Grade by Grade
B. Life Systems · Cells

Keeping Cells Healthy: Cell Division, Cancer and Microbes

B1.2 A3.1 A1.1 A1.5About 55 minutes
Learning goals
  • I can explain why cells divide and what happens when cell division goes out of control (cancer).
  • I can describe things that can damage cells, such as UV rays and tobacco smoke, and how to protect them.
  • I can explain how antibiotics and vaccines work at the level of cells, and why antibiotic resistance is a problem.
  • I can name careers that use cell biology to keep people healthy.

Words to know

cell division
The process by which one cell divides to form two new cells. It lets organisms grow, repair damage and replace worn-out cells.
cancer
A group of diseases in which some cells divide out of control and can invade nearby tissues or spread to other parts of the body.
tumour
A lump formed by cells dividing when they shouldn't. Some tumours are cancer and some are not.
ultraviolet (UV) radiation
Invisible rays from the sun (and tanning beds) that can damage the DNA in skin cells.
antibiotic
A medicine that kills bacteria or stops them from growing. Antibiotics do not work on viruses.
antibiotic resistance
When bacteria change so that an antibiotic no longer works against them.
vaccine
A product that safely trains the immune system's cells to recognize a germ, so the body can fight it off quickly later.

Billions of new cells every day

Right now, your body is making new cells. Skin cells on your surface wear off and are replaced from below. Cells lining your stomach and intestines are replaced every few days. Bone marrow stem cells make millions of new blood cells every second. All of this happens through cell division, following instructions in each cell's DNA, and it is normally carefully controlled: cells divide when new cells are needed and stop when they aren't.

When cell division goes wrong: cancer

If a cell's DNA is damaged, the instructions that control division can be changed. Most damaged cells repair themselves or die. But sometimes a damaged cell keeps dividing when it shouldn't, making more and more copies. These cells can form a lump called a tumour.

  • Some tumours are not cancer: they stay in one place.
  • Cancer cells can invade nearby tissues and spread to other parts of the body through the blood.
  • Cancer is not contagious: you can't catch it from someone.

Things that can damage DNA and raise the risk of some cancers include UV radiation from the sun and tanning beds, chemicals in tobacco smoke, and some viruses. Not every cancer has a known cause, and getting cancer is not someone's fault.

Protecting your cells:

  • Sun safety: when the UV index is 3 or higher (it's in many Canadian weather forecasts), cover up with a hat and clothing, seek shade, and use broad-spectrum sunscreen of SPF 30 or higher. Sunburn is a sign that skin cells have been damaged.
  • Don't smoke or vape. Tobacco smoke damages cells lining the airways and lungs. Vaping exposes the lungs to nicotine and other chemicals; scientists are still studying the long-term effects.
  • Vaccines: Ontario offers students in Grade 7 a vaccine against HPV, a virus that can cause some cancers years later.
  • Healthy habits help all your cells: balanced meals, water, sleep and physical activity.

Treatments use cell biology too. Surgery removes tumours. Chemotherapy and radiation therapy damage cells that are dividing quickly, which is why they work on cancer, and also why they can affect fast-dividing healthy cells, such as those that make hair (causing hair loss during treatment).

Normal: cells fill a gap, then STOPgap (a cut)gap filled, division stopsOut of control: a damaged cell keeps dividingdamaged DNAlump(tumour)
Top: healthy cells divide to fill a gap, then stop. Bottom: a cell with damaged DNA keeps dividing when it shouldn't, and its copies pile up into a lump (a tumour).

Microbes, medicines and your immune system

Bacteria are cells. Most are harmless or even helpful (like many that live in your intestines), but some cause infections. Your immune system uses specialized white blood cells to find and destroy invaders.

  • Antibiotics kill bacteria or stop them from dividing. They target parts of bacterial cells that human cells don't have, such as the bacterial cell wall. They do not work on viruses (which aren't cells), so they don't help with a cold or the flu.
  • Antibiotic resistance: in any large group of bacteria, a few may, by chance, be able to survive an antibiotic. If antibiotics are used when they aren't needed, or a prescription isn't taken as directed, those survivors can multiply. Over time, the antibiotic stops working. This is a serious problem for hospitals around the world.
  • Vaccines show your immune cells a harmless piece or version of a germ, so they remember it and can respond quickly if the real germ ever arrives.
  • Handwashing with soap for about 20 seconds removes many microbes before they can get into your body.
CareerHow it uses cell biology
Medical laboratory technologistTests blood, tissue and other samples, often with microscopes, to help diagnose illness (for example, counting blood cells or identifying bacteria).
Pathologist (a doctor)Examines tissue and cells under a microscope to diagnose diseases such as cancer.
Radiation therapistPlans and gives radiation treatment aimed at cancer cells while protecting healthy tissue.
PharmacistExplains how medicines like antibiotics work and how to take them properly.
Public health inspectorInspects restaurants, pools and water supplies to stop harmful microbes from spreading.
These careers need different amounts of education after high school, from college diplomas to medical school.
Worked example

Let's use the UV index

It's a sunny day in July and the forecast says the UV index will reach 8 at 1 p.m. You have a soccer game from noon to 2 p.m. What should you do, and why does it matter for your cells?

