1.2: Characteristics of Life (2024)

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    What you’ll learn to do: List the defining characteristics of biological life

    Biology is the science that studies life, but what exactly is life? This may sound like a silly question with an obvious response, but it is not always easy to define life. For example, a branch of biology called virology studies viruses, which exhibit some of the characteristics of living entities but lack others. It turns out that although viruses can attack living organisms, cause diseases, and even reproduce, they do not meet the criteria that biologists use to define life. Consequently, virologists are not biologists, strictly speaking. Similarly, some biologists study the early molecular evolution that gave rise to life; since the events that preceded life are not biological events, these scientists are also excluded from biology in the strict sense of the term.

    From its earliest beginnings, biology has wrestled with these questions: What are the shared properties that make something “alive”? And once we know something is alive, how do we find meaningful levels of organization in its structure?

    Learning Objectives
    • List the properties of life
    • Order the levels of organization of living things

    Properties of Life

    1.2: Characteristics of Life (1)

    All living organisms share several key characteristics or functions: order, sensitivity or response to the environment, reproduction, growth and development, regulation, homeostasis, and energy processing. When viewed together, these characteristics serve to define life.

    Order

    Organisms are highly organized, coordinated structures that consist of one or more cells. Even very simple, single-celled organisms are remarkably complex: inside each cell, atoms make up molecules; these in turn make up cell organelles and other cellular inclusions.

    In multicellular organisms (Figure 1), similar cells form tissues. Tissues, in turn, collaborate to create organs (body structures with a distinct function). Organs work together to form organ systems.

    Sensitivity or Response to Stimuli

    1.2: Characteristics of Life (2)

    Organisms respond to diverse stimuli. For example, plants can bend toward a source of light, climb on fences and walls, or respond to touch (Figure 2). Even tiny bacteria can move toward or away from chemicals (a process called chemotaxis) or light (phototaxis). Movement toward a stimulus is considered a positive response, while movement away from a stimulus is considered a negative response.

    Watch this video to see how plants respond to a stimulus—from opening to light, to wrapping a tendril around a branch, to capturing prey.

    Reproduction

    Single-celled organisms reproduce by first duplicating their DNA, and then dividing it equally as the cell prepares to divide to form two new cells. Multicellular organisms often produce specialized reproductive germline cells that will form new individuals. When reproduction occurs, genes containing DNA are passed along to an organism’s offspring. These genes ensure that the offspring will belong to the same species and will have similar characteristics, such as size and shape.

    Growth and Development

    1.2: Characteristics of Life (3)

    Organisms grow and develop following specific instructions coded for by their genes. These genes provide instructions that will direct cellular growth and development, ensuring that a species’ young (Figure 3) will grow up to exhibit many of the same characteristics as its parents.

    Regulation

    Even the smallest organisms are complex and require multiple regulatory mechanisms to coordinate internal functions, respond to stimuli, and cope with environmental stresses. Two examples of internal functions regulated in an organism are nutrient transport and blood flow. Organs (groups of tissues working together) perform specific functions, such as carrying oxygen throughout the body, removing wastes, delivering nutrients to every cell, and cooling the body.

    Homeostasis

    1.2: Characteristics of Life (4)

    In order to function properly, cells need to have appropriate conditions such as proper temperature, pH, and appropriate concentration of diverse chemicals. These conditions may, however, change from one moment to the next. Organisms are able to maintain internal conditions within a narrow range almost constantly, despite environmental changes, through homeostasis (literally, “steady state”)—the ability of an organism to maintain constant internal conditions. For example, an organism needs to regulate body temperature through a process known as thermoregulation. Organisms that live in cold climates, such as the polar bear (Figure 4), have body structures that help them withstand low temperatures and conserve body heat. Structures that aid in this type of insulation include fur, feathers, blubber, and fat. In hot climates, organisms have methods (such as perspiration in humans or panting in dogs) that help them to shed excess body heat.

