INTRODUCTION AND SCIENTIFIC METHOD (ch 1 and 4)

Biology is the systematic study of life.

Atoms  Molecules  Cells  Tissues  Organs  Organ system

Population  Community  Ecosystem  Biosphere

Population: a group of individuals of a species in an area

Community: all populations of all species in a given area

Ecosystem: a community interacting with its environment

Biosphere: all regions that hold life

All living things have similar characteristics: 1. Continual inputs of energy and cycling of materials maintain a life’s complex organization * All organisms require energy and nutrients to sustain themselves

2. Organisms sense and respond to change * Homeostasis – organisms keep conditions in their internal environment within ranges cells tolerate

3. All organisms use information in DNA inherited from parents to function and reproduce * DNA – Info that guide’s organism’s metabolic activities, growth, development, and reproduction

Prokaryotes: single-celled, DNA not contained in nucleus!!!, non membrane bound organelles (bacteria, arheeans)

Eukaryotes: single- or multi-cellular, DNA contained in nucleus, membrane-bound organelles (protists, fungi, plants, animals)

Three-Domain System 1. Bacteria 2. Archea 3. Eukarya (includes all eukaryotes)

Individuals of a species share a unique set of traits * Morphological traits – body parts * Physiological traits - functioning * Behavior traits

Scientific Method 1. Observe - gather through your senses, notice natural world * Don’t be biased

2. Question * Precisely phrase * Testable * Focus on objects, organisms, and events in natural world * Connect to scientific concepts rather than opinions, feelings, beliefs

3. Hypothesize – educated guess; possible answer to question * Must be testable and falsifiable * Null hypothesis – statement of no difference 4. Predict

5. Test

6. Conclusion – answer the hypothesis using data obtained; may need to retest

THE CELL

Traits common to all cells: 1. Plasma membrane 2. Cytoplasm 3. DNA (in nucleus if eukaryotic)

Plasma membrane: boundary that separates the living cell from its surroundings * Selective permeability: some substances cross it more easily than others * Phospholipids are amphipathic: they have hydrophobic and hydrophilic regions * Ions go from regions of higher concentration to lower concentration

Polar Head
Polar Head
Phospholipids
* Most abundant lipid in cell membrane * Nonpolar Tail
Nonpolar Tail
Glycerol + 2 fatty acids + PO4 (negatively charged) * Fatty acid tail (nonpolar) = hydrophobic * PO4 = hydrophilic head (polar) * They are amphipathic – dual “personality” (like water but they also put it away) * IN CELLS: heads on outside, tails on inside * Bubble = “micelle” * Can also form bilayer * Double bond kinks – unsaturated tails prevent close packing * Causes more fluid in membrane

Cholesterol * Bulky and rigid; reduces permeability * Less fluid because less permeable

Selective permeability**** * Small or nonpolar molecules move across phospholipid bilayers quickly * O2, fats, ect. * Charged or large polar substances cross slowly, if at all * Ions, glucose, ect. * Membranes containing phospholipids with longer tails have reduced permeability * Cholesterol decreases membrane permeability * Decreased membrane fluidity causes decreased permeability (molecules in bilayer move slowly) * Unsaturated = more fluid

Fluid-mosaic model: some proteins are inserted into the lipid bilayer, making the membrane a fluid, dynamic mosaic of phospholipids and proteins (moving)

Membrane carbohydrates may be covalently bonded to lipids (forming glycolipids) or more commonly to proteins (forming glycoproteins)
Membrane Carbs and Cell-Cell Recognition * Cells recognize each