(a) (i) Name the protozoan species that is responsible for causing the most serious and even fatal malarial disease. [½]

(ii) Name the host in which the parasite completes its sexual stages and explain the changes taking place. [2]

(iii) How does the parasite damage the human body after entering the blood stream? [1½]

(iv) Suggest two effective preventive measures to control the spread of this disease in endemic regions. [1]

OR

(b) (i) What are bio-fertilizers? [1]

(ii) Name the different types of microorganisms used as bio-fertilizers in organic farming and explain how each contributes to soil fertility. [3]

(iii) Write two advantages of using bio-fertilizers over chemical fertilizers. [1]

Q: (a) (i) Name the protozoan species that is responsible for causing the most serious and even fatal malarial disease. [½] (ii) Name the host in which the parasite completes its sexual stages and explain the changes taking place. [2] (iii) How does the parasite damage the human body after entering the blood stream? [1½] (iv) Suggest two effective preventive measures to control the spread of this disease in endemic regions. [1] OR (b) (i) What are bio-fertilizers? [1] (ii) Name the different types of microorganisms used as bio-fertilizers in organic farming and explain how each contributes to soil fertility. [3] (iii) Write two advantages of using bio-fertilizers over chemical fertilizers. [1]

**PRIMARY (a) — Malaria** **(i) Most serious/fatal malaria (½):** caused by **Plasmodium falciparum** (malignant malaria). **(ii) Host of sexual stages and changes (2)** - The **female Anopheles mosquito** is the host where the parasite completes its **sexual cycle**. - Male and female **gametocytes** taken up with the blood meal mature into **gametes** in the mosquito's gut. - Fertilisation produces a **zygote (ookinete)**, which develops into an **oocyst** on the gut wall. - The oocyst forms numerous **sporozoites** that migrate to the mosquito's **salivary glands**, ready to infect a new human host. **(iii) Damage to the human body (1½)** - Sporozoites enter through the mosquito bite, reach the **liver cells** and multiply, then infect **red blood corpuscles (RBCs)**. - The parasites multiply inside RBCs and **rupture them**, releasing a toxic pigment, **haemozoin**. - Haemozoin causes the characteristic **recurring chill and high fever every 3–4 days**; extensive RBC destruction leads to **anaemia**. **(iv) Two preventive measures (1)** - **Eliminate mosquito breeding** — drain/cover stagnant water; use larvivorous fish (e.g. Gambusia). - **Prevent bites** — use mosquito nets, repellents and insecticide (fumigation) sprays. **OR (b) — Biofertilizers (brief)** - **(i)** Biofertilizers are **living organisms that enrich the nutrient quality of the soil** (mainly bacteria, fungi and cyanobacteria). - **(ii)** *Rhizobium* fixes atmospheric N₂ in legume root nodules; *Azospirillum/Azotobacter* are free-living N₂-fixers; **mycorrhiza (Glomus)** helps roots absorb phosphorus; **cyanobacteria (Anabaena, Nostoc, Oscillatoria)** fix N₂ and add organic matter, especially in paddy fields. - **(iii)** They are **eco-friendly (no pollution)** and **cheap/renewable, improving long-term soil fertility** compared with chemical fertilizers.

Human Health and Disease

Malaria (Plasmodium) / Biofertilizers

Official Answer

PRIMARY (a) — Malaria

(i) Most serious/fatal malaria (½): caused by Plasmodium falciparum (malignant malaria).

(ii) Host of sexual stages and changes (2)

The female Anopheles mosquito is the host where the parasite completes its sexual cycle.
Male and female gametocytes taken up with the blood meal mature into gametes in the mosquito's gut.
Fertilisation produces a zygote (ookinete), which develops into an oocyst on the gut wall.
The oocyst forms numerous sporozoites that migrate to the mosquito's salivary glands, ready to infect a new human host.

(iii) Damage to the human body (1½)

Sporozoites enter through the mosquito bite, reach the liver cells and multiply, then infect red blood corpuscles (RBCs).
The parasites multiply inside RBCs and rupture them, releasing a toxic pigment, haemozoin.
Haemozoin causes the characteristic recurring chill and high fever every 3–4 days; extensive RBC destruction leads to anaemia.

(iv) Two preventive measures (1)

Eliminate mosquito breeding — drain/cover stagnant water; use larvivorous fish (e.g. Gambusia).
Prevent bites — use mosquito nets, repellents and insecticide (fumigation) sprays.

