chapter 4

• Cell


  The smallest structures capable of maintaining life and reproducing, compose all living things
• The human body, which is made up of numerous cells, begins as a single, newly fertilized cell
• Almost all human cells are microscopic in size
• One average-sized adult body consists of 100 trillion cells
• Cell structure


  • Early biologists saw cells as simple membranous sacs containing fluid and a few floating particles
  • Today's biologists know that cells are infinitely more complex
• Generalized cell


  Includes features from all cell types
• Cell


  Consists of three parts: the cell membrane, the nucleus, and, between the two, the cytoplasm
• Cell membrane


  • Separates the material outside the cell, extracellular, from the material inside the cell, intracellular
  • Maintains the integrity of a cell and controls passage of materials into and out of the cell
• Cell membrane composition

  • A double layer of phospholipid molecules
  • Proteins provide structural support, form channels, act as receptor sites, function as carrier molecules, and provide identification markers
• Nucleus


  • The control center of the cell
  • Contains DNA, the genetic material of the cell
  • The nucleolus is the site of ribosome formation
• Cytoplasm

  • The gel-like fluid inside the cell
  • The medium for chemical reactions
  • Provides a platform for organelles to operate
• Cytoplasmic organelles

  • Mitochondrion
  • Ribosomes
  • Endoplasmic reticulum
  • Golgi apparatus
  • Lysosomes
• Cell function


  • Determined by the nature of the proteins present
  • Includes movement of substances across the cell membrane, cell division, and protein synthesis
• Movement of substances across the cell membrane

  1. Simple diffusion

  2. Osmosis

  3. Filtration

  4. Active transport

  5. Endocytosis

  6. Exocytosis
• Cell division

  1. Mitosis

  2. Meiosis
• Somatic cells reproduce by mitosis, which results in two cells identical to the one parent cell
• Meiosis is a special type of cell division that occurs in the production of the gametes, or eggs and sperm
• DNA replication and protein synthesis

  1. DNA in the nucleus directs protein synthesis in the cytoplasm

  2. Messenger RNA carries the genetic information from the DNA in the nucleus to the sites of protein synthesis in the cytoplasm
• Proteins that are synthesized in the cytoplasm function as structural materials, enzymes that regulate chemical reactions, hormones, and other vital substances
• A gene is the portion of a DNA molecule that controls the synthesis of one specific protein molecule
• Cells, tissues, organs, and systems are the four major kinds of structures that compose the human body
• Major human body systems

  • Skeletal
  • Muscular
  • Nervous
  • Endocrine
  • Cardiovascular
  • Lymphatic
  • Respiratory
  • Digestive
  • Urinary
  • Reproductive
• Homeostasis


  • A state of relative constancy of the body's internal environment
  • Depends on the body's ceaselessly carrying on many activities to respond to changes, exchange materials, metabolize foods, and integrate all of the body's diverse activities
• Basic processes of life


  • Organization
  • Metabolism
  • Responsiveness
  • Movement
  • Reproduction
  • Growth
  • Differentiation
  • Respiration
  • Digestion
  • Excretion
• Physical factors from the environment that are required for life include water, oxygen, nutrients, heat, and pressure