Cell wall is absent in which one of the following organisms ?
- A.Bacteria
- B.Diatom
- C.Mushroom
- D.Tapeworm
Correct answer
Explanation
The correct answer is D, Tapeworm. 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. Animal cells lack it, which is why they can change shape and why animals can form tissues such as muscle and nerve. The tapeworm, Taenia, is a flatworm of the phylum Platyhelminthes that lives as a parasite in the human intestine, so its cells too have no wall. Its body is covered instead by a tough outer layer called the tegument that resists the host's digestive juices.
A is wrong because bacteria have a cell wall made of peptidoglycan. B is wrong because diatoms have a cell wall of silica, made of two overlapping halves. C is wrong because a mushroom is a fungus, and fungal cell walls are made of chitin.
Exam tip: cell wall materials: plants cellulose, fungi chitin, bacteria peptidoglycan, diatoms silica; animals have none.
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 →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
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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.
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
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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
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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
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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.
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