Which one of the following organisms does not possess notochord at any stage of its life cycle?
- A.Holothuria
- B.Herdmania
- C.Exocoetus
- D.Salamander
Correct answer
Explanation
The correct answer is A, Holothuria. Holothuria, the sea cucumber, is an echinoderm, a non-chordate group, so it never has a notochord at any stage of life.
A notochord is a flexible rod of cells running along the back of the body, and it is the defining feature of the phylum Chordata, along with a dorsal hollow nerve cord and gill slits. In urochordates it is present only in the larva's tail; in cephalochordates such as Amphioxus it lasts throughout life; in vertebrates it appears in the embryo and is replaced by the backbone. Echinoderms like starfish, sea urchins and sea cucumbers have a water vascular system and tube feet but no notochord.
B is wrong: Herdmania is a urochordate (sea squirt) whose tadpole-like larva has a notochord in its tail.
C is wrong: Exocoetus, the flying fish, is a vertebrate and has a notochord in its embryo.
D is wrong: the salamander is an amphibian, also a vertebrate with an embryonic notochord.
Exam tip: Holothuria = sea cucumber (echinoderm); Herdmania = sea squirt (urochordate, notochord only in larva).
Practice Questions
View allConsider the following animals :
1. Hedgehog
2. Marmot
3. Pangolin
To reduce the chance of being captured by predators, which of the above organisms rolls up/roll up and protects/protect its/their vulnerable parts?
- A.1 and 2
- B.2 only
- C.3 only
- D.1 and 3
Show answer
Hedgehogs and pangolins curl into a tight ball when threatened, covering the soft belly and face with spines or scales; marmots do not.
Read the full explanation →Which one of the following is used in preparing a natural mosquito repellent?
- A.Congress grass
- B.Elephant grass
- C.Lemongrass
- D.Nut grass
Show answer
Lemongrass and its close relative citronella grass yield aromatic oils that keep mosquitoes away, so they are the base of many natural repellents.
Read the full explanation →Which one of the following devices is non-ohmic ?
- A.Conducting copper coil
- B.Electric heating coil
- C.Semi conductor diode
- D.Rheostat
Show answer
A diode does not obey Ohm's law: the current through it is not proportional to the voltage across it. An ohmic conductor gives a straight-line graph of current against voltage, so its resistance stays constant at a fixed temperature.
Read the full explanation →What is the formula mass of anhydrous sodium carbonate? (Given that the atomic masses of sodium, carbon and oxygen are 23 u, 12 u and 16 u respectively)
- A.286 u
- B.106 u
- C.83 u
- D.53 u
Show answer
Anhydrous sodium carbonate is Na₂CO₃, and 2 × 23 + 12 + 3 × 16 = 106 u. Formula mass is the sum of the atomic masses of all the atoms in one formula unit of an ionic compound.
Read the full explanation →Which one of the following minerals is used as a fuel in nuclear power stations ?
- A.Bauxite
- B.Quartz
- C.Feldspar
- D.Pitchblende
Show answer
Pitchblende, or uraninite, is the chief ore of uranium, the fuel used in most nuclear power stations. Pitchblende is a heavy, black mineral made mostly of uranium oxide.
Read the full explanation →