Posted in science

Why do leaves change colour?

The changing colours of the leaves is many people’s favourite part of autumn – the gorgeous hues are pretty much synonymous with the changing of the seasons. There is so much variation as well; many trees display a wide array of yellows, golds, oranges, reds and everything in-between. So, what causes this transformation to occur?

As the days get shorter and darker, there is less light intensity falling on the leaves of trees. This reduced light intensity initiates the breakdown of chlorophyll, a green pigment which is responsible for absorbing light to facilitate photosynthesis. As the chlorophyll begins to break down and be removed from the leaves, other pigments start to become visible. Funnily enough, it is these secondary pigments that cause the vibrant (and picturesque) autumnal colours. The main compounds which are revealed are xanthophyll, carotene and anthocyanins. Xanthophyll and carotene are responsible for the more orange shades, and any red colours are attributed to the anthocyanins.

At the same time as the chlorophyll is being broken down, a specialist layer of cells named ‘cork cells’ build up at the base of the leaf. These cells shut off the veins in the leaf from the rest of the tree, forming a leaf scar which protects the overall plant when the leaf is eventually severed.

The overall colours of the leaves are determined by a combination of environmental factors. Light intensity, temperature and the abundance of water all play roles. For example: the colder the temperature, the redder the leaves. This is due to the anthocyanins being more visible.

Currently there are two main theories as to why leaves change colour; photoprotection and coevolution. The idea behind the photoprotection theory is that as the chlorophyll breaks down and exposes more anthocyanins, they are then able to protect the leaves from damage caused by high light intensity at low temperatures. This helps to reduce photo-oxidation and photo-inhibition, therefore (theoretically) making the reabsorption of nutrients more efficient.

The coevolution theory states that the brighter red the leaves turn, the more toxic the tree is to certain types of insect. This would act as an indicator to the creatures affected, reducing the parasite load of the tree for the onset of winter. Equally, the vibrant colours could attract certain types of insect or bird. This said, neither of these theories has been fully proven, and neither of them provide a justifiable explanation as to how the colour change links to the inevitable dropping of the leaves.

So, to conclude: the fantastic autumnal colours of leaves are produced as chlorophyll breaks down, and no one fully understands why this occurs.

Tabitha Watson

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Posted in science

Smoking – how fast will it kill you?

As of 2015, around 19% of the adult population in the UK were regular smokers, and 1.1 million people labelled themselves as social smokers. Assuming that these are two separate groups of people, that means that 13497621.79 people in the UK smoke. Now, it’s pretty common knowledge that smoking is bad, but what does that actually mean? How ‘bad’ is bad, and how quickly do the negatives take effect?

One of the most well-known effects of long term smoking is, of course, cancer. More specifically, lung cancer (although other areas such as the bladder, kidneys and liver can also be affected). The cancers are caused by structural damage in the DNA of cells. This structural damage then triggers mutations, which can be malignant. This damage and the resultant mutations has been linked to tiny chemicals called polycyclic aromatic hydrocarbons by researchers at the University of Minnesota. When they enter the body, they are able to form metabolites that then attack cells and cause irreparable structural damage. Studies have shown that the concentration of these metabolites in the body peaks between 15 and 30 minutes after the first inhale, meaning that the damage begins to occur almost immediately.

Recent research conducted by the Los Alamos National Laboratory in New Mexico has managed to quantify just how fast these harmful mutations occur. According to their data, every 50 cigarettes carries with it the potential for one serious (i.e. cancerous) mutation. On average, a heavy smoker would consume approximately 20 cigarettes a day. If this is multiplied out, that’s 140 a week. If this is extrapolated again, it can be assumed that they would smoke, on average, 7280 cigarettes in a year. This means that each smoker will experience roughly 145.6 serious mutations per year, and whether or not they are cancerous is completely up to chance. Think Russian Roulette, but with lung cancer.

Scarily, once these changes to the DNA have been made, they cannot be reversed. No amount of avocado and kale smoothies can erase the permanent cellular damage. However, all is not lost. A 50-year-long study of smokers and their habits has recently been concluded by researchers at the University of Oxford, and their findings are fairly positive. Despite smoking knocking approximately 10 years off a person’s average lifespan, if smokers quit before the age of 30 then the risk of dying prematurely is ‘virtually eliminated’.

So, in conclusion, quit while you’re ahead.

Tabitha Watson