Bumblebees: A Man’s Best Friend?

It was as I was mindlessly scrolling through the internet that something caught my eye which is the basis for my next blog post.

I am the first to admit that flying, stinging things are not my favourite type of insect, but I must say I always felt rather sorry for bees, unlike say wasps.

I’ve always been told that every bee’s approach is an all-or-nothing venture, and so although our relationship got off to a rocky start-after my first memory of bees is one being tangled in my hair, (which, let me tell you, was rather traumatic for a toddler and still would be now)- I don’t mind as much their fuzzy little black and yellow bodies buzzing along, because I now appreciate that they prefer to stay out of your way: to sting you is to condemn themselves to death. This is true of the well-known honeybee, however bumblebees have a slightly different story, as I shall explain later, yet I still prefer them to the furious looking wasps.

Thus, it shocked me a little to find out that the first bumblebee has been announced endangered in the U.S. I mean, it has been made very clear that bees are facing a tough time, but it never quite clicked that the fuzzy little things may not be the sign of summer anymore: may not be present at all.

This post looks at bumblebees and the Rusty Patched Bumblebee’s endangered status.

Introduction

Bumblebees are members of the Bombus genus and now over 250 species of bumblebee are known [1].

They are classed as social insects that form colonies with a single queen, although their colonies are smaller than those of their relatives, the honeybees, as they can grow to as few as 50 individuals in a nest [1].

Bumblebees feed on nectar, like their relatives the honeybees. Bumblebees use their long hairy tongues to lap up the liquid and the proboscis (the elongated appendage from the head of an animal-in insects, this is typically an elongated sucking mouthpart which is usually tubular and flexible) is folded under their head during flight. Bumblebees gather nectar to add to the stores inside the nest and pollen is used to feed their young. They use colour and spatial relationships to identify flowers they use to feed from and some species of bumblebees ‘rob nectar’ by making a hole near the base of the flower to access the nectar without touching the pollen. Overall, they are essential agricultural pollinators and thus there is growing concern about their declining numbers in Europe, North America, and Asia [1].

As I have mentioned before, a honeybee generally dies after stinging a human because the barbs on her sting and the relative elasticity of our skin prevents her from pulling her sting out. Thus, she will either be swatted to death or so much of her sting, poison sac and abdominal contents will be left hanging from the stuck sting if she pulls away that she will fly to death (not a very pleasant death, if I say so myself) [2]. On the other hand, female bumblebees can sting repeatedly without injuring themselves because their stings lack the barbs and so they can pull their sting out of the wound. However, bumblebees are generally not normally aggressive and tend to ignore humans and other animals, although they may sting in defence of their nest or if harmed [1].

Rusty Patched Bumblebee

Recently, the U.S. Fish and Wildlife Service announced that the Bombus affinis -rusty patched bumblebee- is “now balancing precariously on the brink of extinction”, when “just 20 years ago,” it was “so ordinary that it went almost unnoticed as it moved from flower to flower”. The rusty patched bumblebee has experienced a swift and dramatic decline since the late 1990s, a shocking 87% decrease in numbers, leaving small, scattered populations in 13 states and one province in the U.S. [3].

The news should not have been surprising however, as only a few months before, the first ever bees were declared endangered in the U.S. In September of 2016, seven species of Hawaiian bees received protection under the Endangered Species Act [4].

We’ll now take a closer look specifically at the rusty patched bumblebee and its importance to us.

In case you ignored them, all rusty patched bumblebees have entirely black heads, but only the workers and males have a rusty-reddish patch located in the centre of their backs. Like the other bumblebees, this species lives in colonies that include a single queen and female workers, and it is only during late summer that the colony produces males and new queens. The queens can be easily distinguished by their larger size [5].

illustrations-of-rusty-patched-bumble-bee

Fig. 2 Illustrations showing a rusty patched bumblebee queen (left), worker (centre) and male (right). [5]

Rusty patched bumblebees are generally not fussy eaters as they gather pollen and nectar from a variety of flowering plants, although since they emerge in early spring and are one of the last species to go into hibernation, they require a constant diverse supply of flowers blooming from April to September [5].

