Needham vs. Spallanzani - Online Tutor, Practice Problems & Exam Prep

John Needham's experiments incorrectly supported spontaneous generation due to poor sterilization methods, believing brief boiling killed all microbes. In contrast, Lazaro Spalanzani's experiments disproved this by sealing flasks with melted glass and boiling broth longer, preventing contamination. Spalanzani observed no microbial growth in sealed flasks, concluding that microbes do not spontaneously generate. His findings laid the groundwork for future research, including Louis Pasteur's work, which ultimately confirmed biogenesis, the principle that life arises from existing life.

Needham vs. Spallanzani

In this video, we're going to begin our lesson on the contradictory experiments conducted by John Needham and Lazaro Spallanzani. Now first, we're going to focus on John Needham's experiments, and then later in a different video, we'll talk about Lazaro Spallanzani's contradictory experiments. Now the big takeaway from this video is that John Needham's results incorrectly supported spontaneous generation. John Needham was an English scientist and priest who tried to experimentally prove spontaneous generation. Although, John Needham was unaware that he had a poor experimental setup and that he incorrectly believed that briefly boiling broth would sterilize it. Sterilization is the process of killing all microbes in a sample, and it turns out that brief boiling is not always enough to sterilize the broth, but he was unaware of that.

In terms of John Needham's experimental results, after he had briefly boiled a flask of broth, incorrectly believing that it was sterile, and after allowing that broth to cool and sealing the broth with a cork, Needham saw microbial growth in his flask. John Needham, in terms of his conclusions, had incorrectly concluded that his sterile flask of broth had spontaneously generated microbes. He believed that his flask was sterile after briefly boiling it, but that was not actually the case.

If we take a look at our image down below, we can get a better understanding of John Needham's experiment. John Needham, who lived from 1713 to 1781 and conducted this experiment in 1745, is depicted saying, "Look, I did it. I proved that spontaneous generation is real." However, he was unaware of his poor experimental setup. In this first part of the experiment, you can see that John Needham took a flask of broth and boiled the broth for a short amount of time. He briefly boiled the broth, incorrectly thinking he was sterilizing it. This also created the potential for contamination during this cooling period because he was unaware that microbes could exist in the air. Then, John Needham sealed his flask with a cork, which is not the best way to seal the flask and prevent contamination. The broth ended up developing microorganisms because, if there were microorganisms in the broth originally, they were not all killed, or microorganisms could have entered the flask during the cooling period, or through the porous cork, contaminating the flask. These were all situations that John Needham had not considered.

The big takeaways from John Needham's experiment are that John Needham had incorrectly believed all microbes died with brief boiling, he incorrectly believed that a cork seal would prevent contamination, and he ended up incorrectly concluding that his experiments supported spontaneous generation because he saw microbial growth here, but he didn't realize that the microbial growth could have come from poor experimental setup. It was not until later when another scientist, Lazaro Spallanzani, realized that something wasn't right with John Needham's experiments.

It was not until 1776 that the scientist, Lazaro Spallanzani, performed a set of experiments to contradict Needham's findings. Although Needham had incorrectly suggested that microbes could spontaneously generate, Lazaro Spallanzani followed up, contradicting his experiment. We'll talk more about Lazaro Spallanzani's contradictory experiments in our next video. But for now, this here concludes our brief introduction to John Needham's experiment and how his results incorrectly supported spontaneous generation. So, I'll see you guys in our next video.

Which of the following cannot be an explanation of the microorganisms present in Needham's flasks?

• A. The microorganisms could have entered his flask after it was boiled and before it was sealed properly.
• B. Microorganisms had developed spontaneously from the molecules in the broth when it was cooled.
• C. He did not boil his broth for a long enough time to completely kill all of the microorganisms.
• D. The cork that he used was porous and allowed microorganisms to enter the sealed flask.

Which of the following individuals argued in favor of the theory of spontaneous generation?

• A. Francesco Redi.
• B. Louis Pasteur.
• C. John Needham.
• D. Lazzaro Spallanzani.
• E. Isaac Newton.

Spallanzani’s Results Disproved Spontaneous Generation

In this video, we're going to focus on Lazzaro Spallanzani's experiment and how his experimental results disproved spontaneous generation. Lazzaro Spallanzani was an Italian physiologist in the 1700s who performed experiments that contradicted Needham's results. Recall from our previous lesson video that Needham's results supported spontaneous generation. Spallanzani proposed that Needham's experiment was flawed and that there were many mistakes throughout his experimental setup. Spallanzani also proposed that living organisms do not spontaneously generate. His experiment was very similar to Needham's, except there were a few key differences. One of those main differences is that in Spallanzani's experiments, he had sealed his flask by melting the glass closed. Sealing the flask by melting it closed helped to prevent microbial contamination.

