Basic 7 · Science · Living Cells
The Animal Cell
In this topic you will explain what cells are, use a microscope to observe cells, and describe the structure and functions of the parts of an animal cell.
By the end of these notes you should be able to:
- Explain that living things are made of cells
- Describe how to use a light microscope to observe cells
- Describe the structure and functions of the parts of an animal cell
What you already know
- Living and non-living things (Upper Primary)
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
- B7.1.2.1.1 – Describe the structure and function of living cells of an animal
Introduction
Every living thing, from a tiny ant to a huge elephant, is made of cells. Cells are so small that we need a microscope to see them.
1. What Is a Cell?
Cell: The smallest unit of life; the basic building block of all living things.
Some organisms, such as bacteria and amoeba, are made of only one cell (unicellular). Others, such as humans, goats and mango trees, are made of millions of cells (multicellular). Groups of similar cells working together form tissues, tissues form organs and organs form organ systems.
| Level | Example |
|---|---|
| cell | muscle cell |
| tissue | muscle tissue |
| organ | heart |
| organ system | circulatory system |
| organism | human being |
2. The Light Microscope
A light microscope uses lenses and light to make small objects look bigger. Its main parts are the eyepiece lens, the objective lenses, the stage (where the slide is placed), the mirror or light source, and the coarse and fine focus knobs.
3. Using a Microscope
- Carry the microscope with one hand under the base and one on the arm.
- Place the slide on the stage and hold it with the clips.
- Start with the lowest-power objective lens.
- Adjust the mirror or light so the view is bright.
- Turn the coarse focus knob slowly, then use the fine focus to make the image clear.
- Switch to a higher-power lens for more detail.
4. Magnification
Magnification tells how many times bigger an object looks. It is found by multiplying the magnification of the eyepiece by that of the objective lens. For example, an eyepiece of ×10 and an objective of ×40 give a total magnification of ×400.
New words
- cell
- The smallest unit of life.
- unicellular
- Made of one cell.
- multicellular
- Made of many cells.
- magnification
- How many times larger an object appears.
Summary
- All living things are made of cells, which form tissues, organs and systems.
- A light microscope uses lenses and light to magnify cells.
- Total magnification is eyepiece magnification multiplied by objective magnification.
Class activity: Microscope Practice
- Identify the parts of the school microscope.
- Observe a prepared animal-cell slide, starting with the lowest power.
- Draw what you see and calculate the magnification used.
You need: Prepared animal-cell slide, Light microscope, Printed animal-cell diagram
Exercises
Answer in your exercise book first, then check your answers.
1. The smallest unit of life is the…
- A. cell
- B. organ
- C. tissue
- D. system
Show answer
Answer: cellBuilding block.2. An eyepiece of ×10 and an objective of ×10 give…
- A. ×100
- B. ×20
- C. ×10
- D. ×1,000
Show answer
Answer: ×100Multiply.3. Humans are multicellular.
- A. True
- B. False
Show answer
Answer: TrueMany cells.4. A group of similar cells working together forms a ______.
Show answer
Answer: tissueNext level.5. State three parts of a light microscope and their functions.
Show answer
Answer: Eyepiece: magnifies; stage: holds the slide; focus knob: makes the image clear.Any three.6. Why should you start with the lowest-power lens?
Show answer
Answer: It gives a wider view, making it easier to find and focus the object before increasing magnification.Locate first.
Lesson 2
- Strand
- Diversity Of Matter
- Sub-strand
- Living Cells
- Indicator
- B7.1.2.1.1 – Describe the structure and function of living cells of an animal
Introduction
Under the microscope, cells from the inside of your cheek look like tiny irregular bags. Each has parts with special jobs, like rooms in a house.
1. Main Parts of an Animal Cell
An animal cell has three main parts that can be seen with a light microscope: the cell membrane, the cytoplasm and the nucleus. Other tiny parts, called organelles, such as mitochondria and ribosomes, can be seen clearly only with an electron microscope.
2. Shape of Animal Cells
Animal cells do not have a fixed shape because they have no cell wall. Their shapes depend on their jobs: red blood cells are round and flat to carry oxygen, nerve cells are long to carry messages, and muscle cells are long and thin to contract.
| Cell | Shape | Job |
|---|---|---|
| red blood cell | round, disc-shaped, no nucleus | carries oxygen |
| nerve cell | long with branches | carries messages |
| muscle cell | long and thin | contracts to cause movement |
| sperm cell | has a tail | swims to fertilise the egg |
3. Preparing a Cheek Cell Slide
- Gently scrape the inside of your cheek with a clean cotton bud.
- Smear it on a clean glass slide.
- Add a drop of methylene blue stain to make the cells visible.
- Cover it gently with a cover slip, avoiding air bubbles.
- Observe under the microscope.
