Basic 7 · Science · Living Cells
The Plant Cell and Comparing Plant and Animal Cells
In this topic you will observe plant cells, state the functions of the organelles in a plant cell, and compare the similarities and differences between plant and animal cells.
By the end of these notes you should be able to:
- Observe and describe the structure of a plant cell
- State the functions of the organelles in a plant cell
- State the similarities and differences between plant and animal cells
What you already know
- The animal cell and the microscope
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
- B7.1.2.1.2 – State the functions of each organelle in a plane cell
Introduction
Peel a thin layer from an onion and look at it under a microscope. You will see neat, brick-like cells arranged side by side. These are plant cells.
1. Observing Onion Cells
- Peel off a thin, transparent layer (epidermis) from inside an onion scale.
- Place it flat on a slide with a drop of water.
- Add a drop of iodine solution to stain the cells.
- Cover with a cover slip and observe under low, then high power.
2. Parts of a Plant Cell
A plant cell has a cell membrane, cytoplasm, nucleus, mitochondria and ribosomes, like an animal cell. In addition, it has a cell wall outside the membrane, a large central vacuole filled with cell sap, and, in green parts of the plant, chloroplasts that contain the green pigment chlorophyll.
3. Shape of Plant Cells
Plant cells usually have a regular, rectangular or box-like shape because the cell wall is firm. This gives plants support and helps them stand upright. Onion cells have no chloroplasts because they grow underground and do not carry out photosynthesis, but leaf cells have many chloroplasts.
| Cell | Feature |
|---|---|
| leaf palisade cell | many chloroplasts for photosynthesis |
| root hair cell | long extension to absorb water |
| guard cell | controls the opening of stomata |
| onion epidermis cell | no chloroplasts; protects the onion scale |
4. Comparing Leaf and Onion Cells
If you observe a thin piece of a green leaf, such as from a water plant, under the microscope, you will see many small green chloroplasts inside the cells. In onion epidermis cells, you see no green colour. This shows that plant cells in different parts of the plant are specialised for different jobs.
New words
- cell wall
- A firm outer layer of plant cells made of cellulose.
- chloroplast
- An organelle containing chlorophyll for photosynthesis.
- vacuole
- A sac filled with cell sap.
- epidermis
- The outer layer of cells of a plant part.
Summary
- Plant cells have a cell wall, a large vacuole and often chloroplasts, in addition to the parts found in animal cells.
- Plant cells usually have a regular box-like shape.
- Onion epidermis cells can be stained with iodine for viewing.
Class activity: Onion Cell Observation
- Prepare an onion epidermis slide with iodine stain.
- Observe the cells under low and high power.
- Draw and label what you see.
You need: Onion epidermis slide, Light microscope, Printed plant-and-animal-cell diagram
Exercises
Answer in your exercise book first, then check your answers.
1. Which part is found in plant cells but not animal cells?
- A. cell wall
- B. nucleus
- C. cytoplasm
- D. cell membrane
Show answer
Answer: cell wallFirm outer layer.2. Onion epidermis cells do not have…
- A. chloroplasts
- B. nuclei
- C. cytoplasm
- D. cell walls
Show answer
Answer: chloroplastsThey grow underground.3. Plant cells usually have a regular shape.
- A. True
- B. False
Show answer
Answer: TrueBecause of the cell wall.4. The green pigment in chloroplasts is ______.
Show answer
Answer: chlorophyllAbsorbs light.5. Name four parts of a plant cell.
Show answer
Answer: Cell wall, cell membrane, nucleus, vacuole (or cytoplasm, chloroplast).Any four.6. Why do leaf cells have many chloroplasts but onion cells have none?
Show answer
Answer: Leaves carry out photosynthesis in light; onion scales grow underground without light.Function and location.
Lesson 2
- Strand
- Diversity Of Matter
- Sub-strand
- Living Cells
- Indicator
- B7.1.2.1.2 – State the functions of each organelle in a plane cell
Introduction
The special parts of a plant cell allow plants to make their own food, stand upright and store water. These jobs explain why plants are so different from animals.
1. Functions of Plant Organelles
| Organelle | Function |
|---|---|
| cell wall | gives shape, strength and support; protects the cell |
| cell membrane | controls what enters and leaves the cell |
| cytoplasm | site of chemical reactions |
| nucleus | controls cell activities; contains DNA |
| large vacuole | stores cell sap (water, sugars, salts); keeps the cell firm |
| chloroplasts | carry out photosynthesis to make food |
| mitochondria | release energy through respiration |
2. Photosynthesis in Chloroplasts
Chloroplasts trap sunlight using chlorophyll and use its energy to turn carbon dioxide and water into glucose (food) and oxygen. The word equation is: carbon dioxide + water → glucose + oxygen (in the presence of light and chlorophyll). The oxygen released is what humans and animals breathe.
3. The Vacuole and Firmness
When the vacuole is full of water, it presses against the cell wall and makes the cell firm, a condition called turgidity. This keeps leaves and young stems upright. When a plant lacks water, the vacuoles shrink, the cells become soft and the plant wilts. Watering a wilted plant restores turgidity.
