Cell Theory: Prokaryotic and Eukaryotic Cells
Principles of Cell Theory
- Cells are the basic unit of living things.
- Every cell comes from another cell.
- Preexisting cells transmit information from one generation to another.
Prokaryotic Cells
Unicellular, prokaryotic DNA is dispersed in the cytoplasm. They have no organelles except for ribosomes, a cell wall, and a plasma membrane that folds. Some have flagella.
Structures:
- Plasma membrane
- Ribosomal DNA
- Cell wall
- Cytoplasm
- Flagella
Eukaryotic Cells
Eukaryotic cells can be unicellular or multicellular. They are found in animals, plants, fungi, protozoa, and algae. DNA is inside the nucleus. They have a cytoskeleton, endoplasmic reticulum, ribosomes, mitochondria, Golgi apparatus, vacuoles, and lysosomes.
Animal Cells
Animal cells have centrioles, no cell wall, and small vacuoles. They exhibit heterotrophic nutrition.
Plant Cells
Plant cells have a cell wall, chloroplasts, and large vacuoles. They exhibit autotrophic nutrition. They are found in plants and algae.
Organelles
Ribosomes: Consist of two subunits. Their function is to help in the protein-making process.
Vacuole: Vesicles that store nutrients, water, waste substances, and reserve substances.
Mitochondria: Have a double membrane. They perform cellular respiration to get energy from nutrients and oxygen. Energy is stored in chemical bonds of ATP. When the cell needs energy, ATP is broken down, releasing energy.
Endoplasmic Reticulum: A network of membranous sacs that stores and transports substances.
Golgi Apparatus: Membranous sacs that receive substances from the endoplasmic reticulum. These substances are transported to the exterior of the cell through the plasma membrane via vesicles.
Lysosome: Vesicles full of digestive substances. They discharge substances into the vacuoles to digest food and obtain nutrients.
Centrioles: Found exclusively in animal cells. There are two mutually perpendicular centrioles involved in the appearance of chromosomes during cell division.
Chloroplast: Found exclusively in plant cells. They are elongated and have a double membrane.
Nucleus: The nucleus has two phases: interphase (growth) and division.
Parts:
- Nuclear membrane: Double membrane with ribosomes attached.
- Nucleolus: Where the components of ribosomes are manufactured.
- DNA: Chromosomes.
- Chromatin: Condensed chromatin during cell division.
Function of the nucleus: Contains the genetic information passed on to daughter cells and controls all cellular processes.
Cellular Functions
Nutrition: The cell exchanges matter and energy through the plasma membrane. Small substances pass directly through the membrane. Large molecules pass through protein channels or vesicles. Large molecules exit the cell via exocytosis and enter via endocytosis.
Anabolism: Formation of large molecules from smaller ones.
Catabolism: Large molecules break into smaller ones, releasing energy.
Heterotrophic nutrition: Complex molecules are broken down into simpler ones.
Autotrophic nutrition: Complex molecules are formed from simpler ones, requiring energy.
Relationship: Responding to a stimulus.
Reproduction: Capacity of a cell to divide into two or more cells equal to the mother cell. The cell duplicates its DNA before dividing to pass genetic information to daughter cells.
Bipartition: The mother cell divides into two equal daughter cells by strangulation. Example: Protozoa and bacteria.
Budding: A daughter cell originates from a bud of the stem cell.
Sporulation: The stem cell divides internally into spores that are then released.