6.14.3: Low Temperatures - Biology

6.14.3: Low Temperatures - Biology

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  • Identify how low temperatures are used for microbial control

Temperature is an important factor for microbial growth. Each species has its own optimal growth temperature at which it flourishes. Human microbial pathogens usually thrive at body temperature, 37ºC. Low temperatures usually inhibit or stop microbial growth and proliferation but often do not kill bacteria. Refrigeration (4ºC) and freezing (-20ºC or less) are commonly used in the food, pharmaceuticals and biotechnology industry.

Refrigeration preserves food by slowing down the growth and reproduction of microorganisms and the action of enzymes which cause food to rot. The introduction of commercial and domestic refrigerators drastically improved the diets of many in the 1930s by allowing foods such as fresh fruit, salads and dairy products to be stored safely for longer periods, particularly during warm weather. It also facilitated transportation of fresh food on long distances.

Refrigeration is also used to facilitate the preservation of liquid medicines or other substances used for research where microbial growth is undesirable, often combined with added preservatives. Fridge temperatures inhibit the proliferation of bacteria better than molds and fungi.

For longer periods of preservation, freezing temperatures are preferred to refrigeration. Since early times, farmers, fishermen, and trappers have preserved their game and produce in unheated buildings during the winter season. Freezing food slows down decomposition by turning residual moisture into ice, inhibiting the growth of most bacterial species.

Freezing temperatures curb the spoiling effect of microorganisms in food, but can also preserve some pathogens unharmed for long periods of time. While it kills some microorganisms by physical trauma, others are sublethally injured by freezing, and may recover to become infectious.

Frozen products do not require any added preservatives because microorganisms do not grow when the temperature of the food is below -9.5°C, which is sufficient in itself to prevent food spoilage. Long-term preservation of food may call for food storage at even lower temperatures.

Key Points

  • Refrigeration (4ºC) and freezing (-20ºC or less) are commonly used in food, pharmaceutical and biotechnology industries.
  • Refrigeration preserves food by slowing down the growth and reproduction of microorganisms as well as the action of enzymes which cause food to rot.
  • Freezing food slows down decomposition by turning residual moisture into ice, inhibiting the growth of most bacterial species. Freezing kills some microorganisms by physical trauma, while sublethally injuring others which may recover to become infectious.

Key Terms

  • proliferation: The process by which an organism produces others of its kind; breeding, propagation, procreation, reproduction.

What is a normal body temperature range?

Normal body temperatures vary depending on many factors, including a person’s age, sex, and activity levels.

The normal body temperature for an adult is around 98.6°F (37°C) , but every person’s baseline body temperature is slightly different, and may consistently be a little higher or lower.

In this article, we discuss the normal ranges of temperature for adults, children, and babies. We also consider factors affecting body temperature, and when to call a doctor.

Body temperature readings vary depending on where on the body a person takes the measurements. Rectal readings are higher than oral readings, while armpit readings tend to be lower.

The table below gives the normal ranges of body temperature for adults and children according to a thermometer manufacturer:

Type of reading0–2 years3–10 years11–65 yearsOver 65 years
Oral95.9–99.5°F (35.5–37.5°C)95.9–99.5°F (35.5–37.5°C)97.6–99.6°F (36.4–37.6°C)96.4–98.5°F (35.8–36.9°C)
Rectal97.9–100.4°F (36.6–38°C)97.9–100.4°F (36.6–38°C)98.6–100.6°F (37.0–38.1°C)97.1–99.2°F (36.2–37.3°C)
Armpit94.5–99.1°F (34.7–37.3°C)96.6–98.0°F (35.9–36.7°C)95.3–98.4°F (35.2–36.9°C)96.0–97.4°F (35.6–36.3°C)
Ear97.5–100.4°F (36.4–38°C)97.0–100.0°F (36.1–37.8°C)96.6–99.7°F (35.9–37.6°C)96.4–99.5°F (35.8–37.5°C)

Normal body temperature readings will vary within these ranges depending on the following factors:

Cooler temperatures slow the repair of DNA damage in tadpoles exposed to ultraviolet radiation: Implications for amphibian declines at high altitude

Rebecca L. Cramp, School of Biological Sciences, The University of Queensland, Brisbane, QLD 4072, Australia.

