Holt: CH. 2 It's Alive!! Or Is It?
CH. 2 It's Alive!! Or Is It?
Section 1 Characteristics of Living Things
1. What Are All Living Things Made Of?
Organism - a living thing; anything that can carry out life processes independently
Made of one or more Cells - the smallest unit that can carry out all the activities of life
Cells are surrounded by a cell membrane
Cell membrane separates the cell from the outside environment
2. How Do Living Things respond to Change?
Respond to changes in their environment
Stimulus - a change that affects how an organism acts
Can be - chemicals, light, sounds, hunger, or anything that causes an organism to react.
Homeostasis - the act of keeping a constant environment inside an organism
Organisms respond in different ways
Hot - Humans sweat
Cold - Humans shiver
Crocodiles lie in sun to get warm
Open their mouths to release heat
3. How Do Organisms Have Offspring?
Sexual reproduction - two parents make an offspring; offspring gets traits from both parents
Most plants and animals
Asexual reproduction - one parent makes offspring; offspring are identical to parent
Most single-celled organisms and some multicellular organisms
Ex. Hydra (buds break off to form new Hydra)
DNA - deoxyribonucleic acid
Contains each organism's instructions - genes (traits)
Heredity - passing traits from parent to offspring
4. Why Do Organisms Need Energy?
All organisms need energy to live
Most get energy from the food they eat (Heterotroph)
Need energy to break down food, to move materials in and out of cells, and to build cells
Use energy to keep up metabolism
Metabolism - all of the chemical reactions that take place in the body
5. How Do organisms Grow?
All organisms grow during some part of their lives.
The cell gets bigger and divides - this makes new organisms
Gets bigger by making more cells
Characteristics of Living Things:
Made of one or more cells
Respond to Changes
Section 2 The Necessities of Life
1. What Do Living Things need?
Almost every organism has the same basic needs
Water, air, a place to live, and food
The cells that make up your body are about 70% to 85% water
Cells need water to keep inside environments stable
Most chemical reactions need water
You lose water when you breathe, sweat, or get rid of wastes
You must constantly replace water
Humans can only survive about 3 days without drinking water
Kangaroo rats never drink
Oxygen, nitrogen, and carbon dioxide are some of the gases in air
Most organisms use oxygen to help break down food for energy
Green plants use carbon dioxide to make food
Place to Live
All living things need a place to live
This puts organisms in Competition for resources
All organisms need food
Food provides - energy & nutrients
Three ways to get food
Producers - (Autotrophs) make their own food using energy from their environment
Ex. Plants, some bacteria and some protists
Photosynthesis - the process of using the sun's energy to make food from carbon dioxide and water
Consumers - (Heterotrophs) eat other organisms to get food
All animals are consumers
Decomposer - break down dead organisms and animal wastes to get food
Ex. Mushrooms (Fungi)
2. What Do Organisms get from Food?
Energy and Nutrients
Nutrients are molecules
Molecules - are made of two or more atoms joined together
In living things, most molecules are combinations of
Carbon, nitrogen, oxygen, phosphorus, and sulfur
Proteins, nucleic acids, lipids, carbohydrates, and ATP are molecules needed by living things.
Proteins - large molecules made up of smaller molecules called amino acids.
Living things break down proteins in food and use the amino acids to make new proteins
to build or fix parts of an organism
to protect the cell
Enzymes - to start or speed up reactions inside a cell
Hemoglobin - (inside a red blood cell) picks up oxygen and delivers it where it is needed
Instructions for making any part of an organism are found in DNA
Nucleic Acid - molecules made of smaller molecules called nucleotides
The order of nucleotides in DNA tells cells which amino acids to use and which order to put them in.
Lipids - molecules that cannot mix with water
Are a form of stored energy - can be broken down to release energy
Fats - solid lipids stored in animals
Oils - liquid lipids stored in plants
Form cell membranes
Phospholipids - make up a membrane
Have a head and tail
Head end faces toward water - tail faces away from water
Carbohydrates - molecules made of sugar
Provide and store energy for cells
Cells breakdown carbohydrates to release energy
Two Types -
Simple Carbohydrates - made of one or a few sugar molecules
Ex. Table sugar and sugar in fruits
Ex. Glucose - the most common energy source
Complex Carbohydrates - made of hundreds of sugar molecules linked together
Plants store glucose as complex carbohydrates (starch)
Ex. Whole-wheat bread, pasta, oatmeal, and brown rice
ATP - a molecule that carries energy in cells
Adenosine triphosphate (ATP)