Year 7 Science Revision
DNA & Inheritance
&
The Structure of the Earth
The Atmosphere
- the gases that surround a planet make up that planets atmosphere
- Earth's Atmosphere
- 78% Nitrogen
- 21% Oxygen
- 1% other gases - 0.04% Carbon Dioxide/0.9% Argon
- Carbon Dioxide
- burning fossil fuels - increase carboon dioxide in the atmosphere
- deforestation - less photosynthesis - more carbon dioxide in the air
Chromosomes, DNA & Genes
The Earth
- Most cells in the body have a nucleus
- the nucleus is the control centre of the cell
- the nucleus contains chromosomes
- chromosomes are long lengths of DNA
- Chromosomes carry genes
- different genes control different characteristics
The Earth is divided into
- The crust: the part we live on - thin outer layer of solid rock
- The mantle: mostly solid - deep down it can flow very slowly (thick liquid)
- The Core: the centre - made of Iron & Nickel
- the Earth's Surface is broken into plates
- they're able to move around slowly
- the plates move suddenly - earthquake
- there are 3 types of Rock
- Sedimentary - layers laid down over millions of years stuck together by minerals
- Igneous - lava above ground, magma below the surface
- Metamorphic - heat & pressure over a long period of time
Environmental & Hereditary
Variation
- different species have different genes
- variation is the differences between living things
- variation also exists within a species
- hair colour
- skin colour
- eye colour
- Hereditary: from your parents
- Environmental: from your friends, neighbourhood, school etc.
- variation can occur in plants
- large leaf size - to help catch sunlight
- small leaf size - to prevent water loss
- Organisms with characteristics that make them better at competing are more likely to survive and reproduce
- organisms compete for:
- food
- shelter
- mates
- water
Photosynthesis
- when plants respire they take in oxygen & release carbon dioxide
- during photosynthesis the plants take in carbon dioxide & release oxygen
- without photosynthesis there would not be enough oxygen in the air
- there would be too much carbon dioxide in the air also
Forces
Interdependence:
plants rely on animals for the carbon dioxide & animals rely on plants for the oxygen
Forces are usually pushes and pulls
- cant be seen - but the effects can (eg. wind)
- are measured in Newtons (N)
- usually act in pairs (opposite forces)
- they always act in a certain direction
- Newton meter - measures forces
Food Chains & Webs
Forces
- food chains/webs show the flow of energy in an ecosystem
- food webs are 2 or more food chains interlinked
- producer: makes its own food (plant)
- primary consumer: eats plants (rabbit)
- secondary consumer: eats primary consumer
- tertiary consumer: eats secondary consumer
- herbivore: eats plants only
- carnivore: eats animals only
- omnivore: eats both plants & animals
Dependence on other Organisms
Forces can make objects do 5 things
- speed up/start moving
- slow down/stop moving
- change direction
- turn
- change shape
Forces can occur between objects that aren't touching
- forces usually occur between objects that are touching
- forces due to gravity, magnetism & static electricity are all non-contact forces
- A change in 1 organism can affect other organisms
- Poisons build up in food chains
Friction
- tries to stop objects sliding past each other
- it is always in the opposite direction to movement
- to push an object out of your way - need to overcome friction
- friction
- 2 surfaces rubbing together
- an object passing through air or water
air & water resistance are frictional forces
Forces
Atmospheric Pressure
- at sea level, there is a lot of atmosphere above you
- the atmosphere weighs a bit so it applies a high pressure
- at the top of a mountain - less atmosphere above you - pressure is lower
- the pressure in liquids increases with depth
- an ecosystem is all the living organisms in one area, plus their environment
- the organisms are interdependent
- they need each other to survive
- all living things depend on plants
- almost all energy on Earth comes from the sun
- Photosynthesis: plants make their own food
- the energy gets passed on from plants to animals when animals eat the plants
Force diagrams
- equal and opposite forces - stationary or moving at a steady speed
- Accelerating - forward force is bigger
- slowing down - backward force is bigger
Gravity
- Gravity is a force that attracts all masses
- the Earth & the moon are attracted by gravity
- the Earth & the Sun are attracted by gravity
- Mass is not a force - weight is
- mass is an amount of stuff - weight is caused by the pull of gravity
- mass of an object never changes - weight can
- mass is measured in kg using an electric balance
- weight is measured in newtons (N) using a newton meter
- weight = mass X gravity
HSW
Independent Variable - what you change in your investigation
Dependent Variable - what you measure
Control Variable - what you keep the same in each experiment
Fair Test - only one variable changed in the experiment
Time - stop watch - seconds (s)
Force - Newton Meter - Newtons (N)
Length (distance) - ruler - m or cm
Temperature - thermometer - degrees celsius
Mean/average - be able to calculate
Anomaly - does not fit the pattern
Prediction - what you think will happen
The Sun & Stars
- the Earth moves around the Sun in an orbit
- the Sun is a star
- the Earth is a planet
- the Sun is luminous (emit light)
- the planets are not
- a galaxy is a large group of stars
- our galaxy is called the Milky Way
- the Sun is our closest star
- a light year is a unit of distance (not time)
- a constellation is a group of stars that form a recognisable pattern
- Orion
- the Plough
Day & Night
- the rotation of the Earth causes days & night
- the Earth rotates about its axis - 24 hours
- the imaginary line running from the North to the South Pole
- facing the Sun - light - day time
- facing away from the Sun - no light - night time
- takes 1 year (365.25 days) to orbit the Sun
- the seasons are caused by the tilt of the Earths axis
- Summer - Earth tilted towards the sun - Suns rays more concentrated - longer, warmer days
- Winter - Earth tilts away from the Sun - Suns rays are more spread out - shorter, colder days