Basic 9 · Science · Living Cells
Specialised Animal Cells
In this topic you will examine the structure and functions of specialised animal cells, such as nerve cells, blood cells, muscle cells and sperm cells, and discuss their roles in the body.
By the end of these notes you should be able to:
- Relate the structures of animal cells to their functions
- Describe blood cells and muscle cells
- Explain the importance of specialised cells to health
What you already know
- Specialised cells
Copy everything that has a blue line on its left into your notebook. The other parts are for reading.
Lesson 1
- Strand
- Diversity Of Matter
- Sub-strand
- Living Cells
- Indicator
- B9.1.2.1.3 – Examine the functions of specialized animal cells such as (nerve blood cells muscle cells and sperm cells) in relation to the existence of humans
Introduction
A message from your toe reaches your brain in a fraction of a second. Specialised cells make this possible.
1. Nerve Cells
Neuron: A nerve cell that carries electrical messages.
| Part | Function |
|---|---|
| dendrites | receive messages |
| cell body | contains the nucleus |
| axon | carries messages over a long distance |
| myelin sheath | insulates, speeds up messages |
| nerve endings | pass messages on |
Some nerve cells are very long. Those in the leg can reach from the spine to the foot. The axon works like a wire, and the myelin sheath is like the plastic coating around it. Nerve cells let you feel, think and move. Damage to them is serious, as most do not regrow. This is one reason why seat belts and helmets are important: they protect the brain and the spine.
2. Sperm Cells
| Part | Function |
|---|---|
| head | carries genetic material |
| acrosome | contains enzymes to enter the egg |
| middle piece | many mitochondria supply energy |
| tail | helps it swim |
The sperm cell is adapted to reach and fertilise an egg. Its streamlined shape and tail let it move. Many mitochondria release the energy needed for swimming. The egg cell, or ovum, is much larger. It contains stored food for the early embryo. When a sperm and an egg join, they form a zygote.
3. Mitochondria
Mitochondria are tiny structures inside cells that release energy from food. Cells that do a lot of work, such as muscle and sperm cells, contain many of them. When you study a cell, its number of mitochondria gives a clue to how active it is.
4. Reflex Actions
When you touch a hot pot, you pull your hand away before you know that it hurts. This is a reflex. A message travels along a nerve cell to the spine, and straight back to the muscles. Reflexes protect the body by acting very fast. They show how specialised nerve cells work together in chains.
New words
- neuron
- A nerve cell.
- axon
- The long fibre of a nerve cell.
- mitochondrion
- A part of a cell that releases energy.
- reflex
- A fast, automatic response.
Summary
- Nerve cells carry messages along long axons.
- Sperm cells are built to swim and enter an egg.
- Mitochondria supply the energy.
Class activity: Reflex Test
- Test your reaction by catching a falling ruler.
- Record the distance.
- Compare your results.
You need: Coloured modelling clay, Printed blood-cell photomicrograph, Printed specialized-animal-cell diagrams
Exercises
Answer in your exercise book first, then check your answers.
1. A nerve cell is also called a…
- A. neuron
- B. zygote
- C. platelet
- D. stoma
Show answer
Answer: neuronTerm.2. Sperm cells have many mitochondria to…
- A. supply energy
- B. store fat
- C. make blood
- D. see light
Show answer
Answer: supply energyFunction.3. The myelin sheath speeds up messages.
- A. True
- B. False
Show answer
Answer: TrueInsulation.4. A fast, automatic response is a ______.
Show answer
Answer: reflexTerm.5. How is a sperm cell adapted to its function?
Show answer
Answer: It has a tail to swim and many mitochondria for energy.Adaptation.6. Why are helmets important?
Show answer
Answer: Most nerve cells do not regrow, so the brain must be protected.Health.
Lesson 2
- Strand
- Diversity Of Matter
- Sub-strand
- Living Cells
- Indicator
- B9.1.2.1.3 – Examine the functions of specialized animal cells such as (nerve blood cells muscle cells and sperm cells) in relation to the existence of humans
Introduction
Your blood is a living tissue. Your muscles are always ready to move. Each has specialised cells.
1. Blood Cells
| Cell | Structure | Function |
|---|---|---|
| red blood cell | disc-shaped, no nucleus, contains haemoglobin | carries oxygen |
| white blood cell | has a nucleus, can change shape | fights infection |
| platelet | a tiny fragment | helps blood to clot |
A red blood cell has no nucleus, which leaves more room for haemoglobin, the iron-rich protein that carries oxygen. Its disc shape gives a large surface area. It is flexible, so that it can squeeze through tiny blood vessels. White blood cells destroy germs, and some of them produce antibodies. Platelets rush to a cut, and they help to form a clot.
2. Sickle Cell Disease
In sickle cell disease, an inherited change in haemoglobin makes red blood cells become sickle-shaped. These stiff cells block small vessels, causing pain, and they break down easily, causing anaemia. It is common in West Africa, and Ghana screens many newborn babies. Both parents must pass on the sickle gene for a child to have the disease. Couples are advised to test for it before marriage. This shows how the shape of a cell affects its function.
3. Muscle Cells
| Type | Location | Control |
|---|---|---|
| skeletal | attached to bones | voluntary |
| smooth | walls of stomach and gut | involuntary |
| cardiac | heart | involuntary, never tires |
Muscle cells are long and contain proteins that slide over each other to make the cell shorter. This is contraction. They contain many mitochondria to supply energy. Muscles work in pairs. When your biceps contracts, your triceps relaxes, and the arm bends. Exercise makes muscles stronger, and it strengthens the heart.
