IGCSE Biology Paper-2: Specimen Questions with Answers 173 - 175 of 203

The allele for detached earlobes is dominant to the allele for attached earlobes.

Two parents are heterozygous for detached earlobes.

What is the probability of their first child having attached earlobes?

Answer

a.

Explanation

The allele for detached earlobes is dominant to the allele for attached earlobes. Two parents are heterozygous for detached earlobes.

• AA - dominant detached earlobes
• Aa - dominant detached earlobes
• aa – recessive attached earlobes

The Allele for Detached Earlobes

	A	a
A	AA detached earlobes	Aa detached earlobes
a	Aa detached earlobes	aa attached earlobes

The actual thickness of the leaf shown in the diagram is , but its thickness in the diagram is 100 mm.

What is the magnification of the diagram?

Answer

a.

Explanation

SI Units

• 1 meter (m) = 1 m
• 1 millimeter (mm)
• 1 micrometer (µm)
• 1 nanometer (nm)

Magnification

Given diagram is showing human excretory system.

Where urine collection takes place in human excretory system?

Answer

a.

Explanation

Urinary Bladder and Urethra

• The urinary bladder is pear-shaped which is made up of smooth and involuntary muscles. The muscles are also known as detrusor muscles (muscles that has the action of expelling a substance) . The lower part or neck of the bladder leads into the urethra. There is a smooth triangular area, called trigonium vesicae.
• The lumen of the urinary bladder is lined by transition epithelium, which has great power of stretching. Two sphincters guard the neck of bladder, inner is involuntary controlled by spinal reflex, and outer is voluntary controlled by cerebral cortex. A person feels the sensation of micturition when the quantity of urine in the bladder is about 300 c. c.