economic english 10 pptx

In other words, if a plant has a gene for making yellow flowers and a gene for making red flowers, the color of the flower will be determined by the dominant gene.. So if the gene for re

 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

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

Cytoplasm

Endoplasmic reticulum

Plasma membrane

Nucleolus Nucleus

Vacuole

Cell wall

Ribosomes

Mitochondria

Centriole

Chloroplast

Lysosome

Animal Cell Plant Cell

Golgi complex

Alleles are alternative versions of the same gene An

organism with two copies of the same allele is

homozy-gous, and one with two different alleles is heterozygous.

For example, a human with one gene for blue eyes and

one gene for brown eyes is heterozygous, while a human

with two genes for blue eyes or two genes for brown eyes

is homozygous Which of the two genes is expressed is

determined by the dominance of the gene

An allele is dominant if it alone determines the

phe-notype of a heterozygote In other words, if a plant has a

gene for making yellow flowers and a gene for making

red flowers, the color of the flower will be determined by

the dominant gene So if the gene for red flowers is

dom-inant, a plant that has both the gene for red and the gene

for yellow will look red The gene for yellow flowers in

this case is called recessive, as it doesn’t contribute to the

phenotype (appearance) of a heterozygote (a plant

con-taining two different alleles) The only way this plant

would make yellow flowers is if it had two recessive

genes—two genes both coding for yellow flowers

For some genes, dominance is only partial and two

different alleles can be expressed In the case of partial

dominance, a plant that has a gene that codes for red

flowers and a gene that codes for white flowers would

produce pink flowers

A Punnett square can be used to represent the

possi-ble phenotypes that offspring of parents with known

genotypes could have Take the example with the yellow

and red flower Let’s label the gene for the dominant red

gene as R and the gene for yellow flowers as r Cross a

plant with yellow flowers (genotype must be rr) with a

plant with red flowers and genotype Rr What possible

genotypes and phenotypes can the offspring have? In a

Punnett square, the genes of one parent are listed on one

side of the square and the genes of the other parent on

the other side of the square They are then combined in

the offspring as illustrated here:

The possible genotypes of the offspring are listed

inside the square Their genotype will be either Rr or rr,

causing them to be either red or yellow, respectively

Sex Determination

In many organisms, one of the sexes can have a pair of unmatched chromosomes In humans, the male has an X chromosome and a much smaller Y chromosome, while the female has two X chromosomes The combination

XX (female) or XY (male) determines the sex of humans In birds, the males have a matched pair of sex chromosomes (WW), while females have an unmatched pair (WZ) In humans, the sex chromosome supplied by the male determines the sex of the offspring In birds, the female sex chromosome determines the sex

Plants, as well as many animals, lack sex chromo-somes The sex in these organisms is determined by other factors, such as plant hormones or temperature Identical twins result when a fertilized egg splits in two Identical twins have identical chromosomes and can

be either two girls or two boys Two children of different sex born at the same time can’t possibly be identical twins Such twins are fraternal Fraternal twins can also

be of the same sex They are genetically not any more alike than siblings born at different times Fraternal twins result when two different eggs are fertilized by two dif-ferent sperm cells

When meiosis goes wrong, the usual number of chro-mosomes can be altered An example of this is Down’s syndrome, a genetic disease caused by the presence of an extra chromosome

Changes in DNA (mutations) occur randomly and spontaneously at low rates Mutations occur more fre-quently when DNA is exposed to mutagens, including ultraviolet light, X-rays, and certain chemicals Most mutations are either harmful to or don’t affect the organ-ism In rare cases, however, a mutation can be beneficial

to an organism and can help it survive or reproduce Ultimately, genetic diversity depends on mutations, as mutations are the only source of completely new genetic material Only mutations in germ cells can create the variation that changes an organism’s offspring

Plant r r

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 B i o l o g i c a l E v o l u t i o n

