SCIJHS 1 • Term 2Topic 6Free Trial Lesson
Living Cells: Plant & Animal Cell Structure
Study cell organelles, functions of nucleus, cytoplasm, membrane, cell wall, chloroplasts, and compare plant and animal cells under a microscope.
Curated Video Lesson
Visual explanation and practical step-by-step walk-through
Comprehensive Study Notes
Aligned with Ghana NaCCA & WAEC BECE syllabus standards
Topic Introduction & Real-World Context:
Every living creature in Ghana—from the giant mahogany tree in Kakum National Park to microscopic bacteria in soil—is built from microscopic cells. Understanding cell biology underpins modern medicine, crop disease resistance, and biotechnology.
What You Will Master in This Lesson (NaCCA Objectives):
Define the cell as the basic structural and functional unit of life.
Identify parts of a light microscope and describe their functions.
Draw and label plant and animal cell diagrams.
State functions of cell organelles: nucleus, cell membrane, cytoplasm, mitochondria, vacuole, cell wall, and chloroplasts.
Compare and contrast plant and animal cell structures.
1. The Cell and the Light Microscope
• Cell Definition:
The cell is the basic structural, functional, and biological unit of all known living organisms. Robert Hooke first coined the term in 1665 when observing dead cork tissue.
• Levels of Biological Organization:
Cells → Tissues → Organs → Organ Systems → Organism
- Cell: e.g. Red blood cell, root hair cell.
- Tissue: Group of similar cells performing a common function (e.g. muscle tissue, xylem tissue).
- Organ: Group of tissues working together (e.g. heart, stomach, leaf).
- Organ System: Group of organs performing a major life process (e.g. digestive system, vascular system).
- Organism: A complete independent living entity (e.g. human, maize plant).
• The Compound Light Microscope:
Used to magnify tiny cell specimens that cannot be seen with the naked human eye:
- Eyepiece (Ocular Lens): Lens at the top you look through, typically magnifies 10x.
- Objective Lenses: Mounted on rotating nosepiece (Low power 4x, Medium power 10x, High power 40x).
- Total Magnification = Eyepiece Magnification × Objective Lens Magnification.
- Stage & Stage Clips: Flat platform where the glass microscope slide is placed and secured.
- Coarse and Fine Adjustment Knobs: Bring the image into rough and razor-sharp focus respectively.
- Diaphragm & Mirror/Light Source: Regulates the amount of light passing through the specimen.
Key Takeaway: Total microscope magnification = Eyepiece lens power × Objective lens power (e.g. 10 × 40 = 400x magnification).
Real-World Application: Medical lab technicians at Korle-Bu Teaching Hospital use light microscopes to identify malaria parasites inside human red blood cells.
2. Major Cell Organelles and Their Vital Functions
Organelles are specialized subcellular structures performing specific metabolic tasks:
• Organelles Present in BOTH Plant and Animal Cells:
1. Nucleus:
- Structure: Spherical organelle enclosed by a double nuclear membrane containing chromatin threads (DNA) and a nucleolus.
- Function: The "control center" of the cell; regulates all metabolic activities, cell growth, protein synthesis, and carries genetic hereditary information.
2. Cell Membrane (Plasma Membrane):
- Structure: Thin, flexible, selectively (semi) permeable membrane composed of a phospholipid bilayer and proteins.
- Function: Encloses cell contents and regulates the transport of substances into and out of the cell.
3. Cytoplasm:
- Structure: Transparent, jelly-like fluid (cytosol) filling the interior of the cell.
- Function: Matrix where cell organelles are suspended; site where numerous metabolic enzymatic reactions (such as glycolysis) take place.
4. Mitochondrion (Plural: Mitochondria):
- Structure: Rod-shaped organelle with an inner folded membrane (cristae).
- Function: Known as the "powerhouse of the cell"; site of aerobic cellular respiration where glucose is broken down to release energy in the form of ATP (adenosine triphosphate).
Key Takeaway: Nucleus = controls cell activities; Membrane = regulates entry/exit; Mitochondria = cellular respiration & ATP energy.
Real-World Application: Active sperm cells and heart muscle cells contain thousands of mitochondria to supply continuous energy for movement and contraction.
3. Plant Cell Specific Structures vs Animal Cells
Plant cells have three unique structural features not found in typical animal cells:
• Plant-Only Structures:
1. Cell Wall:
- A tough, rigid outer protective layer surrounding the cell membrane, made of cellulose fibers.
