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Topicwise Answers

Page No. 95

1. Why is diffusion insufficient to meet the oxygen requirements of multicellular organisms like humans?

Ans: Diffusion is the slow process it’s unable to meet the oxygen requirements of multi-cellular organisms such as humans. Diffusion takes a lot of time to circulate oxygen to all the cells of the body. Besides, in humans oxygen requirement is more at cellular and tissue level. Therefore, through diffusion, it becomes difficult for oxygen to reach all the cells.


2. What criteria do we use to decide whether something is alive?

Ans: Living organisms have some fundamental characteristics like cellular nature, nutrition, metabolism, movement, respiration, excretion, response to stimuli, reproduction, etc... Therefore, the presence of any of these life processes is a fundamental criterion that can be used to decide whether something is alive or not.


3. What are outside raw materials used for by an organism?

Ans: Various outside raw materials used by an organism are as follows:

Food as source of energy. Oxygen for a breakdown of food to obtain energy. Water for proper digestion of food and other functions inside the body.


4. What processes would you consider essential for maintaining life?

Ans: In humans and other vertebrates, certain processes are considered critical for sustaining life. These include respiration, nutrition, digestion, excretion, reproduction, and metabolism. Respiration is one of the important life processes required for sustaining life.


Page No. 101

1. What are the differences between autotrophic nutrition and heterotrophic nutrition?

Autotrophs and Heterotrophs.png

2. Where do plants get each of the raw materials required for photosynthesis?

Ans: Plants require the following raw materials for photosynthesis;

Carbon dioxide: Plants get CO2 from the surrounding atmosphere.

Water: Plants absorb water from the soil by the roots and transport it to other parts.

Sunlight: Main source of energy trapped by chlorophyll.

Inorganic salts: The plants absorb inorganic salts from the soil.


3. What is the role of the acid in our stomach?

Ans: Gastric glands of the stomach secretes an acid called hydrochloric acid. Hydrochloric acid creates an acidic medium which facilitates the action of the enzyme pepsin. It kills most of the harmful bacteria which come along with food.


4. What is the function of digestive enzymes?

Ans: Digestive enzymes play a vital role in the breakdown of food. Digestive enzymes are produced from different glands such as salivary glands (salivary amylase), gastric glands (pepsin), liver (bile juice), pancreas (trypsin and lipase), and small intestine (intestinal juice).

All the digestive enzymes help in the conversion of complex organic substances like carbohydrates, proteins, and fats into glucose, amino acids, and fatty acid respectively.


5. How is the small intestine designed to absorb digested food?

Ans: The small intestine is the site of complete digestion. The inner lining of the small intestine possesses numerous finger-like projections called villi. These villi increase the surface area of the small intestine and help in better absorption of nutrients and minerals from the food.


Page No. 105

1. What advantage over an aquatic organism does a terrestrial organism have with regard to obtaining oxygen for respiration?

Ans: Terrestrial organisms use atmospheric oxygen to breathe whereas aquatic organisms use dissolved oxygen present in water.

As the percentage of oxygen is very low (approximately 1%) in the water, aquatic organisms have to show a much faster rate of breathing as compared to terrestrial organisms to get a sufficient amount of oxygen.


2. What are the different ways in which glucose is oxidised to provide energy in various organisms?

Ans: Glucose breaks down in three different ways to release energy;

Aerobic respiration: It takes place in the presence of oxygen to release more energy (38 molecules of ATP).

Anaerobic respiration: It takes place in the absence of oxygen and releases less energy (2 molecules of ATP).

Lack of Oxygen: When there is a lack of oxygen in our body, glucose oxidises partially and is converted into lactic acid.


3. How is oxygen and carbon dioxide transported in human beings?

Ans: During respiration oxygen and carbon dioxide is exchanged between the alveoli of the lungs and the surrounded blood capillaries. Both oxygen and carbon dioxide are carried out by the blood cells.

  • Blood is the medium of transport for O2 and CO2. About 97 percent of O2 is transported by RBCs in the blood. The remaining 3 percent of O2 is carried in a dissolved state through the plasma.

