NCERT Class 10 Science Solutions: Life Processes

Question:

Cellular Respiration, specifically Aerobic Respiration. The breakdown of pyruvate is a crucial step in aerobic respiration, which releases significant amounts of energy. The location where this process occurs within eukaryotic cells is a key piece of knowledge.


The question asks about the breakdown of pyruvate to produce carbon dioxide, water, and energy. This process is known as aerobic respiration, which occurs in two main stages: glycolysis and the Krebs cycle (also called the citric acid cycle) followed by oxidative phosphorylation. Glycolysis, the initial breakdown of glucose into pyruvate, occurs in the cytoplasm. However, the further breakdown of pyruvate into carbon dioxide, water, and a large amount of energy (ATP) is the primary function of the Krebs cycle and oxidative phosphorylation. These stages of aerobic respiration, where pyruvate is fully oxidized, take place within the mitochondria, often referred to as the “powerhouses” of the cell. Chloroplasts are involved in photosynthesis, and the nucleus contains the cell’s genetic material, neither of which are directly responsible for pyruvate breakdown for energy production.

Answer: B

Question:

The human body has several organ systems that perform specific functions. The question asks to identify the system to which the kidneys belong. Understanding the primary roles of major organ systems in the human body is crucial for answering this question.


The kidneys are vital organs responsible for filtering waste products and excess fluid from the blood to produce urine. This process of removing metabolic waste from the body is known as excretion. The excretory system, which includes the kidneys, ureters, bladder, and urethra, is dedicated to this function. Nutrition involves the intake and utilization of food. Respiration involves the exchange of gases (oxygen and carbon dioxide). Transportation, in a biological context, usually refers to the circulatory system, which carries substances like oxygen, nutrients, and waste products throughout the body, but the kidneys themselves are not the primary transport organs. Therefore, the kidneys are part of the system for excretion.

The final answer is $\boxed{C}$.

Question:

Plants have specialized tissues for transport. Xylem and phloem are the two main vascular tissues. Xylem’s primary role is the movement of water and dissolved minerals upwards from the roots to the rest of the plant. Phloem, on the other hand, transports sugars (food) produced during photosynthesis to various parts of the plant.


The question asks about the function of xylem in plants. Xylem is a complex plant tissue that conducts water and some nutrients from the roots to the leaves. This upward movement is crucial for photosynthesis and maintaining plant structure. While phloem transports food (sugars), xylem is specifically responsible for transporting water. Oxygen is exchanged through stomata and lenticels, not primarily via xylem. Amino acids are transported, but the primary and defining role of xylem is water transport.

The final answer is $\boxed{A}$.

Question:

Organisms are living beings that need to take in substances from their environment to survive and function. These external substances are called raw materials. The primary uses of these raw materials are for energy production, growth, repair, and carrying out life processes.


Organisms use outside raw materials for several essential purposes:

1. Energy Production: Like a car needs fuel, organisms need raw materials to produce energy. For example, plants use sunlight (energy source), carbon dioxide, and water to create glucose through photosynthesis. Animals consume food (which contains organic molecules) and break it down through respiration to release energy for all their activities.

2. Growth and Development: Raw materials provide the building blocks for an organism to grow larger, develop new tissues, and increase in complexity. For instance, proteins, carbohydrates, and minerals are crucial for building bones, muscles, and other body structures.

3. Repair and Maintenance: Cells and tissues constantly get damaged or wear out. Organisms use raw materials to repair these damaged parts and maintain their body’s integrity. This includes repairing wounds, replacing old cells, and maintaining vital functions.

4. Metabolic Processes: Life involves a complex series of chemical reactions called metabolic processes. These reactions require specific raw materials as reactants or as components of enzymes and other molecules that facilitate these processes. For example, water is essential for many biochemical reactions, and minerals act as cofactors for enzymes.

In summary, outside raw materials are fundamental for an organism’s existence, enabling it to obtain energy, grow, heal, and perform all the necessary functions of life.

