AP Biology class blog for discussing current research in Biology

Tag: Winter

“Covid Winter” is Coming: The Power of Humidity in our Return to Normal

As “Covid Winter” approaches, especially in states with seasonal changes such as New York, it calls into question what this will mean for the virus in the coming months. When thinking about when the pandemic will end, temperature, humidity, and seasonal shifts are large factors which work against stopping the spread of the virus. Externally, as the air outside becomes colder, it is able to hold less water vapor, which decreases humidity. HVAC (heating, ventilation, and air conditioning) units inside office buildings work by taking in outside air and heating it to channel through the indoor space, which similarly dries the air out. 

Why is humidity important in preventing the spread of the virus on a biological level? In an aerosol study conducted at Virginia Tech, the researches demonstrated that as humidity levels decrease, the particles of moisture released from actions such as talking, coughing, sneezing become smaller. This becomes a problem because the dry air causes the water in the molecules to evaporate faster, therefore becoming even smaller and staying in the surrounding air for a longer period of time. Any droplets can then travel around the closed, indoor space further. Their minuscule size allows them to be inhaled and move deeper into the lungs, where, as we learned in the video we watched in class, a spike on the virus will insert into a receptor molecule on a healthy cell membrane, allowing it to infect the healthy lung cell, leading to a susceptible person contracting COVID-19 and being able the virus further.

Other coronaviruses, like the common cold, influenza, and rhinoviruses, have exhibited similar spreading patterns dictated by the seasons, demonstrated by flu season occurring in the winter, calming down in summer, and coming back again in fall. Scientists believe COVID-19 could do the same, and are currently conducting research and gathering data to see the correlation between the virus and humidity levels. Stephanie Taylor, a physician and fellow at Har-

An example of how the virus remains in the air after released through talking, singing, etc

vard Medical School, is part of a joint study with the Massachusetts Institute of Technology that “found that the most powerful correlation between national numbers of daily new coronavirus cases and daily Covid-19 deaths was indoor relative humidity.” In reflecting upon their findings, she says that humidity “is so powerful, it’s crazy.” 

The only way to know exactly how the coming winter months will affect the spread of the virus is through time and observation, but it is interesting to look at the biological processes and movement of particles in relation to humidity to understand how the virus may have an increased spread as it becomes colder. I also feel this background helps us be able to make intelligent, informed decisions about the risk of social gatherings as it becomes harder to stay outdoors and the weather changes. What do you think is lying ahead in “Covid Winter?” Do you think we will inevitably have to wait until the humidity changes in spring to declare an official end to the pandemic? 


How do “Evergreen” trees survive such long winters?

800px-Pine_stand_near_Aegviidu,_Jan_2010First let’s start with how trees work, and why normal leaves of the typical tree (deciduous) would not survive during the winter. These trees grow large leaves whose great surface area allows for more photosynthesis to occur. However, water is required for photosynthesis to occur. A good amount of water is transported through the tree’s vascular system by xylem and phloem. Much of this water is required to keep leaves alive. If these leaves were to remain alive during the winter months, the water inside them would freeze and kill them anyways. To retain this water, the tree recalls all water back into the wooden parts of the tree and lets leaves “fall” right before the winter. This is known as the dormant state where the tree survives off of the energy created from photosynthesis performed before losing its leaves. Since the leaves had a large surface area, photosynthesis is done in enough quantity to allow the tree to survive with no photosynthesis for a long winter.

Now, onto why the ‘leaves’ of Evergreen trees stay green and are able to survive such bitter cold winters:
Have you noticed what grows on Evergreen trees? The most common “leaf” is the pine needle. These are very small and thin needles that can be thought of as a leaf tightly coiled together. They cover themselves in a waxy substance called cutin. These needles also require less water to stay alive and perform photosynthesis than leaf. The small amount of water and protective Cutin coating stop any water from freezing and killing any pine needles. Yes, the tiny leaves do not perform as much photosynthesis as a large deciduous leaf, but these pine needles have the qualities necessary to survive the long winter and continue to do photosynthesis throughout the entire winter and provide continuous energy for the tree. Also, some needles do die, and these are immediately replaced by new, healthy needles. This process is different than the one time “fall” of a deciduous tree’s leaves. We will see many more pine trees in cold northern climates and more deciduous trees in warm southern climates. One can think of an Evergreen as a tree that has a continuous energy fueling its growth, while a deciduous tree flourishes with high energy production for three seasons of the year and then “sleeps” for the winter with its stored energy.

If you’re looking to take good care of evergreen trees, it would be best to water any backyard evergreen trees in the season of Autumn to add to its water supply that fuels photosynthesis that goes on (important because of the lack of absorbed water in winter due to it being frozen in the soil).

Which tree do you think is more effective at surviving in its own environment?800px-Pine_stand_near_Aegviidu,_Jan_2010

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