Biology Theories: Cell, Gene, Evolution

Cell Theory

• All living organisms are composed of cells.
• Cells are the fundamental units of life.
• Cells arise from pre-existing cells.
• Cells share similar chemical composition and metabolic activities.
• Energy transfer within cells occurs.
• All basic chemical and physiological functions are carried out inside cells.
• Cell activity depends on the activities of sub-cellular structures.

Gene Theory

• Characteristics of living organisms are controlled by genes passed on from one generation to the next.
• Genetic information is stored, expressed, and utilized by the genome.
• Gene expression mediates the growth and behavior of organisms.
• DNA is passed on from one generation to the next.

Evolutionary Theory

• Characteristics of living organisms change over time due to natural selection and adaptation.
• Diversity of life has evolved over time through mutation, selection, genetic change, and inheritance.
• This theory is supported by various fields including molecular genetics, developmental biology, biochemistry, and paleontology.

Homeostasis

• Homeostasis is the tendency to maintain equilibrium between interdependent elements of processes and systems.
• Positive and negative feedback mechanisms are essential for maintaining homeostasis.

Laws of Thermodynamics

• Energy can neither be created nor destroyed, but can be transferred from one form to another.
• Within an isolated system, entropy always increases.

Prokaryotic Cells

• Lack a nucleus and other membrane-bound organelles.
• DNA is a single circular chromosome without histones.
• The only organelle present is the ribosome.
• Cell division occurs through binary fission.
• They have a cell wall and a plasma membrane.
• They are usually single-celled.
• Examples include bacteria and archaea.

Eukaryotic Cells

• Have a nucleus and other membrane-bound organelles.
• DNA is organized in multiple linear chromosomes with histones.
• Have a complex cytoplasm and cytoskeleton.
• Cell division occurs through mitosis and meiosis.
• They have a cell wall in some cases (plants and fungi).
• They have a plasma membrane.
• They can be single-celled or multicellular.
• Examples include protists, fungi, plants, and animals.

Unicellular vs. Multicellular Organisms

• Unicellular organisms carry out all functions of life within one cell.
• Multicellular organisms have specialized cells that perform different functions and are organized into tissues.

Cell Specialisation

• Cells in multicellular organisms specialize in performing particular jobs.
• This specialization allows for efficient and complex functioning.
• Compartmentalization within cells creates specialized microenvironments.

Functional Barriers: Membranes

• Membranes are semi-permeable barriers that enable compartmentalization.
• They regulate the transport of molecules entering and exiting compartments.

Nucleus

• The nucleus contains DNA.
• It is enclosed by the nuclear membrane.
• Nuclear pores control transport into and out of the nucleus.
• It is the site of DNA replication and RNA transcription.

Cytoskeleton

• Provides structural support, enables movement, and facilitates organization within the cell.
• It is composed of microtubules, actin filaments, and intermediate filaments.

Protein Synthesis and Trafficking

• Protein synthesis occurs on ribosomes attached to the rough endoplasmic reticulum (RER).
• Proteins are processed and secreted by the Golgi apparatus.
• Lipid synthesis occurs in the smooth endoplasmic reticulum (SER).

Mitochondria and Chloroplasts

• Mitochondria are the sites of ATP production (energy).
• Chloroplasts are involved in photosynthesis and energy production.
• Both are double-membraned organelles.

Lysosome and Proteosome

• Lysosomes degrade internalized material and endogenous proteins.
• Proteosomes degrade proteins.

Cell-to-Cell Contacts

• Adhesive molecules enable cells to maintain contact and interact with the extracellular matrix.
• Integrins link the cytoskeleton to the extracellular matrix.
• Adherins junctions and desmosomes provide mechanical support and signaling.
• Gap junctions allow communication between cells through small molecule passage.
• Tight junctions form junctions that prevent even ion passage.

Test your knowledge on three fundamental biological theories: Cell Theory, Gene Theory, and Evolutionary Theory. Explore how cells function, how traits are inherited, and how species evolve over time. This quiz covers key concepts and principles that are foundational to understanding biology.