Chapter 7: Living Things and Air - Your Study Notes!

Hey everyone! Ever thought about the air you breathe? It seems like it's just empty space, but it's actually full of amazing stuff that keeps us, and all living things, alive. In these notes, we're going to become air detectives! We'll discover what's in the air, how plants and animals use it in incredible ways, and why it's so important to keep our air clean. Let's get started!


7.1 What's in the Air?

Air isn't just one thing; it's a mixture of different gases. Think of it like a giant, invisible pizza with different toppings. Some toppings have a huge slice, and others are just tiny sprinkles!

The Main Ingredients of Air

The air around us is mostly made of:

  • Nitrogen (N₂): This is the biggest slice of the pizza, making up about 78% of the air. Most living things can't use it directly from the air, but it's still very important.
  • Oxygen (O₂): This is the second biggest slice, about 21%. This is the gas we need to breathe to live! It's essential for getting energy from our food.
  • Other Gases: The last little slice (about 1%) includes gases like Argon, and a very important one for plants: Carbon Dioxide (CO₂). There is also a tiny amount of water vapour.

Meet the Gases: Properties and Tests

How do we know these gases are there if we can't see them? Scientists have clever ways to test for them! Don't worry, these tests are simple to understand.

Oxygen (O₂)
  • Properties: It's a gas that helps things burn. Without oxygen, you can't light a fire.
  • The Test: We use a 'glowing splint'. A splint is just a small stick of wood.
    1. Light a splint and then gently blow it out so it's still glowing red, but not on fire.
    2. Put the glowing splint into a container of the gas you are testing.
    3. If it's oxygen, the splint will relight and burst back into flame!
  • Real-world examples: We breathe it, it's used in hospitals to help sick people breathe, and welders use it to create very hot flames.
Carbon Dioxide (CO₂)
  • Properties: It does NOT help things burn. It's the gas we breathe out.
  • The Test: We bubble the gas through a special liquid called limewater (calcium hydroxide solution).
    1. Start with clear, colourless limewater.
    2. Bubble the gas through it.
    3. If it's carbon dioxide, the limewater will turn from clear to a milky or cloudy white.
  • Real-world examples: Plants use it to make food, it makes fizzy drinks bubbly, and it's used in some fire extinguishers because it puts out flames.
Nitrogen (N₂)
  • Properties: It's a very unreactive gas. It doesn't help things burn, and it doesn't affect limewater.
  • Real-world examples: It's used to keep food fresh in packets (like crisps) because it stops the food from reacting with oxygen and going stale.
Quick Review Box: Gas Tests Made Easy!

Oxygen (O₂): Glowing splint relights.
Carbon Dioxide (CO₂): Limewater turns milky/cloudy.

Key Takeaway

Air is a mixture of gases, mainly nitrogen and oxygen. We can identify oxygen and carbon dioxide using simple chemical tests.


7.2 The Amazing Food Factory: Photosynthesis

Have you ever wondered how plants eat? They don't have mouths! Instead, they perform a magical process called photosynthesis to make their own food. They are like little green chefs!

The Recipe for Photosynthesis

Just like a chef needs ingredients, a plant needs a few things from its environment to make food.

  • Ingredients: Carbon Dioxide (from the air) + Water (from the soil).
  • Energy Source: Sunlight (captured by a green pigment called chlorophyll).
  • What they make: Glucose (a type of sugar, which is their food) + Oxygen (which is released into the air).

We can write this as a simple word equation:

Carbon Dioxide + Water ---(in the presence of Sunlight & Chlorophyll)---> Glucose + Oxygen

During this process, plants change light energy from the sun into chemical energy stored in the glucose. The plant can use this food for energy straight away, or store it as starch to use later.

Did you know?

Chlorophyll is what makes leaves look green! It's like the solar panel of the plant, absorbing all that sunlight.

Key Takeaway

Photosynthesis is the process where plants use carbon dioxide, water, and sunlight to create their own food (glucose) and release oxygen. It's essential for life on Earth!


7.3 Getting Energy: Respiration

Okay, so plants make food. But how do they (and we!) actually get the energy *out* of that food? The answer is respiration. This process happens in the cells of ALL living things, including plants and animals.

Think of it like this: eating food is like putting petrol in a car, but respiration is like turning the engine on to actually use the petrol and make the car move. Respiration unlocks the energy stored in food.

The Respiration Equation

Respiration is basically the opposite of photosynthesis!

