Cell Growth, Division, and Reproduction Read the lesson title aloud to students.

How do organisms get “bigger”? Limits to Cell Size How do organisms get “bigger”? Ask: Throughout your lives, how has your body gotten larger? How will this baby penguin grow? How do the cells making up its body compare to those making up the parent’s body? Answer: The number of cells increases. (Individual cells do not simply grow larger to make the body larger.) The baby penguin has fewer cells in its body overall than the parent does. Have students reflect on why larger organisms need to be made up of many tiny cells rather than just one or a small number of large cells. Elicit student ideas for why there are no truly “giant” cells.

Limits to Cell Size Organisms will grow more cells. When cells get bigger, they work less efficiently. Ask: Throughout your lives, how has your body gotten larger? How will this baby penguin grow? How do the cells making up its body compare to those making up the parent’s body? Answer: The number of cells increases. (Individual cells do not simply grow larger to make the body larger.) The baby penguin has fewer cells in its body overall than the parent does. Have students reflect on why larger organisms need to be made up of many tiny cells rather than just one or a small number of large cells. Elicit student ideas for why there are no truly “giant” cells.

Chromosomes In eukaryotic cells, DNA is packaged into multiple chromosomes. Use the figure to start a discussion on the structure of eukaryotic chromosomes. Discuss the levels of organization within the chromosome structure. Click to reveal each level of organization: DNA double helix; histone proteins and nucleosome; coils and supercoils; and centromere, sister chromatids, and duplicated chromosome. Ask: What are nucleosomes composed of? Answer: DNA wrapped around histone molecules Ask: Tightly packed nucleosomes form what structure? Answer: coils

Chromosomes In eukaryotic cells, DNA is packaged into multiple chromosomes. DNA double helix duplicated chromosome coils sister chromatids centromere nucleosome Use the figure to start a discussion on the structure of eukaryotic chromosomes. Discuss the levels of organization within the chromosome structure. Click to reveal each level of organization: DNA double helix; histone proteins and nucleosome; coils and supercoils; and centromere, sister chromatids, and duplicated chromosome. Ask: What are nucleosomes composed of? Answer: DNA wrapped around histone molecules Ask: Tightly packed nucleosomes form what structure? Answer: coils supercoils histone proteins

Where is DNA found inside of a eukaryotic cells? INSIDE THE NUCLEUS

Cell Division Produces two daughter cells Cell must replicate DNA before cell division. Explain that to solve the surface-area-to-volume ratio faced by a growing cell, an individual cell divides. The division of a cell produces two daughter cells. Click to reveal the first bullet point. Challenge students to think about what a cell would have to do before it divides. Guide their thinking as necessary by asking them what major components a cell needs (e.g., DNA, cytoplasm). Point out that before it can divide to produce daughter cells, there has to be enough DNA for two cells. Before cell division, the cell must replicate, or make a copy of its DNA. This avoids the problem of information overload. Click to reveal the second bullet point. Tell students: Cell division solves the problem of increasing cell size by decreasing cell volume. Making more cells instead of larger cells keeps the surface-area-to-volume ratio high. Click to reveal the third bullet point. Misconception alert: Students may think that cells get smaller and smaller with each successive cell division. Tell students that cells go through a period of growth after they divide. Remind students that cell division helps a cell avoid the problems of growing too large.

Asexual Reproduction A single parent produces genetically identical offspring. New individuals form from the separation of cells. Distribute the lesson worksheet to the class. Encourage students to use the worksheet to take notes describing the advantages and disadvantages of asexual and sexual reproduction strategies. Suggest that students create one column per strategy and mark each entry they make under a column with an “A” or “D” for “advantage” and “disadvantage.” For extra review, students should define the two strategies in the header row. Remind students that reproduction is one of the most important characteristics of living things. Point out that for a single-celled organism like a bacterium, simple cell division makes the process of reproduction pretty straightforward, and it can allow a population to grow very quickly. This kind of cell division is a form of asexual reproduction, which is the production of genetically identical offspring from a single parent. Click to reveal the bullet points. Lead a discussion about how cell division relates to the process of asexual reproduction. To reinforce students’ knowledge, have them apply what they have learned to their everyday lives. Ask: Why do bacterial infections spread so quickly through a school? Answer: Bacteria can reproduce asexually, so they can reproduce quickly in the right environment, such as a crowded school. Direct students to the photos of kalanchoe and hydra. Ask: Both of these organisms are reproducing asexually. How are they different from the bacterium? Answer: They are multicellular organisms. Point out that tiny plantlets in the kalanchoe can break off and grow into full new plants. The bud on the hydra will eventually pinch off to become a separate individual. Ask: What do the offspring off all three of these organisms have in common? Answer: The offspring share the same genetic material as their parent.

Asexual Reproduction Asexual Reproduction : A single parent produces genetically identical offspring .   An example of asexual reproduction is ___________________________________ and occurs in _______________________ .

Asexual Reproduction Asexual Reproduction : A single parent produces genetically identical offspring .   An example of asexual reproduction is binary fission and this occurs in bacteria. https://www.youtube.com/watch?v=j8_xoM8Wwgs

The Eukaryotic Cell Cycle The cell cycle is when a cell grows, prepares for division, and divides into two new daughter cells. There are 3 parts to the cell cycle. 1. Interphase 2. Mitosis 3. Cytokinesis

The Cell Cycle Eukaryotic cells have a more complex cell cycle than prokaryotic cells.

Color: You need 3 DIFFERENT colors.

WRITE: Cell cycle: The cell cycle is when a cell grows, prepares for division, and divides into two new daughter cells.

Now, color and label Interphase.

Color and label mitosis.

Finally, color and label cytokinesis.