One of the reasons why the rusty patched bumblebees are flying ever closer the edge of extinction is because the habitat they once occupied is slowly being destroyed. The grasslands and tallgrass prairies of the Upper Midwest and Northeast, which the bumblebees once called home, have now been mainly converted to monoculture farms or developed areas, such as cities and roads, and the grasslands that are left are usually too small and isolated to provide the nesting sites (typically underground and abandoned rodent cavities or clumps of grass), overwintering sites (undisturbed soil) for queens and a large array of flowers to be a long-term solution [5].

Another reason for the bumblebees’ fading face from the earth is intensive farming, as many practices which have been adopted, such as increased use of pesticides, loss of crop diversity and loss of hedgerows with their flower populations and legume pastures, have harmed bumblebees. They are especially vulnerable to pesticides because they can absorb the toxins directly through their exoskeleton as through contaminated nectar and pollen [5] and this causes lethal and sub-lethal effects.

Furthermore, global climate change may also play a crucial card because the increased temperature and precipitation extremes; increased drought, early snow melt and late frost events may lead to more exposure or susceptibility to disease, fewer flowering plants [5]. There may also be fewer places for queens to hibernate and nest [5] which may be the final straw for the rapidly decreasing populations because the entire colony relies on the survival of their queen bee through winter-the only member of the colony which survives the season [3].

The Importance of Saying ‘Mi Casa Es Tu Casa’

Well, we all know the intricacies of ecosystems but the rusty patched bumblebees are in fact major contributors to our own food security. They are essential pollinators of blueberries, cranberries, and clover and almost the only insect pollinators of tomatoes. Overall, bumblebees are more effective pollinators than honey bees for some crops because of their ability to ‘buzz crop’, and this is one of the reasons why the economic value of pollination services by native insects (mainly bees) in the United States is around $3 billion per year [5].

One of the main ways people can help is by creating a more bee-friendly garden. Although this is mainly aimed at people living in areas native to the rusty patched bumblebees, you can very well apply this to your own home as almost everywhere there are issues with increasingly more important pollinators being endangered.

This can be as simple as adding a flowering tree or shrub to your garden, or more specifically to the rusty patched bumblebee, native plants such as lupines, asters, bee balm, native prairie plants and spring ephemerals. Or if you’re not one for gardening, just leave some ‘unmowed, brushy’ areas and tolerate bumble bee nests if you find them. On the other hand, if you are a garden enthusiast, try to keep away from pesticides and chemical fertiliser [5].

However, there is still hope as recently the giant panda has been downgraded from ‘endangered’ to ‘vulnerable’ [6], meaning as long as something is done in an effort to help, it may not all be doom and gloom.

References

[1] https://en.wikipedia.org/wiki/Bumblebee

[2] http://www.bumblebee.org/bodySting.htm

[3] https://www.fws.gov/midwest/news/861.html

[4] http://news.nationalgeographic.com/2017/01/bumblebees-endangered-species-rusty-patched/?utm_source=Facebook&utm_medium=Social&utm_content=link_fb20170110news-bumblebees&utm_campaign=Content&sf50288016=1

[5] https://www.fws.gov/midwest/endangered/insects/rpbb/factsheetrpbb.html

[6] http://www.worldwildlife.org/stories/giant-panda-no-longer-endangered

 

Colour change in a teacup

As the revision period looms (I mean, when is there a time when we don’t have to revise?), tea becomes my constant companion. Whether this may be in the form of offering a shoulder to cry on as maths questions refuse to make sense or, by living up to its expectations, that tea can, in fact, solve all your problems by creating the polite deception of wanting to boil the kettle for everyone when you just wish to escape the confining shackles of textbooks.

It was as I was pouring over my chemistry notes on hydrogen and hydroxide ions that tea made another unlikely addition to its already enviable personal statement; it is a real-life example of a colour change.

I am sure this has limitations. For example, I drink my tea with lemon and no milk.

However, I was still intrigued about this magic in my tea cup and here is what I found in my educational revision break.