Glucose + Oxygen ---> Carbon Dioxide + Water + ENERGY

This released energy is what we use for everything: moving, thinking, keeping warm, and growing.

Photosynthesis vs. Respiration: A Quick Comparison

This can be a bit tricky, so let's break it down. It's a common point of confusion!

  • Who does it?
    • Photosynthesis: Only plants (and some other simple organisms).
    • Respiration: ALL living things (plants AND animals).
  • When does it happen?
    • Photosynthesis: Only when there is light (during the day).
    • Respiration: All the time, 24/7!
  • What's the point?
    • Photosynthesis: To store energy by making food.
    • Respiration: To release energy from food.
Key Takeaway

Respiration is the process used by all living cells to release energy from glucose (food). It uses oxygen and produces carbon dioxide and water.


7.4 The Big Breath: Gas Exchange

Gas exchange is simply the swapping of gases between an organism and its environment. For us, it's breathing in oxygen and breathing out carbon dioxide.

Gas Exchange in Plants

Plants "breathe" through tiny pores on their leaves. During the day, they do a lot of photosynthesis, so they take in more carbon dioxide than they release. At night, with no light, they only respire, so they take in oxygen and release carbon dioxide, just like us!

Gas Exchange in Humans

Our breathing system is perfectly designed for gas exchange.

The path of air: Nose/Mouth -> Trachea (windpipe) -> Lungs -> Air Sacs

The real magic happens in the lungs, in millions of tiny bubbles called air sacs (or alveoli). Here, oxygen from the air we breathe in passes into our blood, and carbon dioxide from our blood passes out into the air, ready to be exhaled.

Inhale vs. Exhale - What's the difference?

The air we breathe in is different from the air we breathe out.

  • Inhaled Air: More oxygen, less carbon dioxide, less water vapour.
  • Exhaled Air: Less oxygen, more carbon dioxide, more water vapour, and it's warmer.

The Dangers of Smoking

Smoking is extremely harmful to the breathing system. Cigarette smoke contains tar, a sticky black substance that clogs up the air sacs. This makes it much harder for oxygen to get into the blood. Smoking can cause serious health problems like lung cancer and heart diseases.

Key Takeaway

Gas exchange is how living things get the gases they need and get rid of waste gases. In humans, this happens in the air sacs of the lungs. Smoking severely damages this process.


7.5 Keeping the Balance

Photosynthesis and respiration work together in a beautiful, natural cycle to keep the amounts of oxygen and carbon dioxide in the atmosphere balanced.

  • Photosynthesis removes carbon dioxide from the air and adds oxygen.
  • Respiration removes oxygen from the air and adds carbon dioxide.

Humans Tipping the Scales

Unfortunately, some human activities are disrupting this balance. We are adding too much carbon dioxide to the atmosphere by:

  • Burning fossil fuels (like coal, oil, and gas) for electricity and transport.
  • Deforestation (cutting down large forests). Fewer trees mean less photosynthesis to remove CO₂.

The Greenhouse Effect

Carbon dioxide is a greenhouse gas. This means it traps heat in the atmosphere. Think of it like a blanket around the Earth. A little bit of this is good; it keeps our planet warm enough for life. But by adding too much CO₂, we are making the blanket thicker, trapping too much heat. This leads to an increase in the Earth's temperature, known as global warming, which affects the environment and climate.

Key Takeaway

There's a natural balance of oxygen and carbon dioxide in nature. Human activities, especially burning fossil fuels, are increasing carbon dioxide levels, which enhances the greenhouse effect and warms the planet.


7.6 Air Quality and Our Health

The quality of the air we breathe has a direct effect on our health. Clean air is essential!

What are Air Pollutants?

Air pollutants are harmful substances in the air. Common examples include smoke, dust, and harmful gases from vehicle exhausts and factories. These pollutants can make it difficult to breathe and cause health problems like asthma.

Checking the Air - The AQHI

The Air Quality Health Index (AQHI) is a scale that tells us how polluted the air is right now. It's like a weather report for the air!

  • It is reported on a scale of 1 to 10+ and is grouped into five health risk categories: low, moderate, high, very high and serious.
  • It gives health advice. For example, when the AQHI is very high, people with heart or breathing problems are advised to stay indoors and avoid heavy exercise.
Key Takeaway

Air pollutants can harm our health. The AQHI helps us understand the level of air pollution and gives us advice on how to protect ourselves.


Great job making it through the notes! You've learned so much about the invisible but vital air all around us. Keep being curious!