NCERT Solutions For Class 10 Science Chapter 6 Life Processes

NCERT Solutions For Class 10 Science Chapter 6 Life Processes

Question 1.

1. Describe the mechanism of breathing in human beings.
2. 1. Under normal conditions, what is the rate of breathing per minute?
   2. Why does the rate of breathing increase by 20 to 25 times during vigorous exercise?

Answer:

1. Mechanism of breathing in Humans: Breathing is a complex mechanical process involving muscular movement that alters the volume of the thoracic cavity and thereby that of the lung.

• Breathing occurs involuntarily but its rate is controlled by the respiratory centre of the brain.
• The space of the thoracic cavity increases or decreases by outward and inward movements of the ribs caused by external intercostal and internal intercostal muscles.
• This action is also assisted by the contraction and expansion of the diaphragm. The floor of the thoracic cavity is completely closed by the diaphragm. It is a thin muscular septum separating the abdominal and thoracic cavities.
• Inspiration or inhalation is concerned with the taking in of atmospheric air or oxygen into the thoracic cavity.
• Expiration or exhalation is concerned with the expelling of carbon dioxide from the lungs. It takes place when the volume of the thoracic cavity decreases and the pressure of the contained air in the thoracic cavity increases.

2. (1) Under normal conditions, the rate of breathing is 12 to 18 times per minute.

(2) The rate of breathing during vigorous exercise increases by about 20 to 25 times per minute. This is because, during vigorous exercise, the demand for oxygen increases. Breathing occurs involuntarily but its rate is controlled by the respiratory centre of the brain.

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Question 2.

1. Draw a diagram of the human alimentary canal and label it: Oesophagus, Gall bladder, Liver and Pancreas.
2. Explain the statement, ‘Bile does not contain any enzyme but it is essential for digestion’.

Answer:

1. Bile does not contain any enzyme but it is essential for digestion because:
   1. It maintains an alkaline medium for another enzyme to work.
   2. It helps in the emulsification of fats i.e., converts them into small globules.

Question 3.

1. Write two differences between autotrophic nutrition and heterotrophic nutrition.
2. Draw a diagram showing a cross-section of a leaf and label it:
   Phloem, Xylem, Vascular bundle, Lamina.

Answer:

Question 4.

1. State the reason for the following:
   1. Herbivores need a longer small intestine while carnivores have shorter small intestine.
   2. The lungs are designed in human beings to maximise the area for the exchange of gases.
2. The rate of breathing in aquatic organisms is much faster than that seen in terrestrial organisms.

Answer:

1. 1. Herbivores which eat grass have a longer small intestine for the digestion of cellulose because cellulose takes much time to be digested and it remains for a longer time inside the small intestine. Carnivores which eat meat have a shorter small intestine because meat is easily digestible. Hence, they do not need a longer smaller intestine.
   2. Inside the lungs, the trachea divides and redivides to form numerous fine tubes, the bronchi and bronchioles which finally end in inflated balloon-like structures called alveoli. Alveoli have an extensive network of blood vessels in their thin walls. Hence, they provide a large surface area for the diffusion of gases across their walls.
2. The amount of dissolved oxygen is fairly low compared to oxygen in air. The fishes take in water through their mouths and force it past the gills where the dissolved oxygen is taken up by blood.

Question 5.

1. Draw the structure of a nephron and label the following on it: Glomerulus, Bowman’s capsule, Renal artery, and Collecting duct.
2. What happens to glucose that enters the nephron along with filtrate?

Answer:

Glucose that enters the nephron along with the filtrate after passing through the glomerulus, passes from the tubule of the nephron where it is selectively reabsorbed and sent back to blood.

Question 6.

1. Draw a sectional view of the human heart and label it the Aorta, Pulmonary arteries, Vena cava, and Left ventricle.
2. Why is double circulation of blood necessary in human beings?

Answer:

Double circulation of blood is necessary to:

1. Separate deoxygenated blood from oxygenated blood.
2. Meet high energy and oxygen demands.
3. Maintain constant body temperature.

Question 7.

1. Draw a labelled diagram of the respiratory system of human beings with a diaphragm at the end of expiration.
2. List four conditions required for efficient gas exchange in an organism.

Answer:

The conditions required for efficient gas exchange in an organism are that the membrane should be extensive, thin, highly vascularised and easily permeable to oxygen and carbon dioxide.

Question 8.

1. Draw a schematic representation of the transport and exchange of oxygen and carbon dioxide during the transportation of blood in human beings and label it: Lung capillaries, Pulmonary artery to lungs, Aorta to body, and Pulmonary veins from lungs.
2. What is the advantage of separate channels in mammals and birds for oxygenated and deoxygenated blood?

