DP Biology (first assessment 2025)

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Question SPM.2.HL.TZ0.8

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Date May Specimen-2023 Marks available [Maximum mark: 15] Reference code SPM.2.HL.TZ0.8
Level HL Paper 2 Time zone TZ0
Command term Describe, Explain, Outline Question number 8 Adapted from N/A
8.
[Maximum mark: 15]
SPM.2.HL.TZ0.8

There are a number of advantages to specificity.

(a)

Explain how vaccination can result in specific immunity to a viral disease.

[7]

Markscheme
  1.  vaccinations are specific to a specific disease;
  2.  vaccines contain non-self antigens/antigens from pathogens;
  3.  can be live relative/attenuated version of the virus;
  4.  trigger a primary immune response (without causing the disease);
  5.  lymphocytes with specific receptors (are activated and) produce memory cells;
  6.  (memory cells) cause a faster production of antibodies on a second exposure/exposure to the disease;
  7.  (memory cells) provide long term immunity;
(b)

Outline the role of membrane proteins in the movement of specific ions at specific times in the transmission of nerve impulses.

[4]

Markscheme
  1.  (during depolarization) Na+ channels open;
  2.  allowing Na+ to flow into the axon;
  3.  (during repolarization) K+ channels open;
  4.  allowing K+ to flow out of the axon;
  5.  the Na+/K+ pump returns the (axon) membrane to the resting potential;
  6.  by moving 3Na+ out and 2K+ in;
(c)

Describe the barriers that exist to hybridization between species.

[4]

Markscheme
  1.  courtship behaviour is often complex and unique to a species;
  2.  (at several stages in courtship ritual) rejection occurs if characteristic behaviour not exhibited;
  3.  species-specific egg fertilization;
  4.  compatibility of acrosome with vitelline layer;
  5.  inability of successfully attached wrong species sperm to develop continuity with egg membrane;
  6.  sterility of interspecific hybrids;
  7.  due to differences in chromosome number;

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