Module 2: Organisation of Living Things

Unicellular Organisms (definition and examples)

• Made of a single cell that performs all life processes (e.g. Amoeba, Paramecium, Bacteria).

Unicellular organism - nutrition

• Use phagocytosis (engulfing food), cilia to sweep food in (e.g. Paramecium), or absorb nutrients via diffusion/active transport.

Unicellular organism - gas exchange

• Occurs through the cell membrane by diffusion.

Unicellular organism - waste removal

• Remove wastes (like CO₂, ammonia) by diffusion.

• Use contractile vacuoles to expel excess water.
  

What organelles do unicellular organisms rely on (ie cell membrane)

• Cell membrane (transport), food vacuole, contractile vacuole, mitochondria (energy), lysosomes (digestion).

Multicellular Organisms (definition and examples)

• Made of many specialised cells that form tissues, organs, and systems.

• (e.g. humans, dogs, birds, flowers, mushrooms)

What do cells in a multicellular organism do (functions)

• Cells have specific functions (e.g. nerve, blood, muscle) and depend on each other.

Nutrition and waste removal of multicellular organisms

Nutrition and waste removal done by organ systems (e.g. digestive, circulatory, excretory systems).

How do multicellular organisms move substances?

• Require transport systems (e.g. blood vessels in animals, xylem/phloem in plants) to move substances.

Colonial organisms (definition and examples)

• Made of many unicellular organisms living attached together, often in a colony.
  
  Examples:

  • Algae that live in groups or colonies

  • Bacteria that form clusters or chains

  • Small animals made of connected individuals working together

Why do cells work together in colonial organisms?

• Each cell can survive on its own, but they may work together for movement or reproduction.

Are colonial organisms multicellular? Do they have cell specialisation?

• Not truly multicellular — no cell specialisation like in multicellular organisms.

Do colonial organisms handle its own jobs? Which ones?

• May share resources but each individual cell handles its own nutrition, gas exchange, and waste removal.

What is cell specialisation

• Cells adapt their structure to suit their function, enhancing efficiency.
  

Examples of cell specialisation - muscle cells

• Muscle Cells: Long and thin with many mitochondria to generate energy for contraction.

Examples of cell specialisation - red blood cells

Red Blood Cells: Biconcave shape for maximum surface area for gas exchange, no nucleus to maximize space for hemoglobin.

Examples of cell specialisation - nerve cells

Nerve Cells: Long, thin, and branched to transmit electrical signals over long distances.

Examples of cell specialisation - xylem cells (in plants)

• Xylem Cells (in plants): Hollow tubes that transport water and minerals; lignin in cell walls for strength.

Relationship Between Cell Structure and Function (designed with specific organelles and structures to help them perform their designated tasks efficiently) - muscle cells

• Example 1: Muscle Cells contain more mitochondria for energy during contraction.

Relationship Between Cell Structure and Function (designed with specific organelles and structures to help them perform their designated tasks efficiently) - red blood cells

Example 2: Red Blood Cells are adapted for oxygen transport by being flexible, with a large surface area, and lacking a nucleus.

Relationship Between Cell Structure and Function (designed with specific organelles and structures to help them perform their designated tasks efficiently) - leaf cells

• Example 3: Leaf Cells in plants are packed with chloroplasts to maximize light absorption for photosynthesis.

How are organs formed, and why do they work together?

• Specialised cells form tissues, which then form organs. Organs work together to perform system-wide functions.

How are organs formed, and why do they work together? - example - muscle cells

• Muscle cells form muscle tissue, which forms muscles that help in movement.

How are organs formed, and why do they work together? - example - nervous tissue

• Nervous tissue forms the brain and nerves, which control and coordinate actions within the body.

What are cells

• Cells are the basic units of life.
  
  

What are tissues

Tissues are groups of similar cells working together (e.g. muscle tissue).

What are organs

• Organs are made of different tissues working together (e.g. the heart).
  
  

What are systems

• Systems are groups of organs performing major body functions (e.g. circulatory system).
  
  

What are multicellular organisms

• Multicellular organisms are made of many specialised cells organised into tissues, organs, and systems, allowing complex functions and survival.

