Describe a situation in which a force is exerted for a long time but does no work. Explain.
Unit 6 - Cell Structures & Organelles Introduction to Cell Biology • Cell biology - 300 year old field of the fundamental units of life, first studied by 17th century microscopists. • Robert Hooke 1665: observed cork (dead plant tissue) and noticed small blots. Named them cella, which meant small room. • Anton van Leeuwenhoek 1674: observed pond water, called them “animalcules”. Original samples were determined to be algae later. • The formation of cell theory 1838-1839 • Matthias Scheiden (botanist) and Theodor Schwann (zoologist). • All living beings are composed of cells. • Cells are independent units. • Cells come from pre-existing cells through division. • When it first appeared, cell theory was a controversial theory due to the wide belief of spontaneous generation. • Cloning of animals and plants through single cells = formal proof of cell theory. Microscopy • Human eyes can only see down to 0.2mm • Light microscope (LM) - visible light is passed through the specimen and glass lenses. The refraction of the lens bends the light to magnify the image. • Magnification: ratio of an object’s image size to it’s real size. • Electron microscope (EM) - a focused beam of electrons through a specimen or onto the surface. Modern electron microscopes can achieve a resolution of 0.002nm. Eukaryotes & Prokaryotes • Eukaryote cells - most of the DNAis in the nucleus, bound by a double membrane. • Prokaryote cells - lacks a true nucleus, DNAis concentrated in the nucleoid, technically not