CBSE - Life Processes

Multicellular organisms such as humans possess complex body designs. They have specialised cells and tissues for performing various necessary functions of the body such as intake of food and oxygen. Unlike unicellular organisms, multicellular cells are not in direct contact with the outside environment. Therefore, diffusion cannot meet their oxygen requirements.

Any visible movement such as walking, breathing, or growing is generally used to decide whether something is alive or not. However, a living organism can also have movements, which are not visible to the naked eye. Therefore, the presence of life processes is a fundamental criterion that can be used to decide whether something is alive or not.

An organism uses outside raw materials mostly in the form of food and oxygen. The raw materials required by an organism can be quite varied depending on the complexity of the organism and its environment.

Life processes such as nutrition, respiration, transportation, excretion, etc. are essential for maintaining life.

Autotrophic nutrition	Heterotrophic nutrition
(i) Food is synthesised from simple inorganic raw materials such as CO2 and water.	(i) Food is obtained directly or indirectly from autotrophs. This food is broken down with the help of enzymes.
(ii) Presence of green pigment (chlorophyll) is necessary	(ii) No pigment is required in this type of nutrition.
(iii)Food is generally prepared during day time.	(iii) Food can be prepared at all times
(iv) All green plants and some bacteria have this type of nutrition.	(iv) All animals and fungi have this type of nutrition.

The following raw materials are required for photosynthesis:

 The raw material CO₂ enters from the atmosphere through stomata.

 Water is absorbed from the soil by the plant roots.

 Sunlight, an important component to manufacture food, is absorbed by the chlorophyll and other green parts of the plants.

HCl plays following role in our stomach:

(a) Make the medium acidic for action of enzyme pepsin.

(b) Kills the harmful bacteria present in food

(c) Prevents fermentation of food

Enzymes break-down the various complex components of food into simple and soluble components so that they can be absorbed easily.

The inner lining of 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 transport the absorbed food to each and every cells of the body. Where, it is utilized to obtaining energy and repair of old tissues.

The rate of breathing is slower in terrestrial organisms as compared to aquatic organisms. This is due to the fact that in water, the amount of oxygen is less as compared to air while in aquatic organisms the rate of breathing is faster.

Glucose is first broken down in the cell cytoplasm into a three carbon molecule called pyruvate. Pyruvate is further broken down by different ways to provide energy.

The breakdown of glucose by different pathways can be illustrated as follows.

→ Anaerobic Respiration: This process takes place in absence of oxygen, e.g. in yeast during fermentation. In this case pyruvate is converted into ethanol and carbon dioxide.
→ Aerobic Respiration: In aerobic respiration, breakdown of pyruvate takes place in presence of oxygen to give rise 3 molecules of carbon dioxide and water. The release of energy in aerobic respiration is much more than anaerobic respiration.
→ Lack of Oxygen: Sometimes, when there is lack of oxygen, especially during vigorous activity, in our muscles, pyruvate is converted into lactic acid (3 carbon molecule compounds). Formation of lactic acid in muscles causes cramp.
 

Haemoglobin transports oxygen molecule to all the body cells for cellular respiration. The haemoglobin pigment present in the blood gets attached to four O₂ molecules that are obtained from breathing. It thus forms oxyhaemoglobin and the blood becomes oxygenated. This oxygenated blood is then distributed to all the body cells by the heart. After giving away O₂ to the body cells, blood takes away CO₂ which is the end product of cellular respiration. Now the blood becomes de-oxygenated.

Since haemoglobin pigment has less affinity for CO₂, CO₂ is mainly transported in the dissolved form. This de-oxygenated blood gives CO₂ to lung alveoli and takes O₂ in return.



Transportation of O₂ and CO₂ in blood
 

The exchange of gases takes place between the blood of the capillaries that surround the alveoli and the gases present in the alveoli. Thus, alveoli are the site for exchange of gases. The lungs get filled up with air during the process of inhalation as ribs are lifted up and diaphragm is flattened. The air that is rushed inside the lungs fills the numerous alveoli present in the lungs.

Each lung contains 300-350 million alveoli. These numerous alveoli increase the surface area for gaseous exchange making the process of respiration more efficient.
 

The main components of the transport system in human beings are the heart, blood, and blood vessels.

Heart pumps oxygenated blood throughout the body. It receives deoxygenated blood from the various body parts and sends this impure blood to the lungs for oxygenation.

Being a fluid connective tissue, blood helps in the transport of oxygen, nutrients, CO₂, and nitrogenous wastes.

The blood vessels (arteries, veins, and capillaries) carry blood either away from the heart to various organs or from various organs back to the heart.

Warm-blooded animals such as birds and mammals maintain a 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 (O₂) 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.

In highly organised plants, there are two different types of conducting tissues - xylem and phloem. Xylem conducts water and minerals obtained from the soil (via roots) to the rest of the plant. Phloem transports food materials from the leaves to different parts of the plant body.

The components of xylem tissue (tracheids and vessels) of roots, stems, and leaves are interconnected to form a continuous system of water-conducting channels that reaches all parts of the plant. Transpiration creates a suction pressure, as a result of which water is forced into the xylem cells of the roots. Then there is a steady movement of water from the root xylem to all the plant parts through the interconnected water-conducting channels.