4. The Cell Wall and Support
The cell wall is made of cellulose, a tough fibre. It allows plants to grow tall without a skeleton. Cellulose from plant cell walls is also useful to humans: it forms the fibre in our food and is used to make paper and cotton cloth.
New words
- photosynthesis
- The process by which plants make food using light.
- turgid
- Firm because the vacuole is full of water.
- wilting
- Drooping of a plant due to lack of water.
- cellulose
- The tough material of plant cell walls.
Summary
- The cell wall supports the cell; the vacuole stores sap and keeps cells firm.
- Chloroplasts carry out photosynthesis, producing glucose and oxygen.
- Lack of water causes wilting because vacuoles shrink.
Class activity: Wilting Experiment
- Leave one potted seedling without water and water another for three days.
- Observe and compare the plants.
- Explain the results using vacuoles and turgidity.
You need: Onion epidermis slide, Light microscope, Printed plant-and-animal-cell diagram
Exercises
Answer in your exercise book first, then check your answers.
1. Which organelle carries out photosynthesis?
- A. chloroplast
- B. nucleus
- C. vacuole
- D. mitochondria
Show answer
Answer: chloroplastContains chlorophyll.2. A plant wilts when its vacuoles…
- A. lose water
- B. gain water
- C. make food
- D. divide
Show answer
Answer: lose waterLoss of turgidity.3. Photosynthesis releases oxygen.
- A. True
- B. False
Show answer
Answer: TrueA product.4. The tough material of plant cell walls is ______.
Show answer
Answer: celluloseFibre.5. Write the word equation for photosynthesis.
Show answer
Answer: Carbon dioxide + water → glucose + oxygen (with light and chlorophyll).Equation.6. Explain why a plant without water wilts.
Show answer
Answer: Vacuoles lose water and shrink, the cells lose firmness (turgidity), and the leaves and stems droop.Turgidity.
Lesson 3
- Strand
- Diversity Of Matter
- Sub-strand
- Living Cells
- Indicator
- B7.1.2.2 – State the similarities and difference between a plant cell and animal cell
Introduction
Plant and animal cells share many parts because both are living cells, but they also differ because plants and animals live in different ways.
1. Similarities
- Both have a cell membrane.
- Both have cytoplasm.
- Both have a nucleus containing DNA.
- Both have mitochondria and ribosomes.
- Both carry out respiration to release energy.
2. Differences
| Feature | Plant cell | Animal cell |
|---|---|---|
| cell wall | present | absent |
| shape | regular, box-like | irregular, no fixed shape |
| vacuole | one large central vacuole | small vacuoles or none |
| chloroplasts | present in green parts | absent |
| food storage | starch | glycogen and fat |
| nucleus position | often pushed to the side | usually in the centre |
3. Why the Differences?
Plants make their own food by photosynthesis, so they need chloroplasts. They do not have skeletons, so they rely on cell walls and full vacuoles for support. Animals obtain food by eating and move about, so their cells are flexible and do not need walls or chloroplasts.
4. Using a Venn Diagram
A Venn diagram shows the comparison clearly. In the overlapping part, write the shared parts: cell membrane, cytoplasm, nucleus, mitochondria and ribosomes. In the plant-only part, write cell wall, large vacuole and chloroplasts. In the animal-only part, write small vacuoles, irregular shape and glycogen storage.
5. Cells and Classification
Knowing whether cells have walls and chloroplasts helps scientists classify organisms. Plants have cells with cellulose walls and chloroplasts. Animals have cells without walls. Fungi, such as mushrooms, have cell walls but no chloroplasts, so they cannot make their own food and are classified separately from plants.
New words
- similarity
- A way in which things are alike.
- difference
- A way in which things are not alike.
- glycogen
- The form in which animals store glucose.
- Venn diagram
- Overlapping circles used to compare things.
Summary
- Plant and animal cells both have a membrane, cytoplasm, nucleus, mitochondria and ribosomes.
- Only plant cells have a cell wall, a large vacuole and chloroplasts.
- The differences reflect how plants make food and are supported, while animals eat and move.
Class activity: Cell Comparison Venn Diagram
- Observe onion and cheek cell slides side by side.
- Complete a Venn diagram of their similarities and differences.
- Present your diagram to the class.
You need: Onion epidermis slide, Light microscope, Printed plant-and-animal-cell diagram
Exercises
Answer in your exercise book first, then check your answers.
1. Which part is found in both plant and animal cells?
- A. nucleus
- B. cell wall
- C. chloroplast
- D. large vacuole
Show answer
Answer: nucleusShared part.2. Animal cells store food as…
- A. glycogen
- B. starch
- C. cellulose
- D. chlorophyll
Show answer
Answer: glycogenAnimal storage.3. Animal cells have chloroplasts.
- A. True
- B. False
Show answer
Answer: FalseOnly plants.4. Overlapping circles used to compare things form a ______ diagram.
Show answer
Answer: VennComparison tool.5. State three differences between plant and animal cells.
Show answer
Answer: Plant cells have a cell wall, large vacuole and chloroplasts; animal cells do not.Any three.6. Explain why animal cells do not need cell walls.
Show answer
Answer: Animals have skeletons for support and need flexible cells for movement.Support and movement.
Homework
- Make a table comparing plant and animal cells and draw both.