50 shades of tea

By adding a lemon slice or juice, black tea lightens significantly (shown by figures 1 and 2), and although I have never tried this, by adding lemon to green tea, the tea loses its signature colour and becomes colourless [1].

img_6320

Fig 1. Tea before lemon has been added.

img_6325

Fig 2. Tea after lemon has been added.

Lemon juice is an example of citric acid, which has the chemical formula of C6H8O7. It is a weak tricarboxylic acid that is found mainly in citrus fruit, but also a variety of different fruit and vegetables. Lemons and limes have a particularly high citric acid content as it can make up to 8% of the dry mass of the fruit and the concentration can reach 0.30 mol/L whereas this is significantly lower in fruit such as oranges and grapefruit where the concentration amounts to 0.005 mol/L.  Citric acid itself was isolated by the chemist Carl Wilhelm Scheele in 1784 by crystallising it from lemon juice. The acid can exist in both an anhydrous form, which is formed when it is crystallised from hot water, and a monohydrate form which is created when the acid is crystallised from cold water instead.

Anyway, back to tea.

Tea leaves are rich in polyphenols-a group of chemicals that accounts for almost one third of the mass of a dried leaf and much of the tea’s colour and flavour is due to these compounds. One group of polyphenols is called thearubigins and they are the red-brown pigments which are found in black tea. This group of polyphenols can make up between 7% and 20% of the total mass of dried black tea, and more interestingly, these thearubigins are weak ionising acids, and the anions (otherwise known as negatively charged ions) they produce are highly coloured. For example, if the water used to brew the tea is alkaline, then the colour of the tea will be deeper because of the greater ionisation of the thearubigins, and because the colour of black tea is influenced by the concentration of hydrogen ions in the water [3].

This means that if lemon juice, i.e. citric acid, is added to the tea, then the hydrogen ions will suppress the ionisation of the thearubigins and this will make the tea a lighter colour [3]. Sorry – no real magic this time.

On a side note, however, you may be interested to know that theaflavins-the yellow-coloured polyphenols present in black tea-are not actually involved in the colour change that is associated with a change in acidity [3].

Conclusion

The colour change that you see in your tea cup as you sip slowly in order to extend the tea-drinking break is in fact just evidence of a change in acidity-much like a change in litmus paper that you may have seen in a Chemistry lab.

References

[1]  http://www.thenakedscientists.com/HTML/questions/question/2413/

[2] https://en.wikipedia.org/wiki/Citric_acid

[3] http://superbeefy.com/why-does-black-tea-lighten-or-change-color-when-you-add-lemon-juice-and-what-causes-the-chemical-change/

Nerves, aka the not-so-good wires

Author’s note:

So, just before we explore the workings of message transfer in the human body, I would like to clarify the origins of this blog post. On Saturday 5th November 2016, Cambridge University held a Medicine Taster Day at the Lady Mitchell Hall. This consisted of sample lectures and a run through of the teaching system, among other tips for entry. One of the lectures was titled something along the lines of “How do nerves work?”. As fabulous and interesting as the other lectures were, this one really gave me the most “food for thought”, as they say, and it is on the notes that I made during the lecture that is blog post is based.

Thus, I implore you to understand that writing notes on a topic which a lecturer is comfortably pacing through and later trying to make out the beginning and end of your scrawls is no easy feat (as I’m sure we’ll all find out about in a few years’ time and become masters of note taking). I admit that I wanted to write this solely on my notes to a) review the lecture and b) to see if I understood anything that was being said.

But before any of you future Biology stars start panic (or panic further as may be the case), I did ask for my Biology teacher to look over this post. The message is this: this is a very simplified version of what is happening in real life, especially in the case of amplification. We shall, of course, come to study the topic of nerves in more detail and finesse further in the A Level course.

Oh, and another thing. If any of you dear readers come to learn that any of the figures are incorrect, I sincerely apologise and please do not hesitate to let me know. In the meantime, feel free to blame my poor eyesight (I did find out a while later that my right eye has deteriorated 🙂 ) or my incomprehensible handwriting for any mistakes made.

Introduction

Nerves work in a similar fashion to wires, but when you look at their basic structure, to be honest, they’re a bit of a disappointment to the wire family.

So, if nerves are the “ok” version of copper wires, how do we manage to stay alive?

