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• What are the necessities of life? In other words, what does a living organism need to survive?

• 1.• 2.• 3.• 4.

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•What are the characteristics of living organisms?

The Necessities of Life

Holt, Rinehart and Winston

Water

• About 70% of your body is made mostly of water.

• Most of the chemical reactions involved in metabolism require water.

• You could survive for only about three days without water.

• You get water from the fluids you drink and the food you eat.

Oxygen• Air is a mixture of several different

gases, including oxygen and carbon dioxide.

• Most living things use oxygen in the chemical process that releases energy from food.

• Oxygen may come from the air or may be dissolved in water.

• Organisms that can live without oxygen are anaerobic organisms.

• Organisms that need oxygen are aerobic organisms.

Space

• All organisms need space that contains all of the things they need to survive.

• Space on Earth is limited, so, organisms often compete with each other for food, water, and other necessities.

Energy

• All living things need food. • Food gives organisms energy and

the raw materials needed to carry on life processes.

• The nutrients from food replaces cells and build body parts.

• But not all organisms get food in the same way.

Energy

Making Energy (Food)• Some organisms, such as

plants, are called producers. • Producers can make their own

food. • Like most producers, plants

use energy from the sun to make food from water and carbon dioxide.

• Some producers get energy and food from the chemicals in their environment.

Taking Energy (Food)• Other organisms are called

consumers because they must eat (consume) other organisms to get food.

http://my.hrw.com/sh2/sh07_10/student/flash/visual_concepts/60366.htm

Energy

• Some consumers are decomposers. • Decomposers are organisms that get their

food by breaking down the nutrients in dead organisms or animal wastes.

Ex: mushrooms http://my.hrw.com/sh2/sh07_10/student/flash/visual_concepts/60368.htm

Putting It All Together• Nutrients are made up of molecules. • Molecules found in living things are different

combinations of six elements: – carbon, – hydrogen, – nitrogen, – oxygen, – Phosphorus– sulfur.

• These elements combine to form proteins, carbohydrates, lipids, ATP, and nucleic acids.

Proteins in Action

• Almost all of the life processes of a cell involve proteins.

• Proteins have many different functions. Ex: -hemoglobin –binds oxygen in red blood cells.-enzyme- starts or speeds up chemical reactions in cells.

• Some proteins protect cells. • http://my.hrw.com/sh2/sh07_10/student/flash/

visual_concepts/60044.htm

Carbohydrates

• Molecules made of sugars are called carbohydrates. • Cells use carbohydrates as a source of energy and for

energy storage. • An organism’s cells break down carbohydrates to

release the energy stored in them. • There are two kinds of carbohydrates– simple carbohydrates – complex carbohydrates– http://my.hrw.com/sh2/sh07_10/student/flash/visual_concepts/60029.htm

Lipids and Phospholipids

Lipids• Are compounds that cannot

mix with water. • Lipids store energy. • Lipids form the membranes

of cells.• http://my.hrw.com/sh2/sh07_10/student/flash/

visual_concepts/60035.htm

Phospholipids

• All cells are surrounded by a cell membrane.

• The cell membrane helps protect the cell and keep the internal conditions of the cell stable.

• Phospholipids form much of the cell membrane.

• The head of a phospholipid molecule is attracted to water.

• The tail is not. • When phospholipids are in water, the

tails come together, and the heads face out into the water.

• http://my.hrw.com/sh2/sh07_10/student/flash/visual_concepts/60038.htm

Fats and Oils

• Fats and oils are lipids that store energy.

• When an organism has used up most of its carbohydrates, it can get energy from these lipids.

• Most of the lipids stored in plants are oils.

• Most of the lipids stored in animals are fats.

ATP

• Adenosine triphosphate (uh DEN uh SEEN trie FAHS FAYT), also called ATP, is another important molecule.

• ATP is the major energy-carrying molecule in the cell.

• The energy in carbohydrates and lipids must be transferred to ATP, which then provides fuel for cellular activities.

Nucleic Acids

• Nucleic acids have all the information needed for a cell to make proteins.

• Nucleic acids are made up of molecules called nucleotides (NOO klee oh TIEDZ).

• DNA and RNA are a nucleic acids.

• http://my.hrw.com/sh2/sh07_10/student/flash/visual_concepts/60041.htm