Living Things7th Grade Science

Characteristics of all Living Things

Cellular organization

Contain similar chemicals

Use energy

Grow and develop

Respond to surroundings

Reproduce

Cellular Organization

Cells: basic unit of structure and function

Unicellular: single-celled organisms

Multicellular: organisms composed of many cells, cells are specialized

Similar Chemicals

Water

Carbohydrates – energy source for cells

Proteins and lipids – building materials of cells

Nucleic acids – genetic material, direct cell activity

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?

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?

Needs of Living Things

Energy 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

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?

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?

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?

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

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

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

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.

The Six Kingdoms Archaebacteria

Ancient bacteria

Autotrophic or heterotrophic

Live on ocean floor, salty water, hot springs, intestines

Prokaryotes: cells lack a nucleus

Eubacteria Unicellular prokaryotes

Autotrophic or heterotrophic

Protists Autotrophic or heterotrophic

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 Multicellular eukaryotes

Heterotrophs