1. B cells in the immune system are responsible for:

A. Directly attacking and engulfing pathogens
B. Producing antibodies specific to a pathogen
C. Destroying infected body cells
D. All of the above

Correct answer: B

Rationale: B cells in the immune system are responsible for producing antibodies specific to a pathogen. This is because B cells are a type of white blood cell that play a crucial role in the adaptive immune response. When a B cell encounters a specific pathogen, it differentiates into plasma cells that produce antibodies targeted against that particular pathogen. These antibodies then tag the pathogen for destruction by other immune cells. B cells do not directly attack and engulf pathogens like phagocytes, nor do they destroy infected body cells like cytotoxic T cells. Therefore, option B is the correct answer as it accurately reflects the primary function of B cells in the immune system.

2. An Egyptian model pyramid has a square base side length of 10cm and a height of 8cm. What is its volume?

A. 20 cu cm
B. 40 cu cm
C. 80 cu cm
D. 160 cu cm

Correct answer: D

Rationale: Use the formula for volume of a pyramid: (1/3) * base area * height. Calculate the base area (10cm * 10cm = 100 sq cm) and substitute: (1/3) * 100 sq cm * 8cm = 80 cu cm.

3. What is the term for an organism with two different alleles for a gene?

A. Homozygous
B. Heterozygous
C. Dominant
D. Recessive

Correct answer: B

Rationale: An organism with two different alleles for a gene has a mixed genotype and may exhibit either the dominant or recessive trait depending on the specific gene and its alleles.

4. In the reaction 2Na + 2H2O Ã¢â€ â€™ 2NaOH + H2, what is the limiting reactant when 3 moles of sodium react with 2 moles of water?

A. Na
B. H2O
C. NaOH
D. H2

Correct answer: a

Rationale: Sodium is the limiting reactant because it runs out first in a 1:1 ratio with water.

5. What is the main difference between white and brown adipose tissue?

A. Location only
B. Function and energy metabolism
C. Color only
D. Both white and brown have the same function

Correct answer: B

Rationale: The main difference between white and brown adipose tissue lies in their function and energy metabolism. White adipose tissue is primarily involved in energy storage, while brown adipose tissue is responsible for energy expenditure through thermogenesis. Brown adipose tissue contains a higher density of mitochondria and a unique protein called uncoupling protein 1 (UCP1) that allows for the generation of heat. This key distinction in function and energy metabolism sets white and brown adipose tissue apart, making option B the correct answer.

6. What is the mass number of an element?

A. The number of protons in an atom's nucleus.
B. The number of neutrons in an atom's nucleus.
C. The number of electrons in an atom's valence shell.
D. The number of isotopes of an element.

Correct answer: B

Rationale: The mass number of an element is the total number of protons and neutrons in the nucleus of an atom. It is represented by the symbol A and is written as a superscript to the element's symbol. For example, the mass number of carbon-12 is 12, which means that a carbon-12 atom has 6 protons and 6 neutrons in its nucleus.