  • Nearly 20-25 percent of CO2 is transported by RBCs whereas 70 percent of it is carried as bicarbonate. About 7 percent of CO2 is carried in a dissolved state through plasma.


4. How are the lungs designed in human beings to maximise the area for exchange of gases?

Ans: Lungs play a major role in the respiratory system. In humans, a pair of lungs are designed in such a way that they are lined by a thin membrane, the smaller tubes called bronchioles a balloon-like structure called alveoli, and a network of blood capillaries increase the surface area for the exchange of gases. They are soft spongy and elastic organ enclosed in a thin membranous sac called the pleura.


Page No. 110

1. What are the components of the transport system in human beings? What are the functions of these components?

Ans: The heart, blood, and blood vessels such as arteries and veins are the major components of the transport system.

The heart pumps oxygenated blood throughout the body and receives deoxygenated blood from the various body parts.

Blood and blood vessels (arteries, veins, and capillaries)carry oxygen and nutrients from one part of the body to the other.


2. Why is it necessary to separate oxygenated and deoxygenated blood in mammals and birds?

Ans: The circulatory system of mammals and birds is designed to maintain their constant body temperature. Both mammals and birds are warm-blooded or homeotherms. Their body temperature does not vary with the surrounding temperature.

To maintain constant body temperature these animals need more oxygen to perform more cellular respiration and can produce more energy. The separation of oxygenated and deoxygenated blood allows a highly efficient supply of oxygen to the body required for this purpose.


3. What are the components of the transport system in highly organised plants?

Ans: Components of the transport system are; xylem and phloem.

Xylem- Conducts the water and dissolved minerals to leaves and other parts of the plant body. Hence, it is nothing but water-conducting tissue.

Phloem- Helps in the transportation of food from leaves to the other parts of the plant. Hence, it is also referred to as food conducting tissue.


4. How are water and minerals transported in plants?

Ans: In xylem tissue; vessels and tracheids of the roots, stems, and leaves are interconnected to form a continuous system of water-conducting channels, reaching all parts of the plant. At the root’s cells in contact with the soil actually take up ions, this creates a difference in the concentration of these ions between the root and the soil. Water, therefore, moves into the root from the soil to eliminate this difference this means that there is steadily movement of water into the root. While creating a column of water that is steadily pushed upwards.


5. How is food transported in plants?

Ans: The transport of food in plants is called translocation. It takes place with the help of a conducting tissue called phloem. Phloem transports glucose, amino acids and other substances from leaves to root, shoot, fruits and seeds. Sieve tube and companion cells help in transporting the food in upward and downward directions. Sucrose-like materials are transported using energy from ATP and osmotic pressure, which is caused due to water. This pressure moves the material in the phloem to tissues which have less pressure. This pressure helps in the movement of material in plants.


Page No. 112

1. Describe the structure and functioning of nephrons.

Ans: Structure: Nephron is the filtration/ functional unit of kidney. It consists of a tubule that is connected with the collecting duct at one end and a cup-shaped structure at the other end. This cup-shaped structure is called Bowman’s capsule. Every Bowman’s capsule contains a cluster of capillaries, called the glomerulus. The Bowman’s capsule is continuous as proximal and distal convoluted tubules which are connected by a ‘U’ shaped tube called Henle’s loop.


Glamorous filtration: Filtration of blood takes place in Bowman’s capsule from the capillaries of the glomerulus. This filtrate passes into the tubular part of the nephron. This filtrate contains glucose, amino acids, urea, uric acid, salts, and a major amount of water. As the filtrate moves along with tubules some of them are being re-absorbed as the urine flows along the tube.


2. What are the methods used by plants to get rid of excretory products?

Ans: To get rid of excretory products, plants use the following ways;

  • In many plants waste products are stored in vacuoles of the cells.

  • Some waste products are stored in the leaves. They are removed as the leaves fall off.

  • Some waste products such as resins and gums are stored, especially in nonfunctional old xylem.

3. How is the amount of urine produced regulated?

Ans: The amount of urine produced depends on;

  • Amount of water present in the body.

  • Amount of nitrogenous wastes present in the body.

  • The amount of urine produced is regulated by certain hormones (ADH) which control the movement of water and sodium ions into and out of the nephrons

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