151-3 disc-22fa HW3

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University of Wisconsin, Madison *

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151

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Biology

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Oct 30, 2023

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151-3 Introductory Biology - Discussion Homework 3 Week of September 26, 2022 Name: Katie Scheer Reminder: Submit your homework on Canvas by the start of your scheduled discussion section! Please use a different font color so that your answers stand out. 1. What is the theory of endosymbiosis? How is it hypothesized to have happened? The theory explains how eukaryotic cells might have arisen from prokaryotic cells (One cell taking up residence inside another cell). 2. Mitochondria and chloroplasts are more closely related to prokaryotes than to eukaryotes. What is the evidence for this? Like my answer to question one, mitochondria and chloroplast have double membranes because they were once bacteria ingested by another bacteria. Mitochondria and chloroplast have their own DNA like a prokaryotic cell, just smaller. What are the components of the cytoskeleton in an animal cell? Fill in the table below: Components? How big are they? Describe at least two functions for each component. What are they made of? What is their structure? Microtubules → tubulin 25 nm Helps cell with its shape and the movement of chromosomes in cell division Long, hollow cylinders made of tubulin Microfilaments → actin 7 nm Involved with muscle contraction and maintaining cell shape Double stranded, twisted (helix) polymers made up actin Intermediate filaments → keratin type 8-12 nm Provides strength to cell and they ability to withstand tension Small strands/rods made of proteins like keratin 3. What characteristics of the cell membrane determine what gets into the cell and what doesn’t? That is, what determines the permeability of a cell membrane? The structure of the phospholipid bilayer determines what gets in and out, as well as protein channels. 4. Consider the following diagrams for parts A, B and C. Assume the line is a biological membrane, and the Xs and Os are unknown substances. For each pair of diagrams, assume that time has passed between the first and second diagram leading to the final distribution of the Xs and Os. For each pair, explain what could

have happened to get that result. I’m sorry Vivi, I took time on this question but I still don’t quite understand this concept fully. A) What could have happened to get the result above? How would your answer change if you knew X was a small non-polar molecule? How would it change if you knew X was glucose? Diffusion; molecules go from high concentration to low concentration for a balance on both sides of membranes. If X were a small non-polar molecule, there would be a lot more X’s that crossed since small non-polar molecules cross the membrane more conveniently. So, if X were glucose then there would be less X’s that crossed. ? B) What could have happened to get the result above? How would your answer change if you knew X was a small non-polar molecule? How would it change if you knew X was glucose? Osmosis; substance O cannot pass the membrane while substance X can.

151-3 disc-22fa HW3

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