Life Processes: Class 10 Science answers, notes

Summary

Living things show movement, even tiny molecular movements, as a sign of life. Our bodies are organized structures that can break down over time. So, living things must constantly repair and maintain themselves through life processes. These processes need energy, which comes from food through a process called nutrition. Growth also needs materials from food. Energy from food needs to be converted into a usable form. This often involves chemical changes, and many living things use oxygen for this. This process of getting energy from food is called respiration. Single-celled beings can get food and oxygen directly from their surroundings. But larger beings with many cells need special parts for this. They also need a system to carry food and oxygen to all cells, called a transport system. When energy is made, waste products are also formed. These wastes must be removed from the body, which is called excretion.

Plants make their own food using sunlight, water, and carbon dioxide. This is called autotrophic nutrition, and the process is photosynthesis. The food they make, like sugar, gives them energy. Extra sugar is stored as starch. Animals and fungi cannot make their own food. They eat plants or other animals. This is called heterotrophic nutrition. They use special helpers called enzymes to break down complex food into simpler forms.

In humans, food is broken down in a long tube called the alimentary canal, starting from the mouth. Saliva in the mouth starts breaking down starch. The stomach mixes food with juices that break down proteins. The small intestine is where most digestion happens. It gets juices from the liver and pancreas. Bile from the liver helps break down fats into tiny droplets, similar to how soap cleans dirt. Pancreatic and intestinal juices finish breaking down carbohydrates into glucose, proteins into amino acids, and fats into fatty acids. These simple forms are then absorbed into the blood through the walls of the small intestine, which have many tiny finger-like parts called villi to help absorb more. Water is absorbed in the large intestine, and leftover waste is removed.

Respiration is how cells get energy from glucose. First, glucose is broken into a smaller molecule called pyruvate. If oxygen is present (aerobic respiration), pyruvate is broken down completely in parts called mitochondria to release a lot of energy, carbon dioxide, and water. If oxygen is not present (anaerobic respiration), like in yeast, pyruvate changes into ethanol and carbon dioxide, releasing less energy. Sometimes, our muscles work without enough oxygen and make lactic acid, which causes cramps. The energy released is stored in a molecule called ATP. ATP is like a tiny battery that powers all cell activities.

Living things need to transport substances. In humans, blood carries food, oxygen, and wastes. The heart pumps blood through tubes called blood vessels. Arteries carry blood away from the heart, and veins bring it back. Capillaries are tiny vessels where exchange happens with cells. Plants use xylem tubes to transport water and minerals from roots to leaves. Transpiration, the loss of water from leaves, helps pull water up. Phloem tubes transport food made in leaves to other parts of the plant. This movement in phloem uses energy.

Excretion removes waste. In humans, kidneys filter blood to remove waste like urea, forming urine. Urine is stored in the bladder and then removed. Each kidney has many tiny filters called nephrons. Plants get rid of wastes in different ways, like storing them in leaves that fall off, or as resins and gums. Oxygen from photosynthesis can also be seen as a plant waste product.

Textbook solutions

Intext Questions and Answers I

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

Answer: In multi-cellular organisms, all the cells may not be in direct contact with the surrounding environment. Thus, simple diffusion will not meet the requirements of all the cells. When the body size of animals is large, the diffusion pressure alone cannot take care of oxygen delivery to all parts of the body. For instance, if diffusion were to move oxygen in our body, it is estimated that it would take 3 years for a molecule of oxygen to get to our toes from our lungs.

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

Answer: We tend to think of some sort of movement, either growth-related or not, as common evidence for being alive. For example, we see a dog running, or a cow chewing cud, or a man shouting loudly, or we see them breathing. For plants, we might say they are green or they grow over time. However, a plant that is not visibly growing is still alive, and some animals can breathe without visible movement, so using visible movement as the defining characteristic of life is not enough.

Movements over very small scales, such as movements of molecules, will be invisible to the naked eye. Professional biologists will say that this invisible molecular movement is necessary for life. Living organisms are well-organised structures; they can have tissues, tissues have cells, cells have smaller components in them, and so on. Because of the effects of the environment, this organised, ordered nature of living structures is very likely to keep breaking down over time. If order breaks down, the organism will no longer be alive. So living creatures must keep repairing and maintaining their structures. Since all these structures are made up of molecules, they must move molecules around all the time. Viruses, for example, do not show any molecular movement in them until they infect some cell, which is partly why there is a controversy about whether they are truly alive or not.

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

Answer: Outside raw materials are used by an organism primarily as a source of energy and for building the body. There must be a process to transfer a source of energy from outside the body of the organism, which we call food, to the inside; this process is commonly called nutrition. These sources of energy need to be broken down or built up in the body and must be finally converted to a uniform source of energy that can be used for the various molecular movements needed for maintaining living structures, as well as for the kind of molecules the body needs to grow.

If the body size of the organisms is to grow, additional raw material will also be needed from outside. Organisms also need materials from outside in order to grow, develop, synthesise protein and other substances needed in the body. Since life on earth depends on carbon-based molecules, most of these food sources are also carbon-based. Autotrophs, for instance, also need other raw materials for building their body, such as water, nitrogen, phosphorus, iron, and magnesium, which are taken up from the soil. Nitrogen is an essential element used in the synthesis of proteins and other compounds.

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

Answer: The maintenance functions of living organisms must go on even when they are not doing anything particular. The processes which together perform this maintenance job are life processes. These processes are essential to maintain life.

These essential processes include:

Nutrition: This is a process to transfer a source of energy from outside the body of the organism, which we call food, to the inside. This energy is needed to prevent damage and break-down of living structures. Additional raw material is also needed from outside if the body size of the organism is to grow.
Respiration: This is the process of acquiring oxygen from outside the body, and using it in the process of break-down of food sources for cellular needs.
Transportation: In multi-cellular organisms, a transportation system is needed for carrying food and oxygen, taken up at one place, to all parts of the body. This system also needs to transport waste away from cells to excretory tissue.
Excretion: When chemical reactions use carbon sources and oxygen for energy generation, they create by-products that are not only useless but could even be harmful. These waste by-products are therefore needed to be removed from the body and discarded outside by this process.

