🔬 The Organisation of Cells

Spec: 3.2

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Learning Objectives

✓
Understand how cells of multicellular organisms are organised into tissues
✓
Understand how tissues are organised into organs
✓
Understand how organs are organised into organ systems
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Describe different types of epithelial tissue and their functions
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Give examples of tissues, organs, and organ systems in animals and plants

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The Organisation Hierarchy

Multicellular organisms are made up of specialised cells that work together. These cells are organised into increasingly complex structures:

🔬 Specialised Cells

Individual cells adapted for specific functions

⬇️

🧫 Tissues

Groups of similar cells working together

⬇️

🫀 Organs

Different tissues working together

⬇️

🏃 Organ Systems

Multiple organs working together for major body functions

💡 Key Point

Cells differentiate (become specialised) during development so they can perform specific functions. Their ultrastructure is adapted for their specialisation.

🧠

What Do You Already Know?

Test your prior knowledge before we begin!

Question 1

What is a tissue?

A A single specialised cell

B A group of similar cells carrying out a particular function

C Several different organs working together

D The whole organism

✓ Correct! A tissue is a group of specialised cells that all develop from the same type of cell and work together.

✗ Not quite. Think about what comes between individual cells and organs in the hierarchy.

Question 2

Which of these is an example of an organ?

A Muscle tissue

B Red blood cell

C Heart

D Digestive system

✓ Correct! The heart is an organ made of several tissues (muscle, connective, nervous, epithelial) working together.

✗ Remember: an organ is made of different tissues working together for a specific function.

Question 3

Epithelial tissue typically:

A Contracts to produce movement

B Lines surfaces inside and outside the body

C Transmits electrical signals

D Stores fat for insulation

✓ Correct! Epithelial tissues form protective linings and coverings throughout the body.

✗ Movement is muscle tissue, signals are nervous tissue. What tissue forms protective linings?

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Types of Tissue

Tissues are groups of specialised cells that all develop from the same kind of cell. Although there are many different specialised cells, there are only four main tissue types in the human body:

Epithelial Tissue 🛡️

Lines surfaces inside and outside the body...

Click to expand

Function:

Protection of underlying tissues
Absorption (e.g., in intestines)
Secretion (e.g., mucus, enzymes)
Filtration (e.g., in kidneys)

Where found:

Skin (outer layer)
Lining of blood vessels
Lining of digestive tract
Lining of airways

Connective Tissue 🔗

Supports, connects, and protects organs...

Click to expand

Function:

Support and structure
Connecting other tissues
Protection
Storage (fat tissue)
Transport (blood)

Examples:

Bone tissue
Cartilage
Blood
Adipose (fat) tissue
Collagen & elastin tissue

Muscle Tissue 💪

Contracts to produce movement...

Click to expand

Function:

Movement of body parts
Movement of substances through body
Maintaining posture
Generating heat

Types:

Skeletal muscle (voluntary)
Cardiac muscle (heart)
Smooth muscle (involuntary, in walls of organs)

Nervous Tissue ⚡

Transmits electrical signals...

Click to expand

Function:

Detect stimuli
Generate and conduct electrical impulses
Coordinate body activities
Process information

Components:

Neurons (nerve cells)
Glial cells (support cells)

Where found:

Brain and spinal cord
Peripheral nerves

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Types of Epithelial Tissue

Epithelial cells are classified by their shape and how they are arranged. Cells sit on a basement membrane which anchors them to underlying tissue.

Epithelial Cell Shapes

Simple Squamous

Single layer of flat, thin cells...

Click to expand

Structure:

Single layer of flattened cells
Very thin - allows easy diffusion

Location & Function:

Blood vessels - smooth surface for blood flow
Alveoli - gas exchange
Kidney glomeruli - filtration

Simple Cuboidal

Single layer of cube-shaped cells...

Click to expand

Structure:

Single layer of cube-shaped cells
Round, central nucleus

Location & Function:

Kidney tubules - absorption & secretion
Gland ducts - secretion
Ovary surface - protection

Simple Columnar

Single layer of tall, column-shaped cells...

Click to expand

Structure:

Single layer of tall cells
Elongated nucleus near base
May have microvilli for absorption

Location & Function:

Stomach lining - secretion
Intestinal lining - absorption

Ciliated Columnar

Columnar cells with cilia on surface...

