Characteristics of Living Things 

All living things share a series of characteristics.  Each of the characteristics must be in place in order to classify a phenomena as a living thing.  Following is a list of the characteristics of living things; we will refer to specific elements on this list and how they are related, throughout the semester.  Each characteristic is then addressed in more depth throughout this section.

• All living things are made of cells
• All living things are capable of reproduction
  • Asexual
  • Sexual
• All living things have genetically encoded material
  • DNA (Deoxyribonucleic Acid)
  • RNA (Ribonucleic Acid)
• All living things grow and develop
• All living things respond to external stimuli
• All living things evolve
  • Permanent change in genetic makeup of population over time
• All living things must maintain homeostasis
  • Relatively stable internal situation
  • Osmoregulation, Thermoregulation, Acidity
• All living things require energy
  • Photosynthesis
  • Cellular Respiration

Structure and Function

In biology, a key concept is that structure determines function. The way something is arranged enables it to do its job within an organism. There is great variety within structures and functions though. Structure refers to the form, makeup, or arrangement of a particular organism or a particular part of the organism. Function refers to the job or responsibility of the organism. Basically structure is the build of an organism and the function is it’s abilities.  This concept is developmentally appropriate for very young children as they observe a simple flowering plant.  Children can identify the parts of the plant as well as what each part does for the organism (see Figure 1.).  As students move up through the grades, the idea of form and function can be extended to internal structures e.g. blood cells, organs, muscles & tissues, etc.  In some curricular resources, the concept of structure and function is referenced as form and function.

Figure 1.

Cell Theory

The cell theory states that cells are the basic structural/organizational unit of ALL living things. Every living organism is made up of cells. The structure of the cell and the parts of the cell relate to the jobs that the cells and the cell parts do. All cells come from pre-existing cells.

Jobs of Cells

• Create proteins
• Build nutrients and chemicals
• Breakdown nutrients and chemicals
• Protection
• Transport substances in and out

Cell Types

There are two main types of cells, Prokaryotic and Eukaryotic (figure 15). Prokaryotic cells are found in single celled organisms with no nucleus and no membrane bound organelles but contain genetic material called DNA. A eukaryotic cell contains a nucleus and membrane bound organelles.

Figure 15: Prokaryotic and Eukaryotic Cells

(Shields, 2021)

DNA/RNA

All living things have genetic material called DNA and RNA. Deoxyribonucleic acid (DNA) is a complex molecule that contains all hereditary information to carry from generation to generation. ALL living organisms have DNA within their cells. RNA, or ribonucleic acid is a molecule essential in various biological roles. RNA helps the regulation and expression of genes. Both have similar structures among all living organisms. This topic will be discussed further in the Genetics Section.

(Mackenzie, 2020)

Growth and Development

All living things grow and develop.  This process is commonly reference in stages with a life cycle.  Depending on the organism, in general the initial stage is birth e.g. mammals or hatching e.g. insets, fish, reptiles, birds, amphibians.  In all living things, cellular growth is happening within the organism. Cell growth refers to the increase in the total mass of a cell. Cellular development refers to cell division and gaining final cell type identity. In biology, growth and development are the result of a process called mitosis. Mitosis is a process in which one cell divides into two genetically identical daughter cells. This process is essential to life as it provides new cells and replaces old and dying cells.

Metamorphosis

Insects provide a unique opportunity for studying life cycles with elementary children.  Metamorphosis can either be complete or incomplete.  Complete metamorphosis includes the stages of development: egg, larva, pupa, and adult.  Here the organism goes through a series of complex changes and typically does not look like the adult until the latter stages of development. Incomplete metamorphosis includes the stages of development: egg, nymph, and adult.  Here the nymph hatches directly from the egg and resembles the adult as it begins to grow and develop, despite not having wings or reproductive organs.  Examples of insects which undergo incomplete metamorphosis include grasshoppers, crickets, praying mantis, dragonflies, and earwigs.

Two insects, which undergo complete metamorphosis, lend themselves nicely to inquiry investigations in elementary science: *mealworms and monarch butterflies.  Here students can not only observe the organism at each stage, but also experience the transition between life cycle stages, often in real-time.   Additionally, students can generate questions for investigation regarding food, habitat, prey/predator relationships, and adaptations.  The study of monarch butterflies provides opportunities for citizen science e.g. rearing and tagging and an in-depth look at the concept of migration.  Additional information about monarch butterflies and elementary classroom applications can be found at the following websites:

https://monarchwatch.org/

https://monarchjointventure.org/

https://journeynorth.org/

*Mealworm eggs are too small to been seen with the naked eye.

Reproduction

All living organisms are capable of reproduction either sexually or asexually. Asexual reproduction allows for an organism to reproduce without another member of its species. This means that an asexual organism can reproduce on its own. The other method of reproduction is sexually. This requires genetic material from two different members of the species. Organisms who reproduce sexually MUST find a mate to fertilize the egg. There are many advantages and disadvantages to both methods.