Components of xylem tissue
 

Phloem transports food materials from the leaves to different parts of the plant body. The transportation of food in phloem is achieved by utilizing energy from ATP. As a result of this, the osmotic pressure in the tissue increases causing water to move into it. This pressure moves the material in the phloem to the tissues which have less pressure. This is helpful in moving materials according to the needs of the plant. For example, the food material, such as sucrose, is transported into the phloem tissue using ATP energy.



Components of phloem tissue
 

Nephrons are the basic filtering units of kidneys. Each kidney possesses large number of nephrons, approximately 1-1.5 million. The main components of the nephron are glomerulus, Bowman's capsule, and a long renal tubule.



Structure of a nephron

Functioning of a Nephron:

The blood enters the kidney through the renal artery, which branches into many capillaries associated with glomerulus.

The water and solute are transferred to the nephron at Bowman's capsule.

In the proximal tubule, some substances such as amino acids, glucose, and salts are selectively reabsorbed and unwanted molecules are added in the urine.

The filtrate then moves down into the loop of Henle, where more water is absorbed.

From here, the filtrate moves upwards into the distal tubule and finally to the collecting duct. Collecting duct collects urine from many nephrons.

The urine formed in each kidney enters a long tube called ureter. From ureter, it gets transported to the urinary bladder and then into the urethra.
 

Plants can get rid of excess of water by transpiration. Waste materials may be stored in the cell vacuoles or as gum and resin, especially in old xylem. It is also stored in the leaves that later fall off.
 

The amount of urine produced depends on the amount of excess water and dissolved wastes present in the body. Some other factors such as habitat of an organism and hormone such as Anti-diuretic hormone (ADH) also regulates the amount of urine produced.

The kidneys in human beings are a part of the system for
(a) nutrition.

(b) respiration.

(c) excretion.

(d) transportation.

Ans: (c) excretion.

The xylem in plants are responsible for
(a) transport of water.
(b) transport of food.
(c) transport of amino acids.
(d) transport of oxygen.
Ans: (a) transport of water.

The autotrophic mode of nutrition requires
(a) carbon dioxide and water.
(b) chlorophyll.
(c) sunlight.
(d) all of the above.

Ans: (d) all of the above.

The breakdown of pyruvate to give carbon dioxide, water and energy takes place in
(a) cytoplasm.
(b) mitochondria.
(c) chloroplast.
(d) nucleus.

Ans: (b) mitochondria.

Fats are present in the form of large globules in the small intestine. The small intestine receives the secretions from the liver and the pancreas. The bile salts (from the liver) break down the large fat globules into smaller globules so that the pancreatic enzyme lipase can easily act on them. This is referred to as emulsification of fats. This process takes place in the small intestine.

The role of saliva in the digestion of food:
→ It moistens the food for easy swallowing.
→ It contains a digestive enzyme called salivary amylase, which breaks down starch into sugar.

Autotrophic nutrition takes place through the process of photosynthesis. Carbon dioxide, water, chlorophyll pigment, and sunlight are the necessary conditions required for autotrophic nutrition. Carbohydrates (food) and O₂ are the by-products of photosynthesis.

Aerobic respiration	Anaerobic respiration
It occurs in the presence of O2.	It occurs in the absence of O2.
It involves the exchange of gases between the organism and the outside environment.	Exchange of gases is absent.
It occurs in cytoplasm and mitochondria.	It occurs only in cytoplasm.
It always releases CO2 and H2O.	End products vary.

Anaerobic respiration occurs in the roots of some waterlogged plants, some parasitic worms, animal muscles, and some micro-organisms such as yeasts.

Alveoli provide a surface for the exchange of gases. An extensive network of blood vessels is present in the wall of the alveoli. By lifting our ribs and flatten the diaphragm, the chest cavity becomes spacious. Air is sucked into the lungs and alveoli. The oxygen from the breath, diffuses into the blood and CO₂ from the blood brought from the body, diffuses out into the air.

Haemoglobin is the respiratory pigment that transports oxygen to the body cells for cellular respiration. Therefore, deficiency of haemoglobin in blood can affect the oxygen supplying capacity of blood. This can lead to deficiency of oxygen in the body cells. It can also lead to a disease called anaemia

The human heart is divided into four chambers - the right atrium, the right ventricle, the left atrium, and the left ventricle.
Flow of blood in the heart:
The heart has superior and inferior vena cava, which carries de-oxygenated blood from the upper and lower regions of the body respectively and supplies this de-oxygenated blood to the right atrium of the heart

Flow of blood in the human heart

The right atrium then contracts and passes the de-oxygenated blood to the right ventricle, through an auriculo-ventricular aperture.

Then the right ventricle contracts and passes the de-oxygenated blood into the two pulmonary arteries, which pumps it to the lungs where the blood becomes oxygenated. From the lungs, the pulmonary veins transport the oxygenated blood to the left atrium of the heart.

Then the left atrium contracts and through the auriculo-ventricular aperture, the oxygenated blood enters the left ventricle.