Intext Questions and Answers II

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

Answer: Autotrophic nutrition involves the intake of simple inorganic materials from the environment and using an external energy source like the Sun to synthesise complex high-energy organic material. Heterotrophic nutrition involves the intake of complex material prepared by other organisms.

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

Answer: Plants get carbon dioxide, a raw material required for photosynthesis, from the atmosphere through tiny pores present on the surface of the leaves called stomata; massive amounts of gaseous exchange take place in the leaves through these pores for the purpose of photosynthesis. Water, another raw material used in photosynthesis, is taken up from the soil by the roots in terrestrial plants.

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

Answer: The role of the acid, specifically hydrochloric acid, in our stomach is to create an acidic medium which facilitates the action of the enzyme pepsin.

4. What is the function of digestive enzymes?

Answer: The function of digestive enzymes, which are bio-catalysts, is to break down complex food substances into simpler, smaller molecules. This is done so that these simpler molecules can be absorbed from the alimentary canal and used for the upkeep and growth of the body.

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

Answer: The small intestine is designed to absorb digested food as its inner lining 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.

Intext Questions and Answers III

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

Answer: Terrestrial animals can breathe the oxygen in the atmosphere, but animals that live in water need to use the oxygen dissolved in water. Since the amount of dissolved oxygen is fairly low compared to the amount of oxygen in the air, the rate of breathing in aquatic organisms is much faster than that seen in terrestrial organisms. Terrestrial organisms use the oxygen in the atmosphere for respiration.

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

Answer: Diverse organisms use different ways to break down glucose to provide energy. Some use oxygen to break down glucose completely into carbon dioxide and water, while some use other pathways that do not involve oxygen.

In all cases, the first step is the break-down of glucose, a six-carbon molecule, into a three-carbon molecule called pyruvate. This process takes place in the cytoplasm. Further, the pyruvate may be converted in different ways:

(i) In yeast, during fermentation, which takes place in the absence of air (oxygen) (anaerobic respiration), pyruvate is converted into ethanol and carbon dioxide.
(ii) In our muscle cells, when there is a lack of oxygen, pyruvate is converted into lactic acid, which is also a three-carbon molecule.
(iii) In the mitochondria, in the presence of air (oxygen) (aerobic respiration), the three-carbon pyruvate molecule is broken up to give three molecules of carbon dioxide and water.

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

Answer: In human beings, respiratory pigments take up oxygen from the air in the lungs and carry it to tissues which are deficient in oxygen before releasing it. The respiratory pigment is haemoglobin which has a very high affinity for oxygen and is present in the red blood corpuscles. Thus, oxygen is carried by the red blood corpuscles.

Carbon dioxide is more soluble in water than oxygen is and hence is mostly transported in the dissolved form in our blood plasma. Blood brings carbon dioxide from the rest of the body for release into the alveoli.

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

Answer: Within the lungs, the passage divides into smaller and smaller tubes which finally terminate in balloon-like structures which are called alveoli (singular-alveolus). The alveoli provide a surface where the exchange of gases can take place. The walls of the alveoli contain an extensive network of blood-vessels. If the alveolar surface were spread out, it would cover about 80 m², which demonstrates how efficient exchange of gases becomes because of the large surface available for the exchange to take place. During the breathing cycle, when air is taken in and let out, the lungs always contain a residual volume of air so that there is sufficient time for oxygen to be absorbed and for the carbon dioxide to be released.

Intext Questions and Answers IV

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

Answer: In human beings, blood transports food, oxygen and waste materials. The transport system includes a pumping organ to push blood around the body, a network of tubes to reach all the tissues, and a system in place to ensure that this network can be repaired if damaged. Another type of fluid also involved in transportation is lymph or tissue fluid.

The components and their functions are:

The Heart: The heart is a muscular pumping organ. Its function is to pump blood. It has different chambers to prevent the oxygen-rich blood from mixing with the blood containing carbon dioxide. Oxygen-rich blood is pumped to the rest of the body, and de-oxygenated blood is pumped to the lungs for oxygenation.
Blood Vessels: These are a network of tubes.
- Arteries are the vessels which carry blood away from the heart to various organs of the body.
- Veins collect the blood from different organs and bring it back to the heart.
- Capillaries are the smallest vessels with one-cell thick walls. Exchange of material between the blood and surrounding cells takes place across this thin wall.
Blood: Blood consists of a fluid medium called plasma in which the cells are suspended.
- Plasma transports food, carbon dioxide and nitrogenous wastes in dissolved form.
- Red blood corpuscles carry oxygen.
- Platelet cells circulate around the body and plug leaks by helping to clot the blood at points of injury, which is part of the system to ensure the network can be repaired if damaged.
Lymph (or tissue fluid): This fluid is similar to the plasma of blood but colourless and contains less protein. Lymph carries digested and absorbed fat from the intestine and drains excess fluid from extra cellular spaces back into the blood.

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

Answer: The separation of the right side and the left side of the heart is useful to keep oxygenated and de-oxygenated blood from mixing. Such separation allows a highly efficient supply of oxygen to the body. This is useful in animals that have high energy needs, such as birds and mammals, which constantly use energy to maintain their body temperature.

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

Answer: Plant transport systems will move energy stores from leaves and raw materials from roots. These two pathways are constructed as independently organised conducting tubes. One, the xylem moves water and minerals obtained from the soil. The other, phloem transports products of photosynthesis from the leaves where they are synthesised to other parts of the plant.

4. How are water and minerals transported in plants?

Answer: 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 roots, cells in contact with the soil actively 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 steady movement of water into root xylem, creating a column of water that is steadily pushed upwards.

However, this pressure by itself is unlikely to be enough to move water over the heights that we commonly see in plants. Plants use another strategy to move water in the xylem upwards to the highest points of the plant body. Provided that the plant has an adequate supply of water, the water which is lost through the stomata is replaced by water from the xylem vessels in the leaf. In fact, evaporation of water molecules from the cells of a leaf creates a suction which pulls water from the xylem cells of roots. The loss of water in the form of vapour from the aerial parts of the plant is known as transpiration. Thus, transpiration helps in the absorption and upward movement of water and minerals dissolved in it from roots to the leaves. The effect of root pressure in transport of water is more important at night. During the day when the stomata are open, the transpiration pull becomes the major driving force in the movement of water in the xylem.