Firstly, we’ll look at how nerves work, then the problems they encounter and finally how they try to overcome the issues of transferring current.

Trying hard to be a wire

When a pain fibre is stimulated, pain channels are opened and sodium ions (which have a positive charge) enter at one end of the nerve while the rest remains negatively charged. The next stages are similar to those of a battery, as, the differently charged ions create a current which spreads positive charge through the nerve and this results in the potential of activating something else, such as a synapse.

In comparison to a copper wire in which the speed of this is 28,000,000 m/s, the nerve’s speed is between 0.6 to 100 m/s. However, although this is significantly lower, this is not a limiting factor in the body’s reactions, as the message still travels in milliseconds.

The difficulties begin

As usual, there are problems with all wires, however this is particularly true of nerves, and the problem nerves face is that current leaks out.

nerve-current-leaking-out

Fig 1. Diagram showing longitudinal and membrane resistance in a nerve.

In the diagram above (Fig 1.), RL (red line) is the longitudinal resistance and it is a measure of the resistance the current encounters as it travels along the nerve. The lower this resistance, the easier it is for the current to travel.

Rm (blue line) is the membrane resistance and this is a measure of the resistance given to the current by the cell membrane. The higher this resistance, the less current will escape.

How far can a nerve conduct?

Voltage decreases exponentially, meaning it leaks less.

The distance at which the voltage has decreased by half is called lambda (λ), and it is a ratio of the two resistances aforementioned. In effect, it is a ratio of how much voltage continues travelling along the nerve to how much has leaked out.

λ=√Rm/√RL

This means that high membrane resistance and low longitudinal resistance results in a good signal.

We must also remember that resistance is calculated by:

R = p x l/A

Where:

  • R is resistance
  • p is resistivity
  • l is length
  • A is cross-sectional area

Application

Nerves are very narrow as they normally have a diameter between 0.2 to 2.0 micrometres, meaning that RL is large.

The cell membranes are also very thin, typically between 7.0 to 9.0 nanometres, so Rm is small. This is due to the fact that the membrane is made of two molecules – specifically two phospholipids, as cell membranes are bilayers.

In addition, the axon, which is mainly cytoplasm, has a resistivity of 50 ohm.cm. To put this into perspective, copper wires have a resistivity of 1.7×108 ohm.cm. The poor axon resistivity is because, since nerves are part of the body, they have to be able to change shape, which is the advantage of a conducting liquid.

As a result, a 1 metre long, 1 micrometre diameter nerve has the same resistance as a 22-gauge copper wire, which in other words is a 0.65 nanometre diameter piece of copper stretching to Saturn and back. Five times.

A much-needed rescue

To put it nicely, nerves are probably not the material you would be reaching for if you wanted to transfer some current. As a result of their physical properties of being narrow, thin-walled and not very conductive, their resistance is high, and even non-physics students know that this is not ideal for conducting electricity.

After reading all of this, I’m sure your question is: how are we still alive? This was my question too.

Thankfully, nerves have some tricks up their sleeves, something similar to pulling a rabbit out of a hat.

Myelination

One of these features is myelination of the nerve fibre. The myelin sheath increases the membrane resistance and it means that the signal can travel 3 millimetres more. However taking into consideration that the length of a nerve fibre running from your foot to the central nervous system can be around 1 metre, in the grand scheme of things, 3 millimetres are not that helpful, although certainly much appreciated.

Amplification

The real show stopper trick and literal life saver is the nerve’s power of amplification. This process keeps allowing ions to enter the nerve cell by sodium gated voltage channels in order to sustain the voltage. This makes the signal bigger, as when the channel opens, more positive sodium ions enter and this increases the concentration gradient, as there is more positive charge. Furthermore, the channel is also charged, meaning it moves if voltage changes. This means the channel itself detects a change in the voltage and is able to react to make it greater. Figure 2 demonstrates this process.

amplification-in-nerves

Fig 2. Graph showing the effect of amplification [1].

Problems persist

Because the amplification process requires sodium channels, and channels are required to stimulate pain, the myelin sheath cannot be too thick, as otherwise the sodium channels could not be present, meaning the effect of myelination is not at its highest potential, as it needs to compromise with the other processes.

