Ch. 2 CELLS

Ch. 2 Word Splash Cell Theory stem cells metabolism growth reproduction response Homeostasis nutrition differentiation prokaryotic eukaryotic binary fission PASSIVE TRANSPORT active transport cell division endocytosis exocytosis cell cycle MITOSIS

Pre-Assessment When unspecialized stem cells give rise to specialized cells, what is this process called? Specialization B. Meiosis C. Mitosis D. Differentiation 2. The maximum size of a cell is limited by _____. its need for enough surface area to make exchanges with its environment   the number of organelles that can be packed inside   the materials needed to build it   the amount of food it needs to survive 3. What do limits on maximum cell size depend on? the number of organelles   surface-to-volume ratio   number of surrounding cells     thickness of the cell membrane

How to Calculate Magnification When given a magnified picture, you can use the formula: magnification = length of scale bar (using ruler) / given scale bar value (read value) *Note: both values must be in the same unit before you divide them!

Here’s how to convert from mm (10-3) to μm (10-6):

Ex: magnification = length of scale bar / given scale bar value magnification = _____ mm / .5 μm  ______ μm / .5 μm magnification = ______x

Limiting Cell Size All cells grow, but growth is limited by the surface area to volume ratio Surface area (cell membrane) controls what enters and leaves the cell while the inside of the cell (volume) controls functions related to food/energy/waste

Small Cell Medium Cell Large Cell Cell radius 0.25 units 0.5 units 1.25 units Surface Area (4Πr2) 0.79 units 3.14 units 7.07 units Volume (4/3Πr3) 0.06 units 0.52 units 1.77 units SA:V ratio 13 : 1 6 : 1 4 : 1

Other Modifications to Help increase the SA:V ratio Smaller cells have larger SA to V ratios. To adapt to this concept, large animals don’t have large cells, instead they have more cells. Large cells may change from spherical to long and thin or they may have protrusions/folds to increase their surface area Examples include nerve cells which are narrow and long and intestinal cells which have an increased surface area due to microvilli

Cell Differentiation Sexual reproduction (Meiosis) leads to a single fertilized cell and that cell has the ability to rapidly reproduce and allow the resulting cells to then differentiate into some specific cell type (via chemical signals) The differentiation process is the result of the expression of certain specific genes but not others. DNA carries all possible expressions for any cell type; therefore, each cell contains all the genetic information necessary for the production of the complete organism

Stem Cells Cells that retain their ability to divide and differentiate into various cell types When stem cells divide to form a specific type of tissue (which is determined by the need of the organism) they also produce some cells that remain as stem cells which allows for the continual production of a particular type of tissue Stem cells look like normal cells (lifespan ~ 14 days)

Examples of stem cells include embryonic, umbilical cord of newborn, bone marrow Stem cells are being tested and may be used in the future to do the following: implant stem cells in the brain to rebuild cells destroyed by Parkinson’s or Alzheimer’s implant stem cells into the pancreas of people with certain forms of diabetes Implanting into vertebrae to promote growth of bone tissue for people with chronic pain