Scientific Skills: Variables, Data, and Error Types

Scientific Skills Knowledge Organizer

• Types of variables exist in experiments.
• The independent variable is the one changed.
• The dependent variable is the one measured.
• The control variable is the one that stays the same.

Types of Data

• Categoric data comprises values that are labels.
• Continuous data comprises values that are numbers.
• Only include units in table headings and not within the data itself.

Graphs

• Bar charts are suitable for plotting one piece of categoric data and one piece of continuous data.
• Line graphs are appropriate for two pieces of continuous data.
• A line of best fit should be included on line graphs, and may be a straight line or a curve, but should not "join the dots".

Types of Error

• Systematic errors stem from a problem with the method or equipment used, and cannot be reduced by taking repeat readings.
• Random errors occur whenever something is measured and can be reduced by taking repeat readings.
• Zero errors are caused by equipment not reading zero when it should; can be resolved by resetting the equipment or deducting the false reading from all measurements.

Key Words

• Accurate refers to being close to the true value.
• Anomalous refers to a result that doesn't fit the pattern.
• Precise refers to a small amount of spread around the mean.
• Resolution is the smallest reading on a piece of measuring equipment.
• Reproducible means the same results are obtained by different people for the same investigation.
• Range is the difference between the biggest and smallest values of the independent or dependent variable.
• Volume is the amount of a liquid.

Earth and the Universe

• Attraction occurs when two or more things come together.
• Gravity is the force of attraction between all objects.
• The more mass an object has, the larger the force of gravity it exerts.
• A magnetic field is the area surrounding a magnet that can exert a force on magnetic materials.
• Mass is the amount of matter in something, measured in kilograms (kg).
• An orbit is the path an object takes around a star, planet, or moon.
• Repulsion occurs when two or more things are forced apart

The Seasons and Solar System

• Seasons are the four times of the year (winter, spring, summer, autumn).
• The Solar System consists of the Sun, planets, asteroids, and comets orbiting the Sun.
• A star is a large mass at the center of a Solar System that produces heat and light.
• Weight is the force of gravity on an object, measured in newtons (N).

Days and Nights

• The Earth rotates (spins) on its axis once in 24 hours, causing day and night.
• Planets further from the Sun travel more slowly and take longer to orbit.
• The Earth's axis is tipped, causing different seasons as different parts of the Earth tilt towards the Sun.

Planets

• The order of planets from the Sun is: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
• Magnetic materials can be magnetized or attracted to a magnet such as iron, cobalt, nickel, and steel.
• A magnet's magnetic field is strongest at the poles, where the field lines are most concentrated.
• The Earth behaves as if it contains a giant magnet.
• The structures of the earth include the solid iron and nickle inner core, the liquid layer of iron and nickel in the outer core, the mantle which is classed as a liquid and the crust which is made of land.

Reproduction

• The egg cell is the female sex cell (gamete).
• The sperm cell is the male sex cell (gamete).
• Fertilization is the fusing of male and female sex cells.
• The ovary is the female reproductive organ that releases egg cells.
• The testes are the male reproductive organs which produce sperm cells.
• An embryo is a tiny new human life that grows by cell division from a fertilized egg cell.
• Gestation, also known as pregnancy, is the period between fertilization and birth.
• The placenta is the organ that allows substances to pass between the mother's blood and baby's blood.
• Amniotic fluid surrounds and cushions the foetus.
• A foetus is the unborn baby after around 8 weeks of pregnancy.
• Menstruation is when the lining of the uterus breaks down every month if the egg is not fertilized.
• Sexual reproduction creates new organisms by joining two sex cells.
• Asexual reproduction creates new organisms from only one parent.

Reproductive Systems

• The testes produce millions of sperm.
• Sperm pass through sperm ducts and mix with fluids from glands.
• The penis passes urine and semen out of the male body.
• The urethra carries urine or semen.
• Ovaries contain hundreds of undeveloped female gametes called ova.
• Each ovary is connected to the uterus by an oviduct, which can also be known as the fallopian tube.
• Every month, an egg matures and is released from an ovary.
• The uterus is where a baby develops until birth.
• The cervix keeps the baby in place during pregnancy.
• The vagina is a muscular tube that leads from the cervix to the outside of the woman's body.

The Menstrual Cycle

• The menstrual cycle prepares the female body for pregnancy.
• The process lasts for 28 days.
  • Days 1-5: "period" happens (menstruation), where the uterus lining breaks down.
  • Days 6-13: The uterus lining builds up in preparation of pregnancy, and an egg matures in the ovary.
  • Day 14: An egg is released from the ovary and travels down the oviduct.
  • Days 15-28: The uterus lining stays thick in case the egg is fertilized.

Foetus Development & Placenta

• The feotus relies upon its mother as it develops.
  • Oxygen and nutrients are provided by the mother.
  • Waste is also taken from the feotus to the mother.

Acids and Bases

• An acid is a corrosive substance with a pH lower than 7, caused by a high concentration of hydrogen ions.
• Acidic means having a pH lower than 7.
• An alkali is a base which is soluble in water. Being alkaline means having a pH greater than 7.
• A base reacts with an acid to neutralize it and produce a salt.
• Neutralize means to make neutral by removing any acidic or alkaline nature.
• Neutral describes a substance that is neither acidic nor alkaline, with a pH of 7.
• Litmus paper is an indicator that can be red or blue.
• Red litmus paper turns blue in alkalis, while blue litmus turns red in acids.
• pH is a measure on a scale of acidity or alkalinity.
• Universal indicator paper is stained with universal indicator, a chemical solution that produces many different color changes corresponding to different pH levels.

Different types of solutions

• Dilute acids are safer than concentrated acids, because there are less acid particles.
• A concentrated solution has more acid particles.

Acids and Bases

• Bases are substances that neutralize acids.
• Examples: metal oxides, metal hydroxides, metal carbonates.
• Alkalis: describe bases that dissolve in water.
• Some alkalis are harmful, many are harmless and also useful.
• Cleaning products (eg, bleach, washing powder, oven cleaner) contain alkalis.
• Litmus paper indicates acids or alkalis.