This tube contains several hundred very, very small seeds and each of these seeds contains a perfectly formed embryo. This embryo contains the beginnings of the roots, leaves and a stem and that once it sprouts, it will grow to a fully mature plant that will produce flowers. These flowers, once fertilized will produce fruits and new embryos, which will be enclosed in new seeds. How is this perfectly formed flower made? How do we get such a lovely, lovely structure and how does it survive? How did a plant convert light energy through photosynthesis into sugar? We're going to be answering these questions throughout this course. But first, we have to understand what plants are made of and all plants are made of cells and all plants like all animals start from a single cell. A single cell called an egg cell deep in this flower and deep in all flowers, once fertilized by pollen begins to divide countless times. Such that if we even look at this one small leaf here, this one small leaf contains over 100,000 cells. But these cells don't only divide, they differentiate. What I mean by differentiate is they change their size, they change their shape and they change their functions. So in the end, a root cell is completely different from a flower cell, a petal cell, but they all arose from the original embryo during embryogenesis. So if we look at this mature plant, we can divide it into two systems. There's the part that's above the ground, which is the shoot system. And below the ground, which is the root system. Two different functions. The roots function to both stabilize the plant and to absorb water and nutrients from the soil while the shoot system above the ground does photosynthesis gathers energy. And in the end, produces flowers and a next generation of seeds. But what's common to all of these organs, both the flowers, the leaves and the roots is that they are comprised of cells. And that all of these cells, as I said came from one single fertilized cell. So to understand plant biology, we have to first understand plant cell biology. And really, if we look through a plant, we have a hierarchy of organization. The cell is the basic unit of this organization and function. It is the smallest unit that is independently viable. When many cells come together, we get tissues. When tissues come together, we get an organ and then the organs form the individual such as this plant. But we can also take the individual cell and break it up into its components, such as its organelles and we're gonna learn about the structures of the plant cells later in today's class. And we can even take the various organelles and cut them up and look at the various proteins, the molecules that comprise them. So we have to look at a plant through all its levels of organization to understand the complete hierarchy. What's important to remember is that through all levels of the hierarchy, we have a very close interaction between the structure and the function. For example, the structure of this leaf being wide and spread out is to absorb light for photosynthesis. Where as the structure of the flower is to attract the pollinator, so that it can be pollinated and to make seeds. We also see structure and function at the level of the cells and we'll see the different structures of plant cells. We can even have structure function at the level of the individual molecule. For example, the molecule of chlorophyll, which absorbs light for photosynthesis has a specific structure, which allows it to absorb light. So to understand plants, we need to understand their cells and what they're made of, but how can we study plant cells?