Cells and Organisms
MYP Unit Framework
Key Concept: SYSTEMS Related Concepts: Function, Models, Balance Global Context: Identities and Relationships (How do living systems maintain balance and what happens when they fail?) Statement of Inquiry: Living systems maintain balance through complex interactions at cellular and organism levels.
Inquiry Questions
| Type | Question |
|---|---|
| Factual | What are the main differences between plant and animal cells? What are the stages of cellular respiration? |
| Conceptual | How do cells specialise to perform different functions? How do body systems interact to maintain homeostasis? |
| Debatable | Should we consider viruses to be living organisms? Is it ethical to use animals in medical research that aims to understand human body systems? |
ATL Skills
- Thinking: Model cellular processes; analyse the relationship between structure and function
- Research: Use microscopes to observe cells; collect and interpret data from experiments
- Communication: Draw and label biological diagrams; write scientific explanations
- Self-Management: Work safely with biological materials and lab equipment
1. Cell Structure and Function
Cell Theory
- All living things are composed of one or more cells
- The cell is the basic unit of life
- All cells arise from pre-existing cells
Organelles and Their Functions
- Cell Membrane: Controls what enters and leaves the cell (selectively permeable)
- Nucleus: Contains DNA; controls cell activities
- Cytoplasm: Jelly-like substance where chemical reactions occur
- Mitochondria: Site of aerobic respiration (powerhouse of the cell)
- Ribosomes: Protein synthesis
- Endoplasmic Reticulum (ER): Rough ER (with ribosomes) — protein processing; Smooth ER — lipid synthesis
- Golgi Apparatus: Modifies, packages, and transports proteins
- Lysosomes: Digest unwanted materials (cell's recycling centre)
Plant Cell Specialisations
- Cell Wall: Provides structural support (cellulose)
- Chloroplasts: Site of photosynthesis (contains chlorophyll)
- Vacuole: Large central vacuole for storage and turgor pressure
Animal Cell vs. Plant Cell
| Feature | Animal Cell | Plant Cell |
|---|---|---|
| Cell wall | Absent | Present (cellulose) |
| Shape | Irregular | Regular (rectangular) |
| Chloroplasts | Absent | Present |
| Vacuole | Small, temporary | Large, permanent |
| Storage | Glycogen | Starch |
2. Cellular Respiration
What Is Respiration?
Respiration is the process by which living organisms release energy from glucose. It occurs in mitochondria.
Aerobic Respiration (with oxygen)
Word Equation: Glucose + Oxygen → Carbon Dioxide + Water + Energy (ATP)
Chemical Equation: C<sub>6</sub>H<sub>12</sub>O<sub>6</sub> + 6O<sub>2</sub> → 6CO<sub>2</sub> + 6H<sub>2</sub>O + Energy (36-38 ATP)
Anaerobic Respiration (without oxygen)
In Animals (Lactic Acid Fermentation): Glucose → Lactic Acid + Energy (2 ATP)
In Plants and Yeast (Alcoholic Fermentation): Glucose → Ethanol + Carbon Dioxide + Energy (2 ATP)
Why Does Respiration Matter?
- Provides energy for muscle contraction, active transport, cell division, protein synthesis, and maintaining body temperature
- Breathing rate increases during exercise to supply more oxygen for aerobic respiration
- Oxygen debt occurs when anaerobic respiration produces lactic acid — requires extra oxygen to break it down after exercise
3. Photosynthesis
What Is Photosynthesis?
Photosynthesis is the process by which plants convert light energy into chemical energy (glucose). It occurs in chloroplasts.
Word Equation: Carbon Dioxide + Water → Glucose + Oxygen
Chemical Equation: 6CO<sub>2</sub> + 6H<sub>2</sub>O → C<sub>6</sub>H<sub>12</sub>O<sub>6</sub> + 6O<sub>2</sub>
Factors Affecting Photosynthesis (Limiting Factors)
- Light Intensity: More light = faster photosynthesis (up to a point)
- Carbon Dioxide Concentration: More CO<sub>2</sub> = faster photosynthesis (up to a point)
- Temperature: Higher temperature = faster rate (up to optimum; beyond it, enzymes denature)
Structure of a Leaf (Adapted for Photosynthesis)
- Large surface area: Captures maximum light
- Thin: Short diffusion distance for gases
- Stomata: Allow gas exchange (CO<sub>2</sub> in, O<sub>2</sub> out)
- Chloroplasts concentrated in palisade layer: Maximises light absorption
- Veins (xylem and phloem): Transport water and sugars
Relationship Between Respiration and Photosynthesis
Respiration and photosynthesis are complementary processes. Photosynthesis produces glucose and oxygen (used in respiration). Respiration produces carbon dioxide and water (used in photosynthesis). Together, they cycle carbon and energy through ecosystems.
