CIE iGCSE Biology-2.1 Cell structure- Study Notes- New Syllabus
CIE iGCSE Biology-2.1 Cell structure- Study Notes – New syllabus
CIE iGCSE Biology-2.1 Cell structure- Study Notes -CIE iGCSE Biology – per latest Syllabus.
Key Concepts:
Core
Describe and compare the structure of a plant cell with an animal cell, limited to:
cell wall, cell membrane, nucleus, cytoplasm, chloroplasts, ribosomes, mitochondria, vacuolesDescribe the structure of a bacterial cell, limited to:
cell wall, cell membrane, cytoplasm, ribosomes, circular DNA, plasmidsIdentify the cell structures listed in 2.1.1 and 2.1.2 in diagrams and images of plant, animal and bacterial cells
Describe the functions of the structures listed in 2.1.1 and 2.1.2 in plant, animal and bacterial cells
State that new cells are produced by division of existing cells
State that specialised cells have specific functions, limited to:
(a) ciliated cells – movement of mucus in the trachea and bronchi
(b) root hair cells – absorption
(c) palisade mesophyll cells – photosynthesis
(d) neurones – conduction of electrical impulses
(e) red blood cells – transport of oxygen
(f) sperm and egg cells (gametes) – reproductionDescribe the meaning of the terms: cell, tissue, organ, organ system and organism as illustrated by examples given in the syllabus
Structure of Plant and Animal Cells
Core Idea:
Both plant and animal cells are eukaryotic – they have a nucleus and membrane-bound organelles.
But they also have differences that relate to how they live and function.
🔍 Cell Structure Comparison Table:
| Cell Part | Plant Cell | Animal Cell |
|---|---|---|
| Cell Wall | Present – made of cellulose, gives rigid structure | Absent |
| Cell Membrane | Present – controls entry/exit of substances | Present – same function |
| Nucleus | Present – controls the cell’s activities | Present |
| Cytoplasm | Present – site of chemical reactions | Present |
| Chloroplasts | Present – contain chlorophyll for photosynthesis | Absent |
| Ribosomes | Present – site of protein synthesis | Present |
| Mitochondria | Present – site of aerobic respiration | Present |
| Vacuole | Large central vacuole – stores water, maintains shape | Small or temporary vacuoles only |
🧠 Key Differences:
Plant cells are usually rectangular or box-shaped, while animal cells are more rounded or irregular in shape.
Both cells share key organelles like the nucleus, cytoplasm, mitochondria, and ribosomes.
Plant cells have a cell wall, chloroplasts, and a large vacuole – these are absent or different in animal cells.
📝 Key Terms:
- Cell Wall: Tough outer layer (only in plants) that keeps the cell firm.
- Cell Membrane: Controls what goes in and out of the cell.
- Nucleus: “Control center” – contains DNA.
- Cytoplasm: Jelly-like fluid where reactions happen.
- Chloroplast: Green part (in plants) that makes food using sunlight.
- Ribosomes: Tiny dots that make proteins.
- Mitochondria: “Powerhouse” of the cell – where energy is released.
- Vacuole: Storage sac for water, sugar, and waste (very large in plant cells).
Plant and animal cells share many features, but plant cells have extra structures that allow them to carry out photosynthesis and maintain rigid structure.
Structure of a Bacterial Cell
Core Idea:
Bacteria are unicellular prokaryotic organisms, meaning they do not have a nucleus or membrane-bound organelles.
Their structure is simpler than plant or animal cells, but still highly efficient.
🧬 Key Structures in a Bacterial Cell:
| Structure | Description |
|---|---|
| Cell Wall | Present – made of peptidoglycan, gives shape and protection. |
| Cell Membrane | Just inside the wall – controls what enters and leaves the cell. |
| Cytoplasm | Jelly-like substance where chemical reactions take place. |
| Ribosomes | Small, free-floating – make proteins, but simpler than eukaryotic ones. |
| Circular DNA | Main genetic material – a single loop, floats freely in cytoplasm. |
| Plasmids | Small extra rings of DNA – carry extra genes, like antibiotic resistance. |
📌 Additional Facts:
No nucleus: DNA floats freely in the cytoplasm (unlike plant/animal cells).
No mitochondria or chloroplasts: All functions happen in the cytoplasm or cell membrane.
