Cell Biology: Functions, Theory, and Classification
What are Vital Functions?
Vital functions are the processes that sustain life.
Some functions specialize in groups of cells in a multicellular organism, such as a human.
These include nutrition, relationship (response to stimuli), and reproduction.
Single-celled vs. Multicellular Organisms
The main difference in functioning between a cell in a single-celled organism and one in a multicellular organism is that a single cell must perform all vital functions individually and independently. In contrast, multicellular organisms are more efficient because their cells cooperate, are integrated, and specialized.
Functioning of Multicellular Organisms
Multicellular organisms function like a company, where each worker specializes in a particular job, increasing productivity.
Cell Theory and Technological Advancement
The progress of cell theory is linked to technological advances because the small size of cells required the invention and improvement of microscopes and microscopic technologies for their study.
Four Basic Points of Cell Theory
- All living organisms are composed of one or more cells.
- The chemical reactions of vital functions occur within cells.
- Cells arise from other pre-existing cells.
- Cells contain hereditary material with information that ensures the continuity of species from one generation to another.
Cajal’s Contribution to Cell Theory
Cajal’s techniques for staining nervous tissue demonstrated that nerves are made of cells, allowing cell theory to be generalized to the entire living world.
Oldest Known Fossils
The oldest known fossils are prokaryotic cells, whose representatives are today’s bacteria, dating back about 3,500 million years.
Structure of Bacteria
Bacteria are very simple organisms. They have a cell membrane surrounded by a thicker cell wall, which consists of cellulose. This defining feature makes up a kingdom on its own. They do not have a true nucleus surrounded by an envelope; their DNA is free within the cell, scattered in the cytoplasm, which contains only ribosomes for protein synthesis.
Environments Where Bacteria Can Live
Bacteria can live in a large number of environments, including freshwater, saltwater, soil, glaciers, and within other organisms.
Cellular Nutrition
Cellular nutrition consists of the ingestion of food and its transformation into useful substances within the cell. Unprocessed substances are expelled through egestion.
Role of Relationship (Response to Stimuli)
The role of relationship is the ability to receive information from the environment through stimuli and respond to them appropriately.
Cytokinesis
Cytokinesis consists of the division of the cell membrane and cytoplasm through strangulation.
Phases of Cell Division
The phases of cell division are: Prophase, Metaphase, Anaphase, and Telophase.
Mitosis
Mitosis consists of the division and distribution of chromosomes to two daughter cells.
External Digestion
External digestion involves pouring digestive juices abroad to absorb the nutrients from the digested food.
Classification of Living Things
The classification of living things includes: Monera, Animal, Vegetable (Plantae), Fungi, and Protoctista.
Characteristics of Kingdoms
Monera
- Prokaryotes
- Autotrophic and heterotrophic nutrition
- Unicellular
Animal Kingdom
- Eukaryotic cells
- Heterotrophic nutrition
- Multicellular (with tissues)
- Internal digestion
Vegetable (Plantae) Kingdom
- Eukaryotic cells
- Autotrophic nutrition
- Multicellular (with tissues)
- Internal digestion
Fungi Kingdom
- Eukaryotic cells
- Heterotrophic nutrition
- Unicellular or multicellular (without tissues)
- External digestion
Protoctista Kingdom
- Eukaryotic cells
- Autotrophic and heterotrophic nutrition
- Unicellular or multicellular (without tissues)
- Internal digestion
Autotrophic Nutrition
Autotrophic nutrition is performed by organisms that can make their own food.
Main Characteristic of Prokaryotic Cells
The main characteristic of prokaryotic cells is that they do not have a true nucleus surrounded by an envelope; their DNA is free within the cell, dispersed in the cytoplasm, which contains only ribosomes.