Lecture 10 Outline of Last Lecture I. Angiosperm Reproduction contd. & Plant Growth a. Alternation of Generations b. Angiosperm Lifestyle c. Double Fertilization II. Introduction to Animal Physiology III. Three Trends in the Animal Body Plan a. Symmetry Outline of Current Lecture b. Embryonic Development & Germ Layers c. Segmentation IV. Tet r a p o d s Ta k e t h e l a n d V. Physiological Concepts a. Homeostasis Current Lecture *Clarification on topic from last lecture!*!Endosperm totipotency!-it is possible early in development or in endosperms that are cellularized!-useful for generating sterile plants (garden plants that are invasive)!-if you catch it early in development (before it starts to make a bunch of stuff) — but you can trick it into making a plant that would be triploid (so sterile)!-ALWAYS infertile!-it still can’t generate a fully functioning plant (sexually reproducing) — just as the gametophyte couldn’t!!3 Trends in Body Plan Bio 152 1!!!These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best !used as a supplement to your own notes, not as a substitute. !!Embryonic Development & Germ Layers 2 different animal early embryos on slide (top is jellyfish, bottom is toad) gastrulation: the embryo goes from a mass of undifferentiated cells (all cells are the same and totipotent) into the formation of germ layers (the definition of gastrulation) -germ layers = endoderm, mesoderm, ectoderm (listed inside to outside in embryo) -in jellyfish there are only 2 germ layers (diploblastic) but most other animals have 3 germ layers **video showing first division through gastrulation then neurolation — divides in an ordered way to get mass of undifferentiated cells. Then you see it gastrulate to make the 3 different layers/tissues -outside tissue folds in and makes the neural cord — what will become the back of the organism -starting to form musculature which then causes it to start moving !Gastrulation leads to three germ layers (two in some animals) •the three germ layer have different fates •ectoderm = outer layer, nervous system (outside) •endoderm = digestive and respiratory (inside tissue) — forms a tube which will eventually connect the mouth to the gut •mesoderm = becomes organs, skeleton, muscles and circulatory system (middle tissue) •this is conserved throughout the animal taxa •the blastopore is also labeled but it depends on the organism. In some it becomes the mouth, and in some it becomes the anus (this is not true in the mammals, is true in the chordates) just is an opening into the organism — don’t worry knowing this part !**Clicker Question**!!•This image shows the gastrulation of a human embryo w/ 3 layers. Ectoderm has the primitive streak which will fold in and become the neural tube. Ectoderm, endoderm and mesoderm cells: I. should have the same DNA II. Will have different receptors expressed III. should be totipotent IV. will have the same transcription factors expressed •Answer = B, only I and II •they can’t be totipotent because the germ layers have already started to specialize, they are already in a pathway (blastocysts are what are harvested for stem cell research because that is last phase before they differentiate) •as they differentiate they’re gonna have different proteins expressed, so different transcription factors, etc. !!Segmentation •(in the chordates, arthropods, and annelida) — it occurs currently in 3 separate phyla •it emerged first as replication of identical sections •ex: looking at an earthworm, most of the sections are identical throughout the organism •then specialization occurred — the arthropods w/ some section growing legs, others wings •advantages of segmentation: •better movement •neurological segmentation •sets the stage for appendages •don’t get appendages outside of the organisms that have segmentation •segmentation is something that happens in the embryo, get genes like pair rule genes that give the segments!!**Clicker Question** !•Segment polarity genes, like hedgehog are shared between annelids, chordates and arthropods. What does this suggest? *See image on slide 12 of lecture* !I. Segmentation is an ancestral trait in extant bilaterians II. the non-segmented bilaterians may have lost segmentation III. segmentation evolved three separate times IV. segmentation is a derived trait in arthropods, annelids and chordates •answer = D: both I & II •it evolved once and then got lost in many different species because there was no selective pressure for this trait to be retained in some of the other bilatera •this question was getting at the idea that either this trait evolved 3 separate times almost identically, or only evolved once and then it was lost •it is very unlikely for a whole gene to just appear (always working with toolkit that is there, so you’re selecting for certain things) — much more likely that it would appear once, early on, and then been lost *lost can be either that the genome was lost or turned off !Segmentation in a grasshopper embryo showing the neural ganglia that are segmented (groups/clusters of nerves) this allows for distributed control of the organism in arthropods •segmented nervous system distributed along the length of the nervous system — so wasp could still operate without its head •segmentation allows for this distributed control !Chick embryo (right) and human embryo (left) •segmentation in the human embryo can be seen in the somites which develop into various parts of the body •chick embryo showing migration of cells from the neural crest along the top of the neural tube to form the head !Te t r a p o d s t a k e t h e l a n d •Chordates with skull and teeth but no vertebrae or jaw •see video on Lecture slides 19 ! **Be able to interpret the information presented in the phylum chordata •all of the phyla continue to evolve and specialize after what is shown on the graph, but evolution isn’t going towards mammals !*Clicker Question** !•Are lungs a derived feature in land vertebrates or an ancestral one? Ancestral!•lungs/lung derivatives evolved early on — seen in fish, but used for a different purpose than in land animals !Physiological Concepts Homeostasis !**Clicker Question** !•Baking bread, in the winter I put the dough near the wood stove to encourage it to rise. It rises about twice as