Moreover, the transmission takes time because the passive movement of the signal (i.e. when the signal is not aided by amplification) is still faster than the active movement (the points where amplification takes place) since the amplification process, as we now know, involves sodium channels opening, moving and opening again, which overall is time consuming. 

In addition, there is also the factor of positive feedback. The main idea is that it is triggered by something that it causes and so it is an all or nothing response. What this means is that as one sodium channel opens, then more will open. If the stimulus is not powerful enough, then nothing happens, so the stimulus must be greater than the threshold.

Conclusion

Overall, the structure of the nerve results in it being a poor conductor, however it is because of features such as myelination and amplification that we are still here today, reading this biology blog post.

References

As I have mentioned before: this post has been written from my notes which I took during the lecture: “How do nerves work?” as part of the Medicine Taster Day at Cambridge University. The information is from the lecturer given on the day: 5Th November 2016.

Diagrams:

[1] http://www2.sluh.org/bioweb/apbio/studysheets/ss_nerves_muscles_and_movement.htm

With thanks to:

·Cambridge University for organising the taster day and to the lecturer for providing the fascinating information.

·Miss Lasouska who kindly read this post.

The Misconception of Unset Jelly

As an experimental cook, the conventional fruit which are set in jelly on top of a cake are not good enough. So, fuelled by the desire to find the most original combination of fruit that could adorn a cake creation whilst smothered in jelly, I managed to find a few unusual possibilities, until I met my nemesis: fruit, which no matter how long the jelly sat in the fridge, prevented it from setting.

This post looks at why, and the slight misconception which surrounds the idea that some fruit prevent jelly from setting.

An Introduction to Gelatine

What is gelatine?

Gelatine is a mild tasting protein that is derived from collagen in animal tissue, which in turn is a hard, insoluble, fibrous protein [1]. Collagen is the connective tissue protein that provides strength to muscles and tendons and resiliency to an animal’s skin and bones, meaning that in humans it makes up one third of the total protein content [1]. Furthermore, since it is a structural protein, collagen is found in many parts of an animal’s body as it helps to maintain the structure and shape.

Where does gelatine come from?

Most gelatine is manufactured from pig skin because around 30% of its weight is collagen [2]. Firstly, the pig skin is soaked in dilute hydrochloric acid for roughly 24 hours. This step leads to the unravelling of the crosslinking protein bonds in collagen, resulting in the free protein chains then being extracted. These are filtered, purified and dried into sheets or granules (powder) that contain around 90% gelatine, 8% water and the remaining 2% is salts and glucose [2].

How does gelatine work?

Gelatine has claimed the prize of being different to all other proteins typically used in a kitchen setting, partially because it is the only protein that has the power to thicken liquids. This is why gelatine thickened sauces are ‘crystal clear and syrupy’ rather than opaque and creamy like sauces which use starch or flour as the thickening agent [2]. Gelatine’s unique properties arise from that fact its response to heat is not one that is usually demonstrated by proteins. Normally, food proteins respond to heat by unravelling (meaning they lose their tertiary and potentially secondary structures), and then bonding to one another to coagulate into a firm, solid mass. This is demonstrated by an egg frying since the albumin (liquid protein of the white) firms up into a solid mass of egg white as it is heated. However, gelatine proteins do not readily form bonds with one another, meaning that although heat initially causes them to unravel and disperse like any other protein, the gelatine proteins never form new bonds. This results in the liquid that they are dispersed in remaining as a fluid. Furthermore, because gelatine proteins are also long and stringy, they tend to become interwoven and this leads to the hot liquid in which they are suspended to thicken, although not completely solidify when warm. As the gelatine gradually cools down, the protein strands line up next to each other and twist into long ‘ropes’ and turn the liquid into a firm gel [2].

Plot Twist from an Innocent Addition

Learning from my past experiences, the following fruit should not be added if you wish for your jelly to achieve its intended state:

  • Pineapple
  • Kiwi
  • Figs
  • Papaya
  • Pawpaw
  • Mango
  • Guava
  • Ginger root

There are, as always, some exceptions to this rule, however I will come onto this later.

