Chapter 1

Exploring Botany

IN THIS CHAPTER

Building plants one cell at a time

Finding out about how plants work

Connecting plants and people

Botany is the study of plants, including plant structure, function, reproduction, diversity, inheritance, and more. Plants may seem like they're part of the background of your life, when really they're at the center. The food you eat, the clothes you wear, the materials that make up your home - all these things depend upon plants. Plants remove carbon dioxide from the atmosphere, helping to keep your planet from getting too warm for life as you know it. They provide homes for insects and other animals, filter impurities out of ground water, and help protect shorelines from erosion.

And beyond all these useful things plants do, they're just cool! Plants have many unique strategies that help them survive in all different kinds of environments. They trap and trick insects, grow in the ground or up in the rainforest canopy, and manage to survive everywhere from the glacial arctic to the hot, dry deserts. They seem so different from people, and yet when you really look at how plants grow and function, you'll be surprised at how similar they are to you. This chapter offers an overview of the science of botany, giving you a peek into the mysteries of plants.

Taking a Close Look at Plant Structure

You might not think so, but plants are a lot like you. Their bodies are made of cells (that are organized into tissues (see Chapter 2), and these tissues form the familiar plant organs of roots, stems, and leaves (see Chapter 3). Plant cells use the same basic chemistry as your cells, storing information in DNA, using carbohydrates for energy, and putting proteins to work. And your cells and plant cells are both eukaryotic cells, meaning they have a similar structure that includes a nucleus and cellular organelles.

Plants have many ways of reproducing themselves (see Chapter 4). When plants reproduce sexually, they make special reproductive cells called spores. Many familiar plants make a structure that's even better at starting the next generation - the seed. Seeds protect the plant embryos they carry and nourish them with stored food.

Many familiar plants reproduce sexually by producing showy flowers designed to attract animals to help spread their pollen around. Other flowering plants just dangle their flowers in the wind and let the wind do the work.

Flowers contain the male and female parts of the plant that will participate in sexual reproduction.

Pollen comes from the male part of flowers, carrying and protecting the plant sperm. The female parts of flowers house the ovules that contain the eggs. Pollination occurs when pollen arrives at the female part of the flower. The pollen releases the sperm so that they can fuse with the egg, causing fertilization, and starting the next plant generation. After fertilization in flowering plants, the ovaries within the flowers develop into fruits (see Chapter 4). Some fruits are sweet and fleshy, inviting animals to come eat the fruit and then disperse the seeds. Other fruits are dry and designed to either float on the breeze, hitch a ride on some animal fur, or even explode to release their seeds. Whatever the method, the goal is the same - to find a nice, new home for the embryos inside the seed to grow.

Figuring Out Plant Functions

In addition to being made of cells and having similar chemistry, plants use many of the same strategies that you do to solve life's challenges. Both you and plants need a source of building material, called matter, to build the cells of your body, and you both need a source of energy so that you can build things and move around. And just like you, plants need to transport food and fluids around their bodies. Finally, you and plants both grow and develop, responding to changes in your environment.

Making and using food

The go-to source of matter and energy for all living things is food. Of course, one big difference between you and a plant is that you have to get your food by eating another organism, whereas plants can make their own.

Plants make their own food through the process of photosynthesis (see Chapter 5). Although the process of photosynthesis is pretty complex, you can get the main idea if you think of it like a recipe. The ingredients are carbon dioxide from the atmosphere and water taken up from the soil. You then follow these directions:

1. Use light energy from the sun to combine carbon dioxide and water, rearranging the atoms to form sugar and oxygen.
2. Serve sugar to all parts of the plant that need matter and energy and throw the oxygen gas away.
3. If you have leftovers, you can combine the sugars into starch to store some for later.

When plants want to use some of the sugar they've made to provide themselves with matter and energy, their cells do the same thing that your cells do with food, they break it down in a process called cellular respiration (see Chapter 6). Cellular respiration is a series of chemical reactions that basically unpack food molecules, making the matter and energy available to cells. When cells use cellular respiration to extract all the energy they can from food molecules, they release the waste matter as carbon dioxide and water.

Transporting materials

All the cells of a plant need food to provide them with matter and energy. Plants usually make sugars in their leaves, so they have to ship those sugars from the leaves to the rest of the plant. Likewise, plants take in water through their roots, but they need to get water to the entire plant, especially to the leaves, where it's needed for photosynthesis. So, just like you have veins and arteries to transport blood around your body, plants have vascular tissue that specializes in the transport of sugar and water (see Chapter 7).

Plants transport dissolved sugars using a special type of tissue called phloem, and they transport water and dissolved minerals using a tissue called xylem.

Phloem transports sugar from the leaves where it's made through photosynthesis, to all parts of the plant that need it for growth or that will store it as starch for later. Xylem transports water from the roots up through the plant to supply all the cells with the water they need.

Responding to hormones

Yet another similarity between you and plants is that they use hormones to direct their growth and development (see Chapter 8).

Although plants never go through puberty (lucky plants!), they do undergo major developmental changes, such as when a seed switches from being dormant to beginning to grow or when a flowering plant decides it's the right time of year to start putting on a floral display. Plant hormones also direct responses like helping plants' shoots grow toward the light and causing plant roots to grow downward toward the pull of gravity.

Considering Plant Reproduction and Genetics

Plants grow like, well . weeds. That's because weeds are plants. (Okay, now I'm just being silly.) But seriously, plants grow when groups of cells at their tips, called apical meristems, divide in two to produce new cells. The process of cell division that adds new growth is called mitosis (see Chapter 9). Plants do mitosis pretty much the same way your cells do. Woody plants also do mitosis to grow wider, adding girth to tree trunks.

Plants also reproduce sexually, combining sperm and egg to make the next generation of plants. Plant life cycles are more complicated than those of humans (see Chapter 9), but, just like us, they can use a type of cell division called meiosis to produce cells that have half the genetic material of the parents. These cells ultimately give rise to the sperm and egg cells. Sperm and egg cells fuse, bringing together copies of the DNA from the parent plants.

By following the inheritance of traits from one generation to the next through the science of genetics (see Chapter 10), scientists can figure out how plant genes interact with each other to determine the traits of a plant.

Planet Earth is filled with a glorious diversity of plants. Plants can be as tall as the mighty redwood tree or as small as the tip of a pin. They can grow so rapidly that they go from seed to seed in a month, or live for over a thousand years. Because plants moved onto the land over 400 million years ago, they've evolved to live in every type of environment (see Chapter 11): Today, plants grow in the deserts, in the rainforests, in the oceans, and up on mountains.

Exploring the Wide World of Plants

Botanists study all the different kinds of plants to understand how each one gets what it needs to survive and reproduce. They also compare the structures and DNA code of plants to figure out the relationships between plant groups and reconstruct how plants evolved (see Chapter 12). They've identified the closest relatives to plants (see Chapter 13) and studied how the ancestors of plants had to change in order to survive when they moved from the ocean to the land (see Chapter 14).To survive and reproduce outside of the oceans, plants needed to develop new...