Living things have six key characteristics: cells, response to stimuli, reproduction, DNA, metabolism, and growth/development. The necessities of life are water, air, food, and shelter. Cells contain proteins, carbohydrates, lipids, ATP, and nucleic acids which provide structure and carry out life functions.

1. Is It Alive?
Characteristics of
Living Things
&
Necessities of
Life

2. Characteristics of Living
Things
 What makes something
living or nonliving?
 Is a rock living? What
about a piece of grass?
Or an icicle?
 There are 6
characteristics of
living things

3. #1: Living Things Have Cells
 All living things are
composed of one or
more cells
 What is a cell? A cell
is a membrane-
covered structure that
contains all the
material necessary for
life
 Unicellular = one cell;
multicellular = more
than one cell

4. #2: Living Things Sense and
Respond to Change
 A stimulus is a change that affects the activity of an
organism.
-Examples: chemicals, gravity, light, sound,
hunger, or anything else that activates a
response
 Homeostasis is the maintenance of a stable internal
environment
 Allows us to keep our internal environment in check when
external environment is changing
 Example: When it gets cold outside, our internal temp still
stay 98.6 degrees

5. Homeostasis is kind of like a see-saw, which your body wants to keep
balanced.
-Outside temp is cold, but our bodies don’t plunge into a low
body temp—it works hard to balance our temp at 98.6 degrees, no
matter what the outside weather!

6. #3: Living Things Reproduce
 Sexual reproduction:
two parents produce
offspring that is similar
to both parents
 Asexual reproduction:
single parent produces
offspring that is identical
to the parent

7. #4: Living Things Have DNA
 The cells of ALL living
things contain the
molecule
“deoxyribonucleic acid,
or DNA
 DNA controls structure
and function of the
cells
 Heredity: passing
copies of DNA from
parent to offspring

8. #5: Living Things Use Energy
 Organisms need and use energy to carry out
activities in life
 Metabolism: the total of all the chemical
activities that the organism performs

9. #6: Living Things Grow and
Develop
 We all GROW! It doesn’t
matter if you are a multicellular
or unicellular organism
 We all develop! As we grow,
we go through different stages
in our lives.
 Example: US! Baby->child->teen-
>adult
 Acorn  seedling  sapling 
tree

10. Necessities of Life
 Organisms need 4 things to live:
 Water
Your body is made up of 70 %
water
Most of the chemical
reactions involved in
metabolism require water

11.  Air
A mixture of gases (oxygen and
carbon dioxide)
Organisms on land get oxygen
from the air
Marine animals get dissolved
oxygen from the water or by
coming up for air
Green plants, algae, and some
bacteria need carbon dioxide in
addition to oxygen to undergo
their food making process called
photosynthesis

12.  Food
 Gives us energy and raw materials
needed to carry on life processes such
as replacing cells
 Producers: make their own food
 Consumers: get food by eating other
organisms
 Decomposers: break down nutrients of
dead organisms or animal wastes

13. 5 Building Blocks of Cells
 1) Proteins:
Molecule made up
of amino acids;
helps build and
repair body
structures.
Example: protein
hemoglobin is in red
blood cells and
binds to oxygen to
deliver it throughout
the body

14.  2) Carbohydrates:
molecules made up of
sugar
 A) Simple
carbohydrates: one
sugar molecule, like
table sugar
 B) Complex
carbohydrates:
hundreds of sugar
molecules, such as
plants (potato, whole
wheat)

15.  3) Lipids: do not
dissolve in water;
include fats and
steroids
 A) phospholipids are
the molecules that
form much of the cell
membrane; the head
is attracted to water
but the tail is not—the
tails attract to form
two layers

16.  4)ATP:
“Adenosine
Triphosphate”;
major energy-
carrying molecule
in the cell; provides
energy for the cell

17.  5)Nucleic
Acids: have all
the information a
cell needs to
make proteins;
DNA is a nucleic
acid

18.  Shelter (a
place to live)
 All living
things need
a place to
live that has
all of the
necessities
of life
(enough
space,
food, water,
etc)