economic english 9 ppt

Forms of energy include poten-tial energy and kinetic energy.. The change of potential energy into kinetic energy, and kinetic energy into potential energy, in a pendulum Examples of pot

C ONTACT FORCE

Contact forces are forces that exist as a result of an

inter-action between objects that are physically in contact with

one another They include frictional forces, tensional

forces, and normal forces

The friction force opposes the motion of an object

across a surface For example, if a glass moves across the

surface of the dinner table, there exists a friction force in

the direction opposite to the motion of the glass Friction

is the result of attractive intermolecular forces between

the molecules of the surface of the glass and the surface

of the table Friction depends on the nature of the two

surfaces For example, there would be less friction

between the table and the glass if the table was moistened

or lubricated with water The glass would glide across the

table more easily Friction also depends on the degree to

which the glass and the table are pressed together Air

resistance is a type of frictional force

Tension is the force that is transmitted through a rope

or wire when it is pulled tight by forces acting at each

end The tensional force is directed along the rope or

wire and pulls on the objects on either end of the wire

The normal force is exerted on an object in contact

with another stable object For example, the dinner table

exerts an upward force on a glass at rest on the surface of

the table

N UCLEAR FORCE

Nuclear forces are very strong forces that hold the

nucleus of an atom together If nuclei of different atoms

come close enough together, they can interact with one

another and reactions between the nuclei can occur

Forms of Energy

Energy is defined as the ability to do work We have

already stated that energy can’t be created or destroyed;

it can only change form Forms of energy include

poten-tial energy and kinetic energy

Potential energy is stored energy Kinetic energy is the

energy associated with motion Look at the following

illustration As the pendulum swings, the energy is

con-verted from potential to kinetic, and back to potential

When the hanging weight is at one of the high points, the

gravitational potential energy is at the maximum, and

kinetic energy is at the minimum At the low point, the

kinetic energy is maximized, and gravitational potential

energy is minimized

The change of potential energy into kinetic energy, and kinetic energy into potential energy, in a pendulum

Examples of potential energy include nuclear energy and chemical energy—energy is stored in the bonds that hold atoms and molecules together Heat, hydrodynamic energy, and electromagnetic waves are examples of kinetic energy—energy associated with the movement of molecules, water, and electrons or photons (increments

of light)

 I n t e r a c t i o n s o f E n e r g y

a n d M a t t e r

Energy in all its forms can interact with matter For example, when heat energy interacts with molecules of water, it makes them move faster and boil Waves— including sound and seismic waves, waves on water, and light waves—have energy and can transfer that energy when they interact with matter Consider what happens

if you are standing by the ocean and a big wave rolls in Sometimes, the energy carried by the wave is large enough to knock you down

Waves

Energy is also carried by electromagnetic waves or light waves The energy of electromagnetic waves is related to their wavelengths Electromagnetic waves include radio waves (the longest wavelength), microwaves, infrared radiation (radiant heat), visible light, ultraviolet radia-tion, X-rays, and gamma rays The wavelength depends

on the amount of energy the wave is carrying Shorter wavelengths carry more energy

When a wave hits a smooth surface, such as a mirror,

it is reflected Sound waves are reflected as echoes Mat-ter can also refract or bend waves This is what happens when a ray of light traveling through air hits a water sur-face A part of the wave is reflected, and a part is refracted into the water

Maximum Potential Energy

Maximum Potential Energy

Maximum Kinetic Energy

– P H Y S I C A L S C I E N C E –

Each kind of atom or molecule can gain or lose energy

only in particular discrete amounts When an atom gains

energy, light at the wavelength associated with that

energy is absorbed When an atom loses energy, light at

the wavelength associated with that energy is emitted

These wavelengths can be used to identify elements

Nuclear Reactions

In a nuclear reaction, energy can be converted to matter

and matter can be converted to energy In such processes,

energy and matter are conserved, according to Einstein’s

formula E = mc 2 , where E is the energy, m is the mass

(matter), and c is the speed of light A nuclear reaction is

different from a chemical reaction because in a nuclear

reaction, the particles in nuclei (protons and neutrons)