5. How is food transported in plants?

Answer: The transport of soluble products of photosynthesis is called translocation and it occurs in the part of the vascular tissue known as phloem. Besides the products of photosynthesis, the phloem transports amino acids and other substances. These substances are especially delivered to the storage organs of roots, fruits and seeds and to growing organs. The translocation of food and other substances takes place in the sieve tubes with the help of adjacent companion cells both in upward and downward directions.

Unlike transport in xylem which can be largely explained by simple physical forces, the translocation in phloem is achieved by utilising energy. Material like sucrose is transferred into phloem tissue using energy from ATP. This increases the osmotic pressure of the tissue causing water to move into it. This pressure moves the material in the phloem to tissues which have less pressure. This allows the phloem to move material according to the plant’s needs. For example, in the spring, sugar stored in root or stem tissue would be transported to the buds which need energy to grow.

Intext Questions and Answers V

1. Describe the structure and functioning of nephrons.

Answer: The basic filtration unit in the kidneys, like in the lungs, is a cluster of very thin-walled blood capillaries. Each capillary cluster in the kidney is associated with the cup-shaped end of a coiled tube called Bowman’s capsule that collects the filtrate. Each kidney has large numbers of these filtration units called nephrons packed close together.

Some substances in the initial filtrate, such as glucose, amino acids, salts and a major amount of water, are selectively re-absorbed as the urine flows along the tube. The amount of water re-absorbed depends on how much excess water there is in the body, and on how much of dissolved waste there is to be excreted. The urine forming in each kidney eventually enters a long tube, the ureter, which connects the kidneys with the urinary bladder. Urine is stored in the urinary bladder until the pressure of the expanded bladder leads to the urge to pass it out through the urethra. The bladder is muscular, so it is under nervous control. As a result, we can usually control the urge to urinate. Normally, in a healthy adult, the initial filtrate in the kidneys is about 180 L daily. However, the volume actually excreted is only a litre or two a day, because the remaining filtrate is re-absorbed in the kidney tubules.

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

Answer: Plants use completely different strategies for excretion than those of animals. Oxygen itself can be thought of as a waste product generated during photosynthesis. Plants deal with oxygen as well as CO2. They can get rid of excess water by transpiration. For other wastes, plants use the fact that many of their tissues consist of dead cells, and that they can even lose some parts such as leaves. Many plant waste products are stored in cellular vacuoles. Waste products may be stored in leaves that fall off. Other waste products are stored as resins and gums, especially in old xylem. Plants also excrete some waste substances into the soil around them.

3. How is the amount of urine produced regulated?

Answer: The amount of water re-absorbed in the nephron depends on how much excess water there is in the body, and on how much of dissolved waste there is to be excreted. Normally, in a healthy adult, the initial filtrate in the kidneys is about 180 L daily. However, the volume actually excreted is only a litre or two a day, because the remaining filtrate is re-absorbed in the kidney tubules. This re-absorption process regulates the amount of urine produced.

Exercise Questions and Answers

1. The kidneys in human beings are a part of the system for

(a) nutrition
(b) respiration
(c) excretion
(d) transportation

Answer: (c) excretion.

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

Answer: (a) transport of water.

3. The autotrophic mode of nutrition requires

(a) carbon dioxide and water
(b) chlorophyll
(c) sunlight
(d) all of the above

Answer: (d) all of the above.

4. The breakdown of pyruvate to give carbon dioxide, water and energy takes place in

(a) cytoplasm
(b) mitochondria
(c) chloroplast
(d) nucleus

Answer: (b) mitochondria.

5. How are fats digested in our bodies? Where does this process take place?

Answer: In our bodies, the small intestine is the site of the complete digestion of fats. The food coming from the stomach is acidic and has to be made alkaline for the pancreatic enzymes to act. Bile juice from the liver accomplishes this in addition to acting on fats. Fats are present in the intestine in the form of large globules which makes it difficult for enzymes to act on them. Bile salts break them down into smaller globules increasing the efficiency of enzyme action. The pancreas secretes pancreatic juice which contains enzymes like lipase for breaking down emulsified fats. The walls of the small intestine contain glands which secrete intestinal juice. The enzymes present in it finally convert fats into fatty acids and glycerol.

6. What is the role of saliva in the digestion of food?

Answer: Saliva is a fluid secreted by the salivary glands. The food is wetted by saliva to make its passage smooth through the digestive tract. Saliva contains an enzyme called salivary amylase that breaks down starch, which is a complex molecule, to give simple sugar.

7. What are the necessary conditions for autotrophic nutrition and what are its by-products?

Answer: The necessary conditions for autotrophic nutrition are the availability of carbon dioxide and water, the presence of chlorophyll to absorb light energy, and sunlight as the external energy source.

The by-products of autotrophic nutrition, specifically photosynthesis, are carbohydrates (glucose), oxygen, and water. Oxygen itself can be thought of as a waste product generated during photosynthesis, and oxygen release is the major event during the day.

8. What are the differences between aerobic and anaerobic respiration? Name some organisms that use the anaerobic mode of respiration.

Answer: The differences between aerobic and anaerobic respiration are:

Aerobic respiration takes place in the presence of air (oxygen). It breaks down the three-carbon pyruvate molecule to give three molecules of carbon dioxide and water. The release of energy in this aerobic process is a lot greater than in the anaerobic process. Aerobic breakdown of pyruvate using oxygen takes place in the mitochondria.

Anaerobic respiration takes place in the absence of air (oxygen). In this process, pyruvate may be converted into ethanol and carbon dioxide, or into lactic acid. The release of energy is less compared to aerobic respiration. For example, the conversion to ethanol and carbon dioxide takes place in yeast during fermentation, and the conversion to lactic acid can occur in our muscle cells when there is a lack of oxygen.

An organism that uses the anaerobic mode of respiration is yeast, which converts pyruvate into ethanol and carbon dioxide during fermentation.

