50 Fun Facts About Photosynthesis

Which form of the process, used by plants and algae, releases oxygen?

The oxygen comes from splitting water, not carbon dioxide — a fact proved with radioactive isotopes by Ruben and Kamen.

Which pigment do plants mainly use to absorb light?

It absorbs red and blue light and reflects green, which is why leaves look green.

Why do most plants appear green?

Chlorophyll's absorption peaks are in the violet-blue and red parts of the spectrum.

In which organelle does photosynthesis take place in plants and algae?

A typical plant cell holds 10 to 100 of them, and a square millimetre of leaf interior can pack up to 800,000.

What are the stacks of flattened thylakoid discs called?

Each disc is a thylakoid; the fluid around them is the stroma, where the Calvin cycle runs.

What is the fluid that surrounds the thylakoids called?

It houses RuBisCO and the other enzymes of the light-independent reactions.

Which two energy-carrying molecules are made in the light-dependent reactions?

They power the second stage, where carbon dioxide is captured and reduced to sugar.

What is the light-independent series of reactions that builds sugars called?

Melvin Calvin, Andrew Benson and James Bassham traced the pathway using carbon-14 and paper chromatography.

Which enzyme captures carbon dioxide from the air in the light-independent reactions?

It is probably the most abundant protein on Earth, yet it is remarkably slow, fixing only 3 to 10 CO2 molecules a second.

How many carbons has the sugar to which CO2 is first attached in the dark reactions?

Ribulose 1,5-bisphosphate plus CO2 splits into two three-carbon molecules of 3-phosphoglycerate.

Roughly how many CO2 molecules per second can one carbon-fixing enzyme molecule fix?

Many enzymes manage thousands of reactions a second, which makes RuBisCO the rate-limiting step of the Calvin cycle by day.

Which of these is described as probably the most abundant protein on the planet?

It fills the stroma of every chloroplast in C3 plants.

What wasteful side reaction occurs when the carbon-fixing enzyme binds O2 instead of CO2?

It produces toxic phosphoglycolate and can lose the plant both carbon and nitrogen.

What are the pores in a leaf's surface that let gases in and out called?

The word is Greek for mouth; each pore is flanked by a pair of guard cells that open and close it.

Which photosynthetic pathway do maize and sugarcane use to concentrate carbon dioxide?

They fix CO2 into a four-carbon acid in mesophyll cells and shuttle it to bundle-sheath cells where RuBisCO waits.

Which two scientists gave their names to the C4 pathway discovered in the 1960s?

About 8,100 species, 3% of land plants, use it — but they account for about 23% of terrestrial carbon fixation.

Cacti and many succulents open their leaf pores only at night, using which pathway?

They store the night's CO2 as malic acid and process it by day, separating the two steps in time rather than space.

Which discovery in 1906 was the first detection of that element in living tissue?

Richard Willstätter's work from 1905 laid the ground for Hans Fischer to solve chlorophyll a's structure in 1940.

With what efficiency do plants typically convert light into chemical energy?

Mass-produced solar panels manage roughly 6 to 20 percent; the rest of the absorbed light is mostly lost as heat.

Global photosynthesis captures energy at about what average rate?

That is roughly eight times humanity's total power consumption.

Roughly how much carbon do photosynthetic organisms turn into biomass each year?

That is 91 to 104 petagrams, most of it by ocean plankton and land plants combined.

Who is credited with discovering photosynthesis in 1779 by showing plants need light?

He repeated Priestley's experiments and found sunlight let a plant revive 'injured' air within hours.

Which 17th-century scientist grew a willow in a pot and credited its mass to water?

The soil barely changed weight; he was half right, since much of the mass actually comes from carbon dioxide.

Which English chemist showed a plant could restore air 'injured' by a candle or a mouse?

He isolated oxygen itself in 1774, but missed the crucial role of sunlight.

Which Swiss pastor showed in 1796 that green plants take in CO2 and give off O2 in light?

Nicolas-Théodore de Saussure soon added that water, not just CO2, contributes to a plant's growing mass.

