Basic 7 · Science · Earth Science

Transpiration, Cloud Formation and the Importance of the Water Cycle

In this topic you will demonstrate transpiration in plants, explain how clouds form, and describe the importance of the water cycle to living things and the environment.

By the end of these notes you should be able to:

Demonstrate and explain transpiration
Explain how clouds are formed
Describe the importance of the water cycle

What you already know

Stages of the water cycle

Copy everything that has a blue line on its left into your notebook. The other parts are for reading.

Lesson 1

Strand: Cycles
Sub-strand: Earth Science
Indicator: B7.2.1.1.1 – Explain how the water cycle occurs as a repeated pattern in nature

Introduction

Plants drink water through their roots and release much of it into the air through their leaves. This is transpiration, and it is an important part of the water cycle.

1. What Is Transpiration?

Transpiration: The loss of water vapour from the leaves of a plant through tiny pores called stomata.

Water enters the roots from the soil, travels up the stem through tubes called xylem, and reaches the leaves. There, some is used for photosynthesis and most evaporates through the stomata.

2. Demonstrating Transpiration

Choose a leafy branch on a small plant in the sun.
Cover it with a clear plastic bag and tie the bag firmly around the stem.
Leave it for two to three hours.
Observe water droplets on the inside of the bag.

A clear plastic bag tied over leaves with water droplets inside

Figure 1: Transpiration experiment Draw the transpiration experiment and label it.

3. Explaining the Result

The droplets in the bag come from water vapour released by the leaves. It condensed on the cooler plastic. A control experiment, a bag tied over a stick with no leaves, shows no droplets, proving that the water came from the leaves.

4. Factors Affecting Transpiration

Factors

Factor	Effect
heat	more heat, faster transpiration
wind	wind removes vapour, increasing transpiration
humidity	moist air slows transpiration
light	stomata open in light, increasing transpiration
water in the soil	dry soil reduces transpiration

5. Transpiration and the Plant

Transpiration is useful to the plant. The loss of water from the leaves pulls more water and dissolved minerals up from the roots, a process called the transpiration stream. Evaporation from the leaves also cools the plant on hot days, just as sweating cools our bodies. However, if a plant loses water faster than its roots can absorb it, it wilts.

New words

transpiration: Loss of water vapour from leaves.
stomata: Tiny pores on leaves.
xylem: Tubes that carry water up the plant.
control experiment: A comparison setup without the factor being tested.

Summary

Transpiration is the loss of water vapour through stomata in leaves.
A plastic bag tied over leaves collects droplets, showing transpiration.
Heat, wind, light and dry air increase transpiration.

Class activity: Bag Test

Tie a clear plastic bag over a leafy branch and another over a bare stick.
Leave them for three hours in the sun.
Compare and explain the results.

You need: Clear plastic bottle, Warm water, Ice cubes

Exercises

Answer in your exercise book first, then check your answers.

1. Water vapour leaves the plant through…
- A. stomata
- B. roots
- C. flowers
- D. seeds
Show answer
Answer: stomataLeaf pores.
2. Which condition increases transpiration?
- A. hot, windy weather
- B. cold, still weather
- C. darkness
- D. very humid air
Show answer
Answer: hot, windy weatherFaster evaporation.
3. Water travels up the stem in the xylem.
- A. True
- B. False
Show answer
Answer: TrueWater tubes.
4. Tiny pores on leaves are called ______.
Show answer
Answer: stomataOpenings.
5. Describe an experiment to show transpiration.
Show answer
Answer: Tie a clear plastic bag over a leafy branch and observe droplets forming inside after a few hours.Experiment.
6. Why is a bag over a bare stick used in the experiment?
Show answer
Answer: As a control, to show that the water droplets came from the leaves and not from elsewhere.Fair test.

Lesson 2

Strand: Cycles
Sub-strand: Earth Science
Indicator: B7.2.1.1.1 – Explain how the water cycle occurs as a repeated pattern in nature

Introduction

Clouds may look like soft cotton in the sky, but they are made of billions of tiny water droplets or ice crystals floating in the air.

1. Steps in Cloud Formation

The sun heats the land and water, and water evaporates.
Warm, moist air rises because it is lighter than cool air.
As the air rises, it expands and cools.
The cool air cannot hold all its water vapour.
The vapour condenses on tiny particles of dust, salt or smoke.
Millions of droplets gather together to form a cloud.

2. A Cloud in a Bottle

Pour a little warm water into a clear plastic bottle.
Shake it to make the inside moist.
Place a few ice cubes on top of the bottle opening (or in a small bag on top).
Observe a faint mist forming inside the bottle.

The warm water evaporates, and the vapour cools near the ice and condenses into a small cloud.

Large white clouds building up in a blue sky

Figure 2: Clouds Draw the steps in cloud formation as a flowchart.

3. Types of Clouds

Common clouds

Cloud	Appearance	Weather
cumulus	white and puffy	fair weather; can grow into storm clouds
cumulonimbus	very tall and dark	thunderstorms and heavy rain
stratus	flat grey layers	dull weather and drizzle
cirrus	thin and wispy, high in the sky	fair weather

4. Clouds and Weather in Ghana

In the rainy season, cumulonimbus clouds often build up in the afternoon, bringing thunderstorms in the evening. Farmers watch the clouds to know when to plant. In the harmattan season, the sky becomes hazy because of dust rather than clouds.

