Biology Chapter 3: Cells and Tissues

Study Notes

Cells and Tissues

Cells are the basic structural units of all living organisms.
The human body is composed of approximately 50 to 100 trillion cells.

The Cell Theory

A cell serves as the fundamental structural and functional unit of life.
Organism activities depend on the harmonious functions of their cells.
The principle of complementarity states that a cell's structure dictates its function.
Cellular continuity is essential for the existence of life.

Cell Composition

Most cells consist of four key elements: carbon, hydrogen, oxygen, and nitrogen.
Cells contain about 60% water.

Anatomy of a Generalized Cell

A typical cell has three main components:
- Nucleus
- Cytoplasm (the gel-like substance within the plasma membrane)
- Plasma membrane

The Nucleus

Functions as the cell's control center.
Houses genetic material known as DNA, crucial for:
- Protein synthesis
- Cellular reproduction
Main regions include:
- Nuclear envelope (double membrane with nuclear pores)
- Nucleolus (site of ribosome assembly)
- Chromatin (DNA and proteins that condense into chromosomes during cell division)

The Plasma Membrane

Acts as a transparent barrier that encases cell content and separates it from the external environment.
Constructed based on the fluid mosaic model, which includes:
- Two layers of phospholipids arranged tail-to-tail
- Scattered cholesterol and proteins
- Possible sugar groups forming glycolipids

Phospholipid Arrangement

Hydrophilic "heads" face the outer and inner surfaces; hydrophobic "tails" are oriented inward.
Creates a barrier that is selectively permeable to water-soluble molecules.

Functions of Membrane Proteins

Specialized functions include:
- Enzymatic activity
- Hormone reception
- Transmembrane transport as channels or carriers

Cell Junctions

Cells are adhered through:
- Glycoproteins in the glycocalyx acting as adhesive molecules
- Membrane contours fitting together like a jigsaw
- Specialized membrane junctions, varying in structure and function

Types of Cell Junctions

Tight junctions create impermeable barriers, binding cells into leakproof sheets and preventing substance passage through the extracellular space.

Description

Explore the foundational concepts of cells and tissues in this quiz based on Chapter 3 of Biology. Delve into the cell theory and understand the vital role of cells as the basic units of life. This is essential for grasping the fundamentals of biology and human anatomy.