HS-LS1-4: Modeling Mitosis and Cell Differentiation
In plain English: HS-LS1-4 is the NGSS high school performance expectation that asks students to use a model to show how cell division by mitosis and cell differentiation build and maintain a complex organism. Mitosis makes genetically identical cells for growth, repair and replacement, and differentiation lets cells with the same DNA take on different jobs. It is usually taught in Biology.
Use a model to illustrate the role of cellular division (mitosis) and differentiation in producing and maintaining complex organisms.
Assessment Boundary: Assessment does not include specific gene control mechanisms or rote memorization of the steps of mitosis.
Next Generation Science Standards · Disciplinary Core Idea: From Molecules to Organisms: Structures and Processes · Official standard
Students build and use models that explain how one fertilized egg becomes an organism with trillions of cells of many kinds, and how that organism keeps replacing worn-out and damaged cells. Two processes carry the story. Mitosis copies every chromosome and splits the copies evenly, so each new cell gets the same genetic information as the cell it came from. Differentiation lets cells that carry the same genes become different, because each kind of cell uses a different set of those genes. Students work with physical chromosome models, a cell lineage diagram, root tip data they collect at the microscope and invented data sets on growth and repair, and they critique and revise flawed models.
HS-LS1-4 has no official Clarification Statement. The Assessment Boundary says: "Assessment does not include specific gene control mechanisms or rote memorization of the steps of mitosis." So no activity, homework or quiz item asks students to name or order the phases of mitosis, and differentiation is described only as cells using different genes. How cells switch genes on and off (transcription factors, DNA methylation) is beyond this standard. Meiosis is also beyond this standard and appears only as a contrast.
Learning Objectives
By the end of this lesson, students will be able to:
Use a model to show that mitosis produces two daughter cells with the same number and kinds of chromosomes as the parent cell
Use a doubling model to explain how repeated mitosis turns one fertilized egg into a many-celled organism, and name the limits of that model
Explain with a model how cells that carry identical DNA become specialized by using different genes
Analyze data on dividing cells in root tips, regenerating tissue and healing wounds to explain how mitosis and differentiation maintain an organism
Critique a model of growth, repair or specialization and revise it to fit the evidence
Prior Knowledge Required
Students should already be comfortable with:
Living things are made of one cell or many cells MS-LS1-1
Cell parts have functions, and the nucleus holds the DNA MS-LS1-2
Body systems are made of groups of specialized cells MS-LS1-3
Genes on chromosomes carry instructions for making proteins MS-LS3-1
Project a photo of a newborn next to a photo of a single fertilized egg cell. Ask students to work alone for three minutes, then compare with a partner.
Warm-Up Prompt
"You started as one cell. Now you are made of trillions of cells, and your nerve cells, muscle cells and skin cells look nothing alike. Draw a quick model that shows where all those cells came from and why they are not all the same. Label one thing your model cannot explain yet."
Collect two or three models on the board. Many students draw cells splitting but cannot say why the cells end up different, or they say each cell type has its own DNA. Keep these ideas visible: the lesson tests them.
Direct Instruction15-20 minutes
Mitosis keeps the genetic information the same. Before a cell divides, it copies every chromosome. During mitosis the two copies of each chromosome are pulled to opposite sides, and the cell splits into two daughter cells. Each daughter has the same number and kinds of chromosomes as the parent, so it carries the same genes. The body uses mitosis to grow (more cells), to repair damage and to replace cells that wear out. Students do not need the names of the stages: the key idea is copy, then split evenly.
Differentiation makes cells different. Because every body cell descends from the fertilized egg by mitosis, the cells carry the same genes. A muscle cell, a nerve cell and a skin cell differ because each uses a different set of those genes, so each makes different proteins and takes on a different shape and job. Some cells, called stem cells, stay unspecialized and keep dividing; some of their daughters specialize. Use Diagram 1 to trace a lineage from the fertilized egg to specialized cells.
Chromosome model of one division
A body cell of a fruit fly has 8 chromosomes. Before the cell divides, each chromosome is copied, so each one is made of two identical strands joined together.
Result: The 8 copied chromosomes are split so that one copy of each goes to each side. Each daughter cell gets 8 chromosomes that match the parent cell. The number is kept, not halved.
