Which of these pair of substances must be present for a seed to germinate in a laboratory set-up?

Analyze the question: It asks which pair of substances must be present for germination in a laboratory set-up. The key word is must, so we need the essential conditions only.

Explain the concept: Seed germination needs three basic conditions:

1. Water, which softens the seed coat, activates enzymes and lets the embryo swell.
2. Oxygen, for aerobic respiration to release energy for growth.
3. Suitable temperature (warmth), so that enzymes can work.

Light, soil, manure and microbes are not essential for germination. The seed has its own stored food (in the cotyledons or endosperm), so it does not need soil nutrients until after the seedling has used up those reserves.

Solution:

• A. Microbes and water: Microbes are not needed. They can even attack the seed, so this is wrong.
• B. Heat and water: Both are essential conditions. Heat is the temperature factor, and water is required. This is the best option.
• C. Soil and manure: Neither is needed. A seed can germinate on wet cotton wool in the lab, so this is wrong.
• D. Heat and microbe: Microbes are not required, so this is wrong.

Oxygen is also essential but is not offered in any option. Option B is the only one that pairs two true requirements.

Answer: B. Heat and water

Exam tip: Remember W-O-W for germination: Water, Oxygen, Warmth. Soil, manure, light and microbes are the usual distractors. Light is only needed by some seeds, and nutrients are only needed after germination. In the lab, a seed on moist cotton wool at room temperature will still germinate.