Green is such an ever-present and widespread color in nature that it symbolizes the health and vitality of our natural world. Almost anywhere you go in springtime, you can expect to see green; from mosses and algae to all kinds of herbaceous plants and trees, green dominates our idea of natural landscapes and represents life, growth, and abundance. But why are trees and other plants green?
What makes that color so widespread?
At face value, we know that it’s because plants are green–specifically, when they are healthy and thriving. When plants are unhealthy, dying, reaching the end of their life cycle, or preparing to lose their leaves in the fall, we often see them turn yellow, brown or some other color. We only see those beautiful shades of green in living tissues.
Eating sunlight—Chlorophyll and photosynthesis
Living, healthy plants are green because of a group of greenish pigments called chlorophyll which is part of the molecular machinery that makes photosynthesis possible. Photosynthesis is a biological process that captures energy from the sun and uses it to build food molecules out of carbon dioxide (from the air) and water (often from the ground). People often call this “eating sunlight”, but it is more like “making snacks from sunlight”.
Like any other living thing on Earth, photosynthetic plants have to get food (chemical energy) to fuel their cells and stay alive. The difference between photosynthetic things like plants or algae and, for example, animals or fungi, is that they produce their own food chemicals through photosynthesis by converting light from the sun into chemical bonds that form simple food molecules—sugars. Plants digest these snacks as fuel, or store for later in more complex forms that last longer. These are usually what we call starches (think potatoes or cassava).
So, like the rest of us, plants need to get that bread. Their green color helps them do that. This green pigment is concentrated in special cellular organs called chloroplasts, and plant tissues are typically jam-packed with them, leading to that green color. The “chloro” in chloroplast and chlorophyll comes from the Greek word chloros, which describes a yellowish green.
Ok, so plants are green because a green pigment is a major component of the machinery that helps them convert light into food via photosynthesis. But that leads to another question:
Why is chlorophyll green?
Chlorophyll is a pigment, which is a chemical produced by a living organism that absorbs certain colors and reflects those that it does not absorb. This happens because pigments absorb certain wavelengths of light: without getting too technical, light is a form of radiation that travels in a wave, and our eyes perceive different wavelengths of that light as different colors.
Pigments, then, show up as certain colors to us because they are only absorbing certain colors; if they are absorbing green and blue and yellow wavelengths, then we see them as red, because that’s the color that isn’t totally absorbed. If they are absorbing all color, than the pigment would look black to us, since our eyes aren’t picking up any wavelengths of light.
Chlorophyll in plants and many green algae absorb red and blue light, but don’t absorb all of the green or yellow light that hits them. This reflects some of those wavelengths of light, which our eyes see as green.
So this gives us an idea of the mechanism that makes plants and their chlorophyll green to our eyes. But since there are all kinds of pigments in the world—think about the diversity of colors you’ve seen in nature, many of those are due to pigments!—why are plants only using chlorophylls, a set of green pigments, for their photosynthesis? Aren’t they being inefficient by leaving ‘leftovers’ when converting light to food? Isn’t all that green going to ‘waste’?
Why aren’t plants blue or green or purple?
As it turns out, a lot of the sun’s light that makes the long journey across our solar system, through our atmosphere, and to Earth’s surface every day consists of a lot of yellow- and green-wavelength radiation. We now know that most plants’ chlorophyll absorbs light mostly along blue and red wavelengths. This leaves that green behind and gives plants the beautiful color that we associate with life on earth.
Scientists have been wondering over this “wastefulness” in plants since we first understood chlorophyll’s absorption. Why waste the most abundant visible light when you could get way more light energy and produce way more food?
For a long time, we had three major explanations, which could all be true at once:
Reasons why plants might be green
- Photosynthesis originally evolved deep in the ocean where all life began, and blue light was more abundant there. This would mean that the process of turning light into food evolved around what was available. In that sense, plants don’t absorb green because they are “old-fashioned’. They woul be stuck with the legacy of their history as photosynthetic organisms. Notably, this doesn’t fully explain why they absorb red light, but this idea still holds some water.