9. How are the alveoli designed to maximise the exchange of gases?

Answer: The alveoli are designed to maximise the exchange of gases in several ways. Within the lungs, the passage divides into smaller and smaller tubes which finally terminate in balloon-like structures called alveoli. These alveoli provide a large surface where the exchange of gases can take place; if the alveolar surface were spread out, it would cover about 80 m². The walls of the alveoli contain an extensive network of blood-vessels, facilitating efficient gas transfer. When air is sucked into the lungs, it fills these expanded alveoli. Furthermore, during the breathing cycle, when air is taken in and let out, the lungs always contain a residual volume of air so that there is sufficient time for oxygen to be absorbed and for the carbon dioxide to be released.

10. What would be the consequences of a deficiency of haemoglobin in our bodies?

Answer: Haemoglobin is the respiratory pigment in human beings which has a very high affinity for oxygen and is responsible for taking up oxygen from the air in the lungs and carrying it to tissues which are deficient in oxygen. If diffusion alone were to move oxygen in our body, it would take a very long time for oxygen to reach all parts. Therefore, a deficiency of haemoglobin would mean that the oxygen delivery to all parts of the body would be severely hampered, as the capacity of blood to carry oxygen would be reduced, leading to insufficient oxygen supply to tissues.

11. Describe double circulation of blood in human beings. Why is it necessary?

Answer: In human beings, double circulation involves blood passing through the heart twice during each cycle. 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 collecting this blood, then contracts, and the blood is transferred to the left ventricle as it relaxes. When the muscular left ventricle contracts, the blood is pumped out to the body. De-oxygenated blood comes from the body to the upper chamber on the right, the right atrium, as it relaxes. As the right atrium contracts, the corresponding lower chamber, the right ventricle, dilates, transferring blood to the right ventricle, which in turn pumps it to the lungs for oxygenation. Thus, blood goes through the heart twice during each cycle.

Double circulation is necessary because the separation of the right side and the left side of the heart is useful to keep oxygenated and de-oxygenated blood from mixing. Such separation allows a highly efficient supply of oxygen to the body. This is useful in animals that have high energy needs, such as birds and mammals, which constantly use energy to maintain their body temperature.

12. What are the differences between the transport of materials in xylem and phloem?

Answer: The differences between the transport of materials in xylem and phloem are:

Xylem:

Materials transported: Xylem moves water and minerals obtained from the soil.
Direction of transport: Xylem moves water upwards from the roots to the highest points of the plant body.
Mechanism: Transport in xylem can be largely explained by simple physical forces. There is a steady movement of water into root xylem creating a column of water that is steadily pushed upwards (root pressure). During the day, when the stomata are open, the transpiration pull becomes the major driving force in the movement of water in the xylem.

Phloem:

Materials transported: Phloem transports products of metabolic processes, particularly photosynthesis (like sucrose), from the leaves where they are formed to other parts of the plant. It also transports amino acids and other substances, especially to storage organs and growing organs.
Direction of transport: The translocation of food and other substances in phloem takes place in both upward and downward directions, according to the plant’s needs.
Mechanism: Translocation in phloem is achieved by utilising energy. Material like sucrose is transferred into phloem tissue using energy from ATP. This increases the osmotic pressure of the tissue, causing water to move into it. This pressure moves the material in the phloem to tissues which have less pressure.

13. Compare the functioning of alveoli in the lungs and nephrons in the kidneys with respect to their structure and functioning.

Answer: Alveoli in the lungs and nephrons in the kidneys are both basic functional units crucial for maintaining life, and both involve close interaction with blood capillaries for exchange or filtration.

Alveoli:

Structure: Alveoli are balloon-like structures at the end of respiratory passages in the lungs. They have very thin walls and are surrounded by an extensive network of blood-vessels, providing a large surface area for gas exchange.
Functioning: The primary function of alveoli is the exchange of gases between the air and the blood. Oxygen from the inhaled air diffuses across the alveolar walls into the blood, while carbon dioxide from the blood diffuses into the alveoli to be exhaled. This exchange occurs primarily by diffusion.

Nephrons:

Structure: Nephrons are the filtration units in the kidneys. Each nephron consists of a cluster of very thin-walled blood capillaries called the glomerulus, associated with a cup-shaped end of a coiled tube called Bowman’s capsule, which collects the filtrate, followed by the tubular part.
Functioning: The function of nephrons is to filter waste products from the blood and produce urine. Blood is filtered under pressure in the glomerulus, and the initial filtrate collected in Bowman’s capsule passes through the tubule. As the urine flows along the tube, essential substances like glucose, amino acids, salts, and a major amount of water are selectively re-absorbed back into the blood. The remaining fluid, containing dissolved wastes like urea or uric acid, forms urine, which is then excreted.

Comparison:

Both alveoli and nephrons are designed to maximize surface area for their respective processes.
Alveoli are primarily involved in gas exchange (O₂ uptake, CO₂ removal) driven by diffusion. Their structure is simple, facilitating this rapid exchange.
Nephrons are involved in a more complex process of blood filtration to remove metabolic wastes and regulate water and solute balance. This involves filtration under pressure and selective reabsorption (and secretion), making their structure more intricate with distinct parts for each step.
Both units are essential for removing waste products from the body – alveoli remove gaseous waste (CO₂), while nephrons remove nitrogenous and other soluble wastes.

Extras

Additional MCQs (Knowledge Based)

1. The process by which autotrophs convert light energy into chemical energy is called:

A. Respiration
B. Photosynthesis
C. Transpiration
D. Nutrition

Answer: B. Photosynthesis

2. The breakdown of pyruvate to yield carbon dioxide, water, and energy occurs in the:

A. Cytoplasm
B. Mitochondria
C. Chloroplast
D. Nucleus

Answer: B. Mitochondria

3. Identify the enzyme present in saliva that breaks down starch.

A. Amylase
B. Trypsin
C. Pepsin
D. Lipase

Answer: A. Amylase

4. Which of the following is the energy currency for most cellular processes?

A. ATP
B. Pyruvate
C. Glucose
D. Starch

Answer: A. ATP

5. Respiration that occurs in the absence of oxygen is known as:

A. Aerobic
B. Cellular
C. External
D. Anaerobic

Answer: D. Anaerobic

6. Which of the following are functions of hydrochloric acid in the stomach?
P. Creates an acidic medium for pepsin
Q. Emulsifies fats
R. Kills germs in food
S. Protects the stomach lining