An unexpected culprit

You may have noticed that some of the aforementioned fruit are quite acidic, such as kiwi, and for me, initially, this was why the jelly did not set. However, it was as I did more research that I realised this was not the case.

As far as I am aware, when we study enzymes at school, whether at GCSE or A Level, enzymes seem to take on the role of the keys to existence, the Gods of all things bright and biological, or words to that effect. Or an effect slightly less exaggerated.

And yes, I do not dare disagree with the importance of their function as biological catalysts, whether it be in the baby food industry, slimming food industry or even saving the world by being a part of biological washing powders which require a lower temperature.

However, enzymes are the reason behind your cake masterpiece having a ‘soggy top’ as a result of the jelly not setting, which would lead to a piercing ice-blue stare from Paul Hollywood himself, an ‘It’s a little informal’ comment from the Queen of baking, Mary Berry, and may even provoke Shakespeare’s ‘God has given you one face, and you make yourself another’ exclamation.

Why are enzymes the downfall of jelly?

The listed fruit contain enzymes, in particular, proteases. Pineapple, kiwi, papaya, pawpaw and mango all contain actinidin, papaya and pawpaw also contain papain, pineapple also has bromelain, figs contain ficain and ginger contains zingibain.

The reason that jelly sets is because the collagen proteins in the gelatine form a tangled mesh as a result of being interwoven, meaning that water molecules are trapped, as well as other components of the liquid, and this provides the gelatine its semisolid state when it cools [3].

gelatine-structure

Fig 1. The long gelatine molecules as seen in set jelly [4].

The proteases in the fruit act on gelatine protein, and this can be thought of as the proteases acting as scissors and ‘cutting up’ the long strands of gelatine protein into smaller pieces, so that they can no longer interweave and create a network to trap water and other liquid molecules, meaning the jelly does not set [4]. This is shown in figure 2 and figure 3.

enzymes-acting-on-gelatine

Fig 2. Scissors representing enzymes (proteases) acting on gelatine [4].

shorter-gelatine-molecules

Fig 3. Shorter gelatine molecules after protease action [4].

In addition, it is important to note that pineapple and kiwi contain far more proteases than the other listed fruit. The reason for this difference is unknown, however it may be linked to the idea of repelling pests. As a basic concept, animals and bacteria are made up of proteins meaning that essentially the high levels of proteases in the fruit will digest any of the pests trying to feed on the fruit [4].

Moreover, I should address the exception that I mentioned earlier in the post. The fruit has to be fresh in order for it to ‘rain unset jelly on your cake parade’. For example, canned pineapple will not ruin your showstopper. This is because during the canning process, the pineapple is heated to kill bacteria so that the pineapple can be in the can for a long period of time and not decay [4]. This process also denatures the enzymes which means that they no longer act on the gelatine protein and prevent the jelly form setting. The high heat causes the bonds in the protein of the enzyme to vibrate meaning the bonds break (hydrogen bonds break first). Since hydrogen bonds are an essential part of the tertiary structure of the protein (which create a fibrous chain or globular chain) and the secondary (which is responsible for the protein either being an alpha helix or beta pleated sheet), the two structures of the enzyme are lost. This results in the active site of the enzyme no longer being complementary to the substrate (the gelatine protein molecule), so that no enzyme-substrate complexes form, meaning the gelatine is not catabolised. As a result, the jelly sets in its normal fashion.

Overall, for me the misconception lies in the fact that the fruit which should not be added fresh are rather acidic, especially kiwi. This always seemed to mean that it is the acidic conditions that the prevent the jelly from setting rather than the presence of certain enzymes.

References

[1]   http://www.medicalnewstoday.com/articles/262881.php

[2] http://www.finecooking.com/item/63379/the-science-of-gelatin

[3] https://www.scientificamerican.com/article/bring-science-home-fruit-gelatin/

[4] http://www.thenakedscientists.com/HTML/experiments/exp/science-of-fruit-jellies/

Other websites used

http://chemistry.about.com/od/foodcookingchemistry/a/foods-that-ruin-jell-o.htm

https://en.wikipedia.org/wiki/Actinidain