School of Biological Sciences, Monash University, Melbourne, VIC, Australia

School of Biological Sciences, The University of Queensland, Brisbane, QLD, Australia

School of Biological Sciences, The University of Queensland, Brisbane, QLD, Australia

School of Biological Sciences, The University of Queensland, Brisbane, QLD, Australia

Rebecca L. Cramp, School of Biological Sciences, The University of Queensland, Brisbane, QLD 4072, Australia.

School of Biological Sciences, Monash University, Melbourne, VIC, Australia

School of Biological Sciences, The University of Queensland, Brisbane, QLD, Australia


Ultraviolet B radiation (UVBR) damages the DNA of exposed cells, causing dimers to form between adjacent pyrimidine nucleotides. These dimers block DNA replication, causing mutations and apoptosis. Most organisms utilize biochemical or biophysical DNA repair strategies to restore DNA structure however, as with most biological reactions, these processes are likely to be thermally sensitive. Tadpoles exposed to elevated UVBR at low environmental temperatures have significantly higher rates of mortality and developmental deformities compared with tadpoles exposed to the same levels of UVBR at higher environmental temperatures. We hypothesized that low environmental temperatures impair the primary enzymatic (photolyase) DNA repair pathway in amphibians, leading to the accumulation of DNA damage. To test this hypothesis, we compared DNA repair rates and photolyase gene expression patterns in Limnodynastes peronii. Tadpoles were acutely exposed to UVBR for 1 hr at either 20 or 30°C, and we measured DNA damage and photolyase expression levels at intervals following this exposure. Temperature had a significant effect on the rate of DNA repair, with repair at 30°C occurring twice as fast as repair at 20°C. Photolyase gene expression (6-4 PP and CPD) was significantly upregulated by UVBR exposure, with expression levels increasing within 6 hr of UVBR exposure. CPD expression levels were not significantly affected by temperature, but 6-4 PP expression was significantly higher in tadpoles in the 30°C treatment within 12 hr of UVBR exposure. These data support the hypothesis that DNA repair rates are thermally sensitive in tadpoles and may explain why enigmatic amphibian declines are higher in montane regions where UVBR levels are naturally elevated and environmental temperatures are lower.

Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Weather 6-14-19

A mix of sun and high clouds highlight our Friday weather forecast with afternoon high temperatures today cooler than yesterday into the mid 80’s. The Wenatchee Valley tied a record high temperature Thursday at 95 degrees.

Pacific high pressure will strengthen on Saturday bringing sunny weather conditions to Northcentral Washington and warmer temperatures with highs tomorrow around 90.

Very warm temperatures will continue into Sunday as the Eastern Pacific ridge builds inland. Look for high temperatures on Father’s Day to reach the lower to mid-90s across Northcentral Washington, which is roughly 10 to 15 degrees warmer than normal for this time of year.

The weather pattern becomes more zonal on Monday as the upper level ridge of high pressure flattens and a weak weather system passes to our north. Expect modest cooling and westerly winds to pick up a bit Monday with sunny skies and high temperature near 90 degrees.

Forecast confidence continues to increase that a more meaningful weather pattern shift is shaping up for the middle of next week as a robust Gulf of Alaska trough moves through the Inland Northwest. An associated cold front is likely to bring strong and gusty winds along the lee of the Cascades and the Columbia Basin. Timing and strength of this frontal system is still a bit uncertain, but looks like it may have the potential to increase fire weather concerns. This pattern shift will also bring considerably cooler temperatures. The change begins on Tuesday with sunny skies and high temperatures in the lower 80’s.

The gradual cool down will continue on Wednesday and Thursday under sunny skies, Wenatchee Valley afternoon temperatures will top off in the lower 80’s Wednesday and upper 70’s on Thursday. Overnight low temperatures in the mid 50’s.

Hope everyone enjoys the weekend and especially on Father’s Day Sunday!

Practical Work for Learning

Class practical

Phenolphthalein is an indicator that is pink in alkaline solutions of about pH10. When the pH drops below pH 8.3 phenolphthalein goes colourless. Here, an alkaline solution of milk, lipase and phenolphthalein will change from pink to colourless as the fat in milk is broken down to form fatty acids (and glycerol) thus reducing the pH to below 8.3. The time taken for this reaction to occur is affected by temperature.

