DP Biology (last assessment 2024)

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Question 23M.2.SL.TZ2.7

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Date May 2023 Marks available [Maximum mark: 15] Reference code 23M.2.SL.TZ2.7
Level SL Paper 2 Time zone TZ2
Command term Describe, Distinguish, Explain Question number 7 Adapted from N/A
7.
[Maximum mark: 15]
23M.2.SL.TZ2.7

Eukaryotes are classified into kingdoms, one of which is the animal kingdom.

(a)

Describe the organelles and other structures in animal cells that are visible in electron micrographs.

[7]

Markscheme
  1. plasma membrane is thin layer forming outer boundary;
  2. cytoplasm fills space between membrane and nucleus;
  3. nucleus enclosed in nuclear membrane / nuclear membrane enclosing nucleus;
  4. chromosomes inside the nucleus/ visible during mitosis/ as rods (of condensed DNA);
  5. mitochondria with cristae/double membranes;
  6. (80S) ribosomes seen as dots free in cytoplasm/attached to rough ER;
  7. endoplasmic reticulum is a network interconnected tubes/ membranes /rough ER has ribosomes/ smooth ER does not;
  8. Golgi apparatus with stack of sacs/cisternae/curved or folded membranes/vesicles budding off;
  9. vesicles which are small membrane sacs;
  10. lysosome which contains enzymes/which is densely staining;
  11. any other organelle that would be visible correctly described;

Allow any point made on an annotated diagram.

Do not award any marks for just labels. Descriptions are needed.

Examiners report

Only the strongest candidates were able to describe, rather than state the function of the organelles. As with past questions about cell structure, many thought that a labelled diagram would suffice. Unfortunately, these generally scored zero unless they were well annotated.

(b)

Explain how animal cells produce the ATP that they need.

[5]

Markscheme
  1. respiration/cell respiration;
  2. energy released from glucose/lipids/organic compounds;
  3. anaerobic respiration does not require oxygen;
  4. lactate is produced in anaerobic respiration/word equation for anaerobic respiration;
  5. oxygen used in aerobic respiration;
  6. carbon dioxide and water produced in aerobic respiration/word equation for aerobic respiration;
  7. mitochondria used for aerobic respiration;
  8. larger yield of ATP from aerobic than anaerobic respiration;

 

Examiners report

Most gained a mark for respiration, but many were not able to distinguish between aerobic and anaerobic. Stronger candidates knew that the mitochondrion was used for aerobic respiration, which produced a greater yield of ATP.

(c)

Distinguish between reptiles and amphibians in terms of their recognition features.

[3]

Markscheme
  1. reptiles dry skin versus amphibians moist skin;
  2. reptiles with scales versus amphibians not having scales / reptiles scaly skinversus amphibians soft skin;
  3. reptile eggs have (soft) shells versus amphibian eggs no shell/coated in gel;
  4. reptiles internal fertilisation/sperm enters female versus amphibians external fertilisation
    OR
    amphibians require water for reproduction, reptiles do not;
  5. reptiles do not have larval stage versus amphibians have larval stage;
  6. reptiles do not develop gills versus amphibian larvae have gills;

Both reptile and amphibian should be mentioned in each distinction.

Examiners report

Proved difficult, with few gaining all 3 marks. Correct comparisons were looked for, with dry against moist skin and scaly skin against soft skin not being answered well. Comparisons with fertilization and larval stages were also looked for.

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