 What minor materials they use? Well, I have a list in here, as my memory is not perfect. Plants, like humans, require things like vitamins. For example, we require trace amounts of cobalt for vitamin B12. It's not something we think of on our diet, but we have to have it there. And plants are the same. They also require cobalt. Other micronutrients that they need are boron, chlorine, copper, iron, manganese, molybdenum and iron. It's interesting to think about iron to start with. You don't really think about living iron in plants. There aren't any obvious iron compounds, but funny enough, they need it to synthesize chlorophyll. And so if you don't give them a trace amount of iron in their diet, they go yellow and they die. Which is unfortunate for the plants anyway. So another one, of course, that they need is magnesium. Magnesium is the iron in the middle of the chlorophyll molecule that vibrates and absorbs the light energy and makes chlorophyll look green. So without magnesium, they wouldn't be able to photosynthesize as much. There are substitutes. There are some chlorophylls that don't require magnesium. But it remains the most common trace element that they require. One thing about iron, of course, is that it's a very common element. And you would wonder why a plant would ever have any trouble getting it. But because they absorb everything through their roots and then it interferes with the uptake through the root stops them getting iron. So, for example, if they grow on limestone and the pH is too high, then the iron comes in forms that are in soluble and the plant can't take them out. Iron is also a very limiting nutrient in the oceans. If you look out into the oceans, there's almost no iron in solution at all. And that limits the growth of the phytoplankton, the small floating plants in the middle of the ocean. And in fact, there'd be many experiments with seeding the ocean with soluble forms of iron to encourage phytoplankton blooms. If nothing else, it means possibly taking out carbon dioxide from the atmosphere. And you can see that reflected that necessity for iron when you look at the relationship between falls of dust from the land and the way the phytoplankton grows. There are another one that they require in some amount is phosphorus. Phosphorus is the common, what would you call it, the battery of life in organisms. Almost every energy process requires phosphorus. So of course we know particularly about ATP, which our body burns all the time decomposed into ADP and phosphate. And that gives off the energy that drives our muscles, that makes our brain work and everything else. And it's the same for plants. They also use ATP to drive their photosynthetic processes.