Lab #1: Sizes and Scales
Harry Choi & Gabe Kwong
Calibration
Before any pictures were taken, the microscope was calibrated. The tips of mechanical calipers of known distance were imaged at 20x as well as 90x. The images were analyzed with ImageJ and the following calibration curve relating magnification with pixels/mm was obtained.
20x Magnification
|
90x Magnification
|
C. Elegans
The nematode C. elegans was imaged at 20x as they crawled on the an agar petri dish. The sinusoidal wavelengths of several adults were calculated, one of which is shown below. The wavelength of the larger worm is about 0.48mm. It was noted visually that younger smaller worms were in general more lively and crawled with a characteristically smaller wavelength than larger, older worms.
Fish
Different stages and features of a fish related to the zebrafish were imaged on a Olympus SZX12 dissecting scope.
(Top Left) Several cellular divisions into the life of a zygote during early stage development. Note the relative sizes and geometry of the outer shell, yolk and cells. (Top Right) A dorsal view of an adult fish captured in a micropipette. The lollipop-shaped fish has a head spherical radius of about 500 um with a cylindrical tail 3mm length x 100um in radius. (Bottom Left) A magnification of the highly reflective iris at 90x. The torus geometry and index of refracting may help in gathering light into the pupil. (Bottom Right) An image of a translucent tail with a central cylindrical feature running down it's length. Were this a blood vessel, how long does oxygen need to diffuse to the outer most cells?
Calculations
Composition of the Yolk
From the first picture, the disparity in size between the fertilized egg and yolk can be seen. Throughout the stages of development, the fertilized egg will rely on the nutrients and materials of the yolk to grow. As the resources are gradually depleted the yolk reduces in size, while the young embryo increases in size, essentially trading spaces within the crowded confines of the egg. As the zygote divides, the surface area increases to the 2nd power. Without incorporating new lipids, the zygote will quickly run out of membrane. What percentage of the composition of the egg yolk is phospholipid reserved for the formation of the membranes of daughter cells?
Cell generations, gestation period, and diffusion estimation
Early stage development is an exponential process. From one zygote two daughter cells are formed, from 2 cells 4 are formed and so on. If the assumption is made that the process is collective and binary, then the gestation period (time when the egg is fertilized to hatching) can be estimated. In general eukaryotic cells divide an order of magnitude slower than bacterial cells. In a fully formed adult how important is diffusion in the transport of nutrients?