Doubling model of development
Model: every cell divides once per round and no cell dies. A published estimate puts the human body at about 3 × 10¹³ cells. How many rounds are needed?
Result: After n rounds there are 2n cells. 244 ≈ 1.8 × 10¹³ is too few and 245 ≈ 3.5 × 10¹³ is enough, so at least 45 rounds of division. The model is a starting point: it treats every cell the same, which real embryos do not do.
Maintaining a tissue: red blood cells
An adult has about 2.5 × 10¹³ red blood cells, and each one lasts about 120 days. Mature red blood cells cannot divide. How fast must new ones be made to keep the number steady?
Result: 2.5 × 10¹³ ÷ (120 days × 86,400 s per day) ≈ 2.4 million new red blood cells per second. Stem cells in the bone marrow divide by mitosis, and some of their daughter cells differentiate into red blood cells.
Same DNA, different cells
In 1996 scientists put the nucleus of a sheep udder cell, a fully specialized cell, into an egg cell whose own nucleus had been removed. The egg developed into a lamb, Dolly.
Result: A specialized cell still carried every gene needed to build a whole sheep. Differentiation changes which genes a cell uses, not which genes it has.
Stem cell model: self-renewal
A skin stem cell divides 5 times. Each time, one daughter stays a stem cell and the other divides 3 more times before its daughters specialize as skin cells.
Result: Each division sends 23 = 8 skin cells onward, so 5 × 8 = 40 skin cells. The count of stem cells is the same at the end as at the start: 1.
After each example, ask: "Which part of this is mitosis, which part is differentiation, and what evidence tells you so?" Point out that the doubling model in the second example is useful but wrong in a known way, and ask students what it leaves out.
Guided Practice15 minutes
Pairs analyze invented counts from a microscope study of an onion root. At four distances from the tip, a student counted 200 cells and recorded how many were dividing (cells with thick, visible chromosomes and no nuclear outline). Compare the results with Diagram 2.
Guided practice data: dividing cells in an onion root (invented)
Distance from the tip
Cells counted
Cells dividing
Percent dividing
0-1 mm
200
36
?
1-2 mm
200
22
?
2-3 mm
200
8
?
4-5 mm
200
1
?
Compute the percent of dividing cells in each region (dividing ÷ counted × 100). The results are 18%, 11%, 4% and 0.5%.
Use the data to decide where the root makes most of its new cells.
Cells 4-5 mm from the tip are several times longer than cells near the tip, and some have root hairs. Explain what has happened to these cells, using the word differentiation.
Write a two-sentence explanation of how a root grows longer that uses both mitosis and differentiation and cites one number from the table.
Independent Practice10-15 minutes
Each student critiques this model from a student in another class: "Heart cells and skin cells are different because they have different DNA. Mitosis in the heart copies heart DNA, and mitosis in the skin copies skin DNA." Students use the invented test results below as evidence.
Independent practice data: gene tests on cells from one person (invented)
Gene
Found in heart muscle cells?
Found in skin cells?
Its protein made in heart muscle?
Its protein made in skin?
Heart muscle contraction gene
Yes
Yes
Yes
No
Skin keratin gene
Yes
Yes
No
Yes
Cell energy gene
Yes
Yes
Yes
Yes
Students write (1) one part of the model that the data contradict, (2) a revised model in one or two sentences and (3) one part of the original model worth keeping (mitosis does copy the DNA of a cell faithfully).
Closure5 minutes
Exit ticket: "A cell with 12 chromosomes divides by mitosis, and then both daughters divide again. How many cells are there, and how many chromosomes does each have? Why can these cells still become different kinds of cells later?" (4 cells with 12 chromosomes each; they carry the same genes but can use different ones.) Return to the warm-up models and have students add one arrow labeled mitosis and one labeled differentiation.
Differentiation Strategies
For Struggling Students
Give a partly drawn lineage diagram with the first two rounds of division filled in, and have students add the next round and the chromosome number in each cell
Provide a sentence frame: "Mitosis gives each new cell ___. The cells become different because ___. My evidence is ___."
