Key Points

The Cell Theory states three main principles: all living organisms are composed of one or more cells, the cell is the basic unit of life, and all cells arise from pre-existing cells.

Prokaryotic cells, like bacteria, lack a membrane-bound nucleus and organelles. Eukaryotic cells, found in plants and animals, have a true nucleus and various membrane-bound organelles.

Plant cells are distinguished by a rigid cell wall, chloroplasts for photosynthesis, and a large central vacuole. These structures are absent in animal cells.

The cell membrane is a selectively permeable barrier that controls what enters and exits the cell. Its structure is described by the fluid-mosaic model, consisting of a lipid bilayer with embedded proteins.

Diffusion is the movement of particles from an area of higher concentration to lower concentration. Osmosis is a special case of diffusion, referring to the movement of water across a selectively permeable membrane.

The cell wall is a rigid layer outside the cell membrane in plants, fungi, and bacteria. In plants, it is made of cellulose and provides structural support and protection.

The nucleus contains the cell's genetic material (DNA) organized into chromosomes. It is enclosed by a nuclear membrane and directs all cellular activities.

Mitochondria are organelles that perform cellular respiration, converting glucose and oxygen into ATP (Adenosine Triphosphate), the cell's main energy currency. They possess their own DNA.

Found in plant cells, chloroplasts are the site of photosynthesis. They use sunlight, water, and carbon dioxide to produce glucose and oxygen, as shown by the equation: $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$.

The ER is a network of membranes. Rough ER (RER) is studded with ribosomes for protein synthesis, while Smooth ER (SER) synthesizes lipids and detoxifies substances.

The Golgi apparatus acts like a post office, modifying, sorting, and packaging proteins and lipids from the ER into vesicles for delivery to other destinations.

Ribosomes are small organelles responsible for synthesizing proteins. They can be found freely in the cytoplasm or attached to the rough endoplasmic reticulum.

Lysosomes are membrane-bound vesicles containing powerful digestive enzymes. They break down cellular waste, damaged organelles, and foreign particles.

Vacuoles are membrane-bound sacs used for storage. Mature plant cells have a large central vacuole that stores water and helps maintain cell rigidity (turgor pressure).

Mitosis is a type of cell division where one parent cell divides to produce two genetically identical daughter cells. It is crucial for growth, repair of tissues, and asexual reproduction.

Meiosis is a two-step division process that produces four gametes (sperm or egg cells), each with half the number of chromosomes as the parent cell. This process is essential for sexual reproduction.

In multicellular organisms, cells are organized into hierarchical levels of complexity: Cells form Tissues, tissues form Organs, organs form Organ Systems, and organ systems make up an Organism.