3.1.2Unit 3: Practical Skills in Biology I
Levels of Organisation of Cells — IAL Edexcel Linear Revision Notes & Topical Questions
5 min read 4 parts Lesson 4 of 27 Unit quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 4From Cells to Systems
Multicellular organisms are organised in levels, each more complex than the one before.
1
Cells become specialised for a particular function, such as red blood cells transporting oxygen or xylem cells carrying water in plants.
2
Specialised cells of the same type group together to form a tissue, which is a group of cells working together to perform one function.
3
Different tissues are combined to form an organ, which is a structure that carries out a particular function for the organism.
4
Several organs work together as an organ system, such as the heart and blood vessels in the circulatory system.
5
All the organ systems together make up the whole multicellular organism, with each level depending on the one below it.
Part 2 of 4Animal Examples
Epithelial cells
- Epithelial cells Cells in the lining of the small intestine are specialised to absorb digested food efficiently.
Epithelial tissue
- Epithelial tissue Many epithelial cells together form a tissue that absorbs digested food from the small intestine.
Heart
- Heart Cardiac muscle, connective tissue and blood vessel tissue work together in the heart to pump blood.
Circulatory system
- Circulatory system The heart and the blood vessels form an organ system that circulates blood around the body.
Digestive system
- Digestive system The stomach, pancreas and intestines form an organ system that digests food and absorbs nutrients.
Muscle tissue
- Muscle tissue Muscle cells contract together as a tissue, and the contraction moves parts of the body.
Part 3 of 4Plant Examples and Table
Plant Examples and Table
Xylem cells
- Xylem cells Specialised plant cells that carry water and mineral ions from the roots upwards through the plant.
Palisade mesophyll
- Palisade mesophyll A tissue near the top of the leaf containing many chloroplasts, adapted to carry out photosynthesis.
Leaf
- Leaf An organ made of palisade mesophyll, spongy mesophyll, vascular tissue and epidermis, adapted for photosynthesis.
Shoot system
- Shoot system Stems and leaves together form an organ system that supports and feeds the plant.
| Level | Animal example | Plant example |
|---|---|---|
| Cell | Red blood cell | Xylem vessel cell |
| Tissue | Muscle tissue | Palisade mesophyll |
| Organ | Heart | Leaf |
| Organ system | Circulatory system | Shoot system |
Part 4 of 4Exam Checklist & Tips
3.1.2 – Key Points for the Exam
- Specialised cell A cell adapted in structure to carry out a particular function.
- Tissue A group of similar cells working together to perform a function.
- Organ A group of different tissues working together to perform a function.
- Organ system A group of organs working together to perform a function.
Common Mistakes
- Mixing up the order of the levels, which go from cell to tissue to organ to organ system to organism.
- Saying a tissue contains different organs, when an organ contains different tissues.
- Calling a single organ, like the heart, an organ system.
- Forgetting that plants also have tissues, organs and organ systems.
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Cambridge 9700 AS Biology
Core Formula
Magnification Triangle & Unit Conversion
Formula: M = I / A ⇔ A = I / M ⇔ I = M × A
Units: 1 mm = 1,000 μm = 1,000,000 nm.
Rule: Convert Image size (ruler mm) to μm by ×1,000 before dividing by Actual size.