interact, whereas in a chemical reaction, electrons are lost

or gained by an atom Two types of nuclear reactions are

fusion and fission

Fusion is a nuclear process in which two light nuclei

combine to form one heavier nucleus A fusion reaction

releases an amount of energy more than a million times

greater than the energy released in a typical chemical

reaction This gain in energy is accompanied by a loss of

mass The sum of the masses of the two light nuclei is

lower than the mass of the heavier nucleus produced

Nuclear fusion reactions are responsible for the energy

output of the sun

Fission is a nuclear process in which a heavy nucleus

splits into two lighter nuclei Fission reaction was used in

the first atomic bomb and is still used in nuclear power

plants Fission, like fusion, liberates a great amount of

energy The price for this energy is a loss in mass A heavy

nucleus that splits is heavier than the sum of the masses

of the lighter nuclei that result

Key Concepts

This chapter gave you a crash course in the basics of physical science Here are the most important concepts to remember:

➧All matter is composed of tiny particles called atoms

➧Atoms combine with other atoms to form molecules

➧In a chemical reaction, atoms in molecules rearrange to form other molecules

➧The three common states of matter are solid, liquid, and gas

➧The disorder in the universe is always increasing

➧Mass and energy can’t be created or destroyed

➧Energy can change form and can be trans-ferred in interactions with matter

– P H Y S I C A L S C I E N C E –

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LI F E S C I E N C E E X P L O R E S the nature of living things, from the smallest building blocks of life to the

larger principles that unify all living beings Fundamental questions of life science include:

■ What constitutes life?

■ What are its building blocks and requirements?

■ How are the characteristics of life passed on from generation to generation?

■ How did life and different forms of life evolve?

■ How do organisms depend on their environment and on one another?

■ What kinds of behavior are common to living organisms?

Before Anthony van Leeuwenhoek looked through his homemade microscope more than 300 years ago, people didn’t know that there were cells in our bodies or that there were microorganisms Another common miscon-ception was that fleas, ants, and other pests came from dust or wheat Leeuwenhoek saw blood cells in blood, found microorganisms in ponds, and showed that pests come from larvae that hatch from eggs laid by adult pests However, it took more than 200 years for Leeuwenhoek’s observations to gain wide acceptance and find appli-cation in medicine

C H A P T E R

Life Science

LIFE SCIENCE questions on the GED cover the topics studied in

high school biology classes In this chapter, you will review the basics

of biology and learn the answers to some of the key questions scien-tists ask about the nature of life and living beings

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 T h e C e l l

Today, we know that a cell is the building block of life

Every living organism is composed of one or more cells

All cells come from other cells Cells are alive If blood

cells, for example, are removed from the body, given the

right conditions, they can continue to live independently

of the body They are made up of organized parts,

per-form chemical reactions, obtain energy from their

sur-roundings, respond to their environments, change over

time, reproduce, and share an evolutionary history

All cells contain a membrane, cytoplasm, and genetic

material More complex cells also contain cell organelles

Here is a description of cell components and the

func-tions they serve Also, refer to the figures on the next page

sur-rounds, protects, and supports plant cells Animal

cells do not have a cell wall

the cell It carefully regulates the transport of

materials in and out of the cell and defines the

cell’s boundaries Membranes have selective

per-meability—meaning that they allow the passage

of certain molecules, but not others A membrane

is like a border crossing Molecules need the

molecular equivalent of a valid passport and a

visa to get through

near the center of a cell It is surrounded by a

nuclear membrane and it contains genetic

infor-mation inscribed along one or more molecules of

DNA The DNA acts as a library of information

and a set of instructions for making new cells and

cell components To reproduce, every cell must be

able to copy its genes to future generations This

is done by exact duplication of the DNA

mem-brane, but outside the nucleus

essen-tial in cell maintenance and cell reproduction

They are the site of cellular respiration

(break-down of chemical bonds to obtain energy) and

production of ATP, a molecule that provides

energy for many essential processes in all

organ-isms Cells that use a lot of energy, such as the

cells of a human heart, have a large number of mitochondria Mitochondria are unusual because unlike other cell organelles, they contain their own DNA and make some of their own proteins