Click to expand

Structure:

Columnar cells with cilia (hair-like projections)
Often contains goblet cells that secrete mucus

Location & Function:

Respiratory tract - cilia move mucus & trapped particles
Oviducts - move egg towards uterus

Stratified Squamous

Multiple layers of flat cells...

Click to expand

Structure:

Multiple layers of cells
Basal cells divide, push older cells upward
Surface cells become flattened

Location & Function:

Skin (epidermis) - protection from abrasion
Mouth, oesophagus - protection

Glandular Epithelium

Specialised for secretion...

Click to expand

Structure:

Cells specialized for producing secretions
Germinal layer at base divides to replace cells

Location & Function:

Salivary glands - secrete saliva
Sweat glands - secrete sweat
Digestive glands - secrete enzymes

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Quick Check: Tissues

Question 1

Which type of epithelial tissue would you expect to find lining the alveoli in the lungs?

A Simple squamous

B Simple cuboidal

C Stratified squamous

D Ciliated columnar

✓ Correct! Simple squamous epithelium is very thin, allowing rapid diffusion of gases in the alveoli.

✗ Think about what property is most important for gas exchange - the tissue needs to be very thin!

Question 2

Ciliated epithelium in the respiratory tract helps to:

A Absorb oxygen into the blood

B Move mucus and trapped particles out of the airways

C Produce red blood cells

D Store fat for energy

✓ Correct! The cilia beat in waves to sweep mucus (with trapped dust and microbes) up and out of the airways.

✗ The cilia are hair-like projections that can move. What might they be moving?

Question 3

Which tissue type would provide the best protection against abrasion?

A Simple squamous

B Simple columnar

C Stratified squamous

D Simple cuboidal

✓ Correct! Stratified (multiple layers) provides the best protection - even if surface cells are worn away, there are more underneath.

✗ For protection against wear, would you want a single thin layer or multiple layers of cells?

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Organs

An organ is a structure made of several different tissues grouped together so that they can work effectively to carry out a particular function.

Major Human Organs

🌱 Plant Organs

Plants also have organs! The leaf is an organ composed of vascular tissue (xylem & phloem), epithelial tissue (epidermis), and mesophyll tissue. Other plant organs include stems and roots.

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The Leaf as an Organ

A leaf contains several different tissues working together for photosynthesis:

Cross-Section of a Leaf

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Organ Systems

An organ system is a group of organs working together to carry out particular functions in the body.

Digestive System

🍽️

Click to reveal organs

Organs: Stomach, pancreas, liver, small intestine, large intestine

Function: Breaking down food & absorbing nutrients

Nervous System

🧠

Click to reveal organs

Organs: Brain, spinal cord, peripheral nerves

Function: Coordination, control, sensory processing

Circulatory System

❤️

Click to reveal organs

Organs: Heart, blood vessels, blood

Function: Transport of substances around body

Respiratory System

🫁

Click to reveal organs

Organs: Lungs, trachea, bronchi, diaphragm

Function: Gas exchange - O₂ in, CO₂ out

✏️

Quick Check: Organs & Systems

Question 1

The heart is made of several different tissues working together. This makes it a(n):

A Cell

B Tissue

C Organ

D Organ system

✓ Correct! An organ is made of different tissues (muscle, connective, nervous, epithelial) working together.

✗ Remember the definition: different tissues working together = organ.

Question 2

Which tissue in a leaf is primarily responsible for photosynthesis?

A Upper epidermis

B Palisade mesophyll

C Xylem

D Lower epidermis

✓ Correct! Palisade mesophyll cells are packed with chloroplasts and positioned near the top of the leaf to absorb maximum light.

✗ Think about which cells would have the most chloroplasts and be best positioned for absorbing light.

Question 3

The stomach, pancreas, and intestines all belong to which organ system?

A Circulatory system

B Respiratory system

C Digestive system

D Nervous system

✓ Correct! These organs all work together to break down food and absorb nutrients.

✗ These organs are all involved in processing food...

✏️

Practice Activities

Test your understanding with these interactive exercises!

Fill in the Blanks

Groups of specialised cells working together are called . Several different tissues working together form an . The type of epithelium that lines the alveoli is epithelium, which allows rapid of gases.

🔢

Order the Hierarchy

Drag to arrange from smallest to largest level of organisation:

? Organ system

? Tissue

? Cell

? Organ

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Key Vocabulary

Click a term, then click its matching definition:

Terms

Epithelial tissue

Organ

Organ system

Differentiation

Definitions

Group of organs working together for major body functions

Tissue that lines surfaces inside and outside the body

Process by which cells become specialised

Structure made of different tissues working together

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Final Assessment

Test everything you've learned! Try to answer without looking back.

