Botswana JCE Science (Syllabus 14) flashcards

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

Independent variable

The single factor that the experimenter deliberately changes in an investigation. All other conditions are kept constant so that any effect on the dependent variable can be attributed to it.

Dependent variable

The factor that is measured or observed in an experiment; it responds to changes in the independent variable. In a graph it is plotted on the vertical axis.

Control group

A group in an investigation that is treated in exactly the same way as the experimental group except that the independent variable is not applied, used to show the change is due to the variable tested.

Accuracy versus precision

Accuracy describes how close a measurement is to the true value. Precision describes how close repeated measurements are to one another, so repeated readings may agree closely yet all be inaccurate.

Line graph use

A line graph is drawn when both variables are continuous numerical quantities, such as time and temperature. A bar chart is used when the independent variable is a set of named categories.

Particle arrangement in solids

Particles in a solid are packed closely in fixed positions and vibrate about those positions. This explains the fixed shape and volume of solids and why they cannot be easily compressed.

Physical versus chemical change

A physical change alters form or state without forming a new substance and is usually reversible. A chemical change forms a new substance and is usually difficult to reverse.

Filtration

A separation technique that passes a mixture through filter paper, trapping an insoluble solid as residue while the liquid passes through as filtrate. It cannot separate a dissolved solid.

Crystallisation

A method of recovering a dissolved solid from solution by slowly evaporating the solvent so that the solid forms pure crystals, leaving soluble impurities behind in the remaining liquid.

Neutralisation

The reaction between an acid and a base that produces a salt and water only. The pH moves towards 7, which is why antacids relieve excess stomach acid.

Atom versus compound

An atom is the smallest particle of an element that can take part in a reaction. A compound consists of two or more elements chemically combined in fixed proportions, with properties different from its elements.

Density rule for floating

Density equals mass divided by volume. A solid object floats in a liquid when its density is less than that of the liquid, and sinks when its density is greater.

Chloroplast function

Chloroplasts are green plant cell structures containing chlorophyll. They absorb light energy and use it to combine carbon dioxide and water into glucose, releasing oxygen as a by-product.

Plant versus animal cells

Plant cells have a cellulose cell wall, a large permanent vacuole and often chloroplasts. Animal cells lack a cell wall and chloroplasts and may have small temporary vacuoles.

Photosynthesis equation

Carbon dioxide plus water, using light energy absorbed by chlorophyll, produces glucose plus oxygen. The reaction occurs in chloroplasts and stores energy in the glucose made.

Aerobic respiration

Glucose reacts with oxygen in cells to release energy, producing carbon dioxide and water as waste. It occurs continuously in all living cells, including in darkness.

Energy flow in food chains

Arrows in a food chain point from the organism being eaten to the organism that eats it, showing the direction of energy transfer. Producers occupy the first trophic level.

Red blood cell function

Red blood cells contain haemoglobin, which binds oxygen in the lungs and releases it in tissues. They have no nucleus in mammals, giving more room for haemoglobin and oxygen transport.

Inhalation mechanism

The diaphragm contracts and flattens while the rib cage moves up and out. Thoracic volume increases, pressure inside the lungs falls below atmospheric pressure, and air flows in.

Binomial naming

Each species has a two-part scientific name: the genus name, written with a capital letter, followed by the species name, written in lower case. Both are usually italicised.

Weight versus mass

Mass is the quantity of matter in an object, measured in kilograms and unchanged by location. Weight is the force of gravity on it, measured in newtons, and varies with gravitational field strength.

Friction

A force that opposes relative motion between surfaces in contact. It transfers kinetic energy to thermal energy and can be reduced by lubricants, smooth surfaces or rollers.

Pressure formula

Pressure equals force divided by the area over which it acts, measured in pascals. For a fixed force, reducing the area increases the pressure, as with a sharp knife edge.

Work done

Work is done when a force moves an object in the direction of the force; it equals force multiplied by distance moved, measured in joules. No work is done if there is no movement.

Series circuit rules

In a series circuit there is a single path, so the current is the same at every point. The supply voltage is shared among the components and total resistance is the sum of the resistances.

Parallel circuit rules

In a parallel circuit each branch provides a separate path, so the voltage across each branch is the same. Branch currents add to give the total current and overall resistance is lower.

Ohm's law

For a conductor at constant temperature, current is directly proportional to voltage, so voltage equals current multiplied by resistance. Resistance is measured in ohms.

Earth's internal structure

Earth has a thin rocky crust, a hot semi-solid mantle where convection currents occur, a liquid outer core of iron and nickel, and a solid inner core under great pressure.

Day and night cause

Earth spins on its tilted axis once roughly every 24 hours. The hemisphere facing the Sun experiences day while the other faces away and experiences night.

Seasons cause

Earth's axis is tilted as it orbits the Sun, so each hemisphere receives sunlight at a different angle and for a different number of hours during the year, producing the seasons.

Water cycle processes

Water evaporates from oceans and transpires from plants, condenses into clouds, falls as precipitation, then returns via run-off and infiltration into the ground and rivers.

Rock types

Igneous rock forms when magma or lava cools and solidifies. Sedimentary rock forms from compacted sediment layers and may hold fossils. Metamorphic rock forms when existing rock is altered by heat and pressure.