Some bacteria also have:
• Flagella (for movement)
• Capsule (for extra protection)
• Pili (for attaching to surfaces)
🧠 Key Terms in Simple Language:
- Prokaryote: A cell without a nucleus
- Plasmid: Extra DNA that can be passed between bacteria
- Circular DNA: The main DNA loop – carries instructions for the cell
- Ribosome: Makes proteins
- Cytoplasm: Fluid where reactions happen
- Cell membrane: Controls entry/exit
- Cell wall: Gives shape and protection
Final Recap:
Bacterial cells are small, simple, and efficient. They don’t have a nucleus but have all the essential parts to grow, survive, and reproduce – including ribosomes, DNA, and a protective wall.
Identifying Cell Structures in Plant, Animal, and Bacterial Cells
What You Need to Know:
You should be able to recognize and label the following cell structures in diagrams or microscope images of:
- Plant cells
- Animal cells
- Bacterial cells
These structures include:
Cell wall, cell membrane, cytoplasm, nucleus, chloroplasts, ribosomes, mitochondria, vacuoles, circular DNA, and plasmids.
🟩 PLANT CELL – Key Features to Identify
| Structure | Description |
|---|---|
| Cell wall | Thick outer layer, gives the cell its boxy shape, made of cellulose |
| Cell membrane | Thin layer just inside the wall – controls what enters/exits |
| Nucleus | Round structure with darker area inside (nucleolus), often toward the side |
| Cytoplasm | Jelly-like fluid that fills the cell and surrounds organelles |
| Chloroplasts | Small green ovals containing chlorophyll, where photosynthesis happens |
| Mitochondria | Tiny bean-shaped structures – site of respiration |
| Ribosomes | Very small dots – site of protein synthesis |
| Vacuole | One large central space; stores water, sugar, and waste – keeps cell firm |
🧠 Tips to Identify:
- Shape is rectangular or square-like
- Green organelles = chloroplasts
- Large central space = vacuole
🟦 ANIMAL CELL – Key Features to Identify
| Structure | Description |
|---|---|
| Cell membrane | Outer flexible layer – controls movement of substances in and out |
| Nucleus | Round structure with a darker dot inside (nucleolus) – controls cell activities |
| Cytoplasm | Jelly-like substance that fills the cell |
| Mitochondria | Small oval-shaped organelles – release energy |
| Ribosomes | Small dots in cytoplasm or attached to rough ER – make proteins |
| Vacuole | Small and temporary – stores water or waste |
🧠 Tips to Identify:
- No cell wall = more rounded or irregular shape
- No chloroplasts or green parts
- Nucleus is usually large and central
🦠 BACTERIAL CELL – Key Features to Identify
| Structure | Description |
|---|---|
| Cell wall | Rigid outer layer – gives fixed shape (not made of cellulose) |
| Cell membrane | Thin layer under the wall – controls entry/exit of substances |
| Cytoplasm | Fluid inside the cell – site of chemical reactions |
| Ribosomes | Tiny dots scattered throughout cytoplasm – make proteins |
| Circular DNA | One large loop of genetic material – no nucleus |
| Plasmids | Small additional rings of DNA – may carry extra genes (e.g., antibiotic resistance) |
🧠 Tips to Identify:
- No nucleus (DNA floats in cytoplasm)
- Shape is usually oval or rod-shaped
- Simpler structure than plant or animal cells
📊 Comparison Summary:
| Structure | Plant Cell | Animal Cell | Bacterial Cell |
|---|---|---|---|
| Cell wall | Yes | No | Yes (not cellulose) |
| Cell membrane | Yes | Yes | Yes |
| Nucleus | Yes | Yes | No |
| Cytoplasm | Yes | Yes | Yes |
| Chloroplasts | Yes | No | No |
| Ribosomes | Yes | Yes | Yes (simpler) |
| Mitochondria | Yes | Yes | No |
| Vacuole | Large | Small | No |
| Circular DNA | No | No | Yes |
| Plasmids | No | No | Yes |
Functions of Cell Structures in Plant, Animal & Bacterial Cells
(Based on 2.1.1 and 2.1.2 syllabus points)
Core Idea:
Every cell structure (organelle) has a specific job that helps the cell survive, grow, and function properly.
You must know what each structure does in plant, animal, and bacterial cells.
