Year 10 Science Exam - Semester 2

Earth Science, Physics, Space Science

What is weather?

The short-term atmospheric conditions in a specific place at a specific time, including temperature, humidity, precipitation, wind, and visibility. It can change from minute-to-minute, hour-to-hour, or day-to-day.

What is climate?

The long-term average of weather patterns in a particular region over a period of at least 30 years, including trends in temperature, precipitation, and seasonal variations.

Climate vs Weather

• Weather is short-term and temporary

• Climate describes long-term patterns and averages

What is the nitrogen cycle?

• Movement of nitrogen through atmosphere, soil, plants, animals, and microorganisms

• Makes nitrogen usable by living organisms, like plants, which then pass it through the food chain

What is nitrogen fixation and which organisms perform it?

• Converts atmospheric nitrogen (N₂) into ammonia (NH₃) or related compounds

• Performed by nitrogen-fixing bacteria

  • Root nodules: Rhizobium

  • Free-living: Azotobacter

What is nitrification and which organisms are involved?

• Converts ammonia (NH₃) → nitrites (NO₂⁻) → nitrates (NO₃⁻)

• Nitrifying bacteria involved:

  1. Nitrosomonas: ammonia → nitrite

  2. Nitrobacter: nitrite → nitrate

What is denitrification and which organisms perform it?

• Converts nitrates (NO₃⁻) back into nitrogen gas (N₂)

• Done by denitrifying bacteria, e.g., Pseudomonas and Clostridium

• Usually occurs in oxygen-poor soils

How do these processes connect in the nitrogen cycle?

• Nitrogen fixation adds usable nitrogen to soil

• Nitrification produces plant-absorbable forms

• Plants and animals use nitrogen for growth

• Denitrification returns nitrogen to the atmosphere

• Maintains nitrogen balance in ecosystems

What’s assimilation?

• Process where plants absorb nitrates and ammomium from the soil through their roots

• Incorporate them into their cells to make proteins and nucleic acids

What is ammonification?

• The process where decomposer bacteria and fungi break down organic nitrogen from dead plants and animals or animal waste

• Converts organic nitrogen into ammonia (NH₃) or ammonium ions (NH₄⁺)

• Recycles nitrogen back into the soil, making it available for nitrification

What is the role of leguminous plants in the nitrogen cycle?

• Leguminous plants (e.g., beans, peas, clover) have root nodules containing Rhizobium bacteria

• These bacteria fix atmospheric nitrogen (N₂) into ammonia (NH₃), which the plant can use

• Increase nitrogen content in soil, enriching it for other plants

• Help reduce the need for artificial nitrogen fertilisers in agriculture

How does lightning enrich soil with nitrates?

• Lightning provides enough energy to break nitrogen gas (N₂) molecules in the atmosphere

• Nitrogen atoms combine with oxygen to form nitrogen oxides (NO and NO₂)

• These oxides dissolve in rain to form nitrates (NO₃⁻)

• Nitrates are deposited into the soil, providing a natural source of nitrogen for plants

What causes the natural greenhouse effect?

• Naturally occurring greenhouse gases (e.g., carbon dioxide, methane, water vapour) trap heat in the atmosphere

• Solar radiation enters, warms Earth, and some heat is radiated back

• Greenhouse gases absorb and re-radiate heat, keeping Earth’s temperature suitable for life

What are the effects of the natural greenhouse effect?

• Maintains Earth’s average temperature around 15°C

• Supports life by preventing extreme temperature fluctuations

What causes the enhanced greenhouse effect?

• Human activities increase greenhouse gas concentrations (burning fossil fuels, deforestation, agriculture)

• More heat is trapped than normal, disrupting Earth’s natural energy balance

What are the effects of the enhanced greenhouse effect?

• Global warming and rising average temperatures

• Melting polar ice and glaciers, sea-level rise

• More extreme weather events (storms, droughts, heatwaves)

• Disruption of ecosystems and biodiversity

Greenhouse Effect vs Enhanced Greenhouse Effect

• Natural greenhouse effect: essential for life, balanced

• Enhanced greenhouse effect: human-driven, causes climate change and environmental harm

What causes El Niño?

• Weakening or reversal of the trade winds in the Pacific Ocean

• Warm water from the western Pacific moves east toward South America

• Reduces upwelling of cold, nutrient-rich water near South America

• Alters global weather patterns

What are the impacts of El Niño on Australia?

• Drier conditions, especially in eastern and northern Australia

• Increased risk of drought and bushfires

• Lower agricultural yields due to reduced rainfall

• Warmer than average temperatures

What causes La Niña?

