NCERT INTEXT QUESTIONS
Question 1. Why is diffusion insufficient to meet the oxygen requirements of multicellular organisms like humans?
Sol. Diffusion is insufficient to meet the oxygen requirements of multicellular organisms like humans because of the following reasons:
- The body design is very complex and the oxygen demand is quite high. The oxygen requirements ofan animal cannot be met by the process of diffusion as it is a very slow process.
- All the cells of the body are not in direct contact with the surrounding environment.
- Intake of oxygen in multicellular organism takes place by one organ and used in another organ.
Note: From the alveoli, the oxygen from the air an individual breathe enters into its blood in nearby blood vessels. This is a process called oxygen diffusion
Question 2. What criteria do we use to decide whether something is alive?
Sol. The most important criterion to decide whether something is alive or dead is the movement of a body. All the living things which are alive move by themselves without any external help. A living organism can also have movements at molecular level which are not visible to the naked eyes.
Therefore, living organisms perform certain life processes which include respiration, excretion, reproduction, growth etc.,which enables it to sustain itself
Question 3. What are outside raw materials used by an organism?
Sol. The raw materials required by an organism will vary depending upon the complexity of the organism and its environment. An organism use various outside raw materials given below:
(i) Food: To supply energy, materials like minerals, vitamins etc. for working and maintenance of cells/tissues.
(ii) Water: To provide medium in the body to live and carry out all the metabolic reactions necessary for life.
(iii) Oxygen: It is used for respiration.
Question 4. What processes would you consider essential for maintaining life?
Sol. Life processes like nutrition, respiration, transportation, excretion, locomotion, reproduction etc., are essential for maintaining life.
Question 5. What are differences between autotrophic and heterotrophic nutrition?
Sol. Difference between antotrophic and heterotrophic nutrition
Question 6. Where do plants get such raw materials required for photosynthesis?
Sol. Photosynthesis requires carbon dioxide, sunlight, water, and chlorophyll as its basic raw materials.
(i) Carbon dioxide: It is a gas present in the atmosphere. Plants absorb carbon dioxide through small pores (called stomata) on the surface of their leaves. This is a source of carbon for the plants.
(ii) Water: It is a liquid form, absorbed by the roots, transported through the stem to leaves by a special structures called as xylem tissues.
(iii) Chlorophyll: It is a green coloured pigment in the chloroplasts of the cells. It traps energy from the sunlight.
(iv) Sunlight: It is an important factor for the photosynthesis, which is absorbed by the chlorophyll and other green parts of the plants.
Question 7. What is the role of acid in our stomach?
Sol. The hydrochloric acid in our stomach facilitates the following:
(i) It creates acidic medium by which inactive enzyme pepsinogen is converted to active pepsin, which is a protein digesting enzyme.
(ii) It give signals to pancreas for producing digestive juices and enzymes to further breakdown food.
(iii) It gets mixed with food and kills bacteria present in food.
Question 8. What is the function of digestive enzymes ?
Sol. During digestion of food, different parts of alimentary canal produce different digestive enzymes that help in digestion of different components of food. Different kinds of digestive glands are present in our alimentary canal to help in digestive process by producing enzymes, like:
(i) In mouth ptyalin act on carbohydrates and converts into dextrose and maltose.
(ii) Pepsin acts on proteins and converts into peptones.
(iii) Amylase acts on carbohydrates and converts as maltose.
(iv) Trypsin and peptidases acts on proteins and converts into peptones and amino acids.
(v) Lipase acts on fats and converts into fatty acids and glycerol. Carbohydrates, proteins and fats are finally converts into glucose, amino acids, fatty acids or glycerol respectively
Note:Digestive enzymes are a group of enzymes that break down polymeric macromolecules into their smaller building blocks, in order to facilitate their absorption by the body.
Question 9. How is the small intestine designed to absorb digested food?
Sol. Small intestine is designed for absorption of digested food and transfer into the blood for circulation throughout the body. The digested food is taken up by the wall of the intestine. The inner lining of the small intestine has numerous finger like projections called villi which increase the surface area for absorption. The villi are richly supplied with blood vessels which take the absorbed food to each and every cell of the body where it is utilised for obtaining energy, building up new tissues and repairing of old tissues.
Question 10. What advantage over an aquatic organism does a terrestrial organism have with regard to obtaining oxygen for respiration?
Sol. Terrestrial organism obtains oxygen for respiration from the atmosphere where the oxygen content is high, whereas, aquatic organisms obtain oxygen dissolved in the water which is very low when compared to the amount in atmosphere. For this reason, aquatic animals breathe faster to obtain as much oxygen as possible, on the other hand, terrestrial animal does not have to breathe faster and thus spends less energy than aquatic organism. So, terrestrial organisms have more advantage over the aquatic animals to obtain oxygen for respiration.