intercon-necting membranes associated with the storage, synthesis, and transport of proteins and other materials within the cell

synthesizes, packages, and secretes cellular prod-ucts to the plasma membrane Its function is directing the transport of material within the cell and exporting material out of the cell

intra-cellular digestion Lysosomes have a large pres-ence in cells that actively engage in

phagocytosis—the process by which cells con-sume large particles of food White blood cells that often engulf and digest bacteria and cellular debris are abundant in lysosomes

partic-ipate in digestion and the maintenance of water balance in the cell

cytoplasm of animal cells They participate in cell division

in algae They contain the green pigment chloro-phyll and are the site of photosynthesis—the process of using sunlight to make high energy sugar molecules Ultimately, the food supply of most organisms depends on photosynthesis car-ried out by plants in the chloroplasts

involved in the synthesis of ribosomes, which manufacture proteins

In a multicellular organism, individual cells specialize in different tasks For example, red blood cells carry oxygen, white blood cells fight pathogens, and cells in plant leaves collect the energy from sunlight This cellular organization enables an organism to lose and replace individual cells, and outlive the cells that it is composed of For example, you can lose dead skin cells and give blood and still go on living This differentiation or division of labor in multicellular organisms is accomplished by expression of different genes

– L I F E S C I E N C E –

 M o l e c u l a r B a s i s o f H e r e d i t y

What an organism looks like and how it functions is

determined largely by its genetic material The basic

principles of heredity were developed by Gregor Mendel,

who experimented with pea plants in the 19th century

He mathematically analyzed the inherited traits (such as

color and size) of a large number of plants over many

generations The units of heredity are genes carried on

chromosomes Genetics can explain why children look

like their parents, and why they are, at the same time, not

identical to the parents

Phenotype and Genotype

The collection of physical and behavioral characteristics

of an organism is called a phenotype For example, your

eye color, foot size, and ear shape are components of

your phenotype The genetic makeup of a cell or

organ-ism is called the genotype The genotype is like a

cook-book for protein synthesis and use Phenotype (what an

organism looks like or how it acts) is determined by the

genotype (its genes) and its environment By

environ-ment, we don’t mean the Earth, but the environment

surrounding the cell or organism For example,

hor-mones in the mother’s body can influence the gene

expression

Reproduction

Asexual reproduction on the cellular level is called mito-sis It requires only one parent cell, which, after exactly multiplying its genetic material, splits in two The result-ing cells are genetically identical to each other and are clones of the original cell before it split

Sexual reproduction requires two parents Most cells

in an organism that reproduces sexually have two copies

of each chromosome, called homologous pairs—one from each parent These cells reproduce through mitosis.

Gamete cells (sperm and egg cells) are exceptions They carry only one copy of each chromosome, so that there are only half as many chromosomes as in the other cells For example, human cells normally contain 46 chromo-somes, but human sperm and egg cells have 23 chro-mosomes At fertilization, male and female gametes (sperm and egg) come together to form a zygote, and the number of chromosomes is restored by this union The genetic information of a zygote is a mixture of genetic information from both parents Gamete cells are

manu-factured through a process called meiosis, whereby a cell

multiples its genetic material once, but divides twice, producing four new cells, each contains half the number

of chromosomes present in the original cell before divi-sion In humans, gametes are produced in testes and ovaries Meiosis causes genetic diversity within a species

by generating combinations of genes different from those present in the parents

– L I F E S C I E N C E –

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Cytoplasm

Endoplasmic reticulum Plasma membrane

Nucleolus Nucleus

Vacuole

Cell wall Ribosomes

Mitochondria

Centriole

Chloroplast

Lysosome

Animal Cell Plant Cell

Golgi complex