Biology Class 7: Understanding Cells

Study Notes

Cell Structure and Function

A cell is the basic unit of structure and function in all living organisms.
Cells are the smallest part of the body of every living organism that can carry out all the basic functions of life.

Discovery of Cells

Cells were first discovered by Robert Hooke in 1665 when he observed a slice of cork under a microscope.
Anton Van Leeuwenhoek, a Dutch Scientist, later observed single-celled organisms like bacteria under a microscope.

Cell Theory

The cell theory was proposed by three scientists: Matthias Schleiden, Theodor Schwann, and Rudolf Virchow.
The cell theory states that:
Every living organism is made up of one or many cells.
A cell is the structural and functional unit of living organisms.
New cells arise by the division of pre-existing cells.

Types of Cells

Unicellular organisms: formed of one cell only, e.g., bacteria, Amoeba, Euglena, paramecium, Chlamydomonas, and yeast.
Multicellular organisms: formed of many cells, e.g., Hydra, frog, trees, etc.

Shape of Cells

Cells have different shapes related to the functions they perform.
Examples of cell shapes:
Muscle cells: spindle-shaped.
Nerve cells: long and branched.
Amoeba: irregular shape with pseudopodia.

Size of Cells

The largest cell: ostrich egg, 15-20 cm in diameter.
The smallest cell: red blood cells in the human body (7 micrometer) and bacteria cells (0.3-5.0 micrometer).
The longest cell: nerve cells in the human body (1 meter).

Parts of a Cell

A typical cell has three basic parts:
Cell membrane (plasma membrane): a thin, elastic, and selectively permeable membrane around the cytoplasm.
Cytoplasm: a jelly-like, semi-fluid substance found between the cell membrane and the nucleus.
Nucleus: contains the genetic material of the cell.

Cell Wall (in Plant Cells)

In addition to the cell membrane, plant cells have a cell wall.
The cell wall is non-living, formed of cellulose, and provides rigidity and mechanical support to the cell.

Cell Organelles

Mitochondria: double membrane, rod-shaped bodies that produce energy (ATP) by breaking down food during cell respiration.
Endoplasmic Reticulum (ER): an irregular network of membranes that divide the cytoplasm into channels, helping to transport substances within the cell.
Golgi Complex: stacks of thin membranes concerned with secretion, packaging, and transport of substances like enzymes and hormones within the cell.
Lysosomes: small, round sacs filled with enzymes that can destroy and digest foreign substances.
Ribosomes: tiny granules scattered in the cytoplasm or attached to the ER, responsible for protein synthesis.

Description

Test your knowledge of the basic unit of life - cells! Learn about the structure, function, and discovery of cells, and understand how they form the building blocks of all living organisms. Take this quiz to assess your understanding of the cell chapter in class 7 biology.