Database results:
examBoard: Pearson Edexcel
examType: IGCSE
lessonTitle: Photosynthesis Process
Photosynthesis is one of the most important processes on our planet! It's how plants make their own food using sunlight and it provides the energy that fuels almost all life on Earth. Without photosynthesis, we wouldn't have oxygen to breathe or food to eat.
Key Definitions:
Photosynthesis can be summarised by this equation:
Carbon dioxide + Water → Glucose + Oxygen
6CO2 + 6H2O → C6H12O6 + 6O2
This reaction needs light energy and chlorophyll to happen. The glucose produced can be:
Photosynthesis is crucial because it:
Photosynthesis happens in two main stages: the light-dependent reactions and the light-independent reactions (also called the Calvin cycle).
These reactions take place in the thylakoid membranes of the chloroplasts:
These reactions happen in the stroma of the chloroplasts:
Plants only use about 1% of the sunlight that falls on their leaves for photosynthesis. The rest is reflected or passes through the leaf. Scientists are working on ways to make photosynthesis more efficient to help grow more food for our growing population!
Leaves are perfectly designed for photosynthesis. Let's look at how their structure helps them do their job:
Transparent layer that allows light to pass through to the cells below. It has a waxy cuticle to prevent water loss.
Tall cells packed with chloroplasts. They're arranged like pillars to capture maximum sunlight. This is where most photosynthesis happens.
Loosely packed cells with air spaces between them. These spaces allow gases to move around and reach all cells.
Contains stomata (tiny pores) that allow carbon dioxide in and oxygen out. Guard cells control the opening and closing of stomata.
Contain xylem vessels that bring water to the leaf cells and phloem vessels that carry away the glucose produced.
Tiny structures inside the cells that contain chlorophyll and are the sites of photosynthesis.
The rate of photosynthesis can be affected by several factors:
As light intensity increases, the rate of photosynthesis increases up to a point, then levels off. In bright light, another factor becomes limiting.
Plants in shade have adapted with larger leaves to capture more light.
Photosynthesis is controlled by enzymes, which work best at their optimum temperature (around 25°C for most plants).
Too cold: enzymes work slowly
Too hot: enzymes become denatured (change shape and stop working)
Higher levels of CO2 increase the rate of photosynthesis up to a point. This is why some greenhouses add extra CO2 to boost plant growth.
Without enough water, plants close their stomata to prevent water loss. This also prevents CO2 from entering the leaf, slowing down photosynthesis.
We can prove that photosynthesis has taken place by testing for the presence of starch in leaves. Here's how it's done:
Variegated leaves have some areas that are green and others that are white or yellow. The white/yellow parts lack chlorophyll. If we test these leaves for starch after they've been in the light, only the green parts turn blue-black with iodine. This proves that chlorophyll is essential for photosynthesis!
Scientists can investigate the factors affecting photosynthesis using simple experiments:
Using a water plant like Elodea, we can count the bubbles of oxygen produced per minute under different conditions. More bubbles = faster photosynthesis!
This can be used to test how light intensity, temperature, or CO2 concentration affect the rate of photosynthesis.
We can set up experiments where different parts of a leaf are exposed to different conditions:
After the experiment, we test for starch to see where photosynthesis occurred.
Photosynthesis is the process that powers life on Earth. Plants use light energy to convert carbon dioxide and water into glucose and oxygen. The process takes place in chloroplasts, particularly in the leaves which are specially adapted for this function. The rate of photosynthesis is affected by light intensity, temperature, carbon dioxide concentration and water availability.
Understanding photosynthesis helps us appreciate how plants grow and produce the food and oxygen that we depend on. It also helps us understand how changes in our environment, like increased carbon dioxide levels, might affect plant growth in the future.
Log in to track your progress and mark lessons as complete!
Login NowDon't have an account? Sign up here.