  1. A UV index of 8 is very high (well above 3), so skin cells can be damaged quickly.
  2. Plan protection: apply SPF 30 or higher broad-spectrum sunscreen 15 to 30 minutes before and reapply after sweating; wear a hat and sunglasses; sit in the shade during breaks; drink water.
  3. Why: UV rays can damage the DNA in skin cells. Repeated damage, especially sunburns, raises the risk of skin cancer later in life.

Cover up, use sunscreen, find shade on breaks. Protecting skin now protects the DNA in your skin cells.

Worked example

Let's model antibiotic resistance

An infection has 1 000 000 bacteria. 10 of them can survive the antibiotic better than the rest. A patient feels better after 3 days and stops taking the medicine early, when 1000 of the hardiest bacteria are still alive. Explain what might happen.

  1. The antibiotic killed the easiest bacteria first. The survivors include many of the 10 tougher ones and their offspring.
  2. With the medicine stopped, the survivors divide again (some bacteria can divide every 20 to 30 minutes).
  3. The new population has a larger share of bacteria that resist the antibiotic.
  4. If they spread to other people, the antibiotic will work less well for them too.

Stopping early can leave the toughest bacteria to multiply, helping resistant bacteria spread. Take antibiotics exactly as prescribed, and only for bacterial infections.

1. Before medicine2. Medicine stopped early3. Survivors multiply20 bacteria, 2 resistant3 left, 2 resistant12 bacteria, 8 resistantcan survive the antibiotickilled by it
How resistance spreads: the antibiotic kills the easy bacteria first. If it is stopped early, the few survivors are mostly resistant, and when they multiply, most of the new population is resistant too.
Just for fun

Humming "Happy Birthday" twice takes about 20 seconds, the handwashing time public health agencies recommend. Your hands get clean, and it's someone's birthday somewhere, so it's never the wrong song.

Hands-on activity

Glitter germs: how well does handwashing work?

You need: hand lotion or cooking oil, a teaspoon of fine glitter (it stands in for microbes), a sink, soap, a timer, paper towel, and a helper.

  1. Rub a small amount of lotion on your hands, then sprinkle on a little glitter and rub it all over.
  2. Trial 1: rinse with cold water only for 5 seconds. Count or estimate how much glitter is left (a lot, some, very little). Take a photo if you can.
  3. Re-apply lotion and glitter. Trial 2: wash with soap and water for 5 seconds.
  4. Re-apply. Trial 3: wash with soap and water for 20 seconds, scrubbing between fingers, thumbs, backs of hands and under nails.
  5. Record your results in a table. Shake hands with your helper after one trial: what happens?
  6. Research (A1.1): find out from a reliable source (such as the Public Health Agency of Canada or your local public health unit) how long to wash hands and why. Write the source.
  7. Make a short poster explaining handwashing using what you know about cells.

Safety: keep glitter away from eyes and mouth. Wipe up oily spills so no one slips. Use biodegradable glitter if you can, or collect it on paper towel instead of letting it wash into drains.

What to look for: results that improve from Trial 1 to Trial 3; the explanation that soap helps lift oils (and microbes) off the skin; the shaking-hands step shows how microbes spread. Glitter is only a model: real microbes are invisible.

Your turn

1

Give three reasons your body needs cell division.

2

What is cancer?

3

Name two things that can damage the DNA in cells.

4

Why won't antibiotics cure a cold?

5

How does a vaccine help your cells?

6

Why does chemotherapy sometimes cause hair loss?

7

Name one career that uses a microscope to help diagnose disease.

More practice: warm-up

1

Is cancer contagious?

2

What kind of cells in your blood fight germs?

3

At what UV index should you start protecting your skin?

4

What SPF sunscreen is recommended?

5

For about how long should you wash your hands with soap?

More practice: on your own

1

Explain the difference between a tumour that is not cancer and one that is cancer.

2

Explain, using cells, why a sunburn is a warning sign.

3

Why do doctors not give antibiotics for every sore throat?

4

Explain how antibiotics can kill bacteria without harming your own cells.

5

How does handwashing connect to the cell theory?

Challenge

1

Explain why cancer is more common in older adults, using DNA damage and cell division.

2

A farm uses antibiotics in animal feed to help animals grow faster. Predict one effect on human health, using what you know about resistance.

3

Design a fair test to check whether a sunscreen blocks UV, using UV-sensitive beads (they change colour in UV light). Name the variables.

Check your understanding

Quiz

1.

Cancer happens when…

2.

Antibiotics work against…

3.

Which raises the risk of skin cancer?

4.

A vaccine works by…

5.

Antibiotic resistance spreads when…

6.

Who examines tissue under a microscope to diagnose disease?

For parents and teachers

Big idea: healthy cells divide only when needed. Damage to DNA can lead to uncontrolled division (cancer). We can protect our cells (sun safety, no smoking or vaping, vaccines, handwashing) and use medicines wisely.

Sensitive topic note: this lesson mentions cancer. Some children have family members living with cancer or who have died of it. Reassure them that cancer is not contagious and not anyone's fault, and that treatments keep improving. Let your child ask questions and answer simply.

How to help at home:

  • Check the UV index in the weather forecast together during spring and summer.
  • Do the glitter handwashing activity; it makes the invisible visible.
  • Talk about why your family finishes prescriptions as directed and doesn't ask for antibiotics for colds.

Safety: keep glitter away from eyes; wipe oily spills.

Common difficulties:

  • Thinking antibiotics treat viruses.
  • Thinking all tumours are cancer.
  • Thinking resistance means the person becomes resistant. It is the bacteria that become resistant.