Characteristics of Living Things
THE 6 CHARACTERISTICS
THAT ALL ORGANISMS SHARE
1. Living Things Have Cells
Every living thing is composed of one or more cells
Cell: membrane-covered structure that contains all
of the materials necessary for life
The membrane separates the contents of the cell
from the cell’s environment
Many organisms are made up of only one cell.
Other organisms are made up of trillions of cells.
Most cells are too small to be seen with the naked eye
In organisms with many cells, cells perform
2. Living Things Sense and Respond to Change
A change in an organism’s environment that affects
the activity of the organism is called a stimulus.
Stimuli can be
chemicals, gravity, darkness, light, sounds, tastes, or
anything that causes organisms to respond in some
Is your alarm clock a stimulus? Explain.
Even though an organism’s external environment
may change, the organism must maintain a stable
internal environment to survive.
This is because the life processes of organisms
involve many different kinds of chemical reactions
that can occur only in delicately balanced
The maintenance of a stable internal environment is
Your Body’s Homeostasis
Your body maintains a temperature of about 37 °C.
When you get hot, your body responds by sweating.
When you get cold, your muscles twitch in an
attempt to generate heat. This causes you to shiver.
Whether you are sweating or shivering, your body is
trying to return things to normal.
3. Living Things Reproduce
Organisms make other organisms like themselves.
This can be accomplished in 2 ways
Asexual reproduction: single parent produces offspring that
are identical to the parent. Most single-celled organisms
reproduce in this way.
Sexual reproduction: almost always requires two parents to
produce offspring that will share characteristics of both
parents. Most animals and plants reproduce in this way.
What about Hybrids?
Though very much alive, mules and most other
hybrids cannot reproduce. Hybrids are the result of
mating organisms from different species.
A mule is the offspring of a mare (female horse) and
a jack (male donkey). Mules often live long, healthy
lives, but they never have babies.
4. Living Things Have DNA
The cells of all living things contain a special molecule
called DNA (deoxyribonucleic acid).
DNA provides instructions for making
molecules called proteins.
Proteins take part in almost all of the
activities of an organism’s cells.
Proteins also determine many of an
When organisms reproduce, they pass on copies of
their DNA to their offspring.
The transmission of characteristics from one
generation to the next is called heredity.
Offspring resemble their parents because of heredity.
Debate: Nature vs. Nurture
Scientists have proven that we inherit our physical
characteristics from our parents (nature). They
continue to research whether we inherit our
personalities from our parents. Some scientists say
that where we live and how we are raised are more
What do you think is the more important factor in
who we become, nurture (care) or nature (heredity)?
5. Living Things Use Energy
Organisms use energy to carry out the activities of
These include activities such as making
food, breaking down food, moving materials into and
out of cells, and building cells.
An organism’s metabolism is the total of all of the
chemical activities that it performs
6. Living Things Grow and Develop
All living things, whether single celled or many
celled, grow during periods of their lives.
Growth in single-celled organisms occurs as the cell
Organisms made of many cells grow mainly by
increasing their number of cells.
In addition to getting larger, living things may
develop and change as they grow.
An apple tree is a living thing. Can it make oranges?
Why or why not?
What is the difference between growth and
Name three activities of an organism that require
The Simple Bare
Necessities of Life
WHAT ORGANISMS NEED TO SURVIVE
Provides organisms with the energy and raw
materials needed to carry on life processes and to
build and repair cells and body parts
Producers: produce their own food through
Consumers: consume other organisms to get food
Decomposers: get their food by breaking down the
nutrients in dead organisms or animal wastes
Your cells and the cells of almost all living organisms are
approximately 70% water
Most of the chemical reactions involved in metabolism require
Organisms differ greatly in how much water they need and
how they obtain it
Humans could survive for 3 days without water and obtain
water from the fluids we drink and the food we eat
Kangaroo rats that live in the desert never drink. They get all
of their water from its food.
Mixture of several different gases including oxygen
and carbon dioxide
Most living things use oxygen in the chemical
process that releases energy from food.