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.

Transport of materials in xylem	Transport of materials in phloem
Xylem tissue helps in the transport of water and minerals.	Phloem tissue helps in the transport of food.
Water is transported upwards from roots to all other plant parts.	Food is transported in both upward and downward directions.
Transport in xylem occurs with the help of simple physical forces such as transpiration pull.	Transport of food in phloem requires energy in the form of ATP.

Alveoli	Nephrons
Structure	Structure
Alveoli are tiny balloon-like structures present inside the lungs.	Nephrons are tubular structures present inside the kidneys.
The walls of the alveoli are one cell thick and it contains an extensive network of blood capillaries.	Nephrons are made of glomerulus, bowman’s capsule, and a long renal tube.
Function	Function
The exchange of O2 and CO2 takes place between the blood of the capillaries that surround the alveoli and the gases present in the alveoli.	The blood enters the kidneys through the renal artery.
Alveoli are the site of gaseous exchange.	The blood is entered here and the nitrogenous waste in the form of urine is collected by collecting duct.Nephrons are the basic filtration unit.

1. Which of the following statements about the autotrophs is incorrect?
(a) They synthesise carbohydrates from carbon dioxide and water in the presence of sunlight and chlorophyll
(b) They store carbohydrates in the form of starch
(c) They convert carbon dioxide and water into carbohydrates in the absence of sunlight
(d) They constitute the first trophic level in food chains
Ans. (c) They convent carbon dioxide and water into carbohydrates in the absence of sunlight.

2. In which of the following groups of organisms, food material is broken down outside the body and absorbed?
(a) Mushroom, green plants, Amoeba
(b) Yeast, mushroom, bread mould
(c) Paramecium, Amoeba, Cuscuta
(d) Cuscuta, lice, tapeworm

Ans. (b) Yeast, mushroom, bread mould

Explanation: All of them are saprotrophs. In saprotrophic mode of nutrition, food material is broken down outside the body and absorbed.

3. Select the correct statement
(a) Heterotrophs do not synthesise their own food
(b) Heterotrophs utilise solar energy for photosynthesis
(c) Heterotrophs synthesise their own food
(d) Heterotrophs are capable of converting carbon dioxide and water into carbohydrates
Ans. (a) Heterotrophs do not synthesise their own food.
Explanation: Heterotrophs depend on other organisms for food.

4. Which is the correct sequence of parts in human alimentary canal?
(a) Mouth →stomach →small intestine →oesophagus →large intestine
(b) Mouth →oesophagus →stomach →large intestine →small intestine
(c) Mouth →stomach →oesophagus →small intestine →large intestine
(d) Mouth →oesophagus →stomach →small intestine →large intestine
Ans. (d) Mouth →oesophagus →stomach →small intestine →large intestine

5. If salivary amylase is lacking in the saliva, which of the following events in the mouth cavity will be affected?
(a) Proteins breaking down into amino acids
(b) Starch breaking down into sugars
(c) Fats breaking down into fatty acids and glycerol
(d) Absorption of vitamins
Ans. (b) Starch breaking down into sugars 

Explanation: Salivary amylase converts starch into sugar. Digestion of proteins and fats does not take place in mouth, hence options (a) and (c) are incorrect.

6. The inner lining of stomach is protected by one of the following from hydrochloric acid. Choose the correct one
(a) Pepsin
(b) Mucus
(c) Salivary amylase
(d) Bile
Ans. (b) Mucus
Explanation: Mucus protects the inner lining of stomach from hydrochloric acid.

7. Which part of alimentary canal receives bile from the liver?
(a) Stomach
(b) Small intestine
(c) Large intestine
(d) Oesophagus
Ans. (b) Small intestine
Explanation: Bile from gall bladder goes to small intestine through hepatopancreatic duct.

8. A few drops of iodine solution were added to rice water. The solution turned blueblack in colour. This indicates that rice water contains
(a) complex proteins
(b) simple proteins
(c) fats
(d) starch
Ans. (d) Starch
Explanation: Starch makes a dark blue complex with iodine. This is the most often used test to check the presence of starch in something.

9. In which part of the alimentary canal food is finally digested?
(a) Stomach
(b) Mouth cavity
(c) Large intestine
(d) Small intestine
Ans. (d) Small intestine
Explanation: Partial digestion of food takes place in mouth and stomach. Digestion does not happen in large intestine. It is the small intestine, where digestion is completed.

10. Choose the function of the pancreatic juice from the following
(a) trypsin digests proteins and lipase carbohydrates
(b) trypsin digests emulsified fats and lipase proteins
(c) trypsin and lipase digest fats
(d) trypsin digests proteins and lipase emulsified fats 
Ans. (d) Trypsin digests proteins and lipase emulsified fats
Explanation: Trypsin completes the digestion of protein. Lipase digests emulsified fat to convert it into fatty acids and glycerol.

11. When air is blown from mouth into a test-tube containing lime water, the lime water turned milky due to the presence of
(a) oxygen
(b) carbon dioxide
(c) nitrogen
(d) water vapour
Ans. (b) Carbon dioxide
Explanation: Carbon dioxide reacts with limewater Ca(OH)2 to form calcium carbonate which makes the lime water milky.

