Biology Cell Theory and Types

Cell Theory

• All living things are made of one or more cells, or their byproducts.
• Cells are the basic unit of life, capable of carrying out all life processes.
• All cells arise from pre-existing cells, not from non-living matter.

Types of Cells

• Prokaryotic cells: These are the most ancient cell type, still found today. They are simple, single-celled organisms lacking a membrane-bound nucleus. A key example is bacteria cells.

• Eukaryotic cells: These are more complex cells that can exist as single or multicellular organisms. They have a more complex internal organization, including a nucleus. Examples include amoebas, plants, and animals.

Cell Organelles

• Cells contain smaller parts called organelles, each with specific functions for maintaining life processes.
• Some organelles are common to both plant and animal cells while others differ.

Cell Membrane

• A flexible, protective barrier that holds the cell's contents and regulates the exchange of substances.
• It communicates with other cells and provides support.
• Composed of a phospholipid bilayer, where the outside of the membrane is hydrophilic (attracted to water) and the inside is hydrophobic (repelled by water).
• Also a semi-permeable membrane, controlling what substances enter and leave the cell.

Cytoplasm

• The jelly-like substance filling the cell.
• Surrounds the organelles.
• Contains nutrients needed by the cell and is where many chemical reactions occur.
• Allows movement of nutrients and organelles within the cell.

Nucleus

• Controls all cell activities and contains all genetic information (DNA).
• Surrounded by a nuclear envelope with pores to allow material transport.

Inside the Nucleus

• Genetic information is stored in chromosomes.
• Chromosomes contain DNA, which carries coded instructions for all cell activities.
• The nucleolus is a dense region inside the nucleus where ribosomes are made. (Ribosomes are the protein factories of the cell).

Vacuoles

• Membrane-bound, fluid-filled organelles that store nutrients, wastes, and other substances.
• In plant cells, a large central vacuole stores water, maintaining cell firmness.
• Animal cells have smaller vacuoles.

Mitochondria

• Often called the "power plants" of the cell.
• They convert chemical energy (from sugar) into energy usable by the cell (cellular respiration).

Lysosomes

• Small, round organelles filled with enzymes.
• Digest invading bacteria or damaged cell parts.
• Only found in animal cells.

Endoplasmic Reticulum (ER)

• A network of interconnected tubes that transports materials within the cell.
• Rough ER: Associated with protein production, studded with ribosomes.
• Smooth ER: Associated with fat and oil production, lacks ribosomes.

Golgi Apparatus

• Receives proteins from the ER.
• Modifies, sorts, and packages them for delivery within or outside the cell.
• Involved in mucus production.
• Looks like a stack of flattened membranes.

Cytoskeleton

• An internal network of protein fibers that maintains the cell's shape.

Organelles in Plant Cells

• Only certain organelles are found specifically in plant cells, like the cell wall.
• The cell wall is a rigid structure providing strength, protection, and support.

Chloroplasts

• Found in plant cells and some algae.
• Contain chlorophyll, which uses sunlight to convert carbon dioxide and water into sugar and oxygen (photosynthesis).