WJEC Biology for AS Level Student Book: 2nd Edition

Exam practice questions 1 The photomicrograph below is of Spirogyra ; an autotrophic organism that inhabits fresh water ponds and ditches. (a) Identify the organelles labelled A and B . [2] (b) The actual width of the cell between points X–Y was 32.3 μm. Calculate the magnification that was used to take the photomicrograph. [2] (c) During the day the concentration of solutes in the pond water changes due to evaporation. However, the length of the spirogyra cells remain almost constant. What can you conclude about how the structure of the cell wall enables Spirogyra to survive in different solute concentrations? [4] (d) Below is a photomicrograph of the bacteria Nostoc , which also inhabits fresh water ponds and ditches. They were once thought to belong to the same group of organisms as Spirogyra and thought to have the same cellular structure. Evidence from electron microscopy has now grouped these two separately. Conclude what cell types are present in Spirogyra and Nostoc . Identify two differences and one similarity (not labelled in the photomicrographs) between these two species that would be revealed by electron microscopy. [3] (Total 11 marks) [© WJEC Unit 1 2016 Q3 ]  Unit 1 Exam practice questions 133