Cells Scanning electron microscope image of a leaf from a Black Walnut tree. Image shows a cross-section of a cut leaf, itsupper epidermal layer, mesophyll layer with palisade cells and vascular bundles, and lower epidermal layer. The protrusion at center is just over 50 microns tall. (Dartmouth Electron Microscope Facility/Dartmouth College)#

Fish gills

Scanning electron microscope image of an ant Scanning electron microscope image of an ant. Its eye is approximately 300 microns wide.

Pollen from a variety of common plants: sunflower, morning glory, hollyhock, lily, primrose and caster bean. The largest one at center is nearly 100 microns wide. (Dartmouth Electron Microscope Facility/Dartmouth College) #

Cells carry out all functions necessary for life growth: an irreversible increase in size homeostasis: keeping conditions inside the organisms within tolerable limits metabolism: chemical reactions inside the cell, including cell respiration to release energy nutrition: obtaining food, to provide energy and the materials needed for growth reproduction: producing offspring either sexually or asexually sensitivity: perceiving and responding to changes in the environment

What is the cell theory? all living things are made of one or more cells the cell is the smallest unit of life all cells come from pre-existing cells

Evidence for the cell theory? All living things are made of one or more cells microscopes allow us to observe that all living things are either unicellular or multicellular Robert Hooke: pioneering microscopist, cork cell Antonio Van Leeuwenhook: master lens maker, animacules http://science.howstuffworks.com/innovation/scientific-experiments/scientific-method4.htm

Evidence for the cell theory? The cell is the smallest unit of life nothing smaller than a cell can survive independently subcellular structures cannot survive independently (nuclei, ER, golgi, chloroplasts, mitochondria) the lower limit on cell size is about 200nm, large enough for DNA, ribosomes, and membranes

Evidence for the cell theory? All cells come from pre-existing cells: Does this imply that life ALWAYS existed? Contradicts with geological evidence Exception made for the origin of life, when cells arose from non-living substances

Relative sizes of cells molecules: ~ 1 nm cell membrane thickness: ~ 10 nm viruses: ~ 100 nm bacteria: ~ 1 µm organelles: up to 10 µm eukaryotic cells: up to 100 µm http://www.cellsalive.com/howbig.htm

Prokaryotic vs. Eukaryotic cells All cells contain small specialized structures called organelles Prokaryotes = cells that do not have membrane bound organelles (e.g. most unicellular organisms, such as bacteria) Eukaryotes = cells that contain membrane bound organelles (e.g. most multicellular organisms, such as us!)

Cell types http://www.wiley.com/college/boyer/0470003790/animations/cell_structure/cell_structure.htm Textbook pages p. 171 – 187

Microscope tutorial

Prokaryotic vs. Eukaryotic cells All cells contain small specialized structures called organelles Prokaryotes = cells that do not have membrane bound organelles (e.g. most unicellular organisms, such as bacteria) Eukaryotes = cells that contain membrane bound organelles (e.g. most multicellular organisms, such as us!)

Animal vs. Plant cells Plant cell Animal cell Outer cell wall + plasma membrane => fixed, angular shape Plasma membrane => flexible, rounded shape Chloroplast No chloroplast Large vacuole Vacuole No centriole Centrioles http://www.cellsalive.com/cells/cell_model.htm

Why is the cell small?

Why is the cell small? Surface area determines rate of exchange Volume determines metabolism As cell size increases, volume increases proportionally faster than SA => SA: V ratio decreases Low SA reduces rate of exchange while high V increases metabolic demands Cell cannot meet needs of metabolic demands

Stem Cell Research & Beyond

Why do cells look so different? Stem cells = Cells that retain capacity to divide and differentiate along different pathways (pluripotent) multicellular organisms can differentiate into a variety of interdependent cell types each specialized to carry out a subset of functions  greater efficiency cellular differentiation achieved through differential gene expression all cells in an organism have identical DNA

Stargardt’s disease Junvenile Macular Degeneration http://ghr.nlm.nih.gov/condition/stargardt-macular-degeneration

Lymphoma Blood cell tumors that develop from lymphocytes http://en.wikipedia.org/wiki/Lymphatic_system

What’s the problem? Use of embryonic stem cells, often obtained from laboratories carrying out in vitro fertilization (IVF) Death of embryo – taking human life? Adult stem cells: limited to differentiating into cell types of their tissue of origin & difficult to find in the tissue due to rarity

microbe

plant

http://learn.genetics.utah.edu/content/cells/scale/