01:119:115 Lecture Notes - Lecture 5: Symmetry In Biology, Tooth Enamel, Homeobox
8 Jul 2015
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Three characteristics describe basic features shared by all animals. The way organisms obtain nutrients: nutrition: process if organisms taking in and making use of food material, animals must ingest organic molecules by eating other living organisms, materials eaten are digested within body using enzymes. Animals are multicellular with specialized tissues: animal cells do not have cell walls like plant cells, extracellular proteins that provide support and connect cells to each other (figure 6. 28) Collagen is most abundant: cells with similar structure and function form tissues that act as a unit. Most animals go through sexual reproduction: union of haploid gametes then develop into multicellular diploid stage, zygote produced after flagellated sperm fertilizes non-motile egg, zygote goes through cleavage. Cleavage is mitosis of the cells without cell growth between divisions: cleavage leads to formation of blastula (hollow ball of cells) figure 32. 2. Cavity inside ball is blastocoel: blastula then goes through gastrulation producing gastrula in the end.