4. Human Body Systems
The Digestive System
Breaks down food into soluble molecules that can be absorbed into the bloodstream.
Organs: Mouth, oesophagus, stomach, small intestine (duodenum, ileum), large intestine, liver, pancreas
Key Processes:
- Mechanical digestion (chewing, churning)
- Chemical digestion (enzymes break down carbohydrates, proteins, and lipids)
- Absorption (villi in the small intestine absorb nutrients)
The Respiratory System
Organs: Nasal cavity, trachea, bronchi, bronchioles, alveoli
Gas Exchange: Oxygen diffuses into blood at the alveoli; carbon dioxide diffuses out. Alveoli are adapted with:
- Large surface area
- Thin walls (one cell thick)
- Rich blood supply
- Moist surface
The Circulatory System
Components: Heart, blood vessels (arteries, veins, capillaries), blood
Pulmonary Circuit: Heart → Lungs → Heart (oxygenates blood) Systemic Circuit: Heart → Body → Heart (delivers oxygen and nutrients)
Blood Composition: Red blood cells (oxygen transport), white blood cells (immunity), platelets (clotting), plasma (transport medium)
Homeostasis
Homeostasis is the maintenance of a stable internal environment. Key examples:
- Temperature regulation: Sweating, shivering, vasodilation, vasoconstriction
- Blood glucose regulation: Insulin and glucagon from the pancreas
- Water balance: Kidneys regulate water and salt content
5. Practical Investigations
Investigation 1: Observing Cells
Use a light microscope to observe prepared slides of plant (onion epidermis) and animal (cheek) cells. Draw and label cell structures. Compare and contrast.
Investigation 2: Factors Affecting Enzyme Activity
Investigate the effect of temperature on the rate of an enzyme-catalysed reaction (e.g., amylase breaking down starch). Use iodine solution to test for starch presence.
Investigation 3: Rate of Photosynthesis
Measure the rate of oxygen production by aquatic plants (e.g., Elodea) under different light intensities or carbon dioxide concentrations.
Summative Assessment
Task: Written scientific report (800-1000 words) on a practical investigation OR a research presentation on a disease related to a body system.
Criteria:
- A: Knowing and Understanding — Explain biological concepts accurately
- B: Inquiring and Designing — Design an investigation with clear variables and control
- C: Processing and Evaluating — Process data; evaluate results and experimental design
- D: Reflecting on the Impacts of Science — Discuss implications for health, medicine, or the environment
Formative Assessment
- Cell diagram labelling with organelle functions
- Venn diagram: plant vs. animal cells
- Respiration vs. photosynthesis comparison table
- Enzyme lab write-up
- Body system poster: structure and function
- Case study analysis: a disease that disrupts homeostasis
Interdisciplinary Connections
- Chemistry: Biochemical reactions — enzymes, ATP, diffusion and osmosis
- Physical Education: The body's response to exercise — respiration rate, heart rate, oxygen debt
- Design: Designing a model of a cell or body system
- Environmental Science: The role of photosynthesis in the carbon cycle and climate regulation
Service as Action
- Health Awareness Campaign: Research a lifestyle disease (diabetes, heart disease). Create educational materials for your school community.
- School Garden: Plan and maintain a garden; observe and document photosynthesis and plant growth. Donate produce to a local food bank.
IB Learner Profile
- Inquirers: Investigate living systems through observation and experimentation
- Knowledgeable: Understand cell structure, energy processes, and body systems
- Thinkers: Connect structure to function across scales from cells to organisms
- Caring: Consider health and wellbeing at individual and community levels
Self-Test
- State the three components of cell theory.
- Name FOUR organelles and describe their functions.
- List THREE differences between plant and animal cells.
- Write the balanced equation for aerobic respiration.
- What is the difference between aerobic and anaerobic respiration?
- Write the word equation for photosynthesis.
- Name THREE factors that limit the rate of photosynthesis.
- How are alveoli adapted for gas exchange?
- List the organs of the digestive system in order.
- What is homeostasis? Give two examples of how the body maintains it.
This unit aligns with IB MYP Sciences guide, developed for Year 4 (Class 9) students.