A. P and Q
B. P and R
C. Q and S
D. R and S

Answer: B. P and R

7. The tiny pores present on the surface of leaves used for gaseous exchange are:

A. Stomata
B. Villi
C. Alveoli
D. Nephrons

Answer: A. Stomata

8. Xylem: Transport of water :: Phloem: ____________.

A. Transport of oxygen
B. Transport of food
C. Gaseous exchange
D. Water absorption

Answer: B. Transport of food

9. Identify the odd one out concerning the components of the human excretory system.

A. Kidney
B. Ureter
C. Alveoli
D. Urethra

Answer: C. Alveoli

10. In humans, the oxygen-rich blood from the lungs first enters which chamber of the heart?

A. Right atrium
B. Left atrium
C. Right ventricle
D. Left ventricle

Answer: B. Left atrium

11. Which of the following is NOT a primary function of blood in the human body?

A. Transport of oxygen
B. Production of hormones
C. Transport of food
D. Transport of waste

Answer: B. Production of hormones

12. The finger-like projections inside the small intestine that increase the surface area for absorption are called:

A. Cilia
B. Alveoli
C. Nephrons
D. Villi

Answer: D. Villi

13. The process of removal of harmful metabolic wastes from the body is termed:

A. Nutrition
B. Respiration
C. Transportation
D. Excretion

Answer: D. Excretion

14. What is the site of complete digestion of carbohydrates, proteins, and fats in the human alimentary canal?

A. Stomach
B. Small intestine
C. Large intestine
D. Oesophagus

Answer: B. Small intestine

15. Identify the respiratory pigment responsible for transporting oxygen in human blood.

A. Chlorophyll
B. Haemoglobin
C. Melanin
D. Myoglobin

Answer: B. Haemoglobin

16. The functional filtration units in the kidneys are known as:

A. Neurons
B. Alveoli
C. Villi
D. Nephrons

Answer: D. Nephrons

17. Select the organism that exhibits heterotrophic nutrition by breaking down food material outside its body and then absorbing it.

Identifier	Organism	Description
W	Amoeba	Engulfs food particles
X	Green plant	Synthesises its own food
Y	Yeast	Secretes enzymes externally
Z	Human	Ingests and digests internally

A. W
B. X
C. Y
D. Z

Answer: C. Y

18. The loss of water in the form of vapour from the aerial parts of a plant is known as:

A. Photosynthesis
B. Respiration
C. Guttation
D. Transpiration

Answer: D. Transpiration

19. The contraction phase of the heart’s ventricles is referred to as:

A. Diastole
B. Systole
C. Peristalsis
D. Diffusion

Answer: B. Systole

20. Which component of blood is primarily involved in the clotting process?

A. Red blood cells
B. White blood cells
C. Plasma
D. Platelets

Answer: D. Platelets

21. What type of circulation is observed in fishes, where blood passes through the heart only once during one complete cycle?

A. Double
B. Single
C. Incomplete
D. Systemic

Answer: B. Single

22. Which of the following events occur during the process of photosynthesis?
P. Absorption of light energy by chlorophyll
Q. Conversion of light energy to chemical energy
R. Reduction of carbon dioxide to carbohydrates
S. Breakdown of glucose

A. P, Q, and R
B. P, Q, and S
C. P, R, and S
D. Q, R, and S

Answer: A. P, Q, and R

23. The movement of food through the alimentary canal by rhythmic contraction of muscles is called:

A. Peristalsis
B. Diffusion
C. Osmosis
D. Emulsification

Answer: A. Peristalsis

24. Identify the substance that is NOT a product of anaerobic respiration in yeast.

A. Ethanol
B. Carbon dioxide
C. Energy
D. Water

Answer: D. Water

25. Which of the following is NOT a method used by plants for excretion?

A. Storing waste in leaves
B. Active transport via nephrons
C. Releasing waste as resins
D. Excreting waste into soil

Answer: B. Active transport via nephrons

26. Bile juice, which aids in fat digestion, is produced by the:

A. Pancreas
B. Stomach
C. Gall bladder
D. Liver

Answer: D. Liver

27. Guard cells: Stomatal opening :: Diaphragm: ____________.

A. Blood filtration
B. Breathing mechanism
C. Food digestion
D. Nerve impulse

Answer: B. Breathing mechanism

28. In which form do plants primarily store carbohydrates that are not used immediately?

A. Glucose
B. Starch
C. Glycogen
D. Cellulose

Answer: B. Starch

29. The initial step in cellular respiration, the breakdown of glucose into pyruvate, takes place in the:

A. Mitochondria
B. Nucleus
C. Chloroplast
D. Cytoplasm

Answer: D. Cytoplasm

30. Identify the structures within the lungs that are the primary sites of gaseous exchange.

A. Bronchi
B. Alveoli
C. Trachea
D. Larynx

Answer: B. Alveoli

Additional MCQs (Competency Based)

1. Assertion (A): During intense physical activity, muscle cells may switch to a pathway that converts pyruvate to lactic acid. [Analysis]
Reason (R): This conversion occurs in the presence of abundant oxygen to maximize energy release.

(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R does not explain A.
(c) A is true but R is false.
(d) A is false but R is true.

Answer: (c) A is true but R is false.

2. A student observes a microscopic single-celled organism in a pond water sample. The organism lacks specialized structures for breathing or feeding. How does this organism likely acquire oxygen and nutrients?

(a) Through active transport mechanisms concentrated in specific cell regions.
(b) Primarily by simple diffusion across its entire cell surface.
(c) By engulfing large particles through a fixed cellular mouth.
(d) Using contractile vacuoles to pump substances inward.

Answer: (b) Primarily by simple diffusion across its entire cell surface.

3. Assertion (A): Desert plants often open their stomata and take in carbon dioxide primarily during the night. [Understanding]
Reason (R): This adaptation helps to minimize water loss through transpiration during the hot, dry daytime conditions.

(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R does not explain A.
(c) A is true but R is false.
(d) A is false but R is true.

Answer: (a) Both A and R are true and R is the correct explanation of A.

