QUESTIONS REVIEW Lab 5 Development Describe the main stages of sea urchin development
Describe the main stages of corn seedling development.
Except in rare cases, no more than one sperm is able to fertilize an egg. Describe the cellular mechanisms that prevent polyspermy.
Why are embryonic cells in the early stages of sea urchin development smaller in size than the original egg cell?
Experimental Methods Which cellular component does each of the following stains bind to? Stain Cellular Component Safranin Crystal violet Fast green Methylene blue DAPI
In the course of a research project, you find that a certain common food preservative halts development in sea urchin embryos at the morula stage because it interferes with cell cytoskeleton assembly. What effect would you expect this chemical to have on human liver cells?
Using a spectrophotometer and a series of chloroplast suspensions of known concentration, you determine the following relationship between absorbance and the concentration of choloroplasts in solution: Absorbance = 0.05 + 0.001 (# chloroplasts/ml) 1) Knowing that chlorophyll has a peak absorbance of around 450 nm, which wavelength would you use to determine the absorbance of your chloroplast suspension? 2) If the absorbance of a given chloroplast suspension was 0.675, how many chloroplasts/ml does it contain?
ANSWER KEY Development Describe the main stages of sea urchin development 1) Fertilization of egg by free-swimming sperm; formation of fertilization membrane to prevent polyspermy 2) Repeated cellular division (2 cells, 4 cells, 8 cells, etc.) to form a ball of cells called the morula 3) Blastulation ball of cells develops a hollow interior to form a blastula 4) Gastrulation an invagination (blastopore) forms on the surface of the embryo; three tissue layers (endoderm, mesoderm, ectoderm) begin to form. This stage is called a gastrula. 5) Pluteus free-swimming stage in which the sea urchin begins to feed Describe the main stages of corn seedling development. 1) Fertilization of plant ovule inside flower ovary 2) Division of fertilized ovule to form mass of small identical cells 3) Protective coat forms around plant embryo; this structure is called the seed (note that the embryo can stay dormant for several months or years inside the seed even longer in some plant species!) 4) Germination once placed an appropriate environment, the seed coat weakens and the embryo resumes development 5) Emergence of radicle, embryonic root 6) Emergence of coleoptile, embryonic stem and leaves 7) Further development into mature plant Except in rare cases, no more than one sperm is able to fertilize an egg. Describe the cellular mechanisms that prevent polyspermy. Two reactions take place to prevent polyspermy: fast 1) block to polyspermy: fusion of egg and sperm depolarizes cell membrane, preventing entry of other sperm (this is only a temporary block to polyspermy however) 2) slow block to polyspermy the cortical reaction: the eggs endoplasmic reticulum begins to pump Ca++ into the cytoplasm, causing specialized vesicles called cortical granules to burst. The cortical granules release enzymes which cause the plasma membrane of the egg to separate from the vitelline layer, a structure just outside the plasma membrane. The separation between these two layers prevents the entry of more sperm and is visible as the halo, or fertilization membrane, you saw under the microscope.
Why are embryonic cells in the early stages of sea urchin development smaller in size than the original egg cell? The cells are dividing very quickly, but in the early stages of its development the urchin embryo is not able to feed. Without nourishment, the cells cannot grow bigger, so each division produces smaller cells.
Experimental Methods Which cellular component does each of the following stains bind to? Stain Cellular Component Safranin Nucleus Crystal violet Bacterial cell walls Fast green Cellulose (in plant cell walls) Methylene blue Nucleus DAPI Nucleus (fluorescent stain)
In the course of a research project, you find that a certain common food preservative halts development in sea urchin embryos at the morula stage because it interferes with cell cytoskeleton assembly. What effect would you expect this chemical to have on human liver cells? As you may have guessed, this is a trick question! It can be dangerous to extrapolate the results of scientific experiments too far. In this experiment, you might conclude that the chemical affects urchin embryos, and that it has the potential to affect the embryos of other closely related species as well. But you dont know what effect the chemical will have on human liver cells. You did not test it on the cells of a fully developed organ, or even on the cells of a vertebrate animal. Using a spectrophotometer and a series of chloroplast suspensions of known concentration, you determine the following relationship between absorbance and the concentration of choloroplasts in solution: Absorbance = 0.05 + 0.001 (# chloroplasts/ml) 1) Knowing that chlorophyll has a peak absorbance of around 450 nm, which wavelength would you use to determine the absorbance of your chloroplast suspension? You want to measure your samples at the wavelength where absorbance is greatest. Since chloroplasts contain a lot of chlorophyll, 450 nm is a good wavelength to choose. 2) If the absorbance of a given chloroplast suspension was 0.675, how many chloroplasts/ml does it contain? 0.675 = 0.05 + 0.001x x = 625 chloroplasts/ml