4. Diet and Cells
Cells need nutrients. Iron from kontomire, beans and meat helps to make haemoglobin. Protein from fish, eggs and groundnuts builds muscle. Calcium helps nerves and muscles to work. A lack of iron can cause anaemia, which is common among teenage girls and pregnant women in Ghana. Eating a balanced diet supplies what your cells need to do their work.
New words
- haemoglobin
- The protein that carries oxygen.
- platelet
- A cell fragment that helps clotting.
- contraction
- The shortening of a muscle.
- anaemia
- A shortage of red blood cells or haemoglobin.
Summary
- Red cells carry oxygen, and white cells fight germs.
- Muscle cells contract and need much energy.
- Diet supplies what cells need.
Class activity: Cell Compare
- Make a table of blood cells.
- Note the structure and function of each.
- Share how they are adapted.
You need: Coloured modelling clay, Printed blood-cell photomicrograph, Printed specialized-animal-cell diagrams
Exercises
Answer in your exercise book first, then check your answers.
1. Which cell fights infection?
- A. white blood cell
- B. red blood cell
- C. platelet
- D. nerve cell
Show answer
Answer: white blood cellFunction.2. Red cells lack a…
- A. nucleus
- B. membrane
- C. surface
- D. colour
Show answer
Answer: nucleusAdaptation.3. Cardiac muscle is in the heart.
- A. True
- B. False
Show answer
Answer: TrueMuscle.4. The protein that carries oxygen is ______.
Show answer
Answer: haemoglobinTerm.5. Give two foods rich in iron.
Show answer
Answer: Kontomire and beans.Any two.6. How does sickle cell disease show the link between shape and function?
Show answer
Answer: Sickle-shaped cells block vessels and break down, so they cannot carry oxygen well.Application.
Lesson 3
- Strand
- Diversity Of Matter
- Sub-strand
- Living Cells
- Indicator
- B9.1.2.1.3 – Examine the functions of specialised animal cells in relation to their structure
Introduction
Specialised cells are like skilled workers. When they cooperate, the body runs smoothly.
1. Cells Working Together
| Cell | Role |
|---|---|
| nerve cell | sends a signal to the muscles |
| muscle cell | contracts to move the leg |
| red blood cell | brings oxygen |
| white blood cell | protects from infection |
| lung cell | exchanges gases |
2. Other Specialised Cells
| Cell | Function | Adaptation |
|---|---|---|
| ciliated cell | moves mucus in airways | tiny hairs |
| goblet cell | makes mucus | large mucus store |
| egg cell | supplies food to embryo | large, food-filled |
| bone cell | builds bone | lays down minerals |
| retina cell | detects light | light-sensitive pigment |
| skin cell | protects the body | tightly packed |
Cells lining the airways have cilia, which beat to move mucus and trapped dust out of the lungs. Smoking damages these cells, and this is one reason why smokers cough. Understanding cells explains why certain habits cause illness.
3. When Cells Fail
| Problem | Effect |
|---|---|
| too few red cells | anaemia |
| too few white cells | weak immunity |
| HIV attack on white cells | AIDS if not treated |
| destroyed nerve cells | paralysis |
| uncontrolled division | cancer |
HIV infects certain white blood cells, weakening the immune system. Antiretroviral medicines allow people to live long, healthy lives. People living with HIV should not suffer stigma or discrimination. Malaria parasites invade red blood cells and destroy them, and this causes fever and anaemia.
4. Keeping Cells Healthy
- Eat a balanced diet.
- Exercise regularly.
- Sleep enough.
- Avoid smoking, alcohol and drugs.
- Drink clean water.
- Get vaccinated.
- Reduce exposure to harmful chemicals.
5. Medicine and Cells
Doctors use blood tests to find out what is happening in cells. Vaccines train white blood cells to recognise germs. Blood donations save lives, particularly those of mothers who bleed in childbirth and of children with severe malaria. The National Blood Service Ghana collects blood from voluntary donors, who must be adults. When you are old enough, consider giving blood.
New words
- cilia
- Tiny hairs on a cell.
- immunity
- The body's defence against disease.
- stigma
- Unfair shame attached to a condition.
- vaccine
- A substance that trains the immune system.
Summary
- Specialised cells cooperate in all activities.
- Failure of cells causes disease.
- Healthy habits protect cells.
Class activity: Body Team
- Choose an activity like running.
- List the cells involved.
- Explain the role of each.
You need: Coloured modelling clay, Printed blood-cell photomicrograph, Printed specialized-animal-cell diagrams
Exercises
Answer in your exercise book first, then check your answers.
1. Which cell has tiny hairs?
- A. ciliated cell
- B. red blood cell
- C. bone cell
- D. sperm tail
Show answer
Answer: ciliated cellAdaptation.2. HIV attacks…
- A. white blood cells
- B. bones
- C. teeth
- D. hair
Show answer
Answer: white blood cellsDisease.3. Vaccines train white blood cells.
- A. True
- B. False
Show answer
Answer: TrueImmunity.4. Unfair shame attached to a condition is ______.
Show answer
Answer: stigmaTerm.5. Why do smokers cough?
Show answer
Answer: Smoking damages ciliated cells, so mucus builds up.Effect.6. How does malaria affect blood cells?
Show answer
Answer: Parasites invade and destroy red blood cells, causing anaemia.Disease.
Homework
- Write a paragraph on how three types of cells work together when you play.