Cell Membranes, Transport, Surface Extensions, and Cell Junctions

Comprehensive Question and Answer flashcards reviewing cell membrane structure, organelles, cell surface extensions, transport mechanisms, membrane proteins, chemical signaling, and cell junction types.

What term describes a molecule that possesses both hydrophilic and hydrophobic parts?

Amphipathic

Which types of molecules can and cannot cross the cell membrane lipid bilayer?

Hydrophobic molecules can cross the cell membrane to enter or exit, while hydrophilic molecules cannot cross.

What is the definition of cytoplasm?

The material located between the plasma membrane and the nucleus.

What is the cytosol (intracellular fluid)?

The clear gel embedding the other cellular components, also referred to as intracellular fluid (ICF).

What are cellular inclusions?

Accumulated cell products within the cell, such as lipids, pigments, and bacteria.

What is the primary function of microvilli, and how much can they increase surface area?

Microvilli serve primarily to increase surface area, providing up to $40$ times more surface area in cells specialized for absorption, such as in the small intestine.

What are the primary functions of cilia in human respiratory and reproductive tracts?

They help move mucus from the lungs and trachea up to the throat, and help move the egg through the fallopian tubes to the uterus.

What is the only human cell type that possesses a functional flagellum?

The sperm cell.

What are pseudopods, and how are they used by cells?

Pseudopods are cytoplasm-filled extensions ranging from filamentous to blunt fingerlike processes that cells use to crawl and engulf particles.

What is osmosis?

The diffusion of water through a specific channel protein (aquaporin) or directly through the lipid bilayer.

How does facilitated diffusion transport solutes across the cell membrane?

A solute binds to a receptor site on a transport protein, inducing a shape change in the protein that releases the solute on the other side of the membrane down its concentration gradient.

What are the distinguishing characteristics of active transport?

Active transport requires a transporter protein, uses energy (ATP), can move substances up their concentration gradient, and can create concentration gradients.

What cellular process is shown in this $100,000\times$ photomicrograph?

A secretory vesicle releasing its contents by exocytosis.

What is the difference between phagocytosis and pinocytosis?

Phagocytosis involves engulfing particles using pseudopods, whereas pinocytosis involves the uptake of fluid droplets into pinocytotic vesicles.

What type of membrane protein functions as a cell-identity marker?

A glycoprotein that distinguishes the body's own cells from foreign cells.

How do gated ion channels differ from non-gated ion channels?

Non-gated ion channels are constantly open to allow ions through, whereas gated ion channels open and close to permit ion passage only at certain times.

What four forms of chemical signaling are depicted in this summary diagram?

Autocrine, signaling across gap junctions, paracrine, and endocrine signaling.

What is the function of tight junctions in epithelial tissue?

They act as impermeable junctions that prevent molecules from passing through the intercellular space and allow epithelial cells to be functionally asymmetric (apical vs. basolateral).

What are desmosomes?

Anchoring junctions that bind adjacent cells together and help form an internal tension-reducing network of fibers.

What are gap junctions, and what protein channels do they use?

Communicating junctions that allow ions and small molecules to pass between cells for intercellular communication, using channel structures called connexons.