Module 17.1: Effects of Heat

Meaning of Heat

Heat is a form of energy that is transferred from a hotter object to a colder object. Heat energy causes changes in the physical state, size, temperature, and sometimes the chemical nature of substances.

Heat is not the same as temperature.

• Temperature tells us how hot or cold something is.

• Heat refers to the energy that causes the temperature to rise.

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Effects of Heat on Substances

Heat has several effects on substances. These effects can be grouped as follows:

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1. Heat Causes Expansion of Substances

When heat is applied to a substance, the particles gain energy and move faster, causing the substance to expand.

• Solids expand slightly when heated

• Liquids expand more than solids

• Gases expand the most

Examples

• Railway tracks are laid with gaps to allow expansion when heated.

• Electric wires sag more during hot afternoons.

• Hot air balloons rise because heated air expands and becomes lighter.

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2. Heat Causes Change of State

Heat can change a substance from one state to another.

Change	Example
Solid → Liquid (Melting)	Ice turning into water
Liquid → Gas (Evaporation/Boiling)	Water boiling into steam
Gas → Liquid (Condensation)	Steam turning into water
Liquid → Solid (Freezing)	Water turning into ice

Explanation
When heat is added, particles move faster and break free from fixed positions. When heat is removed, particles slow down and come closer together.

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3. Heat Raises the Temperature of Substances

When heat is applied to a substance, its temperature increases.

Examples

• Water becomes hot when placed on fire.

• Food cooks faster at higher temperatures.

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4. Heat Can Cause Chemical Changes

In some cases, heat leads to permanent chemical changes.

Examples

• Burning of wood

• Baking of bread

• Cooking of food

These changes cannot be reversed.

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5. Heat Affects Living Organisms

Heat plays an important role in life processes.

Examples

• Plants need warmth to grow well.

• Extreme heat can cause dehydration in humans.

• Cold temperatures can slow body activities.

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Summary of Effects of Heat

• Causes expansion

• Changes states of matter

• Increases temperature

• Causes chemical changes

• Affects living things

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Module 17.2: Modes of Heat Transfer

Heat energy can move from one place to another in three main ways:

1. Conduction

2. Convection

3. Radiation

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1. Conduction

Definition
Conduction is the transfer of heat through a substance without the movement of the substance itself. It usually occurs in solids.

Explanation
When one end of a solid is heated, the particles vibrate faster and pass energy to neighboring particles.

Good Conductors

• Metals (copper, iron, aluminium)

Poor Conductors (Insulators)

• Wood

• Plastic

• Rubber

Examples

• A metal spoon becomes hot when placed in hot soup.

• Cooking pots are made of metal.

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2. Convection

Definition
Convection is the transfer of heat in liquids and gases through the movement of the fluid itself.

Explanation

• Hot fluid becomes less dense and rises.

• Cold fluid becomes denser and sinks.
  This movement sets up convection currents.

Examples

• Boiling water in a pot

• Sea breeze and land breeze

• Warm air rising in a room

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3. Radiation

Definition
Radiation is the transfer of heat without any medium. Heat travels in the form of waves.

Explanation
Radiation does not need solids, liquids, or gases.

Examples

• Heat from the sun reaching the earth

• Feeling warmth from fire without touching it

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Comparison of Modes of Heat Transfer

Mode	Medium Needed	Example
Conduction	Solid	Metal spoon
Convection	Liquid/Gas	Boiling water
Radiation	No medium	Heat from sun

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UNIT 18: PHYSICAL AND CHEMICAL CHANGE

Module 18.1: Meaning of Physical and Chemical Changes

Physical Change

Definition
A physical change is a change that affects only the physical appearance of a substance without forming a new substance.

Characteristics

• No new substance is formed

• Change is usually reversible

• Chemical composition remains the same

Examples

• Melting of ice

• Cutting paper

• Dissolving sugar in water

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Chemical Change

Definition
A chemical change is a change in which a new substance is formed.