12. The correct sequence of anaerobic reactions in yeast is

Ans. (d)
Explanation: Breakdown of pyruvate; under anaerobic condition; takes place in cytoplasm of yeast. Ethanol and carbon dioxide are produced at the end of this reaction.


13. Which of the following is most appropriate for aerobic respiration?



Ans. (d)
Explanation: In aerobic respiration, breakdown of pyruvate takes place in mitochondria. Carbon dioxide and water are produced at the end of this reaction.

14. Which of the following statement(s) is (are) true about respiration?
(i) During inhalation, ribs move inward and diaphragm is raised
(ii) In the alveoli, exchange of gases takes place i.e., oxygen from alveolar air diffuses into blood and carbon dioxide from blood into alveolar air
(iii) Haemoglobin has greater affinity for carbon dioxide than oxygen
(iv) Alveoli increase surface area for exchange of gases
(a) (i) and (iv)
(b) (ii) and (iii)
(c) (i) and (iii)
(d) (ii) and (iv)

Ans. (d) (ii) and (iv)

Explanation: Statement (i) is incorrect. During inhalation, ribs move outward and diaphragm is lowered. Statement (iii) is incorrect because haemoglobin has greater affinity for oxygen than carbon dioxide.


15. Which is the correct sequence of air passage during inhalation?
(a) Nostrils →larynx →pharynx →trachea →lungs
(b) Nasal passage →trachea →pharynx →larynx →alveoli
(c) larynx →nostrils →pharynx →lungs
(d) Nostrils →pharynx →larynx →trachea →alveoli
Ans. (d) Nostrils →pharynx →larynx →trachea →alveoli
Explanation: Refer to fig 6.9 (NCERT Text book) to see the correct sequence of organs in human respirator system.

16. During respiration exchange of gases take place in
(a) trachea and larynx
(b) alveoli of lungs
(c) alveoli and throat
(d) throat and larynx
Ans. (b) Alveoli of lungs
Explanation: Trachea and larynx just serve as passage for air. Exchange of gases takes place in alveoli; where oxygen diffuses into blood and carbon dioxide comes out of blood.

17. Which of the following statement (s) is (are) true about heart?
(i) Left atrium receives oxygenated blood from different parts of body while right atrium receives deoxygenated blood from lungs
(ii) Left ventricle pumps oxygenated blood to different body parts while right ventricle pumps deoxygenated blood to lungs
(iii) Left atrium transfers oxygenated blood to right ventricle which sends it to different body parts
(iv) Right atrium receives deoxygenated blood from different parts of the body while left ventricle pumps oxygenated blood to different parts of the body
(a) (i)
(b) (ii)
(c) (ii) and (iv)
(d) (i) and (iii)
Ans. (c) (ii) and (iv)
Explanation: Deoxygenated blood circulates through right part of the heart, while oxygenated blood circulates through left part of the heart. Atrium receives blood, while ventricle pumps the blood out.


18. What prevents backflow of blood inside the heart during contraction?
(a) Valves in heart
(b) Thick muscular walls of ventricles
(c) Thin walls of atria
(d) All of the above
Ans. (a) Valves in heart
Explanation: Walls of heart facilitate the pumping action only and have no role in preventing backflow of blood.

19. Single circulation i.e., blood flows through the heart only once during one cycle of passage through the body, is exhibited by
(a) Labeo, Chameleon, Salamander
(b) Hippocampus, Exocoetus, Anabas
(c) Hyla, Rana, Draco
(d) Whale, Dolphin, Turtle
Ans. (b) Hippocampus, Exocoetus, Anabas
Explanation: In option �a�; salamander is amphibian, while chameleon is reptile; and they have three chambered heart. Thus, these animals show partial double circulation. In option �c� all animals are amphibians.

In option �d� whale is mammal, while turtle is reptile. Mammals have four-chambered heart and completely double circulation.

20. In which of the following vertebrate group/groups, heart does not pump oxygenated blood to different parts of the body?
(a) Pisces and amphibians
(b) Amphibians and reptiles
(c) Amphibians only
(d) Pisces only
Ans. (d) Pisces only
Explanation: This happens because of single circulation.

21. Choose the correct statement that describes arteries.
(a) They have thick elastic walls, blood flows under high pressure; collect blood from different organs and bring it back to the heart
(b) They have thin walls with valves inside, blood flows under low pressure and carry blood away from the heart to various organs of the body
(c) They have thick elastic walls, blood flows under low pressure; carry blood from the heart to various organs of the body
(d) They have thick elastic walls without valves inside, blood flows under high pressure and carry blood away from the heart to different parts of the body.
Ans. (d) They have thick elastic walls without valves inside, blood flows under high pressure

22. The filtration units of kidneys are called
(a) Ureter
(b) Urethra
(c) Neurons
(d) Nephrons
Ans. (d) Nephrons
Explanation: Due to this, nephron is called the functional unit of Kidney.
23. Oxygen liberated during photosynthesis comes from
(a) water
(b) chlorophyll
(c) carbon dioxide
(d) glucose
Ans. (a) water
Explanation: Splitting of water molecule, results in liberation of oxygen and hydrogen. Hydrogen is utilized for reduction of carbon dioxide so that carbohydrate can be made.

