Chapter 8

 The boundary between the cell and its environment  Controls what enters and exits the cell (selective permeability) - nutrients, wastes, water  Maintain homeostasis

 Movement of particles from high  low concentration  Happens because of the random movement of particles  Three things affect the rate of diffusion: - concentration (how much), temperature, and pressure

 Diffusion results in an evenly distributed solution - when this happens its called dynamic equilibrium

 Osmosis is the diffusion of water.  From high  low concentration  In a cell, water always tries to reach an equal concentration on both sides of the membrane.  Important in maintaining homeostasis

 Hypotonic Solution: - more water outside the cell than inside - water moves into the cell - cell swells  Hypertonic Solution: - more water inside the cell than outside - water moves out of the cell - cell shrinks

 Isotonic Solution: - amount of water is the same outside and inside the cell - cell stays the same

 Movement of particles across membranes by diffusion  High  low concentration  Requires no energy  Passive transport with the help of transport proteins is called facilitated diffusion

 Movement of materials through a membrane against a concentration gradient.  Low  high concentration  Energy required  Uses carrier proteins

 Transport of large particles: endocytosis – cell surrounds and takes in material from its environment exocytosis – expulsion or excretion of materials from a cell (wastes, indigestible particles)

 Diffusion limits cell size!! - short distances = fast and efficient diffusion - long distances = slow and inefficient diffusion  DNA limits cell size  Surface area-to-volume ratio - as a cell size increases, its volume increases faster than its surface area - what does this mean for the cell?

Chapter 8.2

 Remember the cell theory states that all cells come from preexisting cells.  Cell division is the process by which new cells are produced from one cell.  We lose cells constantly throughout the day and they are constantly being replaced.

 Carriers of the genetic material (DNA) that is copied and passed from generation to generation.  Located in the nucleus  Exist as chromatin (uncoiled) for most of its life.  Before cell division, the chromatin (DNA) coils up tightly and is called chromosomes

1. Chromatid 2. Centromere 3. Short arm 4. Long arm

 The sequence of growth and division of a cell.  Cells go through two general periods: - growth period (interphase) - division period (mitosis)

 The majority of a cells life is spent here  G 1 phase – cell growth  S phase – DNA is copied  G 2 phase – growth and getting ready for cell division

 Starts with one cell and results in two identical cells (daughter cells)  Four phases of mitosis: 1. Prophase (longest phase) - chromosomes coil up and double - nuclear envelope and nucleolus break down and disappear - spindle fibers form - centrioles migrate to opposite poles

2. Metaphase: - chromosomes line-up in middle - spindle fibers attach to centromeres of chromosomes 3. Anaphase: - chromosomes separate and move to opposite poles

4. Telophase: - chromosomes uncoil (back into chromatin) - spindle fibers breakdown - nucleolus and nuclear envelope reappear

 Division of the cytoplasm  In animal cells, plasma membrane pinches in and forms a cleavage furrow.  In plant cells, a rigid cell plate is formed across the equator of the cell.

Cell  tissue  organs  organ system  organism

 Enzymes control the cell cycle  If the cell cycle gets out of control, then cells divide without stopping.  Cancerous cells form masses called tumors