The Characteristics of Life

AP Biology

Notes: #1

Life’s Diversity & Unity

Life has extensive diversity.

Despite its diversity, all living things are

composed of the same chemical elements

that make-up non-living things.

Yet, all living things have fundamental

characteristics that they share and help

distinguish from non-living things.

The Characteristics of Life

Biologists have devised a list of 8

characteristics that all life shares.

Something can be considered alive ONLY if it

displays ALL 8 of these characteristics.

Anything that possesses all 8 of the

characteristics of life is called an organism.

The 8 Characteristics of Life: 1. Organization/Order – has cellular organization (all organisms are made of 1 or more cells)

cell tissue organ system organism

2. Reproduces – DNA is the common genetic material

3. Growth & Development

4. Metabolism – acquires materials for energy

5. Responds to Stimuli – responds to the environment

6. Homeostasis/Regulation – maintains internal balance

7. Evolutionary Adaptations – As a group, organisms adapt and change over time.

8. Organic – Carbon is the basis of all biological molecules found in living organisms

The Characteristics of Life

All life begins with the cell.

Cell = smallest unit of life.

In multi-cellular organisms, similar cells cluster together to form tissues.

1. Life has Cell(s) & is based on Cellular Organization:

"Omnis cellula e cellula”

(Every cell out of a cell) Rudolf Carl Virchow (1821 – 1902)

A Hierarchy of Biological

Organization

The hierarchy of life

– extends through many levels of biological

organization

The levels:

Atom Molecule Cell Tissue

Organ System Organism Population

Community Ecosystem Biosphere

Emergent Properties

Each new level of biological organization

has “emergent properties”.

Emergent Properties = features that result

due to interactions between parts

making up the whole that do not exist in

the parts alone.

“IN THE LIVING WORLD, THE WHOLE IS

INDEED MORE THAN THE SUM OF ITS

PARTS.”

The Characteristics of Life

2. Life reproduces:

All living organisms are able to produce live offspring.

SPECIES = group

of organisms that

can breed &

produce fertile

offspring

Life comes from life!

Sexual

Asexual

DNA/Genes

All living

organisms contain

genetic

information that

can be passed on

through

generations.

Each offspring’s

DNA is unique!

Growth: an increase in the

size or mass of an

organism due to an

increase in the size &

number of cells

Development: all of the

changes that take place

throughout the life span of

an organism

All living organisms grow & develop during their life spans.

3. Life Grows & Develops:

4. Life requires Energy/Metabolism: Life acquires, stores, & processes nutrient

molecules from “food” for energy.

The Characteristics of Life

PRODUCERS: most plants &

some unicellular organisms use

solar energy to make their own

food & fuel their activities.

CONSUMERS: organisms that cannot

make their own food get energy by

consuming other organisms.

What is Metabolism?

All chemical reactions in the cell that make

parts or products from nutrient molecules

to utilize or create energy.

Two Types:

– Anabolism = synthesis reactions (to produce

& store energy)

– Catabolism = breaking down reactions (to

release energy)

“Here Comes the Sun…”

ULTIMATE SOURCE OF ENERGY = SUN!

Photosynthesis = process of transforming

solar energy into chemical energy stored in the

chemical bonds between organic nutrient

molecules

Cellular Respiration = process of acquiring

energy by metabolizing nutrient molecules

produced by photosynthesis

Byproducts of each support the other!

The Characteristics of Life

Living things have the ability to react

(or respond) to an environmental

condition or stimulus.

Physiological or Behavioral Response

– often results in movement

Necessary to help ensure survival of

the organism & help it to carry out

daily activities or behaviors.

5. Life Responds to Stimuli:

Venus flytrap

What is Stimuli?

Stimulus = anything in the

internal or external

environment that causes a

response

Response = reaction to a

stimulus; can be a

behavior change or

physical and/or chemical

response

The Characteristics of Life

6. Maintains Homeostasis:

All living organisms are able to maintain a relatively constant internal environment or condition.

Homeostasis: the regulation of an

organism’s internal environment within

certain boundaries to maintain

conditions suitable for life.

Organisms maintain homeostasis

by depending on:

Behavior

Innate Control Mechanisms

– Release of Enzymes, Hormones, Nerve

Impulses, etc.

– Positive & Negative Feedback Mechanisms

are Essential for Internal Regulation:

Organisms maintain dynamic balance by “switching

on & off” physiological pathways

Pathways can create products that stimulate new

pathways or even shut themselves “off.”

7. Life Adapts and Evolves:

The Characteristics of Life

Living things must adapt to their environment to survive.

If a “trait” is advantageous,

– it becomes an adaptation.

– it can help some individuals survive

– it is passed on to future generations.

OVER LOTS OF TIME,

– the population’s genes can change/evolve

– because more individuals have the adaptation.

Adaptation = an

inherited trait that

gives an advantage

to organisms in their

environment & is

passed on

Evolution = changes in

the genetic make-up

of an organism over

time

Evolution occurs by natural selection of

adaptations.

Clarifying Evolution, Adaption, and

Natural Selection

Evolution = the theory on how changes in a

population (i.e. group of interbreeding species)

occurs over extended time

– assumes that the “how” or mechanism by which

adaptations occur in a species is natural selection

Natural Selection = the mechanism by which

evolutionary adaptations occur over time in

response to a population’s environment

Adaptation = the product of natural selection; a

trait or physical modification that makes organisms

better suited for their environment

Evolutionary View on Life

Began in 1859 when Charles Darwin

published On the Origin of Species by

Natural Selection

Origin of Species

Highlighted:

– Natural Selection

– Descent with Modification

Figure 1.18

When Natural Selection Occurs

A population’s have heritable variations or

traits.

– exposed to the environment all the time.

Selection occurs when traits in a

population give an organism an advantage

for survival and successful reproduction.

– Thus, selection is when heritable variations

favor the reproductive success of some

individuals over others.

Products of Natural Selection

Are exquisite adaptations of organisms to

the special circumstances of their way of

life and their environment

Evolution Supports the Theme of

“Descent with Modification”

“Descent with Modification” explains

why life has both unity and diversity.

– UNITY: All organisms share common

defining features of life, suggesting they

“descended” from a common ancestor

– DIVERSITY: The process of evolution

allows species to modify features in order

to adapt to different ways of life. This

allows for life to be diverse.

The Characteristics of Life 8. Life is ORGANIC: Living organisms are made of

molecules with lots of Carbon atoms!

Carbon…the “stuff” of life

Organic molecules contain a variety of atomic

elements.

– i.e. hydrogen, oxygen, nitrogen, phosphorus, & sulfur

Yet, carbon atoms are the most predominant

structures in organic molecules

– typically linked as carbon-to-carbon bonds

All cells share a common set of carbon-containing

molecules (called “organic molecules”) dissolved

or dispersed in H20 as a common medium of

housing and interaction.