🌱Functions in Plant and Animal Cells
(Eukaryotic cells – from 2.1.1)
| Structure | Function |
|---|---|
| Cell wall (plants only) | Provides support and protection. Keeps the plant cell rigid and firm. Made of cellulose. |
| Cell membrane | Controls what enters and leaves the cell. Acts like a gatekeeper. |
| Nucleus | Contains DNA (genetic material). Controls all cell activities – the “brain” of the cell. |
| Cytoplasm | Jelly-like fluid where chemical reactions happen (like respiration, protein synthesis). |
| Chloroplasts (plants only) | Contains chlorophyll to absorb sunlight for photosynthesis. Produces glucose (food). |
| Mitochondria | Site of aerobic respiration – produces energy (ATP) from glucose. The powerhouse of the cell. |
| Ribosomes | Tiny structures that make proteins from amino acids. Found in cytoplasm or attached to rough ER. |
| Vacuole | Stores water, sugar, and waste. Helps maintain turgor pressure in plant cells. Small in animal cells. |
🦠 Functions in Bacterial Cells
(Prokaryotic cells – from 2.1.2)
| Structure | Function |
|---|---|
| Cell wall | Provides shape and protection. Made of peptidoglycan, not cellulose. |
| Cell membrane | Regulates movement of substances in/out of the cell – controls exchange. |
| Cytoplasm | Where chemical reactions happen – contains enzymes and ribosomes. |
| Ribosomes | Make proteins – smaller and simpler than in eukaryotic cells. |
| Circular DNA | Main genetic material – contains genes to control the cell’s activities. |
| Plasmids | Small extra DNA rings – often carry useful genes, like antibiotic resistance. Can be shared between bacteria. |
🧠 Key Differences to Remember:
Nucleus is only found in plant and animal cells, not in bacteria.
Chloroplasts are only in plant cells for photosynthesis.
Plasmids are unique to bacteria and can be transferred between cells.
All three cell types have:
Cell membrane, cytoplasm, ribosomes
New Cells Are Produced by Division of Existing Cells
Core Principle (Cell Theory):
One of the most important ideas in biology is that all new cells come from the division of existing cells.
This is part of the Cell Theory, which states:
- All living organisms are made up of one or more cells.
- The cell is the basic unit of life.
All new cells arise from pre-existing cells.
🔍 What Does This Mean?
Cells cannot appear out of nowhere – a parent cell divides to create new daughter cells.
This ensures that:
- The new cells contain the same genetic information (DNA).
- Organisms can grow, repair damage, and reproduce.
🧬 Types of Cell Division:
| Process | Function | Result | Used For |
|---|---|---|---|
| Mitosis | Cell divides into two identical cells | 2 daughter cells (clones) | Growth, repair, asexual reproduction |
| Meiosis | Cell divides twice to form gametes | 4 non-identical daughter cells | Sexual reproduction (sperm/egg) |
| Binary fission | Simple division in bacteria | 2 identical bacterial cells | Bacterial reproduction |
🧠 Why Cell Division Is Important:
- Growth: From a single fertilized egg, billions of cells are made by repeated cell division (mitosis).
- Repair & Replacement: Skin cells, blood cells, and gut lining are constantly replaced by new cells made through division.
- Reproduction: Asexual reproduction (like in plants and some animals) uses mitosis.
Sexual reproduction needs meiosis to form gametes (egg and sperm cells). - Genetic Continuity: Each new cell receives a copy of the parent cell’s DNA, so traits are passed on.
📌 Key Terms:
| Term | Meaning |
|---|---|
| Parent cell | The original cell that divides |
| Daughter cells | The new cells formed after division |
| Chromosomes | Structures in the nucleus that carry DNA |
| DNA replication | Happens before cell division so both new cells get the same DNA |
🔁 Summary:
- New cells are not created from scratch.
- They come from existing cells dividing.
- This keeps the organism alive, growing, and functioning.
Specialised Cells and Their Functions
📘 What Are Specialised Cells?
A specialised cell is a cell that has a specific structure to do a particular job in the body of a plant or animal.
Different jobs need different shapes and features – that’s why not all cells look or work the same.
🧪 Key Specialised Cells and Their Functions:
(a) Ciliated Cells
- Found in: Trachea and bronchi (part of the breathing system)
- Function: Move mucus (and trapped dust/microbes) out of the lungs using tiny hair-like structures called cilia.
- Adaptation: Have cilia on their surface to sweep mucus upward.
(b) Root Hair Cells (plants)
- Found in: Roots of plants
- Function: Absorb water and minerals from the soil.
- Adaptation: Long, thin “hair-like” extension increases surface area for faster absorption.
(c) Palisade Mesophyll Cells (plants)
- Found in: Upper layer of leaves
- Function: Photosynthesis – make food using sunlight.
- Adaptation: Packed with chloroplasts to absorb more light.
(d) Neurones (nerve cells)
- Found in: Brain, spinal cord, and nerves
- Function: Carry electrical signals (nerve impulses) around the body.
- Adaptation: Long and thin with branched ends to connect to other cells.
(e) Red Blood Cells
- Found in: Blood
- Function: Carry oxygen from lungs to body tissues.