Lesson organisation

This investigation could be carried out as a demonstration at two different temperatures, or in a group of at least 5 students with each student working at a different temperature. This would allow students to collect repeat data at their allocated temperature. Or it could be an investigation carried out by one student.

Apparatus and Chemicals

For each group of students:

Measuring cylinder (or syringe), 10 cm 3 , 2

Beaker, 100 cm 3 , 2 (for milk and sodium carbonate solution)

Beaker, 250 cm 3 , 2 (to act as water baths for temperatures below room temperature)

For each temperature:

For the class – set up by technician/ teacher:

Milk, full-fat or semi-skimmed, 5 cm 3 per student per temperature assessed

Phenolphthalein in a dropper bottle (Note 2)

5% lipase solution, 1 cm 3 per student per temperature assessed

Sodium carbonate solution, 0.05 mol dm – 3 , 7 cm 3 per student per temperature assessed

Electric hot water baths set to a range of temperatures, each containing a thermometer, a test-tube rack and a beaker of lipase solution.

Health & Safety and Technical notes

Sodium carbonate solution, 0.05 M. Make with 5.2 g of anhydrous solid, or 14.2 g of washing soda per litre of water. See CLEAPSS Hazcard it is an IRRITANT at concentrations over 1.8 M.

Ethanol (IDA) in the phenolphthalein indicator is described as HIGHLY FLAMMABLE on the CLEAPSS Hazcard (flash point 13 °C) and HARMFUL (because of presence of methanol).

Electric water baths should be safety checked in accordance with your employer’s instructions.

Take care with thermometers and brief students how to react if they are broken.

1 Lipase solution is best freshly made, but it will keep for a day or two in a refrigerator. Don’t try to study different temperatures on different days for the same investigation the activity of the enzyme will change and it will not be a fair test.

2 Phenolphthalein is described as low hazard on CLEAPSS Hazcard. Refer to Recipe card (acid-base indicators): Dissolve 1 g in 600 cm 3 of IDA then make up to 1 litre with water. Label the bottle highly flammable. Suppliers of phenolphthalein solution may not use IDA it also may be diluted. Follow any hazard warning on supplier’s bottles.


SAFETY: Keep the phenolphthalein solution away from sources of ignition.

Wear eye protection and quickly rinse any splashes of enzyme solution or sodium carbonate from the skin.


a Make up lipase solution and suitable quantities of the other solutions.

b Set up the water baths at a range of temperatures and put a beaker of lipase, containing a 2 cm 3 syringe into each water bath. Cover a range of temperatures up to around 60°C. An ice-bath will maintain a temperature of 0°C, until all the ice is melted.


c Label a test tube with the temperature to be investigated.

d Add 5 drops of phenolphthalein to the test tube.

e Measure out 5 cm 3 of milk using a measuring cylinder (or syringe) and add this to the test tube.

f Measure out 7 cm 3 of sodium carbonate solution using another measuring cylinder (or syringe) and add this to the test tube. The solution should be pink.

g Place a thermometer in the test tube. Take care as the equipment could topple over.

h Place the test tube in a water bath and leave until the contents reach the same temperature as the water bath.

i Remove the thermometer from the test tube and replace it with a glass rod.

j Use the 2 cm 3 syringe to measure out 1 cm 3 of lipase from the beaker in the water bath for the temperature you are investigating.

k Add the lipase to the test tube and start the stopclock/ stopwatch.

l Stir the contents of the test tube until the solution loses its pink colour.

m Stop the clock/ watch and note the time in a suitable table of results.

Teaching notes

The quantities used should take approximately 4 minutes to change from pink to white at normal laboratory temperature. If this is not the case, change the concentration of enzyme to alter the speed of the reaction (more enzyme will reduce the time or increase the speed). Students will need to use the same volume at each temperature.

Digestion of fat produces fatty acids (and glycerol) that neutralise the alkali, sodium carbonate, thus lowering the pH and changing phenolphthalein from pink to colourless. You could use a pH probe or data logger, or another indicator.

You could add washing-up liquid to the solution (1 or 2 drops per 250 cm 3 ), to emulsify the fats which will provide a larger surface area for enzyme action. This will demonstrate the effect of bile salts. Or bile salts could be used.

