Learn concepts of trait heredity observing varieties of apples and onions. Lesson includes testing apple ripeness activities.
INSTRUCTIONS
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.
Procedures
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.
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?
