Glossary: C-E

Cell

Definition: The smallest structural and functional unit of an organism, which is typically microscopic and consists of cytoplasm and a nucleus enclosed in a membrane. All living organisms are composed of one or more cells. Cells are the basic building blocks of life.

Examples:

• Animal Cell: A typical eukaryotic cell, enclosed by a plasma membrane and containing a membrane-bound nucleus and other organelles.
• Plant Cell: A eukaryotic cell that has a cell wall, chloroplasts, and a large central vacuole, in addition to the structures found in animal cells.
• Bacterial Cell: A prokaryotic cell that lacks a nucleus and other membrane-bound organelles.

Context/Function: Cells are responsible for carrying out all of the processes of life. They take in nutrients, convert them into energy, and carry out specialized functions. Cells also contain the body's hereditary material and can make copies of themselves.

Chlorophyll

Definition: A green pigment, present in all green plants and in cyanobacteria, responsible for the absorption of light to provide energy for photosynthesis. Chlorophyll is found in the chloroplasts of plant cells.

Examples:

• Chlorophyll a: The most common type of chlorophyll, found in all photosynthetic organisms.
• Chlorophyll b: A type of chlorophyll that is found in plants and green algae.
• Chlorophyll c: A type of chlorophyll that is found in diatoms and brown algae.

Context/Function: Chlorophyll is essential for photosynthesis, the process by which plants use sunlight to convert carbon dioxide and water into glucose and oxygen. This process provides the energy for most ecosystems on Earth.

Chromosome

Definition: A thread-like structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes. Chromosomes are not visible in the cell’s nucleus—not even under a microscope—when the cell is not dividing.

Examples:

• Humans: Have 23 pairs of chromosomes, for a total of 46.
• Fruit Flies: Have 4 pairs of chromosomes.
• Dogs: Have 39 pairs of chromosomes.

Context/Function: Chromosomes are essential for cell division and the transmission of genetic information from one generation to the next. They ensure that DNA is accurately copied and distributed.

DNA (Deoxyribonucleic Acid)

Definition: A self-replicating material which is present in nearly all living organisms as the main constituent of chromosomes. It is the carrier of genetic information. The structure of DNA is a double helix, which resembles a twisted ladder.

Examples:

• Gene: A segment of DNA that codes for a specific protein.
• Genome: The complete set of DNA in an organism.
• Genetic Code: The set of rules by which information encoded in genetic material (DNA or RNA sequences) is translated into proteins.

Context/Function: DNA contains the instructions for building and maintaining an organism. It is passed from parents to offspring, and it is the basis of heredity.

Ecosystem

Definition: A biological community of interacting organisms and their physical environment. Ecosystems can be of any size, from a small pond to a large forest. They are complex and dynamic systems that are constantly changing.

Examples:

• Forest Ecosystem: A community of trees, plants, animals, and microorganisms that live in a forest.
• Coral Reef Ecosystem: A diverse underwater ecosystem that is built by corals.
• Desert Ecosystem: A community of plants and animals that are adapted to living in a dry, arid environment.

Context/Function: Ecosystems provide a variety of services that are essential for human well-being, such as clean air and water, food, and medicine. They also play an important role in regulating the Earth's climate.

Enzyme

Definition: A substance produced by a living organism which acts as a catalyst to bring about a specific biochemical reaction. Enzymes are proteins that have a specific three-dimensional shape. This shape allows them to bind to a specific molecule, called a substrate, and catalyze a specific reaction.

Examples:

• Digestive Enzymes: Break down food into smaller molecules that can be absorbed by the body.
• Metabolic Enzymes: Catalyze the reactions that produce energy and build new molecules.
• DNA Polymerase: An enzyme that synthesizes DNA molecules from deoxyribonucleotides.

Context/Function: Enzymes are essential for all biochemical reactions that occur in living organisms. They speed up the rate of these reactions, allowing them to occur at a rate that is compatible with life.

Eukaryote

Definition: An organism consisting of a cell or cells in which the genetic material is DNA in the form of chromosomes contained within a distinct nucleus. Eukaryotes include all living organisms other than the eubacteria and archaebacteria.

Examples:

• Animals: Multicellular eukaryotes that are heterotrophic.
• Plants: Multicellular eukaryotes that are autotrophic.
• Fungi: Multicellular or unicellular eukaryotes that are heterotrophic.
• Protists: A diverse group of eukaryotic microorganisms.

Context/Function: Eukaryotic cells are more complex than prokaryotic cells. They have a variety of organelles that allow them to carry out a wide range of functions. The evolution of the eukaryotic cell was a major step in the history of life on Earth.

Evolution

Definition: The process by which different kinds of living organisms are thought to have developed and diversified from earlier forms during the history of the earth. Evolution is driven by natural selection, which is the process by which organisms that are better adapted to their environment are more likely to survive and reproduce.

Examples:

• The evolution of the horse: The horse has evolved from a small, dog-sized animal to the large, powerful animal that it is today.
• The evolution of antibiotic resistance in bacteria: Bacteria have evolved to become resistant to antibiotics, which is a major public health problem.
• The evolution of the human brain: The human brain has evolved to become larger and more complex, which has allowed us to develop language, culture, and technology.

Context/Function: Evolution is the central organizing principle of biology. It explains the diversity of life on Earth and the relationships between different organisms. Understanding evolution is essential for understanding the world around us.