Levels of Organization in the Human Body

Cells

Basic unit of all living things.

Tissues

A group of cells of similar structure working together for a specific function.

Organs

A group of tissues working together for a specific function.

System

A group of organs working together for a specific function.

Epithelial tissue

Consists of tightly packed sheets of cells covering surfaces and lining body cavities.

Simple Epithelial

Epithelial tissue that is a single layer, e.g., alveoli of lungs.

Layered Epithelial

Epithelial tissue that is multiple layers, e.g., skin.

Connective Tissue

Consists of cells widely spaced with large amounts of matrix surrounding cells and may also have embedded fibres.

Types of Connective Tissue

Includes cartilage, ligaments, tendons, bone tissue, adipose (fat) tissue, and fluid: blood.

Function of Connective Tissue

Joining and supporting other tissues.

Muscular Tissue

Tissue that can contract and relax to bring about movement.

Skeletal Muscle

Striated muscle attached to skeleton; action is under voluntary control.

Smooth Muscle

Found in blood vessels, digestive tract, uterus, etc.; tissue is not striated, cells are tapered, and action is involuntary.

Cardiac Muscle

Found in the heart; tissue is striated and branched, and action is involuntary.

Nervous Tissue

Transmits nerve impulses.

Neurons

Nerve cells that contain long cytoplasmic extensions.

Cell organelles

Structures within the cell that maintain life processes and require the input of materials and the removal of wastes.

Cell membrane

Protection and regulates movement of materials into and out of the cell.

Cytoplasm

Suspends organelles within the cell.

Ribosomes

Site of protein synthesis.

Nucleus

Control of cellular activity; contains genetic blueprint.

Mitochondria

Site of aerobic respiration.

Lysosome

Sac containing digestive enzymes which acts on contents of vesicles.

Golgi apparatus

Modification and packaging of proteins ready for secretion from the cell.

Endoplasmic reticulum

Site of chemical reactions and cellular transport system; can be rough (with ribosomes) or smooth (no ribosomes).

Centrioles

Formation of spindle fibres in cellular division.

Fluid mosaic model

Describes the cell membrane as a phospholipid bilayer with embedded proteins, components in constant motion.

Phospholipid molecule

Composed of a hydrophilic phosphate head and a hydrophobic lipid tail.

Passive transport

Movement of substances from high concentration to low concentration, requiring no energy expenditure.

Simple diffusion

Movement of small or fat-soluble substances directly through the cell membrane.

Facilitated diffusion

Transport of substances assisted by carrier or channel proteins moving down a concentration gradient.

Osmosis

Movement of water from high-water concentration to low-water concentration across a semi-permeable membrane.

Active transport

Movement of substances from low concentration to high concentration, against the concentration gradient, requiring energy (ATP).

Exocytosis

Transport of materials out of the cell.

Endocytosis

Transport of materials into the cell.

Phagocytosis

Taking in of solid material.

Pinocytosis

Taking in of liquid material.

Surface area to volume ratio

The ratio that affects the rate of exchange of materials across the cell membrane; larger ratios lead to faster exchange.

Concentration gradient

The difference in concentration between two areas; greater differences lead to faster rates of exchange.

Molecule size

The larger the size of the molecule, the slower the diffusion rate.