24. The blood leaving the tissues becomes richer in
(a) carbon dioxide
(b) water
(c) heamoglobin
(d) oxygen
Ans. (a) carbon dioxide
Explanation: Carbon dioxide accumulates in tissues because of respiration in cells. Thus, blood leaving the tissues becomes richer in carbon dioxide.

25. Which of the following is an incorrect statement?
(a) Organisms grow with time
(b) Organisms must repair and maintain their structure
(c) Movement of molecules does not take place among cells
(d) Energy is essential for life processes
Ans. (c) Movement of molecules does no take place among cells
Explanation: Movement of molecules is an important aspect of life process and it is necessary that such movements take place among cells.

26. The internal (cellular) energy reserve in autotrophs is
(a) glycogen
(b) protein
(c) starch
(d) fatty acid
Ans. (c) Starch
Explanation: Plants store food in the form of starch. 

27. Which of the following equations is the summary of photosynthesis? 
(a) 6CO2 + 12H2O → C6H12O6 + 6H2O
(b) 6CO2 + H2O + Sunlight → C6H12O6 + O2 + 6H2O
(c) 6CO2 + 12H2O + Chlorophyll + Sunlight → C6H12O6 + 6O2 + 6H2O
(d) 6CO2 + 12H2O + Chlorophyll + Sunlight → C6H12O6 + 6CO2 + 6H2O

Ans. (c) 
Explanation: Option ‘a’ shows correct reaction. But option ‘c’ shows correct reaction as well as other important factors of reaction. Option ‘b’ is not a balanced equation. Option ‘d’ shows carbon dioxide among the products; which is wrong. 

28. Choose the event that does not occur in photosynthesis
(a) Absorption of light energy by chlorophyll
(b) Reduction of carbon dioxide to carbohydrates
(c) Oxidation of carbon to carbon dioxide
(d) Conversion of light energy to chemical energy
Ans. (c) Oxidation of carbon to carbon dioxide

29. The opening and closing of the stomatal pore depends upon
(a) oxygen
(b) temperature
(c) water in guard cells
(d) concentration of CO2 in stomata
Ans. (c) Water in guard cells
Explanation: When water enters the guard cells. they become turgid and facilitate the opening of guard cells. When water comes out of guard cells, they become flaccid and facilitate the closing of guard cells.

30. Choose the forms in which most plants absorb nitrogen
(i) Proteins
(ii) Nitrates and Nitrites
(iii) Urea
(iv) Atmospheric nitrogen
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (i) and (iv)
Ans. (b) (ii) and (iii)
Explanation: Plants cannot take up atmospheric nitrogen and hence option ‘iv’ is incorrect. Protein is synthesized by plants and hence option ‘i’ is incorrect

31. Which is the first enzyme to mix with food in the digestive tract?
(a) Pepsin
(b) Cellulase
(c) Amylase
(d) Trypsin
Ans. (c) Amylase
Explanation: Amylase is present in saliva; which is secreted in mouth. Hence, this is the first enzyme to mix with food.

32. Which of the following statement(s) is (are) correct?
(i) Pyruvate can be converted into ethanol and carbon dioxide by yeast 
(ii) Fermentation takes place in aerobic bacteria
(iii) Fermentation takes place in mitochondria
(iv) Fermentation is a form of anaerobic respiration
(a) (i) and (iii)
(b) (ii) and (iv)
(c) (i) and (iv)
(d) (ii) and (iii)
Ans. (c) (i) and (iv)
Explanation: Fermentation takes place in anaerobes. Fermentation does not take place in mitochondria. Hence, Options (ii) and (iii) are incorrect. 

33. Lack of oxygen in muscles often leads to cramps among cricketers. This results due to
(a) conversion of pyruvate to ethanol
(b) conversion of pyruvate to glucose
(c) non-conversion of glucose to pyruvate
(d) conversion of pyruvate to lactic acid
Ans. (d) conversion of pyruvate to lactic acid
Explanation: In case of excess demand of energy in muscles, anaerobic respiration takes place in muscle cells. This results in accumulation of lactic acid in muscles which results in cramps.

34. Choose the correct path of urine in our body
(a) kidney →ureter →urethra →urinary bladder
(b) kidney →urinary bladder →urethra →ureter
(c) kidney →ureters →urinary bladder →urethra
(d) urinary bladder →kidney →ureter →urethra
Ans. (c) kidney →ureters →urinary bladder →urethra
Explanation: Refer to fig: 6.13 (NCERT Text book) for proper sequence of organs in excretory system.

35. During deficiency of oxygen in tissues of human beings, pyruvic acid is converted into lactic acid in the
(a) cytoplasm
(b) chloroplast
(c) mitochondria
(d) golgi body
Ans. (a) cytoplasm
Explanation: Anaerobic respiration takes place in cytoplasm. 
 