Let students use a calculator table of powers of 2 (21 to 220) for the doubling questions so the focus stays on the model
For Advanced Students
Ask students to build the doubling model in a spreadsheet, then change one assumption of their choice and describe how the predicted number of cells changes
Have students compare a tissue that is renewed quickly (the lining of the gut) with one whose cells rarely divide in adults (heart muscle) and predict how each responds to damage
Ask students to design a way to test whether a specialized plant cell still has all the genes needed to grow a whole plant
Assessment Guidance
What to Look For
Check that students say mitosis keeps the chromosome number the same and gives identical genetic information, and that they do not say mitosis makes cells different. Look for explanations of differentiation that separate having a gene from using it. Listen for the idea that different cell types have different DNA, and for students who think adults no longer need cell division. Do not grade students on naming the stages of mitosis: the Assessment Boundary rules that out.
02
Classroom Activities
3 Activities
1
Pipe Cleaner Chromosomes: Copy, Split, Specialize
25 minPairs
Pairs build a physical model of a cell with 4 chromosomes (a long and a short chromosome from each of two parents), run it through two rounds of mitosis, and then give each of the four resulting cells a job. The model makes two ideas visible: the chromosome set stays the same, and cells with the same genes can still specialize.
Materials per Pair
16 pipe cleaner pieces: 4 long and 4 short in color 1, 4 long and 4 short in color 2 (the teacher cuts the short pieces in advance and folds every cut end over)
4 paper plates (cells) and 4 index cards
1 gene card per plate, all identical, listing 6 genes: contraction protein, signal-carrying protein, keratin, oxygen-carrying protein, cell energy enzymes, insulin
4 job cards dealt by the teacher: muscle cell, nerve cell, skin cell, stem cell
Procedure
Put one long and one short piece of each color on the first plate: this cell has 4 chromosomes.
Copy: twist a matching piece onto each chromosome, so each one has two identical strands.
Split: untwist the pairs and move one strand of each chromosome to each of two new plates. Check that each plate has the same 4 chromosomes as the first cell had.
Repeat the copy and split with both plates, ending with 4 plates. Record the chromosomes on each plate.
Put an identical gene card on each plate. Draw a job card for each plate and circle the genes that cell uses (every cell uses the cell energy genes).
Safety: keep wire ends folded and away from eyes; no scissors are needed.
Discussion Questions
Compare the chromosomes on your four plates. What is the same? Compare the circled genes. What is different?
In one group's model, one daughter plate ended up with 5 chromosomes and the other with 3. Which step went wrong, and why would it matter to a real cell?
Name one thing a real cell does that this model does not show. (For example, real chromosomes carry thousands of genes, and how a cell turns genes on is not modeled here; that is beyond this standard.)
Modification for Distance Learning
Students use paper strips or a drawing app for chromosomes and share a photo or screenshot of each round, with the four gene cards labeled.
2
Root Tip Microscope Lab: Where Are Cells Dividing?
25 minPairs
Pairs use commercially prepared, already stained onion root tip slides to collect their own evidence. They count dividing and non-dividing cells in two regions of the root and use the counts to explain where growth by mitosis happens and where cells differentiate.
Procedure
Find the root tip on low power. Locate region 1, just behind the tip, and region 2, about 3 mm farther up the root.
Switch to high power. In each region, count 50 cells in a row, marking each as dividing (thick, visible chromosomes, no nuclear outline) or not dividing. Repeat in a second field, for 100 cells per region.
Pool the pair counts with three other pairs, so each region has 400 cells.
Sketch one cell from each region at the same magnification and note its length.
Safety: carry the microscope with one hand on the arm and one under the base; use the coarse focus knob only on low power so the lens does not crack the slide; if a slide breaks, tell the teacher and do not pick up the glass; unplug the lamp by the plug, not the cord. Use only prepared slides: no acid or stain is used in class.
Sample Data (invented)
Pooled counts: region 1, 64 of 400 cells dividing; region 2, 6 of 400 cells dividing. Cells in region 2 are much longer, and some have root hairs.
Discussion Questions
Compute the percent of dividing cells in each region. In the sample data, about how many times larger is the share in region 1?
Region 2 cells are longer and some have root hairs. What does this suggest they have done since they were made near the tip?
Use your counts to explain why a root needs both mitosis and differentiation to grow longer and to take up water.
Modification for Distance Learning
Students count cells on printed or online micrographs of the two regions with a grid laid over them, then pool counts on a shared spreadsheet.
3
Regrowth Stations: Which Process Does the Work?
