Ever since the early days of human space travel, back in the 1960s, astronauts have run experiments involving plants in space. Over a million seeds of rocket (two kilograms of rocket seeds) are shortly due to take off from Florida, bound for the International Space Station, as part of British ESA astronaut Tim Peake’s six-month Principia mission.
Experiments have so far shown how plants respond to very low levels of gravity. Germinating seeds send their roots towards the pull of gravity and their shoots away from it, even when its tug is 10,000 times weaker than on Earth. Plants actually feel which way is up!
The ISS being fully operational, international space agencies can now study the effects of radiation and weightlessness on plant life in precisely controlled conditions.
Light and Plants
In green plants, both photosynthesis and respiration occur. Photosynthesis is a natural process whereby plants and other live organisms convert light energy from the Sun, into chemical energy that can be later released to fuel the organisms’ activities. This chemical energy is stored in carbohydrate molecules, such as sugars, synthesised from carbon dioxide and water.
Oxygen is normally released as a by-product of the chemical reaction that takes place. Photosynthesis maintains atmospheric oxygen levels and supplies all of the organic compounds and most of the energy necessary for life on Earth.
In relatively bright light, photosynthesis is the dominant process (meaning that the plant produces more food than it uses during respiration). At night, or in the absence of light, photosynthesis essentially ceases.
Under such conditions, the plant consumes food (for growth and other metabolic processes). Respiration is the dominant process.
Aerobic respiration requires oxygen O2 in order to generate ATP – Adenosine Tri-Phosphate, often called the “molecular unit of currency”, a nucleotide used to transport chemical energy within cells for metabolism. The products of this respiration process are carbon dioxide and water.
The level of photosynthetic activity in a green plant can be estimated by placing the plant inside a sealed container and measure the rate at which oxygen is produced. When such an experiment is performed, it is found that increasing the brightness (intensity) of the light increases the rate of photosynthesis, but only up to a certain point, beyond which increasing the brightness of the light has little or no effect on the rate of photosynthesis.
Conversely, reducing the brightness of the light causes a decrease in photosynthetic activity. The light intensity at which the net amount of oxygen produced is exactly zero, is called the compensation point for light. At this point, the consumption of oxygen by the plant due to cellular respiration is equal to the rate at which oxygen is produced by photosynthesis.
The compensation point for light intensity varies according to the type of plant, but it is typically 40 to 60 W/m2 for sunlight. The compensation point for light can be reduced by increasing the amount of carbon dioxide available to the plant, allowing the plant to grow under conditions of lower illumination.
For this reason, special techniques need to be developed to increase yields in space. If the response to light is decreased, will the plants behave and grow in the same way as they do on Earth? If we colonise the Moon or Mars, would we be able to cultivate crops in the same way?
Survival of the Species
Each astronaut on the ISS requires 5kg of food and water everyday, according to the European Space Agency (ESA). They receive regular supplies from Earth.
“The human race is expanding and exploring further and further afield and one day – we don’t know when – we will have human beings exploring the rest of the Solar System. It takes a long time to get to the other planets and this means we will have to be able to provide food for astronauts on long duration missions and the only way to do that is to grow it,” Tim Peake told BBC News.
Turning Half a Million Students into Space Biologists
After spending several months on board the ISS, the rocket seeds will return to land in the Pacific Ocean in the spring of 2016. After returning to the UK, the space rocket seeds will be packaged up with batches of identical seeds that have remained on Earth.
The rocket seeds will then be distributed to 10,000 schools where students will use them in scientific experiments and ultimately find out whether their six-month stay in space affected them at all. They will plant the seeds that have been in orbit, and compare the growth of rocket leaves with normal plants.
Participating schools will each receive two packets of 100 seeds to grow and compare, and a collection of fun and inspiring curriculum linked teaching resources and posters, tailored according to the age of your pupils (Key Stages 1 and 2 or Key Stages 3, 4 and 5).
The Royal Horticultural Society and UK Space Agency will run the experiment. The mission is called ‘Rocket Science‘.