What are stem cells

Stem cells are special cells that haven’t decided what job to do yet. They can:

1. Divide and make more stem cells, and

2. Change into different types of specialised cells (like muscle, nerve, or blood cells)

What is cell differentiation (+ stem cell becoming something example)

• Cells become specialised for a specific function.
  

• This happens during development from stem cells.
  

• Example: A stem cell → becomes a red blood cell to carry oxygen.

Purpose of cell specialisation (+example of nerve cell)

• Specialised cells have structures suited to their job.
  

• E.g. nerve cells have long extensions to carry messages.

Specialised cells form tissues with specific roles. What are built from these tissues, and what are their purpose?

• Specialised cells form tissues with specific roles.
  

• Organs are built from these tissues for complex tasks.

What is the purpose of organ systems? (+examples w/ purpose)

• Organ systems work together to keep the body functioning.

Examples

• Circulatory system – moves blood, oxygen, and nutrients (includes heart, blood vessels)

• Respiratory system – helps you breathe (includes lungs, trachea)

• Digestive system – breaks down food (includes stomach, intestines)

• Nervous system – sends messages (includes brain, spinal cord, nerves)

• Muscular system – helps you move (includes muscles)

• Skeletal system – supports your body (includes bones)

• Excretory/urinary system – removes waste (includes kidneys, bladder)

• Reproductive system – involved in making babies (includes ovaries, testes)

justify the hierarchical structural organisation of organelles, cells, tissues, organs, systems and organisms - reason 1: efficiency (+example of cells specialising)

• Each level has a specific role, making the whole system work more efficiently.
  

• Example: Cells specialise, tissues group similar cells, organs combine tissues for complex functions.

justify the hierarchical structural organisation of organelles, cells, tissues, organs, systems and organisms - reason 2: coordination (+example of the nervous system)

• Hierarchical structure allows for clear organisation and better coordination.
  

• Systems (e.g. nervous system) coordinate organs to respond to changes in the environment.

justify the hierarchical structural organisation of organelles, cells, tissues, organs, systems and organisms - reason 3: complexity made manageable

• Breaking life down into levels helps manage complex processes like digestion or movement.
  

• Each level builds on the one before it, creating order and control.

justify the hierarchical structural organisation of organelles, cells, tissues, organs, systems and organisms - reason 4: Specialisation and Division of Labour (+example of white blood cells vs red blood cells)

• Different cells/tissues/organs perform unique tasks, which increases productivity.
  

• E.g. red blood cells carry oxygen, while white blood cells fight infection.

justify the hierarchical structural organisation of organelles, cells, tissues, organs, systems and organisms - reason 5: Survival and Adaptability

• The structure supports the organism's ability to survive, grow, and respond.
  

• Systems work together (like respiratory and circulatory) to meet the needs of the organism.

Role of organelles

• Role: Small structures inside cells that carry out specific tasks (e.g., mitochondria for energy, nucleus for storing DNA).
  

Justification of organelles

• Justification: Organelles allow cells to perform complex tasks efficiently within a small space.

Role of cells

• Role: Basic unit of life, carrying out all functions needed to stay alive (e.g., metabolism, growth).
  
  

Justification of cells

• Justification: Cells are the smallest functional unit, where all processes for life happen.
  
  

Role of tissues

Role: Groups of similar cells working together for a common function (e.g., muscle tissue for movement).

Justification of tissues

Justification: Tissues help perform more complex tasks that individual cells can't do alone.

Role of organs

• Role: Made of different tissues working together to perform specific functions (e.g., heart pumps blood).

Justification of organs

• Justification: Organs combine tissues to carry out specialized tasks that are vital for the organism.
  
  

Role of organ systems

Role: Groups of organs that work together to perform broad functions (e.g., digestive system processes food).

Justification of organ systems

• Justification: Organ systems allow for complex, coordinated functions necessary for survival.

Role of organisms

• Role: Complete living beings made up of many organ systems (e.g., humans, plants).

Justification of organisms

• Justification: Organisms are the highest level of organization, with all systems working together to keep the organism alive.

What are autotrophs

Autotrophs are living things that make their own food.

How do autotrophs such as green plants produce their own food?

Autotrophs, such as green plants, produce their own food through photosynthesis.