(a) The process in plants that links light energy with chemical energy
 Ans. Photosynthesis
(b) Organisms that can prepare their own food
 Ans. Autotrophs
(c) The cell organelle where photosynthesis occurs
 Ans. Chloroplast
(d) Cells that surround a stomatal pore
 Ans. Guard cells
(e) Organisms that cannot prepare their own food
 Ans. Heterotrophs
(f) An enzyme secreted from gastric glands in stomach that acts on proteins.
 Ans. Pepsin 

This is an incorrect statement. All plants carry on respiration throughout 24 hours and thus give out carbon dioxide throughout the 24 hours. But photosynthesis happens only in presence of sunlight and oxygen is released during daytime.

When water enters the guard cells, they become turgid. This results in opening of stomatal pore. When water exits from the guard cells, they become flaccid. This results in closing of stomata

The plant which is kept in continuous light live longer. We know that plant release carbon dioxide during respiration. In case of plant which is being kept in dark, carbon dioxide will accumulate in the container. This will finally result in lack of oxygen for the plant and plant would die. In case of plant which is being kept in light, carbon dioxide shall be utilized during photosynthesis. This will help in maintaining the availability of oxygen for respiration. As a result, this plant will live longer.

If plant is releasing carbon dioxide and taking in oxygen during the day, it means that respiration is happening in plant. But it does not mean that photosynthesis is not happening. Carbon dioxide released after respiration comes out of stomata. For photosynthesis, the plant takes in carbon dioxide from atmosphere. In other words, plant does not depend on respiration for carbon dioxide for photosynthesis.

Fish can take in oxygen which is dissolved in water. For this, they show adaptation in the form of gills. But fish does not have the ability to utilize oxygen from air. Due to this, a fish can comfortably live in water but dies when it is taken out of water.

Autotroph	Heterotroph
1. Organisms that prepare their own food.	1. Organisms that are dependent on other organisms for food.
2. They have chlorophyll.	2. They lack chlorophyll.

Nutrition is required by every organism for various purposes. An organism needs energy to carry out various activities, and this energy comes from food. An organism also needs raw materials for growth and repair. These raw materials come from food. This shows that nutrition is a necessity for an organism.

Green plants are the main conducts through which solar energy is trapped and channeled to all other organisms. Green plants are the main source of food (directly or indirectly) for most of the heterotrophs. Without green plants, no animal shall be able to get food and thus no animal would survive. Hence, almost all life forms would be wiped out if green plants disappear from earth.

If leaves of a healthy potted plant are coated with Vaseline, it will clog the stomatal pores on leaves. Blockage of stomata will stop transpiration and exchange of gases from leaves. Transpiration plays an important role in ascent of sap in plants. Hence, lack of transpiration will stop ascent of sap. Moreover, stoppage of exchange of gases would also stop respiration and photosynthesis in leaves. This will result in death of leaves and finally the plant would die due to lack of food.

Aerobic respiration	Anaerobic respiration
1. Oxygen is utilised for the breakdown of respiratory substrate.	1. Oxygen is not required.
2. It takes place in cytoplasm (glycolysis) and inside mitochondria (Krebs cycle)	2. It takes place in cytoplasm only.
3. End products are carbon dioxide and water	3. End products are lactic acid or ethanol and carbon dioxide.
4. More energy is released.	4. Less energy is released.

Match the words of Column (A) with that of Column (B)

Ans. (a)-(ii), (b)-(i), (c)-(iv), (d)-(iii)

Artery	Vein
1. Have thick elastic, muscular walls.	1. Have thin, non-elastic, walls.
2. Lumen is narrow.	2. Lumen is wide.
3. Carry blood from heart to all body parts.	3. Carry blood from all body parts to heart.
4. Carry oxygenated blood (except pulmonary artery).	4. Carry deoxygenated blood (except pulmonary vein).

Leaves show following adaptations for photosynthesis:
 (a) Flat surface to allow greater exposure to sunlight
 (b) Presence of chlorophyll to trap solar energy
 (c) Larger number of stomata on lower surface. 

The food of herbivores contains a huge amount of cellulose. The animals need the assistance of certain bacteria to digest cellulose and this process takes time. Due to this, herbivores have longer small intestine than carnivores. Meat is easier to digest and hence carnivores have small intestine which is much smaller than in herbivores.

Mucus plays important role in digestive system. Mucus prevents the inner lining of digestive system from becoming dry. This helps in easier movement of food through the digestive system. Moreover, mucus in stomach protects the inner lining from damage by hydrochloric acid. So, lack of mucus will result in damage to the inner lining of stomach. It may result in gastric ulcers.

Fat is present in the form of large globules. For the concerned enzyme, it is difficult to digest large globules of fat. Emulsification of fat results in fat breaking into smaller globules. After that, becomes easier for the enzyme to digest fat.

Alimentary canal has muscular walls. Due to this, the alimentary canal contracts and relaxes in alternative fashion. This movement in alimentary canal is called peristalsis. Food moves inside the alimentary canal because of peristalsis.

