Plants are everywhere. Ever noticed something about their colour? Yes, most of them are green.

Have you wondered why are plants green? Like why not orange or blue?

Utsuka and Jigyasa had the same question, too! Join them in this episode to know exactly why plants are green.

In our Ask A Scientist segment, listen to Gitanjali Yadav, who studies plants using computers! If you want to learn more about her work, check out her website.

To get instant updates on all the upcoming episodes of IndiaAsksWhy, follow IndiaBioscience on Spotify.

You can send your questions to Utsuka and Jigyasa at indiaaskswhy@​gmail.​com, or join their Telegram group for updates and fun science discussions.

Join Utsuka and Jigyasa as India becomes more curious, one question at a time!

Podcast duration: 12 min 54 sec

Stay tuned for more updates from IndiaAsksWhy!

Utsuka — U, Jigyasa — J

Transcripts with Timestamps

[00:08] U & J: Hi everyone! I am Utsuka. I am Jigyasa and you are listening to ​‘India Asks Why?’ a science podcast supported by India Bioscience. Where we do the research for you to get smarter. Join us as India becomes more curious. One question at a time!

[00:35] U: Plants are everywhere and most of them are green. But wait. Have you ever paused and wondered why that is the case? Like why aren’t all plants blue in color? Utsuka & Jigyasa have had the same question too. So join them to know why plants are green.

In the second segment, both of them get to ask their questions about why plants are green to Dr. Geetanjali Yadav, who is a plant scientist and a computational biologist at NIPGR, India as well as at the University of Cambridge. Not only that, they get to hear about the origin of photosynthesis and learn about her computational biology work and get a peek into what else a scientist does other than actually doing science. So stay tuned!

[01:36] J: Uff! It’s getting so sunny these days. I can’t even look up without the sunlight piercing my eyes. I wonder, how plants stay in the scorching sun all day?

[01:49] U: Oh Jigyasa! Plants need sunlight to prepare their food. They photosynthesize, meaning they convert the sun’s energy to food. If you remember from your science class there is a pigment called chlorophyll that absorbs light energy.

[02:06] J: And it is green in color? That’s why plants have a green color. Right? But hold on. My question is, why is chlorophyll green in color?

[02: 21] U: That’s an interesting question. As we know, visible light is made of seven colors, the colors of a rainbow. The color that we associate with something is the color that it reflects. A banana looks yellow precisely because it reflects yellow and absorbs other colors. If something absorbs all the light from the same, it looks black.

[02:43] J: Oh! That makes sense. Plants are green precisely because they reflect the green light. But this still doesn’t answer my question. Why does chlorophyll reflect green light?

[02:55] U: To answer that question, we need to go back to the sun. So the most energy radiated by our sun is the green light of the visible spectrum.

[03:07] J: Sooo, wait! More energy means more food. So wouldn’t it be a good idea for plants to absorb all the green energy and for that matter absorb all the energy from the sun?

[03:18] U: Well Jigyasa, More energy is not always better. In this case, the plants cannot handle such situations of intense green light very well. So for example, the clouds might block the sunlight or there could be a sudden shade. Unlike us, they can’t just move to catch the sunlight, you see. So this sudden presence and absence of green light can lead to a sort of short circuit in the chlorophyll’s home.

[03:49] J: Is this like the short circuit in our homes when there is a power fluctuation?

[03:56] U: Exactly. So what do these plants do? They play safe. They just reject some green light and mainly work with blues and reds which are at the ends of the visible spectrum. So these blues and reds are less intense and comparatively more stable than the green.

[04:10] J: Wow! That’s interesting. I wonder how the plants develop this strategy?

[04:15] U: Well obviously they didn’t come up with this overnight. It took them millions and millions of years of evolution to come to where they are now.

[04:27] J: And now it’s time to ask a scientist.

[04:32] J: Welcome back! We now have Dr. Geetanjali Yadav online to answer some of our questions. Utsuka, ask away!

[04:40] U: So Dr. Yadav, even though most plants are green some aren’t. Why is that?

[04:47] G: As far as plants go, the color green is essentially the color of chlorophyll as we know. But the main point for you to know is that greenness is related to photosynthesis. It is literally like the plants take sunlight and water and they split the water to create sugars, and carbohydrates. So that means you can just make food out of clean air. So the plants that are not doing photosynthesis are not green. So the plants are green as well as non-green. There are many non-green plants such as the ghost plant in India which is also completely devoid of pigments. So there are pigments and the presence and absence of the pigment decide the color of the plant.

