The Nature and Variety of Living Organisms Comprehensive Study Guide
Characteristics of Living Organisms (Section )
The MRS C GREN Acronym: All living organisms share eight specific functions that define their nature and distinguish them from non-living matter. These can be categorized as follows:
Movement: The ability of an organism to change its position or place.
Reproduction: The process by which organisms produce offspring, which can occur through either sexual or asexual means.
Sensitivity: The capacity of an organism to detect stimuli in its environment (such as light) and provide appropriate responses to those stimuli.
Control: The ability of an organism to regulate and maintain its internal environment, a process known as homeostasis.
Growth: The permanent increase in the mass or size of an organism.
Respiration: The biochemical process used to produce energy; this can occur aerobically (with oxygen) or anaerobically (without oxygen).
Excretion: The removal of toxic materials and waste products that result from various chemical reactions within the body.
Nutrition: The absorption of nutrients used for various biological functions, primarily growth and tissue repair.
Eukaryotic Cell Structures and Functions (Section )
Definition of Eukaryotes: Organisms whose cells contain a nucleus and other membrane-bound organelles located within a plasma membrane.
Subcellular Structures and Their Roles:
Nucleus:
Function: Contains the genetic material (DNA), which serves as the code for producing specific proteins.
Structure: It is enclosed within a dedicated nuclear membrane.
Cytoplasm:
Function: A liquid substance where most chemical reactions take place.
Contents: It contains enzymes, which are biological catalysts (specific proteins) that increase the rate of chemical reactions. It also houses the various organelles.
Cell Membrane:
Function: Selectively controls the entry and exit of substances in the cell.
Structure: Features receptor molecules used for cell identification and communication.
Mitochondria:
Function: The primary site for aerobic respiration reactions, which provide the energy required by the cell.
Ribosomes:
Function: The site of protein synthesis.
Location: Often found attached to a structural network called the rough endoplasmic reticulum.
Variety of Eukaryotic Organisms: Plants and Animals
Plants:
Examples: Cereals such as maize, herbaceous legumes such as peas, or sunflowers.
Complexity: Multicellular organisms.
Photosynthesis: Cells contain chloroplasts which harbor chlorophyll pigments; these pigments absorb solar energy for photosynthesis.
Support Structures: They possess cell walls made of cellulose to provide strength and support.
Storage and Rigidity: They contain a permanent vacuole filled with cell sap, which maintains cell rigidity.
Carbohydrate Storage: Carbohydrates are stored in the form of starch.
Trophic Level: Plants are Autotrophs, meaning they synthesize their own food.
Animals:
Examples: Mammals such as humans and insects such as flies.
Complexity: Multicellular organisms.
Trophic Level: Animals are Heterotrophs and cannot photosynthesize.
Structural Differences: They do not possess cell walls.
Systemic Coordination: They have nervous systems used to coordinate movement and respond to the environment.
Carbohydrate Storage: Carbohydrates are stored in the form of glycogen.
Variety of Eukaryotic Organisms: Fungi and Protoctists
Fungi:
Structure: The body is generally organized into a mycelium, which consists of thread-like structures known as hyphae. These hyphae contain many nuclei.
Examples: Mucor and Mushrooms exhibit the typical hyphal structure; yeast is a single-celled exception.
Cell Wall Composition: Cell walls are composed of chitin.
Saprotrophic Nutrition: Fungi feed on dead organic matter via extracellular secretion of digestive enzymes. These enzymes break food down into smaller components outside the body, which are then absorbed by the fungus.
Carbohydrate Storage: May store carbohydrates as glycogen.
Protoctists:
Nature: These are single-celled organisms.
Animal-like Features: Examples include Amoeba, which typically live in pond water.
Plant-like Features: Examples include Chlorella, which possess chloroplasts.
Pathogenic Activity: Certain protoctists are harmful, such as Plasmodium, the organism responsible for causing Malaria.
Prokaryotic Organisms
Definition: Organisms that lack a nucleus and membrane-bound organelles.
Bacteria:
Physical Characteristics: Very small, single-celled organisms.
Examples:
Lactobacillus bulgaris: A rod-shaped bacterium used in the production of yogurt.
Pneumococcus: A spherical bacterium that acts as a pathogen, causing pneumonia.
Internal Anatomy: They lack a nucleus but contain a circular chromosome of DNA. They also contain cytoplasm, a cell membrane, and small rings of DNA called plasmids.
Cell Wall: Their cell walls are made of peptidoglycan.
Nutrition: While some can perform photosynthesis, most bacteria function as decomposers or parasites, feeding on other living or dead organisms.
Pathogens and Infectious Agents (Section )
Definition of Pathogens: Organisms that cause disease. These include certain fungi, bacteria, protoctists, and viruses.
Viruses:
Examples: Tobacco Mosaic Virus (TMV), which inhibits chloroplast formation; Influenza virus; and HIV (Human Immunodeficiency Virus), which leads to AIDS.
Nature: These are small particles (significantly smaller than bacteria) and are not considered living organisms.
Reproduction and Parasitism: They are obligate parasites that can only reproduce inside living cells. They can infect every type of living organism.
Mechanism of Infection: A virus hijacks the cellular machinery of the host to produce millions of copies of itself. The host cell eventually bursts (cell bursting), allowing the virus to spread to other cells.
Structure: They lack a cellular structure, consisting instead of a protein coat and one type of nucleic acid (either DNA or RNA).
Bacterial Pathogens:
Example: Salmonella, which causes food poisoning.
Reproduction: They reproduce rapidly through a process called binary fission.
Disease Mechanism: They produce toxins that cause damage to host cells.
Protist Pathogens:
Example: Plasmodium, which causes malaria.
Nature: Parasitic organisms that utilize animals as hosts.
Fungal Pathogens:
Example: Athlete’s foot.
Spread: They produce spores that can be dispersed through the wind or through physical contact between people.
Treatment: Fungal infections are typically treated with fungicides.