Xylem

• Xylem
  Carries water and minerals from the roots to the leaves. It is made of hollow, tube-like cells and also provides structural support.
  
  

Phloem

Phloem
Transports sugars (produced in photosynthesis) from the leaves to other parts of the plant. Phloem is made of living cells.

Epidermis

• Epidermis
  The outer layer of cells on leaves, stems, and roots. It protects the plant and helps reduce water loss. In leaves, it often contains stomata for gas exchange.
  
  

Root Hair

• Root Hair
  Tiny extensions of root cells that increase the surface area for absorbing water and nutrients from the soil.
  
  

Stem

• Stem
  Supports the plant and contains vascular tissue (xylem and phloem) that transports water, nutrients, and sugars between roots and leaves.
  
  

Leaf

Leaf
The main site of photosynthesis. Contains chloroplasts in the mesophyll and is adapted for gas exchange and light absorption.

Stomata function

• Function: Stomata are pores found mainly on the underside of leaves. They control gas exchange (CO2 in, O2 out) and water vapor loss (transpiration).
  
  

Somata structure

• Structure: Surrounded by two guard cells that regulate the opening and closing of the pore, allowing the plant to control water loss and maintain homeostasis.
  
  

Waxy Cuticle function

• Function: The waxy cuticle is a waterproof layer covering the outer surface of the leaf, primarily made of cutin.
  
  

Waxy Cuticle structure

• Structure: It helps reduce water loss and provides protection from pathogens and environmental stress.
  
  

Upper Epidermis function

• Function: The upper epidermis is the outer layer of cells that provides protection and helps with preventing water loss.
  
  

Upper Epidermis structure

• Structure: The cells are usually thin-walled and lack chloroplasts. The surface may be covered by the waxy cuticle.
  
  

Lower Epidermis function

• Function: Like the upper epidermis, the lower epidermis provides protection, but it also contains stomata for gas exchange.
  
  

Lower Epidermis structure

Structure: The lower epidermis often has more stomata compared to the upper side of the leaf.

Palisade mesophyll cells function

• Function: These cells are the main site of photosynthesis due to their high chloroplast content.
  
  

Palisade mesophyll cells structure

• Structure: Column-like cells arranged tightly beneath the upper epidermis. The cells are elongated and rich in chloroplasts, maximizing light absorption for photosynthesis.
  
  

Spongy Mesophyll Cells function

• Function: They help with gas exchange and contain fewer chloroplasts than palisade cells.
  
  

Spongy Mesophyll Cells structure

• Structure: Loosely packed cells with large intercellular spaces that allow gases (like CO2 and O2) to diffuse throughout the leaf.
  
  

Vascular bundle function

• Function: The vascular bundle contains both xylem and phloem, responsible for transporting water, nutrients, and sugars throughout the plant.
  
  

Vascular bundle structure

• Structure: Xylem vessels (for water transport) are generally located towards the inside of the bundle, while phloem (for sugar transport) is located towards the outside.

Alveoli

• Alveoli are tiny air sacs found at the end of bronchioles in mammalian lungs.
  
  

Purpose of Alveoli

• They are the site of gas exchange, where oxygen diffuses into the blood and carbon dioxide diffuses out.
  
  

Key features of alveoli that assist in efficient gas exchange

• Large surface area due to millions of alveoli.
  

• Thin walls (one-cell thick) to allow quick diffusion.
  

• Moist lining to dissolve gases for easier diffusion.
  

• Rich capillary network to maintain a concentration gradient.

Respiratory system of mammals (e.g. humans, dogs)

• Organs: nose/mouth → trachea → bronchi → bronchioles → alveoli
  
  

Use lungs for breathing; rely on muscle contractions (diaphragm and intercostal muscles) to ventilate.

Respiratory system of fish

• Use gills for gas exchange.
  
  

• Water flows over gill filaments where counter-current exchange maximises oxygen absorption.
  
  

• Gills have a large surface area and rich blood supply.

Respiratory system of insects

• Use a tracheal system with spiracles (openings) on the body surface.
  
  

• Air travels through tracheae and tracheoles directly to tissues.
  
  

• No blood is involved in gas transport.

