Identify the tissue labelled II.

Outline one piece of evidence that the tissue labelled I is phloem tissue.

Explain how aphid stylets can be used to study the movement of solutes in plant tissues.

Xylem

It has a stylet embedded in it
OR
Aphids insert their stylets into phloem

Is closer to the surface/exterior/outside the xylem

Cells smaller than xylem tissue «below it»

Smaller «companion» cells are adjacent to larger «sieve tube» cells

Aphids tap into phloem with their stylets «to use sap as a food source»

Plants grown in radioactive CO₂/¹⁴CO₂ incorporate it into carbohydrate

Phloem contents/sap/fluid flows through the stylet

Aphid body severed/cut from stylet «after stylet inserted into phloem»

Analyze «sap/fluid exuded from stylet» for solutes/carbohydrates
OR
Radioactive-labelled carbon can be detected «in the phloem sap»

Stylets at different parts of the plant can show sequence/rate of movement

The vast majority of candidates were able to correctly label this as xylem although many respondents on the G2 form indicated that they found the diagram difficult.

Most candidates were able to score the one mark for this part of the question as many alternatives were given in the markscheme. However, many candidates did not seem to know what an aphid stylet was and mistakenly talked about the stylet ‘growing’ or referred to it as part of the root. 

This was a discriminating question with better candidates able to clearly explain how aphid stylets were used to study the movement of solutes in phloem, also referring to the use of radioactive carbon dioxide. Many unfortunately seemed to have not been exposed to this topic, used imprecise language, referred to the aphid stylet as if it were a piece of lab equipment they could use, or left this blank.