    Energy Processing

    All organisms use a source of energy for their metabolic activities. Some organisms capture energy from the sun and convert it into chemical energy in food (photosynthesis); others use chemical energy in molecules they take in as food (cellular respiration).

    1.2: Characteristics of Life (5)

    Levels of Organization of Living Things

    Living things are highly organized and structured, following a hierarchy that can be examined on a scale from small to large. The atom is the smallest and most fundamental unit of matter. It consists of a nucleus surrounded by electrons. Two or more atoms are joined together by one or more chemical bonds to form molecule. Many molecules that are biologically important are macromolecules, large molecules that are typically formed by polymerization (a polymer is a large molecule that is made by combining smaller units called monomers, which are simpler than macromolecules). An example of a macromolecule is deoxyribonucleic acid (DNA) (Figure 6), which contains the instructions for the structure and functioning of all living organisms.

    1.2: Characteristics of Life (6)

    Some cells contain aggregates of macromolecules surrounded by membranes; these are called organelles. Organelles are small structures that exist within cells. Examples of organelles include mitochondria and chloroplasts, which carry out indispensable functions: mitochondria produce energy to power the cell, while chloroplasts enable green plants to utilize the energy in sunlight to make sugars. All living things are made of cells; the cell itself is the smallest fundamental unit of structure and function in living organisms. (This requirement is why viruses are not considered living: they are not made of cells. To make new viruses, they have to invade and hijack the reproductive mechanism of a living cell; only then can they obtain the materials they need to reproduce.) Some organisms consist of a single cell and others are multicellular. Cells are classified as prokaryotic or eukaryotic. Prokaryotes are single-celled or colonial organisms that do not have membrane-bound nuclei or organelles; in contrast, the cells of eukaryotes do have membrane-bound organelles and a membrane-bound nucleus.

    In most multicellular organisms, cells combine to make tissues, which are groups of similar cells carrying out similar or related functions. Organs are collections of tissues grouped together performing a common function. Organs are present not only in animals but also in plants. An organ system is a higher level of organization that consists of functionally related organs. Mammals have many organ systems. For instance, the circulatory system transports blood through the body and to and from the lungs; it includes organs such as the heart and blood vessels. Organisms are individual living entities. For example, each tree in a forest is an organism. Single-celled prokaryotes and single-celled eukaryotes are also considered organisms and are typically referred to as microorganisms.

    All the individuals of a species living within a specific area are collectively called a population. For example, a forest may include many pine trees. All of these pine trees represent the population of pine trees in this forest. Different populations may live in the same specific area. For example, the forest with the pine trees includes populations of flowering plants and also insects and microbial populations. A community is the sum of populations inhabiting a particular area. For instance, all of the trees, flowers, insects, and other populations in a forest form the forest’s community. The forest itself is an ecosystem. An ecosystem consists of all the living things in a particular area together with the abiotic, non-living parts of that environment such as nitrogen in the soil or rain water. At the highest level of organization (Figure 7), the biosphere is the collection of all ecosystems, and it represents the zones of life on earth. It includes land, water, and even the atmosphere to a certain extent.

    Practice Question

    From a single organelle to the entire biosphere, living organisms are parts of a highly structured hierarchy.

    1.2: Characteristics of Life (7)

    Which of the following statements is false?

    1. Tissues exist within organs, which exist within organ systems.
    2. Communities exist within populations, which exist within ecosystems.
    3. Organelles exist within cells, which exist within tissues.
    4. Communities exist within ecosystems, which exist in the biosphere.
    Show Answer

    Statement b is false: populations exist within communities.

    Check Your Understanding

    Answer the question(s) below to see how well you understand the topics covered in the previous section. This short quiz does not count toward your grade in the class, and you can retake it an unlimited number of times.