[05: 32] J: So going a little backward in time, how did the plants evolve to photosynthesize? Like did they evolve from a green ancestor?

[05: 42] G: So photosynthesis, you have to basically think about the origin of photosynthesis which is not in plants at all. Plants never began photosynthesis. Photosynthesis began in the oceans. And it began with bacteria. The first time when oxygenic photosynthesis began was in these people called the cyanobacteria, blue-green algae. They began oxygenic photosynthesis which means when you are splitting a water molecule, it splits into two molecules of oxygen. And that moment of time or that single evolution of that single reaction, the oxygenic photosynthesis changed the phase of the earth that led to the evolution of so many other kinds of organisms, most important plants. So chlorophyll was the one that couldn’t accept green. Chlorophyll has this particular chromophore inside it that cannot take the green. Because it can’t take the green, or because it can’t absorb green light, it throws it back out. And so you see only green. And lichen and moss and everybody was visible only green because they were having chlorophyll.

[06: 44] U: You study photosynthesis in the lab, right? How do you study and what test does it involve?

[06:50] G: The major reaction that we are interested in is photosynthesis and in photosynthesis, we are particularly interested in looking at the efficiency of photosynthesis and how it can be improved. We grow clammy in the lab. We call it clammy, we grow it in test tubes and our job is to be able to visualize it first of all through a microscope. We do a lot of microscopy-based experiments but we are also interested in what are the genes that get switched on at night, and during the day. How does the plant know, when it is morning when it is dusk when it is dawn, pre-dawn, nighttime, everything? So we grow these clammy in the lab and during different points in time, during day and night, every hour literally; we stop the growth, immediately extract the DNA and the RNA, and then we sequence it, and then we do a lot of data analysis with it. That’s how we study these.

[07:45] J: So does that mean you spend a lot of time with your microscope as well as on your laptop analyzing all that data?

[07:53] G: The microscopy work is not something you can do in a short bit. So that is done by my students and some of them are full-time sitting on the microscope. So there are different people assigned to different tasks as you would have in a scientific laboratory and we all work together. So that you know we are able to find the patterns that we are searching for.

[08:13] U: So Dr. Yadav, what does a typical day in your life look like?

[08:19] G: So if you just take a typical day with me. So I may have different meetings with my students, collaborators, and my colleagues in funding agencies during the day. But I prefer to keep some time for teaching, at least 2 hours for teaching and I also prefer to keep some time for research. During that time of research, I do mostly writing papers, thinking about new ideas, and trying to understand what our results have been. As a scientist, I have discovered that you are not really that white lab coat-wearing rat who is doing benchwork and experiments all the time or now the time teaching, yes. That’s not what it is. As a scientist, I find myself to be the manager of a small-scale company. We need funds. We need to be able to run the lab, pay the people who are working for us, buy new equipment for them, be able to send them out, be able to publish their papers, pay for the charges and sustain the lab. So you have got to be a corporate sector manager. To a large extent, it’s like being the CEO of a company. My own little, small holder company which I have in the lab. But that’s critically important. So that’s a very complicated business on a day-to-day level.

[09:38] U: What’s your message to someone who is interested in a career in science?

[09:45] G: So if you are interested in a career in science, please make sure that you put aside some time in your life, in your day to ask yourself, ​“what are the questions that are unanswered?” just look outside, anywhere around you… is there a question that is unanswered that science has not yet been able to answer? I had questions when I was growing up. I used to be in the forest most of the time and I used to wonder why trees and leaves have such different shapes. And why don’t trees, all of them, have the same kind of canopies? Ask as many questions as you can. Even if you can’t ask your teachers, ask yourselves those questions. Because you will remember them later in life and maybe you will be the one finding those answers, right? So that’s for a career in science, I think.

[10:37] U: So now Jigyasa, do you understand the reason behind why all plants are green?

[10:43] J: yes, plants have evolved to use the red and blue light at the end of the spectrum and they reflect the green light. They do this to prevent short-circuiting in the photosynthetic machinery. Dr. Geetanjali studies one such machinery in microbes. She says plants evolved from photosynthesizing microbes in the ocean which were already green long ago. Her lab generates gigantic amounts of data on the genes which regulate photosynthesis and they use computers to make sense of all that data.

[11:16] U: …and we learned that being a scientist is kind of like being the CEO of a company.

[11:25] J: But listeners, what we know about the plants might change when we get more evidence with time.

[11:33] U: Who knows, in the future, you might be the one who will be studying these plants and you will find out something that we never knew before…

[11:40] J: So… stay curious

U & J: And ask questions!