The second main way that Spallanzani's experiment differed from Needham's is that Spallanzani boiled his broth for a significantly longer period of time in comparison to Needham's brief boiling. Notice over here on the far left, we're showing you an image of Lazzaro Spallanzani who lived from 1729 to 1799 and conducted this experiment in 1767. You can see here we have a flask filled with this liquid broth. One of the main differences between Spallanzani's experiment and Needham's experiment is that Spallanzani sealed his flask by melting the glass closed. With this arrow here, the glass, the top of the glass is melted closed to prevent microbial contamination. The longer boiling allowed for a greater chance of sterilizing the broth or killing all of the microbes in the broth because brief boiling does not really kill all microbes, whereas longer boiling is more likely to kill all microbes.

Spallanzani realized that as long as there were no cracks in his glass that was sealed closed, there were absolutely no microorganisms that grew in his flask. However, if he intentionally introduced a small crack into the flask, it created an opportunity for microbes to enter and contaminate the flask. By cracking the flask, the cracks allowed microorganisms to grow. You can see that there is microbial growth in the flask that has the crack in it. But as long as there's no crack, there were no microorganisms. That's exactly what we see here in the results for Spallanzani's experiment. Spallanzani never saw microbial growth in the sealed flasks. He only saw microbial growth in the flasks that were cracked open. He was able to conclude from these results that microbes do not spontaneously generate because if they did spontaneously generate, then you would expect microbes to spontaneously generate even in the flask that was sealed closed. He also concluded that the cracked flasks allowed microbes to enter from the air.

Over here on this part of the image, we have some important conclusions from Spallanzani's experiment. Number 1 being that melting the flasks closed helped prevent contamination, and that was one of the main differences between Spallanzani's and Needham's experiment. Number 2 was that boiling the broth for a longer period of time helped to kill all of the microbes to ensure that there were no microbes that would be able to grow. Number 3, cracked flasks were contaminated by microbes in the air. And number 4, he was able to conclude that microbes in the broth did not spontaneously develop or spontaneously generate, because they did not generate in his sealed flask. Spallanzani helped to disprove spontaneous generation.

Now there were still some opposers to Spallanzani's experiments. These opposers claimed that Spallanzani's sealed flask excluded some unknown vital source, from the broth that was needed for spontaneous generation. Basically, what they were suggesting is that the sealed flask just prevented some unknown, vital source, such as maybe oxygen, for example, from entering into the flask, and that is what was preventing spontaneous generation. There was still some skepticism, even after Spallanzani's experiment. Some people still believed that spontaneous generation was likely. It was not until another scientist by the name of Louis Pasteur came around to set up another experiment that finally disproved spontaneous generation once and for all. But for now, we will talk about Louis Pasteur's experiments later in a different video. This concludes our introduction to Spallanzani's experiment and how his results disprove spontaneous generation. I'll see you all in our next video.

Spallanzani set out to disprove spontaneous generation by, however his findings were not accepted by all. Why did some scientists disprove his findings?

• A. He did not boil the broth for long enough.
• B. He boiled the broth too long, killing the 'vital source' that some believed was needed for spontaneous generation.
• C. He used the wrong type of flask and cork to seal his flask.
• D. He did not allow air in the flask which some believed was needed for spontaneous generation.
• E. A and C.
• F. B and D.

Needham vs. Spallanzani Experimental Design

In this video, we're going to do a side by side comparison of John Needham's and Lazaro Spallanzani's experimental design. And once again, Lazaro Spallanzani's experiments differed from John Needham's experiments in two significant ways. Number 1, Lazaro Spallanzani completely sealed the flasks by melting the flasks closed before he boiled the broth in the flask. And this is important because this helped ensure that no microbes could enter into the broth after boiling the broth. Now the second significant way that Spallanzani's differed from John Needham's is that Spallanzani boiled the broth for a significantly longer period of time. A longer boiling time helps to ensure that all of the microbes were killed by the heat, whereas shorter and brief boiling like what Needham did may not necessarily kill all of the microbes, and so there may still be some lingering microbes in the broth.

Now if we take a look at our image down below, notice that the top half of the image is focused on John Needham's experiment. Whereas the bottom half of the image is focused on Lazaro Spallanzani's experiment. And so, focusing on John Needham's experiment first, notice that Needham did not seal the flask by melting it closed and so the flask remained open to the environment. Also, he only boiled his broth for a brief period of time, a short period of time. Short boiling times may not necessarily kill any microbes that might be in the broth originally. And so there could be some lingering microbes even after a short period of boiling. Also, he allowed the broth to cool for a short period of time, which allowed for the opportunity for microbes to enter the flask from the air and contaminate the flask after boiling. And so where Needham thought that his flask was going to be sterile, it turns out that he was incorrect because there could have been lingering microbes or the microbes could have contaminated the flask from the air.

