Unit 4: Characteristics of Living Things Objectives: By the end of the lesson, students should be able to: To recognize and describe the characteristics of living things Review Review with students these six easily observable characteristics of living things: 1. movement (which may occur internally, or even at the cellular level) 2. growth and development 3. response to stimuli 4. reproduction 5. use of energy 6. cellular structure Core Standards: Life Science MS-LS14. Use argument based on empirical evidence and scientific reasoning to support an explanation for how characteristic animal behaviors and specialized plant structures affect the probability of successful reproduction of animals and plants respectively. Misconceptions: All cells are the same size and shape There are no single celled organisms Some living parts of organisms are not made of cells Plants are not made of cells Cells do not eliminate waste Animal cells do not carry out essential life functions for themselves Materials: a computer and projector a tech center (if available) student pages with sample answers (attached); also open to click on hyperlink videos whole class or independently Engagement: Students will examine several objects in video format and list characteristics of life and a description of the characteristics observed. Exploration: Student response sheets. Explanation: Defining "life" is a very difficult task, and scientists don’t all agree on a common list of the characteristics of life. Some of the other characteristics that the students may discover in their research, and which are often listed in textbooks, include those listed below. Many of these traits are not limited to living things. For example, fire uses energy, grows, and can reproduce, but it is not considered alive in part because it cannot evolve; its traits are necessary, but not sufficient, for life. NASA scientist Bruce Jakosky, in his book The Search for Life on Other Planets, provides a generally accepted definition of something being “alive” if it 1) utilizes energy from some source to drive chemical reactions, 2) is capable of reproduction, and 3) can undergo evolution. Characteristics of Living Things All organisms use energy (metabolism). All organisms maintain a stable internal environment (homeostasis). All organisms detect and respond to select external stimuli. All organisms can engage in movement (which may occur internally, or even at the cellular level). All organisms show growth and development; that is, specialization of cells or structures. (Even unicellular organisms show a tiny amount of growth, and single cells repair and use materials from the environment to replace internal structures as needed.) All organisms reproduce. (Even if an individual can’t reproduce, its species can.) In addition, an individual’s cells are constantly reproducing themselves. All organisms have nucleic acid as the hereditary molecule. All organisms show adaptation, which occurs at the individual level and is tightly related to homeostasis. All organisms are made of one or more cells. All organisms exhibit complex organization, grouping molecules together to form cells; at a higher level, cells are organized into tissues, organs, and organ systems. All organisms exhibit evolution over time due to mutation and natural selection (which operates at the species level). Elaboration: Have students conduct Internet research on "characteristics of life." Do all sources agree on the characteristics? Are there characteristics not covered in this activity? Do all scientists agree on a common list of "characteristics of life"? What are the limitations of videos? Discuss which characteristics of life students are unable to identify in the videos. How might they be able to observe these characteristics in select organisms? If all of the characteristics of life are required to classify something as "alive," how can we account for those individuals who are definitely alive, but that do not reproduce (for example, people without children or a sterile mule)? Is a virus alive? Ask students to keep in mind the information from this activity, and to conduct Internet research to discover how scientists answer this question. Evaluation: Accuracy in student recordings. Characteristics of Life Data Table Sample Answers Category Characteristics of Life C. elegans (Caenorhabditis elegans) Movement, use of energy, reproduction Video: Moving C. elegans Sea Urchins (Lytechinus pictus) Growth and development, made of cells The cell divides twice to become four cells. The new cells are smaller than the original cells. Reproduction, movement The sea urchin sperm swim to the egg; the egg raises a membrane. Movement, use of energy, cells The white blood cells move around a lot, which requires energy. Movement, made of cells Green spots move inside the cells; leaf cells surrounded by walls. Movement, made of cells, growth and development The stem cells in the first video move a lot. The specialized heart cells developed from embryonic stem cells. Movement, use of energy The amoeba uses energy to move around. Growth and development, movement, reproduction, made of cells The cells of the embryo divide into more cells, and the embryo develops into a baby fish that moves a lot inside the egg. Video: Sea urchin cell division Sea Urchins (Lytechinus pictus) Video: Sea urchin fertilization Blood Cells Video: Human white blood cells Cellular Structure and Function Video: Elodea leaf cells Stem Cells Videos: Compare Mouse embryonic stem cells—movie 1 with Heart cells grown from mouse embryonic stem cells— movie 1 Cell Motility Video: Crawling Amoeba Zebrafish (Danio rerio) Video: Zebrafish development Description of Observed Characteristics The worms crawl to locate their food (source of energy); their eggs are visible. Name Date Observing the Characteristics of Life In this activity, you’ll identify observable characteristics of life in videos of various organisms and describe those characteristics. Review What are six easily observable characteristics of living things? 1. 2. 3. 4. 5. 6. To Do and Notice If your teacher is displaying the videos: Record one or more of the characteristics that you observe for each category and describe it on the data table that follows. If you are doing this activity independently: 1. On the data table, click on each category name in turn. 2. Read the introduction, then play the video. 3. Record one or more of the characteristics that you observe for each category and describe it on your data table. continued Name Date Characteristics of Life Data Table Category C. elegans (Caenorhabditis elegans) Video: Moving C. elegans Sea Urchins (Lytechinus pictus) Video: Sea urchin cell division Sea Urchins (Lytechinus pictus) Video: Sea urchin fertilization Blood Cells Video: Human white blood cells Cellular Structure and Function Video: Elodea leaf cells Stem Cells Videos: Compare Mouse embryonic stem cells—movie 1 with Heart cells grown from mouse embryonic stem cells— movie 1 Cell Motility Video: Crawling Amoeba Zebrafish (Danio rerio) Video: Zebrafish development Characteristics of Life Description of Observed Characteristics
