living things

It’s Alive!! Or, Is it?

THE 6 CHARACTERISTICS THAT ALL ORGANISMS SHARE

Characteristics of Living Things

1. Living Things Have Cells

Every living thing is composed of one or more cells

Cell: membrane-covered structure that contains all of the materials necessary for life

The membrane separates the contents of the cell from the cell’s environment

Many organisms are made up of only one cell.

Other organisms are made up of trillions of cells.

Most cells are too small to be seen with the naked eye

In organisms with many cells, cells perform specialized functions

2. Living Things Sense and Respond to Change

A change in an organism’s environment that affects the activity of the organism is called a stimulus.

Stimuli can be chemicals, gravity, darkness, light, sounds, tastes, or anything that causes organisms to respond in some way

Is your alarm clock a stimulus? Explain.

Self-Check

Homeostasis

Even though an organism’s external environment may change, the organism must maintain a stable internal environment to survive.

This is because the life processes of organisms involve many different kinds of chemical reactions that can occur only in delicately balanced environments.

The maintenance of a stable internal environment is called homeostasis.

Your Body’s Homeostasis

Your body maintains a temperature of about 37 °C.

When you get hot, your body responds by sweating.

When you get cold, your muscles twitch in an attempt to generate heat. This causes you to shiver.

Whether you are sweating or shivering, your body is trying to return things to normal.

3. Living Things Reproduce

Organisms make other organisms like themselves.

This can be accomplished in 2 ways

Asexual reproduction: single parent produces offspring that are identical to the parent. Most single-celled organisms reproduce in this way.

Sexual reproduction: almost always requires two parents to produce offspring that will share characteristics of both parents. Most animals and plants reproduce in this way.

What about Hybrids?

Though very much alive, mules and most other hybrids cannot reproduce. Hybrids are the result of mating organisms from different species.

A mule is the offspring of a mare (female horse) and a jack (male donkey). Mules often live long, healthy lives, but they never have babies.

4. Living Things Have DNA

The cells of all living things contain a special molecule called DNA (deoxyribonucleic acid).

DNA provides instructions for making molecules called proteins.

Proteins take part in almost all of the activities of an organism’s cells.

Proteins also determine many of an organism’s characteristics.

When organisms reproduce, they pass on copies of their DNA to their offspring.

The transmission of characteristics from one generation to the next is called heredity.

Offspring resemble their parents because of heredity.

Debate: Nature vs. Nurture

Scientists have proven that we inherit our physical characteristics from our parents (nature). They continue to research whether we inherit our personalities from our parents. Some scientists say that where we live and how we are raised are more important (nurture).

What do you think is the more important factor in who we become, nurture (care) or nature (heredity)? Why?

5. Living Things Use Energy

Organisms use energy to carry out the activities of live.

These include activities such as making food, breaking down food, moving materials into and out of cells, and building cells.

An organism’s metabolism is the total of all of the chemical activities that it performs

6. Living Things Grow and Develop

All living things, whether single celled or many celled, grow during periods of their lives.

Growth in single-celled organisms occurs as the cell gets larger.

Organisms made of many cells grow mainly by increasing their number of cells.

In addition to getting larger, living things may develop and change as they grow.

Think/Pair/Share

An apple tree is a living thing. Can it make oranges? Why or why not?

What is the difference between growth and development?

Name three activities of an organism that require energy.

WHAT ORGANISMS NEED TO SURVIVE

The Simple Bare Necessities of Life

Food

Provides organisms with the energy and raw materials needed to carry on life processes and to build and repair cells and body parts

Producers: produce their own food through photosynthesis

Consumers: consume other organisms to get food

Decomposers: get their food by breaking down the nutrients in dead organisms or animal wastes

Water

Your cells and the cells of almost all living organisms are approximately 70% water

Most of the chemical reactions involved in metabolism require water

Organisms differ greatly in how much water they need and how they obtain it

Humans could survive for 3 days without water and obtain water from the fluids we drink and the food we eat

Kangaroo rats that live in the desert never drink. They get all of their water from its food.

Air

Mixture of several different gases including oxygen and carbon dioxide

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

Organisms that live on land get oxygen from the air

Organisms living in water either take in dissolved oxygen from the water or come to the water’s surface to get oxygen from the air

A Place to Live

All organisms must have somewhere to live that contains all of the things they need to survive.