Answer:

It is necessary to separate oxygenated and deoxygenated blood in mammals and birds because they need high energy and a large amount of oxygen. The separation of oxygenated and deoxygenated blood provides high oxygen supply to the organs.

Question 9.

1. Draw a diagram to show the nutrition in Amoeba and label the parts used for this purpose. Mention any other purpose served by this part other than nutrition.
2. Name the glands associated with the digestion of starch in the human digestive tract and mention their role.
3. How is the required pH maintained in the stomach and small intestine?

Answer:

Pseudopodia serves the purpose of locomotion apart from nutrition.

The salivary gland is associated with the digestion of starch in the human digestive tract. It secretes saliva with the help of the enzyme salivary amylase which converts starch into maltose (sugar).

Gastric glands present on the walls of the stomach release HCl acid. HCl creates an acidic medium, which facilitates the action of the enzyme pepsin. Bile juice from live makes the food alkaline in the small intestine for the pancreatic enzymes to act.

Question 10.

1. Leaves of a healthy potted plant were coated with vaseline to block the stomata. Will this plant remain healthy for long? State three reasons for your answer.
2. State any two differences between autotrophic nutrition and heterotrophic nutrition.

Answer:

1. No, this plant will not remain healthy for long. The plant will begin to die because
   1. Gaseous exchange will not take place.
   2. No absorption of CO₂, hence no photosynthesis.
   3. Transpiration will not occur; hence no transport of water.
2. Differences

Question 11. Explain the process of nutrition in Amoeba.
Answer:

Amoeba is a unicellular animal which follows the holozoic mode of nutrition. The process of obtaining food by Amoeba is called phagocytosis.

The various steps involved in phagocytosis are:

1. Ingestion: Amoeba ingests food particles by forming temporary finger-like projections called pseudopodia around it. The food is engulfed forming a food vacuole.
2. Digestion: Inside the food vacuole, complex substances are broken down into simpler ones by digestive enzymes.
3. Absorption: The digested food present in the food vacuole diffuses into the cytoplasm. After this, the food vacuole disappears.
4. Assimilation: Food absorbed is used by Amoeba for various processes.
5. Egestion: The remaining undigested material moves to the surface of the cell, the cell membrane ruptures at any place and undigested food is thrown out of the body.

Question 12. Describe the alimentary canal of man.
Answer:

Alimentary canal of man: It measures about 8 to 10 metres in length and extends from mouth to anus. It has the following parts.

Mouth: It consists of the oral cavity, through which food is ingested. It contains teeth, tongue and three pairs of salivary glands.

Pharynx: The oral cavity opens into the pharynx. The swallowing mechanism guides the masticated food through the pharynx into a tube, called oesophagus.

Oesophagus: It is a muscular, tubular part of the alimentary canal. The muscular movement called peristalsis carries the food down to the stomach.

Stomach: It is a J-shaped sac-like muscular structure that serves as a storehouse of food. It is a large organ which expands when food enters it. The muscular wall helps in mixing food thoroughly with more digestive juices.

Small Intestine: It is about 6 metres in length and has three divisions, i.e., duodenum (the first part is C-shaped, and begins from the pyloric stomach), jejunum and ileum.

Large Intestine: The ileum passes into the large intestine, which can be divided into two parts anterior colon and posterior rectum. The terminal part of the rectum is called the anal canal. It opens through the anus, guarded by sphincter muscles. It allows the faecal matter to be egested out.

Question 13. Explain the process of breathing in man.
Answer:

Breathing in humans involves the following steps:

1. Inspiration: When we breathe in, the muscles between ribs contract causing the rib cage to move upward and outward, and the diaphragm contracts and moves downward. As the chest cavity becomes large, the air is sucked in from outside into the lungs, the lungs get filled up with air and expand.
2. Gaseous exchange: Haemoglobin in RBCs binds with oxygen and carries it along the body with blood. As blood passes through the tissue of the body, the oxygen from blood diffuses into cell whereas CO2 produced during respiration diffuses into the blood and is carried to the lung.
3. Expiration: When we breathe out, the muscles between the ribs relax causing the rib cage to move downward and inward and the diaphragm relaxes and moves upward. As the chest cavity becomes smaller, air is pushed out from the lungs.

Question 14. Explain the importance of soil for plant growth.
Answer:

Soil is important for plant growth due to following reasons:

1. Soil provides a base on which terrestrial and aquatic plants grow.
2. Soil is a reservoir of water and minerals, essential for all metabolic activities of a plant.
3. The roots of the plant take oxygen for the process of respiration.
4. Some plants also form symbiotic associations with microbes present in the soil to absorb minerals.

