IGCSE Biology Paper-4: Specimen Questions with Answers 122 - 124 of 279

Question 122


Describe in Detail


Calcium, a mineral salt, is needed in the diet.

Explain the role of calcium in the body and the effect of calcium deficiency.


Calcium Helps Our Body With

  • Building strong bones and teeth
  • Clotting blood

  • Sending and receiving nerve signals

  • Squeezing and relaxing muscles

  • Releasing hormones and other chemicals

  • Keeping a normal heartbeat

Calcium Deficiency Symptoms Can Include

  • Mental confusion, irritability, depression, and anxiety

  • Tooth decay

  • Insufficient blood clotting

  • Bone fractures

  • Osteopenia or osteoporosis

  • Growth and development delays in children

  • Heart problems involving blood pressure and heart rhythm


Fig. is a photomicrograph of part of a cell from the pancreas that produces enzymes that are released into the small intestine.

The Photomicrograph

Question 123 (1 of 2 Based on Passage)


Write in Short

Short Answer▾

Structure D is part of the nucleus of the cell.

State one function of a nucleus.


Some of the main functions of the nucleus include:

  • Protein synthesis, cell division, and differentiation
  • Control the synthesis of enzymes involved in cellular metabolism

  • Controlling hereditary traits of the organism

  • Store DNA strands, proteins, and RNA

  • Site of RNA transcription - e. g. mRNA required for protein synthesis

Question 124 (2 of 2 Based on Passage)


Describe in Detail


State the names of the structures labelled C and B in Fig.


C — Endoplasmic reticulum

B — Mitochondria

Function of ER

  • Functions of smooth ER include lipid metabolism (both catabolism and anabolism; they synthesize a variety of phospholipids, cholesterol, and steroids) .
  • Glycogenolysis (degradation of glycogen; glycogen being polymerized in the cytosol) .

  • Drug detoxification (by the help of the cytochrome P-450) .

  • The endoplasmic reticulum provides an ultrastructural skeletal framework to the cell and gives mechanical support to the colloidal cytoplasmic matrix.

  • The exchange of molecules by the process of osmosis, diffusion and active transport occurs through the membranes of the endoplasmic reticulum.

  • The endoplasmic reticulum is the main component of the endomembrane system, also called the cytoplasmic vacuolar system or cytocavity network.

  • The endoplasmic membranes contain many enzymes that perform various synthetic and metabolic activities. Further, the endoplasmic reticulum provides an increased surface for various enzymatic reactions.

  • The endoplasmic reticulum acts as an intracellular circulatory or transporting system.

  • As a growing secretory polypeptide emerges from the ribosome, it passes through the RER membrane and gets accumulated in the lumen of RER. Here, the polypeptide chains undergo tailoring, maturation, and molecular folding to form functional secondary or tertiary protein molecules.

  • RER pinches off certain tiny protein-filled vesicles which ultimately get fused to cis Golgi.

  • The ER membranes are found to conduct intra-cellular impulses. For example, the sarcoplasmic reticulum transmits impulses from the surface membrane into the deep region of the muscle fibers.

  • The ER membranes form the new nuclear envelope after each nuclear division.

  • The SER contains several key enzymes that catalyze the synthesis of cholesterol which is also a precursor substance for the biosynthesis of two types of compounds— the steroid hormones and bile acids.

  • RER also synthesize membrane proteins and glycoproteins which are cotranslationally inserted into the rough ER membranes. Thus, the endoplasmic reticulum is the site of the biogenesis of cellular membranes.

Functions of Mitochondria

  • The most important function of mitochondria is to produce energy. Mitochondria produce the molecule adenosine triphosphate (ATP) , one of the cell’s energy currencies that provide the energy to drive a host of cellular reactions and mechanisms.

  • The simpler molecules of nutrition are sent to the mitochondria to be processed and to produce charged molecules. These charged molecules combine with oxygen and produce ATP molecules. This process is known as oxidative phosphorylation.

  • Mitochondria may also produce heat (brown fat) , and accumulate iron-containing pigments (Heme ferritin) , ions of Ca2+ and HPO42– (or phosphate; e. g. , osteoblasts of bones or yolk proteins) .

  • Mitochondria help the cells to maintain the proper concentration of calcium ions within the compartments of the cell.

  • The mitochondria also help in building certain parts of blood and hormones like testosterone and estrogen.

  • The liver cell’s mitochondria have enzymes that detoxify ammonia.

  • The mitochondria also play an important role in the process of apoptosis or programmed cell death.

  • Abnormal death of cells due to the dysfunction of mitochondria can affect the function of an organ.