Question:

Digestion is the process of breaking down complex food molecules into simpler ones that can be absorbed. Fats (lipids) are a type of nutrient that require specific enzymes for their breakdown. Key concepts include enzymes, hydrolysis, emulsification, and the role of different digestive organs.


Fats are digested in our bodies through a process called lipid digestion. This primarily occurs in the small intestine, with some preliminary action in the stomach.

The process begins with bile, produced by the liver and stored in the gallbladder. Bile salts emulsify large fat globules into smaller droplets. This increases the surface area of the fats, making them more accessible to digestive enzymes.

The main enzymes involved in fat digestion are lipases, primarily pancreatic lipase, which is secreted by the pancreas into the small intestine. There are also lingual lipase (secreted in the mouth, active in the stomach) and gastric lipase (secreted in the stomach).

Pancreatic lipase hydrolyzes triglycerides (the main form of dietary fat) into monoglycerides and free fatty acids. These simpler molecules, along with bile salts, form micelles. Micelles are tiny structures that transport the digested fats to the surface of the intestinal cells (enterocytes) for absorption.

After absorption, within the enterocytes, monoglycerides and fatty acids are reassembled into triglycerides and packaged into lipoproteins called chylomicrons. These chylomicrons are then absorbed into the lymphatic system and eventually enter the bloodstream.

Therefore, fat digestion takes place in the stomach (to a limited extent) and primarily in the small intestine.

Question:

The core concept is understanding the fundamental characteristics that distinguish living organisms from non-living matter. These characteristics are universal to all forms of life, regardless of their complexity.


To decide whether something is alive, we look for a set of observable characteristics or processes that are common to all living things. These criteria include:

Growth: Living organisms generally increase in size or number over time. This can be through cell division or an increase in cell size.

Reproduction: Living things can produce offspring, passing on their genetic material to the next generation. This ensures the continuity of the species.

Nutrition: All living organisms need to obtain and utilize food or energy from their environment to sustain life processes.

Respiration: Living beings carry out a process to release energy from the food they consume, typically involving the intake of oxygen and release of carbon dioxide.

Excretion: Organisms eliminate metabolic waste products from their bodies.

Movement: While not all living things move overtly, all exhibit some form of internal movement of substances or have the capacity for movement in response to stimuli.

Responsiveness (Irritability): Living organisms can detect and respond to changes in their environment.

Cellular Organization: All known living organisms are composed of one or more cells, which are the basic units of life.

Metabolism: This refers to the sum of all chemical processes that occur within a living organism to maintain life, including both constructive (anabolism) and destructive (catabolism) processes.

Question:

Digestion involves breaking down complex food molecules into simpler ones that the body can absorb. Saliva is a fluid produced in the mouth that plays a role in the initial stages of this process. Key enzymes and properties of saliva are important to understand.


Saliva plays a crucial role in the digestion of food in several ways:
1. Moistening and Lubricating Food: Saliva contains water and mucin, a glycoprotein. This combination moistens the food particles, making them soft and forming a cohesive bolus (a rounded mass of food). This makes it easier to chew (masticate) and swallow the food, preventing choking.

2. Chemical Digestion of Carbohydrates: Saliva contains an enzyme called salivary amylase (also known as ptyalin). This enzyme begins the chemical breakdown of complex carbohydrates (starches) into simpler sugars, specifically maltose. While this process is initiated in the mouth, it continues for a short while in the stomach until the acidic environment inactivates the salivary amylase.

3. Cleansing the Mouth: Saliva helps to wash away food particles and bacteria from the mouth, thereby preventing tooth decay and maintaining oral hygiene.

4. Antibacterial Action: Saliva contains lysozyme, an enzyme that has antibacterial properties. It helps to kill some of the bacteria present in the food, thus protecting against infections.