Because the amount of space on Earth is limited, organisms often compete with each other for food, water, and other necessities.

Think/Pair/Share

Why are decomposers categorized as consumers? How are they different from producers?

Why are most cells 70% water?

How might a cave, an ant, and a lake meet the needs of an organism?

WHAT CELLS ARE MADE UP OF

The Chemistry of Life

Basic Chemistry

Everything, alive or not, is made up of tiny building blocks called atoms.

A substance made up of one type of atom is called an element.

When 2 or more atoms join together, they form a molecule.

Molecules found in living things are usually made of different combinations of six elements: Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorous, and Sulfur.

Proteins

Almost all of the life processes of a cell involve proteins. After water, proteins are the most abundant materials in cells.

Proteins are large molecules that are made up of subunits called amino acids.

Organisms break down these proteins in food to supply the cells with amino acids. These amino acids are then linked together to form new proteins.

Proteins in Action

Proteins have many different functions.

Some form structures that are easy to see like feathers, spider webs, and hair.

Others are at work at the cellular level.

Hemoglobin is a protein in red blood cells that attaches to oxygen so that oxygen can be delivered throughout the body.

Math Break: How Much Oxygen?

Each red blood cell carries about 250 million molecules of hemoglobin.

How many molecules of oxygen could a single red blood cell deliver throughout the body if every hemoglobin molecule attached to four oxygen molecules?

250,000,000x 4

1,000,000,000 molecules of oxygen

Carbohydrates

Group of compounds made of sugars

Cells use carbohydrates as a source of energy and for energy storage

When an organism needs energy, its cells break down carbohydrates to release the energy stored in the carbohydrates.

2 types of carbohydrates

Simple: made of 1 sugar molecule or a few sugar molecules linked together

Examples: table sugar and the sugar in fruits

Complex

Too Much Sugar!

When an organism has more sugar than it needs, its extra sugar may be stored in form of complex carbohydrates

Complex carbohydrates are made of hundreds of sugar molecules linked together

Your body makes some complex carbohydrates and stores them in your liver

Plants make a complex carbohydrate called starch

When you eat mashed potatoes or french fries, you are eating a potato plant’s stored starch

Lipids

Compounds that cannot mix with water

Fats and oils are lipids that store energy. When an organism has used up most of its carbohydrates, it can obtain energy from these lipids.

The structures of fats and oils are almost identical, but at room temperature most fats are solid and oils are liquid.

Most lipids stored in plants are oils, while most of the lipids stored in animals are fats.

Is that a Fact!

Fats and lipids are also vital to nerve formation and function.

Fat acts as an insulator on the nerve, speeding up the electrical impulse that the nerve is carrying.

Phospholipids

All cells are surrounded by a structure called a cell membrane.

Phospholipids are the molecules that form much of the cell membrane. When these phospholipids are in water, like in a cell, the tails come together and the heads face out into the water.

This happens because the head of a phospholipid molecule is attracted to water while the tail is not.

Nucleic Acids

Compounds made up of subunits called nucleotides

A nucleic acid may contain thousands of nucleotides.

Nucleic acids are sometimes called the blueprints of life because they contain all the information needed for the cell to make all of its proteins

DNA is a nucleic acid.

A DNA molecule is like a recipe book titled How to Make Proteins.

When a cell needs to make a certain protein, it gets information from DNA to direct how amino acids are hooked together to make that protein.

The Cell’s Fuel

ATP (adenosine triphosphate) is the major fuel used for all cell activities that require energy.

When food molecules, such as carbohydrates and fats, are broken down, some of the released energy is transferred to ATP molecules.

The energy in carbohydrates and lipids must be transferred to ATP before the stored energy can be used by cells to fuel their life processes.

Weird Science

Fireflies produce their flashing light by a chemical reaction. The enzyme luciferase acts on the chemical luciferin in the presence of ATP to create the light.

Scientists now use luciferase in the laboratory to study everything from heart disease to muscular dystrophy.

Think/Pair/Share

What are the subunits of proteins? Of starch? Of DNA?

What do carbohydrates, fats, and oils have in common?

Are all proteins enzymes? Why or why not?