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Unlock This CoursePhotosynthesis is one of the most important processes on Earth. Without it, there would be no food, no oxygen and no life as we know it! Every time you take a breath, eat an apple, or enjoy the shade under a tree, you're benefiting from photosynthesis. It's the amazing process that allows plants to make their own food using sunlight, water and carbon dioxide from the air.
Key Definitions:
Unlike animals, plants can't hunt for food or pop to the shops! They must make their own food through photosynthesis. This process converts light energy into chemical energy stored in glucose, which plants use to grow, repair themselves and reproduce.
A word equation shows us what goes into a chemical reaction and what comes out, using everyday language instead of chemical symbols. It's like a recipe that tells us the ingredients and what we'll make with them.
The word equation for photosynthesis is:
Carbon dioxide + Water → Glucose + Oxygen
(in the presence of light and chlorophyll)
Carbon dioxide: Plants absorb this gas from the air through tiny pores called stomata in their leaves.
Water: Plants absorb water through their roots from the soil.
Light energy: Usually from the sun, captured by chlorophyll in the leaves.
Chlorophyll: The green pigment that makes photosynthesis possible.
Glucose: The sugar that plants use for energy and to build other substances.
Oxygen: Released into the air as a waste product - lucky for us!
The symbol equation uses chemical formulas instead of words. It's more precise and shows exactly how many atoms of each element are involved. Don't worry if it looks scary at first - we'll break it down step by step!
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
(in the presence of light and chlorophyll)
Each chemical formula tells us which elements are present and how many atoms of each element there are:
The numbers in front of the formulas (like the 6 in 6CO₂) tell us how many molecules we need. We need 6 molecules of carbon dioxide and 6 molecules of water to make 1 molecule of glucose and 6 molecules of oxygen gas. This is because atoms can't be created or destroyed in chemical reactions - they just get rearranged!
Chemical equations must be balanced, meaning the same number of each type of atom appears on both sides. Let's count:
Left side: 6 carbon, 18 oxygen, 12 hydrogen
Right side: 6 carbon, 18 oxygen, 12 hydrogen
Perfect balance! ⚖
Photosynthesis isn't just something that happens in textbooks - it's occurring all around us, every second of every day. Let's explore some fascinating examples of how this process impacts our world.
The Amazon rainforest produces about 20% of the world's oxygen through photosynthesis. With over 400 billion trees, it processes massive amounts of CO₂ daily. A single large tree can produce enough oxygen for two people per day! This is why the Amazon is often called "the lungs of the Earth."
While the basic equation remains the same, different plants have adapted photosynthesis to suit their environments:
Roses, daisies and most garden plants do photosynthesis during the day when sunlight is available. They open their stomata to take in CO₂ and release O₂.
Cacti and succulents have adapted to conserve water. They open their stomata at night to collect CO₂, storing it until daylight when they can use the sun's energy for photosynthesis.
Pond weed and water lilies get their CO₂ from dissolved carbon dioxide in water. You can actually see oxygen bubbles forming on their leaves during photosynthesis!
The rate of photosynthesis can change depending on environmental conditions. Understanding these factors helps explain why plants grow differently in various situations.
More light generally means faster photosynthesis, up to a point. This is why plants grow towards windows and why greenhouse growers use artificial lights.
Photosynthesis involves enzymes, which work best at optimal temperatures (usually around 25°C for most plants). Too hot or too cold and the process slows down.
More CO₂ in the air can increase photosynthesis rates. This is why some greenhouse growers add extra CO₂ to boost plant growth.
Scientists and students can test whether photosynthesis is occurring using simple experiments. These tests help us understand when and where the process happens.
Place a piece of pond weed (like Elodea) in a test tube filled with water, then invert it in a beaker of water. Put it in bright light and watch for bubbles of oxygen gas collecting at the top of the test tube. You can test if it's oxygen by inserting a glowing splint - it will relight if oxygen is present!
Chlorophyll is essential for photosynthesis. We can prove this by comparing green leaves with variegated leaves (leaves with white and green patches). Only the green parts can photosynthesise because only they contain chlorophyll.
Chlorophyll absorbs red and blue light very well but reflects green light. This is why we see leaves as green - it's the colour that chlorophyll doesn't absorb!
Photosynthesis is the foundation of almost all life on Earth. It connects plants, animals and the atmosphere in a beautiful cycle that has been running for billions of years.
Photosynthesis and respiration work together to maintain the balance of gases in our atmosphere:
All the oxygen in our atmosphere originally came from photosynthesis! Early photosynthetic bacteria and plants gradually built up oxygen levels over billions of years, making it possible for oxygen-breathing life forms like us to evolve.
Photosynthesis is truly one of nature's most important processes. By understanding both the word and symbol equations, you can appreciate how plants convert simple ingredients into the food and oxygen that support all life on Earth.