DP Biology (first assessment 2025)

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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.

(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;

 

(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.

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