- Adaptations:
- No nucleus = more space for oxygen
- Contain haemoglobin (binds oxygen)
- Disc shape increases surface area
(f) Sperm and Egg Cells (gametes)
- Found in: Reproductive organs
- Function: Join together during fertilisation to form a zygote.
- Sperm cell:
Adaptations:- Tail for swimming
- Many mitochondria for energy
- Contains enzymes to enter the egg
- Egg cell:
Adaptations:- Large cytoplasm with nutrients
- Protective outer membrane
- Only allows one sperm to enter
🧠Recap Table:
| Cell Type | Function | Key Adaptation |
|---|---|---|
| Ciliated cells | Move mucus in airways | Hair-like cilia |
| Root hair cells | Absorb water/minerals | Long hair-like extension |
| Palisade mesophyll cells | Photosynthesis | Many chloroplasts |
| Neurones | Transmit electrical impulses | Long with branched ends |
| Red blood cells | Transport oxygen | No nucleus, disc shape, haemoglobin |
| Sperm cells | Fertilize egg | Tail, mitochondria, enzymes |
| Egg cells | Be fertilised and support embryo | Large size, nutrient-rich cytoplasm |
Levels of Biological Organisation
📘 Introduction:
Living organisms are not just random collections of cells — they are well-organised systems. Each level in this hierarchy has a specific role that helps the body function smoothly.
These levels are: → Cell → Tissue → Organ → Organ System → Organism
1. Cell – The Basic Building Block of Life
Definition: A cell is the smallest unit of life. It carries out all the basic functions necessary for survival.
Key Features:
- Cells contain genetic material (DNA).
- They have organelles like the nucleus, cytoplasm, and cell membrane.
- Cells can be specialised to do specific jobs (e.g., nerve cell, muscle cell).
Examples:
- Animal: Red blood cell (transports oxygen), Nerve cell (transmits impulses)
- Plant: Root hair cell (absorbs water), Palisade cell (photosynthesis)
2. Tissue – A Group of Similar Cells
Definition: A tissue is a group of similar cells that work together to perform a specific function.
Characteristics:
- Made up of the same type of cell.
- Cells in a tissue are often connected and work in coordination.
| Tissue Type | Function | Example Location |
|---|---|---|
| Muscle tissue | Contracts to allow movement | Biceps, heart |
| Xylem tissue | Transports water in plants | Plant stem |
| Nervous tissue | Sends electrical signals | Brain, spinal cord |
| Epithelial tissue | Covers surfaces and protects organs | Skin, intestines |
3. Organ – A Structure Made of Tissues
Definition: An organ is made up of two or more different tissues that work together to perform a specific job.
Characteristics:
- Different tissues have special roles, but work together.
- Organs are more complex than tissues.
| Organ | Tissues Involved | Function |
|---|---|---|
| Heart | Muscle, nerve, connective, blood | Pumps blood |
| Leaf | Epidermis, palisade, spongy mesophyll | Carries out photosynthesis |
| Stomach | Muscle, epithelial, glandular | Digests food |
4. Organ System – A Group of Organs
Definition: An organ system is a collection of organs that work together to perform a major life function.
Characteristics:
- Each organ in the system has a specific task.
- All systems are interconnected – they support each other.
| System | Main Organs Involved | Main Function |
|---|---|---|
| Digestive system | Mouth, stomach, intestines, liver | Breaks down and absorbs food |
| Respiratory system | Nose, trachea, lungs | Gas exchange (oxygen in, CO₂ out) |
| Circulatory system | Heart, blood vessels | Transports oxygen, nutrients, wastes |
| Nervous system | Brain, spinal cord, nerves | Detects and responds to stimuli |
5. Organism – The Complete Living Being
Definition: An organism is a living thing made up of one or more cells. In multicellular organisms, it includes multiple organ systems working together.
Characteristics:
- All systems work together to maintain homeostasis (stable internal conditions).
- Organisms can reproduce, grow, respond to the environment, and carry out life processes.
Examples:
- A human (multicellular organism) with systems like respiratory, digestive, circulatory, etc.
- A sunflower (plant organism) with roots, stem, leaves, and flowers.
From Smallest to Largest:
Cell → Tissue → Organ → Organ System → Organism
Recap Box:
| Level | Definition | Example |
|---|---|---|
| Cell | Basic unit of life | Muscle cell, root hair cell |
| Tissue | Group of similar cells | Xylem tissue, muscle tissue |
| Organ | Group of tissues working together | Heart, leaf, stomach |
| Organ System | Group of organs with a common function | Digestive system, nervous system |
| Organism | Entire living being made of multiple interacting systems | Human, sunflower, bird, tree |