    Use this quiz to check your understanding and decide whether to (1) study the previous section further or (2) move on to the next section.

    https://assessments.lumenlearning.co...sessments/6847

    Contributors and Attributions

    CC licensed content, Original

    • Introduction to Characteristics of Life. Authored by: Shelli Carter and Lumen Learning. Provided by: Lumen Learning. License: CC BY: Attribution

    CC licensed content, Shared previously

    Public domain content

    1.2: Characteristics of Life (2024)

    FAQs

    1.2: Characteristics of Life? ›

    Most living things need food, water, light, temperatures within certain limits, and air. Living things have a variety of characteristics that are displayed to different degrees: they respire, move, respond to stimuli, reproduce and grow, and are dependent on their environment.

    What are the characteristics of living things answer? ›

    Most living things need food, water, light, temperatures within certain limits, and air. Living things have a variety of characteristics that are displayed to different degrees: they respire, move, respond to stimuli, reproduce and grow, and are dependent on their environment.

    What are the 7 characteristics of life *? ›

    The seven characteristics what makes an organism living are: Environmental responses, cells, change and growth, reproduction, having complex chemistry, and homeostasis and energy processing. Sometimes non-living things can portray some of the above characteristics, but a living being consists of all.

    What are the 5 characteristics of life? ›

    Big Ideas: All living things have certain traits in common: Cellular organization, the ability to reproduce, growth & development, energy use, homeostasis, response to their environment, and the ability to adapt.

    What are the 3 characteristics of life? ›

    All living things detect changes in their environment and respond to them. All living things grow and develop. All living things are capable of reproduction, the process by which living things give rise to offspring. All living things are able to maintain a constant internal environment through homeostasis.

    What is a living thing answer? ›

    Living things are made up of a cell or cells. They obtain and use energy to survive. A unique ability to reproduce, ability to grow, ability to metabolize, ability to respond to stimuli, ability to adapt to the environment, ability to move, and last but not least an ability to respire.

    What is life function? ›

    Living organisms are systems made from cells and are capable of life functions such as reproduction, metabolism, response to stimuli, and homeostasis. Nonliving things are either living things that have died or inanimate objects that were never alive.

    What are few characteristics of living things? ›

    Trustworthyegoistproblem-solving
    meticulousgarrulousability to take decisions
    calculatingwilling to take risk

    Do all living things have DNA? ›

    DNA is all the same chemical

    That's because DNA looks exactly the same in every organism on Earth. All living things have DNA. And whether it comes from you, a pea plant, or your pet rat, it's all the same molecule. It's the order of the letters in the code that makes each organism different.

    Why is it important to classify living things? ›

    The classification system provides great deal of information about the characteristics of organisms. Using scientific names can therefore act as a shorthand method for describing a plant or animal.

    What is the smallest unit of life? ›

    The cell is the smallest unit of life that can divide, multiply, grow and respond to stimuli from the environment. The cell structure is colloidal. The vital signs called life, manifest itself in this colloidal environment called protoplasm.

    What are the 10 characteristics of living? ›

    All living organisms share several key characteristics or functions: order, sensitivity or response to the environment, reproduction, adaptation, growth and development, regulation, homeostasis, energy processing, and evolution.

    How to identify living things? ›

    Before identifying individual species, scientists classify living things into groups. These groups are based on their appearance, movement, how they reproduce and genetic makeup. A BioBlitz gives people the chance to take a closer look at what lives in an area and identify species that may otherwise go unnoticed.

    What do living things respond to? ›

    All living things are able to respond to stimuli in the external environment. For example, living things respond to changes in light, heat, sound, and chemical and mechanical contact.

    What are the characteristics of life paragraph? ›

    All living organisms share several key characteristics or functions: order, sensitivity or response to the environment, reproduction, growth and development, regulation, homeostasis, and energy processing. When viewed together, these characteristics serve to define life.

    What is characteristic of life quizlet? ›

    1) Living things are made up of cells. 2) Living Things reproduce. 3) Living Things are based on genetic code. 4) Living things grow and develop.

    What are the characteristics of living things pdf? ›

    All living things share certain characteristics: 1) They are made of cells, metabolize energy, respond to stimuli, reproduce, evolve over generations, and maintain homeostasis.

    What are 10 characteristics of life? ›

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