Photograph A shows the root of a plant when it was positioned horizontally. The root was kept in the dark and left in this position. Photograph B was taken three days later. (a) (i) Complete the sentence by putting a cross (✗) in the box next to your answer. The process that resulted in the type of root growth shown in photograph B is A negative gravitropism B negative phototropism C positive gravitropism D positive phototropism (ii) Explain how this change in root growth has occurred.

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Photograph A shows the root of a plant when it was positioned horizontally - Edexcel - GCSE Biology - Question 3 - 2014 - Paper 1

Question 3

Photograph A shows the root of a plant when it was positioned horizontally. The root was kept in the dark and left in this position. Photograph B was taken three day... show full transcript

Worked Solution & Example Answer:Photograph A shows the root of a plant when it was positioned horizontally - Edexcel - GCSE Biology - Question 3 - 2014 - Paper 1

Step 1

Complete the sentence by putting a cross (✗) in the box next to your answer.

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Answer

The correct option is C - positive gravitropism. This indicates that the root is responding positively to gravity, growing downward.

Step 2

Explain how this change in root growth has occurred.

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Answer

The change in root growth can be explained as follows:

Auxin, a plant hormone, accumulates on the lower side of the root due to gravitational pull.
This accumulation inhibits the elongation of cells on the lower side, causing them to grow slower.
Conversely, the cells on the upper side continue to elongate, leading to a bending effect in the root.
As a result, the root grows downward, demonstrating positive gravitropism.

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