Small intestine has specialized structures to facilitate absorption. The inner lining of small intestine has numerous folds; to increase the area of absorption. The finger-like projections inside the small intestine are richly supplied by blood vessels. This also helps in absorption of food. Due to this, absorption of digested food occurs mainly in the small intestine.

Match Group (A) with Group (B)

Ans. (a)-iv (b)-iii (c)-i (d)-ii

The availability of oxygen is much less in aquatic environment than in terrestrial environment. Due to this, aquatic organisms need to work harder to obtain oxygen. Hence, rate of breathing in aquatic organisms is much faster than in terrestrial organisms.

In human heart, blood passes through the heart twice during one cardiac cycle. The deoxygenated blood comes to the heart and goes to the lungs for oxygenation. Simultaneously, the oxygenated blood comes to the heart from lungs and goes to different organs. Due to this, blood circulation in human heart is called double circulation.

Four-chambered heart gives following advantages:
(a) There is clear cut division of labour among different chambers. Atria receive blood and ventricles pump the blood.
(b) There is complete segregation of oxygenated and deoxygenated blood in the heart.
(c) Heart’s efficiency is more in this design. 

Following are the major events during photosynthesis:
 (a) Absorption of light energy by chlorophyll
 (b) Conversion of light energy into chemical energy.
 (c) Splitting of water molecules into hydrogen and oxygen.
 (d) Reduction of carbon dioxide to form carbohydrate. 

(a) Cloudy days
Ans. Availability of sunlight is less on cloudy days. This will reduce the rate of photosynthesis.
(b) No rainfall in the area
 Ans. No effect
(c) Good manuring in the area
 Ans. No effect
(d) Stomata get blocked due to dust
 Ans. Opening of stomata is essential for availability of carbon dioxide for photosynthesis. Blockage of stomata will reduce the rate of photosynthesis. 

ATP is called the energy currency in living organisms. It is produced in mitochondria during respiration

All of them are parasites. They live on or inside the body of another organism to get food. They always harm their hosts.

Role of mouth in digestion of food:
 (a) Ingestion of food happens through mouth.
(b) Mastication of food breaks the food into smaller particles.
(c) Saliva makes the food slippery so that it becomes easy to swallow the food.
(d) Salivary amylase converts starch into sugar

Gastric glands secrete hydrochloric acid, pepsin and mucus. They have following functions:
(a) Hydrochloric acid kills any germ which may be present in food. It makes the environment in the stomach acidic; which is essential for functioning of gastric enzyme.
 (b) Pepsin digests protein.
(c) Mucus prevents the inner lining of stomach from getting damaged by hydrochloric acid. 

Column (A)	Column (B)
(a) Trypsin	(i) Pancreas
(b) Amylase	(ii) Liver
(c) Bile	(iii) Gastric glands
(d) Pepsin	(iv) Saliva

Ans. (a)- i (b)- iv (c)- ii (d)- iii

(a) Trypsin
 Ans. Protein
(b) Amylase
 Ans. Starch
(c) Pepsin
 Ans. Protein
(d) Lipase
 Ans. Fat 

Blood flow through vein does not exert pressure on the walls of veins. Due to this, they do not need thick walls. Hence, veins have thin walls as compared to arteries.

Platelets play an important role in clotting of blood. Clotting of blood is defense mechanism. It prevents excess loss of blood in case of injury. Lack of platelet will not allow the blood to clot. This will result in excess loss of blood in case of injury. This may prove fatal for the person.

Plants remain fixed at a place because they do not need to move in search of food. As a result, plants do not need to have locomotion, the way animals do. Moreover, most of the movements of substances in plants happen through passive transport; which does not need energy. Due to this, the energy requirement in plants is low as compared to animals.

Root hairs have thin walls. Due to this, water enters the root hairs because of osmosis. Water from root hairs continuously moves into the root xylem. To maintain the osmotic gradients, the cells of root hairs take up ions from the soil.

Significance of transpiration:
 (a) It creates transpiration pull to facilitate ascent of sap.
 (b) Ascent of sap is necessary to make water available for photosynthesis.
 (c) It helps a plant to get rid of excess water. 

Leaves play important role in excretion in plants. Most of the carbon dioxide exits through stomata in leaves. Many excretory products accumulate in leaves. Plants shed leaves to get rid excretory products.

Amoeba shows holozoic nutrition which is comprised of following steps:
 Ingestion, Digestion, Absorption, Assimilation and Egestion

 
Ingestion: Amoeba makes finger-like projections outside its body. These projections are called pseudopodia. Amoeba traps food particle with pseudopodia. After that, amoeba takes in the food particle; along with water.
Digestion: Amoeba makes food vacuole after ingesting the food particle. Enzymes are released in the food vacuole for digestion.
Absorption: After digestion, nutrients enter the cytoplasm through osmosis.
Assimilation: Nutrients are utilized by the cell for various purposes.
Egestion: Food vacuole goes near the cell membrane to empty its contents outside the cell. This results in expulsion of waste materials from the cell. 

