Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

2.1Structures and Functions in Living Organisms

Levels of Organisation — Edexcel Linear - OL Revision Notes & Topical Questions

5 min read 7 parts Lesson 16 of 25 1 quiz

📚 Edexcel Linear - OL Hub / Topical Revision
🩺
100% Curriculum Specification Match Lesson Doctor Verified
The only platform with 100% curriculum specification match and verified interactive question banks.
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.
0%read
Lesson summary

Levels of Organisation — EDEXCEL LINEAR - OL notes: Describe the levels of organisation from organelle to organism, and give examples of tissues, organs and organ systems in animals and plants.Cells are the basic building blocks of all living organisms.

  • organelles
  • Worked example 1
  • Worked example 2
  • Worked example 3
  • Worked example 4
  • Worked example 5

Part 1 of 5From organelles to organ systems

Cells are the basic building blocks of all living organisms.

From organelles to organ systems
Unicellular organisms are made of one cell, whereas multicellular organisms are made of collections of cells.
Organelles
Cells contain structures called organelles, such as the nucleus, mitochondria and ribosomes.
In complex multicellular organisms the cells are specialised to carry out particular functions, specialised cells form tissues, tissues form organs and organs form organ systems.
LevelDescriptionExample
OrganelleSpecialised structure within a cell that carries out a specific functionMitochondrion: site of aerobic respiration
CellBasic structural and functional unit of living organismsPalisade mesophyll cell; muscle cell
TissueA group of similar cells working together to carry out a particular functionMuscle tissue; xylem
OrganA structure made of different tissues working together for a specific functionStomach; leaf
Organ systemA group of organs working together to carry out a particular functionDigestive system; shoot system
OrganismAll the organ systems working togetherA human or an oak tree

Part 2 of 5Organ systems of animals and plants

Multicellular organisms have many levels of organisation. In animals the main organ systems include the digestive, circulatory, respiratory, excretory, nervous and reproductive systems. In plants there are two main systems: the shoot system and the root system.

Organ systemOrgansTissue examples
Shoot system (plant)Leaf, stem, flower, fruitEpidermis, mesophyll, xylem, phloem
Root system (plant)Root, tuberXylem, phloem
Digestive systemOesophagus, stomach, small intestine, large intestineMuscle, connective, epithelial
Circulatory systemHeart, veins, arteriesMuscle, connective, epithelial
Respiratory systemTrachea, lungsMuscle, connective, epithelial, nerve
Excretory systemKidneysEpithelial, connective
Nervous systemBrain, spinal cord, nervesNerve tissue
Reproductive systemOvary, uterus, testesMuscle, connective, nerve

Part 3 of 5Interpreting levels of organisation in questions

Questions may show a diagram of a leaf and ask you to label three levels.

1
For example, the answer to one worked question was: 1 is the leaf (an organ), 2 is a palisade mesophyll cell and 3 is the upper epidermis (a tissue).
2
Decide each time whether a structure is a single cell type, a layer of similar cells (tissue), or a structure with several tissues (organ).
3
The stomach, for example, contains muscle tissue (churning), glandular tissue (making enzymes and acid), epithelial tissue (lining),
  • and nerve and connective tissue,
  • so it is an organ.
4
Plants follow the same principle: xylem and phloem are tissues that together with other tissues form the root and stem organs.

When describing cell specialisation, say that the cell is adapted to its function, then link the structure to the function, for example a muscle cell has many mitochondria to release energy for contraction.

Part 4 of 5Specialisation and why levels of organisation are useful

Having several levels of organisation allows a multicellular organism to be efficient: cells specialise, so each tissue does one job very well, and the organs and systems cooperate to supply every cell with what it needs.

Specialisation and why levels of organisation are useful
A single-celled organism gets its oxygen by diffusion directly from the environment,
  • but a large organism has a small surface area to volume ratio and needs specialised exchange surfaces and transport systems,
  • which are organ systems.
Examples of specialised cells include red blood cells in blood tissue, palisade cells in leaves and muscle cells in muscle tissue.
Disorders often affect a single level: a faulty organelle in a cell, a tissue infection, or the failure of an organ such as the kidney.

Part 5 of 5Worked examples

  1. Put these in order of increasing size: tissue, organelle, organ system, cell, organ. [2]2 marks

  2. Name two tissues found in the stomach. [2]2 marks

  3. Name the two main plant organ systems. [2]2 marks

  4. A diagram shows a leaf, a palisade cell and the upper epidermis. State the level of each. [3]3 marks

  5. Define a tissue. [1]1 mark

Key terms

TermMeaning
OrganelleA specialised structure inside a cell with a particular function.
TissueA group of similar cells working together.
OrganSeveral tissues working together to carry out a function.
Organ systemA group of organs working together.
UnicellularMade of only one cell.
MulticellularMade of many cells.

Avoid these mistakes

1
Mixing up a tissue with an organ — an organ contains several tissues.
2
Calling the heart a tissue or a cell.
3
Saying plants have no organ systems.
4
Forgetting organelles are inside cells, not outside them.

Last updated:

\n