GCSE Combined Science Flashcards

What is the role of the ribosome in a cell?

Answer: To synthesise proteins from amino acids following mRNA instructions

Ribosomes are the sites of protein synthesis in cells. They read the mRNA (messenger RNA) sequence, which carries instructions from DNA, and assemble amino acids in the correct order to build proteins.

What is the difference between speed and velocity?

Answer: Speed is a scalar (magnitude only); velocity is a vector (magnitude and direction)

Speed is a scalar quantity — it only has magnitude (e.g., 50 km/h). Velocity is a vector — it has both magnitude and direction (e.g., 50 km/h north). This distinction is crucial in physics calculations.

What is the formula for calculating density?

Answer: Density = mass ÷ volume

Density = mass ÷ volume (ρ = m/V). It is measured in kg/m³ or g/cm³. A denser material has more mass packed into the same volume. A substance floats if its density is less than the liquid it is placed in.

What happens to the rate of an enzyme-catalysed reaction above the optimum temperature?

Answer: It decreases rapidly as the enzyme denatures

Above the optimum temperature, the enzyme's active site changes shape (denatures) and the substrate can no longer fit. The reaction rate falls sharply. Enzymes do not recover from denaturation.

What is the atomic number of an element?

Answer: The number of protons in the nucleus

The atomic number (proton number) is the number of protons in the nucleus of an atom. It uniquely identifies an element and determines its position in the periodic table. In a neutral atom, it also equals the number of electrons.

What is the greenhouse effect?

Answer: The trapping of heat by greenhouse gases in the atmosphere, warming the Earth's surface

The greenhouse effect occurs when greenhouse gases (CO₂, methane, water vapour) absorb outgoing infrared radiation from the Earth's surface and re-emit it back, warming the planet. Enhanced greenhouse effect from human activity causes climate change.