Animal & Plant Cell Structure
All living organisms are composed of cells. Plant and animal cells are eukaryotic (containing a membrane-bound nucleus and organelles), whereas bacterial cells are prokaryotic and carry their DNA free in the cytoplasm as a single circular chromosomal loop and small rings called plasmids.
- Nucleus
- Organelle that contains DNA and controls cell activities.
- Cytoplasm
- A jelly-like substance where most chemical reactions occur.
- Cell membrane
- Controls the movement of substances in and out of the cell.
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Mitochondria
Function in the Cell:
Site of aerobic respiration, releasing energy (ATP) for the cell. Folded inner membrane increases surface area for enzymes.
Exact GCSE / A-Level Exam Wording:
Mark scheme trap: Never say 'produces energy'! Always write 'site of aerobic respiration, which releases energy'.
Magnification = Image Size ÷ Actual Size (I = A × M). Convert cm → mm (×10) → µm (×1000) before dividing!Exam notes: Eukaryotes vs Prokaryotes, Specialised Cells & Microscopy
- All plant and animal cells are eukaryotic (they have a true membrane-bound nucleus, mitochondria, and 80S ribosomes). Bacterial cells are prokaryotic (much smaller, NO nucleus: DNA is a single circular chromosome loop free in the cytoplasm plus small rings of DNA called plasmids).
- For magnification calculations, always use the triangle I = A × M (Image size = Actual size × Magnification) and convert both numbers to the same unit before dividing: 1 mm = 1,000 µm (micrometres) and 1 µm = 1,000 nm (nanometres).
- Electron microscopes use a beam of electrons instead of light, giving a much higher magnification (up to ×2,000,000) and much higher resolution (ability to distinguish two close points as separate), allowing scientists to see internal sub-cellular structures like ribosomes and mitochondrial cristae.
| Cell Structure | Animal Cell (Eukaryote) | Plant Cell (Eukaryote) / Bacteria (Prokaryote) |
|---|---|---|
| Nucleus | Present (contains linear DNA chromosomes) | Present in Plant / Absent in Bacteria (free circular DNA loop + plasmids) |
| Cell Membrane & Ribosomes | Present in all cells | Present in both Plant and Bacterial cells |
| Mitochondria | Present (site of aerobic respiration) | Present in Plant / Absent in Bacteria (respiration on plasma membrane) |
| Cell Wall | Absent in animal cells | Plant wall = Cellulose / Bacterial wall = Peptidoglycan (murein) |
| Chloroplasts & Permanent Vacuole | Absent in animal cells | Present in green plant cells / Absent in bacteria |
Key Concepts & Exam Definitions (12)
- Nucleus
- Organelle that contains DNA and controls cell activities.
- Cytoplasm
- A jelly-like substance where most chemical reactions occur.
- Cell membrane
- Controls the movement of substances in and out of the cell.
- Mitochondria
- The site of aerobic respiration.
- Ribosomes
- The site of protein synthesis.
- Chloroplasts
- Contain chlorophyll and are the site of photosynthesis (plant cells only).
- Cell wall
- Made of cellulose, provides structure and support to the cell (plant cells only).
- Prokaryotic (Bacterial) Cell Structure
- Single-celled organisms (0.5-5 µm) with NO nucleus and NO membrane-bound organelles (no mitochondria or chloroplasts). Genetic material is a single circular DNA loop in the cytoplasm plus small extra rings of DNA called plasmids (which often carry antibiotic-resistance genes).
- Light Microscope vs Electron Microscope
- Light microscopes use light lenses (max magnification ~×1,500, resolution ~200 nm; can view living cells in colour). Electron microscopes use electron beams (max magnification ~×2,000,000, resolution ~0.2 nm; allows sub-cellular structures like ribosomes and plasmids to be seen, but specimens must be dead in a vacuum).
- Magnification Formula & Unit Conversions
- Magnification = Image size ÷ Actual size (M = I / A). To convert mm to µm, multiply by 1,000. To convert µm to mm, divide by 1,000. Example: an image 30 mm wide of a cell that is 15 µm across has magnification = 30,000 µm ÷ 15 µm = ×2,000.
- Specialised Animal Cells (Sperm, Nerve, Muscle)
- Sperm cell: tail (flagellum) for swimming, middle section packed with mitochondria for energy, acrosome enzymes in head to digest egg coat, haploid nucleus. Nerve cell: long axon to carry impulses, myelin sheath to insulate and speed up transmission, dendrites to connect to other neurones.
