Plants are Clever, 3

Plant metabolism

David Beeson, 24th November 2020

Posh words, like metabolism, frighten some folks. Not you, I’m certain. This word just means the total chemistry inside an organism. And we, plants and even our friend Covid-19 are bundles of chemicals, and they all work via chemical reactions. Yup, you and me are bags of chemistry. If the chemistry goes wrong, we are ill or die.

The study of body chemistry is called biochemistry, and that was my degree. I hated it! It never made sense … which is why I spent much of my life teaching it. Surely, I could do better than my university.

Bios = life, so, biochemistry – the chemistry of life.

Green plants trap carbon dioxide and water using sunlight energy and make things, chemicals, such as glucose.

Energy being the critical word, above.

Animals would start the diagram above from their food, rather than photosynthesis … the end products of digestion, releasing chemicals such as glucose.

In order to grow, an organism, plant, animal or virus, needs to make new chemicals. Building new chemicals is called ANABOLISM. *1 on the diagram. And we all know that making things needs energy.

That energy comes from breaking chemicals down, CATABOLISM. * 2 on the diagram.

So we have an equation: anabolism + catabolism = metabolism.

In a conventional power station we ‘burn’ (catabolism) coal or oil (both energy-rich) to make energy-rich electricity, which we use to make or do things (anabolism).

In organisms the equivalent of the electricity is an energy carrier, abbreviated to ATP. The organism’s energy currency. *3 above.

If the organism runs out of ATP, it is dead.

In most situations the anabolic reactions of making the ATP is called RESPIRATION. Take some cyanide and it stops respiration … and you know the result. No ATP, no life. But, there are lots of catabolic processes. Some need oxygen, some do not – e.g. fermentation to make alcohol needs no oxygen.

Clever, isn’t it.

BUT, organisms need other things in anabolism. To make bones, humans need calcium. Blood needs iron. Plants cannot live only from the outputs from photosynthesis. They need calcium to make cells stick together, iron and magnesium for chlorophyll and nitrates to make DNA, amino acids and proteins. In most plants these inorganic / mineral extras come from the soil. And many folks add fertilizers to ensure these are not in short supply, and limit growth. Me, seldom, as I prefer to add compost or mulched wood.

Ah, but some plants live where the soil is deficient in these extras. They grow in water-logged peaty soils … bogs. So, obtain their extras from capturing and digesting other living organisms, that have these chemicals. These are the CARNIVOROUS PLANTS.

Oval-leaved sundew in a bog near Wareham.

Some books call this type of plant – insectivorous, but they consume anything they can grab – including, in big plants, mammals. In the UK we have: sundews, butterworts and bladderworts. Elsewhere there are pitcher plants and the wonderful Venus fly trap.

The capture mechanisms are all clever diversions from the basic plant design to obtain their anabolic extras. And the ability to find these ‘little extras’ determines which plant lives where, as soil pH also influences mineral availability. Alkaline soils have a different spectrum of available minerals than a neutral or acid one. Different soil pH, different ecology.

Round-leaved sundew
Chasser prairie in Okefenokee Swamp, Georgia, USA. A stunning place with sheets of bladderworts and huge pitcher plants. Put it on your ‘to go to’ list. Amazing place.

So, now you know … a touch of biochemistry can help sort out your ecology!

Homework – look up bladderworts, you’ll not be sorry. Fascinating plants – look for them in the New Forest, Studland Heath and Wareham Forest.

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