Introduction to Cells

Introduction to Cells

1. Cell Theory

   • all organisms are composed of one or more cells
   • cells are the smallest unit of life
   • all cells come from pre-existing cells
   • Questioning Cell Theory
     • Striated Muscle Fibres
       • very long cells with multiple nuclei
       • challenges the idea that cells function as autonomous units with a single nucleus
     • Aseptate Fungal Hyphae
       • hyphae - threadlike structures, white and fluffy
       • hyphae are partitioned by internal walls - septa
       • some fungi have no septa
       • challenges the idea that living structures are made of discrete cells
     • Giant Algae
       • Acetabularia
       • challenges the idea that living organisms are made of microscopic cells

2. Cells

   • plasma membrane - separates inner contents from surroundings
   • genetic material - instructions for cell's activities
   • chemical reactions catalyzed by enzymes
   • release energy that powers their activities
   • smallest structures that can survive by themselves

3. Functions of Life

   • Metabolism - chemical reactions inside the cell, including cell respiration to release energy
   • Homeostasis - the maintenance of a constant internal environment
   • Reproduction - production of offspring, either asexually or sexually
   • Excretion - removal of the waste products of metabolism
   • Response - the ability to react to changes in the environment
   • Growth - a permanent increase in size and/or dry mass
   • Nutrition - obtaining food to provide the energy and materials needed for growth
   • Paramecium
     • metabolism - reaction in cytoplasm, catalyzed by enzymes
     • homeostasis - contractile vacuole controls water content, gas exchange through plasma membrane
     • reproduction - asexual reproduction by binary fission
     • excretion - through plasma membrane
     • response - cilia beat and move organism in response to changes in the environment
     • growth - assimilates biomass and grows until it divides
     • nutrition - food vacuoles, heterotroph
   • Chlorella
     • metabolism - cytoplasmic reactions catalyzed by enzymes
     • homeostasis - exchange of gases through plasma membrane
     • reproduction - asexual
     • response - cilia beat and move organism in response to changes in the environment
     • excretion - through plasma membrane
     • growth - grows until it divides
     • nutrition - makes food by photosynthesis

4. Multicellular Organisms

   • single mass of cells fused together
   • Caenorhabditis elegans
     • 959 cells
     • hermaphrodite
     • mouth, pharynx, anus, intestine
     • feeds on decomposing matter
   • Emergent Properties
     • the whole is greater than the sum of its parts
     • cells --> tissues --> organs --> organ system --> organism
     • new properties come from the interaction of the various parts

5. Cell Sizes

   • Molecule - 1 nm
   • membrane - 10 nm
   • virus - 100 nm
   • bacteria - 1 um
   • organelle - 10 um
   • cell - 100 um
   • Limiting
     • SA:V
     • rate of metabolism <-- volume
     • rate of material exchange <-- SA
     • V ^ SA ^ but SA slower than V so SA:V ratio falls