25 minGroups of 3-4
Three stations each show a case of an organism rebuilding lost parts. At each station, groups draw a model of where the new cells come from and label every arrow as mitosis, differentiation or both. Groups rotate every 7 minutes and use the last 4 minutes to compare models.
Stations
Station 1, flatworm fragments (invented data card): Planarian flatworms carry many stem cells. Researchers cut 10 untreated worms and 10 worms treated to destroy their dividing stem cells. After 10 days, 10 of 10 untreated fragments had regrown a head; 0 of 10 treated fragments had.
Station 2, basil cuttings (live): The class set 3 basil stems in cups of water a week earlier. Students look for new roots near the cut end and record the number of roots on each stem. Safety: wash hands after handling plants and water, and wipe up spills at once.
Station 3, mouse liver (data card): When two thirds of a mouse liver is removed in a research study, the remaining liver grows back to about its original mass in roughly one to two weeks, mainly because the remaining, already specialized liver cells divide.
Discussion Questions
At which station do most of the new cells come from specialized cells that divide, rather than from stem cells?
What does the difference between 10 of 10 and 0 of 10 at Station 1 tell you about where the new head cells come from?
At Station 2, the new roots have cells unlike the cells of the basil stem they grew from. Which two processes does your model need, and in what order?
Challenge Variation
Groups plan an investigation to find out whether basil cuttings form roots faster in light or in dark. They name the independent and dependent variables, the controls and the number of cuttings per group.
03
Diagrams & Visual Aids
2 diagrams
Diagram 1: A Cell Lineage Model from the Fertilized Egg to Specialized Cells
Two rounds of mitosis turn the fertilized egg into four cells, each with the same 46 chromosomes (the human number). Each cell then uses a different set of the same genes and specializes. The stem cell stays unspecialized and keeps dividing, so the body keeps a supply of cells that can replace lost ones. A real embryo goes through far more rounds than the two shown.
Diagram 2: Dividing Cells at Four Distances from an Onion Root Tip
The guided-practice counts, drawn to scale. The share of dividing cells is largest in the first millimeter and falls with distance, so new root cells are made near the tip by mitosis. Farther up, cells stop dividing, grow longer and differentiate.
04
Homework Assignment
~30 min
HS-LS1-4 Homework: Modeling Growth, Repair and Specialization
Directions: All data sets are invented for practice unless a problem says otherwise. You do not need the names of the stages of mitosis. Show calculations, draw a model where asked, and end each problem with a sentence that names your evidence.
Part 1: Mitosis in Models (Problems 1-2)
A body cell of a house cat has 38 chromosomes. (a) How many chromosomes does each daughter cell have after mitosis? (b) Starting from this one cell, all cells divide 6 times in a row and none die. How many cells are there, and how many chromosomes do they hold all together? (c) A classmate's model splits the 38 chromosomes 19 and 19 between the daughters without copying them first. Explain what would happen to the cells after a few rounds, and fix the model.
In a model embryo (invented), every cell divides every 30 minutes for the first 5 hours. (a) How many rounds of division happen, and how many cells are there at 5 hours? (b) Make a table of the number of cells every half hour for the first 2 hours and sketch the graph. (c) At what time does the number first pass 500? (d) Give two reasons a real embryo would not keep following this model for days.
Part 2: Differentiation and Evidence (Problems 3-4)
In the 1950s, scientists grew single cells taken from a carrot root in a nutrient broth, and some of them grew into complete carrot plants with green leaves. (a) What does this tell you about the genes in a carrot root cell? (b) Carrot roots growing underground are orange, not green, yet the top of a carrot root that sticks out of the soil into sunlight can turn green. Use the idea of differentiation to explain both observations. (c) Draw a model with one root cell, one leaf cell and their shared genes that shows your explanation.
Mice in a research study were given a treatment that destroys the dividing cells of the bone marrow. Group A then received bone marrow cells from a healthy mouse; group B received none. The table gives the white blood cell count as a percent of normal (invented data). Week 0: A 100, B 100. Week 1: A 30, B 30. Week 2: A 45, B 20. Week 4: A 80, B 10. Week 6: A 95, B 5. (a) Find the change from week 1 to week 6 for each group. (b) Explain the difference using mitosis and differentiation. (c) Group A later also regained red blood cells and platelets. What does this suggest about the cells that were transplanted?