- Nothing in nature is perfect. Nature makes mistakes! The billions of years of natural selection that led to living species is not a direct line toward perfection. Instead, it’s a wandering path of what’s good enough to succeed at any given time in an ever-changing world. This can lead to solutions that get the job done, but are not the absolute ideal. This idea also has some support. It seems very reasonable, and definitely applies to the more complete picture we have come across recently.
- Green and yellow light actually yield too much energy, which can be destructive to plants’ cells rather than helpful. Imagine trying to drink enough water if someone was pouring out an Olympic-sized swimming pool on your head. Recent research shows that this idea might be the closest thing to the truth.
So what do we know now about green plants?
In 2020, a team of engineers, physicists and plant scientists took a different look at this question. What would be the advantages of plants’ harnessing light on the edges of the hyper-abundant green-yellow light from the sun, rather than the most abundant light? They specifically focused on the photosynthetic “machinery” within the chloroplasts that harnesses light energy to build food molecules.
It’s helpful to think about this machinery as a dam or a water-mill. Water moves through a mill’s wheel, or a dam’s turbines, bringing kinetic (movement) energy. The mill converts that energy into electricity or mechanical power for grinding grain, running saws, or something else useful. The molecular “machines” inside of plants do something similar with the ‘flow’ of light energy from the sun.
The chlorophyll pigments absorb frequencies of light that they want. Next, they use that energy to change the energetic state of an electron. Then, they can use those energized electrons for useful chemical reactions. Like water through a turbine or water wheel, the electron passes efficiently down through a chain of molecules to create a series of energetic bonds. Ultimately, these create food molecules for the plant, which they consume or use to construct tissues.
The ideal sunlight diet: Managing the “light mill”
Just like a dam or a mill, having too much or too little flow is not helpful, and in fact can damage the machinery and make it difficult to use. A massive flood could wipe out a waterwheel or undercut a dam, while a drought degrade or stop up equipment.
Getting it all going again has start-up costs and is highly impractical. On a molecular level, the plants’ green machinery may be damaged by too much or too little light. This happens when excessive excited electrons react with things that the plant doesn’t want them to or when the chain of electron reactions trickles to a halt, breaking the whole process and requiring a restart.
Remember the team of scientists and engineers thinking of advantages of red and blue light? Well, they figured that maybe taking light from those “shoulder” colors meant that when the flow of light hitting leaves fluctuated, that the amount of energy gained would fluctuate less. So when shading, the movement of the sun, or even the swaying of other leaves affected the amount of light, the leaves would still have steady energy flow. The advantage was not efficiency, that is, getting as much light as possible, but stability: keeping a certain, perhaps lower, level of ‘flow’ going through their dam that is as steady as possible to keep the machinery operational.
They found strong support for this idea in existing plants. The authors also found that photosynthetic organisms like certain bacteria and algae that absorbed colors other than green did so because, in their particular life circumstances, those colors enabled them to do the same thing: hedge their bets and keep a steady flow of energy.
The bottom line
Question: Why are plants green?
Answer: Because Chlorophyll is green!
Question: Why is chlorophyll green?
Answer: Because it absorbs red and blue light, reflecting some of the green!
Question Why does chlorophyll absorb red and blue but not all green?
Answer: To keep the plant’s photosynthetic machinery healthy and working, and avoid absorbing too little or too much energy
If you think about it, this is a pretty beautiful lesson in nature: sometimes reliability is the best option; finding the absolute best performance may often come at a loss but settling for a little less can come on out on top in the long run.
Thanks for reading why are trees green!
Do you have plant questions you’d like to see answered on Gulo In Nature? Send me a message or comment below!
