Question SPM.1B.SL.TZ0.2
| Date | May Specimen-2023 | Marks available | [Maximum mark: 7] | Reference code | SPM.1B.SL.TZ0.2 |
| Level | SL | Paper | 1B | Time zone | TZ0 |
| Command term | Calculate, Draw, Identify, Suggest | Question number | 2 | Adapted from | N/A |
The micrograph shows a transverse section of a leaf from a flowering plant.
[Source: Houseman, J. and Ford, M., 2014. Dicot leaf L. [image online] Available at: https://commons.wikimedia.org/wiki/
File:Dicot_leaf_L.jpg Distributed under the terms of the Creative Commons Attribution License 4.0 (CC BY-SA 4.0). https://creativecommons.org/licenses/by-sa/4.0/deed.en Image cropped and re-coloured.]
Draw a plan diagram in the right-hand box with labels to show the distribution of tissues in this transverse section of a leaf.
[3]
- palisade mesophyll;
- spongy mesophyll;
- lower epidermis;
- upper epidermis;
- xylem/phloem/vascular bundle;
1 mark for each correctly labelled tissue shown as a layer in proportion.
Calculate the actual thickness of the leaf, from upper to lower surface along the line a–b, showing your working.
[2]
- correct measurement of the line on the image (/1mm);
- correct calculation and including units;
Allow ECF – ruler measurements / 1mm
Suggest a reason for using a lower power objective lens when first focusing on a slide under the microscope.
[1]
- it is easier to find the specimen using a low power objective lens
OR
there is a larger field of view/depth of focus; - it is easier to locate the most interesting part of the specimen with a low power objective lens;
- most microscopes are calibrated so that once in focus using the low power objective lens they will be close to focus using the higher power, so this helps focusing;
- reduced risk of cracking the slide;
Identify one adaptation of the leaf for the absorption of light visible in this micrograph.
[1]
- double layer of palisade cells;
- palisade layer on upper surface;
- dimensions of palisade cells maximize light absorption;
- thin/transparent epidermis/cuticle;