Chapter Outline

Life Science

Life science: the study of all living things

Characteristics of Living Things

• Living things have a life cycle of five stages: beginning; growth; maturity; decline; death
• Living things depend on a source of energy.
• Living things reproduce.
• Living things respond to stimuli.
• Living things are composed of cells.

The Cell

The cell is the basic unit of life.

Common characteristics of cells:

• cell membrane—a protective, soft and flexible covering
• nucleus—the control center of the cell
• cytoplasm—a jellylike fluid of important organic molecules
• organelles—specialized structures within the cytoplasm
• cell wall—supportive structure surrounding the cell membrane (in plant cells)
• chloroplasts—organelles that contain chlorophyll (in plant cells)

Heredity

The study of genetics determines how characteristics are passed from an organism to its offspring. The following structures and processes all play a role in an organism’s genetic makeup:

• DNA—a large, complex molecule in the shape of a double helix (spiral) found in a cell's nucleus
• chromosome—a single DNA molecule that is made up of genes, the coded instructions for individual traits
• dominant gene—one gene in a gene pair that determines the effect of the gene pair
• recessive gene—a gene that has no effect if a dominant gene is present
• mitosis—the division of a cell resulting in the formation of two new cells, each containing the identical genetic information of the original cell
• mutation—a change in a DNA molecule that creates a set of coded instructions that are different from those contained in the original cell
• species—organisms that have the same number of chromosomes and look alike

Characteristics of Simple Organisms

Unicellular organisms are single-celled organisms that carry on all of life's essential activities:

• prokaryotes—organisms, such as bacteria, whose cells do not contain a nucleus or other specialized structures
• eukaryotes—organisms, such as amoebas, whose cells do contain a nucleus and other specialized structures

Simple multicellular organisms are simple organisms made up of more than one cell:

• fungi—simple plants, such as mushrooms, that do not contain chlorophyll
• moss—the main type of nonvascular plant, a plant that has no specialized tissue to transport water and nutrients to its parts
• fern—the simplest type of vascular plant, a plant that has specialized tissue to transport water and nutrients to its parts

Characteristics of Flowering Plants

Flowering plants are complex multicellular organisms with a variety of specialized structures:

• roots—used for anchoring a plant to the ground and absorbing water and minerals from the soil
• stems—used for holding leaves up to the sunlight and for transporting water and minerals from the roots
• leaves—the site of photosynthesis, the process in which food (sugar) results from a chemical process involving water and carbon dioxide gas in the presence of sunlight
• flowers—the place in which the reproductive parts of a plant are located

Characteristics of Animals

An invertebrate is an animal without a backbone or a skull. More than 95 percent of all animals are invertebrates. Some of the most common types are listed below:

• sponges—water-dwelling invertebrates that do not have a head, arms or legs, nerves, or a central digestive pathway
• jellyfish—invertebrates that have a digestive cavity and a central nervous system
• worms—invertebrates with a segmented body and a nervous system that responds to both light and sound
• mollusks—invertebrates that usually have a soft body covered by a protective shell
• arthropods—invertebrates that have jointed limbs and an exoskeleton (a hard outer covering)

Vertebrates are animals with a backbone and a skull. Cold-blooded vertebrates cannot control their own body temperature:

• fish—vertebrates that live in water and use gills for breathing
• amphibians—vertebrates that go through two different life phases, the first in water and the second on land
• reptiles—vertebrates that live on land but are most comfortable near water

Warm-blooded vertebrates can control their own body temperature:

• birds—vertebrates that have wings and fly
• mammals—vertebrates that directly give birth to live young

Animal Behavior

Behavior refers to activities that animals engage in to ensure their survival or the survival of their species:

• animal senses—sight, hearing, smell, taste, and touch
• biological timekeeping—an internal biological clock that acts to control natural behavioral cycles such as sleeping and eating
• navigation—means of finding direction and distance
• animal defenses—running away, natural camouflage, a protective outer layer or shell, an ability to fight back, and the ability to play dead
• social behavior—communicating, courtship, playing, and living peacefully in a group
• toolmaking—the knowledge and ability to make tools to aid in life processes

Communities of Living Things

An ecosystem is made up of a community of populations of organisms, all the habitats of the organisms, and all the natural resources that affect the community:

• habitat—a home for a population of organisms
• population—all the organisms in a single species
• food chain—an interdependence of a group of animals and plants in which one eats the other to survive
• food web—many different food chains that are linked in a complex circular relationship

The Theory of Evolution

The modern theory of evolution began with the work of Charles Darwin in the mid-1800s. The main ideas that form the theory of evolution are listed below.

• There are genetic variations among the members of every species. A genetic variation is called a mutation. Some mutations produce favorable traits that help an organism survive. Some mutations produce unfavorable traits.
• An ecosystem can support only a limited number of each species. Competition for food, shelter, and other resources limits the population of each species.
• Members of a species with the most favorable traits are the ones most likely to survive. Members that survive will pass these favorable traits on to offspring.

Darwin's theory of evolution predicts that evolution takes place slowly—perhaps over hundreds of thousands of years—as species gradually become better adapted to a slowly changing environment.

Catastrophic events can cause a type of rapid evolution called punctuated equilibrium.

The Fossil Record

A fossil is the preserved remains or traces of an ancient living thing. An organism’s fossil can tell us many things about the organism:

• when an organism first appeared on Earth
• how an organism differed from its ancestors
• characteristics of an organism's life
• how long the organism was on Earth before dying
• what caused an organism to become die

Fossils also tell us many things about the first appearance of different types of life on Earth:

• The earliest form of life appears to have been blue-green algae that appeared on Earth about 3.5 billion years ago.
• The first complex organisms, jellyfish and worms, began appearing on Earth about 680 million years ago.
• The first ocean-dwelling vertebrates appeared about 570 million years ago.
• The first amphibians appeared about 400 million years ago.
• The first land-dwelling reptiles, including dinosaurs, appeared about 300 million years ago.
• The first land-dwelling mammals appeared about 100 million years ago.
• Mammals became the dominant life form on Earth about 65 million years ago, following the sudden extinction of dinosaurs.