Unit 2 Multicellularity, Development, and Reproduction PDF

UNIT 2 ====== Learning Outcomes ----------------- In this unit, the student should be able to: 1. list the five essential developmental processes in the development of the multicellular organism, 2. describe the major reproductive strategies of eukaryotes, 3. explain the trade-offs betwe...

UNIT 2 ====== Learning Outcomes ----------------- In this unit, the student should be able to: 1. list the five essential developmental processes in the development of the multicellular organism, 2. describe the major reproductive strategies of eukaryotes, 3. explain the trade-offs between asexual and sexual reproduction, and 4. compare and contrast the three types of life cycle of a eukaryotes, **Time Frame:** 4 hours Lec; 6 hours Lab/2 weeks Content ------- Cell Size --------- - Some cells also use geometric tricks to get around the surface-area-to-volume problem. For instance, some cells are long and thin or have many protrusions from their surface, features that increase surface area relative to volume. - Other solutions are to divide into two cells or the development of organelles that perform specific tasks. These adaptations lead to the development of larger and more complex cells called eukaryotic cells. - A more sophisticated solution is multicellularity, where an organism is made of multiple cells with specialized functions. The rest of this reading provides an overview of the requirements and consequences of multicellularity. Multicellularity and Specialization ----------------------------------- Processes that Control Development and Specialization ----------------------------------------------------- 1. **Cell proliferation:** reproduction of new cells via mitosis; this process is critical for adding new cells (and thus mass) to body, making it larger 2. **Programmed cell death:** death of specific cells; this process may seem like a bad thing, but certain cells actually have to die at certain stages for normal development. An example is human digits; during development, we have cells between our fingers which must die at precise times during development; otherwise, there would be webbing between our fingers. 3. **Cell movement** or **differential expansion:** movement to new locations in the body (in animals) or differential expansion of cells in a specific direction (in plants); the process of gastrulation, which forms the gut, is the most dramatic example of cell movement in animals. Another interesting example is the movement of the testicular tissue from the abdomen to the scrotum in male development (testicles arise from the same tissue that creates ovaries in females). Plant cells cannot move due to their cell wall, and instead differentially expand to cause the plant to bend. 4. **Induction:** cell-cell communication or signaling; this process is critical for cells recognizing where they are in the body during development, and thus what type of cell they should become. Cell-cell communication can occur directly between immediately adjacent cells, or over long distances in concentration gradients. Any signaling molecule that helps specify cell fate that is present in a concentration gradient is called a **morphogen**; the amount of morphogen a cell detects helps determine what that cell will become. 5. **Cell differentiation:** the process of becoming a specific cell type, such as a bone cell or a muscle cell; this is often the final result of all the other processes, where a cell goes from an unspecified (embryonic) type to a final, specialized type of cell with a specific job in the organism. Eukaryotic Reproduction ----------------------- - **Mitosis:** splitting into two (usually equal) halves (like binary fission, but with a nucleus; binary fission occurs in prokaryotes, while mitosis occurs in eukaryotes). All eukaryotes use mitosis, either to produce a new organism, or to produce new cells within a multicellular organism. - **Multiple fission**: splitting into more than 2 cells. Some fungi and some microbial eukaryotes reproduce through multiple fission. - **Budding**: outgrowth of a new cell from an old cell/new organism from old organism. Budding can occur when a single cell buds from a parent cell, or when multiple cells bud off of a larger organism. Budding occurs in some animal life stages (such as hydra in sea anemones, and the parasitic stage of flatworms) some fungi, and some microbial eukaryotes. - **Fragmentation**: mature organism splits into fragments capable of forming new organisms. Reproduction by fragmentation occurs in some fungi, some animals (such as starfish) and some plants. - **Spores**: specialized cells capable of forming a new organism; usually haploid and produced by meiosis. Reproduction by spores occurs in land plants and fungi. - **Parthenogenesis**: development of unfertilized egg into new organism. Parthenogenesis occurs in some animals (including some arthropods and some lizard species) and in some plants. - **Polyembryony**: fertilized egg splits to form genetically identical clones. Polyembryony can occur in some animals and some plants. - **Vegetative growth**: growth of new organism from meristematic cells without spores or gametes. Vegetative growth is a common reproductive strategy in plants. Pros and Cons of Sexual and Asexual Reproduction ------------------------------------------------ Eukaryotic Life Cycle --------------------- - **Gametogenesis**: making gametes - **Mating**: getting gametes together - **Fertilization**: fusing gametes into one cell - **Gamete**: a mature haploid male or female germ cell that is able to unite with another of the opposite sex in sexual reproduction to form a zygote - **Spore**: a small, typically one-celled, reproductive unit capable of giving rise to a new individual without sexual fusion Suggested Activity ------------------ "Reproduction Buddies" ---------------------- 1. Go to the [[https://www.nationalgeographic.org/interactive/reproduction-buddies/]](https://www.nationalgeographic.org/interactive/reproduction-buddies/) and play the reproduction buddies. There are nine stages of the game. Complete all the stages. Get a screenshot of each stage, print, and paste it in the box below. Stage 1 Stage 2 --------------- 1. What are the two types of reproduction and describe its key differences? 2. Describe how the following organism reproduce based on the game you played: a. *Amoeba* b. Starfish c. Sponge d. Carrots e. Bees 3. What is the difference between fragmentation and budding? 4. How are the genes split up in sexual reproduction