Kijani ni rangi ya kawaida na ya kawaida katika mazingira, na ni ishara ya afya na nguvu ya mazingira. Karibu kila mahali unapoenda wakati wa majira ya kuchipua, unaweza kutarajia kuona kijani kibichi; kutoka mwani na mwani hadi aina zote za mimea na miti, kijani kibichi huongoza wazo letu la mandhari ya asili na inawakilisha maisha, ukuaji, na wingi. Lakini kwa nini miti na mimea mingine ni ya kijani? Ni nini kinachofanya rangi hiyo iwe maarufu sana? Kwa thamani ya uso, tunajua kwamba ni kwa sababu mimea ni kijani - hasa, wakati wao ni afya na kusitawi. Mimea inapokuwa na afya mbaya, ikifa, ikifikia mwisho wa mzunguko wake wa maisha, au ikijitayarisha kupoteza majani yake wakati wa vuli, mara nyingi huanza kuwa na rangi ya manjano, kahawia au rangi nyingine. Tunaona rangi hizo maridadi za kijani-kibichi tu katika tishu zilizo hai. Chlorophyll na photosynthesis: Mimea ya kijani kibichi na yenye afya ni ya kijani kibichi kwa sababu ya kikundi cha rangi ya kijani kibichi inayoitwa chlorophyll ambayo ni sehemu ya mashine ya molekuli ambayo inafanya photosynthesis iwezekanavyo. Photosynthesis ni mchakato wa kibiolojia ambao huchukua nishati kutoka kwa jua na kuitumia kujenga molekuli za chakula kutoka kwa kaboni dioksidi (kutoka hewani) na maji (mara nyingi kutoka ardhini). Mara nyingi watu huita jambo hilo "kula mwanga wa jua", lakini ni kama "kufanya vitafunio kutokana na mwanga wa jua". Kama viumbe wengine wote walio hai duniani, mimea ya fotosynthetic inahitaji chakula (nishati ya kemikali) ili kuchochea chembe zao na kubaki hai. Tofauti kati ya vitu vya photosynthetic kama mimea au mwani na, kwa mfano, wanyama au kuvu, ni kwamba wao kuzalisha kemikali zao wenyewe chakula kupitia photosynthesis kwa kubadilisha mwanga kutoka jua katika vifungo kemikali kwamba fomu rahisi chakula molekuli sukari. Mimea huyachoma vyakula hivyo kama mafuta, au huvihifadhi kwa ajili ya baadaye katika aina tata zaidi ambazo hudumu kwa muda mrefu zaidi. Kwa kawaida, hizo huitwa starches (fikiri viazi au manioc). Kama ilivyo kwa wanadamu wengine, mimea inahitaji chakula. Rangi yao ya kijani huwasaidia kufanya hivyo. Pigmenti hii ya kijani huhifadhiwa katika chembe za kipekee za mwili zinazoitwa chloroplasts, na kwa kawaida tishu za mimea hujazwa na rangi hiyo ya kijani. Neno "chloro" katika kloroplas na klorofili linatokana na neno la Kigiriki chloros, linalomaanisha rangi ya kijani-kibichi. Mimea ni kijani kwa sababu rangi ya kijani ni sehemu muhimu ya mashine ambayo husaidia kubadilisha mwanga kuwa chakula kupitia photosynthesis. Lakini hilo linaongoza kwenye swali jingine: Kwa nini klorofili ni ya kijani? Chlorophyll ni rangi ya rangi inayotokana na viumbe hai, ambayo huchukua rangi fulani na kutafakari zile ambazo hazipati. Kwa sababu rangi huchukua urefu fulani wa mawimbi ya mwanga, mwanga ni aina ya mnururisho unaosafiri kwa mawimbi, na macho yetu huona urefu tofauti wa mawimbi ya mwanga huo kama rangi tofauti. Pigmenti, basi, huonekana kama rangi fulani kwetu kwa sababu zinachukua rangi fulani tu; ikiwa zinachukua urefu wa mawimbi ya kijani na bluu na manjano, basi tunaona kama nyekundu, kwa sababu hiyo ni rangi ambayo haijapunguzwa kabisa. Kama wao ni kunyonya rangi zote, kuliko rangi ingekuwa kuangalia nyeusi kwetu, tangu macho yetu si kuchukua upanuzi wowote wa mawimbi ya mwanga. Chlorophyll katika mimea na algae nyingi