Describe in brief on any five. a) Describe the sporogony phase of life cycle of Plasmodium. b) Draw a well labelled diagram of internal structure of heart of Frog. (No description required) c)…

a) Sporogony Phase of Life Cycle of Plasmodium

The life cycle of Plasmodium (the causative agent of malaria) consists of two main phases: sporogony (asexual reproduction in the mosquito vector) and schizogony (asexual reproduction in the human host). The sporogony phase occurs inside the Anopheles mosquito and involves the following stages:

1. Ingestion of Gametocytes: When an infected human is bitten by a female Anopheles mosquito, the mosquito ingests male and female gametocytes along with the blood meal.

2. Fertilization (Syngamy):

   • Inside the mosquito’s gut, the male gamete (microgamete) fertilizes the female gamete (macrogamete), forming a zygote.
   • The zygote is motile and is called the ookinete.

3. Formation of Oocyst:

   • The ookinete penetrates the gut wall of the mosquito and forms a cyst-like structure called an oocyst on the outer surface of the gut.

4. Sporozoite Formation (Sporogony):

   • Inside the oocyst, the zygote undergoes meiosis and mitotic divisions to produce thousands of sporozoites (infective form for humans).
   • The oocyst ruptures, releasing sporozoites into the mosquito’s hemocoel (body cavity).

5. Migration to Salivary Glands:

   • The sporozoites migrate to the salivary glands of the mosquito, where they remain until the mosquito bites another human.

Significance: This phase ensures the transmission of Plasmodium from mosquito to human, completing the life cycle.

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b) Internal Structure of the Heart of a Frog

Key Features:

• 3-chambered heart: 2 atria (left and right) and 1 ventricle.
• Incomplete septum: Allows partial mixing of oxygenated and deoxygenated blood.
• Conus arteriosus: Acts as a partial separation for blood flow to lungs and body.

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c) Causes of Wildlife Extinction

Wildlife extinction is driven by both natural and anthropogenic (human-induced) factors. The major causes include:

1. Habitat Destruction and Fragmentation:

   • Deforestation, urbanization, and agricultural expansion destroy natural habitats.
   • Example: Amazon rainforest clearance leads to loss of species like the jaguar and harpy eagle.

2. Pollution:

   • Chemical pollutants (pesticides, heavy metals) accumulate in food chains (e.g., DDT causing eagle population decline).
   • Plastic waste harms marine life (e.g., sea turtles ingesting plastic bags).

3. Climate Change:

   • Rising temperatures and altered weather patterns disrupt ecosystems.
   • Example: Polar bears losing Arctic ice habitat.

4. Over-exploitation and Hunting:

   • Poaching for ivory (e.g., African elephants), rhino horns, and exotic pets.
   • Overfishing depletes marine species (e.g., bluefin tuna).

5. Invasive Species:

   • Non-native species introduced by humans outcompete or prey on native species.
   • Example: Brown tree snake in Guam causing bird extinctions.

6. Disease and Parasites:

   • Emerging diseases (e.g., chytrid fungus killing amphibians like the Panamanian golden frog).

7. Genetic Factors:

   • Small populations suffer from inbreeding depression, reducing genetic diversity.
   • Example: Northern white rhino (only 2 females left).

8. Natural Disasters:

   • Volcanic eruptions, wildfires, and droughts can wipe out local species.
   • Example: Yellowstone fires (1988) affecting grizzly bears.

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d) Functions of the Liver in a Frog

The liver of a frog performs metabolic, detoxification, and storage functions, similar to other vertebrates but adapted to amphibian physiology. Key functions include:

Amphibian-Specific Adaptations:

• Urea cycle: Frogs excrete urea (unlike mammals that excrete ammonia directly), reducing water loss in terrestrial stages.
• Hibernation support: Liver glycogen reserves sustain energy during aestivation (summer dormancy) or hibernation.

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e) Miller & Urey’s Experiment (1953)

Objective: To test the Oparin-Haldane hypothesis that organic molecules (building blocks of life) could form spontaneously under prebiotic Earth conditions.

Procedure:

1. Setup:

   • A closed glass apparatus simulating Earth’s early atmosphere (reducing environment: methane (CH₄), ammonia (NH₃), hydrogen (H₂), water vapor (H₂O)).
   • Electric sparks (simulating lightning) were passed through the mixture for one week.

2. Observations:

   • Amino acids (e.g., glycine, alanine) were detected in the liquid at the bottom of the apparatus.
   • Other organic compounds formed included:
     • Hydrocyanic acid (HCN)
     • Urea
     • Lactic acid
     • Simple sugars (e.g., formaldehyde)

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3. Significance:
   • Demonstrated that abiotic synthesis of organic molecules is possible under primitive Earth conditions.
   • Supported the idea that life’s building blocks could have formed naturally, leading to the origin of life.

Limitations:

• Used a reducing atmosphere (modern evidence suggests early Earth had CO₂ and N₂).
• Did not produce nucleic acids (DNA/RNA) or lipids (later experiments by Fox and Orgel addressed this).

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f) Drawbacks of the Theory of Natural Selection

Charles Darwin’s theory of natural selection explains evolution but has several limitations and criticisms:

1. Lack of Explanation for the Origin of Life:

   • Natural selection explains changes in existing life but does not address how life first arose from non-living matter.

2. Incomplete Understanding of Genetic Variation:

   • Darwin did not know about genes, mutations, or DNA; he relied on blending inheritance, which was later disproven by Mendel’s laws.

3. No Mechanism for Sudden Changes:

   • Natural selection acts gradually, but some evolutionary changes (e.g., punctuated equilibrium) occur rapidly over short geological timescales.

4. Limited Explanation for Beneficial Traits:

   • Some traits (e.g., peacock’s tail) seem disadvantageous for survival but are favored by sexual selection, which Darwin acknowledged but did not fully integrate.

5. Environmental Determinism:

   • Overemphasizes external pressures (predation, climate) while underplaying internal genetic programs (e.g., Hox genes in development).

6. No Explanation for Altruism:

   • Kin selection (later proposed by W.D. Hamilton) explains altruistic behaviors (e.g., worker bees sacrificing for the hive), but Darwin’s original theory struggled with this.

7. Assumes Infinite Time:

   • While Earth is old (~4.5 billion years), some evolutionary transitions (e.g., fish to tetrapods) require unlikely coincidences of mutations.

8. Does Not Explain Speciation Fully:

   • Allopatric speciation (geographic isolation) is well-explained, but sympatric speciation (same habitat) remains debated.

9. Overlooks Epigenetics:

   • Modern genetics shows that environmental factors can alter gene expression (epigenetics) without changing DNA sequence, which Darwin’s theory did not account for.

10. Cultural Evolution Not Addressed:

    • Natural selection explains biological evolution but not cultural evolution (e.g., human technology, language).

Modern Synthesis: Later, neo-Darwinism (combining Darwin’s theory with Mendelian genetics) and evolutionary biology addressed many of these gaps.

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g) Characteristic Features of Class Mammalia

Mammals are vertebrate animals with hair/fur, mammary glands, and three middle ear bones. Key characteristics include:

Subclasses of Mammals:

1. Prototheria (Monotremes):

   • Egg-laying mammals (e.g., platypus, echidna).
   • Lack teats; secrete milk through skin pores.

2. Metatheria (Marsupials):

   • Pouched mammals (e.g., kangaroo, koala).
   • Embryos develop in a marsupium after short gestation.

3. Eutheria (Placental Mammals):

   • Placenta nourishes embryos in the uterus (e.g., humans, lions, bats).
   • Most diverse group (~95% of mammal species).