Methanol is toxic because
- A.methanol coagulates the protoplasm
- B.methanol gets oxidised to methanal in liver which coagulates the protoplasm
- C.methanol gets oxidised to acetic acid in liver which coagulates the protoplasm
- D.methanol gets oxidised to CO in liver which coagulates the protoplasm
Correct answer
Explanation
The correct answer is B. In the liver, methanol is oxidised to methanal (formaldehyde), which coagulates protoplasm and damages cells.
Methanol, CH3OH, is the simplest alcohol and is sometimes mixed into illicit liquor. The liver enzyme alcohol dehydrogenase turns it into methanal, which reacts with proteins and makes the protoplasm of cells coagulate, much as an egg white sets on heating. Methanal is further changed into methanoic (formic) acid, which makes the blood acidic and attacks the optic nerve. Even a small amount of methanol can therefore cause blindness, and larger amounts cause death. This is why ethanol meant for industry is denatured by adding methanol, making it unfit to drink.
A is wrong because methanol itself does little harm; the damage is done by what it becomes in the liver. C is wrong because acetic acid comes from the oxidation of ethanol, not methanol. D is wrong because the liver does not turn methanol into carbon monoxide.
Exam tip: methanol becomes methanal and then formic acid and can cause blindness; ethanol becomes ethanal and then acetic acid.
Practice Questions
View allIn plant cells, RNA is present in
- A.cytoplasm only
- B.nuclei and cytoplasm only
- C.nuclei, cytoplasm, mitochondria, chloroplast and endoplasmic reticulum
- D.nuclei, cytoplasm, mitochondria, chloroplast and ribosomes
Show answer
In plant cells RNA is found in the nucleus, the cytoplasm, mitochondria, chloroplasts and ribosomes. RNA is made in the nucleus, where DNA is copied into messenger, transfer and ribosomal RNA; the nucleolus in particular is rich in ribosomal RNA.
Read the full explanation →Cell wall is absent in which one of the following organisms ?
- A.Bacteria
- B.Diatom
- C.Mushroom
- D.Tapeworm
Show answer
The tapeworm is an animal, and animal cells have no cell wall, only a cell membrane. A rigid cell wall lies outside the cell membrane in plants, fungi, most bacteria and many protists, giving the cell shape and protection.
Read the full explanation →In which one of the following types of connective tissues in animals does fat get stored?
- A.Adipocyte
- B.Chondrocyte
- C.Osteocyte
- D.Reticulocyte
Show answer
Adipocytes are the fat cells of adipose tissue, a loose connective tissue that stores fat in animals. Adipose tissue lies mainly beneath the skin and around organs such as the kidneys and heart.
Read the full explanation →Which one of the following agents does not contribute to propagation of plants through seed dispersal?
- A.Wind
- B.Fungus
- C.Animal
- D.Water
Show answer
Seeds are carried away from the parent plant by wind, water and animals, but fungi play no part in seed dispersal.
Read the full explanation →Which one of the following is essential for thyroid gland to make thyroxin?
- A.NaCl
- B.KCl
- C.Cholesterol
- D.Iodine
Show answer
Thyroxine is an iodine-containing hormone, so the thyroid gland cannot make it without iodine from the diet. The thyroid is a butterfly-shaped gland in the neck.
Read the full explanation →