4. Match the digestive enzyme with the substance it primarily acts upon:

Column A (Enzyme)	Column B (Substance)
(i) Salivary Amylase	1. Proteins (in stomach)
(ii) Pepsin	2. Emulsified Fats
(iii) Trypsin	3. Starch
(iv) Lipase	4. Proteins (in small intestine)

Codes:

(a) (i)–3, (ii)–1, (iii)–4, (iv)–2
(b) (i)–1, (ii)–3, (iii)–2, (iv)–4
(c) (i)–3, (ii)–4, (iii)–1, (iv)–2
(d) (i)–2, (ii)–1, (iii)–3, (iv)–4

Answer: (a) (i)–3, (ii)–1, (iii)–4, (iv)–2

5. Arrange the following events in the process of human digestion in the correct sequence from initial intake:

(i) Action of pepsin on proteins in an acidic medium.
(ii) Emulsification of fats by bile salts.
(iii) Initial breakdown of starch by salivary amylase.
(iv) Complete digestion of carbohydrates, proteins, and fats by pancreatic and intestinal enzymes.

(a) (iii) → (i) → (ii) → (iv)
(b) (i) → (iii) → (iv) → (ii)
(c) (iii) → (ii) → (i) → (iv)
(d) (ii) → (i) → (iii) → (iv)

Answer: (a) (iii) → (i) → (ii) → (iv)

6. In a healthy adult, approximately 180 litres of filtrate are produced by the kidneys daily. However, only about 1 to 2 litres of urine are excreted per day. What does this significant difference in volume primarily indicate?

(a) Most of the water from the initial filtrate is not needed by the body.
(b) The kidneys are inefficient at filtering waste products.
(c) The bladder has a very large storage capacity for the filtrate.
(d) A vast majority of the water from the initial filtrate is reabsorbed.

Answer: (d) A vast majority of the water from the initial filtrate is reabsorbed.

7. Assertion (A): During the daytime, the major gaseous release from green plants is oxygen. [Understanding]
Reason (R): Carbon dioxide produced during plant respiration in the day is largely utilized for photosynthesis.

(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R does not explain A.
(c) A is true but R is false.
(d) A is false but R is true.

Answer: (a) Both A and R are true and R is the correct explanation of A.

8. A variegated leaf (having green and non-green patches) from a plant that was destarched and then exposed to sunlight for several hours is tested for starch. Which observation is expected?

(a) The entire leaf turns blue-black, indicating starch presence throughout.
(b) Only the non-green patches turn blue-black.
(c) Only the green patches turn blue-black.
(d) No part of the leaf turns blue-black.

Answer: (c) Only the green patches turn blue-black.

9. Match the part of the human respiratory system with its key characteristic or function:

Column A (Part)	Column B (Characteristic/Function)
(i) Nostrils	1. Supported by C-shaped cartilage rings
(ii) Trachea	2. Actual site of gas exchange with blood
(iii) Alveoli	3. Filters incoming air with hairs/mucus
(iv) Diaphragm	4. Muscle that aids in breathing mechanism

Codes:

(a) (i)–3, (ii)–1, (iii)–2, (iv)–4
(b) (i)–1, (ii)–3, (iii)–4, (iv)–2
(c) (i)–3, (ii)–2, (iii)–1, (iv)–4
(d) (i)–4, (ii)–1, (iii)–2, (iv)–3

Answer: (a) (i)–3, (ii)–1, (iii)–2, (iv)–4

10. Sequence the path of deoxygenated blood as it enters the heart and is pumped for oxygenation, then returns as oxygenated blood to be pumped to the body:

(i) Blood is pumped from the right ventricle to the lungs.
(ii) Oxygenated blood flows from the lungs into the left atrium.
(iii) Deoxygenated blood from the body enters the right atrium.
(iv) Oxygenated blood is pumped from the left ventricle to the body.
(v) Blood passes from the right atrium to the right ventricle.

(a) (iii) → (v) → (i) → (ii) → (iv)
(b) (v) → (iii) → (ii) → (i) → (iv)
(c) (iii) → (i) → (v) → (iv) → (ii)
(d) (ii) → (iv) → (iii) → (v) → (i)

Answer: (a) (iii) → (v) → (i) → (ii) → (iv)

11. “The exit of food from the stomach is regulated by a sphincter muscle which releases it in small amounts into the small intestine.” What is the most significant advantage of this controlled release?

(a) It allows the stomach to reabsorb most nutrients before food moves on.
(b) It prevents the food from becoming too alkaline too quickly.
(c) It ensures efficient and complete digestion by not overwhelming the small intestine.
(d) It helps in maintaining a constant body weight by limiting food passage.

Answer: (c) It ensures efficient and complete digestion by not overwhelming the small intestine.

12. It is estimated that if diffusion alone were responsible for oxygen transport in the human body, it would take about 3 years for an oxygen molecule to travel from the lungs to the toes. This fact primarily underscores the:

(a) Extremely slow rate of cellular respiration in toe cells.
(b) Large volume of oxygen required by the human body.
(c) Critical importance of a specialized circulatory system with respiratory pigments.
(d) Inefficient absorption of oxygen by the lungs.

Answer: (c) Critical importance of a specialized circulatory system with respiratory pigments.

13. Statement 1: Autotrophic organisms synthesize complex organic molecules from simple inorganic raw materials using an external energy source.
Statement 2: Heterotrophic organisms derive their energy directly from sunlight to produce their own food.

(a) Both the statements are true.
(b) Both the statements are false.
(c) Statement 1 is true, and Statement 2 is false.
(d) Statement 1 is false, and Statement 2 is true.

Answer: (c) Statement 1 is true, and Statement 2 is false.

14. Assertion (A): Arteries, which carry blood away from the heart, generally possess thick and elastic walls. [Analysis]
Reason (R): The blood flowing through arteries is under high pressure as it is pumped directly from the heart.

(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R does not explain A.
(c) A is true but R is false.
(d) A is false but R is true.

Answer: (a) Both A and R are true and R is the correct explanation of A.

15. Assertion (A): Transpiration, the loss of water vapour from aerial parts of a plant, contributes to the upward movement of water through the xylem. [Understanding]
Reason (R): Root pressure is the sole mechanism responsible for water transport in very tall trees.

(a) Both A and R are true and R is the correct explanation of A.
(b) A is true but R is false.
(c) Both A and R are true but R is not the correct explanation of A.
(d) A is false but R is true.

Answer: (b) A is true but R is false.

16. A person notices they bleed for an unusually long time from a small cut. A deficiency in which component of blood is most likely responsible for this?

