1. Living Things
7th Grade Science

2. Characteristics of all Living Things
Cellular organization
Contain similar chemicals
Use energy
Grow and develop
Respond to surroundings
Reproduce

3. Cellular Organization
Cells: basic unit of structure and function
Unicellular: single-celled organisms
Multicellular: organisms composed of many cells, cells are specialized

4. Similar Chemicals Water Carbohydrates – energy source for cells
Proteins and lipids – building materials of cells
Nucleic acids – genetic material, direct cell activity

5. Response to Surroundings
Stimulus: a change in an organism’s surroundings that causes the organism to react
Temperature
Light
Sound
Response: an action or change in behavior, reaction to a stimulus
Examples?

6. Life Comes from Life
Spontaneous generation: mistaken idea that living things come from nonliving sources
Redi and Pasteur both performed experiments to disprove spontaneous generation
How could you prove that life does not come from nonliving sources?

7. Needs of Living Things Energy Water Space Stable internal conditions
Autotrophs: organisms that make their own food
Heterotrophs: organisms that cannot make their own food
Water
Obtain chemicals from surroundings
Break down food
Move substances within their bodies
Reproduce
Space
Stable internal conditions
Homeostasis: stability despite changes in environment

8. The Origin of Life Early Earth had a different atmosphere than today
3.6 billion years ago, nitrogen, water vapor, carbon dioxide, and methane were most abundant
Early life forms did not need oxygen
Early organisms probably unicellular, ocean dwelling life forms
Major gases today are nitrogen and oxygen
Scientists hypothesize that electric current through the old mixture of gasses created proteins
How would life come about after this?

9. The First Cells
Scientists hypothesize that cells formed gradually over millions of years in Earth’s waters
Fossil record supports this hypothesis
First organisms probably heterotrophs – as their numbers increased the food supply decreased, so at some point some organisms developed the ability to make their own food
Oxygen is a waste product of autotrophs – more oxygen changed the atmosphere
Why is this a theory and not fact?

10. Classification
The process of grouping things based on their similarities
Biologists use classification to organize living things into groups so that they are easier to study
Taxonomy: the study of how things are classified
Once an organism is classified, we know a lot about that organism already!
Example: you see a fish you’ve never seen before, but you know it’s a fish – how do you know it’s a fish? What characteristics does it have?

11. Aristotle vs. Linnaeus
Aristotle observed animal appearance, behavior, movement
Grouped animals into those that fly, swim, or walk
Used subgroups to further classify
Binomial nomenclature: two-part names
Genus: first part of name, groups organisms that are similar and closely related
Species: second part of name, group of similar organisms that can reproduce

12. Levels of Classification
Today’s system combines Aristotle’s and Linnaeus’ systems
Seven levels of classification – organisms grouped by shared characteristics (p. 223)
Kingdom
Phyla (phylum – singular)
Class
Order
Family
Genus
Species

13. Classification and Evolution
Darwin’s theory of evolution changed classification
Certain organisms are similar because they share a common ancestor/evolutionary history
Species with similar evolutionary histories are classified more closely together
Remember discussion of fossils, body structures, early development
Scientists also look closely at cellular evidence

14. The Classification System
Taxonomic key: a series of paired statements that describe the physical characteristics of different organisms
P. 227
In pairs, work on the Living Mysteries activity.

15. The Six Kingdoms Archaebacteria Fungi Eubacteria Plant Protists Animal
Ancient bacteria
Autotrophic or heterotrophic
Live on ocean floor, salty water, hot springs, intestines
Prokaryotes: cells lack a nucleus
Eubacteria
Unicellular prokaryotes
Protists
Unicellular or multicellular
Eukaryotes: cells have a nucleus
Fungi
Mushrooms, molds, mildew
Most multicellular eukaryotes
Few unicellular eukaryotes (yeast)
All heterotrophs
Plant
Multicellular eukaryotes
Autotrophs
Animal
Heterotrophs