Cells & Life
Cell Structure: Plant, Animal, and the Microscope
1st Year · 2nd Year · 3rd Year (Junior Cert)
- ✓By the end of this lesson students will be able to identify the main organelles in typical plant and animal cells.
- ✓By the end of this lesson students will be able to describe the function of the nucleus, mitochondria, chloroplasts, and cell wall.
- ✓By the end of this lesson students will be able to compare and contrast the structure of plant and animal cells.
- ✓By the end of this lesson students will be able to outline the basic steps for using a light microscope to observe cells.
- ✓By the end of this lesson students will be able to explain the importance of safety precautions when using a microscope.
Key concepts
The fundamental unit of life. All living organisms are made of cells.
A small, specialised structure within a cell that carries out a specific function.
A eukaryotic cell that possesses a cell wall, chloroplasts, and a large central vacuole, in addition to other organelles found in animal cells.
A eukaryotic cell that lacks a cell wall, chloroplasts, and a large central vacuole.
A large, usually spherical organelle that controls all cell activities and contains the cell's genetic material (DNA) in the form of chromosomes.
Oval-shaped organelles often referred to as the "powerhouses" of the cell. They are the site of aerobic respiration, where food is broken down to release energy for the cell's activities.
Green organelles found in plant cells and some protists. They contain the pigment chlorophyll and are the site where photosynthesis takes place, converting light energy into chemical energy (food).
A rigid, outer layer found in plant cells (made primarily of cellulose), fungi, algae, and bacteria. It provides structural support, protection, and prevents excessive water uptake. Animal cells do not have a cell wall.
A thin, flexible outer boundary of an animal cell, and found just inside the cell wall in plant cells. It controls the movement of substances into and out of the cell. It is selectively permeable.
The jelly-like substance that fills the cell and surrounds the organelles. Most chemical reactions of the cell occur here.
A membrane-bound sac within the cytoplasm. In plant cells, there is typically one large, permanent central vacuole that stores water, nutrients, and waste products, and helps maintain turgor pressure. Animal cells may have small, temporary vacuoles.
An instrument that uses visible light and a system of lenses to magnify images of small specimens.
The degree to which the apparent size of an object is increased. Total magnification = eyepiece lens magnification x objective lens magnification.
The ability of a microscope to distinguish between two closely spaced objects as separate entities, providing a clear and detailed image.
Key facts to remember
- 1Cells are the fundamental building blocks of all living organisms.
- 2Plant cells are distinguished by the presence of a cell wall, chloroplasts, and a large permanent central vacuole, which are absent in animal cells.
- 3Both plant and animal cells possess a nucleus, cytoplasm, cell membrane, and mitochondria.
- 4The nucleus acts as the control centre of the cell, housing its genetic material.
- 5Mitochondria are vital for releasing energy through the process of aerobic respiration.
- 6Chloroplasts are the sites of photosynthesis in plant cells, converting light energy into food.
- 7The cell wall provides essential structural support and protection to plant cells.
- 8A light microscope is used to magnify small biological specimens, allowing for detailed observation of cell structures.
Worked examples
Example 1
Examine the diagram of a plant cell below. Identify the organelles labelled A, B, C, and D, and state one function for each.
Answer
A: Cell Wall - Provides structural support and protection to the plant cell. B: Chloroplast - Site of photosynthesis, where light energy is converted into chemical energy (food). C: Nucleus - Controls all cell activities and contains the genetic material (DNA). D: Mitochondrion - Site of aerobic respiration, releasing energy for the cell's activities.
Assume a standard plant cell diagram where A is the outermost layer, B is a green oval, C is the large central sphere, and D is a smaller oval with internal folds.
Example 2
Outline three key differences between a typical plant cell and a typical animal cell.
Answer
1. Plant cells have a rigid cell wall outside the cell membrane, while animal cells do not. 2. Plant cells contain chloroplasts for photosynthesis, while animal cells do not. 3. Plant cells typically have one large, permanent central vacuole, whereas animal cells usually have small, temporary vacuoles or none at all.
Focus on distinct structural differences.
Example 3
Describe the correct procedure for setting up a light microscope to view a prepared slide of onion cells, ensuring a clear image is obtained.
Answer
1. Place the microscope on a flat, stable surface and connect it to power. 2. Rotate the revolving nosepiece to select the lowest power objective lens (e.g., x4 or x10). 3. Place the prepared slide of onion cells onto the stage and secure it with the stage clips, ensuring the specimen is centred over the light source. 4. Looking through the eyepiece, use the coarse focus knob to slowly lower the objective lens towards the slide until the image appears roughly in focus. (Alternatively, raise the stage until the lens is close to the slide, then lower it while looking through the eyepiece). 5. Use the fine focus knob to make the image sharp and clear. 6. Adjust the diaphragm or light intensity control to achieve the best contrast and brightness for viewing the cells. 7. If a higher magnification is required, rotate the nosepiece to a higher power objective lens. Crucially, only use the fine focus knob for focusing at higher magnifications to avoid damaging the slide or lens.
Always start with the lowest power objective lens and use the coarse focus knob first, then fine focus. Only use fine focus at higher magnifications.
Common mistakes
- ✗Confusing the functions of mitochondria (energy release) and chloroplasts (food production).
- ✗Incorrectly stating that animal cells lack a cell membrane; they only lack a cell wall.
- ✗Failing to identify the large central vacuole as a distinct feature of plant cells.
- ✗Using the coarse focus knob when viewing with high power objective lenses, which can damage the slide or lens.
- ✗Drawing unlabelled or poorly labelled diagrams of cells in exams.
Exam tips
- ★Practise drawing and clearly labelling diagrams of both plant and animal cells, including all key organelles.
- ★Create a table to compare and contrast the structures present in plant and animal cells.
- ★Thoroughly learn the specific function of each major organelle (nucleus, mitochondria, chloroplasts, cell wall, cell membrane, cytoplasm, vacuole).
- ★Understand the correct and safe procedure for using a light microscope, including the function of its main parts.
- ★When describing practical work, always include relevant safety precautions.
Ready to practise?
Try a problem on this topic
Snap a photo or type a question — get step-by-step working instantly.