O-LevelBiologyHuman Nutrition5090/22 · May/June 2023 · Q210 Marks

Describe physical digestion in humans and explain its importance.

(a)Describe physical digestion in humans and explain its importance.[4]
(b)(i)State the name of the chemical present in the stomach that kills many ingested bacteria.[1]
(b)(ii)Bacteria that are not killed in the stomach may cause disease. State the term used to describe: • organisms that cause disease. • the type of immunity gained after infection by organisms that cause disease.[2]
(c)Disease can be caused by viruses. Yellow fever is an example of a disease caused by a virus. Outline how a weakened form of the virus that causes yellow fever can be used to give a person long-term immunity against the disease.[3]

Mark scheme

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

[4] 1 makes food into smaller pieces AW + no chemical change ; 2 chewing OR teeth + grind AW ; 3 assists AW + movement of food / swallowing ; 4 increases surface area + of food; 5 for chemical digestion / enzyme action ; 6 peristalsis OR stomach + churns AW ; 7 mixing + with enzymes ;
[1] hydrochloric acid / HCl ;
[2] (bacteria that cause disease) pathogen; (type of immunity) active;
[3] 1 vaccine / vaccination ; 2 antigens + (on virus) / virus recognised as foreign ; 3 lymphocytes ; 4 produce / release AW + antibodies ; 5 memory cells ;

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