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Human Health and Disease — BIOLOGY STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceBIOLOGYHuman Health and Disease4 Marks
Question
Explain the life cycle of Plasmodium (with diagram).
✓

Answer

→Plasmodium enters the human body in the form of sporozoites when an infected female Anopheles mosquito bites a human.
→Initially this parasite multiplies in the liver cells and then invades the blood cells causing RBC's to rupture.
→Rupture of RBC releases a toxic substance called hemozoin, which causes chills and high fever for 3 to 4 days.
→At this stage, when a female Anopheles mosquito bites an infected person, the parasite enters the mosquito's body, where it develops further.
→There they multiply and form sporozoites.
→This sporozoite is stored in the salivary gland of the mosquito.
→When this infected female mosquito bites a person, the parasite enters her body and develops.
→Malaria parasite requires two hosts to complete its life cycle,
(1) Man,(2) Mosquitoes.
→Reproduction in Plasmodium
→Asexual reproduction in humans:
→The parasite reproduces in the human RBC and destroys the RBC.
→In RBC the sexual stage (germ cells) develop male and female germs (male- microgamete, female-mega gamete).
→These genes enter mosquitoes from humans through mosquito bites.
→Sexual reproduction in mosquito:
→The sexual genes (Gametes) entered into the mosquito from the human being are fertilized in the intestine of the mosquito and induce development.
→In order to develop, the sporozoite stage is stored in the salivary gland of the mosquito.
→Malaria is a disease caused by Plasmodium- like parasites in humans.
→Different species of Plasmodium like (Plasmodium falciparum, Plasmodium vivax, Plasmodium ovale) are responsible for different types of malaria.
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Mutation explains the relationship between gene and DNA. The effects of large deletions and rearrangement in a segment of DNA results in loss or gain of gene and its function. Insertion or deletion of one or two bases changes the reading frame from the point of insertion or deletion. A classical example of point mutation is a change of single base pair in the gene for beta globin chain that results in change of amino acid residue glutamate to valine and results into a diseased condition called sickle cell anaemia.

  1. A mutation is a change produced by an alteration in the genetic mechanism and.
  1. May arise spontaneously.
  2. Is always induced by the environment.
  3. Is never advantageous.
  4. Is not inherited.
  1. The DNA code for glutamic acid is CTC or CTT. The code for valine is CAA or CAT. In sickle cell haemoglobin, valine is present instead of glutamic acid.

Assuming a single base pair substitution has occurred, what is the mRNA code in the affected mutant?

  1. CUU
  2. GAA
  3. GAG
  4. GUA
  1. A mutation involving the substitution of one nitrogenous base for another has altered the base sequence of a DNA molecule, coding for four amino acids, as shown below.

Normal A-G-C-A-T-G-G-A-T-C-C-T

Mutant A-G-C-A-T-G-C-A-T-C-C-T

The table shows six codons and the corresponding amino acids into which each is translated.

mRNA codon
Amino acid
AAG
Lysine
CUA
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The mutation has changed the amino acid.

  1. Leucine to valine.
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  1. Assertion : Insertion or deletion of three or its multiple bases, insert or delete one or multiple codons and so one or multiple amino acids.

Reason: Reading frame remains unaltered with insertion or deletion of three or its multiple bases.

  1. Both assertion and reason are true, and reason is the correct explanation of assertion.
  2. Both assertion and reason are true, but reason is not the correct explanation of assertion.
  3. Assertion is true, but reason is false.
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  1. Part of the amino acid sequences in normal and sickle cell haemoglobin are shown.
Normal haemoglobin Sickle cell haemoglobin
Thr-Pro-Glu-Glu Thr-Pro-Val-Glu
mRNA codons for these amino acids are

Glutamine (Glu) GAA GAG

Praline (Pro) CCU CCC

Threonine (Thr) ACU ACC

Valine (Val) GUA GUG

Which transfer RNA molecule is involved in the formation of this part of the sickle cell haemoglobin?

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Unlike animals, plants cannot runaway for their defence, therefore, they have evolved an astonishing variety of morphological and chemical defences against herbivores. Thorns are the most common morphological means of defence. Many plants produce and store chemicals that make the herbivore sick when they are eaten, inhibit feeding or digestion, disrupt its reproduction or even kill it. Some plants produce highly poisonous chemicals and that is why no cattle or goats browse on those plants. A wide variety of chemical substances that we extract from plants on a conunercial scale are produced by them actually as defence against grazers and browsers.

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