells

• {"point":"Cells are the fundamental units of life, discovered by Robert Hooke in 1665."}
• {"point":"The nucleus acts as the control center of the eukaryotic cell, containing genetic material."}
• {"point":"Mitochondria are called the 'powerhouse' because they generate energy (ATP) through respiration."}
• {"point":"Plant cells are distinguished by the presence of a cell wall, chloroplasts, and a large central vacuole."}
• {"point":"Animal cells lack a cell wall and chloroplasts, and have small vacuoles."}
• {"point":"Prokaryotic cells (e.g., bacteria) lack a membrane-bound nucleus; their genetic material is in a region called the nucleoid."}
• {"point":"Eukaryotic cells (e.g., plants, animals) have a well-defined, membrane-bound nucleus."}
• {"point":"Genes are units of inheritance located on chromosomes within the nucleus."}
• {"point":"Organisms can be unicellular (made of a single cell, e.g., Amoeba) or multicellular (made of many cells, e.g., humans)."}

Exam Focus: Diagrams and Functions

For exams, you absolutely must practice drawing and labeling diagrams of both plant and animal cells. A large portion of marks in this chapter comes from diagram-based questions. Be prepared to identify an organelle from a diagram and state its specific function. Questions comparing plant and animal cells, or prokaryotic and eukaryotic cells, are very common. Also, be ready for 'why' questions like, 'Why is the mitochondrion called the powerhouse of the cell?' or 'Why do plant cells have a rigid cell wall?'. Clear, concise answers that directly address the function are key to scoring full marks.

Practice Questions with Solutions

• Who discovered the cell and how? Robert Hooke discovered the cell in 1665 while observing a thin slice of cork under a microscope. He saw box-like structures which he named 'cells'.
• Name two organelles found only in plant cells. Cell wall and Plastids (e.g., chloroplasts).
• What is the primary function of the nucleus? The nucleus controls all the activities of the cell and contains the genetic material (chromosomes/DNA) which is passed from one generation to the next.
• Differentiate between prokaryotic and eukaryotic cells based on the nucleus. Prokaryotic cells have an undefined nuclear region called a 'nucleoid' and lack a nuclear membrane. Eukaryotic cells have a well-defined nucleus enclosed by a nuclear membrane.

Frequently Asked Questions

Frequently Asked Questions