Visualizing Human Bio Ch 4

Cells

Building blocks of life; humans have trillions of them which differ in shape and size; highly organized and dynamic.

Cell theory

All living things are composed of cells; all cells arise from preexisting cells through cell division; cells contain hereditary material, which they pass to daughter cells during cell division; the chemical composition of all cells is quite similar; the metabolic processes associated with life occur within cells.

Basic parts of the cell

A barrier called the plasma membrane (in animals) or cell wall (in plants and bacteria); a fluid called cytosol, which supports multiple types of organelles, each with a function vital to the life of the cell; a nucleus.

Prokaryotic cells

Early life forms were prokaryotic (meaning 'before nucleus'), adapting to extreme environments; no internal membrane-bound compartments (only genetic material as organelles); no nucleus; genetic material floats in their cytoplasm, anchored at one spot to the cell wall; they survive as bacteria and archaebacteria.

Eukaryotic cells

Eukaryotic (which means, 'true nucleus') cells have a nucleus & organelles; plant, animal, and fungal cells are eukaryotic; believed to have evolved from prokaryotic ancestors, which took in smaller, energy-producing prokaryotic cells.

Plant cells

Plant cells have organelles not found in animal cells; the central vacuole maintains cell pressure; chloroplasts produce energy through photosynthesis; many believe that chloroplasts originated as bacteria that were 'adopted' by the plant cell.

Cell membrane

Separates the cell from the extracellular fluid; composed of two layers of phospholipids, interspersed with proteins, fats, and sugars; phospholipids are arranged in a double layer, or bilayer, with the hydrophilic (water-loving) polar heads oriented toward the aqueous environment both inside and outside the cell; the hydrophobic (water-fearing) non-polar, lipid portion of the molecules is in the center; proteins and lipids associated with the cell membrane have sugars attached to their external surface (glycoproteins and glycolipids); semipermeable barrier that allows nutrients to enter the cell and waste products to exit it (movement is either passive or active); integral (transmembrane) and channel proteins.

Passive transport

Passive movement includes filtration, diffusion, and facilitated diffusion, none of which require the cell to expend energy.

Diffusion

The movement of a substance from an area of high concentration towards an area of lower concentration; diffusion of water across a semi-permeable membrane is osmosis.

Osmosis

Water cannot cross the phospholipid bilayer, so it must travel through proteins; usually, the extracellular fluid is isotonic to the cells (aka has the same osmotic pressure), and water flows equally into and out of the cell through transport proteins; a hypotonic solution (water with a lower concentration of solutes than the cytosol) may cause a cell to burst; in contrast, a hypertonic solution (with a higher concentration of solutes) may cause a cell to shrivel up.

Facilitated diffusion

A process that allows substances to cross membranes with the assistance of special proteins.

Transport proteins

Proteins in the lipid bilayer that serve as channels for solutes to enter and exit the cell.

Simple diffusion

Transport of solutes across the membrane down their concentration gradients without expending energy.

Active transport

Process that uses energy to move molecules across membranes against their concentration gradient.

ATP

Energy source derived from the breakdown of adenosine triphosphate, used in active transport.

Examples of active transport

Uptake of digested nutrients from the small intestine, collecting iodine in thyroid gland cells, and returning sodium ions to the blood by the kidneys.

Endocytosis

Process of taking extracellular molecules and particles into the cell via vesicle formation.

Exocytosis

Process used to remove secretory products or waste products from the cell.

Intramembrane pumps

Transport proteins that move ions or small molecules across the plasma membrane in either direction.

Sodium/Potassium ATPase

A common reciprocal pump that moves two potassium ions into the cell while pumping three sodium ions out.

Organelles

Components of a cell that play a role in regulating the life and death of cells.

Flagella

Single, long whiplike structures that propel the cell forward; the only human cell that moves by flagellum is the sperm.

Cilia

Shorter extensions that look like hairs or eyelashes; they line the upper respiratory tract and fallopian tubes to move mucus and eggs.

Nucleus

The largest organelle in a cell that contains the cell's genetic library, covered by a phospholipid membrane.

Nuclear envelope

The double phospholipid bilayer surrounding the nucleus, punctuated by nuclear pores.

Mitochondria

Bean-shaped organelles that convert digested nutrients into usable energy (ATP) and require oxygen.

Cellular respiration

Processes in the mitochondria that produce ATP and carbon dioxide.

Cell communication

Essential process for maintaining stability and organization inside the human body, allowing cells to function as a tissue.

Chemical messengers

Signals sent from cell to cell that include information about timing of cell divisions and health of adjacent cells.

Signal transmission routes

Three different routes for cell communication, varying in speed and distance.