Chapter 22 Part 1 The Basic Unit of Life – the Cell
The Big Idea- All living things are made up of one or more units called cells
Biology: the study of Life
Biology is the study of life and living things
A biologist is anyone who uses the scientific method to study life
An organism is an individual living thing such as a plant or an animal.
Branches of Biology- most of these overlap with other fields
Zoology- study of animals
Botany- study of plants
Microbiology- study of small microscopic organisms
Paleontology- study of extinct organisms
Cytology- study of cells
Genomics- study of the total hereditary content of various organisms
There are a lot more branches and sub-branches
But what exactly makes a living thing alive?
In order to answer this we have to first consider the features of living things.
Characteristics of Living Things
1. Are made up of one or more units called cells
2. Are based on a universal genetic code
3. Obtain and use energy
4. Grow and develop
5. Maintain a stable environment
6. Reproduce
7. Respond to their environment
8. Evolve
1. Living things are made up of cells
Cell- basic unit of structure and function in living things; though small in size, cells are complex and
highly organized
Organisms are of two types:
Unicellular- an organism consisting of a single cell; bacteria, protists, some fungi
Multicellular- an organism consisting of many cells; some of which are typically specialized
for particular functions
2. Living things are based on a universal genetic code
All organisms store the complex information they need to live, grow and reproduce in a genetic code
written in the molecule DNA (deoxyribonucleic acid)
That information is copied and passed from parent to offspring
With a few minor variations, life’s genetic code is almost identical in every living organism on earth
3. Living things obtain and use energy
the energy is conserved and changed from one type of energy to another
Autotroph- organism that makes it’s own food for energy (producer)
Photosynthetic autotroph- uses sunlight as its energy source to make food (photosynthesis)
Chemotrophic autotroph- use the energy from chemical reactions as its source of energy to
make food ( obscure group)
Heterotroph- organisms that get their food from an outside source- cannot make it themselves- use
the processes of cellular respiration and fermentation to release energy from food (consumer)
Chemotrophic heterotroph- organisms that can obtain energy by taking in organic molecules
and then breaking them down
Phototrophic heterotroph- organisms that are able to use sunlight for energy but also require
organic compounds for energy (obscure group)
Metabolism- the sum total of all the chemical reactions in the body – the balance of catabolism
and anabolism
Catabolism- the final breakdown of complex substances to simpler substances
Anabolism- any process in a living organism that involves putting together, or synthesizing
complex substances from simpler substances
4. Living things grow and develop
Growth can be accomplished in two ways:
Increase in cell size (baby cell grows bigger)
Increase in cell number (for multi-cellular organisms)
Development involves maturation
A butterfly goes through a metamorphosis to change from a egg, to larva, to pupa to butterfly
Female egg cells mature during menstruation
Organisms have some type of life cycle that takes them from birth to death- some are more
complicated than others but all living things have them
5. Living things maintain themselves- they maintain a stable environment
They make structures and repair damaged structures
They maintain their internal environment
Using energy to keep conditions inside their cells within certain limits is called homeostasis
More on maintaining environment
Def- homeostasis- an organism’s ability to maintain constant or stable conditions that are necessary
for life
Ex- sweating or shivering to maintain temperature; blood pressure, etc.
6. Living things can reproduce as a species
Reproduction- producing new organisms of the same type
Asexual reproduction- a single organism produces new organisms that are genetically identical
to itself- bacteria, protists, fungus, plants, some animals
Sexual reproduction- a process in which two cells, normally from different organisms unite to
produce the first cell of a genetically different organism – bacteria (simple) protists, fungus,
plants, animals
7. Living things can respond to their environment
Responses can be rapid or slow
Stimulus- anything in the environment that causes an organism to react
Irritability- no, not grumpiness!- it’s the ability of an organism to respond to stimuli (plural of
stimulus)
8. Taken as a group, living things evolve
Over generations, groups of organisms evolve, or change over time
Evolutionary change links all forms of life to a common origin more than 3.5 billion years ago
Evidence of this shared history is found in all aspects of living and fossil organisms, from physical
features to structures of proteins to sequences of information in DNA.
Any structure, behavior or internal process that enables an organism to respond to environmental
factors and live to produce offspring is called an adaptation
Adaptations are inherited from previous generations
The gradual change in a species through adaptations over time is evolution