National Agricultural Literacy Curriculum Matrix
Apple Science: Comparing Apples and Onions
3 - 5
40 - 60 minutes
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.
- 1 red apple
- 1 red onion
- Gala apples (or other slow-to-brown variety like Empire or Cortland), 1 per group
- Granny Smith apples (or other tart, green variety like Crispin or Pippin), 1 per group
- McIntosh apples (or other soft-flesh variety like Braeburn or Red Delicious), 1 per group
- Measuring tapes, 1 per group
- Scales that weigh in grams, 1 per group
- Apple Data Sheet, 1 per student
- How Does it Grow? Apples video
Essential Files (maps, charts, pictures, or documents)
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
Did you know? (Ag Facts)
- At last count, more than 7,500 apple varieties have been identified worldwide.1
- More than 2,500 varieties are grown in the United States – 100 of which are grown for commercial sale.1
- Apples ripen or soften ten times faster at room temperature than if they were refrigerated.1
Background Agricultural Connections
Interest Approach – Engagement
- Show students a red apple and a red onion. Ask, “Which one would you like to eat in a pie? How can you tell the difference between the apple and the onion?”
- As a class, list the physical characteristics of the apple and the onion. Point out that many of these characteristics are heritable traits that can be used to tell apples from onions.
- Optional: Show other types of fruits and vegetables that have both similar and different characteristics. Have students observe, record, and discuss the similarities and differences.
Activity 1: Apple Exploration
- Divide the students into small groups. Provide each group with a Gala, Granny Smith, and McIntosh apple (or other similar varieties); one measuring tape; one scale; and an Apple Data Sheet for each student.
- Have students record the color and smell of each apple variety on their data sheets.
- Have students predict each apple’s weight in grams and circumference in centimeters.
- Teaching Tip: When students make predictions, encourage them to use a known variable for comparison. For example, if you are using gram weights, have a student place 100 grams in one hand and an apple in the other. This way, the student has a known quantity against which to compare the apple’s weight and a basis for making his/her prediction. As soon as one apple’s mass is known, the apple can then become the next known quantity.
- Have students measure the actual weight and circumference of each apple.
- Have students make a prediction about how many seeds are in each apple.
- Cut each apple open for the groups, designating one slice for observing how long it takes the apple to turn brown. Ask students to observe the inner characteristics of the apple and record on their data sheets the color of the inside flesh and the actual number of seeds inside each apple.
- Cut each apple into small sections and allow students to taste the differences among the apples. As they are tasting, remind them to pay attention to the texture (crunchy, juicy, etc.) of the apple as well as the flavor. Be sure to follow proper health and safety regulations for step 7, or ask the cafeteria workers to slice the apples for tasting. Have students record their observations on the data sheet.
- Using the background information, explain to students why apples turn brown after they are cut. If any of their apples have started to turn brown, have them record on their data sheets that these varieties are fast to brown. Ask them to continue observing their cut apples to compare their rate of browning as you do the next activity.
- Discuss the variation that students observed between different apple varieties. Explain to students that these variations are examples of traits that can be passed from parent to offspring.
Activity 2: Apples in the Orchard
- Show students the How Does it Grow? Apples video.
- Use the following discussion questions to explore the video:
- Why don’t farmers grow apples from seed? (Each seed is genetically unique, meaning that when it grows into a mature tree, the apples it produces will be different from those produced by its parent trees.)
- What is grafting? (The process of joining a cut stem—or bud—with the trunk of another tree so that the two grow together.)
- Why do apple farmers graft their trees? (Grafting allows farmers to “clone” the apple trees that produce the fruit they want. A grafted branch has the same genetic makeup as the tree it was taken from.)
- Do all apple varieties ripen at the same time? (No, some varieties ripen earlier than others, so planting different varieties allows farmers to extend their length of harvest.)
- Explain to students that apples have been selectively bred for thousands of years to produce the varieties that we know today. Apple breeders, unlike farmers, plant apple trees from seed in order to find and develop new traits. Under human cultivation, the traits that give apple trees a survival advantage are the traits that are most useful and desirable to people. Ask students to brainstorm all the different traits they can think of that might be desirable in an apple tree (e.g., pest resistant, grows fast, has strong branches, produces big apples, juicy apples, sweet apples, crisp apples), and write them on the board.
- Circle all the traits that are directly related to the fruit of the apple tree (e.g., produces big apples, juicy apples, sweet apples, crisp apples). Point out that these are like the characteristics that students observed and recorded on their Apple Data Sheets.
- Based on the information from their data sheets, ask students to vote on which apple variety was their favorite. Imagine that an apple breeder crossed the two favorite class varieties. What characteristics might the resulting apple have?
Concept Elaboration and Evaluation
After conducting these activities, review and summarize the following key concepts:
- Inherited traits are passed from parents to offspring.
- The characteristics of different apple varieties are examples of inherited traits.
- Knowledge of inherited traits is important to apple production; apples grown from seed may have different characteristics from their parents while an apple produced through grafting will be genetically identical to its parent.
- Under human cultivation, the traits that give apple trees a survival advantage are the traits that are most useful and desirable to people.
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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:
- 1 = clear (no color)
- 2 = trace of color (tips of seeds are brown)
- 3 = 1/4 color
- 4 = 1/2 color
- 5 = 3/4 color
- 6 = fully brown
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:
- 1 = flesh all green
- 2 = some loss of green from center of fruit
- 3 = heavy green band 1/2 inch (1.27 cm) thick under skin
- 4 = heavy green band 1/4 inch (6.35 mm) thick
- 5 = heavy green band 1/8 inch (3.17 mm) thick
- 6 = green essentially gone from under skin
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:
- 1 = all blue-black (full starch)
- 2 = all blue-black except in seed cavity and halfway to vascular area (oval area around core)
- 3 = all blue-black except in seed cavity and vascular area
- 4 = half blue-black
- 5 = blue-black just under skin
- 6 = no blue-black (free of starch)
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.
Suggested Companion Resources
- An Apple Tree Through the Year (Book)
- First Apple (Book)
- How Do Apples Grow? (Book)
- In the Garden with Dr. Carver (Book)
- Johnny Appleseed (Book)
- Stinky and Stringy: Stem & Bulb Vegetables (Plants We Eat) (Book)
- Parent/Offspring Cards (Kit)
- Pompom Punnett Square Kit (Kit)
- America's Heartland: Maine-ly Apples (Multimedia)
- Apples (Multimedia)
- Have We Engineered the Perfect Apple? video (Multimedia)
- Top 10 Foods That Originally Looked Totally Different (Multimedia)
- Ag Today (Booklets & Readers)
- All About Apples (Website)
Agricultural Literacy Outcomes
Science, Technology, Engineering & Math
- Identify examples of how the knowledge of inherited traits is applied to farmed plants and animals in order to meet specific objectives (i.e., increased yields, better nutrition, etc.) (T4.3-5.c)
Education Content Standards
3-LS3: Heredity: Inheritance and Variation of Traits
3-LS3-1Analyze the interpret data to provide evidence that plants and animals have traits inherited from parents and that variation of these traits exists in a group of similar organisms.
Common Core Connections
Language: Anchor Standards
CCSS.ELA-LITERACY.CCRA.L.6Acquire and use accurately a range of general academic and domain-specific words and phrases sufficient for reading, writing, speaking, and listening at the college and career readiness level; demonstrate independence in gathering vocabulary knowledge when encountering an unknown term important to comprehension or expression.