In this 7th grade science lesson, students identify desirable traits in plants and take cuttings from parent plants to facilitate asexual propagation and produce offspring with identical DNA.
After this lesson, students will be able to:
- Explain why plants are reproduced asexually
- Understand that asexual offspring are genetically identical to the mother plant
- Use cuttings to propagate perennial plants
During this lesson, students will:
- Identify three reasons for reproducing plants asexually in the garden
- Identify the cutting as genetically identical to the mother plant
- Successfully propagate a plant asexually
- Wooden flat of growing medium (we use perlite)
- Perennial plants with branches available for cutting
- Examples of a rooted cutting and a mature, potted up cutting
- Visual aid
Before You Begin
- Collect and prepare all the materials
- Create the visual aid
- Set up seating area near greenhouse
At the Opening Circle
- Welcome students and introduce the lesson. Explain that students will be rotating through a cuttings lab where they will learn how to generate more plants using asexual reproduction.
- Ask students what they already know about genetics and how traits are passed from generation to generation.
- Then ask students to share what they know about how plants typically reproduce.
- Explain that as gardeners, we often produce more plants by sowing seeds in the greenhouse and that the seed is the offspring of the plant. This is sexual reproduction.
- Explain that today, students will learn how to produce more plants through asexual reproduction and clone them rather than using seeds.
- Ask students what they think will happen to the DNA when the plants are cloned.
- Review garden jobs and closing circle activity: tasting.
- Divide students into working groups. During their garden jobs, students will take a break to take an asexual cutting from a perennial plant.
In the Field
- Gather students near the greenhouse and review that in this lab, they will learn one method of generating more plants through asexual reproduction with cuttings.
- Explain that a cutting refers to a small branch that we take from a mature plant and turn into a clone of the plant it was taken from.
- Give examples of some of the traits you look for in a mother plant: fragrance, vigor, disease resistance, color of flower etc.
- Reference the visual aid and explain the process while demonstrating each step. How to take the strike from the mother plant, importance of exposing the nodes, trimming the upper leaves, and placing the cutting at a 45-degree angle in the growing medium.
- Prompt students to think about why it would benefit the grower to place the strike at an angle rather than straight down.
- Explain that we use perlite because it is sterile.
- Review what happens to the DNA of the cutting.
- Show students an example of a rooted cutting several months old and a mature, 1 year old potted up cutting.
- Ask students why a grower would choose to use asexual propagation. Discuss with students that there are three main reasons. It is faster than propagating by seed, you can select desirable traits, and it is cost effective.
- Explain that students will walk through the garden and collect strikes from perennial plants to bring back and place in the tray of perlite.
- Have each student take a cutting of the perennial plant, expose the nodes and trim the upper leaves.
- Once all students have taken a cutting, have each one place their cutting in the wooden flat at a 45-degree angle, label it, and have one student water the flat when everyone is finished.
- As students are preparing their cuttings, ask them the following questions.
- Are these cuttings genetically identical to the mother plant? (yes!)
- Why is it important to expose the nodes? (from the nodes branches, leaves, or roots can grow).
- Why do we clip off the upper leaves on a cutting? (to minimize transpiration and help keep the plant moist)
At the Closing Circle
Have a few students serve a seasonal tasting harvested and prepared as part of their working group's garden job.
DNA (Deoxyribonucleic acid)