5. Taste Perception: Saliva dissolves food particles, allowing the taste buds on the tongue to detect the flavors. Without saliva, we would not be able to properly taste our food.

Question:

Transport system in plants involves vascular tissues (xylem and phloem) responsible for moving water, minerals, and food throughout the plant. Highly organized plants have specialized structures for this efficient transport.


The transport system in highly organized plants is primarily composed of two vascular tissues:

1. Xylem:
* Function: Responsible for the transport of water and dissolved mineral salts from the roots to all other parts of the plant, including the stem, leaves, and flowers. It also provides mechanical support to the plant.
* Components: Xylem tissue is made up of several types of cells: tracheids, vessels, xylem parenchyma, and xylem fibers. Vessels and tracheids are the main water-conducting elements.

2. Phloem:
* Function: Responsible for the translocation of manufactured food (sugars, primarily sucrose) from the leaves (where photosynthesis occurs) to other parts of the plant where it is needed for growth or storage, such as roots, fruits, and growing tips. This process is called translocation.
* Components: Phloem tissue consists of sieve tubes, companion cells, phloem parenchyma, and phloem fibers. Sieve tubes and companion cells are crucial for food transport.

Together, xylem and phloem form the vascular bundles, which are organized into a continuous system throughout the plant, ensuring efficient and timely distribution of essential substances.

Question:

Autotrophic nutrition is the process by which organisms produce their own food using inorganic substances. This process relies on specific environmental factors and internal requirements. Photosynthesis is the primary mechanism for autotrophic nutrition in plants and some other organisms.


The necessary conditions for autotrophic nutrition, primarily photosynthesis, are:

1. Sunlight: This is the energy source that drives the process of photosynthesis. Chlorophyll in the plant cells absorbs light energy.

2. Carbon Dioxide (CO2): This is a raw material that plants take in from the atmosphere through small pores called stomata, usually located on the leaves. CO2 provides the carbon atoms needed to build glucose.

3. Water (H2O): Plants absorb water from the soil through their roots. Water is essential for the chemical reactions of photosynthesis and also provides hydrogen atoms.

4. Chlorophyll: This is a green pigment found in chloroplasts within plant cells. Chlorophyll’s primary role is to capture light energy from sunlight. Without chlorophyll, photosynthesis cannot occur.

5. Suitable Temperature: Photosynthesis is an enzymatic process, and enzymes function optimally within a specific temperature range. Extremely high or low temperatures can denature the enzymes, hindering or stopping the process. Generally, moderate temperatures are favorable.

Question:

Plants do not have specialized excretory organs like animals. Their excretory products are generally less toxic. They get rid of these products through various simple mechanisms, often by storing them or releasing them into the environment.


Plants eliminate excretory products through several methods:

1. Transpiration: Water vapor, a waste product of respiration and photosynthesis, is primarily released through stomata on leaves during transpiration. This is a major way plants get rid of excess water and some dissolved inorganic waste products.

2. Secretion through Lenticels: Some waste products can also be released through lenticels, which are pores on the bark of woody stems and roots.

3. Shedding of Parts: Plants often store waste products in older leaves, bark, or fruits that are eventually shed. For example, fallen leaves carry away accumulated waste. Similarly, waste products can be deposited in fruits that are then eaten by animals or decompose.

4. Deposition in Vacuoles: Waste products, such as resins, gums, and latex, can be stored in specialized vacuoles within plant cells. These may be isolated in dead cells or tissues that are later shed.

5. Secretion into the Soil: Some waste products can be released into the surrounding soil through their roots. This can include organic acids and other compounds.

Question:

The transport of food in plants is primarily carried out by a specialized vascular tissue called phloem. This process is known as translocation and it moves sugars produced during photosynthesis from source (usually leaves) to sink (parts of the plant that need energy, like roots, fruits, and growing tissues). The movement of sugars in the phloem is a passive process driven by pressure gradients and requires energy expenditure by the plant.