Plant Reproduction

Plants also provide a wonderful opportunity for students to experience life cycles while applying structure and function principles.  Begin by observing a simple seed and identify its parts and each part’s job.  Observe a planted seed over time and collect data on growth rate and changes observed as he plant develops.  Encourage students to generate questions about plants which can be investigated and researched in the elementary science setting.  Investigations may include, the effects of various growing conditions, how plants generate their food, where/how the mass of the plant comes from, etc.

Beyond plants in general, students at the upper grades levels can begin to focus on specific part of the plants and the structure and function inherent within e.g. the flower of a plant.  Many flowers contain the male and female structures for plants to produce seeds which the can be dispersed in a variety of manners.  Plants with flowers which contain both male and female reproductive organs are known as hermaphroditic, or perfect flowers; examples include lilies, potatoes,  apples, tomatoes, and Alstroemeria. 

Some flowers contain only male or female reproductive structures; these are known as dioecious plants.  Examples include kiwi, willow, pumpkins, bananas, and corn.

Resource:

Interactive plant structure and function resource for elementary students:

https://web.extension.illinois.edu/gpe/index.cfm

Energy

All living things require energy. Most living organisms obtain energy through photosynthesis and cellular respiration and use it through metabolism. The purpose of both processes is to produce chemical energy or ATP. The two processes differ but are actually complementary reactions within the environment. Most producers undertake both photosynthesis (or chemosynthesis)  and cellular respiration while consumers undertake ONLY cellular respiration. Photosynthesis converts the energy from the sun into chemical energy (ATP) that is then used for food. Cellular respiration occurs in the mitochondria of organisms and is the process used to break down glucose (sugar) in the presence of oxygen and release energy in the form of ATP. The relationship between the two is that the waste product of photosynthesis (oxygen) is used in cellular respiration and the waste product in cellular respiration (carbon dioxide) is used in photosynthesis.

Response to Environment

All living things respond to external stimuli. This means that there is a signal coming from the environment indicating a changed response from the organism. Sometimes the response is automatic, such as removing a hand from a hot surface and sometimes it is involuntary, such as sweating to cool off one’s body. Whether it is automatic or involuntary, the organism responds and tries to adapt to the environment. The way the organism responds, varies on the organism itself and the stimulus. The way a plant reacts to physical touch may be different than the way a human reacts. The “touch me not” plant closes up when it is touched. Depending on the specific human, they may “close up” or they may embrace you or high five you back. Examples of external stimuli include: weather, light, smells, sounds, danger, irritants etc.

Homeostasis

All living things must maintain homeostasis. Homeostasis is the maintenance of an established internal environment. Basically homeostasis is the optimal condition for organisms to function properly. It is the body’s attempt to maintain a constant state of balance within itself. This includes maintaining body temperature and fluid balance. The body does this while simultaneously obtaining the proper nutrients for the energy to maintain this “same state”.

How does one maintain homeostasis?

Our body is full of sensors that are measuring various things and sending that information to your brain. The information is transferred through negative feedback loops within the organism. The brain takes that information in and works hard to keep everything stable and working properly. This can be seen in many different ways. For example: when a human organism works out, they (most likely) produce sweat. The internal body temperature was rising due to the physical activity so the sensors went through the negative feedback loop and told the brain to cool the body down by sweating.

What happens if there is a disruption?

When homeostasis is disrupted and the sensors cannot use the negative feedback loop to tell the brain what is going on, it can be a disaster for the organism, even life threatening. Using the sweat example from before, if one is unable to cool themselves down, they may experience heatstroke. Malfunctions can happen for a variety of reasons including deficiency and toxicity.

Concepts for Review – Living Things

1. Briefly describe the concept of structure and function. Provide examples from both plants and animals.
2. List the characteristics of living things and provide examples.
3. Explain how plants create their own food; specify what phenomena are needed to do this as well as how it is done.
4. Identify the reproductive organs of a lily flower; specify the role played by each part.
5. Explain the difference between photosynthesis and cellular respiration.
6. Identify the difference between monocots and dicots. Explain how one can recognize each.
7. Provide example of a living organism responding to a stimuli; do this for both a plant and an animal.
8. Choose a non-living thing and identify which characteristics of living things are missing, therefore making it non-living.
9. Explain homeostasis in your own words; describe why this condition is beneficial to living things.
10. Clarify the difference between complete and incomplete metamorphosis.
11. What is meant by the term life cycle and how does it relate to living things?
12. Why are good observation skills important for elementary children, especially when examining living things?

Practice Quiz – Living Things

Click on this link to check your understanding.

https://docs.google.com/forms/d/e/1FAIpQLSc3d6aGQLMysiTjOKTOVrlFYq1mKxkZoh-ePCaqkP3_RZZPzw/viewform?vc=0&c=0&w=1&flr=0