Cellular Life: Structure, Function, and Processes

Cell Theory: The Foundation of Life

The cell is the fundamental structural and anatomical unit of all organisms; all living things are formed by one or more cells. The cell is the physiological and functional unit; any cell can sustain itself. Cells originate from pre-existing cells.

Common Characteristics of Cells

All cells share fundamental characteristics:

• An outer membrane that separates the cell from its external environment.
• A set of internal structures, called organelles, where vital cellular processes are performed.
• Genetic material (DNA) that transmits cellular processes and commands to offspring.

Cell Types Based on Genetic Material

Prokaryotic Cells

These are simple and primitive cells, such as bacteria. Their genetic material is dispersed freely in the cytoplasm, without a nuclear membrane. They have few cellular organelles and do not form tissues or organs.

Eukaryotic Cells

These are complex and evolved cells, found in animals and plants. Their genetic material is enclosed within a nuclear membrane. Eukaryotic cells possess many cellular organelles.

Exclusive Structures of Animal and Plant Cells

Plant Cells

Plant cells uniquely possess a cell wall and chloroplasts.

Animal Cells

Animal cells uniquely possess lysosomes, centrioles, cilia, and flagella.

Key Organelle Functions

• Cell Wall: Provides protection, rigidity, and consistency to plant cells.
• Chloroplasts: The site of photosynthesis in plant cells.
• Lysosomes: Perform cellular digestion and eliminate old organelles or waste in animal cells.
• Cilia and Flagella: Responsible for cell movement or the movement of surrounding fluid.
• Cytoplasm: The jelly-like substance filling the cell, where organelles float and the nucleus is located.
• Ribosomes: Primarily responsible for protein synthesis.
• Mitochondria: The site where cellular respiration produces energy.

Essential Cell Components Defined

• Cell Membrane: The outer boundary of the cell, featuring channel-like openings that control the passage of substances between the cell's interior and exterior.
• Nucleus: The control center of the cell, housing genetic information. It is formed by the nuclear membrane, chromatin, and nucleoli.
• Ribosomes: Organelles where protein synthesis occurs. They are composed of RNA and proteins and are only visible under a microscope.
• Endoplasmic Reticulum: A network of branched membranes extending throughout the cytoplasm, forming a system of channels. It transports, distributes, and stores substances.
• Golgi Apparatus: A stack of flattened, membrane-bound sacs with secretory functions.
• Mitochondria: The powerhouses of the cell, where cellular respiration takes place. This process releases energy from organic molecules.
• Vacuoles: Storage organelles for substances like lipids and pigments. They are typically larger in plant cells.

Molecular Functions and Location

Nucleic Acids (DNA and RNA): These molecules direct cellular functions and are primarily located within the cell's nucleus.

Cellular Nutrition Types

Autotrophic Nutrition

Cells that feed themselves by manufacturing energy-rich organic matter, a process called photosynthesis. This is exclusive to plant cells and some bacteria.

Heterotrophic Nutrition

Cells that obtain nutrients by incorporating pre-existing organic matter from external sources.

Photosynthesis vs. Cellular Respiration

Photosynthesis

A process carried out in a unique organelle of plant cells, the chloroplast, to produce energy.

Cellular Respiration

The process where nutrients are broken down to release energy. This occurs in the mitochondria of both animal and plant cells.

Understanding Cellular Metabolism

Metabolism: The sum of all chemical processes by which cells utilize their nutrients to sustain life.

Metabolic Processes: Catabolism and Anabolism

• Catabolism: A set of chemical reactions involving the degradation of nutrients to release energy.
• Anabolism: Chemical reactions in which small organic molecules are synthesized into larger or more complex molecules, requiring energy.

Cell Division and Its Phases

Cell Division: The process by which one parent cell divides into two or more daughter cells. Key phases include:

• Duplication of DNA.
• Division of the nucleus (karyokinesis).
• Division of the cytoplasm (cytokinesis).

Key Terms in Cell Division and Genetics

• Diploid: A cell containing a complete set of chromosomes (2n).
• Haploid: A cell containing half the number of chromosomes (n).
• Mitosis: A type of cell division where the DNA duplicates, resulting in two daughter cells with the same number of chromosomes as the parent cell.
• Meiosis: A type of cell division where chromosomes are divided, and daughter cells receive half the number of chromosomes from the progenitor cell. This process is essential for sexual reproduction.
• Chromatin: The genetic material (DNA and proteins) dispersed within the nucleus when the cell is not dividing. It is not visible under a light microscope.
• Chromosomes: Condensed and organized DNA molecules that become visible during cell division. They ensure genetic material is accurately shared between two daughter cells. Chromosomes are important components of cells and are where genes are located.

Mutations and Mutagenic Agents

• Mutations: Errors in the genetic material (DNA) that cause changes.
• Mutagenic Agents: Physical and chemical factors that can cause mutations.

Defining Microorganisms

Microorganism: A group of diverse, very small living beings, visible only under a microscope.

Characteristics of Microorganisms

Microorganisms are characterized by:

• High multiplication speed.
• Adaptability to various environments (air, aquatic, inside living beings).
• Visibility only under a microscope.

Beneficial Microorganisms

Beneficial microorganisms play crucial roles as:

• Decomposers.
• Producers of medicines.
• Fermenters.