What happens to a plant if the shoot tip is cut off and replaced by an agar block containing auxin? it will

Step 1: Analyze the question The shoot tip is removed and replaced with an agar block containing auxin. We need to decide what happens to the plant's growth.

Step 2: The concept Auxin (e.g., IAA) is a plant growth hormone made in the shoot tip (apical meristem). It moves down the stem and stimulates cell elongation in the region just behind the tip, which makes the shoot grow longer.

• If the tip is removed and nothing replaces it: the source of auxin is lost, so shoot elongation stops (or slows greatly).
• If the tip is removed and replaced with an agar block containing auxin: the block supplies the auxin that the tip would have supplied. The auxin diffuses down into the stem, so growth carries on as it would have with the tip.

Step 3: Eliminate the options

• A. Stop growing: this happens only if the tip is removed without replacement, so it is wrong here.
• B. Grow rapidly: the agar block replaces the normal auxin supply. It does not add extra auxin beyond the natural level, so there is no reason for unusually fast growth.
• C. Continue to grow normally: the auxin source is restored, so growth continues as before. This fits.
• D. Die completely: removing the tip does not kill a plant, so this is wrong.

Step 4: Answer The agar block with auxin acts as a substitute for the shoot tip, so the plant continues to grow normally.

Exam tip: Remember the three classic shoot-tip experiments:

1. Tip intact: normal growth.
2. Tip removed: growth stops.
3. Tip removed and replaced with an auxin agar block: growth resumes or continues.

If a question says "replaced by auxin", think "restored", not "stopped" or "boosted".