Science - Term 2, 2023

Exam Block Grind

Why are planets visible?

They reflect light from the sun.

What is a star?

An immense mass of hydrogen undergoing a fusion reaction that produces helium and enormous amounts of light and heat.

What is apparent magnitude?

The scale that describes the relative brightness of stars seen from Earth.

How does the apparent magnitude scale work?

The lower the number, the bright the star.

What does each level of the apparent magnitude scale change by?

About 2.5 times the previous.

What is absolute magnitude?

The amount of light a star emits.

What does the amount of light that a star emits depend on?

The interaction between the size and the surface temperature of the star.

How can stars be classified?

By their:

1. size

2) Temperature (red=cooler, blue=hotter)

3) Brightness/magnitude

What is the main sequence?

Where most stars fall on the Hertzsprung-Russell diagram.

How is a star plotted on the Hertzsprung-Russell diagram?

The absolute brightness is plotted against its surface temperature.

How is a star’s mass related to it’s appearance?

Low mass = cooler and less bright.

Why do stars appear to twinkle?

The light travelling from a star is distorted by the earth’s moving atmosphere. The image changes slightly and appears to twinkle.

What is a constellation?

The group of stars in each region of the sky.

How many regions is the sky divided into?

88

Why do the constellations visible depend on the time of the year?

As the earth orbits the sun, we change our position, and therefore our view of the sky.

Why are the zodiac constellations special?

They pass through the ecliptic.

What is the ecliptic?

The path the sun follows in the sky over the course of a year.

Where is a star born?

In a nebula.

What is a nebula?

Gas and dust-dense parts of space that reach 100 atoms per cubic cm, causing gravity to take hold and collapse the gas and dust, forming clumps that also collapse.

What are stable stars powered by?

A fusion reaction within their core that converts hydrogen to helium.

How does a star become a red giant?

If a star is less than 8 times the mass of our sun, the helium builds up and forms a shell around the core. The shell expands and the stars swells, and as it cools, it becomes a red giant.

What does a red giant produce?

Fusion in the core of a red giant produces heavier elements like beryllium, neon and oxygen.

What is a planetary nebula?

The outer layers of a dying red giant that are thrown into space while the core flares brightly.

How are white dwarfs formed?

The remains of a red giant after a planetary nebula.

How are black dwarfs formed?

A white dwarf slowly cools, becoming a black dwarf that disappears from view.

How is a supergiant formed?

Stars larger than our sun swell into supergiants.

What is the death of a supergiant called?

The huge explosion of a supergiant is called a supernova.

What do supernovas form?

Heavy elements, like lead and iron.

How is a neutron star formed?

The super-dense remains of a supernova have a strong gravitational pull that forces electrons and protons together that form a neutron star.

How are black holes formed?

The cores of a neutron star sometimes have so much gravity that they collapse in on themselves, forming black holes.

What force forms galaxies?

Gravitational force groups stars together.

What type of galaxy is the Milky Way?

A spiral galaxy with two arms.

What is responsible for the formation of the stars, planets, solar systems, and galaxies?

The gravitational forces between all objects in the universe.

What is an exoplanet?

A planet found not in our solar system.

Do all nebulae glow?

No - some absorb nearby light and appear as dark spots.

How big is the observable universe?

27 billion light years.

How many km does light travel per second?

300,000km.

What is a geocentric view of the universe?

Seeing the universe with the earth at the centre.

Why are observatories placed at high altitudes?

To reduce the distortion of images that result from light passing through the atmosphere.

Why were adaptive optics developed?

To eliminate image distortion by measuring and then correcting atmospheric effects.

Why did non-optics telescopes have to be developed?

Because not everything in the universe emits radiation in the visible range.

How are black holes seen?

X-rays that are emitted are detected.

What does ultraviolet light show?

Hot stars

What does visible light show?

Hot stars, planets, nebulae, and galaxies./

What does infrared light show?

Cool stars, regions of star birth, and cool dusty regions

What do radio waves show?

They aren’t affected by dust, so they detect other galaxies that can’t be seen with optical telescopes.

How do scientists produce sharper images from a telescope?

They point a group of telescopes at the same object to get a sharper image.

How does the Theory of Relativity support the idea of universe expansion?

It showed that it was possible for energy to be changed into matter, supporting that the fabric of space could expand.

What was Hoyle’s theory of the model of the universe?

The Steady State Theory proposed that the expansion of the universe comes from the continuous creation of hydrogen throughout the universe. This hydrogen becomes stars, which grow and then explode, so matter is constantly created at a rate that keeps the average density of the universe the same as it expands.

What was Gamow’s theory?

The Big Bang Theory proposed that an explosion at the birth of the universe created all hydrogen and some helium, and that those elements formed the first stars, whose explosions created new elements, and matter began to spread throughout the universe, forming the complex elements we have today.

What caused the rejection of the Steady State theory?

Quasars were found only at large distances, rather than dispersed throughout the universe, and the cosmic microwave background radiation was found.

How old is the universe?

13\.7 billion years old

What are the 3 main pieces of evidence supporting the Big Bang theory?

1. There’s evidence of the universe expanding: galaxies are moving further apart.

2. It explains the abundance of hydrogen, helium, and other elements in the universe.

3. Astronomers have observed the cosmic background radiation throughout the universe - the ‘afterglow’ of the big bang explosion

What did Christian Johann Doppler suggest that the Doppler effect also applied to?

