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Life Science: Session 2

Classifying Living Things: The Plant Kingdom

What features distinguish plants from other life forms?

leaf and leaf cells
Leaf (inset) and leaf cells. Roll your mouse over the
word "cell wall" to highlight this structure.

Plants are eukaryotic organisms, meaning their cells contain nuclei as well as organelles. They are multicellular and have the ability to make their own food. Plant cells are different from animal cells because they have a cell wall. The cell wall, made of a compound called cellulose, gives structural support to plants, allowing them to stand tall. Plant cells are also unique from animal cells in that they contain an organelle called chloroplast, where they use the energy from sunlight to convert carbon dioxide and water into food during the process of photosynthesis. A chemical in chloroplasts that is involved in photosynthesis — chlorophyll — is what gives plants their green color.

How are plants important to people?

As well as being important food sources, plants are well known as a source of many important chemicals that are used in medicine, cosmetics, and agriculture. Because land plants are unable to move, they have evolved multiple adaptations to facilitate their success and ability to thrive in a range of ecosystems. For instance, many plants produce pesticides to protect themselves from insects. These pesticides have practical uses for humans. In fact, caffeine is technically a pesticide! Other chemicals may be toxins to dissuade larger animals from eating the plant leaves or fruits. Conversely, some chemicals are actually produced to attract animals — the scents of flowers are good examples. Other ways of attracting animals include special colors and shapes of flower and leaf parts as well as nectar production. The purpose of these enticements is to encourage animals to stop by and eat, ultimately leading to pollination of the flowers and increasing reproductive output.

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