• Strengthening of the trade winds in the Pacific Ocean

• Warm water pushed further west toward Australia and Asia

• Enhanced upwelling of cold water near South America

• Opposite weather pattern to El Niño

What are the impacts of La Niña on Australia?

• Wetter conditions, particularly in eastern and northern Australia

• Increased risk of floods and cyclones

• Higher agricultural yields in some regions due to more rainfall

• Cooler than average temperatures in some areas

How does global warming affect sea ice and ocean temperatures?

• Rising global temperatures cause polar ice to melt, reducing sea ice coverage

• Warmer air and ocean water increase ocean temperatures, affecting marine ecosystems

Example of sea ice loss

• Arctic sea ice has declined significantly over the past decades

• Polar bears lose habitat for hunting and breeding, threatening populations

Example of increased ocean temperatures

• Great Barrier Reef in Australia suffers from coral bleaching

• Warmer waters stress corals, causing them to expel algae and turn white

• Reduces biodiversity and affects fisheries and tourism

How are marine organisms impacted by global warming?

• Rising sea temperatures:

  • Causes coral bleaching (e.g., Great Barrier Reef)

  • Disrupts breeding and migration patterns of fish and marine mammals

• Ocean acidification:

  • Increased CO₂ dissolves in seawater, lowering pH

  • Weakens shells and skeletons of molluscs, corals, and some plankton

• Loss of sea ice:

  • Polar species like penguins and polar bears lose habitat

  • Reduces hunting grounds and breeding areas

• Changes in ocean currents:

  • Alters nutrient distribution, affecting plankton growth and entire food webs

• Extreme weather events:

  • Storms and cyclones damage reefs and coastal habitats

• Overall impact:

  • Decline in biodiversity, reduced fish stocks, and disruption of marine ecosystems

What is the importance of ocean currents in regulating global climate?

• Transport heat around the planet, moving warm water from the equator toward the poles and cold water from the poles toward the equator

• Help regulate regional climates (e.g., Gulf Stream keeps Western Europe warmer)

• Influence rainfall and weather patterns, affecting droughts and monsoons

How do ocean currents affect marine life?

• Distribute nutrients through upwelling, supporting plankton growth and the marine food chain

• Influence migration routes and breeding grounds of fish, whales, and turtles

• Maintain oxygen levels and temperature ranges necessary for marine species survival

• Changes in currents due to climate change can disrupt ecosystems, reduce fish stocks, and affect biodiversity

What is the carbon cycle?

• The carbon cycle is the movement of carbon through the atmosphere, biosphere, hydrosphere, and geosphere

• Ensures carbon is available for life, stored in plants, animals, soils, oceans, and rocks

What is photosynthesis in the carbon cycle?

• Plants, algae, and some bacteria absorb carbon dioxide (CO₂) from the atmosphere

• Convert CO₂ and sunlight into glucose (C₆H₁₂O₆) and oxygen (O₂)

• Removes carbon from the atmosphere and stores it in living organisms

What is respiration in the carbon cycle?

• Plants, animals, and microbes release carbon dioxide back into the atmosphere by breaking down glucose for energy

• Occurs in all living organisms continuously

What is decomposition in the carbon cycle?

• Decomposers (bacteria and fungi) break down dead organisms and waste

• Release carbon back into the soil and atmosphere as CO₂ or methane (CH₄)

What is consumption in the carbon cycle?

• Animals eat plants or other animals, transferring carbon through the food chain

• Carbon becomes part of their bodies until released via respiration, waste, or death

What is combustion in the carbon cycle?

• Burning of fossil fuels, wood, or other organic matter

• Releases stored carbon back into the atmosphere as CO₂

What is mining in the carbon cycle?

• Extraction of fossil fuels like coal, oil, and natural gas

• Makes carbon stored underground available for combustion

What is sedimentation (fossil fuel formation) in the carbon cycle?

• Dead plants and animals are buried and compressed over millions of years

• Forms coal, oil, and natural gas, storing carbon in the Earth’s crust for long periods

How do the processors for the cabron cycle connect?

• Photosynthesis removes CO₂ from the atmosphere

• Respiration, decomposition, and combustion return CO₂ to the atmosphere

• Consumption transfers carbon through ecosystems

• Sedimentation and fossil fuel formation store carbon long-term

• Mining and burning fossil fuels release stored carbon, influencing global climate

What is a model that shows the natural cycling of matter in the biosphere?