  • This protocol is based on a pH dependent result, so is not suitable for assessing the effect of different pHs on lipase.
  • It would be possible to vary the concentration of the lipase and look at the effect of enzyme concentration on the breakdown of fat in milk.
  • Different types of milk could be used Jersey, full cream, semi-skimmed and skimmed, to explore the effect on the reaction of changing fat concentration (substrate concentration).

Question 6 on the student question sheet opens the doors to a more extensive piece of research on this enzyme.

Let’s begin by plotting them all on the same number line.

The number line has positive numbers to the right of zero and negative numbers to the left of zero. This means that numbers farther to the right are always greater than those to the left. In terms of temperature, the coldest temperature (the least number) is all the way to the left, and the warmest temperature (the greatest number) is all the way to the right.

We can now list the temperatures from coldest to warmest:

Sophia is incorrect. It is common for students to compare negative numbers as if they were positive and to assume that the one with the greatest magnitude is the greatest number. However, $-23$ is to the left of $-14$ on the number line, and so it is less than $-14$. Thus $-23 lt -14$ and Anchorage was colder.

Again, the coldest temperature corresponds to the least number. So the warmest temperature corresponds to the greatest number. Since $-55 gt -89$ the average temperature on Mars is warmer than the coldest temperature on Earth.

Principles of cryopreservation

Cryopreservation is the use of very low temperatures to preserve structurally intact living cells and tissues. Unprotected freezing is normally lethal and this chapter seeks to analyze some of the mechanisms involved and to show how cooling can be used to produce stable conditions that preserve life. The biological effects of cooling are dominated by the freezing of water, which results in the concentration of the solutes that are dissolved in the remaining liquid phase. Rival theories of freezing injury have envisaged either that ice crystals pierce or tease apart the cells, destroying them by direct mechanical action, or that damage is from secondary effects via changes in the composition of the liquid phase. Cryoprotectants, simply by increasing the total concentration of all solutes in the system, reduce the amount of ice formed at any given temperature but to be biologically acceptable they must be able to penetrate into the cells and have low toxicity. Many compounds have such properties, including glycerol, dimethyl sulfoxide, ethanediol, and propanediol. In fact, both damaging mechanisms are important, their relative contributions depending on cell type, cooling rate, and warming rate. A consensus has developed that intracellular freezing is dangerous, whereas extracellular ice is harmless. If the water permeability of the cell membrane is known it is possible to predict the effect of cooling rate on cell survival and the optimum rate will be a tradeoff between the risk of intracellular freezing and effects of the concentrated solutes. However, extracellular ice is not always innocuous: densely packed cells are more likely to be damaged by mechanical stresses within the channels where they are sequestered and with complex multicellular systems it is imperative not only to secure cell survival but also to avoid damage to the extracellular structure. Ice can be avoided by vitrification--the production of a glassy state that is defined by the viscosity reaching a sufficiently high value (approximatly 10(13) poises) to behave like a solid, but without any crystallization. Toxicity is the major problem in the use of vitrification methods. Whether freezing is permitted (conventional cryopreservation) or prevented (vitrification), the cryoprotectant has to gain access to all parts of the system. However, there are numerous barriers to the free diffusion of solutes (membranes), and these can result in transient, and sometimes equilibrium, changes in compartment volumes and these can be damaging. Hence, the processes of diffusion and osmosis have important effects during the introduction of cryoprotectants, the removal of cryoprotectants, the freezing process, and during thawing. These phenomena are amenable to experiment and analysis, and this has made it possible to develop effective methods for the preservation of a very wide range of cells and some tissues these methods have found widespread applications in biology and medicine.

South Africa: 14 All-Time Monthly Low Temperature Records Fell Yesterday (May 28), with “Widespread Snow” Accompanying the Freeze

These record low May temperatures were set ACROSS the southernmost tip of Africa, although the east appears to have been disproportionately hit.

The “II AGR” weather station in Buffelspoort –located NW of Johannesburg– set a new “Lowest Minimum” temperature on Thursday, May 28 of -2C (35.6F) — a reading which comfortably usurped the station’s previous all-time lowest May minimum of 0.9C (33.6F) set back on May 10, 1970.

Secunda –located amidst the coalfields of the Mpumalanga province– was another region to suffer its lowest May temperature on record. The town logged a bone-chilling -3.9C (25F) on Thursday morning, which surpassed the old record of -3.3C (26F) from May 29, 1994.

