Biology (Part-IV) (UPSC)

Total Questions: 66

1. How do most insects respire? [2007]

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]

Correct Answer: (b) Fallopian tube
Solution:

• Fertilization is the natural life process, which is carried out by the fusion of both male and female gametes, which results in the formation of a zygote. In humans, the process of fertilization takes place in the fallopian tube.
• During this process, semen comprising thousands of sperms are inseminated into the female vagina during coitus. The sperms move towards the uterus and reach the opening of the fallopian tube. only a few sperms will succeed in reaching the opening of the fallopian tube.
• The secondary oocyte releases from the matured Grafian follicle of the ovary and enters into the fallopian tube, where it is fertilized within 24 hours, after which it is released from the ovary.
• Though surrounded by several sperms, the oocyte is fertilized by a single sperm. During meiosis-II, the sperm enters the secondary oocyte and completes the meiosis. After this, the secondary oocyte is known as the egg.
• Both sperm and egg can show their vitality only to a limited period. Sperm is alive for 48–72 hours in a female reproductive system, whereas the egg can be fertilized for 24 hours before it is released.

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

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]

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.
The liver performs several activities in the human body. Some of the major functions of the liver are mentioned below:
• The liver helps to regulate the blood chemical levels.
• The liver produces bile, which helps to remove the waste product away and bile helps in the breakdown of fat in the small intestine.
• The liver produces blood plasma proteins like albumin.
• Glycogenesis, the process of storing excess glucose in the form of glycogen, occurs in the liver. Excess glucose is converted to glycogen for storage. For energy and to balance and generate glucose when needed, glycogen can be converted back to glucose.
• Haemoglobin is processed in order to make use of its iron content. The liver stores iron that is found in the heme group of blood haemoglobin.
• Cholesterol and specific proteins are produced to aid in the transport of fats throughout the body.
• The liver converts poisonous ammonia to urea which can be excreted by the urine. Urea is the end product of protein metabolism.

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

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.
• Naturally occurring digestive enzymes are proteins that your body makes to break down food and aid digestion. Digestion is the process of using the nutrients found in food to give your body energy, help it grow and perform vital functions.
• “When you eat a meal or a snack, digestion begins in the mouth,” explains Dehnard. “Our saliva starts breaking down food right away into a form that can be absorbed by the body. There are a lot of different points in the digestive process where enzymes are released and activated.”
• Your stomach, small intestine and pancreas all make digestive enzymes. The pancreas is really the enzyme “powerhouse” of digestion. It produces the most important digestive enzymes, which are those that break down carbohydrates, proteins and fats.

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]

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.
Small intestine turns semi-solid food into liquid so your body can absorb the nutrients you need. To do that, your small intestine:
• Delivers digestive juices and enzymes that combine with bile to allow the digestive process.
• Breaks down and liquefies semi-solid food so your body can absorb and use the nutrients.
• Absorbs nutrients and water through the villi in mucosa, which is the inner lining of your small intestine.
• Turns what’s left behind into digestive waste that moves to your large intestine and eventually leaves your body in the form of poop (stool).

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

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.
Spiders have:
• two main body parts, the head and thorax combined called the cephalothorax and an abdomen
• eight walking legs
• simple eyes; spiders usually have eight eyes (some have six or fewer), but few have good eyesight.
• jaws adapted for tearing or piercing prey
• a pair of pedipalps
• abdominal silk spinning organs
• anterior abdominal genital opening.

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

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]

Correct Answer: (c) 7.35-7.45
Solution:

Blood is slightly alkaline and the pH of blood varies from 7.35-7.45.
Blood
• It transports substances like digested food from the small intestine to the other parts of the body. It carries oxygen from the lungs to the cells of the body. It also transports waste for removal from the body.
• Blood is a liquid, which has cells of various kinds suspended in it. The fluid part of the blood is called plasma.
• One type of cells are the red blood cells (RBC) which contain a red pigment called haemoglobin.
• Haemoglobin binds with oxygen and transports it to all the parts of the body and ultimately to all the cells. The presence of haemoglobin makes blood appear red.
• The blood also has white blood cells (WBC) which fight against germs that may enter our body.
• The clot is formed because of the presence of another type of cells in the blood, called platelets.

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

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

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.
The liver performs several activities in the human body. Some of the major functions of the liver are mentioned below:
• The liver helps to regulate the blood chemical levels.
• The liver produces bile, which helps to remove the waste product away and bile helps in the breakdown of fat in the small intestine.
• The liver produces blood plasma proteins like albumin.
• Glycogenesis, the process of storing excess glucose in the form of glycogen, occurs in the liver. Excess glucose is converted to glycogen for storage. For energy and to balance and generate glucose when needed, glycogen can be converted back to glucose.
• Haemoglobin is processed in order to make use of its iron content. The liver stores iron that is found in the heme group of blood haemoglobin.
• Cholesterol and specific proteins are produced to aid in the transport of fats throughout the body.
• The liver converts poisonous ammonia to urea which can be excreted by the urine. Urea is the end product of protein metabolism.