OR (b) — Biofertilizers (brief)

(i) Biofertilizers are living organisms that enrich the nutrient quality of the soil (mainly bacteria, fungi and cyanobacteria).
(ii) Rhizobium fixes atmospheric N₂ in legume root nodules; Azospirillum/Azotobacter are free-living N₂-fixers; mycorrhiza (Glomus) helps roots absorb phosphorus; cyanobacteria (Anabaena, Nostoc, Oscillatoria) fix N₂ and add organic matter, especially in paddy fields.
(iii) They are eco-friendly (no pollution) and cheap/renewable, improving long-term soil fertility compared with chemical fertilizers.

Plasmodium falciparumfemale Anophelessporozoiteshaemozoinschizogonygametocytes oocystbiofertilizersnitrogen fixation

Marking Scheme

1(a)(i) 0.5 mark: Plasmodium falciparum.
2(a)(ii) 2 marks: female Anopheles mosquito (0.5) + sexual-stage changes — gametocytes to gametes, fertilisation to zygote/ookinete, oocyst forming sporozoites that reach the salivary glands (1.5).
3(a)(iii) 1.5 marks: sporozoites multiply in liver then RBCs, rupture RBCs releasing haemozoin causing recurrent chill and fever and anaemia.
4(a)(iv) 1 mark: any two preventive measures — remove stagnant water/larvivorous fish, mosquito nets/repellents, insecticide spraying.
5OR (b)(i) 1 mark definition; (ii) 3 marks for named microbes with roles (Rhizobium, Azotobacter/Azospirillum, mycorrhiza, cyanobacteria); (iii) 1 mark for two advantages over chemical fertilizers.

Hint

Falciparum = fatal; sexual cycle in female Anopheles; haemozoin toxin causes the 3–4 day fever; for the OR, name one microbe per nutrient role.

Quick Oral Answer

The most fatal malaria is caused by Plasmodium falciparum; its sexual stages are completed in the female Anopheles mosquito, and in humans it multiplies in the liver and RBCs, bursting them and releasing haemozoin that triggers the recurrent chill and fever.

Analysis & Explanation

Concept

Malaria is a digenetic disease: the asexual (schizogony) cycle occurs in humans (liver + RBCs) and the sexual cycle (gametogony, sporogony) in the female Anopheles. The exam splits marks across the species, the definitive host, the pathology, and prevention.

Sequence anchors

Human: sporozoite → liver → RBC multiplication → rupture → haemozoin → fever.
Mosquito: gametocytes → gametes → zygote/ookinete → oocyst → sporozoites → salivary glands.

Exam trap

The female Anopheles is the definitive host (sexual stages), while humans are the intermediate host. Naming the toxin haemozoin and the 3–4 day fever cycle earns full pathology marks.

OR — biofertilizer logic

Give a named organism for each nutrient role: N₂-fixation (Rhizobium, Azotobacter, cyanobacteria) and P-uptake (mycorrhiza). Vague answers like 'bacteria help soil' do not score.

Real-world relevance

P. falciparum causes the majority of malaria deaths worldwide; the Azolla–Anabaena association is used as a green biofertilizer in rice cultivation.

Common Mistakes

1Naming Plasmodium vivax instead of Plasmodium falciparum for the most serious/fatal malaria.
2Stating the human as the host of the sexual stages — the sexual cycle is completed in the female Anopheles mosquito.
3In the OR part, listing only 'bacteria' without naming specific microbes and their distinct roles (N-fixation vs phosphorus uptake).

Interesting Facts

The toxin haemozoin, released when infected RBCs burst in synchrony, is responsible for the characteristic recurrent chill-and-fever pattern of malaria.

Ronald Ross won the 1902 Nobel Prize for demonstrating that the female Anopheles mosquito transmits the malarial parasite.

The Azolla-Anabaena symbiosis is used as a natural biofertilizer in rice paddies, fixing atmospheric nitrogen directly into the flooded field.

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Frequently Asked Questions

Which Plasmodium species causes the most serious malaria?

Plasmodium falciparum causes the most serious and potentially fatal (malignant) malaria. Other species such as P. vivax, P. malariae and P. ovale cause milder forms of the disease.

In which host does Plasmodium complete its sexual stages?

The sexual stages are completed in the female Anopheles mosquito. Gametocytes taken up in a blood meal form gametes, fertilise to make a zygote (ookinete), develop into an oocyst, and release sporozoites that migrate to the salivary glands.

What are biofertilizers?

Biofertilizers are living organisms — chiefly bacteria, fungi and cyanobacteria — that enrich soil nutrient quality, mainly by fixing atmospheric nitrogen or by helping roots absorb phosphorus, thereby improving soil fertility naturally.