za kijani huchukua mwanga mwekundu na bluu, lakini haichukui mwanga wote wa kijani au manjano ambao huwapiga. Hii inaonyesha baadhi ya urefu wa mawimbi ya nuru, ambayo macho yetu huona kama kijani. Hii inatuonyesha jinsi mimea na klorofili yake inavyoonekana kuwa ya kijani kwa macho yetu. Lakini kwa kuwa kuna aina zote za rangi duniani - fikiria juu ya utofauti wa rangi umewahi kuona katika asili, wengi wa wale ni kutokana na rangi! -kwa nini ni mimea tu kutumia chlorophylls, seti ya rangi ya kijani, kwa photosynthesis yao? Je, si kuwa na ufanisi kwa kuacha'mabaki' wakati wa kubadilisha mwanga kwa chakula? Je, si kwamba kijani wote kwenda kwa "matumizi mabaya"? Kwa nini mimea si ya bluu au ya kijani au ya zambarau? "Kama inavyoonekana, mwanga mwingi wa jua ambao hufanya safari ndefu kupitia mfumo wetu wa jua, kupitia anga yetu, na hadi uso wa Dunia kila siku unajumuisha mnururisho mwingi wa urefu wa wimbi la manjano na kijani. """ Sasa tunajua kwamba mimea mingi hufyonza nuru hasa katika mawimbi ya bluu na nyekundu. Hii inaacha kijani nyuma na kutoa mimea rangi nzuri ambayo tunahusianisha na maisha duniani. Wanasayansi wamekuwa wakishangaa juu ya "uchakaa" huu katika mimea tangu tulipofahamu kwa mara ya kwanza kunyonya kwa klorofili. Kwa nini kupoteza nuru inayoonekana kwa wingi wakati unaweza kupata nishati zaidi ya nuru na kuzalisha chakula zaidi? Kwa muda mrefu, tulikuwa na maelezo matatu makuu, ambayo yote yanaweza kuwa kweli kwa wakati mmoja: Sababu kwa nini mimea inaweza kuwa ya kijani - Photosynthesis awali ilibadilika ndani ya bahari ambapo maisha yote yalianza, na mwanga wa bluu ulikuwa mwingi zaidi. Hii inamaanisha kwamba mchakato wa kugeuza nuru kuwa chakula ulibadilika kulingana na kile kilichopatikana. Kwa maana hiyo, mimea haichukui kijani kwa sababu ni "ya zamani". Wangekamatwa na urithi wa historia yao kama viumbe wanaotengeneza mwangaza. Hasa, hii haionyeshi kikamilifu kwa nini wao kunyonya mwanga mwekundu, lakini wazo hili bado ana baadhi ya maji. - Hakuna kitu katika asili kilicho kamilifu. Asili hufanya makosa! Mabilioni ya miaka ya uteuzi wa asili ambayo ilisababisha spishi zilizo hai si mstari wa moja kwa moja kuelekea ukamilifu. Badala yake, ni njia ya kutangatanga ya nini ni nzuri ya kutosha kufanikiwa wakati wowote katika ulimwengu daima kubadilika. Hii inaweza kusababisha ufumbuzi ambao kupata kazi kufanyika, lakini si kamili bora. Wazo hili pia lina utegemezo fulani. Inaonekana kuwa yenye busara sana, na kwa hakika inatumika kwa picha kamili zaidi ambayo tumekutana nayo hivi karibuni. - Nuru ya kijani na manjano kwa kweli hutoa nishati nyingi sana, ambayo inaweza kuharibu seli za mimea badala ya kusaidia. Kwa mfano, fikiria mtu akinywa maji mengi sana, na mtu akimwaga maji ya kidimbwi cha Olimpiki kichwani mwako. Utafiti wa hivi karibuni unaonyesha kwamba huenda wazo hilo ndilo lililo karibu zaidi na ukweli. Sasa tunajua nini kuhusu mimea ya kijani? Katika mwaka wa 2020, timu ya wataalamu wa uhandisi, fizikia na wanasayansi wa mimea waliangalia swali hili kwa njia tofauti. Ni nini itakuwa faida ya mimea <unk> harnessing mwanga juu ya kingo za hyper-mengi ya kijani-njano mwanga kutoka jua, badala ya mwanga wengi zaidi? Walizingatia hasa "mashine" ya fotosynthetic ndani ya chloroplasts ambayo hutumia nishati ya mwanga kujenga molekuli za chakula. Ni muhimu kufikiria mashine