IGCSE Biology Paper-1: Specimen Questions with Answers 151 - 152 of 208

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Question 151

Question

MCQ▾

Which feature is characteristic of both annelids and arthropods?

Choices

Choice (4)

a.

wings

b.

segmented bodies

c.

compound eyes

d.

jointed limbs

Answer

b.

Explanation

  • Features of Annelida:- Bilateral and Protostomia, Eucoelomate, eumetazoans whose long, narrow and worm like body is divided into ring-like, true or metameric segments (Gr. , annulus = little ring) , and the skin usually bears unjointed, chitinous appendages, termed setae. Commonly known as “segmented worms.”
  • Features of Arthropoda:- Bilateral, triploblastic body segmented and divided into head, thorax, and abdomen. Segmentation marked only externally; number of segments or somite՚s fixed and each has its separate exoskeleton of thick and hard, chitinous cuticle secreted by epidermis of body wall. Head somite՚s always fused. Each segment bears a pair of lateral jointed appendages adapted for food ingestion, locomotion, respiration, copulation, etc.
Features of Arthropoda

Question 152

Question

MCQ▾

Enzymes are affected by

Choices

Choice (4)

a.

Activator/Inhibitor

b.

pH

c.

Temperature

d.

All a., b. and c. are correct

Answer

d.

Explanation

Factors Affecting Enzyme Function

  • Temperature: Enzyme functions optimally at certain temperature. As the temperature increases the kinetic energy also increases, molecules move faster, and it increases the chance of substrate colliding the enzyme՚s active site and binding followed by reaction. But if the temperature is too high, the enzyme protein denatures (cools) , thereby destroying the shape of active binding site (cannot bind to the substrate anymore) and decreasing the enzyme reaction rate.
  • pH (measure of acidity) : Enzymes function optimally at certain pH and are certainly sensitive to the changes in the pH. Changes in the pH can make or break chemical bonds in the active binding site and thereby decreasing its effectiveness. If the pH is too high (acidic) or low (basic) , the enzyme denatures. However, there are exceptions, digestive enzymes in the stomach function at pH of 3 - 4.
  • Concentration of the substrate: As the enzyme concentration increases, the rate of reaction also increases until a point when the amount of substrate available becomes limited. Similarly, when the substrate concentration is low, the rate of reaction is also slow.

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