Part 3: Build and Revise a Model (Problems 5-6)
Model of a small patch of skin (invented numbers): 500 stem cells each divide once a day. One daughter stays a stem cell; the other divides 2 more times, and all of its daughters specialize as skin cells. (a) How many new skin cells does the patch make per day? (b) The surface loses 2,000 dead skin cells a day. Is the patch stable, growing or thinning? (c) Predict what happens if half of the stem cells are lost in a burn, and describe one change in the model that could let the patch recover.
Cells were counted at the edge of a small skin cut (invented data). Dividing cells per square millimeter: day 0, 5; day 1, 12; day 2, 40; day 3, 34; day 5, 15; day 7, 6. (a) On which day is division highest, and how many times the day 0 value is it? (b) Draw a model of the healing cut that shows where mitosis and differentiation happen. (c) Write a claim, evidence and reasoning paragraph explaining why the count falls again by day 7.
Rubric
Criterion
Full Credit (2 pts)
Partial Credit (1 pt)
Mitosis
States that mitosis keeps the chromosome number and genetic information the same; doubling calculations correct
Correct idea with one calculation error, or correct calculation with an unclear explanation
Differentiation
Separates having a gene from using it, and ties specialization to the genes a cell uses
Mentions specialization but implies cell types have different DNA
Models
Model shows both processes, is labeled, and its limits are named
Model shows one process only or is unlabeled
Evidence
Claims cite specific numbers or observations from the data
Claims are general or do not refer to the data
05
Quiz: 20 Questions
Interactive, with answers
Instructions
Data sets are invented unless a question says otherwise, and no question asks for the names of the stages of mitosis. Your score updates as you answer, and Reset quiz clears everything so you or your students can try again.
Multiple choice: pick an option to check it. Short answer: write your answer, then reveal the model answer.
0 of 20 answered · 0 correct
Question 1 of 20 · Multiple Choice
A body cell with 20 chromosomes divides by mitosis. How many chromosomes does each daughter cell have?
Answer: C
The cell copies every chromosome and then splits the copies evenly, so each daughter has 20, the same as the parent. Choice A halves the number, which happens in meiosis (beyond this standard), not mitosis. Choice B counts the copied strands before the split as if they all stayed in one cell.
Question 2 of 20 · Multiple Choice
Which model best explains why almost all the cells in your body carry the same genes?
Answer: A
Mitosis passes a full, identical chromosome set to each daughter cell, so the cells of one body share one set of genes. Choice B is the idea that cell types have different DNA, which gene tests and cloning experiments contradict. Choices C and D describe processes that do not build the body.
Question 3 of 20 · Multiple Choice
In a doubling model, one cell divides and every new cell divides again, with no cell death. How many cells are there after 8 rounds?
Answer: D
Each round doubles the number, so after 8 rounds there are 28 = 256 cells. Choice A multiplies 2 × 8 instead of raising 2 to the 8th power. Choice B computes 82. Choice C is 27, one round short.
Question 4 of 20 · Multiple Choice
A student counted 150 cells in each of four regions of a bean root (invented data): region A, 12 dividing; region B, 30 dividing; region C, 3 dividing; region D, 9 dividing. Which region is most likely closest to the growing tip?
Answer: B
The growing tip is where the most cells are dividing. Region B has 30 ÷ 150 = 20% dividing, more than A (8%), D (6%) or C (2%). Choice C picks the region with the fewest dividing cells, where cells have mostly stopped dividing and differentiated.
Question 5 of 20 · Multiple Choice
A nerve cell and a skin cell from the same person look and work very differently. Which statement best explains why?
Answer: B
Both cells come from the fertilized egg by mitosis and carry the same genes; they differ because each uses a different set of genes and so makes different proteins. Choice A is a frequent misconception that gene tests contradict. Choice D is wrong because body cells are made by mitosis.
Question 6 of 20 · Multiple Choice
Which result would be the strongest evidence that a fully specialized animal cell still has all of the genes needed to build a whole animal?
Answer: D
If the nucleus of a specialized cell can direct the development of a whole frog, it must still hold every gene needed. Choice A shows the cell can divide, not that it has all the genes. Choice C shows specialization, which fits either model, so it cannot decide between them.
Question 7 of 20 · Multiple Choice
A student's model shows a stem cell that divides into two specialized cells every time it divides. What is the main problem with this model for a tissue that must be renewed for a lifetime?