Question 11. What are the different ways in which glucose is oxidised to provide energy in various organisms?
Sol. Every living organism respires for getting oxygen which is essential for releasing energy from food. Glucose is the nutrient of food which provides energy on decomposition. Glucose decomposes in the following ways:
(i) Aerobic respiration: During this respiration, breakdown of pyruvate takes place in the presence of oxygen to give rise to three molecules of carbon dioxide along with the release of energy and water. The release of energy takes place in the form of ATP.
(ii) Anaerobic respiration : It takes place in the absence of oxygen during which pyruvate is either converted into ethanol and carbon dioxide as in yeast or lactic acid as in human muscles during vigorous exercise. Very little amount of energy (ATP) is produced during anaerobic respiration.
Question 12. How is oxygen and carbon dioxide transported in human beings ?
Sol. Exchange of gases takes place between the alveoli of lungs and the surrounding blood capillaries.
Mechanism for the transportation of02 and CO2 in human beings:
- Oxygen and carbon dioxide both are absorbed by the blood capillaries from the lung alveoli by the process called diffusion.
- Transport of oxygen and carbon-dioxide occurs with the help of respiratory pigment called haemoglobin. It gets attached to four oxygen molecules that are obtained from breathing. Thus, it forms oxyhaemoglobin and the blood becomes oxygenated and is then distributed to all the body cells by the heart.
- After giving away oxygen to the body cells, blood takes away carbon dioxide which is the end product of cellular respiration. Now, the blood becomes deoxygenated. Since, haemoglobin pigment has less affinity for carbon dioxide, it is mainly transported in the dissolved form. This deoxygenated blood gives carbon dioxide to lung alveoli and takes oxygen in return.
Question 13.How are the lungs designed in human beings to maximise the area for exchange of gases?
Sol. In the lungs, trachea divides into smaller tubes, called ‘bronchi’ which inturn
forms ‘bronchioles’. The bronchioles terminate in balloon – like structures, called as ‘alveoli’. Each lung contains 300 – 350 million alveoli. The alveoli provide maximum surface for exchange of gases. The alveoli have very thin walls and contain an extensive network of blood vessels to facilitate exchange of gases.
Question 14. What are the components of the transport system in human beings ? What are the functions of these components?
Sol. Transportation in human beings is carried out by the circulatory system. The components of the transport system in human beings are given in following flowchart:
The functions performed by the components of the transport system are as follows:
(i) Blood: Blood is a mobile connective tissue fluid. It supply nutrients and oxygen to all the living cells and taking away waste products as well as carbon dioxide away from them. The specific function of blood also includes defense, distribution of heat and maintanance ofhomeostasis.
(ii) Heart : Heart is a conical muscular structure that brings about circulation of blood by its pumping activity. It collects deoxygenerated blood from various body parts and pumps oxygenated blood.
(iii) Blood vessels
- Arteries carry blood coming from heart to various organs of the body. These generally carry oxygenated blood.
- Veins carry blood from various parts of the body towards the heart. Veins carry deoxygenated blood except pulmonary veins that bring oxygenated blood form lungs to the heart.
- Capillaries form network inside body organs. It allows food and oxygen to diffuse from the blood to cells, and at the same time, allow waste to diffuse from cells into the cells.
The functions performed by the components of the transport system are as follows:
(i) Blood: Blood is a mobile connective tissue fluid. It supply nutrients and oxygen to all the living cells and taking away waste products as well as carbon dioxide away from them. The specific function of blood also includes defense, distribution of heat and maintanance of homeostasis.
(ii) Heart Heart is a conical muscular structure that brings about circulation of blood by its pumping activity. It collects deoxygenerated blood from various body parts and pumps oxygenated blood.
(iii) Blood vessels
- Arteries carry blood coming from heart to various organs of the body. These generally carry oxygenated blood.
- Veins carry blood from various parts of the body towards the heart. Veins carry deoxygenated blood except pulmonary veins that bring oxygenated blood form lungs to the heart.
- Capillaries form network inside body organs. It allows food and oxygen to diffuse from the blood to cells, and at the same time, allow waste to diffuse from cells into the cells.
Question 15. Why is it necessary to separate oxygenated and deoxygenated blood in mammals and birds?
Sol. It is necessary to separate oxygenated and deoxygenated blood in mammals and birds because if both type of blood gets mixed up in the body the amount of oxygen reaching the organs would be insufficient for their efficient working. As both birds and mammals are warm-blooded animals so they maintain their constant body temperature by cooling themselves when they are in a hotter environment and by warming their bodies when they are in a cooler environment. Hence, these animals require more oxygen (02) for more cellular respiration so that they can produce more energy to maintain their body temperature. Thus, it is necessary for them to separate oxygenated and de-oxygenated blood, so that their circulatory system is more efficient and can maintain their constant body temperature.