Also, John Needham sealed his flasks by using a cork, which is porous. A porous cork, meaning that it has pores in it and has holes in it, allows for microbes to pass through the cork and enter into the flask. And so here we're showing you how microbes can enter through the porous cork and still contaminate the flask. And so where John Needham saw microbial growth and attributed it to spontaneous generation, he was incorrect. The microbes could have come from being either lingering microbes after short boiling times or microbes that simply just entered into the flask from the air.

Now down below, we're showing you Spallanzani's experiment, in which you can see he sealed his flask by melting the glass closed. Melting the glass helped to prevent contamination throughout his experiment. Then he boiled his broth for a significantly longer period of time, which helped to ensure that all of the microbes that may have been existing in the broth were killed and that his broth was actually sterile. And so what you can notice is that in Spallanzani's experiments, the microbes were absent. And because the microbes were absent, he suggested that spontaneous generation was not the way for microbes to develop. And so you can see there is no spontaneous generation here.

And once again, even after Spallanzani's experiment, some people still remained skeptical of this idea of biogenesis, that life only comes from life and that life cannot spontaneously generate. They remained skeptical even after Spallanzani's experiment. And so it was not until almost 100 years later after Spallanzani's experiment that another French scientist by the name of Louis Pasteur, was able to confirm Spallanzani's findings using another simple experiment, with a custom flask. And so we'll get to talk about Louis Pasteur's experiment in our next lesson video. But for now, this here concludes our lesson comparing John Needham's and Lazaro Spallanzani's experimental design, and we'll be able to get some practice applying these concepts as we move forward. So I'll see you all in our next video.

Needham performed an experiment by boiling chicken broth, placing it in a sterile flask, and then sealing the flask. After a few days, he observed microorganism growth in the flask. What was the major flaw of his experiment?

• A. Boiling the broth activated dormant microorganisms that were not present before boiling.
• B. Melting the flasks closed did not allow fresh air to interact with the broth, stopping microorganisms from developing.
• C. Needham boiled the broth too long, killing the 'vital source' needed to develop microorganisms.
• D. He did not boil the broth long enough to kill all microorganisms and he did not seal the flask properly.
• E. The flasks he used were cracked, and microorganisms from the air contaminated the broth.

Here’s what students ask on this topic:

What were the main differences between John Needham's and Lazaro Spallanzani's experiments?

The main differences between John Needham's and Lazaro Spallanzani's experiments were in their sterilization methods and sealing techniques. Needham briefly boiled his broth and sealed the flask with a porous cork, which allowed for microbial contamination. In contrast, Spallanzani boiled his broth for a significantly longer period and sealed the flask by melting the glass closed, effectively preventing contamination. These differences led to Needham incorrectly supporting spontaneous generation, while Spallanzani disproved it by showing no microbial growth in his sealed flasks.

How did John Needham's experimental setup lead to incorrect conclusions about spontaneous generation?

John Needham's experimental setup led to incorrect conclusions about spontaneous generation due to several flaws. He briefly boiled the broth, which did not kill all microbes, and sealed the flask with a porous cork, allowing microbes to enter. Additionally, he allowed the broth to cool while uncovered, further exposing it to airborne microbes. These factors resulted in microbial growth, which Needham mistakenly attributed to spontaneous generation, not realizing the contamination was due to his poor experimental setup.

Why did Lazaro Spallanzani's experiments disprove spontaneous generation?

Lazaro Spallanzani's experiments disproved spontaneous generation by addressing the flaws in Needham's setup. Spallanzani boiled the broth for a longer period, ensuring sterilization, and sealed the flasks by melting the glass closed, preventing contamination. He observed no microbial growth in the sealed flasks, concluding that microbes do not spontaneously generate. This demonstrated that life arises from existing life, not spontaneously, laying the groundwork for the principle of biogenesis.

What were the key conclusions from Lazaro Spallanzani's experiments?

The key conclusions from Lazaro Spallanzani's experiments were: 1) Melting the flasks closed prevented microbial contamination. 2) Boiling the broth for a longer period ensured all microbes were killed. 3) Cracked flasks allowed microbes to enter from the air, leading to contamination. 4) Microbes did not spontaneously generate in sealed flasks, disproving spontaneous generation. These findings supported the principle of biogenesis, which states that life arises from existing life.

How did the scientific community react to Spallanzani's findings on spontaneous generation?

While Lazaro Spallanzani's findings significantly challenged the idea of spontaneous generation, the scientific community's reaction was mixed. Some scientists accepted his conclusions, recognizing the importance of his improved experimental methods. However, others remained skeptical, arguing that Spallanzani's sealed flasks excluded a vital source, such as oxygen, necessary for spontaneous generation. This skepticism persisted until Louis Pasteur's experiments later definitively disproved spontaneous generation, confirming the principle of biogenesis.