Mutations cause change over time The result of a series

of such changes is evolution, or as Darwin put it,

“descent with modification.” The great diversity on our

planet is the result of more than 3.5 billion years of

evo-lution The theory of evolution argues that all species on

Earth originated from common ancestors

Evidence for Evolution

Several factors have led scientists to accept the theory of

evolution The main factors are described here

of evidence is the fossil record Fossils are the

remains of past life Fossils are often located in

sedimentary rocks, which form during

compres-sion of settling mud, debris, and sand The order

of layers of sedimentary rock is consistent with

the proposed sequence in which life on Earth

evolved The simplest organisms are located at

the bottom layer, while top layers contain

increas-ingly complex and modern organisms, a pattern

that suggests evolution

from the fact that species tend to resemble

neigh-boring species in different habitats more than

they resemble species in similar, but far away,

habitats

provides us with another line of evidence It

refers to the fact that the limb bones of different

species, for example, are similar Species that

closely resemble one another are considered more

closely related than species that do not resemble

one another For example, a horse and a donkey

are considered more closely related than a horse

and a frog Biological classifications (kingdom,

phylum, class, order, family, genus, and species)

are based on how organisms are related

Organ-isms are classified into a hierarchy of groups and

subgroups based on similarities that reflect their

evolutionary relationships

of evidence for evolution Embryos go through

molecular biology confirms the lines of descent suggested by comparative anatomy and fossil record

Darwin also proposed that evolution occurs gradually,

through mutations and natural selection He argued that

some genes or combinations of genes give an individual a survival or reproductive advantage, increasing the chance that these useful combinations of genes will make it to future generations Whether a given trait is advantageous depends on the environment of the organism Natural selection is only one of several mechanisms by which gene frequency in a population changes Other factors include mating patterns and breeding between popula-tions

 I n t e r d e p e n d e n c e o f O r g a n i s m s

The species in communities interact in many ways They compete for space and resources, and they can be related

as predator and prey, or as host and parasite

Plants and other photosynthetic organisms harness and convert solar energy and supply the rest of the food chain Herbivores (plant eaters) obtain energy directly from plants Carnivores are meat eaters and obtain energy by eating other animals Decomposers feed on dead organisms The flow of energy can then be repre-sented as follows:

Sun → Photosynthetic organisms → Herbivores → Carnivores → Decomposers The food chain is not the only example of the inter-dependence of organisms Species often have to compete for food and space, so that the increase in population of one can cause the decrease in population of the other Organisms also may have a symbiotic relationship (live in close association), which could be classified as

parasitism, mutualism, or commensalism In a parasitic

relationship, one organism benefits at the expense of the

other Commensalism is symbiosis in which one

organ-ism benefits and the other is neither harmed nor

rewarded In mutualism, both organisms benefit.

Humans probably come closest to being a species with

seemingly infinite reproductive capacity Our population

keeps increasing Our only danger seems to come from

viruses and bacteria, which at this point, we more or less

have under control When we need more food, we grow

more, and when we need more space, we clear some by

killing off other biomes By doing this, humans modify

ecosystems and destroy habitats through direct

harvest-ing, pollution, atmospheric changes, and other factors

This attitude is threatening current global stability and

has the potential to cause irreparable damage

 B e h a v i o r o f O r g a n i s m s

Even the most primitive unicellular organisms can act to

maintain homeostasis More complex organisms have

nervous systems The simplest organism found to have

learning capability is a worm, suggesting a more complex

nervous system The function of the nervous system is collection and interpretation of sensory signals as trans-mission of messages from the center of the nervous sys-tem (brain in humans) to other parts of the body The nervous system is made of nerve cells, or neurons, which conduct signals in the form of electrical impulses Nerve cells communicate by secreting excitatory or inhibitory

molecules called neurotransmitters Many legal and

ille-gal drugs act on the brain by disrupting the secretion or absorption of neurotransmitters

Many animals have sense organs that enable them to detect light, sound, and specific chemicals These organs provide the animals with information about the outside world Animals engage in innate and learned social behavior These behaviors include hunting or searching for food, nesting, migrating, playing, caring for their young, fighting for mates, and fighting for territory Plants also respond to stimuli They turn toward the sun and let their roots run deeper when they need water

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EA RT H A N D S PA C E science are concerned with the formation of the Earth, the solar system and the

universe, the history of Earth (its mountains, continents and ocean floors), the weather and seasons

on Earth, the energy in the Earth system, and the chemical cycles on Earth

 E n e r g y i n t h e E a r t h S y s t e m s

Energy and matter can’t be created or destroyed But energy can change form and travel great distances

Solar Energy

The sun’s energy reaches our planet in the form of light radiation Plants use this light to synthesize sugar mol-ecules, which we consume when we eat the plants We obtain energy from the sugar molecules and our bodies use it Ultimately, our energy comes from the sun The sun also drives the Earth’s geochemical cycles, which will

be discussed in the next section

The sun heats the Earth’s surface and drives convection within the atmosphere and oceans, producing winds