Safety: Use only clean, new cotton buds and dispose of them safely. Wash your hands after the activity.
New words
- cell membrane
- The thin outer layer that controls what enters and leaves the cell.
- cytoplasm
- The jelly-like substance inside the cell.
- nucleus
- The control centre of the cell.
- organelle
- A tiny part of a cell with a special function.
Summary
- An animal cell has a cell membrane, cytoplasm and nucleus, plus tiny organelles.
- Animal cells have no fixed shape; their shapes suit their jobs.
- Cheek cells can be prepared and stained for viewing.
Class activity: Cheek Cell Observation
- Prepare a cheek cell slide with the teacher's guidance.
- Observe and draw the cells.
- Label the visible parts.
You need: Prepared animal-cell slide, Light microscope, Printed animal-cell diagram
Exercises
Answer in your exercise book first, then check your answers.
1. The control centre of the cell is the…
- A. nucleus
- B. cytoplasm
- C. membrane
- D. vacuole
Show answer
Answer: nucleusControls activities.2. Which animal cell has no nucleus?
- A. red blood cell
- B. nerve cell
- C. muscle cell
- D. cheek cell
Show answer
Answer: red blood cellRoom for oxygen.3. Animal cells have a cell wall.
- A. True
- B. False
Show answer
Answer: FalseOnly a membrane.4. The jelly-like substance in a cell is the ______.
Show answer
Answer: cytoplasmInside the cell.5. Name three parts of an animal cell seen under a light microscope.
Show answer
Answer: Cell membrane, cytoplasm, nucleus.Main parts.6. Explain why nerve cells are long.
Show answer
Answer: Their length allows them to carry messages over long distances in the body.Shape suits function.
Lesson 3
- Strand
- Diversity Of Matter
- Sub-strand
- Living Cells
- Indicator
- B7.1.2.1.1 – Describe the structure and function of living cells of an animal
Introduction
Each part of a cell has a job. Together they keep the cell alive, just as different workers keep a school running.
1. Functions of the Main Parts
| Part | Function | Comparison |
|---|---|---|
| cell membrane | controls what enters and leaves the cell | the school gate |
| cytoplasm | where most chemical reactions take place | the school compound |
| nucleus | controls cell activities and contains genetic material (DNA) | the headteacher's office |
| mitochondria | release energy from food (respiration) | the power house |
| ribosomes | make proteins | the workshop |
| small vacuoles | store water, food and wastes | the store room |
2. The Nucleus and Inheritance
The nucleus contains chromosomes made of DNA. DNA carries instructions that decide features such as eye colour and height. When a cell divides, each new cell receives a copy of these instructions. This is how characteristics are passed from parents to children.
3. Mitochondria and Energy
Mitochondria use oxygen to break down glucose from food, releasing energy. This process is called respiration. Cells that use a lot of energy, such as muscle cells, have many mitochondria. This is why athletes need good food and oxygen.
4. Cells Working Together
No organelle works alone. The nucleus sends instructions, ribosomes make proteins, mitochondria provide energy, and the membrane brings in food and oxygen and removes wastes. If one part fails, the whole cell can die, which may lead to disease.
New words
- mitochondria
- Organelles that release energy from food.
- ribosome
- An organelle that makes proteins.
- DNA
- The genetic material that carries instructions in the nucleus.
- respiration
- Releasing energy from food in cells.
Summary
- The membrane controls movement in and out; the cytoplasm is where reactions occur.
- The nucleus controls the cell and carries DNA; mitochondria release energy; ribosomes make proteins.
- Organelles work together to keep the cell alive.
Class activity: Cell Model Making
- Use a clear plastic bag, gel or porridge, and beans or seeds to model an animal cell.
- Label each part with its function.
- Present your model and explain how the parts work together.
You need: Prepared animal-cell slide, Light microscope, Printed animal-cell diagram
Exercises
Answer in your exercise book first, then check your answers.
1. Which organelle releases energy?
- A. mitochondria
- B. nucleus
- C. ribosome
- D. membrane
Show answer
Answer: mitochondriaPower house.2. Proteins are made in the…
- A. ribosomes
- B. vacuoles
- C. cell membrane
- D. nucleus only
Show answer
Answer: ribosomesWorkshop.3. The nucleus contains DNA.
- A. True
- B. False
Show answer
Answer: TrueGenetic material.4. Releasing energy from food in cells is called ______.
Show answer
Answer: respirationUses oxygen.5. State the functions of the cell membrane and the nucleus.
Show answer
Answer: Membrane: controls what enters and leaves; nucleus: controls cell activities and carries DNA.Two functions.6. Why do muscle cells have many mitochondria?
Show answer
Answer: They need a lot of energy to contract, and mitochondria release energy.Energy demand.
Homework
- Draw and label an animal cell and write the function of each part.