- Cell Differentiation & Stem Cells
- Differentiation is the process by which a cell changes to become specialised for its job (expressing specific genes). Most animal cells lose the ability to differentiate after an early embryonic stage, whereas many plant cells (in meristems) retain the ability to differentiate throughout the plant's life.
Quick-Fire Flashcards (9)
Click any card to check the answer, then mark it as Known to track your progress.
Which organelle is the site of protein synthesis?
Name three structures found in plant cells but not animal cells.
What is the function of the cell membrane?
Where does aerobic respiration take place?
What does the permanent vacuole contain?
How is DNA stored in a bacterial (prokaryotic) cell compared to an animal (eukaryotic) cell?
A mitochondrion measures 45 mm in a photograph taken at a magnification of ×15,000. What is its actual length in micrometres (µm)?
What is the difference between magnification and resolution?
Where are stem cells found in plants, and how do they differ from adult human stem cells?
Exam-Style Questions & Mark Schemes (6)
Write or think through your answer first, then click Check Mark Scheme to see the exact points examiners award marks for.
- Q1
Compare the structure of a typical animal cell with a typical plant cell.
Click “Check Mark Scheme” to compare your answer, Both contain a nucleus, cytoplasm, cell membrane, mitochondria, and ribosomes. Plant cells also contain a cell wall, chloroplasts, and a permanent vacuole.
- Q2
Explain why muscle cells have many mitochondria.
Click “Check Mark Scheme” to compare your answer, Muscle cells need a lot of energy for contraction; mitochondria release energy through aerobic respiration.
- Q3
What is the function of chloroplasts?
Click “Check Mark Scheme” to compare your answer, They absorb light energy to make food (glucose) by photosynthesis.
- Q4
A student draws a palisade mesophyll cell 60 mm long. The actual length of the cell is 80 µm. Calculate the magnification of the student's drawing, showing every step of your working. [3 marks]
Click “Check Mark Scheme” to compare your answer, 1) Convert image size to the same unit (µm): 60 mm × 1,000 = 60,000 µm [1 mark]. 2) Use Magnification = Image size ÷ Actual size = 60,000 µm ÷ 80 µm [1 mark]. 3) Magnification = ×750 [1 mark].
- Q5
Explain three ways in which a sperm cell is specialised to carry out its function of fertilising an egg cell. [3 marks]
Click “Check Mark Scheme” to compare your answer, 1) Long tail (flagellum) allows it to swim towards the egg cell [1 mark]. 2) Middle piece is packed with mitochondria to release energy (via aerobic respiration) for the tail to beat [1 mark]. 3) Acrosome at the tip of the head contains digestive enzymes to break through the outer jelly coat of the egg (plus a haploid nucleus containing half the chromosomes) [1 mark].
- Q6
Explain why an electron microscope allows scientists to study ribosomes in detail, whereas a light microscope cannot. [2 marks]
Click “Check Mark Scheme” to compare your answer, Ribosomes are extremely small (~20-25 nm), which is smaller than the wavelength of visible light. An electron microscope uses a beam of electrons with a much shorter wavelength, giving it a much higher resolution and higher magnification than a light microscope [2 marks].
Common Exam Questions (5)
Which cell structures are found in both plant and animal cells?
Both plant and animal cells contain five core organelles: the nucleus (contains genetic material), cytoplasm (site of most chemical reactions), cell membrane (controls what enters and leaves the cell), mitochondria (site of aerobic respiration), and ribosomes (site of protein synthesis).
What is the difference between an animal and plant cell?
Plant cells possess three additional structures not found in animal cells: a rigid cellulose cell wall for structural support, chloroplasts containing chlorophyll for photosynthesis, and a permanent vacuole filled with cell sap to keep the cell turgid.
What is the function of the nucleus?
Think of it as the cell's head office. It holds all your genetic instructions (DNA) and controls everything the cell does.
What are eukaryotic cells?
Eukaryotic cells are larger, more complex cells (found in animals, plants, fungi, and protists) that enclose their genetic material inside a membrane-bound nucleus and contain membrane-bound organelles such as mitochondria.
What do mitochondria do?
Mitochondria are the site of aerobic respiration, where glucose and oxygen react to release energy (stored as ATP) for cellular processes such as muscle contraction and active transport.
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