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Students will explore heredity concepts by comparing observable traits of apples and onions, collecting data on the traits of different apple varieties, and learning about apple production. Additional activities include hands-on methods for testing apple ripeness.
Interest Approach — Engagement
Activity 1: Apple Exploration
Activity 2: Apples in the Orchard
grafting: a plant that has a twig or bud from another plant attached to it so they are joined and grow together
heredity: the passing on of characteristics from parents to offspring
plant breeding: the purposeful manipulation of plant species in order to produce desired characteristics
trait: a quality or characteristic that makes one person, animal, or thing different from another
If you take the time to observe, similarities can be found even between an apple and an onion. And certainly you will notice many traits that make them different too. Close observation of the traits of living things is the first step to understanding heredity.
Apples have been selectively bred for thousands of years to produce the varieties that we know today. Honeycrisp, Gala, Red Delicious, Granny Smith, and the many other apples in the grocery store all come from the same species of tree, but they have distinctly different characteristics. Some are sweet and others are tart. Some are good for baking, while others are best eaten fresh. Some store well for a long time, but others need to be used soon after ripening. Knowledge of how traits are inherited in apples has allowed breeders to develop the many different varieties found in orchards and grocery stores around the world.
Apples can reproduce by seed, but farmers almost never grow apple trees from seed. In order for apple fruit and seeds to form, the flowers of the tree must first be pollinated. Some fruit trees can self-pollinate, but apple trees must be cross-pollinated with pollen from a different variety of apple tree. This means that each apple seed is genetically unique, and there is no guarantee that the tree it grows into will produce fruit anything like that of its parents. If a farmer started an apple orchard by growing trees from seed, each tree would produce apples with different flavors, colors, and ripening times, making it difficult to manage and market the crop. So, most apple orchards begin by grafting a desirable apple variety onto a strong rootstock. A section of a stem with leaf buds is inserted into the trunk of another. The two will fuse together and the stem section will grow and produce apples just like the tree it was taken from.
While wild variability is not desirable to farmers, it is the working palette of plant breeders. Breeders plant apple trees from seed in order to bring out new characteristics and combine characteristics from desirable varieties. Breeders work not only to provide consumers with new, tasty varieties of apples, but also to create apple trees that are resistant to disease and pests and have other traits that make it easier for farmers to grow a healthy, reliable crop. The process of selective breeding takes many, many years, but modern biotechnology provides innovative techniques that allow breeders to develop new traits more quickly.
In 2015, the first genetically modified apple varieties were approved for sale in the United States. The Arctic Apples contain a trait that prevents them from turning brown when they are sliced or bruised. The flesh of most apples will turn brown when exposed to air. This is due in large part to an enzyme called polyphenoloxidase, which causes many fruits to produce brown pigment when exposed to oxygen and may change their texture and flavor. Methods like cooking or lowering the pH of cut apples can minimize the activity of this enzyme and prevent browning. In Arctic Apples, a gene silencing technique was used to prevent the apples from producing polyphenoloxidase and thus make them resistant to browning.
Activity 1: Apple Exploration
Activity 2: Apples in the Orchard
Concept Elaboration and Evaluation
After conducting these activities, review and summarize the following key concepts:
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Grocery Store Fruit and Vegetable Characteristics
Many grocery stores have informational sheets on fruits and vegetables. Have students go to the grocery store with a parent or other adult and find out information about a particular fruit or vegetable from the manager of the Produce Department. For example: How many kinds of apples are carried by the grocery store? Which apples are best for cooking, eating or storing? Which apple has the shortest growing season, the longest growing season? Which apple sells the best? Which are the most expensive and why? Where do apples grow in your state?
Students observed browning in different varieties of apples, but what about browning under different conditions? Have your students think of ways they might slow the browning of apples (add lemon juice, wrap apple slices in plastic, put them in the freezer, etc.). Cut slices of apples, and compare the rate of browning under the different conditions suggested by the students. Make observations over two or three days. Don’t forget to provide a control slice (a sliced apple with nothing done to it).
Testing Apple Ripeness
Apple growers try to pick their apples at precisely the right time. They have several ways to test for ripeness that students can try in the classroom. These observations will work best with apples picked in the early fall when you can find varying stages of ripeness—they will not work well with apples from the grocery store.
Seed Color Test
Rate the color of the seeds in the apple. A ripe apple has brown seeds. Apple growers use the following scale:
Flesh Color Test
Check the flesh color of the apple by holding a very thin slice—about 1/16th of an inch (1.58 mm)—up to a bright light. A ripe apple has almost no green flesh. Apple growers use the following scale:
Have students give their apple a rating from 1 to 6. Remind students that these tests for ripeness involve a skill that scientists must develop—the ability to make careful observations.
Divide the class into groups. Give each group an apple, and have them cut the apple in half at a right angle to the core. Apply iodine to the cut surface, drain away any excess, and allow it to stand for a few minutes. (Emphasize that iodine is poison and is not to be taken internally.) The apple will turn a dark purple or blue-black wherever starch is present. Remind students that in a ripe apple the starch has changed to sugar, so a ripe apple will have very little dark stain. Have students give their apple a rating from 1 to 6 based on the amount of dark stain on the apple. A rating of 6 indicates a perfectly ripe apple. Note: This test works well at any time of year with bananas, which are commonly available at varying stages of ripeness.
Apple growers commonly use the following rating system:
Read Issue 6 of Ag Today titled Plants & Animals...Providing Food, Fiber, and Energy! This reader can be printed or accessed digitally. Explore the facts about the renewable and non-renewable resources that make the products and byproducts we need for survival. Learn how agriculture provides energy through biofuels and hydropower, fiber through cotton and wool, and various food products from plants and animals that have been improved through biotechnology and crossbreeding.
Activity 1 and the Interest Approach of this lesson were originally developed as part of the Utah Fifth Grade Science Teacher Resource Book (TRB3). The TRB3 was designed as a textbook for teaching Utah science curriculum and covers all the objectives of each standard and benchmark.
The apple ripeness tests suggested under Additional Activities are based on tests described in the 2014-15 Penn State Tree Fruit Production Guide, Part VI Harvest and Postharvest Handling.
Debra Spielmaker and Sara Hunt
Utah Agriculture in the Classroom