Question 1

What is the correct order of organisation from simplest to most complex?

A Tissue → Cell → Organ → Organ system

B Cell → Tissue → Organ → Organ system

C Organ → Tissue → Cell → Organ system

D Cell → Organ → Tissue → Organ system

✓ Correct! Cells → Tissues → Organs → Organ systems

✗ Remember: similar cells form tissues, different tissues form organs, organs form systems.

Question 2

Which type of epithelial tissue would be best adapted for absorbing nutrients in the small intestine?

A Stratified squamous

B Simple columnar with microvilli

C Ciliated columnar

D Simple squamous

✓ Correct! Simple columnar cells with microvilli (finger-like projections) increase surface area for maximum absorption.

✗ For absorption, you need cells with increased surface area. What structures increase surface area?

Question 3

The nervous system includes which of the following?

A Heart, blood vessels, blood

B Stomach, pancreas, intestines

C Brain, spinal cord, peripheral nerves

D Lungs, trachea, diaphragm

✓ Correct! The nervous system coordinates body activities through the brain, spinal cord, and nerves.

✗ Think about which organs are involved in transmitting electrical signals...

Question 4

In a leaf, the function of the spongy mesophyll is to:

A Carry out most photosynthesis

B Transport water to the leaf

C Allow gases to circulate via air spaces

D Prevent water loss

✓ Correct! Spongy mesophyll has air spaces that allow CO₂ to reach cells and O₂ to leave.

✗ The spongy mesophyll has lots of air spaces between cells. What would these be for?

Question 5

Which of the following is NOT one of the four main tissue types in animals?

A Epithelial

B Connective

C Vascular

D Nervous

✓ Correct! The four main animal tissue types are: epithelial, connective, muscle, and nervous. Vascular tissue is found in plants!

✗ The four types are epithelial, connective, muscle, and nervous. One of these options is a plant tissue!

Question 6

Stratified squamous epithelium is found in the skin because it:

A Allows rapid diffusion of substances

B Can secrete mucus for lubrication

C Provides protection against physical abrasion

D Moves substances along its surface

✓ Correct! Multiple layers of cells provide protection - even if surface cells are damaged, there are more underneath.

✗ "Stratified" means multiple layers. Why would multiple layers be useful for skin?

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Key Takeaways

🔬

Cells → Tissues

Similar specialised cells group together to form tissues

🧫

4 Tissue Types

Epithelial, connective, muscle, nervous

🫀

Tissues → Organs

Different tissues work together in organs

🏃

Organs → Systems

Organs work together in organ systems

🛡️

Epithelial Types

Squamous, cuboidal, columnar - shape matches function

🌿

Plant Organs

Leaves, stems, roots contain multiple tissues

Learning Objectives

The Organisation Hierarchy

💡 Key Point

What Do You Already Know?

Question 1

Question 2

Question 3

Types of Tissue

Epithelial Tissue 🛡️

Function:

Where found:

Connective Tissue 🔗

Function:

Examples:

Muscle Tissue 💪

Function:

Types:

Nervous Tissue ⚡

Function:

Components:

Where found:

Types of Epithelial Tissue

Epithelial Cell Shapes

Simple Squamous

Structure:

Location & Function:

Simple Cuboidal

Structure:

Location & Function:

Simple Columnar

Structure:

Location & Function:

Ciliated Columnar

Structure:

Location & Function:

Stratified Squamous

Structure:

Location & Function:

Glandular Epithelium

Structure:

Location & Function:

Quick Check: Tissues

Question 1

Question 2

Question 3

Organs

Major Human Organs

🌱 Plant Organs

The Leaf as an Organ

Cross-Section of a Leaf

Organ Systems

Digestive System

Nervous System

Circulatory System

Respiratory System

Quick Check: Organs & Systems

Question 1

Question 2

Question 3

Practice Activities

Fill in the Blanks

Order the Hierarchy

Key Vocabulary

Terms

Definitions

More Practice Questions

Question 1

Question 2

Question 3

Question 4

Final Assessment

Question 1

Question 2

Question 3

Question 4

Question 5

Question 6

Your Final Score

Key Takeaways

Cells → Tissues