62 min video•april 11, 2019
The second part of the review series finished macroevolution and started cell structure and function. Speciation is the formation of new species from a common ancestor via evolution. Some examples include the maggot flies and lizards. Sympatric speciation is the idea that speciation can result even when related organisms live in the same habitat. Some reasons are habitat differentiation, in which mutations allow different species to use different parts of the habitat for survival. Sexual selection is how animals mate with each other; if a species does not have the right mating dance or behavior, no animal is going to mate with that animal. Polyploidy is having more than 2 paired sets of chromosomes. Adaptive radiation is when different sectors of the species fill different roles given by the environment; for example, if one sector already inhabits the ocean, the other will try to inhabit the land, and so forth. Phylogenetic trees show the commonalities between related species- the closer the common ancestor, the more related they are. When using a table or graph on the AP Exam, make sure to read carefully whether the data is talking about similarities or differences. Also, don’t feel weird or anxious about empty cell in the table; just look at the other column-row pair that matches the empty cell. Next, we started talking about cell structure and transport. Some important organelles to know are the mitochondria, nucleus, vacuole, Golgi Apparatus, and lysosomes, etc. The two types of classifications are prokaryotic and eukaryotic. Some differences include no nucleus vs nucleus, single, circular DNA vs DNA in tight chromatids, and no organelles vs many organelles. The plasma membrane surrounding the cytoplasm and organelles is structured as a phospholipid bilayer with hydrophilic heads and hydrophobic tails. This structure is important because it determines what can passively and actively pass through the cell. Some goals of the cell, including the membrane, include transport, cell signaling, cell-cell recognition, intercellular joining, and attachment to the extracellular matrix(ECM). When talking about transport, remember that there are two kinds: passive and active. Passive transport requires no net energy input and happens when a particle is moving down a concentration gradient(from high to low). When a molecule moves along a gradient from high to low, it is called diffusion. The diffusion of water is called osmosis. Facilitated diffusion is when a molecule travels down the gradient but via a pump or a channel. Since there is a hydrophilic and hydrophobic section, some molecules or ions cannot pass through easily even if the concentration gradient allows for diffusion. Instead, they can move through a channel that opens and closes depending on inner vs outer concentration and signals. Active transport is a transport that requires a net input of energy and usually moves a particle from low to high concentration. While most active transport occurs through channels and pumps, it is different than facilitated diffusion because the molecule is moving against the gradient, not with it. We wrapped up by briefly talking about cell environments: hypo-, hyper-, and isotonic. While we did not get that far into it, we will definitely continue this next week.