A-LevelBiologyCell structure9700/21 · May/June 2023 · Q111 Marks

Fig. 1.1 is a transmission electron micrograph of a cell from the stem of sago pondweed, Stuckenia pectinata.

(a)(i)State the evidence from Fig. 1.1 that shows that the cell is from the stem of S. pectinata and not from the mesophyll of a leaf.[1]
(a)(ii)Complete each row in Table 1.1 to identify a cell structure shown in Fig. 1.1 that carries out the function listed. Table 1.1 function name of cell structure letter on Fig. 1.1 gas exchange production of subunits of ribosomes active transport of ions aerobic respiration[4]
(b)(i)Name the process that is occurring at X.[1]
(b)(ii)Some of the vesicles formed by the Golgi body pass to the vacuole. These vesicles contain proteins that have been folded correctly and some that have not folded into their correct shapes. The proteins that have not folded correctly pass to the vacuole where they are broken down. Explain how proteins that have not folded correctly are broken down in the vacuole.[3]
(c)Small vacuoles in S. pectinata may have roles similar to lysosomes in animal cells. Describe the role of lysosomes in animal cells in defence against pathogens.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2023). The mark or mark type is shown in brackets.

[1] any one from: no chloroplasts (present); presence of (many) small vacuoles / no large vacuole / no central vacuole ; central nucleus or nucleus not located at the, edge / periphery ;
[4] one mark per row ;;;; If 0 marks, allow 1 mark if name of cell structure column completed correctly function: gas exchange, name: cell surface membrane, letter: A function: production of subunits of ribosomes, name: nucleolus / nucleoli, letter: C function: active transport of ions, name: cell surface membrane / tonoplast/vacuolar membrane / mitochondrial membrane(s) / nuclear envelope, letter: A / F / E / B function: aerobic respiration, name: mitochondrion / mitochondria, letter: E
[1] endocytosis / pinocytosis; R phagocytosis
[3] any three from: 1 hydrolysis / use water to break bonds ; A ref. to hydrolytic enzymes 2 (action of) protease(s) / peptidases / proteolytic enzyme(s); 3 peptide bonds broken ; R if part of a list with other bonds not found in proteins, such as glycosidic, ester, phosphodiester 4 to form, peptides / amino acids ;
[2] 1 formation of phagolysosomes / described ; A fusion with, phagosomes / phagocytic vesicle or vacuole 2 breakdown / digestion, of, pathogen / bacteria / microorganisms / AW ; A kill / destroy, pathogen / bacteria / microorganisms / AW one from: 3 (by) two named enzymes ; e.g. lysozyme, protease, lipase, carbohydrase, nuclease 4 any two named substrates that are hydrolysed ; e.g. polysaccharides, peptidoglycans, proteins, lipids, glycogen, nucleic acid(s) 5 to form, harmless / useful / soluble / AW, products ; I ref. to breakdown of organelles