NSTSE key terms

The process by which green plants use sunlight, water and carbon dioxide to make glucose and release oxygen. Chlorophyll in chloroplasts captures the light energy needed to drive this reaction.

The green pigment inside chloroplasts that absorbs light energy for photosynthesis. It absorbs red and blue light most strongly and reflects green light, which is why leaves look green.

The breakdown of glucose in cells to release usable energy, typically using oxygen and producing carbon dioxide and water. It is the opposite balance of photosynthesis and happens in all living cells.

The movement of water molecules through a partially permeable membrane from a dilute solution to a more concentrated one. It explains water uptake by roots and the wilting of plants.

The random spreading of particles from a region of higher concentration to a region of lower concentration. It needs no membrane or energy and moves oxygen into cells and carbon dioxide out.

The difference in concentration of a substance between two regions. A steeper gradient makes diffusion faster, so particles move more quickly from the crowded side to the less crowded side.

The thin, partially permeable layer surrounding a cell. It controls which substances enter and leave, and it is the barrier across which osmosis and diffusion take place.

A rigid outer layer made mainly of cellulose that surrounds plant cells. It gives shape and support and is fully permeable, so it does not control which substances pass through.

A green organelle found in plant cells where photosynthesis occurs. It contains chlorophyll and is the site where light energy is converted into chemical energy in food.

Organelles in which aerobic respiration takes place. They release energy from glucose for cell activities and are especially numerous in active cells such as muscle fibres.

A protein that speeds up a specific chemical reaction in living things without being used up. Each enzyme works best at a particular temperature and pH and is denatured by extremes.

The breakdown of large food molecules into smaller soluble ones that can be absorbed into the blood. Mechanical and chemical digestion work together, with enzymes doing the chemical part.

The taking in of digested food molecules through the wall of the small intestine into the bloodstream. Villi increase the surface area so that absorption happens quickly and efficiently.

The comparison of an object's outer surface area with its internal volume. Small objects have a large ratio, which helps exchange of gases and heat, while larger objects have a smaller ratio.

The bending of light as it passes from one transparent medium into another of different optical density. It occurs because light changes speed and explains why a straw looks bent in water.

The bouncing back of light from a surface. The angle of incidence equals the angle of reflection, and smooth surfaces give clear images while rough surfaces scatter light.

A curved piece of transparent material that refracts light to form an image. A convex lens converges light and a concave lens diverges it, and both are used in spectacles and cameras.

The distance between the centre of a lens and its principal focus. A short focal length gives a more powerful lens and a larger magnification for a given object distance.

The rule that current through a conductor is directly proportional to the potential difference across it, provided temperature stays constant. It is written as V equals I times R.

The opposition to the flow of electric current in a circuit, measured in ohms. It increases with longer wires, thinner wires and higher temperature for most metal conductors.

The rate of flow of electric charge past a point in a circuit, measured in amperes. In metal wires the moving charges are electrons and current flows in the opposite direction to them.

The principle that every action force has an equal and opposite reaction force acting on a different body. It explains recoil, rocket thrust and walking, where feet push back on the ground.

The product of an object's mass and its velocity, measured in kilogram metres per second. In a closed system the total momentum before a collision equals the total after it.

A push or pull that can change an object's speed, direction or shape, measured in newtons. The net force on an object determines its acceleration according to Newton's second law.

A substance that releases hydrogen ions in water, turns blue litmus red and reacts with bases to form salts. Common examples include hydrochloric acid and citric acid in lemon juice.

A substance that neutralises an acid to form a salt and water, often by accepting hydrogen ions. Soluble bases are called alkalis and turn red litmus blue.

A numbered scale from 0 to 14 that measures how acidic or alkaline a solution is. Values below 7 are acidic, 7 is neutral and values above 7 are alkaline.

A whole number greater than 1 whose only positive divisors are 1 and itself. Examples are 2, 3, 5, 7, 11 and 13, and 2 is the only even prime number.

A number that divides another number exactly without leaving a remainder. For example, the factors of 12 are 1, 2, 3, 4, 6 and 12, and 1 is a factor of every whole number.

The result of multiplying a number by a whole number. Multiples of 4 include 4, 8, 12, 16 and so on, and every number is a multiple of itself and of 1.

The highest common factor, meaning the largest number that divides two or more given numbers exactly. It is found by listing factors or by using prime factorisation together.

The lowest common multiple, meaning the smallest number that is a multiple of two or more given numbers. It is used to add fractions with different denominators and to solve cycle problems.

A comparison of two or more quantities of the same kind, written with a colon. A ratio such as 3:2 means the first quantity is one and a half times the second.

A statement that two ratios are equal, such as 2:3 equals 4:6. In direct proportion both quantities increase together, while in inverse proportion one falls as the other rises.

A fraction or ratio expressed as a part out of one hundred. To convert a fraction to a percentage, multiply by 100, so three quarters becomes 75 percent.

Interest calculated only on the original principal using the formula principal times rate times time divided by 100. It does not earn interest on interest as compound interest does.

Interest calculated on the principal plus any interest already added, so the amount grows faster each period. It is found using the formula amount equals principal times one plus rate over 100 raised to the time.

A technique for solving proportion problems by first finding the value of one unit and then multiplying. If 5 pens cost 40 rupees, one pen costs 8 and 7 pens cost 56.

The sum of a set of values divided by how many values there are, also called the arithmetic mean. It gives a single value that represents the whole group.