characteristics of living organisms

defining life

Five characteristics are used to define life. All living things share these characteristics. All living things: 1. 2. 3. 4. 5. are made of one or more cells. need energy to stay alive. respond to stimuli in their environment. grow and reproduce. maintain a stable internal environment.

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living things are made of cells

Cells are the basic building blocks of life. They are like tiny factories where virtually all life processes take place. Some living things, like the bacteria in Figure 2.1, consist of just one cell. They are called single-celled organisms. You can see other single-celled organisms in Figure 2.2. Some living things are composed of a few to many trillions of cells. They are called multicellular organisms. Your body is composed of trillions of cells. Regardless of the type of organism, all living cells share certain basic structures. For example, all cells are enclosed by a membrane. The cell membrane separates the cell from its environment. It also controls what enters or leaves the cell.

living things need energy

Everything you do takes energy. Energy is the ability to change or move matter. Whether its reading these words or running a sprint, it requires energy. In fact, it takes energy just to stay alive. Where do you get energy? You probably know the answer. You get energy from food. Figure {{ref|MS-LS-SE-02-03-Food|below}] shows some healthy foods that can provide you with energy. Just like you, other living things need a source of energy. But they may use a different source. Organisms may be grouped on the basis of the source of energy they use. In which group do you belong? Producers such as the tree in Figure 2.1 use sunlight for energy to produce their own food. The process is called photosynthesis, and the food is sugar. Plants and other organisms use this food for energy. Consumers such as the raccoon in Figure 2.1 eat plantsor other consumers that eat plantsas a source of energy. Some consumers such as the mushroom in Figure 2.1 get their energy from dead organic matter. For example, they might consume dead leaves on a forest floor.

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living things respond to their environment

When a living thing responds to its environment, it is responding to a stimulus. A stimulus (stimuli, plural) is something in the environment that causes a reaction in an organism. The reaction a stimulus produces is called a response. Imagine how you would respond to the following stimuli: Youre about to cross a street when the walk light turns red. You hear a smoke alarm go off in the kitchen. You step on an upturned tack with a bare foot. You smell the aroma of your favorite food. You taste something really sour. It doesnt take much imagination to realize that responding appropriately to such stimuli might help keep you safe. It might even help you survive. Like you, all other living things sense and respond to stimuli in their environment. In general, their responses help them survive or reproduce. Watch this amazing time-lapse video to see how a plant responds to the stimuli of light and gravity as it grows. Why do you think it is important for a plant to respond appropriately to these stimuli for proper growth? MEDIA Click image to the left or use the URL below. URL:

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living things grow and reproduce

Like plants, all living things have the capacity for growth. The ducklings in Figure 2.4 have a lot of growing to do to catch up in size to their mother. Multicellular organisms like ducks grow by increasing the size and number of their cells. Single-celled organisms just grow in size. As the ducklings grow, they will develop and mature into adults. By adulthood, they will be able to reproduce. Reproduction is the production of offspring. The ability to reproduce is another characteristic of living things. Many organisms reproduce sexually. In sexual reproduction, parents of different sexes mate to produce offspring. The offspring have some combination of the traits of the two parents. Ducks are examples of sexually reproducing organisms. Other organisms reproduce asexually. In asexual reproduction, a single parent can produce offspring alone. For example, a bacterial cell reproduces by dividing into two daughter cells. The daughter cells are identical to each other and to the parent cell.

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living things maintain a stable internal environment

The tennis player in Figure 2.5 has really worked up a sweat. Do you know why we sweat? Sweating helps to keep us cool. When sweat evaporates from the skin, it uses up some of the bodys heat energy. Sweating is one of the ways that the body maintains a stable internal environment. It helps keep the bodys internal temperature constant. When the bodys internal environment is stable, the condition is called homeostasis. All living organisms have ways of maintaining homeostasis. They have mechanisms for controlling such factors as their internal temperature, water balance, and acidity. Homeostasis is necessary for normal life processes that take place inside cells. If an organism cant maintain homeostasis, normal life processes are disrupted. Disease or even death may result.

instructional diagrams

No diagram descriptions associated with this lesson

questions

__All organisms respond to their environment.

-->  a. true

b. false

__Some living things do not need energy.

a. true

-->  b. false

__All living things get food by eating other organisms.

a. true

-->  b. false

__Some organisms consume dead organic matter such as dead leaves.

-->  a. true

b. false

__Cells are the basic units of structure and function of all living things.

-->  a. true

b. false

__All organisms grow by increasing the number of their cells.

a. true

-->  b. false

__All organisms must mate to produce offspring.

a. true

-->  b. false

___organism that eats other organisms for food

a. reproduction

b. response

c. producer

d. homeostasis

e. energy

f. stimulus

-->  g. consumer

___condition in which an organism has a stable internal environment

a. reproduction

b. response

c. producer

-->  d. homeostasis

e. energy

f. stimulus

g. consumer

___something in the environment that causes a reaction in an organism

a. reproduction

b. response

c. producer

d. homeostasis

e. energy

-->  f. stimulus

g. consumer

___organism that uses energy to make food

a. reproduction

b. response

-->  c. producer

d. homeostasis

e. energy

f. stimulus

g. consumer

___reaction produced by a stimulus

a. reproduction

-->  b. response

c. producer

d. homeostasis

e. energy

f. stimulus

g. consumer

___production of offspring

-->  a. reproduction

b. response

c. producer

d. homeostasis

e. energy

f. stimulus

g. consumer

___ability to change or move matter

a. reproduction

b. response

c. producer

d. homeostasis

-->  e. energy

f. stimulus

g. consumer

Microscopic organisms include

a. bacteria

b. archaea

c. protists

-->  d. all of the above

Which of the following is a characteristic of all organisms?

a. multiple cells

-->  b. need for energy

c. sexual reproduction

d. all of the above

Living things can do all of the following except

a. grow

-->  b. create energy

c. respond to stimuli

d. maintain homeostasis

How many cells make up your body?

a. hundreds

b. thousands

c. millions

-->  d. trillions

An example of a producer is a(n)

-->  a. tree

b. raccoon

c. mushroom

d. earthworm

Multicellular organisms include

a. algae

-->  b. plants

c. bacteria

d. two of the above

Which statement is true about sexual reproduction?

a. It involves just one parent

b. Offspring are identical to the parent

c. Offspring of both sexes are always produced

-->  d. none of the above

diagram questions

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