(a) Haemoglobin
(b) White blood cells
(c) Plasma
(d) Platelets

Answer: (d) Platelets

17. Match the component of the circulatory system with its primary role:

Column A (Component)	Column B (Primary Role)
(i) Plasma	1. Essential for blood clotting
(ii) Red Blood Corpuscles	2. Carries the respiratory pigment for oxygen transport
(iii) Platelets	3. Fluid medium transporting CO2, food, wastes
(iv) Lymph	4. Tissue fluid similar to plasma but with less protein

Codes:

(a) (i)–3, (ii)–1, (iii)–4, (iv)–2
(b) (i)–2, (ii)–3, (iii)–1, (iv)–4
(c) (i)–4, (ii)–1, (iii)–2, (iv)–3
(d) (i)–3, (ii)–2, (iii)–1, (iv)–4

Answer: (d) (i)–3, (ii)–2, (iii)–1, (iv)–4

18. Assertion (A): In mammals and birds, the heart has four distinct chambers that keep oxygenated and deoxygenated blood completely separate. [Knowledge]
Reason (R): This separation ensures a less efficient supply of oxygen, which is suitable for warm-blooded animals.

(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R does not explain A.
(c) A is true but R is false.
(d) A is false but R is true.

Answer: (c) A is true but R is false.

19. Assertion (A): Viruses exhibit molecular movements and characteristics of life only when they are inside a host cell. [Understanding]
Reason (R): All entities that show molecular movement are definitively classified as living organisms.

(a) Both A and R are true and R is the correct explanation of A.
(b) A is true but R is false.
(c) Both A and R are true but R is not the correct explanation of A.
(d) A is false but R is true.

Answer: (b) A is true but R is false.

20. Assertion (A): The process of obtaining oxygen from outside the body and using it to break down food sources for cellular energy is termed respiration. [Knowledge]
Reason (R): Nutrition is the process by which an organism takes in food and utilizes it.

(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.

Answer: (b) Both A and R are true but R is not the correct explanation of A.

21. Arrange the following structures in the correct order that air passes through them during a normal human inhalation, starting from the external environment:

(i) Alveoli
(ii) Pharynx (Throat)
(iii) Trachea (Windpipe)
(iv) Nostrils
(v) Bronchioles

(a) (iv) → (iii) → (ii) → (v) → (i)
(b) (iv) → (ii) → (v) → (iii) → (i)
(c) (ii) → (iv) → (iii) → (i) → (v)
(d) (iv) → (ii) → (iii) → (v) → (i)

Answer: (d) (iv) → (ii) → (iii) → (v) → (i)

22. An aquatic animal like a fish is observed to open and close its mouth and gill slits much more frequently per minute than a terrestrial mammal breathes. This higher rate in fish is primarily because:

(a) Fish have a higher metabolic rate than mammals.
(b) The concentration of dissolved oxygen in water is significantly lower than in air.
(c) Water is denser than air, requiring more effort to move.
(d) Fish gills are less efficient at extracting oxygen than mammalian lungs.

Answer: (b) The concentration of dissolved oxygen in water is significantly lower than in air.

23. Statement 1: Phloem tissue in plants is responsible for the transport of water and dissolved minerals from the roots to the leaves.
Statement 2: Xylem tissue primarily transports sugars (products of photosynthesis) from the leaves to other parts of the plant, a process requiring energy.

(a) Both the statements are true.
(b) Statement 1 is true, and Statement 2 is false.
(c) Both the statements are false.
(d) Statement 1 is false, and Statement 2 is true.

Answer: (c) Both the statements are false.

24. A person consumes a meal rich in carbohydrates. Which enzyme begins the chemical digestion of these carbohydrates, and where does this process start?

(a) Pepsin in the stomach.
(b) Salivary amylase in the mouth.
(c) Lipase in the small intestine.
(d) Trypsin in the small intestine.

Answer: (b) Salivary amylase in the mouth.

Additional Questions and Answers

1. Define autotrophic nutrition.

2. Define heterotrophic nutrition.

Answer: Heterotrophic nutrition involves the intake of complex material prepared by other organisms.

3. What is nutrition?

Answer: Nutrition is a process to transfer a source of energy from outside the body of the organism, which we call food, to the inside.

4. What is respiration?

Answer: The process of acquiring oxygen from outside the body, and to use it in the process of break-down of food sources for cellular needs, is what we call respiration.

5. What is excretion?

Answer: The biological process involved in the removal of harmful metabolic wastes from the body is called excretion.

6. What is the function of peristaltic movements in the alimentary canal?

Answer: The function of peristaltic movements, which are rhythmic contractions of muscles in the lining of the alimentary canal, is to push the food forward all along the gut.

7. What is the role of bile salts in digestion?

Answer: The role of bile salts in digestion is to break down large globules of fats present in the intestine into smaller globules, thereby increasing the efficiency of enzyme action on them.

8. Why is mucus secreted in the stomach?

Answer: Mucus is secreted in the stomach to protect the inner lining of the stomach from the action of hydrochloric acid under normal conditions.

9. Where does glycolysis occur in the cell?

Answer: The break-down of glucose, a six-carbon molecule, into a three-carbon molecule called pyruvate, which is the first step in respiration (glycolysis), takes place in the cytoplasm.

10. In which organelle does aerobic respiration take place?

Answer: Aerobic respiration, which involves the breakdown of pyruvate using oxygen, takes place in the mitochondria.

11. Which molecule stores energy released during cellular respiration for use in other processes?

Answer: The energy released during cellular respiration is immediately used to synthesise a molecule called ATP, which is used to fuel all other activities in the cell.

12. What is the function of valves in the heart?

Answer: The function of valves in the heart is to ensure that blood does not flow backwards when the atria or ventricles contract.

13. Why do ventricles have thicker walls than atria?

Answer: Ventricles have thicker muscular walls than the atria do because ventricles have to pump blood into various organs.

14. How does transpiration contribute to water movement in plants?

Answer: Transpiration, which is the evaporation of water molecules from the cells of a leaf, creates a suction which pulls water from the xylem cells of roots. Thus, transpiration helps in the absorption and upward movement of water and minerals dissolved in it from roots to the leaves.