Characteristics

• New substance is formed

• Change is irreversible

• Energy is absorbed or released

Examples

• Burning wood

• Rusting of iron

• Cooking food

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Module 18.2: Examples of Physical and Chemical Changes

Examples of Physical Changes

• Freezing water into ice

• Breaking a bottle

• Stretching a rubber band

These changes can often be reversed.

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Examples of Chemical Changes

• Burning charcoal

• Baking bread

• Milk turning sour

These changes cannot be reversed.

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Differences Between Physical and Chemical Changes

Physical Change	Chemical Change
No new substance	New substance formed
Reversible	Irreversible
Change in form	Change in composition

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UNIT 19: Introduction to Ecosystem

An ecosystem is a community of living organisms (plants and animals) interacting with one another and with their non-living environment such as air, water, soil, and sunlight.
In every ecosystem, energy flows from one organism to another, mainly through feeding relationships.

Examples of ecosystems include:

• Forest ecosystem

• Grassland ecosystem

• Pond ecosystem

• Farm ecosystem

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MODULE 19.1: FOOD CHAIN AND FOOD WEB

Meaning of Food Chain

A food chain is a simple feeding relationship that shows how energy passes from one living organism to another in an ecosystem.

In a food chain:

• Each organism feeds on the one before it

• Energy flows in one direction only

Example of a Food Chain

Grass → Goat → Human

This means:

• Grass produces food

• Goat eats grass

• Human eats goat

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Components of a Food Chain

1. Producers

Producers are green plants that make their own food using sunlight through photosynthesis.

Examples:

• Grass

• Maize

• Algae

Producers form the first level of the food chain.

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2. Consumers

Consumers are organisms that cannot make their own food and must feed on plants or other animals.

Types of consumers include:

a. Primary consumers

• Feed directly on producers

• Usually herbivores
  Examples: Goat, Cow, Grasshopper

b. Secondary consumers

• Feed on primary consumers

• Usually carnivores or omnivores
  Examples: Snake, Frog

c. Tertiary consumers

• Feed on secondary consumers
  Examples: Hawk, Eagle

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3. Decomposers

Decomposers are organisms that break down dead plants and animals into simpler substances and return nutrients to the soil.

Examples:

• Bacteria

• Fungi

Decomposers help to maintain soil fertility and keep the environment clean.

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Meaning of Food Web

A food web is a complex network of interconnected food chains in an ecosystem.

Unlike a food chain, a food web shows that:

• One organism can have more than one source of food

• Energy flows through many different paths

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Importance of Food Webs

• Shows real feeding relationships in nature

• Makes ecosystems more stable

• Prevents total collapse if one organism dies

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Differences Between Food Chain and Food Web

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Importance of Food Chains and Food Webs

• Help in understanding energy flow

• Maintain balance in the ecosystem

• Support survival of organisms

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MODULE 19.2: ENERGY TRANSFER IN THE ECOSYSTEM

Meaning of Energy Transfer

Energy transfer refers to the movement of energy from one organism to another through feeding relationships in an ecosystem.

The sun is the main source of energy in all ecosystems.

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How Energy Enters the Ecosystem

• Energy from the sun is trapped by green plants

• Plants convert sunlight into food energy through photosynthesis

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Flow of Energy in an Ecosystem

Energy flows in this order:
Sun → Producer → Consumer → Decomposer

Energy:

• Moves in one direction only

• Is lost as heat at every stage

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Energy Loss in the Ecosystem

Not all energy is passed on because:

• Some energy is used for movement

• Some is lost as heat

• Some is used for growth and repair

This is why:

• There are fewer organisms at higher levels of a food chain

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Importance of Energy Transfer

• Supports growth and survival of organisms

• Maintains balance in nature

• Explains population size in ecosystems

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GTLE EXAM TIPS

• Be able to define key terms

• Use examples

• Understand cause-and-effect

• Interpret diagrams

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