Biology (Part-IV) (UPSC)

1. How do most insects respire? [2007]

(a) Through skin
(b) Through gills
(c) By lungs
(d) By tracheal system

Correct Answer: (d) By tracheal system

Solution:Most insects respire through tracheal system that lies on a network of small tubes that channel O₂ directly to the different part of the body. The tracheal system is composed of chitin-ringed tubes called trachea that connect directly to the air through opening in the body wall called spiracles.

2. In human beings, normally in which one of the following parts, does the sperm fertilize the ovum? [2007]

(a) Cervix
(b) Fallopian tube
(c) Lower part of uterus
(d) Upper part of uterus

Correct Answer: (b) Fallopian tube

Solution:Fallopian tube is a tube like structure that carries egg from the ovary to uterus. In this tube the sperm meets to ovum and fertilization occurs.

3. Which one of the following parts of the human brain is the regulating centre for swallowing and vomiting? [2007]

(a) Cerebellum
(b) Cerebrum
(c) Medulla oblongata
(d) Pons

Correct Answer: (c) Medulla oblongata

Solution:The bottom part of the brain stem is called the Medulla oblongata. The medulla oblongata has nerve centres to control many vital body processes like swallowing, vomiting, breathing and heart beat etc.

Medulla directly controls many "ANS responses, in addition to playing an accessory role in the control of certain areas of body. It also has a stake in overall major motor functions, or body movement. *Autonomic nervous system--in other words, 'automated" nervous system-automatically responds to the situation you're in without you needing to think about it. It controls everything from the dilation of your pupils to your breathing pattern.

4. Production of which one of the following is a function of the liver? [2007]

(a) Lipase
(b) Urea
(c) Mucus
(d) Hydrochloric acid

Correct Answer: (b) Urea

Solution:Urea is the main nitrogenous excretory product of Ureotelic animals, produced by liver cells from deaminated excess amino-acids via the urea cycle.

5. Which one of the following is not a digestive enzyme in the human system? [2007]

(a) Trypsin
(b) Gastrin
(c) Ptyalin
(d) Pepsin

Correct Answer: (b) Gastrin

Solution:Gastrin is a hormone, which stimulates secretion of digestive enzyme in stomach. Trypsin, Pepsin and Ptyalin are the digestive enzymes of human system.

6. Which one of the following is the correct sequence in the order of decreasing length of the three structural parts given below of small intestine in the human body? [2007]

(a) Jejunum - Duodenum - Ileum
(b) Ileum - Duodenum - Jejunum
(c) Jejunum - lleum - Duodenum
(d) Ileum - Jejunum - Duodenum

Correct Answer: (d) Ileum - Jejunum - Duodenum

Solution:The correct sequence in the order of decreasing length of the three structural parts are lleum - Jejunum - Duodenum of small intestine.

7. In which of the following kinds of organisms is the phenomenon found where in the female kills the male after copulation? [2008]

(a) Dragonfly
(b) Honeybee
(c) Spider
(d) Pit viper

Correct Answer: (c) Spider

Solution:Sexual cannibalism is identified only in spiders. In which female organism kills the male before during or after copulation. In most species in which it occurs, sexual connibalism is related to the larger size of female due to sexual dimorphism.

8. For which one of the following snakes is the diet mainly composed of other snakes? [2008]

(a) Krait
(b) Russell's viper
(c) Rattlesnake
(d) King cobra

Correct Answer: (d) King cobra

Solution:King cobra feeds on other snakes.

King cobras take anomalous behaviour to an extreme. While the females are the only snakes to build a nest, the males appear to be the only ones to deliberately hunt down egg-laden females.

9. What is the pH level of blood of a normal person? [2008]

(a) 4.5-4.6
(b) 6.45-6.55
(c) 7.35-7.45
(d) 8.25-8.35

Correct Answer: (c) 7.35-7.45

Solution:Blood is slightly alkaline and the pH of blood varies from 7.35-7.45.

10. Assertion (A): In human body, liver has important role in fat digestion. [2008]

Reason (R): Liver produces two important fat-digesting enzymes.

(a) Both A and R are individually true and R is the correct explanation of A
(b) Both A and Rare individually true but R is not the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true

Correct Answer: (c) A is true but R is false

Solution:The liver secretes bile that forms and stores glycogen and plays an important role in metabolism of protein and fat. It does not contain digestive enzymes and as such does not take part directly in digestion.