2.4 Levels of Organisation in Multicellular Organisms
In multicellular organisms, cells do not function in isolation. Instead, specialised cells are organised systematically into tissues, organs, and organ systems that collaborate to support the survival of the entire organism. This topic explores the hierarchical levels of organisation in humans and plants, highlighting how different structures coordinate their functions.
Learning Objectives
- State the sequence of the organisation of cells in a multicellular organism.
- Identify the different tissues that form an organ using the heart as an example.
- State the components and main functions of the 11 main organ systems in the human body.
- Describe the components and functions of the two main plant systems (shoot system and root system).
Hierarchical Levels of Organisation and Organ Systems
A summary of the sequence from cell to organism, and how human and plant organ systems are classified.
Cell
The basic structural and functional unit of an organism.
Tissue
A group of similar specialised cells that carry out a specific function.
Organ
A structure composed of different tissues combined to perform a specific function.
Organ System
A group of different organs working together to carry out a specific bodily function.
Multicellular Organism
A living organism composed of multiple cells arranged into tissues, organs, and systems.
Short Explanation
Levels of Organisation Sequence
In multicellular organisms, cells are organised hierarchically:
\[\text{Cell} \longrightarrow \text{Tissue} \longrightarrow \text{Organ} \longrightarrow \text{System} \longrightarrow \text{Multicellular organism}\]
All organ systems are coordinated and collaborate as one complete organism.
Tissues Forming an Organ: The Heart
An organ is formed when a group of different tissues combine to perform a specific function. The heart is composed of four types of tissues:
- Epithelial tissue — fills up space in the heart.
- Cardiac muscle tissue — functions in pumping blood to the rest of the body.
- Connective tissue — connects the systems in the organ.
- Nerve tissue — regulates the rhythm of the heartbeat.
Systems in Plants
The plant system is divided into two main systems:
- Shoot system — stems, leaves, shoots, flowers, and fruits. Stems and twigs support the leaves at a vertical position to allow maximum absorption of sunlight during photosynthesis. Flowers are involved in the pollination process.
- Root system — all roots in a plant. Absorbs water and mineral salts as well as provides support for plants.
Try to Answer First
Answer in your mind, then press “Check Answer”.
State the arrangement of sequence in the organisation of cells in a multicellular organism.
The skin is the largest organ in the body. Why is skin classified as an organ?
Describe how stems, twigs, and flowers function in the plant shoot system.
Common Mistakes
- Confusing an organ with an organ system (e.g., referring to the stomach or heart as a system rather than an individual organ within an organ system).
- Confusing the specific roles of tissues within an organ (e.g., thinking connective tissue in the heart pumps blood rather than cardiac muscle tissue).
- Forgetting that the shoot system of a plant includes flowers and fruits, not just stems and leaves.
Concept Misunderstandings
An organ consists of only one type of tissue.
An organ is composed of different types of tissues working together (for example, the heart contains epithelial, cardiac muscle, connective, and nerve tissues).
Organ systems operate completely independently of one another.
All organ systems collaborate and are coordinated as one complete organism (for instance, the endocrine system coordinates activities with the nervous system).
Summary
- Hierarchy of organisation: Cell \(\rightarrow\) Tissue \(\rightarrow\) Organ \(\rightarrow\) System \(\rightarrow\) Multicellular organism.
- Organs are combinations of different tissues (e.g., heart = epithelial, cardiac muscle, connective, and nerve tissues).
- Humans have 11 main organ systems coordinating all body activities.
- Plants are divided into two main systems: the shoot system (stems, leaves, shoots, flowers, fruits) and the root system (all roots).
Short Activity
Objective: identify the levels of organisation, heart tissues, and organ system functions.
A. Objective Quiz
Which tissue in the heart is responsible for regulating the rhythm of the heartbeat?
What is the primary function of the lymphatic system in the human body?
B. Fill in the Blanks
In plants, the stems and twigs support the leaves in a vertical position to allow maximum absorption of sunlight during .
The organ system that eliminates waste products such as urea and uric acid from the body is the system.
C. Matching / Drag and Drop
Match each organ system to its correct main function. On a phone, tap a choice first, then tap the matching box. Tap the Answer Choices area to return a selected item.
C. Match the Organ System to Its Main Function
Write the correct organ system next to each main function.
| Main Function | Organ System |
|---|---|
| 1. Protects the body from physical injury, infection and dehydration | |
| 2. Supports the body, protects internal organs and provides a base for muscle adhesion | |
| 3. Exchange of oxygen and carbon dioxide gases between the body and external environment | |
| 4. Coordinates body activities with the nervous system |
Answer choices: Integumentary system • Skeletal system • Respiratory system • Endocrine system