hii kama bwawa au kinu cha maji. Maji husafiri kupitia gurudumu la kinu, au turbine za bwawa, na kuleta nishati ya kinetic (harakati). Kiwanda hicho hubadilisha nishati hiyo kuwa umeme au nguvu za mashine za kusaga nafaka, kusaga visaga, au kitu kingine chochote chenye manufaa. "Mashine" za molekuli ndani ya mimea hufanya jambo kama hilo na "mtiririko" wa nishati ya nuru kutoka kwa jua. Pigmenti za klorofili huchukua masafa ya nuru wanayotaka. Kisha, hutumia nishati hiyo kubadili hali ya nishati ya elektroni. Kisha, wanaweza kutumia elektroni hizo zenye nishati kwa ajili ya athari zenye manufaa za kemikali. Kama vile maji kupitia turbine au gurudumu la maji, elektroni hupita kwa ufanisi chini kupitia mlolongo wa molekuli ili kuunda safu ya vifungo vya nishati. Hatimaye, hizo hutokeza molekuli za chakula kwa ajili ya mmea, ambazo hutumia au kutumia kutengeneza tishu. "Kama vile bwawa au kinu, kuwa na mtiririko mwingi au mdogo sana sio muhimu, na kwa kweli inaweza kuharibu mashine na kuifanya iwe ngumu kutumia.""" Mafuriko makubwa yanaweza kuharibu gurudumu la maji au kuharibu bwawa, huku ukame ukiharibu au kukomesha vifaa. Kufanya yote yaende tena kuna gharama za kuanza na ni vigumu sana. Katika kiwango cha molekuli, mashine za mimea za kijani zinaweza kuharibiwa na nuru nyingi sana au kidogo sana. Hii hutokea wakati elektroni kupita kiasi excited kuitikia na mambo ambayo mmea hataki yao au wakati mnyororo wa athari za elektroni trickles kwa kusimamishwa, kuvunja mchakato mzima na kuhitaji kuanza upya. Kumbuka timu ya wanasayansi na wahandisi wakifikiria faida za mwanga mwekundu na bluu? "Walifikiri kwamba labda kuchukua mwanga kutoka kwa rangi hizo za ""mabega"" ilimaanisha kwamba wakati mtiririko wa mwanga ukianguka kwenye majani ulipobadilika, kiasi cha nishati iliyopatikana ingebadilika kidogo." Kwa hiyo, wakati giza, mwendo wa jua, au hata kutikisika kwa majani mengine kunapoharibu kiasi cha mwanga, majani bado yangekuwa na mtiririko wa nishati thabiti. Faida haikuwa ufanisi, yaani, kupata nuru nyingi iwezekanavyo, lakini utulivu: kuweka kiwango fulani, labda cha chini, cha'mtiririko' unaopita kupitia bwawa lao ambao ni thabiti iwezekanavyo kuweka mashine inafanya kazi. Walipata utegemezo mkubwa kwa wazo hili katika mimea iliyopo. Watafiti pia waligundua kwamba viumbe vya photosynthetic kama vile bakteria na mwani fulani ambao huchukua rangi nyingine isipokuwa kijani, walifanya hivyo kwa sababu, katika hali zao maalum za maisha, rangi hizo ziliwawezesha kufanya kitu kimoja: kuhifadhi bets zao na kudumisha mtiririko wa nishati. Swali la mwisho: Kwa nini mimea ni ya kijani? Jibu: Kwa sababu klorofili ni ya kijani! Swali: Kwa nini klorofili ni ya kijani? Jibu: Kwa sababu hufyonza nuru nyekundu na bluu, ikirudisha sehemu ya kijani! Swali: Kwa nini klorofili huchukua rangi nyekundu na bluu lakini si rangi ya kijani? "Kuweka mashine ya photosynthesis ya mmea katika hali nzuri na kufanya kazi, na kuepuka kunyonya nishati kidogo au nyingi sana, ni somo zuri sana katika asili: wakati mwingine kuegemea ni chaguo bora; kupata utendaji bora kabisa mara nyingi inaweza kuja kwa hasara, lakini kukaa kwa kidogo kidogo inaweza kuja juu kwa muda mrefu. """ Asanteni kwa kusoma kwa nini miti ni ya kijani! Je, una maswali ya mimea ambayo ungependa kuona kujibiwa kwenye Gulo In Nature? Nipeleke ujumbe au maoni hapa chini!