Organisms that live on land get oxygen from the air
Organisms living in water either take in dissolved
oxygen from the water or come to the water’s surface
to get oxygen from the air
A Place to Live
All organisms must have somewhere to live that
contains all of the things they need to survive.
Because the amount of space on Earth is limited,
organisms often compete with each other for food,
water, and other necessities.
Why are decomposers categorized as consumers?
How are they different from producers?
Why are most cells 70% water?
How might a cave, an ant, and a lake meet the needs
of an organism?
The Chemistry of Life
WHAT CELLS ARE MADE UP OF
Everything, alive or not, is made up of tiny building
blocks called atoms.
A substance made up of one type of atom is called an
When 2 or more atoms join together, they form a
Molecules found in living things are usually made of
different combinations of six elements:
Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorous, and
Almost all of the life processes of a cell involve
proteins. After water, proteins are the most
abundant materials in cells.
Proteins are large molecules that are made up of
subunits called amino acids.
Organisms break down these proteins in food to
supply the cells with amino acids. These amino acids
are then linked together to form new proteins.
Proteins in Action
Proteins have many different functions.
Some form structures that are easy to see like
feathers, spider webs, and hair.
Others are at work at the cellular level.
Hemoglobin is a protein in red blood cells that
attaches to oxygen so that oxygen can be delivered
throughout the body.
Math Break: How Much Oxygen?
Each red blood cell carries about 250 million
molecules of hemoglobin.
How many molecules of oxygen could a single red
blood cell deliver throughout the body if every
hemoglobin molecule attached to four oxygen
1,000,000,000 molecules of oxygen
Group of compounds made of sugars
Cells use carbohydrates as a source of energy and for
When an organism needs energy, its cells break
down carbohydrates to release the energy stored in
2 types of carbohydrates
Simple: made of 1 sugar molecule or a few sugar
molecules linked together
Examples: table sugar and the sugar in fruits
Too Much Sugar!
When an organism has more sugar than it needs, its
extra sugar may be stored in form of complex
Complex carbohydrates are made of hundreds of
sugar molecules linked together
Your body makes some complex carbohydrates and
stores them in your liver
Plants make a complex carbohydrate called starch
When you eat mashed potatoes or french fries, you
are eating a potato plant’s stored starch
Compounds that cannot mix with water
Fats and oils are lipids that store energy. When an
organism has used up most of its carbohydrates, it can
obtain energy from these lipids.
The structures of fats and oils are almost identical, but at
room temperature most fats are solid and oils are liquid.
Most lipids stored in plants are oils, while most of the
lipids stored in animals are fats.
Is that a Fact!
Fats and lipids are also vital to nerve formation and
Fat acts as an insulator on the nerve, speeding up the
electrical impulse that the nerve is carrying.
All cells are surrounded by a structure called a cell
Phospholipids are the molecules that form much of
the cell membrane. When these phospholipids are in
water, like in a cell, the tails come together and the
heads face out into the water.
This happens because the head of a phospholipid
molecule is attracted to water while the tail is not.
Compounds made up of subunits called nucleotides
A nucleic acid may contain thousands of nucleotides.
Nucleic acids are sometimes called the blueprints of
life because they contain all the information needed
for the cell to make all of its proteins
DNA is a nucleic acid.
A DNA molecule is like a recipe book titled
How to Make Proteins.
When a cell needs to make a certain protein, it gets
information from DNA to direct how amino acids are
hooked together to make that protein.
The Cell’s Fuel
ATP (adenosine triphosphate) is the major fuel used
for all cell activities that require energy.
When food molecules, such as carbohydrates and
fats, are broken down, some of the released energy is
transferred to ATP molecules.
The energy in carbohydrates and lipids must be
transferred to ATP before the stored energy can be
used by cells to fuel their life processes.
Fireflies produce their flashing light by a chemical
reaction. The enzyme luciferase acts on the chemical
luciferin in the presence of ATP to create the light.
Scientists now use luciferase in the laboratory to
study everything from heart disease to muscular
What are the subunits of proteins? Of starch? Of
What do carbohydrates, fats, and oils have in
Are all proteins enzymes? Why or why not?