IGCSE Biology Paper-2: Specimen Questions with Answers 128 - 129 of 203

Question 128

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Question

MCQ▾

What is the definition of an allele?

Choices

Choice (4)
a.A version of a gene
b.A segment of DNA
c.The genetic makeup of an organism
d.Other name of a gene

Answer

a.

Explanation

  • Factor: ‘Gene’, which consists of DNA, Mendelian factor is a unit of inheritance, which passes from one generation to the next through the gamete and controls the expression of a character in the organisms. In modern genetics, it is called and genes are responsible for the inheritance and expression of a character.
  • Allele or Allelomorph: Ex: Tallness (T) anddwarfness (t). Contrasting forms of a gene, which are found on the same locus in the two homologous chromosomes & control the expression of a trait, are called alleles.
  • Phenotype: Ex: Red colour, tallness or dwarfness etc. It represents the expression of external appearance like colour, shape etc. of an individual.
  • Genotype: Ex: The genotype of hybrid tall pea plants is Tt, pure tall TT and dwarf tt. It indicates the genetic constitution of an individual.
A version of a gene

A Version of a Gene

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Question 129

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MCQ▾

After taking a long deep breath we do not respire for some seconds due to

Choices

Choice (4)
a.less in blood
b.more in blood
c.more in blood
d.less in blood

Answer

d.

Explanation

  • Blood cannot become more than 100 % saturated with oxygen. In deep breathing, more carbon dioxide is washed out of the blood. After taking long breath, more oxygen is inhaled than required. Therefore, it takes more time to be processed and be converted into carbon dioxide.
  • This makes oxygen cling more strongly to haemoglobin in red blood cells and therefore oxygen delivery to the tissues is made worse and causes oxygen toxicity. However, comparatively, more carbon dioxide levels can improve oxygen delivery. Hence lungs keep carbon dioxide levels high in inhaled air and therefore in the blood.
  • Other reason may include the oxygen inhaled is mixed with blood and is transported to whole body, and then it gets back to lungs in form of carbon dioxide and is released through the nose. When we take long deep breath our lung is full of oxygen, there is residual oxygen left in the lungs, which takes time. Due to this respiration is delayed.