Answer: A
If both daughters always specialize, no stem cell is left after the division, so renewal stops. Real stem cells keep at least one daughter as a stem cell on average (self-renewal). Choice C is wrong because mitosis keeps the chromosome number. Choice B is the opposite of what the model predicts.
Question 8 of 20 · Multiple Choice
A tissue in a model organism has 6,000,000 cells, and each cell lasts 30 days before it dies and is shed. About how many new cells per day must the tissue make to stay the same size?
Answer: C
To replace every cell once in 30 days, the tissue makes 6,000,000 ÷ 30 = 200,000 cells per day. Choice D multiplies instead of dividing. Choices A and B are off by a factor of 10.
Question 9 of 20 · Multiple Choice
On a microscope slide of a growing plant tip, 45 of 300 cells are dividing. What percent of the cells are dividing?
Answer: A
45 ÷ 300 = 0.15, which is 15%. Choice B reports the count as a percent. Choice C divides 300 by 45. Choice D forgets to multiply by 100.
Question 10 of 20 · Multiple Choice
A doubling model predicts 2n cells after n rounds, but a real embryo examined after the same time has fewer cells than predicted. Which revision to the model fits this evidence?
Answer: D
Fewer cells than 2n means some cells divided less often or were lost, so the revised model adds uneven division rates and cell death. Choice B would give more cells, not fewer. Choice A would not change the number of cells.
Question 11 of 20 · Multiple Choice
Heart muscle cells rarely divide in adults. After a heart attack kills a patch of heart muscle, what does this predict about how the damaged patch heals?
Answer: B
If heart muscle cells seldom divide, they cannot replace the lost muscle, and other cells that can divide fill the gap with scar tissue. Choice A ignores the evidence that these cells rarely divide. Choice D ignores the other cell types in the heart that can still divide.
Question 12 of 20 · Multiple Choice
A student compares a young leaf bud with a full-grown leaf from the same plant. Which prediction best fits the model of growth by mitosis and differentiation?
Answer: C
A growing part makes new cells by mitosis, and once a leaf reaches full size its cells have mostly stopped dividing and specialized. Choice B confuses size with growth rate. Choice D is wrong because mitosis keeps the chromosome number the same.
Question 13 of 20 · Multiple Choice
A dog body cell has 78 chromosomes. It has copied all of its chromosomes and is about to divide. Which describes the two daughter cells?
Answer: A
The copies are split evenly, so each daughter gets one copy of every chromosome: 78, the same set as the parent. Choice C counts every strand of the copied chromosomes as a separate chromosome in each daughter. Choice B halves the number, as in meiosis.
Question 14 of 20 · Multiple Choice
In a lineage diagram, cell X divides many times. Each time, one daughter looks like X and keeps dividing, and the other becomes a blood cell. What is cell X?
Answer: B
A stem cell divides to renew itself and to give daughters that specialize, which is exactly the pattern of X. Choice A is wrong because specialized blood cells do not keep producing more cells like themselves in this way. Choice D is wrong because every living cell uses some of its genes.
Question 15 of 20 · Short Answer
In a doubling model with no cell death, how many rounds of division does it take for one cell to become at least 1,000,000 cells? Show your reasoning.
219 = 524,288 is too few and 220 = 1,048,576 is enough, so 20 rounds. Real tissues need more divisions because some cells die and cells divide at different rates.
Question 16 of 20 · Short Answer
A student writes: "Mitosis is what makes the different kinds of cells in the body." Critique the statement and revise it.
Mitosis alone makes identical cells: it copies the chromosomes and splits them evenly. The differences come from differentiation, when cells use different sets of the same genes. Revised: "Mitosis makes more cells with the same genes, and differentiation makes those cells different by changing which genes they use."
Question 17 of 20 · Short Answer
Invented test results for one person: the gene for albumin (a blood protein made by the liver) is found in liver cells and in skin cells, but albumin is made only in liver cells. What claim do these data support? Explain.
Claim: liver and skin cells have the same genes, but only liver cells use the albumin gene. The gene is present in both cell types, so skin cells did not lose it; they simply do not use it. This supports differentiation as a change in which genes are used, not in which genes are present.
Question 18 of 20 · Short Answer
A stem cell divides 4 times. Each time, one daughter stays a stem cell and the other divides 3 more times, after which all of its daughters specialize. How many specialized cells are made, and how many stem cells remain?