- Function: Gives the plant cell a fixed, rigid rectangular shape; provides mechanical support and prevents the plant cell from bursting when it absorbs water (turgor pressure). Fully permeable.
2. Chloroplasts:
- Disc-shaped organelles containing the green photosynthetic pigment chlorophyll.
- Function: Absorbs solar light energy and synthesizes glucose during photosynthesis.
3. Large Central Permanent Vacuole:
- A large fluid-filled cavity enclosed by a membrane called the tonoplast, filled with cell sap (water, dissolved sugars, and mineral salts).
- Function: Maintains internal osmotic pressure and turgidity to keep non-woody plant stems upright.
• Direct Structural Comparison Table:
| Feature | Plant Cell | Animal Cell |
| :--- | :--- | :--- |
| **Shape** | Regular, fixed rectangular shape | Irregular, flexible, rounded shape |
| **Cell Wall** | Present (composed of cellulose) | Completely absent |
| **Chloroplasts** | Present in green photosynthetic cells | Absent |
| **Vacuole** | One large permanent central vacuole | Small, temporary vacuoles (if present) |
| **Nucleus Position** | Pushed to the side (periphery) by vacuole | Usually centrally located |
| **Food Storage** | Stored as Starch granules | Stored as Glycogen granules |
Key Takeaway: Remember the 3 Cs of Plant Cells: Cell Wall, Chloroplasts, and Central Vacuole. Animal cells have none of these three.
Real-World Application: Wilted cassava leaves stand upright again after rain because water fills the plant cell vacuoles, restoring firm turgor pressure against the cell walls.
Common Mistakes Students Make in BECE Examinations:
⚠️Claiming that plant cells do NOT have a cell membrane—plant cells have BOTH an outer cell wall AND an inner cell membrane underneath it!
⚠️Confusing the cell wall (fully permeable, made of cellulose) with the cell membrane (semi-permeable).
⚠️Drawing animal cells with rigid straight lines like rectangles.
⚠️Forgetting that mitochondria are present in plant cells as well as animal cells.
Teacher's BECE Exam Pro-Tips:
⭐In BECE diagram questions: Label lines must be straight, parallel if possible, drawn with a ruler, and must not cross each other.
⭐State the three key differences between plant and animal cells clearly: (1) Cell wall present in plants, absent in animals, (2) Chloroplasts present in plants, absent in animals, (3) Large central vacuole in plants, small temporary vacuoles in animals.
Quick Revision Summary Checklist:
Can list the hierarchy: Cells → Tissues → Organs → Systems → Organism.
Can calculate total microscope magnification.
Know functions of nucleus, cell membrane, cytoplasm, mitochondria, cell wall, and chloroplasts.
Can accurately list 4 differences between plant and animal cells.
Step-by-Step Worked Examples (2)
Real BECE exam-standard problems with complete solution steps
Example 1: Distinguishing Plant Cells from Animal Cells in the Lab
Problem StatementA student observes an unknown slide under a school light microscope and notes: a distinct green color, rigid rectangular boundaries, and a large central vacuole pushing the nucleus to the periphery. Is this a plant or animal cell? Give two reasons.
Step-by-Step Solution:
Conclusion: It is a PLANT cell.
Reason 1: The presence of chloroplasts (indicated by the distinct green pigment chlorophyll).
Reason 2: The presence of a rigid cellulose cell wall giving a fixed rectangular shape.
Reason 3: A large permanent central vacuole that displaces the nucleus to the side.
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Key Takeaway / Exam Rule: Cell wall, chloroplasts, and a large central vacuole are the three decisive microscopic indicators of a plant cell.
Example 2: Explaining the Function of the Mitochondria
Problem StatementWhy do muscle cells in the human heart have a significantly greater number of mitochondria than skin epithelial cells?
Step-by-Step Solution:
Step 1: Mitochondria are responsible for aerobic cellular respiration, which produces adenosine triphosphate (ATP) energy.
Step 2: Heart muscle cells are constantly contracting without rest throughout life, requiring large quantities of continuous energy.
Step 3: Skin cells are primarily protective and have comparatively low metabolic energy demands.
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Key Takeaway / Exam Rule: The density of mitochondria in a cell directly reflects its metabolic energy requirements.
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