Exceptional snowfall has been accompanying the low temps.

“We’ve got ground-level snow in quite a few places,” said Richard le Sueur of SnowReportSA while on popular SA radio show CapeTalk on May 27.

“The front swept in from the west and has gone right across the country … We’ve had snow on the Western Cape mountains, the Southwestern Cape and through the Southern Cape and into the Eastern Cape … also, in Lesotho and the Northern Cape … So, pretty much widespread snow,” said le Sueur.

“We’re going to see a chilly winter,” he concluded.

Eskom senior technical officials Aviwe Mehlomakulu and Ulrich Van Der Merwe braved the – 1degree snows and icy terrain in the mountainous area in Ceres to restore supply after a six hour outage yesterday. @Eskom_SA

&mdash SikonathiMantshantsh (@SikonathiM) May 27, 2020

South Africa: Snow Shuts Down Major Roads in Eastern Cape

&mdash Global Issues Web (@globalissuesweb) May 27, 2020

A total of 14 never-before-seen-in-May low temperature records were set across South Africa on May 28 alone ( link here ) — a blast of Antarctic air forced its way unusually-far north on the back of a meridional (wavy) jet stream flow an increasing phenomena, and one strongly linked to the historically low solar activity we’re currently experiencing.

GFS May 28 Temp Anomalies [ ]

Even NASA agrees, in part at least, with their forecast for this upcoming solar cycle (25) revealing it will be “ the weakest of the past 200 years ,” with the agency correlating previous solar shutdowns to prolonged periods of global cooling here .

Don’t fall for bogus warm-mongering political agendas — our future is one of ever-descending COLD & CROP LOSS.

Prepare accordingly — learn the facts, relocate if need be, and GROW YOUR OWN.

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Grand Solar Minimum + Pole Shift

[Thank you to Albert Van Lingen for bringing this story to my attention.]

How Photosynthesis Works

Photosynthesis defines the process by which plants and some bacteria manufacture glucose. Scientists summarize the process as follows: using sunlight, carbon dioxide + water = glucose + oxygen. The process occurs within special structures called chloroplasts located in the cells of leaves. Optimum photosynthetic rates lead to the removal of greater amounts of carbon dioxide from the local atmosphere, producing greater amounts of glucose. Since glucose levels within plants are difficult to measure, scientists utilize the amount of carbon dioxide assimilation or its release as a means to measure photosynthetic rates. During the night, for example, or when conditions are not prime, plants release carbon dioxide. Maximum photosynthetic rates vary between plant species, but crops such as maize can achieve carbon dioxide assimilation rates as high as 0.075 ounce per cubic foot per hour, or 100 milligrams per decimeter per hour. To achieve optimum growth of some plants, farmers keep them in greenhouses that regulate conditions such as humidity and temperature. There are three temperature regimes over which the rate of photosynthesis changes.

Record-breaking low temperatures in Colorado

Winter Weather Advisories and Warnings in addition to Wind Chill Advisories are in effect for much of the state through Sunday night. The arctic air mass that took over the midwest has backed into Colorado, producing the coldest temperatures we've seen in years. Low temperatures tonight should reach -6 degrees in Colorado Springs and Pueblo with wind chill values to -25 degrees, hence the advisories. Snow showers overnight will cover roads and make traveling anywhere in Colorado quite difficult. If you do have to travel, make sure to pack a survival kit in case of an emergency. With these types of temperatures, frostbite to exposed skin is possible in less than 15 minutes.

Sunday: Snow showers will continue through the morning hours and begin to tapper off during the afternoon, but expect road conditions to be poor the entire day. Snowfall totals should range from 2-5in along the I-25 corridor with upwards of 6-9in across the eastern plains. High temperatures to 2 degrees in Colorado Springs and Pueblo, which would make for the coldest Valentine's Day on record. Low temperatures Sunday night will be the coldest yet, down to a staggering -12 degrees in Colorado Springs and -15 in Pueblo.

Extended: Warming into the teens by Monday and back to a more seasonal pattern starting Tuesday. With the worst of the storm ahead of us, Tuesday can't come soon enough.

The KRDO StormTracker 13 weather app is available for download in the iOS app store and in Google Play.

Watch the video: Investigating the effect of high temperatures on permeability of cell membranes (February 2023).