Question 15. Draw the diagram of the alimentary canal of man and label the following parts. Mouth, Oesophagus, Stomach, Intestine.
Answer:

The diagram of the alimentary canal of man and its parts are shown as follows:

Question 16. How do carbohydrates, proteins and fats get digested in human beings?
Answer:

Digestion of carbohydrates starts from:

Buccal cavity: The food receives saliva in the buccal cavity, which contains salivary amylase. It breaks down starch into simple (glucose) sugar.

In small intestine

Pancreatic juice contains pancreatic amylase, which acts in further breakdown of starch.

Intestinal juice contains the following

Intestinal amylase hydrolyses the remaining starch and glycogen.

Digestion of proteins starts

In the stomach: An inactive form of pepsin is secreted, known as pepsinogen, which in the presence of HCl forms pepsin and digests protein.

Pepsinogen + HCl → Pepsin

In small intestine

1. Pancreatic juice secretes trypsinogen, chymotripsinogen (inactive form of trypsin) which on activation forms trypsin and digests protein.
2. Intestinal juice

Digestion of Fats begins

In small intestine

Bile emulsifies fats into smaller droplets

Pancreatic juice present in the small intestine acts as follows:

Intestinal juice acts as follows:

Question 17. Explain the mechanism of photosynthesis.
Answer:

The process by which green plants make their own food in the form of glucose from CO₂ and HO by using sunlight energy in the presence of chlorophyll, is called photosynthesis. Oxygen gas is released during photosynthesis.

It occurs in green plants by the following steps:

1. Sunlight energy is absorbed by chlorophyll.
2. This energy is converted into chemical energy. C₆H₁₂O₆+6O₂
3. Water molecule is split into hydrogen and oxygen molecules. The oxygen gas produced as a by-product goes into the air.
4. The hydrogen released during the above reaction is utilised for reduction of CO₂ from carbohydrates by utilising the chemical energy.
5. The extra glucose is stored as starch in the leaves of the plant.

Questionb 18. Explain the three pathways of breakdown in living organisms.
Answer:

In the process of respiration, the first step is the breakdown of glucose, a 6-carbon molecule breaks into 2 molecules of a 3-carbon molecule called pyruvate. This process takes place in the cytoplasm.

The subsequent breakdown pathway depends on the absence or presence of oxygen as follows:

Aerobic respiration: It takes place in the mitochondria in the presence of oxygen. Pyruvic acid is converted into carbon dioxide and water, thus releasing a lot of energy.

Anaerobic respiration: It takes place in the cytoplasm in the absence of oxygen. Pyruvic acid is converted either into CO₂ and ethanol (inthe  case of microbes, i.e., fermentation in yeast) or into lactic acid (in the case of muscle cells during sudden. activity in humans.)

Question 19. Describe the flow of blood through the heart of human beings.
Answer:

Flow of blood through the human heart: Oxygen-rich blood from the lungs comes to the thin-walled upper chamber of the heart on the left, the left atrium.

• The left atrium relaxes when it is collecting this blood. It then contracts, to enter the next chamber, the left ventricle, which expands, so that the blood is transferred to it. When the muscular left ventricle contracts the blood is pumped out to the body.
• Deoxygenated blood reaches from the body to the upper chamber on the right, the right. atrium, and it expands. As the right atrium contracts, the corresponding lower chamber, the right ventricle, dilates.
• This transfers blood to the right ventricle, which in turn pumps it to the lungs for oxygenation. Since ventricles have to pump blood into various organs, they have thicker muscular walls than the atria do.

The whole process is repeated continuously. The blood circulatory system in humans is an example of double circulation since the blood travels twice through the heart in one complete cycle.

1. The pathway of blood from the heart to the lungs and back to the heart is called pulmonary circulation.
2. The pathway of blood from the heart to the rest of the body and back to the heart is called systemic circulation.

These two together make a double circulatory system.

Question 20. Describe the process of urine formation in kidneys.
Answer:

Urine is formed in the kidneys in the nephron i.e., the structural and functional unit of the kidney. Blood at high pressure travels into these tubules by the tuft of blood capillaries called glomerulus.

The following steps are involved in the process:

1. Filtration: Blood enters the glomerulus through the afferent arterials, it passes under pressure that results in filtration of blood. Water and small molecules are forced out of glomerular capillary walls and Bowman’s capsule. Large molecules remain in the blood of the glomerulus.
2. Selective reabsorption: Some molecules are selectively reabsorbed into the blood. The glomerular filtrate flows through the proximal convicted tubule, U-shaped Henle’s loop and distal convoluted tubule. The useful substances present such as glucose, amino acids and salts are reabsorbed by a process which requires energy.
3. Tubular secretion: Some nitrogenous waste products like creatinine and some other substances like K+ are removed from the blood by DCT and are added to the urine. The urine formed is collected in the urinary bladder.