Colorado Agriscience Curriculum
Section: Unit 4: Plant Reproduction Plant Reproduction Sexual Reproduction in Plants
Lesson Number 2:
Colorado Agricultural Education Standards: AS 11/12.4 The student will demonstrate an understanding of physiological processes in agriculturally important plants HRT 11/12.2 The learner will understand and describe the anatomy of horticulture plants. Colorado Science Standards: SCI 1.1 Asking questions and stating hypotheses, using prior scientific knowledge to help guide their development SCI 3.1 Students know and understand the characteristics of living things, the diversity of life, and how living things interact with each other and with the environment. Using examples to explain the relationship of structure and function in organisms. Describing the pattern and process of reproduction and development in several organisms. Describing how DNA serves as the vehicle for genetic continuity and the source of genetic diversity upon which natural selection can act.
SCI 3.3.5 SCI 3.3.6
Student Learning Objectives (Enablers) As a result of this lesson, the student will … Objective 1: Explain sexual reproduction of plants and it importance to plant survival. Objective 2: Explain how pollination occurs and describe the different types of pollination. Objective 3: Explain fertilization in flowering plants. Time: Instruction time for this lesson: 55 minutes. Tools, Equipment, and Supplies Power Point or Colored Overheads Complete Flowers Dissection Kit Introduction to Plant and Soils Science and Technology Text (page 57) Crayons or Colored Pencils
Key Terms. Chromosomes Deoxyribonucleic acid (DNA) Double Fertilization Fruit Haploid Scarification Sexual Reproduction Interest Approach
Cotyledons Diploid Embryo Genes Hybrid Zygote
Cross-Pollination Disseminate Endosperm Germination Pollination Self-Pollination
Acquire perfect or complete flowers from a floral shop (They will usually give you flowers that are about to be discarded). Work with the class in a dissection to show the students the various parts of a flower. Dissect the flower and demonstrate to students how the pollen gets from the anther to the stigma and then grows the pollen tube and travels down through the style to fertilize the egg. Students should be able to see how thee various parts of the flower interact for pollination and fertilization to occur.
Summary of Content and Teaching Strategies
Objective 1. Explain sexual reproduction of plants and it importance to plant survival. Slide 2: Sexual Reproduction in flowering plants involves flowers, fruits, and seeds. In sexual reproduction, sperm carried in the pollen from the male part of a flower fuses with the egg in the female part of the flower. Both the sperm and the egg contribute genetic material to the new life within the seed. What advantage does sexual reproduction provide to the plant? For survival, a plant species must live to reproduce in its environment. However, the earth and the environment have been changing since the beginning of time. Plants adapted to conditions thousands of years ago may not be able to survive in today’s conditions. Sexual reproduction gives the plant species the means to change with a changing environment. Every time sexual reproduction occurs there is a recombining of genetic material. Some genetic changes are beneficial. Plants receiving genes that enable them to adapt to a changed environment are more likely to survive to pass genes onto their offspring. Thus, species evolve in order to survive.
Objective 2. Explain how pollination occurs and describe the different types of pollination. Slides 3-4 Slide 3: Flowering plants have evolved with a number of methods to accomplish pollination. Pollination is the transfer of pollen from the male to the female part of a plant. Colorful, scented flowers attract birds, insects, bats, and other animals. These creatures unknowingly pick up pollen from the anthers and, when they visit another flower, deposit the pollen on the stigma. Pollinators are rewarded by the plant with food. They feed on nectar, which is a sugary, energy rich food made in the flower or the pollen itself, which is a food rich in protein. Other plants rely on the wind to transfer pollen to the stigma. The force of the wind physically moves pollen from on flower to another. Since there is no need to attract pollinators, these plants do not produce colorful flowers with large petals, scents, or nectar. Plants that depend on wind for pollination actually rely on luck for the pollen of a plant species to blow onto the stigma of the same species. Plants that depend on wind for pollination produce a great abundance of pollen to improve the odds that pollination will occur. Ragweed, many trees, and grasses are wind-pollinated plants. Hay fever suffers are well aware of when they are producing pollen. When the pollen of a plant pollinates a flower on the same plant, it is called self-pollination. Some plants have this ability; others do not. When the pollen of plant pollinates the flower of another plant, it is said to be cross-pollination. Cross-pollination is required for most varieties of apple trees. Also, it is important to understand that plants must be closely related for crosspollination to occur. For example, an oak tree cannot pollinate a soybean plant. Once the pollen lands on the stigma, it grows a thin pollen tube down the style to the ovary. The cell within the grain of pollen divides to form two sperm nuclei. These travel down the pollen tube to the embryo sac that holds the egg. Slide 4: Display the diagram on slide four. Utilize a Go-With-The-Flow E-Moment to capture the anatomy of pollination into the student’s notes.
