Living Organisms: Characteristics, Classification & Kingdoms
Characteristics of Living Organisms
Movement: Change of position or place by an action.
Respiration: Chemical reactions in cells that break down nutrient molecules and release energy for metabolism.
Sensitivity: Capacity to react to stimuli presented by the environment.
Growth: Permanent increase in size and dry mass.
Reproduction: Processes that make more of the same kind of organism.
Excretion: Removal of waste products.
Nutrition: Taking in of materials for energy, growth, and development.
Viruses
- Viruses are not classified as living because they do not have the ability to complete these processes. Viruses are non-cellular and consist of genetic material surrounded by a protein coat. When they reach a target cell, they inject this genetic material into the cell, which is then replicated to reproduce the virus. This harms the target cell, which is unable to function normally.
Classification Systems
Species: Groups of organisms that can reproduce to produce fertile offspring.
Binomial System: Scientific naming of organisms made up of two parts: genus and species. For example, humans are classified as Homo sapiens.
Dichotomous Keys
Used to identify unfamiliar organisms.
Each key is made up of pairs of contrasting features.
Starts with general characteristics and moves on to more specific ones.
Classification and Evolutionary Relationships
Having a common ancestor makes two species of animal be part of the same group.
DNA helps in the classification of animals by studying their internal structure.
Kingdoms
The five kingdoms are Animal, Plant, Fungus, Prokaryote, and Protoctista. The features of cells can be used to help categorize organisms into one of these kingdoms. For example, animal cells do not contain a cell wall or chlorophyll, whereas plant cells do.
Features of cells:
● Cytoplasm – A jelly-like material within the cell in which reactions occur. The cytoplasm contains organelles such as the nucleus and ribosomes.
● Cell membrane – A thin membrane that surrounds the cell. It controls entry and exit of substances.
● DNA – Genetic material contained in the nucleus which codes for proteins.
● Ribosomes – Site of protein synthesis.
● Enzymes – Catalyze reactions such as respiration in the cell.
Animal Kingdom
Within the animal kingdom, organisms are further categorized into vertebrates and arthropods. Vertebrates are animals which contain a backbone, such as mammals, birds, reptiles, amphibians, and fish. Arthropods do not contain a backbone and are identified through their exoskeleton and segmented body. Arthropods include myriapods, insects, arachnids, and crustaceans.
Plant Kingdom
The plant kingdom is split into flowering and non-flowering plants.
There are two divisions of flowering plants: dicotyledons and monocotyledons, which are identified by their leaves.
Feature | Monocotyledon | Dicotyledon |
Leaf shape | Long and narrow | Broad |
Leaf veins | Parallel | Branching |
Cotyledons | One | Two |
Grouping of flower parts (Petals, sepals, and carpels) | Threes | Fives |
Non-flowering plants, such as ferns, reproduce through spores rather than by producing seeds. Ferns have well-developed stems, leaves, and roots.
Fungi
Made up of thread-like Hyphae. They reproduce by spores.
Prokaryotes
Microscopic organisms; they have no proper nucleus.
Protoctista
Single-celled organisms containing a nucleus.