Question 16. What are the components of the transport system in highly organised plants?
Sol. The highly organised plants have the following components of transport system
(i) Xylem – It consists of vessels and tracheids. Xylem helps to conduct water and minerals from soil to the leaves.
(ii) Phloem – It consists of sieve tubes and companion cell. Phloem helps to transport food materials from leaves to various parts of the plant including roots.
Question 17. How are water and minerals transported in plants?
Sol. The water and minerals are transported by xylem tissue in the plants. Xylem vessels and tracheids form a continuous system of water conducting channels reaching all parts of the plant. The process of transpiration also plays an important role in transport of water and minerals in the plants.
Hence, the transport of water and minerals takes place in the following ways:
(i) Transport of water and minerals by root pressure: The xylem tissue is present in stems, roots, leaves of the plant. The root cells that are in close contact with the soil actively uptake ions, which create a difference between in the concentration of soil and roots cells, due to this difference water and minerals moves into the root cells and transported in various parts of the plant.
(ii) Transport of water and minerals by transpiration: There is a continuous loss of water through stomata in the form of water vapour, this process is known as transpiration. Transpiration creates a suction which helps in absorption and upward movement of water and minerals from roots to leaves of the plant.
Question 18. How is food transported in plants?
Sol. Phloem transports food materials from leaves to different parts of the plant (roots, fruits, seeds and growing parts). This process is called translocation. This function is done by sieve tubes and companion cells of phloem. The movement of food particles takes place upward and downward.
•Food is transferred from leaf cells or from the site of storage into phloem tissue. For this energy is required which is provided by the ATP molecules. This energy increases the osmotic pressure, as a result, water from outside moves into the phloem. This pressure maintains the movement of food through all the parts of plants.
Question 19. Describe the structure and functioning of nephrons.
Sol. Structure of nephron: Nephron is the structural and functional unit of kidney. It consists of a tubule which is connected with 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 glomerulus. The blood enters into glomerulus through the afferent arteriole of renal artery and leaves it through efferent arteriole. Collecting tubule collects urine from the nephrons (cellular structures in the kidney that filter-blood and form urine) and moves it into the renal pelvis and ureter
Functions of nephron:
(i) Filtration: Filtration of blood takes place in Bowman’s capsule from the capillaries of glomerulus. The 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.
(ii) Reabsorption: As the filtrate flows along the tubule, useful substances such as glucose, amino acids, salts and water are selectively reabsorbed into the blood by capillaries surrounding the nephron tubule. The amount of water reabsorbed depends on the need of the body and also on the amount of wastes to be excreted.
(iii) Urine formation: The filtrate which remains after reabsorption is called urine. Urine contains dissolved nitrogenous waste, i.e. urea and uric acid, excess salts and water. Urine is collected from nephrons by the collecting duct to carry it to the ureter.
Question 20. What are the methods used by plants to get rid of excretory products?
Sol. Like animals, plants also pass out the excretory wastes by the following methods:
(i) During photosynthesis, oxygen is produced as a by-product which is passed out from the plant body through stomata.
(ii) The plants take in excess amount of water from the soil for getting required amount of mineral salts. The excess amount of water is released through transpiration.
(iii) Some waste products such as resins and gums are stored, especially in non-functional old xylem.
(iv) Some waste products such as tannins, resins, gums are stored in bark, thereby removed as peeled off.
(v) Plants excrete some waste products through roots into the soil around them.
Question 21. How is the amount of urine produced regulated?
Sol. The amount of urine largely depends on the amount of water reabsorbed. It is regulated in the following ways:
(i) When water is abundant in the body tissues, large quantities of dilute urine is excreted out. When water is less in quantities in the body tissues, a small quantity of concentrated urine, with less water content, is excreted out.
(ii) The amount of dissolved wastes, especially nitrogenous wastes, (urea uric acid and salts) are present in the body. When there is more quantity of dissolved wastes in the body, more quantity of water is required to excrete them. So, the amount of urine produced increases. When the amount of these substances in the body is less, then less urine is produced.
(iii) The amount of urine produced is also regulated by ADH (Antidiuretic hormone) which control the movement of water and Na+ ions into and out of the nephrons.
Exercise
Question 1. The kidneys in human beings are a part of the system for
(a) nutrition (b) respiration
(c) excretion (d) transportation
Sol. (c) Kidneys are located in the abdomen, one on either side of the backbone. Urine produced in the kidneys passes through the ureter into the urinary bladder where it is stored and passes out from the body through urethra.
Question 2. The xylem in plants are responsible for
(a) transport of water
(b) transport of food
(c) transport of amino acids
(d) transport of oxygen
Sol. (a) Xylem is responsible for water and inorganic minerals transporation from roots to shoots and leaves.
