Cell Theory, Cell Specialization, and Cell Replacement, and The Origin of Cells 1.1 & 1.5

Essential Idea: The evolution of multicellular organisms allowed cell specialization and cell replacement 1.1 Introduction to Cells Understandings: According to the cell theory, living organisms are composed of cells   Organisms consisting of only one cell carry out all functions of life in that cell Surface area to volume ratio is important in the limitation of cell size Multicellular organisms have properties that emerge from the interaction of their cellular components Specialized tissues can develop by cell differentiation in multicellular organisms Differentiation involves the expression of some genes and not others in a cell’s genome The capacity of stem cells to divide and differentiate along different pathways is necessary in embryonic development and also makes stem cells suitable for therapeutic uses Applications: Questioning the cell theory using atypical examples: striated muscle, giant algae, aseptate fungal hyphae Investigate functions of life in Paramecium and one named photosynthetic unicellular organism Use of stem cells to treat Stargardt’s disease and one other named condition Ethics of the therapeutic used of stem cells from specially created embryos, from the umbilical cord blood of a new-born baby and from an adult’s own tissues Skills: Calculation of the magnification of drawings and the actual size of structures and ultrastructure’s shown in drawings or micrographs.

1.5 The Origin of Cells Understandings:   Essential Idea: There is an unbroken chain of life from the first cells on Earth to all cells in organisms alive today 1.5 The Origin of Cells Understandings: Cells can only be formed by division of pre-existing cells.   The first cells must have arisen from non-living material The origin of eukaryotic cells can be explained by the endosymbiotic theory Application: Evidence from Pasteur’s experiments that spontaneous generation of cells and organisms does not now occur on Earth

I. Cell Theory Scientific Theories 1. Substantial explanation of a natural phenomenon 2. An endpoint that represents understandings developed from extensive observation, experimentation and logical inferences ***A Theory cannot become a Law – a law is the “what”, a theory is the “why” or “how” ***

B. 3 Major Points 1. All organisms are composed of 1 or more cells Cells are the smallest unit of life All cells come from pre-existing cells a. Pasteur’s experiment

C. Organisms can be unicellular or multicellular

D. Cells have many common features Surrounded by a membrane Contain genetic material which contains the instructions for the cell’s activities Activities are often chemical reactions catalyzed by enzymes Have their own energy systems to power the cell

E. Atypical Examples 1. Muscle cells – large, multiple nuclei 2 E. Atypical Examples 1. Muscle cells – large, multiple nuclei 2. Fungal hyphae –cells can exchange nuclei, sometimes not divided by membrane 3. Giant algae and slime molds – can be as big as 10cm

II. Functions of Life Metabolism, reproduction, homeostasis, excretion, growth, response, nutrition

III. Surface Area to Volume Ratio As a cell grows, both surface area (amount of membrane) and volume increase, but volume increases at a faster rate Surface area needed to get food and O2 in, and waster and CO2 out Larger the volume, more food and oxygen required, more waste and CO2 produced This limits cell size – need enough surface area to support the volume Large cell modifications – elongation, folded membranes

IV. Differentiation Cells become specialized to a function Determined by which genes are turned on/off Some lose/reduce ability to reproduce once differentiated (nerves, muscles) while other reproduce rapidly and constantly (skin)

V. Emergent Properties Groups working together to perform a function

VI. Stem Cells Undifferentiated Pluripotent – can become any type of cell (embryonic stem cells) Multipotent – slightly differentiated but can still become many cell types (ex. bone marrow)

Stem Cell Therapy 1. Use stem cells to replace dead or damaged differentiated cells 2. Called “Therapeutic cloning” 3. Ex. Create new brain cells for Parkinson’s or Alzheimer’s, or new pancreas cells for diabetics

Stargardt’s disease – recessive genetic that causes a defect in the processing of Vitamin A 1. Vitamin A – essential for retina cells to properly respond to light 2. Results in loss of vision by age of 20 3. In 2010, stem cells were used to regenerate photo receptors in retina

Controversy 1. Embryonic stem cells – obtained from IVF clinics

VII. Endosymbiotic Theory Prokaryotes engulfed other prokaryotes to become eukaryotes Key Points ~ 2 billion years ago Eukaryote developed symbiotic relationship with the prokaryotes it had engulfed a. Eukaryote offered shelter, protection, prokaryotes did jobs for eukaryote 3. Prokaryote modified to become mitochondria, chloroplast

Evidence to Support 1. Mitochondria and Chloroplasts a. Size of most prokaryotes b. Divide independently by fission c. Have their own ribosomes, produce their own proteins d. Have their own DNA, circular chromosome e. Double membrane (consistent with being engulfed)

Hatena – protist that can ingest food but also can ingest algae and use its photosynthesis to provide it with food Elysia – slug that ingests algae 4. DNA – Genetic Code is universal