Objective 3. Explain fertilization in flowering plants. Slides 5 – 9 Slide 5: Fertilization in flowering plants is unlike fertilization in any other living organism. This is because both sperm nuclei in the pollen grain are involved in fertilization. Flowering plants actually have a double fertilization. One fertilization occurs when one sperm fuses with the egg. The resulting cell is called a zygote. In this process, the sperm carries genetic material from the male part of the flower. The egg contains genetic material from the female part of the flower. The resulting seed contains a combination of genetic material received from the male and female parts of a flower. The other fertilization has the second sperm nuclei fusing with two nuclei in the embryo sac. It develops into the endosperm. The ovule of the flower becomes the seed. Slide 6: The offspring of genetically different parents is said to be a hybrid. People have greatly improved agricultural crops and animals through hundreds of years of hybridization. The first farmers saved seed from their best plants for planting the following year. Over many generations of saving the best seed and discarding the less valuable seed, crops changed. In many cases, you would find it difficult to recognize the distant ancestors of today’s crops and animals. For example, ancient corn looked more like a grass than today’s hybrids. The advantage of hybridizing is the best traits of each parent may be expressed in the offspring. Those traits might be expressed as more vigorous growth, insect and disease resistance, or uniformity. Slides 7 – 8: An understanding of genetics is necessary when hybridizing plants. Genetic information is stored in every cell of a plant or animal in long molecular chains made of deoxyribonucleic acid or DNA. Segments of the DNA, called genes, code for life processes and the appearance of a plant. For instance, genes in a petunia plant may code for a red flower. Genes in that petunia plant also tell it when to flower and haw many petals to make. An individual plant may have 100,000 genes informing it what to do and how to look. The genes are arranged in a set of chromosomes. Normal cells contain a double set of chromosomes and are said to be diploid. Reproductive cells, sperm and egg, have a single set of chromosomes and are said to be haploid. When fertilization occurs, both the sperm and the egg contribute a single set of chromosomes. Each cell of the resulting seed ends up with a normal double set. In this way, traits from each of the parent plants may be passed on to the offspring. Slide 9: Use a Go-With-The-Flow E-Moment to get the diagram of fertilization into the student’s notes.
Review/Summary. All of you did a great job today. We covered a lot of information about sexual reproduction in plants and began to take a look at plant genetics. Let’s take a few minutes to look back at what we have learned today. Without looking back in your notes what was sexual reproduction in plants? Very good, sexual reproduction involves flowers, fruit, and seed. It involves the union of sperm or pollen with the ovum or egg. Sexual reproduction is what enables plants to evolve to continue to survive in a changing environment. What is pollination? Great, pollination is simple the transfer of pollen from the anthers of one flower to the stigma of another flower. There are two types of pollination, self-pollination and cross-pollination. Self-pollination is the result from the pollen on one plant landing on the stigma of the same plant. Cross-pollination is when pollen from the anther of one plant pollinates the stigma of a different plant. Finally, we learned about fertilization. Fertilization is necessary in flowering plants for a seed to develop. Double fertilization is unique to plants; no other organism utilizes this process. The first fertilization occurs when a sperm unites with the ovum creating a zygote. The second fertilization occurs when the second sperm unites with the zygote in the embryo sac creating the endosperm. Hybrids result from cross-pollination and results in hybrid vigor or the passing on of the best traits from each parent. Genetic information is stored in every cell of the plant in DNA. Segments of DNA, called genes, establish a code for how the plant looks and functions. Those genes are arranged into chromosomes. Most chromosomes appear as diploid which is a pair or set of chromosomes. Sex cells are haploid, which is to say they contain one chromosome and when fertilization occurs the two single chromosomes are united to form a complete set that is once again a diploid. Utilize a Crayon E-Moment to highlight the most important information in their notes. Application Extended classroom activity: Using fast plants duplicate Mendel’s genetic experiment. FFA activity: Using LifeKnowledge HS 60 show how through natural selection, the positives traits of plants are selected, just as individuals select positive relationships to help them grow as a person. SAE activity: Invite a local seed dealer to come visit with the class and describe his career and what it entails.