UNIT 3

Plants and Trees

Plants are living organisms and differ from animals in that generally, they do not move. The defining characteristic of plants is that most perform photosynthesis. Green plants produce most of the world’s molecular oxygen and are the basis of many of the planet’s ecosystems. Many grain, fruit, and vegetable producing plants have been domesticated for ages, becoming the foundation of humankind’s diet. Plants have been used as ornaments and decorations, in medicines and drugs, and play a role in many cultures.

A tree is a plant with an elongated stem, or trunk, support-ing branches and leaves or needles. Trees play a significant role in reducing erosion and moderating the climate. They remove carbon dioxide from the atmosphere and store large quantities of carbon in their tissues. Trees and forests provide a habitat for many species of animals and plants. Trees provide shade and shelter, timber for construction, fuel for cooking and heating, and fruit for food.

TOPIC 3A : The Power of Producers

The process of photosynthesis is what makes a plant a producer. Photosynthesis is the method by which plants use carbon dioxide, water, and light from the sun to create sugars to feed the plant and oxygen as a byproduct. This method is essential for life on earth because it produces oxygen for the atmosphere, but also because it is the source of energy for all living things. Photosynthesis not only produces energy for the plant itself, but because the plant has produced energy, primary consumers (herbivores) can consume the plant to receive energy.

In order to understand how plants perform photosynthesis, it is important to understand the different parts of a plant. This unit will focus on vascular plants, meaning they contain the plant form of a circulatory system.

The roots of the plant help to anchor it into the ground. They also absorb water and the nutrients carried with it into the plant. The stem (or trunk when referring to trees) provides support for the plant. It is also where the vascular tissue is housed. Woody plants like trees and shrubs feature a complex anatomy, including:

  • Xylem, or sapwood, brings the water and the nutrients up from the roots to the leaves.
  • Cambium is a very thin layer of tissue that helps the plant grow new xylem cells, phloem cells, or new cambium cells.
  • Phloem, or inner bark, carries the sap (sugar made during photosynthesis) from the leaves to the rest of the plant.

The leaves create the food for the plant with the process of photosynthesis. They capture energy from the sun with chlorophyll (the green pigment in the leaves), absorb carbon dioxide through tiny pores on their surface called stomata, and mix it with water to produce oxygen as a byproduct and sugar as food for the plant. The flowers of the plant are the hub for pollination. Flowers are designed to spread pollen from one plant to another using various methods. The fruit of a plant, botanically speaking, is the ripened portion of the flower and contains one or more seeds. It can be dry or fleshy, and is often edible.

TOPIC 3B: The Importance of Change

Because plants are living things, they go through many changes both throughout the year and throughout their lives. Some of these changes occur during their growth cycle from seed to soil, while others occur due to seasons (See more in the Weather unit) or more severe changes in their environment. Like many animals, plants have a life cycle and many display some fascinating adaptations in order to survive in their habitats. These life cycle changes and adaptations play an important role in the different ecosystems where we find plants.