• The ecosystem or biogeochemical cycle model illustrates how matter moves through living and non-living components of the biosphere

• Components of the model:

  • Producers (plants, algae): take in nutrients and carbon via photosynthesis

  • Consumers (animals): obtain matter by eating producers or other consumers

  • Decomposers (bacteria, fungi): break down dead organisms and waste, returning nutrients to the soil

  • Abiotic components (air, water, soil): provide nutrients and carbon for living organisms

• Flows in the model:

  • Nutrients and elements like carbon, nitrogen, and phosphorus cycle between organisms and the environment

  • Energy flows one-way through the food chain, while matter cycles continuously

• Purpose: shows how matter is recycled, maintaining ecosystem balance and sustaining life

What is a light year?

The distance light travels in one Earth year.

Approx. 9.46 trillion km

Trillion in scientific notation

10¹²

How to convert between light years (ly) and kilometres?

Light years → kilometers: ly × 9.46 × 10¹²

Kilometers → light years: km ÷ 9.46 × 10¹²

What’s a parsec?

A unit used to measure astronomical distances based on geometry rather than the speed of light.

• 1 parsec ≈ 3.26 light years

• 1 parsec ≈ 3.086 × 10¹³ km

Converting between light years and parsecs

Parsecs: ly ÷ 3.26

Ly: pc × 3.26

How to convert between parsecs and kilometres?

Parsecs → kilometers: pc × 3.08 × 10¹³

Kilometres → parsecs: km ÷ 3.08 × 10¹³

What is parallax?

The apparent shift in a star’s position when viewed from different locations.

By measuring the angles to the stars and using trigonometry, the distance to the star can be calculated.

Why does parallax occur?

Because Earth changes position as it orbits the Sun, causing nearby stars to appear to move slightly relative to distant stars.

What two positions are used to measure parallax?

Observations taken six months apart - when Earth is on opposite sides of its orbit.

What does a smaller parallax angle mean

The further away the star is

How is the distance to a star calculated using parallax?

Distance (in parsecs) = 1 ÷ parallax angle

Why can parallax only be used for nearby stars?

Because for distant stars, the parallax angle becomes too small to measure accurately.

What is a nebula?

A large cloud of gas and dust in space, where stars begin to form.

How do stars form from a nebula?

Gravity pulls the gas particles together, causing heat and pressure to rise at the center. Eventually, it may become hot enough to “ignite” forming a protostar.

What are the 2 most common gases found in nebulae?

1. Hydrogen

2. Helium

They are the smallest and most abundant elements in the universe.

What is nuclear fusion?

The process where atomic nuclei combine to form heavier elements, releasing huge amounts of energy and powering stars.

What causes nuclear fusion?

The immense temperature and pressure in a star’s core force hydrogen nuclei close enough to overcome their natural repulsion, allowing them to fuse and release energy.

What is a protostar?

A forming star created when gravity pulls gas and dust from a nebula together, heating up as it collapses.

What is a main sequence star (MSS)?

A stable star where hydrogen is fused into helium at the core, releasing energy and balancing gravity.

What is a red giant (or red supergiant)?

A large, cool star that forms after hydrogen runs out and helium fusion begins, causing the star to expand.

Red supergiant only: This nuclear fusion releases enormous amounts of energy, causing the star to expand again, reaching 100 million to 1 billion km in diameter.

What is a planetary nebula?

The outer layers of a dying average star that drift into space, leaving the hot core behind. These clouds of gas may eventually reform new stars.

What is a white dwarf?

The small, hot, dense core left after a planetary nebula; it slowly cools and fades.

What is a black dwarf?

A theoretical final stage of a white dwarf’s life where it is very hot but no longer produces energy through fusion. Over trillions of years, it will cool down and stop glowing completely.

What is a supernova?

A massive explosion that occurs when a large star runs out of fuel and its core collapses.

What is a neutron star?

The extremely dense core left after a supernova, made mostly of neutrons.

What is a black hole?

A point in space with gravity so strong that not even light can escape, formed from the collapse of a very massive star.

Life cycle of an average-sized star

1. Nebula

2. Protostar

3. Main Sequence Star

4. Red Giant

5. Planetary Nebula

6. White Dwarf

Life cycle of a massive star

1. Nebula

2. Protostar

3. Main Sequence Star

4. Red Supergiant

5. Supernova

6. Neutron Star (if not too massive) or Black Hole (if extremely massive)

What is the brightness of a star?

How much light or energy it gives off.

What is apparent brightness?

• How bright a star appears from Earth.

• It depends on both the star’s actual light output and its distance from us.

• A nearby dim star can look brighter than a faraway luminous one.

What is absolute brightness?