Question 3. The autotrophic mode of nutrition requires
(a) carbon dioxide and water (b) chlorophyll
(c) sunlight (d) all of these
Sol. (d) All the green plants are called autotrophs. This is due to the fact that the green plants make their own food from very simple substances like carbon dioxide and water that is present in the surroundings. They do this by the process of photosynthesis. These green plants contain a green pigment called chlorophyll which further helps in making food by absorbing energy received from the sunlight. Thus, the autotrophic mode of nutrition requires CO2, H20, chlorophyll and sunlight.
Question 4. The breakdown of pyruvate to give carbon dioxide, water and energy takes place in
(a) cytoplasm (b) mitochondria
(c) chloroplast (d) nucleus
Sol. (b) Breakdown of pyruvate using oxygen takes place in the mitochondria which break up the three-carbon pyrurate molecule to give three molecules of CO2.
Question 5. How are fats digested in our bodies ? Where does this process take place?
Sol. The small intestine is the site of complete digestion of fats. Bile juice makes the acidic food into alkaline form. Bile juice converts the fat into fine globules. This process is called emulsification and converted form of fat is called emulsified fat. Lipase, fat digesting enzyme of pancreatic juice converts fat globules into fatty acid and glycerol.
Question 6. What is the role of saliva in the digestion of food?
Sol. Saliva is secreted by salivary glands. It has following important roles in the digestion of food:
(i) The primary role of saliva is to mix with the food, moisten it, and enable it to form bolus (small balls) that are easy to swallow and pass through the esophagus (food pipe) into the stomach.
(ii) Saliva also contains an enzyme called salivary amylase or ptyalin which breaks down complex carbohydrates like starch into simpler carbohydrates like maltose and dextrin which are then further broken down in the stomach.
Question 7. What are the necessary conditions for autotrophic nutrition and what are its by-products?
Sol. The necessary conditions for autotrophic nutrition are as follows:
(i) Presence of chlorophyll in the living cells.
(ii) Provision of supply of water to green parts or cells of the plant either through roots or by surrounding environment.
(iii) Availability of sufficient sunlight to provide the energy required to carry out photosynthesis.
(iv) Sufficient supply of carbon dioxide which is one of the important components for the formation of carbohydrates during photosynthesis. The whole process can be demonstrated by the following reaction –
Question 8. What are the differences between aerobic and anaerobic respiration ? Name some organisms that use the anaerobic mode of respiration.
Sol. Difference between aerobic and anaerobic respiration
Anaerobic respiration occurs in yeast, certain bacteria and internal parasites like tapeworm.
Question 9. How are the alveoli designed to maximize the exchange of gases?
Sol. The alveoli are the small balloon-like structures present in the lungs. The walls of the alveoli consist of extensive network of blood vessels. Each lung contains 300-350 million alveoli, making it a total of approximately 700 million in both the lungs. The thin, moist, permeable walls of alveoli facilitate quick diffusion and exchange of gases. Moreover it is richly supplied with blood capillaries. When the air is inhaled, it gets filled in the alveoli due to which they expand and provide maximum space for the exchange of gases.
Note: The alveolar area, if spread out, it covers about 80 m2 which is more than human body surface area
Question 10. What would be the consequences of a deficiency of haemoglobin in our bodies?
Sol. Haemoglobin is a respiratory pigment present in the RBC of the blood. It has high affinity for oxygen which carries it from lungs to various tissues
and cells of all the organs of the body. Therefore, deficiency of haemoglobin in blood can affect the oxygen supplying capacity of blood. This would cause less respiration and less energy will be liberated, which leads an individual to a disease known as anaemia.
Question 11. Describe double circulation in human beings. Why is it necessary?
Sol. Double circulation is a process in which blood flows twice through the heart. Process of double circulation can be done in the following ways:
(i) First of all the blood is collected from various organs into the right atrium. The right atrium then contracts and passes the deoxygenated blood to the right ventricle, through an auriculo-ventricular aperture.
(ii) Then the right ventricle contracts and passes the deoxygenated blood into the two pulmonary arteries, which pumps it to the lungs where the blood becomes oxygenated.
(iii) From the lungs, the pulmonary veins transport the oxygenated blood to the left atrium of the heart.
(iv) Then the left atrium contracts and through the auriculo-ventricular aperture, the oxygenated blood enters the left ventricle.
(v) The blood passes to aorta from the left ventricle. The aorta gives rise to many arteries that distribute the oxygenated blood to all the regions of the body
Double circulation is necessary in human being to separate oxygenated and deoxygenated blood because this makes their circulatory system more efficient and helps in maintaining constant body temperature.
Question 12. What are the differences between the transport ofmaterials inxylem and phloem?
Question 13. Compare the functioning of alveoli in the lungs and nephrons in the kidneys with respect to their structure and functioning.
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