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Characteristics of Living Things

I. IntroductionA. To be considered living, an organism must be made up of cells and be able to reproduce, grow,

respond to stimuli, perform certain chemical activities (metabolize), and move.

1. These characteristics or functions are what distinguish living things from nonliving thing.

II. The Characteristics of Living Thing

A. Made up of cells1. All organisms are made up of one or more cells.

2. cell = the smallest unit of an organism that can perform all of the processes necessary for life.

3. Cells contain DNA which controls all of the activities and functions of the cell as well as the

structure and traits that make up the organism.

B. Reproduction

1. reproduction = the process by which living things produce thesame kindof living thing.

a. It is important to note that like produces like (ex. cats produce cats; roses produce roses).

2. There are 2 different types of reproduction:a. asexual reproduction = reproduction in which offspring come from only one parent.

1. The offspring will be genetically identical to the parent, having all of its parents traits.

2. Examples: bacteria split to form 2 new bacteria cells; growing a new plant from a cutting.b. sexual reproduction = reproduction requiring two parents or two parent cells coming together1. The offspring will get some of their traits from one parent and some from the other.1. Example: pollen fertilizing the egg in a flower.

C. Growth and Development

1. growth = when living things increase in size and become more complex.

a. For a many-celled organism, growth happens when the number of cell in its body increases.

2. development = all of the changes an organism goes through as it grows.a. Examples: a tadpole develops into a frog; an egg develops into a caterpillar and then into a

butterfly.

3. Organisms must grow and mature to adulthood.

a. In biology, an organism is an adult when it is able to reproduce.a. Humans grow to be adults in about 14 to 18 years; dogs become adults in about 2 years,

lima beans become adults in a few weeks, and some insects can change from an egg to anadult in a few days.

4. life span = the length of time an organism can be expected to live.

a. Even though there is an average life span calculated for a certain type of organism, theactual life span of an individual organism depends on many factors.

1. These include such things as genetics, environment, exposure to disease, and the

availability of the resources it needs to live (such as food and water).

D. Response to Stimuli

1. stimulus = any change in the environment that causes an organism to react or respond.

2. response = the action taken by the organism to react to the stimulus.

a. Organisms must be able to respond to stimuli to get the things they need (ex. plants growtoward light), to prevent injury (ex. you pull your hand away from a hot stove), and to

survive in their environment (ex. a worm retreats into its burrow when touched).1. See the back of this page for examples of responses.

3. homeostasis = the ability of an organism to keep the conditions inside its body the same or

balanced even when conditions in the environment change.

a. For homeostasis to occur, the organism must respond to the changes in the environment(stimuli) and make adjustments to stay in balance.

b. Example: your body sweats when hot to try to cool down and return to its normal temperature.

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E. Metabolism

1. metabolism = all of the chemical activities in an organism that allow it to live, grow, and

reproduce.a. The chemical activities that take place in an organisms body involve breaking down

complex substances into simpler substances that the body needs or taking simple substances

and combining them to form complex substances (ex. to make parts of cells for growth).b. One of the most important chemical activities for an organism is the breaking down of food

to release its energy. This happens in a series of steps:

1. ingestion = getting food into the organism (eating).a. Some organisms may put food in their mouths while others absorb it directly into their

bodies. Plants do not ingest food because they make it through photosynthesis.2. digestion = the process by which the food is broken down into simpler substances.3. respiration = the process by which organisms take in oxygen and combine it with the

simpler substances from digestion to release the energy in the food.4. excretion = the process of getting rid of the waste materials formed.

a. If not removed, the wastes will build up in the organism and eventually poison it.

F. Movement

1. movement = to change position from one location to another.

a. Those organisms that can move do so to be able to:

1. find food and water.2. find shelter.3. escape danger.4. find a mate to reproduce.

2. Plants do not move in the same way animals do. What some people consider movement is

really growth toward a stimulus (ex. stems growing toward sunlight may make it appear that

the plant has moved toward the light).

Examples of Responses to Stimuli

How the Organism Responds

positive = responds by moving/growing toward the stimulus.

negative = responds by moving/growing away from the stimulus.

Prefix Meaningphoto- response to the stimulus of light

thermo- response to the stimulus of temperature change

chemo- response to the stimulus of chemicals

geo- response to the stimulus of gravity

thigmo-response to the stimulus of touch

Root Wordstropism = a growth response to stimulus (the plant grows toward or away from the stimulus).

taxis = a response to a stimulus that involves moving toward or away from the stimulus.

Examples:

1. A plant has a positive phototropism to sunlight (it grows toward the light).2. The roots of a plant have a positive geotropism (the roots grow down toward the gravity) but the

stem has a negative geotropism (the stem grows in a direction opposite of gravity). 3. The worm has a negative thigmotaxis (it moves away from touch).