The human alimentary canal has following parts:
Buccal Cavity: Buccal cavity contains tongue, teeth and salivary glands. Food enters the digestive system through buccal cavity.
Oesophagus: Buccal cavity is connected to a long tube-like structure; called oesophagus. Oesophagus has a valve to prevent the backflow of food into mouth.
Stomach: Stomach is a J-shaped organ. The buccal cavity opens into the stomach. Walls of stomach are composed of muscles. Gastric glands are present in the stomach. These glands secrete hydrochloric acid, pepsin and mucus.
Small Intestine: This is long and highly coiled structure. The lumen of the small intestine is smaller than that of large intestine. The stomach opens into small intestine. The hepatopancreatic duct opens into the small intestine. Villi are present in small intestine to facilitate absorption of food.

Large Intestine: This is shorter than small intestine. The lumen of large intestine is larger than that of small intestine.
Rectum: Large intestine opens into rectum. Waste materials and undigested food are stored in rectum. 
 

Breathing involves two step, viz. inhalation and exhalation.
Inhalation: The process of taking in air called inhalation. During this process, ribs come out and diaphragm moves down. This increases the volume inside the lungs and reduces the pressure in lungs. As a result, air moves towards the lungs.
Exhalation: The process of giving out air is called exhalation. During this process, ribs go in and diaphragm moves up. This reduces the volume inside the lungs and increases the pressure in lungs. As a result, air moves out of the lungs. 

Importance of soil for plant growth:
 (a) Soil provides the base on which a plant can grow.
 (b) Soil serves as reservoir of water for plants.
 (c) Soil serves as reservoir of different minerals which are essential for growth of plants.
 (d) Soil contains many organic materials which provide nutrients to plants. 

Digestion of carbohydrates: Digestion of carbohydrates begins from buccal cavity.
Salivary amylase converts starch into sugar. Other complex carbohydrates are converted into glucose in the small intestine.
Digestion of Proteins: Protein is partially digested in the stomach. For this, stomach secretes the enzyme pepsin. In small intestine, pancreatic juice provides the enzymes trypsin and chymotrypsin. These enzymes complete the digestion of proteins.
 Digestion of Fats: Digestion of fats takes place in small intestine. Bile; from liver; emulsifies the fat. Due to this, fat is broken into small globules. This makes it easier for the enzyme to digest fat. Lipase is the enzyme which converts fat into glycerol and fatty
acid. 

Photosynthesis is the process by which green plants prepare their food in the presence of sunlight. Green plants utilize carbon dioxide and water to make carbohydrate. The reaction of photosynthesis can be shown by following equation:

The whole process of Photosynthesis is composed of following steps:
 (a) Absorption of light energy by chlorophyll
 (b) Conversion of light energy into chemical energy
 (c) Splitting of water molecules into hydrogen and oxygen.
 (d) Reduction of carbon dioxide to form carbohydrate
 These steps need not take place one after another immediately. For example;
desert plants take up carbon dioxide at night to make an intermediate. During daytime,  they make carbohydrate. After photosynthesis, carbohydrate is converted into starch and starch is stored in different plant organs. 
 

The breakdown of sugar can be shown by following diagram:
In all organisms, glucose is first converted into pyruvate. Glucose is a 6-carbon molecule, while pyruvate is a 3-carbon molecule.

This step is same in all organisms and it happens in cytoplasm. Further breakdown of pyruvate can happen in any of the following ways:

In Yeast: In yeast, breakdown of pyruvate take place in absence of oxygen. Due to this, it is called anaerobic respiration. Pyruvate is broken down into ethanol and carbon dioxide.
In muscle cells: During strenuous physical activity, the energy demand from muscle cells suddenly increases. This is compensated by anaerobic respiration in muscle cells. In such a situation, pyruvate is broken down into lactic acid.

In mitochondria: In this case, breakdown of pyruvate takes place in presence of oxygen. Due to this, it is called aerobic respiration. Pyruvate is broken down into carbon dioxide and water. Aerobic respiration is the norm is most of the living beings. 
 

Blood flow through the human heart takes place in following steps: 

• Deoxygenated blood from different organs comes to the right atrium through the vena cava.
• From the right atrium, blood goes to the right ventricle. The tricuspid valve between the right atrium and right ventricle prevents the backflow of blood.
• From the right ventricle, blood goes to the lungs through pulmonary artery. Inside the lungs, carbon dioxide is removed from the blood and oxygen enters the blood.
• From the lungs, blood goes to the left atrium through pulmonary vein.
• From the left atrium, blood goes to the left ventricle.
• From the left ventricle, blood is pumped into the aorta so that it can be supplied to different organs. 
 

The functional unit of kidney is called nephron.
A nephron is composed of a tuft of blood capillaries and highly coiled ducts. The tuft of blood capillaries is surrounded by a cup-shaped structure; called Bowman’s capsule.
• Waste material from blood are filtered out of the capillaries and they go through the wall of Bowman’s capsule.
• After that, the waste material and water pass through the ducts. When the mixture of water and other materials move through the duct, some materials and water are reabsorbed. This depends on excess amount of water present in the body.
• After reabsorption of water and other material, urine becomes concentrated. This then goes to the collecting duct.
• Urine from collecting ducts moves through ureter into the urinary bladder. From the urinary bladder, urine is expelled from the body as and when required.