Measuring Growth by Biomass: Videos & Practice Problems

Measuring microbial growth can be effectively achieved by assessing biomass, which refers to the mass of an organism. One common method for determining biomass is through the use of a spectrophotometer, an instrument that measures light absorbance values, denoted as A. These absorbance values are crucial for evaluating the turbidity of a liquid culture, which indicates the cloudiness caused by microbial growth.

The relationship between turbidity and biomass is significant: higher turbidity correlates with a greater biomass of organisms. This is because an increased number of organisms leads to a cloudier solution. However, it is important to note that high turbidity results in lower detected light levels. In essence, high turbidity corresponds to high absorbance values, indicating that more light is absorbed by the microbial cells rather than transmitted through the culture.

When using a spectrophotometer, light is directed through a liquid culture. As the light passes through, some is scattered, some is absorbed, and some is transmitted. The transmitted light is detected and converted into an absorbance value, which ranges from 0 to 1. For instance, an absorbance value of 0.08 suggests low biomass and low turbidity, while a value of 0.41 indicates high biomass and high turbidity due to significant microbial growth.

In summary, the spectrophotometer serves as a valuable tool for quantifying microbial growth by measuring absorbance values. Higher absorbance values reflect greater biomass, thereby providing insight into the extent of microbial growth in a culture. Understanding this relationship is essential for accurately measuring and interpreting microbial growth dynamics.

Measuring microbial growth can be effectively achieved by assessing the total weight of the microbial cells in a culture. This method involves the use of a centrifuge, an instrument designed to spin samples at high speeds, generating centrifugal forces that cause the microbial cells to settle at the bottom of the container, forming what is known as a cell pellet.

To begin, a liquid culture containing the microbial growth is placed in the centrifuge. As the centrifuge spins, the cells are pulled downwards, leaving behind a liquid portion known as the supernatant. After centrifugation, the supernatant is carefully removed to avoid disturbing the cell pellet that has formed at the bottom of the tube.

Once the supernatant is decanted, the next step is to weigh the cell pellet. It is essential to first weigh the empty tube to ensure accurate measurement. The weight of the cell pellet is determined by subtracting the weight of the empty tube from the combined weight of the tube and the pellet. This process allows for quantifying microbial growth: a heavier cell pellet indicates a greater amount of microbial growth.

In summary, the total weight measurement method provides a straightforward approach to quantifying microbial growth by utilizing centrifugation to isolate and weigh the cells. This technique is valuable in various microbiological studies and applications, enabling researchers to assess the growth dynamics of microbial populations effectively.