You are currently viewing Experiment: How Sunlight Affects Mould Growth – By Kevin Wang


The primary question the experiment sought to answer was to find out which conditions were the best and worst for growing mould on bread, either indoors in the dark, partial sunlight or fully outdoors. Based upon preliminary knowledge, the initial hypothesis of the experiment was that more light would slow down the growth of mould, and so outdoor conditions would result in the least mould on the bread, followed up indoor light exposure, with darkness resulting in the most growth. The experiment was divided into the above three categories, each of which had two “trials” (pieces of bread) tested over the course of 8 days. Mould growth was measured by the area of mould in square centimetres using a paper grid laid over the bread, and because bread naturally has bacteria and is ideal for mould, no initial preparation was required to induce growth. The results of the experiment confirmed the hypothesis; though there were several experimental errors, the trend was clear: by the last day, the most mould had grown on bread kept in darkness, followed the bread kept indoors but not in the dark, with the least being outdoor bread. Overall, the experiment showed that even in any condition, mould is capable of surviving, but also that certain conditions are better to store food in.


This project will study how light can affect the growth of mould. This is important to investigate because it impacts on daily life, such as the longevity of the shelf life of our food. Mould is a type of fungus that grows in places that have the correct amount of food, water, temperature, and oxygen. Mould grows well on bread, because people tend to leave it out in the open, and bread does not have the ability to control its temperature. Mould grows spores, which then reproduce to create more spores, and bread is a good place for the spores to grow (Farrelly). 

Key Words 

  • Mould is a type of fungus that produce spores, which are the airborne particles of mould, which the mould consumed it and reproduced it. Mould tends to live in locations where we rarely go to, such as windows, corners, etc. It also thrives in dark places where they can get the least amount of sunlight, but still the sustainable amount of food, water, temperature, and oxygen. 
  • Spores are the airborne particles of mould, which the mould consumed it and reproduced it. They fly around the air and attach to whatever it flows into. They don’t really affect you, since spores cannot grow in a lot of places, but if they are stuck in places where mould usually grow, they will live there and reproduce other spores. 
  • Sunlight is the electromagnetic radiation that comes from the sun and often produces heat. Because the mould tends to grow in moist places, the sunlight will evaporate the mould, and it will delay the mould growth.  
  • Moist is when a liquid is condensed on a surface or inside something, and it is essential to mould growth because the spores feed off of liquid. 

Facts of Mould 

Through their research, scientists have discovered that mould needs sustainable amounts of moisture to grow, so when there’s sunlight, it can evaporate the moisture and inhibit mould growth. Moulds tends to grow in damp and dark places, so the mould doesn’t have to face sunlight. Sunlight itself might not kill mould, but it may remove the conditions for mould growth (Urbauer). 

Mould on Bread 

Bread usually attracts the most mould since it is often left out in the open and it has a good food source. Also, food is a good place for the mould to produce spores and reproduce, since the spores can absorb the nutrients, and they usually have water in them. Bread is especially good for mould, since it is made from yeast, and moulds grow off of the yeast because it is a fungus (“Mold on Food” article). 

Locations of Mould 

Mould can grow in lots of different places when the right conditions exist. When there are other factors such as sunlight or no light, it can affect the speed at which mould grows or it can completely diminish it. Different surfaces also impact at the speed at which mould grows because some places are not as easily affected by sunlight, while other places are. There are also different levels of nutrients on surfaces for mould to grow and when the moisture and yeast of the bread, it seems like a good surface to study. 


The most important points to consider here are the impacts of moisture and sunlight on mould growth. Scientific research has been discovered that these are the most important factors for improving or inhibiting the movement and speed of mould growth. Other important factors include: the amount of nutrients on the surface, and the temperature around the mould. These factors all combine to impact the way in which mould spores travel, attach, and growth. 


  • Farrelly, Lauren. “How Does Mold Grow on Food?”,2/3/2019. Sciencing 
  • “Mold on Food: What Happens If You Eat & How to Prevent Moldy Food?” Mold Busters, 10/3/2019. BustMold 
  • Urbauer, Thomas. “Does Mold Grow Faster in the Light or Dark?”, 18 Nov. 2019. Sciencing 


If bread is exposed to more sunlight, then the growth of mould will be slower.


The amount of sunlight going into the mold. The mold growth due to the amount of sunlight given.
  • Room Temperature.
  • The type of bread.
  • The location.

Procedures We Did + Materials We Used

  • Bread – 6 slices of fresh bread
  • 6 medium size Ziplock bags
  • Transparent measurement grid – each square must be 0.25 Cm2
  • Tape to stick the bags to the windows                                                                             


1. 6 pieces of bread were put in the 6 Ziplock bags
2. 3 different locations were chosen:

3. Ziplock bags were tapped to the windows.

  • i. Window with direct sunlight
  • ii. Window with no direct sunlight
  • iii. Shelf – a tray was used to cover the bread so it was in darkness.
4. Each school day, the samples were inspected.
5. The measurement grid was used to measure any mould growth on the samples was record in the data table
6. Steps 4 – 6 were repeated for 7 days (excluding the weekends).

Mould Graph

Matthew and Kevin
Location of sample Mould Growth (cm2)
Day 1 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7 Day 8
Outside Window 1 0 0 0 N/A N/A 35 65 78
Outside Window 2 0 0 0 N/A N/A 11 14 24
Inside Corridor Window 1 0 0 0 N/A N/A 20 24 31
Inside Corridor Window 2 0 0 0 N/A N/A 17 56 61
Dark (No sunlight) 1 0 0 1 N/A N/A 69 86 120
Dark (No sunlight) 2 0 0 9 N/A N/A 137 177 234

Mould Graph


Based on the collected data, the experiment on mould growth confirms our hypothesis. The experiment clearly showed that light inhibits mould from growing quickly, but dark, indoor environments helped it multiply. The most interesting part of the experiment was seeing how quickly and easily mould spreads on food, and how we store it can make a big change. Since most foods are stored indoors or in the dark, the experiment shows how important it is to check for mould since it grows so fast. One point that was learned after the experiment was the structure and growing patterns of mould: it not only spreads very quickly from one spot, but it can also travel to different areas in the air and start new mould growths (which happened on the bread). This then showed that mould is made of spores, which allow it to spread around rooms from one food to another. In conclusion, the experimental process was proof of the importance of how food is stored, and how quickly it can become rotten with mould if not kept fresh.

This Post Has 2 Comments

  1. Garry

    Great work!

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