Today is Thursday, March 14 th, 2019

Transcription

1 In This Lesson: Cells, Cell History, General Characteristics (Lesson 2 of 5) Today is Thursday, March 14 th, 2019 Pre-Class: Compare the two animals below. Write in your notebook any and all observations you make about the two animals with only your eyes, especially their differences. Write as many as you can! x434,0.jpg

2 Today s Agenda Be able to make an educated guess as to the function of an unfamiliar structure. Know at least a little about the history of the cell s discovery. Be able to recite the three parts of the Cell Theory. Software art? Brain break. Where is this in my book? P. 193 and following

3 By the end of this lesson You should be able to describe the Cell Theory and how cells were first discovered. You should be able to define the general properties of cells.

4 Lynx and Hare

5 Why? Why do these animals have those traits? What s the form? What s the function?

6 Form and Function As the Zoo s rhyme goes: Eyes on the side, I like to hide; eyes in the front, I like to hunt. The structure (or form) of something is always secondary to its function.

7 Form and Function Why does this giraffe have a long neck? Form: Long neck. Function: Reaches food up high.

8 Form and Function Why does this butterfly have eyes? Form: Eye spots. Function: Confuses predators.

9 Form and Function Why does this cheetah have the black tear drops on its face? Form: Black tear lines. Function: Keeps out sun glare.

10 Form and Function What color is this polar bear s fur? And what color is its skin? Form: Clear fur, black skin. Function: Lets light in, skin warms in sun, can still blend in.

11 Form Follows Function A characteristic s form is always shaped by its function. You could also say, Form follows function.

12 Function Following Form? An opposite example might be headlights in NASCAR. For those of you that don t know, the headlights aren t real. They re stickers! In this case, the look isn t for any purpose at all. This doesn t happen in biology.

13 Form & Function Activity Turn to your neighbor and think of at least five examples of an instance of form (or structure) following function in nature. You have 1 minute (less if we re off topic). Imaginary bonus points if you can think of something whose function and structure are not consistent with one another.

14 Discovering The Cell It all started way back in 1665 when Robert Hooke looked at a piece of cork under a microscope. Robert Hooke?

15 Anton van Leeuwenhoek Hooke saw dead cells, but Leeuwenhoek first observed living unicellular (one-celled) organisms in pond water, along with blood and sperm cells. Done around the time Hooke saw cork.

16 So they got credit and fame Of course not! immediately, right? Many times across science s history, research that breaks ground takes a while to really set in. In this case, it took nearly 200 years, when Schwann and Schleiden (and Virchow, to some extent) confirmed that cells are the smallest units of life, and gave Cell Theory its start.

17 Cell Theory (write this down - it s important) Cell theory is a way to fit the concept of cells into the rest of biology. It has 3 parts: All living things are made of one or more cells. Cells are the basic units of structure and function [organization] in organisms. All cells arise from existing cells. Johnson, G. & Raven, P. (2004). Biology. Holt, Rhinehart, and Winston: Austin

18 Cell Theory Video It turns out the Cell Theory had a bit of a weird origin. Let s take a look

19 Why is the Cell Theory important? It disproved the theory of Spontaneous Generation! Hypotheses based on Spontaneous Generation on the coming slides

20 Spontaneous Generation Maggots come from rotting meat.

21 Spontaneous Generation Rats come from damp roofs. The coming rat plague!

22 Disproving Spontaneous Generation So how do you disprove something like this? It seems obvious, but can you prove it? Design an experiment! Talk to your partner and take a minute and 57 seconds.

23 Francisco Redi Redi filled six jars with decaying meat: 3 were open containers 3 had fine nets over them Sure enough, the three open containers had maggots and the three with nets didn t. Where did the maggots come from? What was the purpose of the sealed jars?

24 Some More About Cells Cells are the smallest unit of life. BioScale! ale/ Scale of the Universe As we all know, cells are tiny. How many cells are in the human body? Your body contains 100,000,000,000,000 cells (that s 100 trillion, which is also not enough money to pay our national debt)

25 Cell Size Average cell size: micrometers Biggest cells?

26 Large Cells Ostrich Egg

27 Large Cells Sciatic Nerve WARNING: Graphic picture next slide

28 Large Cells Sciatic Nerve

29 Back to Form and Function So now the big question. Why is it cells are so small? Why aren t big organisms just made of bigger cells?

30 Let s try an alternate question If you buy a gallon of water in one bottle and then you buy a gallon of water in many bottles which option gets you more water? Either choice. They re the same. But which option uses more packaging material? The smaller bottles. Key: Cells want a HIGH surface area to volume ratio.

31 Cell Size To answer the question of why cells are so small, we re going to look at a similar relationship in biology. Which of these spheres has a greater surface area? Volume?

32 Wingspan to Height Ratio Let s try exploring this with a different ratio: Wingspan (arm length) to height. If you extend your arms out to your sides, most people will find that the distance between your fingertips (left hand to right hand) is equal to your height...or pretty close. People with longer arms than their heights have a wingspanto-height ratio greater than 1. People with shorter arms than their heights have a wingspan-to-height ratio lower than 1. Obviously equal lengths means a ratio of 1 exactly. I need two volunteers. Let s also read David Epstein Wingspan and Height in the NBA

33 Surface Area to Volume Ratio Cube 1 2 cm Cube 2 4 cm 2 cm 2 cm 4 cm 4 cm Cube 1 Cube 2 Proportion Volume 8 cm 3 64 cm 3 8x more volume Surface Area 24 cm 2 96 cm 2 4x more surface Proportion 3x more surface 1.5x more surface

34 SA to Volume Ratio

35 Surface Area to Volume Ratio Generally speaking, smaller objects have more surface area relative to their volumes than larger objects. So why are larger organisms composed of many, many small cells, instead of being composed of larger cells?

36 Surface Area to Volume Ratio Imagine that you are a cell. You need to get some tiny but important molecule to the center of yourself as fast as possible. Having a larger surface area to volume ratio means you have more area for the molecule to enter but a smaller distance for it to go once it gets inside. Cells like to do things fast, so this is very handy.

37 Membrane Action et cetera Cells take in and release substances through their membranes. Like Goldilocks, the size of the cell has to be just right for things to work efficiently. Not too big, not too small What exactly the cell is doing will be part of our next few lessons.

38 A Little Preview Find a blank section of your notebook and label it Unit 2 Predictions. I will provide you with four scenarios. Three of them will be live, and the other will be a diagram. Your job is to [SILENTLY] write a detailed prediction and possible explanation for what will happen in each situation.

39 Unit 2 Predictions Take your time doing this. Be thorough. Do not talk during this. The point is to get your brain moving on this topic, not to mooch off someone else s brainpower. Like I said, be detailed. Write what will happen. Write what will happen at the molecular level. What will we see? Why?

40 Prediction 1 If I add three drops of this food coloring to this beaker of water, what will happen? What will it look like at first? Will it change? How will it be different? Why? What are the molecules doing?

41 Prediction 2 If I put a baby carrot in a beaker of water and another baby carrot in a beaker of water plus lots of salt, what will happen? Will the carrots change? Will the water change? Will both? Why?

42 Prediction 3 I am going to spray this room spray in the classroom. What will happen? Describe in detail!

43 Prediction 4 In this tube, water can cross the border in the middle. The solute cannot. There is more solute on the right than on the left.

44 Closure Which has a greater surface-area-tovolume ratio an elephant or a mouse?