Earth and Space Science

HUMANS HAVE always wondered about the origin of the Earth

and the universe that surrounds it What kinds of matter and energy are

in the universe? How did the universe begin? How has the Earth evolved? This chapter will answer these fundamental questions and review the key concepts of Earth and space science

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waves Tsunamis, or tidal waves, are different They result

from underwater earthquakes, volcanic eruptions, or

landslides, not wind

Energy from the Core

Another source of Earth’s energy comes from Earth’s

core We distinguish four main layers of Earth: the inner

core, the outer core, the rocky mantle, and the crust The

inner core is a solid mass of iron with a temperature of

about 7,000° F Most likely, the high temperature is

caused by radioactive decay of uranium and other

radioactive elements The inner core is approximately

1,500 miles in diameter The outer core is a mass of

molten iron that surrounds the solid inner core

Electri-cal currents generated from this area produce the earth’s

magnetic field The rocky mantle is composed of silicon,

oxygen, magnesium, iron, aluminum, and calcium and is

about 1,750 miles thick This mantle accounts for most

of the Earth’s mass When parts of this layer become hot

enough, they turn to slow moving molten rock, or

magma The Earth’s crust is a layer from four to 25 miles

thick, consisting of sand and rock

The upper mantle is rigid and is part of the

litho-sphere (together with the crust) The lower mantle flows

slowly, at a rate of a few centimeters per year The crust

is divided into plates that drift slowly (only a few

cen-timeters each year) on the less rigid mantle Oceanic

crust is thinner than continental crust

This motion of the plates is caused by convection

(heat) currents, which carry heat from the hot inner

mantle to the cooler outer mantle The motion results in

earthquakes and volcanic eruptions This process is

called plate tectonics.

Tectonics

Evidence suggests that about 200 million years ago, all

continents were a part of one landmass, named Pangaea

Over the years, the continents slowly separated through

the movement of plates in a process called continental

drift The movement of the plates is attributed to

con-vection currents in the mantle The theory of plate

tec-tonics says that there are now twelve large plates that

slowly move on the mantle According to this theory,

earthquakes and volcanic eruptions occur along the lines

where plates collide Dramatic changes on Earth’s

land-scape and ocean floor are caused by collision of plates

These changes include the formation of mountains and

valleys

 G e o c h e m i c a l C y c l e s

Water, carbon, and nitrogen are recycled in the bios-phere A water molecule in the cell of your eye could have been, at some point, in the ocean, in the atmosphere, in

a leaf of a tree, or in the cell of a bear’s foot The

circula-tion of elements in the biosphere is called a geochemical

cycle.

Water

Oceans cover 70% of the Earth’s surface and contain more than 97% of all water on Earth Sunlight evapo-rates the water from the oceans, rivers, and lakes Living beings need water for both the outside and the inside of their cells In fact, vertebrates (you included) are about 70% water Plants contain even more water Most of the water passes through a plant unaltered Plants draw on water from the soil and release it as vapor through pores in their leaves, through a process called

transpiration.

Our atmosphere can’t hold a lot of water Evaporated water condenses to form clouds that produce rain or snow on to the Earth’s surface Overall, water moves from the oceans to the land because more rainfall reaches the land than is evaporated from the land (See the figure

on the next page.)

Carbon

Carbon is found in the oceans in the form of bicarbon-ate ions (HCO3 −), in the atmosphere, in the form of car-bon dioxide, in living organisms, and in fossil fuels (such

as coal, oil, and natural gas) Plants remove carbon diox-ide from the atmosphere and convert it to sugars through photosynthesis The sugar in plants enters the food chain, first reaching herbivores, then carnivores, and finally scavengers and decomposers All these organ-isms release carbon dioxide back into the atmosphere when they breathe The oceans contain 500 times more carbon than the atmosphere Bicarbonate ions (HCO3) settle to the bottoms of oceans and form sedimentary rocks Fossil fuels represent the largest reserve of carbon

on Earth Fossil fuels come from the carbon of organisms that had lived millions of years ago Burning fossil fuels releases energy, which is why these fuels are used to power human contraptions When fossil fuels burn, car-bon dioxide is released into the atmosphere

Since the Industrial Revolution, people have increased the concentration of carbon dioxide in the atmosphere

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