SPM Science flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Mitosis versus meiosis

Mitosis produces two genetically identical diploid daughter cells for growth and repair. Meiosis produces four genetically varied haploid gametes, halving chromosome number, with crossing over and independent assortment increasing variation.

Photosynthesis equation

Carbon dioxide plus water, in the presence of light and chlorophyll, produces glucose and oxygen: 6CO2 + 6H2O -> C6H12O6 + 6O2. Light energy is converted to chemical energy stored in glucose.

Aerobic respiration equation

Glucose plus oxygen produces carbon dioxide, water and energy: C6H12O6 + 6O2 -> 6CO2 + 6H2O + energy. It releases far more energy per glucose molecule than anaerobic respiration.

Osmosis definition

Osmosis is the net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane, without requiring external energy.

Homeostasis and negative feedback

Homeostasis keeps internal conditions such as temperature and blood glucose within narrow limits. Negative feedback detects a deviation, triggers a corrective response, and stops once the normal level is restored.

Dominant and recessive alleles

A dominant allele expresses its trait even when only one copy is present; a recessive allele expresses only when two copies are present. Genetic diagrams predict offspring ratios such as 3:1.

Energy flow in ecosystems

Energy enters food chains as sunlight captured by producers. At each trophic level most energy is lost through respiration, heat and excretion, so only about ten percent transfers to the next level.

Ionic versus covalent bonding

Ionic bonds form when electrons transfer from metal to non-metal, creating oppositely charged ions held by electrostatic attraction. Covalent bonds form when non-metals share electron pairs.

Mole concept formulas

Number of moles n equals mass in grams divided by molar mass, and also equals concentration times volume in dm3 for solutions. One mole contains 6.02 x 10^23 particles.

pH and neutralisation

pH below 7 is acidic, 7 is neutral, above 7 is alkaline. Acid plus base gives salt plus water; the reaction is neutralisation and can be followed by titration with an indicator.

Electrolysis of solutions

Electrolysis uses direct current to decompose an electrolyte. At the cathode cations gain electrons (reduction); at the anode anions lose electrons (oxidation). Reactivity and ion concentration decide products.

Factors affecting reaction rate

Rate increases with higher concentration, higher temperature, larger surface area, and presence of a catalyst. These increase collision frequency or the fraction of collisions with sufficient activation energy.

Alkanes versus alkenes

Alkanes are saturated hydrocarbons with only single carbon-carbon bonds and general formula CnH2n+2. Alkenes contain one double bond, formula CnH2n, and decolourise bromine water.

Polymers and monomers

Polymers are large molecules built from repeating small units called monomers. Addition polymerisation joins alkene monomers without losing atoms; condensation polymerisation releases small molecules such as water.

Kinematics equations

For constant acceleration: v = u + at, s = ut + 1/2at^2, and v^2 = u^2 + 2as. Symbols mean initial velocity u, final velocity v, acceleration a, displacement s, time t.

Newton's second law

The resultant force on an object equals its mass multiplied by its acceleration (F = ma). Force is measured in newtons, mass in kilograms, and acceleration in metres per second squared.

Conservation of momentum

In a closed system with no external resultant force, total momentum before a collision or explosion equals total momentum after. Momentum equals mass times velocity, measured in kg m/s.

Work energy and power

Work equals force times displacement in the force direction; power equals work divided by time. Kinetic energy is 1/2mv^2 and gravitational potential energy is mgh.

Specific heat capacity

Heat energy gained or lost equals mass times specific heat capacity times temperature change (Q = mc theta). Specific heat capacity is the energy needed to raise 1 kg by 1 degree C.

Refraction and Snell's law

Light bends when it changes speed between media. Snell's law states n = sin i / sin r. Light entering a denser medium slows and bends towards the normal.

Total internal reflection

When light travels from a denser to a less dense medium beyond the critical angle, it reflects entirely inside. This principle underlies optical fibres and certain prisms.

Ohm's law

Current through a conductor is directly proportional to potential difference across it, provided temperature is constant: V = IR. Resistance is measured in ohms and current in amperes.

Series and parallel circuits

In series, current is the same everywhere and voltages add. In parallel, voltage is the same across branches and currents add; total resistance in parallel is less than the smallest branch resistance.

Electrical power and energy

Power equals voltage times current (P = VI), and energy used equals power times time (E = VIt). Electrical energy is commonly billed in kilowatt-hours.

Transformer voltage ratio

For an ideal transformer, primary voltage divided by secondary voltage equals primary turns divided by secondary turns. A step-up transformer has more secondary turns; power is unchanged.

Earth's layered structure

Earth comprises a crust, mantle, outer core and inner core. The crust and upper mantle form tectonic plates that move on the semi-molten asthenosphere, causing earthquakes and volcanism.

Rock cycle

Igneous rock forms from cooled magma or lava; sedimentary rock forms from compacted deposited sediments; metamorphic rock forms when existing rock is altered by heat and pressure.

Renewable versus non-renewable energy

Renewable resources such as solar, wind, hydroelectric and biomass are replenished naturally. Fossil fuels and nuclear fuel are finite and release pollutants or long-lived waste.

Controlling variables

A fair experiment changes only the manipulated variable, measures the responding variable, and keeps all other variables constant so that observed effects can be attributed to the change made.

Writing a hypothesis

A hypothesis is a testable statement linking the manipulated and responding variables, such as 'the higher the temperature, the faster the reaction'. It must be falsifiable by data.

Graph plotting rules

Plot the manipulated variable on the horizontal axis and the responding variable on the vertical axis. Label axes with quantity and unit, use a uniform scale, and draw a smooth best-fit line.

Precision and accuracy

Precision is how close repeated readings are to each other; accuracy is how close a reading is to the true value. Random errors reduce precision; systematic errors reduce accuracy.