Cell Membrane and Nucleus Quiz

Cell Membrane

• The cell membrane is a thin barrier composed of lipids and proteins that separates the cell's contents from its surroundings.
• It acts as a physical barrier and selectively controls the movement of molecules between the intracellular fluid (ICF) and extracellular fluid (ECF).
• The cell membrane consists of a lipid bilayer with embedded proteins.
• The lipid bilayer is composed of phospholipid molecules, with hydrophilic heads facing the watery environments inside and outside the cell, and hydrophobic tails facing inwards.
• Membrane proteins can be peripheral (loosely attached) or integral (embedded within the lipid bilayer).
• Transmembrane proteins extend all the way through the membrane.
• Membrane proteins play various roles, including receptors for hormones, pumps for transporting substances, ion channels, adhesion molecules, and cell recognition antigens.

Nucleus

• The nucleus is typically the largest single cell component.
• It's surrounded by a nuclear envelope perforated by nuclear pores.
• The nucleus houses DNA, the genetic material, which directs protein synthesis and serves as the genetic blueprint during cell replication.

Cytoplasm

• Cytoplasm contains various organelles, each with a specific function.
• Cytoskeleton: An interconnected system of protein fibers and tubes that provides cell shape, framework, and regulates movements.
• Cytosol: Intracellular fluid (ICF), a semi-liquid, gel-like mass within the cell.
• Organelles: Structures suspended in the ICF that work in an integrated manner.

Organelles

• Endoplasmic reticulum (ER): A series of membranes containing protein and lipid manufacturing factories (ribosomes). Ribosomes produce proteins.
• Golgi complex: Processes, sorts, packages, and directs raw proteins to their proper destinations.
• Lysosomes: Contain powerful enzymes that break down organic molecules and remove worn-out organelles.
• Peroxisomes: House oxidative enzymes that degrade toxic wastes produced by cells or ingested toxins.
• Mitochondria: The powerhouses of the cell, extracting energy from food nutrients and transforming it into usable ATP (adenosine triphosphate) for cellular activities. The number varies depending on the cell's energy needs.
• Ribosomes: Make proteins by translating RNA into chains of amino acids, following the sequence controlled by DNA. They exist free in the cytosol or attached to the rough ER.

Levels of Structural Complexity

• Chemical Level: Includes all chemical substances necessary for life, such as atoms, ions, and molecules.
• Cellular Level: Cells are the basic structural and functional units of the human body, with various types (e.g., muscle, nerve, blood).
• Tissue Level: A tissue is a group of cells performing a specific function. The basic tissue types in the human body include epithelial, muscle, nervous, connective tissues, and glands.
• Organ Level: An organ consists of two or more tissues working together for a specific function (e.g., heart, liver, stomach).
• System Level: An association of organs with a common function. The human body has 11 major systems, including digestive, nervous, endocrine, circulatory, respiratory, urinary, reproductive, muscular, lymphatic, skeletal, and integumentary (skin and glands).

Body Composition

• The average young adult male has 18% of body weight as protein, 7% as minerals, 15% as fat, and 60% as water.

Body Fluids and the Internal Environment

• Intracellular fluid (ICF): Located inside cells.
• Extracellular fluid (ECF): Located outside cells, further divided into:
  • Interstitial fluid: Surrounds cells.
  • Blood plasma: The liquid component of blood.
• The volume of total body water is roughly 60% of body weight in men and 50% in women.

Membrane Transport

• Membrane Permeability: The ability of a membrane to allow substances to cross. Membranes can be permeable (allow everything), impermeable (allow nothing), or selectively permeable (allow some substances).
• Factors influencing membrane permeability:
  • Solubility of the particle in lipids (lipid-soluble particles pass through more easily).
  • Size of the particle.

Types of Membrane Transport

• Passive Transport (Diffusion): Does not require energy; relies on the kinetic movement of molecules, using energy from molecular movement.
  • Simple Diffusion: Molecules or ions move through membrane openings or intermolecular spaces without interacting with carrier proteins.
  • Facilitated Diffusion: A carrier protein facilitates the movement of molecules across the membrane.
  • Osmosis: The movement of water across a selectively permeable membrane from a region of high water concentration (low solute concentration) to a region of low water concentration (high solute concentration). Water tends to move from areas of high water potential to low water potential.
• Active Transport: Requires energy (ATP) to move substances across the membrane against their concentration gradient.
  • Primary Active Transport: Uses energy directly from ATP to move substances.
  • Secondary Active Transport: Uses the energy stored in the concentration gradient of one substance to move another substance.

Active Transport Examples

• Na+/K+ pump: A primary active transport system that pumps Na+ out of the cell and K+ into the cell.
• Glucose transport in the intestine: A secondary active transport system that uses the Na+ gradient, established by the Na+/K+ pump, to move glucose into the cells.

Homeostasis

• Homeostasis describes the state of maintaining nearly constant conditions in the internal environment.
• It is essential for the survival of all organisms.
• Each organ and tissue contributes to maintaining homeostasis by performing specific functions.
• Examples:
  • The lungs provide oxygen to the ECF to replenish oxygen used by cells.
  • The kidneys maintain constant ion concentrations.
  • The gastrointestinal system provides nutrients.