Science Basics | Observation, Experiments and Scientific Reasoning, Set 1

The green granules are chloroplasts, which use the energy of light to carry out photosynthesis. The nucleus is the structure associated with genetic information, and the vacuole contains cell sap. Note too that not every cell of a plant contains chloroplasts.

P waves travel faster than S waves, so the slight shaking from the P waves is normally recorded first, with the stronger shaking of the S waves arriving afterwards. Being stronger and travelling faster are not the same thing.

In a series circuit with no branches, the current is the same everywhere, so it is 0.30 A. Electrical energy is converted to heat and so on in a resistor, but the current itself is not halved each time it passes through one.

Density is mass divided by volume, so 54 ÷ 20 = 2.7 g/cm³. The figure 0.37 divides volume by mass and 74 adds mass and volume, neither of which is how density is found.

The shift toward pH 7 is explained by neutralization between the acid and the alkali, producing a salt. If the amounts and concentrations do not balance, however, acid or alkali is left over, so mixing does not always give pH 7.

Shading part of the same leaf allows the difference in starch formation to be compared with conditions other than exposure to light held as constant as possible. This is a control for testing whether light is necessary; the foil does not supply starch.

With the object inside the focal point, no real image can be caught on a screen on the far side of a convex lens; what forms is a virtual image seen from the object's side. That moving the screen alone cannot produce a real image is what distinguishes this from the case with the object outside the focal point.

Where isobars are closer together, the pressure difference per unit distance — the pressure gradient — is greater, and the wind is generally stronger. With the conditions held equal as here, point A can be read as stronger, though real winds are also affected by terrain and friction.

The combined series resistance is 10 + 20 = 30 Ω, so the current is 6.0 ÷ 30 = 0.20 A. The voltage across resistor B is 0.20 × 20 = 4.0 V. In a series circuit the current is common, but because the resistances differ the voltages across them are not the same.

In a chemical change the total mass of reactants and products together is conserved. In B the reading fell because the gas produced left the vessel and so left what was being weighed. In A the gas is retained inside, so the reading for the whole apparatus does not change.