He predicted that there would be a change in the frequency of light emitted from a moving source.

What do dark lines in stars show?

The dark lines is the absorption of light by different substances. The dark lines show elements that are present in the star.

What is ‘red shift’?

A shift to lower frequencies that results from a star’s movement away from the Earth.

What is ‘blue shift’?

A shift to higher frequencies that results from a star’s movement towards the Earth.

What does the Doppler shift of galaxies tell us?

That galaxies in our Local Group are moving towards us, and that distant galaxies are moving away at a considerable speed.

What does Hubble’s Law state?

That the further a galaxy is, the faster it is moving away. (this can be seen no matter where you observe it from)

What is the cosmic microwave background radiation?

The ‘afterglow’ of radiation leftover from the Big Bang.

How are galaxies formed?

Stars group together, bound by gravitational forces.

What is a fossil?

Evidence of past life.

How is a fossil formed?

If an organism is covered shortly after it dies, no oxygen can get to its dead form, which mean microorganisms can’t decay it. Over millions of years, the pressure preserves the fossil.

What is the fossil record?

It provides information about the order in which groups of living things appeared on Earth.

What is the absolute age of a fossil?

An estimate of its age, using technology that dates the rock.

What is the relative age of a fossil?

The comparison of the fossil to other fossils that have a known ‘age’.

What is radiometric dating?

Carbon dating measures the decay of carbon-14 in comparison to the remaining carbon-12, because carbon-12 doesn’t deplete.

What can disturb rock layers?

Faults or folds in the rock.

How do scientists date rocks older than 50,000 years old?

They measure of ratio of uranium-238 to lead-206.

What is evolution?

The genetic change in a population over time.

What is the Lamarckian theory of evolution?

Jean Baptiste Lamarck believed that acquired characteristics over an organism’s lifetime was passed onto its offspring. He also believed that if a feature wasn’t being used, it would shrink and eventually be lost over succeeding generations.

How was Lamarckian evolution disproved?

August Weissman chopped the tails off of rats, and then had them breed. The offspring did have tails, which meant that the acquired characteristics weren’t passed on.

Why did Darwin believe in natural selection?

His study of the finches in the Galapagos found that the 13 different species of finch had similar features but different characteristics that suited their environment. This lead him to believe that organisms adapted overtime to survive better.

What caused Darwin to finally publish his findings?

Alfred Wallace had identical findings, corroborating his theory.

When did Darwin submit his findings?

He submitted both his and Wallace’s papers to the Linnean Society Science Conference in 1859.

What is biogeography?

The study of the variation in living things in relation to geographic regions. It was the name to the studies that led both Darwin and Wallace to their findings.

List evidence of natural selection:

Biogeography, the fossil record, comparative anatomy, embryology, and DNA hybridisation.

What does the fossil record show?

It shows how species have evolved over time, as well as showing ‘transitional forms’ that display what happened as species evolved.

What is comparative anatomy?

The comparison of the basic structure of different species.

What is a homologous structure?

A bone or structure that has similar base structures to other animals, but a different function. It shows there is descent from a common ancestor.

What is a vestigial structure?

A non-functioning remnant of similar organs in other species (ie. human tailbone).

What does comparative anatomy show?

It shows anatomical signs of evolution (called homologous structure). Functions may be different, but the basic structure is the same, showing there is a common ancestor.

What is convergent evolution?

When unrelated species in similar environments develop similar structures, as a result of the selection pressures, NOT common ancestry.

What is an example of analogous convergent evolution?

Butterflies and bats have very similar wing structures, but don’t share a common ancestor.

What is embryology?

The study of organisms that have similar embryonic development stages because they are related.

Example of embryology:

The early embryo of fish, amphibians, reptiles, birds, and mammals all have gills, but the fish are the only ones who retain this, showing evolution.

What is DNA hybridisation?

The comparison of DNA in different species to determine how closely they’re related. The closer the match in DNA sequence, the more closely related.

What does biochemistry prove about evolution?

There is a ‘universal’ genetic code, suggesting a common ancestor amongst all things on earth. The comparison of a particular protein is one of the strongest pieces of evidence for relationships among organisms.

What is an observable event?

A change in species that has been observed and studied. They show that evolution is an ongoing process.

What is natural selection?

The theory that organisms who are better suited to their environment will flourish, and others will die off, leading to the evolution of a species.

What are examples of an environment’s selective agents?

Predators, chemicals, or disease-causing organisms.

Example of survival of the fittest:

The Galapagos finches that had beaks more suited to obtaining their local food source survived, while others died. The offspring of the successful finches were more likely to have that characteristic, passing it on to younger generations.

What is a species?

A group of organisms that are capable of interbreeding to produce fertile offspring.

What is speciation?

The formation of a new species.

What are the two ways that speciation can occur?

Phyletic evolution or branching/divergent evolution.

What is phyletic evolution?

When a population of a species changes over time to become a new species.

What is branching/divergent evolution?

When a population is divided into 2+ populations and prevented from interbreeding, and have different selective pressures on them, favouring different characteristics. Speciation has occurred when the two groups can no longer successfully interbreed.

What is adaptive radiation?

When the divergent evolution of a species has resulted in the formation of many species that adapt to a variety of environments.

What is convergent evolution?

When a group of unrelated species develop similar characteristics because their environment has similar selection pressures. (ie. sharks and dolphins)

What is coevolution?

The response of one species’ evolution to another (ie. birds & flowers).