Who won the 1961 Nobel Prize in Chemistry for working out the carbon-fixation cycle?

The pathway is often called the Calvin-Benson-Bassham cycle after his collaborators.

Which organism did Calvin's team use to trace carbon fixation with carbon-14?

Within a fraction of a second of light, the CO2 turned up in a three-carbon molecule, phosphoglyceric acid.

Who first showed the process is a light-driven redox reaction, via purple sulfur bacteria?

His general equation put 'H2A' as the electron donor — water in plants, hydrogen sulfide in his bacteria.

What did Robert Emerson's experiments with red and blue light reveal?

Red alone suppressed the reaction; red plus blue boosted it, pointing to PSII (up to 600 nm) and PSI (up to 700 nm).

What did Samuel Ruben and Martin Kamen prove using radioactive isotopes?

Robert Hill's isolated-chloroplast experiments of 1937-39 had pointed the same way.

Who coined the term 'photosynthesis' in 1893?

He also offered 'photosyntax'; the winning word combines Greek for gleam and arranging together.

Which stain did Julius von Sachs use to show that sunlit leaves make starch?

A bleached leaf that had been in sunlight turned black with the stain; a shaded one did not.

Theodor Engelmann's 1882 experiment showed the light-to-energy conversion happens where?

He shone a spectrum onto algae and watched oxygen-seeking bacteria gather at the red and blue bands.

Which organisms produced the oxygen that transformed Earth's early atmosphere?

Their excess oxygen made the evolution of complex life possible.

What is the rise of free oxygen around 2,400 million years ago called?

It is also called the Oxygen Catastrophe because it wiped out much anaerobic life.

How old, in years, are the oldest fossils thought to be of photosynthetic organisms?

The first direct evidence, preserved thylakoid membranes, is younger at 1.75 billion years.

According to endosymbiotic theory, what were chloroplasts originally?

Chloroplasts still carry a circular chromosome and bacterial-type ribosomes.

Which sea slug keeps chloroplasts from the algae it eats and photosynthesises with them?

The 'eastern emerald elysia' sucks out algal cells like a straw and stores the chloroplasts in its own tissue.

What do purple bacteria split instead of water, releasing sulfur rather than oxygen?

This may have been the dominant photosynthesis in the sulfidic oceans of the 'Boring Billion'.

Which pigment do some archaea use as a light-driven proton pump?

It fixes no carbon and releases no oxygen, and may be the oldest form of photosynthesis, per the Purple Earth hypothesis.

Which pigment colours red algae and lets them use blue-green light in deep water?

Brown algae and diatoms rely on fucoxanthin instead.

What are the yellow, orange and red accessory pigments in plants called?

They colour carrots, pumpkins and flamingos alike, and absorb violet-to-green light.

What actually splits water in photosystem II?

The oxygen-evolving complex holds four manganese ions and one calcium ion.

What does the cyclic light reaction at photosystem I produce?

The electron loops back to where it started, hence the name.

Which four main factors limit the rate of photosynthesis?

Blackman and Matthaei's early-1900s experiments showed temperature affects the dark reactions but not the photochemical ones.

What process in mitochondria is essentially the reverse of photosynthesis?

Photosynthesis reduces CO2 to carbohydrate; respiration oxidises carbohydrate back to CO2 to release energy.

What is 'alarm photosynthesis' in plants like Amaranthus?

An oxalate oxidase enzyme converts the released oxalate to CO2 during drought.

Where do cacti and euphorbias, adapted to strong sun, mainly carry out photosynthesis?

Most plants concentrate chloroplasts in leaves, but arid-adapted species move the job to their green stems.

What tiny structures in some photosynthetic bacteria concentrate CO2 for carbon fixation?

Carbonic anhydrase inside releases CO2 from bicarbonate ions faster than it can escape.

Which international effort aims to give the world's top grain crop the C4 pathway?

Rice is the world's most important human food, and C4 plants like maize photosynthesise far more efficiently.