15. Which mineral element is essential for protein synthesis in plants?

Answer: Nitrogen is an essential mineral element used in the synthesis of proteins and other compounds in plants.

16. What is the role of Bowman’s capsule in urine formation?

Answer: The role of Bowman’s capsule, which is the cup-shaped end of a coiled tube associated with each capillary cluster in the kidney, is to collect the filtrate during urine formation.

17. What is selective reabsorption in the kidney?

Answer: Selective reabsorption in the kidney is the process where some substances in the initial filtrate, such as glucose, amino acids, salts, and a major amount of water, are re-absorbed as the urine flows along the tube.

18. Where is urine stored before excretion?

Answer: Urine is stored in the urinary bladder until the pressure of the expanded bladder leads to the urge to pass it out through the urethra.

19. Through which structures do plants release oxygen produced during photosynthesis?

Answer: Plants release oxygen produced during photosynthesis through stomata, which are tiny pores present on the surface of the leaves where massive amounts of gaseous exchange takes place.

20. Where are resins and gums stored in plants?

Answer: Resins and gums, which are plant waste products, are stored especially in old xylem.

21. Why do many plants store waste products in leaves and later shed them?

Answer: Many plants store waste products in leaves that fall off as a technique to get rid of waste material, using the fact that they can lose some parts such as leaves.

22. Explain how phloem tissue translocates food from leaves to other parts of the plant.

Material like sucrose is transferred into phloem tissue using energy from ATP. This increases the osmotic pressure of the tissue causing water to move into it. This pressure moves the material in the phloem to tissues which have less pressure. This allows the phloem to move material according to the plant’s needs. For example, in the spring, sugar stored in root or stem tissue would be transported to the buds which need energy to grow.

23. Compare ethanol fermentation and lactic acid fermentation in terms of products and conditions.

Answer: The comparison is as follows:

In ethanol fermentation, pyruvate is converted into ethanol and carbon dioxide. This process takes place in yeast during fermentation and occurs in the absence of air (oxygen); it is a form of anaerobic respiration.
In lactic acid fermentation, which occurs when there is a lack of oxygen in our muscle cells, pyruvate is converted into lactic acid, which is also a three-carbon molecule. This build-up of lactic acid in our muscles during sudden activity causes cramps.

24. Describe how vessels and tracheids are structurally adapted for water transport in plants.

Answer: In xylem tissue, vessels and tracheids of the roots, stems and leaves are structurally adapted for water transport in plants by being interconnected to form a continuous system of water-conducting channels reaching all parts of the plant.

25. Explain how sieve tubes and companion cells work together in the translocation of food.

Answer: Sieve tubes and companion cells work together in the translocation of food as the translocation of food and other substances takes place in the sieve tubes with the help of adjacent companion cells, occurring in both upward and downward directions.

26. Describe the sequence of organs and enzymes involved in the digestion of carbohydrates in the human alimentary canal.

Answer: The digestion of carbohydrates in the human alimentary canal involves the following sequence:

It begins in the mouth. Here, saliva, secreted by the salivary glands, contains an enzyme called salivary amylase that breaks down starch, which is a complex molecule, to give simple sugar.
The small intestine is the site of the complete digestion of carbohydrates. The walls of the small intestine contain glands which secrete intestinal juice. The enzymes present in intestinal juice finally convert complex carbohydrates into glucose.

27. Explain the role of ATP in cellular respiration and how it fuels other reactions.

Answer: During the process of respiration, organic compounds such as glucose are broken down to provide energy in the form of ATP. The energy released during cellular respiration is immediately used to synthesise a molecule called ATP, which is used to fuel all other activities in the cell. ATP is the energy currency for most cellular processes.

In these processes, ATP is broken down, giving rise to a fixed amount of energy which can drive the endothermic reactions taking place in the cell. When the terminal phosphate linkage in ATP is broken using water, energy is released. This ATP is used to provide energy for other reactions in the cell, such as the contraction of muscles, protein synthesis, and conduction of nervous impulses.

28. Explain how the structural features of the human heart, including chamber separation and valves, contribute to efficient double circulation.

Answer: The structural features of the human heart contribute to efficient double circulation in the following ways:

The human heart has different chambers to prevent the oxygen-rich blood from mixing with the blood containing carbon dioxide. The separation of the right side and the left side of the heart is useful to keep oxygenated and de-oxygenated blood from mixing. Such separation allows a highly efficient supply of oxygen to the body, which is essential for efficient double circulation where blood goes through the heart twice during each cycle.
Valves in the heart ensure that blood does not flow backwards when the atria or ventricles contract, further contributing to the efficiency of blood circulation.

29. Explain why transpiration pull is necessary in addition to root pressure for water transport in tall plants.

Answer: Root pressure by itself is unlikely to be enough to move water over the heights that we commonly see in plants, especially tall plants. Therefore, plants use another strategy, transpiration pull, to move water in the xylem upwards to the highest points of the plant body. During the day when the stomata are open, the transpiration pull becomes the major driving force in the movement of water in the xylem, making it necessary in addition to root pressure for adequate water transport in tall plants.

30. Explain how selective reabsorption and filtrate formation in nephrons maintain body-fluid homeostasis.

Answer: Selective reabsorption and filtrate formation in nephrons maintain body-fluid homeostasis through the following processes:

In nephrons, filtrate formation occurs when blood passes through capillary clusters, and the filtrate is collected in Bowman’s capsule. This initial filtrate contains substances like glucose, amino acids, salts, and a major amount of water, along with waste products.
Selective reabsorption then occurs as this filtrate flows along the tube of the nephron. Essential substances such as glucose, amino acids, salts, and a major amount of water are selectively re-absorbed. The amount of water re-absorbed depends on how much excess water there is in the body, and on how much dissolved waste there is to be excreted. This process of filtering out waste products and then selectively reabsorbing necessary water and solutes helps maintain the correct balance of water and dissolved substances in the body, which is crucial for body-fluid homeostasis.

Ron'e Dutta

Ron'e Dutta is a journalist, teacher, aspiring novelist, and blogger who manages Online Free Notes. An avid reader of Victorian literature, his favourite book is Wuthering Heights by Emily Brontë. He dreams of travelling the world. You can connect with him on social media. He does personal writing on ronism.

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