Respiratory system of amphibians (e.g. frogs)

• Use lungs, skin, and lining of the mouth (buccal cavity).
  
  

• Skin must remain moist to allow gas diffusion.
  
  

• Capable of cutaneous respiration (gas exchange through skin).

Mammals

Group	Definition	Examples
Mammals	Warm-blooded animals with hair/fur; feed young with milk	Humans, dogs, whales

Amphibians

Group	Definition	Examples
Amphibians	Cold-blooded; live in water as young and on land as adults	Frogs, salamanders

Reptiles

Group	Definition	Examples
Reptiles	Cold-blooded; dry, scaly skin; lay eggs on land	Snakes, lizards, turtles

What is photosynthesis

• Photosynthesis occurs in chloroplasts, mainly in the palisade mesophyll of leaves.
  
  

• It produces glucose (a sugar) and oxygen using:
  
  

  • Carbon dioxide (from air)
    
    

  • Water (from roots)
    
    

  • Light energy (from the sun)

Word equation for photosynthesis

Word equation:
Carbon dioxide + water → glucose + oxygen (in the presence of sunlight and chlorophyll)

What is the main product of photosynthesis, and what is its purpose?

• Glucose is the main product of photosynthesis.
  

• It can be:

  • Used immediately for cellular respiration to make energy (ATP)

  • Converted to starch for storage

  • Used to make cellulose (for cell walls)

  • Transported to other parts of the plant for growth

What is glucose transported as, and what is the movement called? Where does the flow go?

• Glucose is transported as sucrose (a soluble sugar) via the phloem.
  
  

• This movement is called translocation.
  
  

• Direction of flow: from source (leaves) to sink (roots, fruits, growing parts).

What are the systems that transport sugars, and water and minerals?

• Phloem: Moves sugars (products of photosynthesis)

  • Two-way movement

  • Relies on active transport and pressure flow
    

• Xylem: Moves water and minerals (inputs for photosynthesis)

  • One-way movement (from roots to leaves)

Outline alveoli in mammals

• Tiny air sacs found in clusters at the ends of bronchioles in the lungs.
  

• One cell thick (thin walls made of squamous epithelial cells).
  

• Surrounded by capillaries (network of tiny blood vessels).
  

• Large surface area and moist inner surface.
  

Function of alveoli

• Site of gas exchange in mammals (oxygen in, carbon dioxide out).
  
  

• Oxygen diffuses from alveoli → capillaries, into red blood cells.
  
  

• Carbon dioxide diffuses from capillaries → alveoli to be exhaled.
  

Why is alveoli efficient

• Efficient due to:
  

  • Thin walls → short diffusion distance
    

  • Moist surface → gases dissolve easily
    

  • Large surface area → more diffusion
    

  • Rich blood supply → maintains concentration gradient
    

Waxy cuticle (leaf structure in plants)

• Waxy cuticle: Waterproof layer on top surface to reduce water loss.

Upper epidermis (leaf structure in plants)

• Upper epidermis: Transparent to let light through.

Palisade mesophyll (leaf structure in plants)

• Palisade mesophyll: Tightly packed, rich in chloroplasts, where most photosynthesis happens.

Spongy mesophyll (leaf structure in plants)

• Spongy mesophyll: Loosely packed cells with air spaces → gas exchange area.
  

Stomata (leaf structure in plants)

• Stomata: Tiny pores (mainly on lower surface) surrounded by guard cells; open/close to control gas exchange and water loss.

What do the vascular bundles contain?

• Xylem → transports water into the leaf.
  

• Phloem → transports sugars out of the leaf.

How does gas exchange occur in leaves? Where does it occur?

• CO₂ in, O₂ out through stomata.
  

• Occurs mostly in the spongy mesophyll.
  

How does transpiration occur in leaves?

• Transpiration: Water evaporates from stomata → helps pull more water up via xylem.

Parts of the respiratory system - mammals

• Nose/Mouth
  → Air enters the body
  Trachea
  → Tube that carries air to the lungs
  Bronchi
  → Two main branches leading to each lung
  Bronchioles
  → Smaller air tubes inside the lungs
  Alveoli
  → Tiny air sacs where oxygen enters the blood and carbon dioxide leaves