• The star’s true brightness — how bright it would appear if it were 10 parsecs (32.6 light years) away.

• This lets astronomers compare stars fairly, without distance affecting the result.

• If the value is less than 1, it is brighter than our sun

• Greater than 1 indicates a star is less bright than the sun

Brightness of each type of star?

• Red dwarfs: faint

• Main Sequence Star: moderate

• Red giants: bright

• Red supergiants: extremely bright

• White dwarfs: faint

• Supernovae: brightest of all (but short lived)

What is a Cepheid variable?

A type of star that regularly gets brighter and dimmer due to changes in its size and temperature.

What causes a Cepheid variable’s brightness to change?

The star expands and contracts in a repeating cycle, which alters its temperature and light output.

What is the period–luminosity relationship?

The longer the period (time between brightness peaks), the brighter the Cepheid’s true luminosity.

How do astronomers use Cepheid variables to find a star’s absolute brightness?

They measure the star’s period of brightness variation, then use the period–luminosity relationship to calculate its true brightness (absolute magnitude).

How can Cepheid variables be used to find distance?

By comparing the star’s absolute brightness (true luminosity) with its apparent brightness (how bright it looks from Earth).

Why are Cepheid variables important in astronomy?

They act as “standard candles” — reliable distance markers for measuring how far away galaxies and stars are.

What determines a star’s colour?

Its surface temperature.

What colour are the hottest stars?

Blue — with surface temperatures above 25,000 °C.

What colour are medium-temperature stars like the Sun?

Yellow — around 6,000 °C.

What colour are the coolest stars?

Red — about 2,000–3,500 °C.

What is the general relationship between star colour and temperature?

Hotter stars appear bluer, while cooler stars appear redder.

What is a Hertzsprung-Russell diagram?

A diagram that shows the relationship between the brightness and temperature of a star.

With this info, we can identify what stage of its life cycle a star is in.

Why are 90% of stars found in the MSS?

It’s the longest and most stable phase in a star’s life.

How do galaxies form?

Small density differences after the Big Bang caused matter to clump together. Over time, these clumps formed stars, which grouped into galaxies containing stars and planets.

What is the Doppler effect in light?

The change in the observed wavelength (and colour) of light caused by the motion of the source relative to the observer.

What happens to light from an object moving towards us?

The wavelengths are compressed, making the light appear bluer — this is called a blue shift.

What happens to light from an object moving away from us?

The wavelengths are stretched, making the light appear redder — this is called a red shift.

What does a red shift tell astronomers?

That the object (like a galaxy) is moving away from Earth.

What does a blue shift tell astronomers?

That the object is moving towards Earth.

Why is the Doppler effect important in astronomy?

It helps scientists measure how fast stars and galaxies are moving, and supports evidence that the universe is expanding.

What is Cosmic Microwave Background Radiation (CMB)?

The faint microwave afterglow of the Big Bang, left over as the universe expanded and cooled.

How does CMB support the BBT?

It shows that the universe began as hot and dense, then expanded.

What makes up a universe?

Billions of galaxies that are all many light years away from each other

What does the BBT describe?

The universe began with an enormous explosion of energy and then it expanded from an extremely small, extremely hot and extremely dense state.

Evidence of the BBT

1. CMB

2. Redshift/blueshift

3. Abundance of light elements (Hydrogen, Helium)

What does the Solid State Theory describe?

The universe is infinite in extent and that it has always existed in a similar form to what is observed today

BBT vs SST

BBT:

• Starting point

• Expansion from a singularity from a hot, dense state to its current structure

SST:

• External universe with no begging or end/eternal universe with no beginning or end

Stages of evolution in the universe

1. Singularity forms

2. Time and space form; space expands rapidly

3. Light matter forms – electrons, positrons

4. Heavier matter forms – protons, neutrons

5. Universe cools; reaches size of solar system

6. Universe cools to 10¹⁰ °C

7. Atomic nuclei form

8. Universe cools to 3000 °C

9. First stars appear

10. Galaxies begin to form

What are positrons?

• The antimatter version of an electron

• It has the same mass as an electron.

• It has the same amount of charge, but it’s positive instead of negative.

How does the relative abundance of hydrogen and helium support the Big Bang Theory?

• After the Big Bang, the universe was extremely hot and dense.

• Fusion turned some hydrogen into helium before the universe cooled.

• This left about 75% hydrogen and 25% helium.

• These amounts match what we observe today.

• Shows there were fusion at the beginning of our universe

What are the five main reasons we explore space today?

Scientific discovery, national security, commercial profit, benefits for life on Earth, and ensuring our future.