New words

cloud: A mass of tiny water droplets or ice crystals in the air.
cumulonimbus: A tall, dark storm cloud.
humid: Containing a lot of water vapour.
condensation nuclei: Tiny particles on which vapour condenses.

Summary

Clouds form when warm, moist air rises, cools and its vapour condenses on tiny particles.
A cloud in a bottle models this process.
Types of clouds include cumulus, cumulonimbus, stratus and cirrus, each linked to different weather.

Class activity: Cloud in a Bottle

Make a cloud in a bottle using warm water and ice.
Observe and describe the mist.
Explain how it models real cloud formation.

You need: Clear plastic bottle, Warm water, Ice cubes

Exercises

Answer in your exercise book first, then check your answers.

1. Clouds are made of…
- A. tiny water droplets or ice crystals
- B. smoke only
- C. cotton
- D. dust only
Show answer
Answer: tiny water droplets or ice crystalsCondensed vapour.
2. A tall, dark cloud that brings thunderstorms is…
- A. cumulonimbus
- B. cirrus
- C. stratus
- D. cumulus only
Show answer
Answer: cumulonimbusStorm cloud.
3. Rising air cools as it goes higher.
- A. True
- B. False
Show answer
Answer: TrueIt expands.
4. Air that contains a lot of water vapour is ______.
Show answer
Answer: humidMoist.
5. Explain why rising air forms clouds.
Show answer
Answer: It cools as it rises, so water vapour condenses into droplets that form clouds.Cooling.
6. Why is the sky hazy during the harmattan?
Show answer
Answer: Dust carried by the dry harmattan wind fills the air.Dust, not cloud.

Lesson 3

Strand: Cycles
Sub-strand: Earth Science
Indicator: B7.2.1.1.2 – Describe the importance of the water cycle in nature

Introduction

Every glass of water, every harvest and every hydroelectric power station depends on the water cycle. Without it, life on Earth would not be possible.

1. Importance to Living Things

It provides fresh water for drinking, cooking and washing.
It supplies rain for crops and pastures.
It refills rivers, lakes and underground water used by people and animals.
It purifies water: evaporation leaves salt and impurities behind.
It spreads heat around the Earth, helping control climate.

2. Importance to the Economy

The water cycle and the economy

Area	How the water cycle helps
farming	rain waters crops such as maize, cocoa and rice
electricity	rivers fill the Akosombo, Kpong and Bui dams
fishing	rivers and lakes support fish
water supply	Ghana Water Limited takes water from rivers and reservoirs such as Weija
transport	boats on Lake Volta and rivers

A large reservoir supplying water to a city

Figure 3: Reservoir Draw how rainwater reaches your home tap.

3. Disruptions to the Water Cycle

Human activities can disrupt the water cycle. Deforestation reduces transpiration and rainfall. Galamsey and pollution make river water unsafe. Paving large areas increases run-off and flooding. Climate change can bring droughts in some places and floods in others.

4. Protecting the Water Cycle

We can protect the water cycle by planting trees, protecting river banks and wetlands, avoiding pollution, harvesting rainwater in tanks, and using water carefully. Communities that protect their forests and rivers enjoy more reliable rainfall and water supply.

New words

reservoir: A large natural or artificial lake used to store water.
drought: A long period with little or no rain.
wetland: Land that is often covered with water, such as a marsh.
rainwater harvesting: Collecting and storing rainwater for use.

Summary

The water cycle provides fresh water, rain for crops and water for rivers and lakes.
It supports farming, electricity, fishing, water supply and transport.
Deforestation and pollution disrupt it, while tree planting and careful water use protect it.

Class activity: Water Cycle Importance Debate

List five ways the water cycle benefits your community.
Identify one human activity that disrupts it locally.
Propose and present a solution.

You need: Printed water-cycle diagram, Printed photographs of a Ghanaian farm, Reservoir, Printed water-cycle stage cards

Exercises

Answer in your exercise book first, then check your answers.

1. Which is a benefit of the water cycle?
- A. rain for crops
- B. more litter
- C. more noise
- D. air pollution
Show answer
Answer: rain for cropsFarming.
2. A long period without rain is a…
- A. drought
- B. flood
- C. reservoir
- D. wetland
Show answer
Answer: droughtDry period.
3. Deforestation can reduce rainfall.
- A. True
- B. False
Show answer
Answer: TrueLess transpiration.
4. Collecting and storing rainwater is rainwater ______.
Show answer
Answer: harvestingWater saving.
5. State three ways the water cycle supports Ghana's economy.
Show answer
Answer: Farming, electricity from dams, fishing (or water supply, transport).Any three.
6. Explain how evaporation helps purify water.
Show answer
Answer: When water evaporates, salts and impurities are left behind, so the water vapour and rain are fresh.Natural purification.

Homework

Draw and label a full water cycle diagram showing transpiration and cloud formation.