IGCSE Biology Paper-4: Specimen Questions with Answers 256 - 258 of 279

Passage

All mammals have a double circulatory system. Fig. shows part of the human double circulatory system.

Muscular Wall of Heart

Question 256 (2 of 3 Based on Passage)

Edit

Write in Brief

One Liner▾

Name the muscular wall that separates the left and right sides of the human heart.

Explanation

A wall of muscle called the septum separates the left and right atria and the left and right ventricles.

Question 257 (3 of 3 Based on Passage)

Edit

Write in Short

Short Answer▾

Describe what is meant by the term double circulation.

Explanation

Double Circulation System

In such system, for one complete circulation through the body, the blood passes twice through the heart:

  • To the lungs and back: It is called Pulmonary circulation or Lesser circulation (due to Lesser distance of the lungs from the heart.
  • To the body organs and back: It is called Systemic circulation or Greater circulation (covering greater distance from heart to the body−organs. e. g. Amphibians, Reptiles, Birds and Mammals. (Because of single ventricle, the amphibians and reptiles have incomplete double circulation) .

Pulmonary Vein and Artery

Passage

DNA controls cell function by controlling the production of proteins.

Question 258 (1 of 2 Based on Passage)

Edit

Write in Short

Short Answer▾

Proteins are coded for by a length of DNA.

What is the name given to the length of DNA which codes for a protein?

Explanation

The genes in DNA encode protein molecules, which are the “workhorses” of the cell, carrying out all the functions necessary for life. For example, enzymes, including those that metabolize nutrients and synthesize new cellular constituents, as well as DNA polymerases and other enzymes that make copies of DNA during cell division, are all proteins.

In the simplest sense, expressing a gene means manufacturing its corresponding protein, and this multilayered process has two major steps. In the first step, the information in DNA is transferred to a messenger RNA (mRNA) molecule by way of a process called transcription. During transcription, the DNA of a gene serves as a template for complementary base-pairing, and an enzyme called RNA polymerase II catalyzes the formation of a pre-mRNA molecule, which is then processed to form mature mRNA. The resulting mRNA is a single-stranded copy of the gene, which next must be translated into a protein molecule.