Each committed daughter gives 23 = 8 specialized cells, so 4 × 8 = 32 specialized cells, and 1 stem cell remains to keep dividing.
Question 19 of 20 · Short Answer
Why must a cell copy its chromosomes before it divides by mitosis? Predict what would happen over several generations of cells if it did not.
Copying gives two full sets, so each daughter can receive a complete, identical set. Without copying, each division would split one set, so the daughters would get only part of the genes, and after a few rounds cells would be missing genes they need and could not survive or work properly.
Question 20 of 20 · Short Answer
A mouse grows from about 1 g at birth to about 20 g as an adult, and its average cell size stays about the same. Estimate the minimum number of rounds of doubling needed, and explain why the real number of divisions is larger.
The mass grows 20 times, so the number of cells grows about 20 times. 24 = 16 is too few and 25 = 32 is enough, so at least 5 rounds (about 4.3 doublings). The real number is larger because cells die and are replaced all through life, so many divisions only replace lost cells.
0 of 20 answered · 0 correct
06
Frequently Asked Questions
10 Questions
What does HS-LS1-4 mean?
HS-LS1-4 asks students to use a model to show how mitosis and cell differentiation produce a complex organism and keep it working. Mitosis supplies new cells with the same genetic information, and differentiation turns those cells into specialized types. The code stands for High School, Life Science, core idea 1 (From Molecules to Organisms: Structures and Processes), performance expectation 4.
Do students need to memorize the phases of mitosis for HS-LS1-4?
No. The official Assessment Boundary says assessment does not include rote memorization of the steps of mitosis. Teachers may still show what dividing cells look like, but the assessed idea is that chromosomes are copied and split evenly, so the daughter cells match the parent cell.
Is HS-LS1-4 taught in Biology?
Yes, it is usually taught in a high school Biology course, often in a unit on cells or on cell division and growth. Integrated science courses place it in their life science units.
What models work well for mitosis and differentiation?
Physical models such as pipe cleaner or bead chromosomes, cell lineage diagrams, flow charts from a fertilized egg to tissues, and simple math models of doubling all work. The strongest lessons have students use a model to explain data and then say where the model fails, since every model leaves something out.
If every cell has the same DNA, how do cells become different?
Cells become different by using different genes. A muscle cell and a skin cell carry the same genes, but each uses its own set, so they make different proteins and take different shapes. How cells switch genes on and off is a gene control mechanism, which the Assessment Boundary leaves out of this standard.
What is the difference between mitosis and meiosis?
Mitosis makes two cells with the same chromosome number as the parent, for growth and repair; meiosis makes sex cells with half the number. Meiosis is not part of HS-LS1-4; it belongs with inheritance and variation in HS-LS3-2.
What are stem cells, and why are they part of this standard?
Stem cells are unspecialized cells that can keep dividing and give rise to specialized cells. They connect the two halves of the standard: stem cells divide by mitosis, and some of their daughters differentiate. Bone marrow, skin and the lining of the gut keep stem cells that replace lost cells throughout life.
How does mitosis maintain the body after it has stopped growing?
Adults keep dividing cells to replace cells that wear out and to repair injuries. Blood cells, skin cells and the cells lining the gut are replaced all the time, while some cell types, such as most nerve cells, rarely divide in adults. Growth stops, but cell division does not.
What mistakes do students often make with HS-LS1-4?
A frequent mistake is saying that different cell types have different DNA. Other common errors are saying mitosis halves the chromosome number, treating copied chromosomes as extra chromosomes, and thinking cell division stops after childhood. Ask students to explain data, not only to define terms, to bring these ideas out.
How does HS-LS1-4 connect to other standards?
It builds on middle school ideas that organisms are made of cells (MS-LS1-1) and that body systems are made of specialized cells (MS-LS1-3). It sits beside HS-LS1-1 (DNA and proteins) and HS-LS1-2 (levels of organization), and it leads to HS-LS3-1 and HS-LS3-2, where students study how chromosomes pass traits to offspring and how variation arises.
07
Related Standards
6 standards
These standards connect to HS-LS1-4: prerequisites to review first, parallel standards at the same level, and next steps that build on it.
Before this lesson
MS-LS1-1Prerequisite
Investigate evidence that living things are made of one cell or many cells
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