Food, mainly in the form of sucrose, is transported throughout a plant by the phloem tissue. This process is called translocation. Photosynthesis in the leaves produces sugars. These sugars are then loaded into the phloem sieve tubes. This loading increases the concentration of sugars in the phloem sap. Water then moves from the xylem into the phloem by osmosis, creating a high pressure at the source. At the sink, where sugars are utilized or stored, they are unloaded from the phloem. This unloading reduces the concentration of sugars, lowering the pressure in the phloem sap at the sink. The pressure difference between the source and the sink drives the bulk flow of phloem sap, carrying the food from where it is produced to where it is needed. This movement is bidirectional, meaning food can be transported up or down the plant depending on the location of the source and sink.

Question:

The stomach secretes hydrochloric acid (HCl). This acid plays a crucial role in digestion by creating an acidic environment. This environment is important for the activation of enzymes and the breakdown of food.


The acid in our stomach, primarily hydrochloric acid (HCl), plays several vital roles in digestion:
1. Activation of Pepsinogen: The stomach secretes an inactive enzyme precursor called pepsinogen. The acidic environment (pH 1.5-3.5) created by HCl converts pepsinogen into its active form, pepsin. Pepsin is the main enzyme responsible for breaking down proteins into smaller peptides.
2. Killing Microorganisms: The highly acidic nature of the stomach acts as a barrier against harmful microorganisms, such as bacteria and viruses, that may be ingested with food. This helps prevent infections and diseases.
3. Denaturation of Proteins: The acid helps to denature proteins. Denaturation unfolds the complex three-dimensional structure of proteins, making them more accessible to enzymatic digestion by pepsin.
4. Aiding in the Absorption of Vitamin B12: While not its primary role, the acidic environment contributes indirectly to the absorption of vitamin B12 by helping to release it from food proteins.

Question:

Diffusion is the movement of substances from an area of high concentration to an area of low concentration. Multi-cellular organisms have many cells, and the oxygen needs to reach all of them.


Diffusion relies on the concentration gradient and the distance over which the substance needs to travel. In multi-cellular organisms, cells are located deep within the organism, far from the external environment. The rate of diffusion is too slow to transport enough oxygen from the surface of the organism to all the internal cells in a timely manner. This is because as the distance increases, the time taken for diffusion also increases significantly. If diffusion were the only means of oxygen transport, the inner cells would not receive sufficient oxygen, leading to their death. Therefore, multi-cellular organisms have evolved specialized respiratory and circulatory systems to facilitate rapid and efficient transport of oxygen to all their cells.

Question:

Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize foods with the help of chlorophyll pigment. The primary raw materials for photosynthesis are carbon dioxide, water, and sunlight.


Plants obtain the raw materials required for photosynthesis from different sources:
1. Carbon Dioxide (CO2): Plants absorb carbon dioxide from the atmosphere through small pores called stomata, which are typically found on the surface of their leaves.
2. Water (H2O): Plants absorb water from the soil through their roots. This water is then transported upwards to the leaves through the xylem vessels.
3. Sunlight: Sunlight, which provides the energy for photosynthesis, is absorbed by chlorophyll, the green pigment present in chloroplasts within plant cells, primarily in the leaves.

Question:

Respiration in living organisms, focusing on the difference in oxygen availability and diffusion in aquatic vs. terrestrial environments. Key concept: gaseous exchange and the medium through which it occurs.


Terrestrial organisms have a significant advantage over aquatic organisms in obtaining oxygen for respiration because atmospheric air contains a much higher concentration of oxygen compared to dissolved oxygen in water. Air, being less dense and less viscous than water, allows for more efficient diffusion of oxygen into the respiratory organs of terrestrial animals (like lungs). Aquatic organisms must extract oxygen from water, which has a lower oxygen content and requires more energy expenditure and specialized respiratory structures (like gills) to achieve sufficient oxygen uptake.

Question:

Digestion is the process of breaking down complex food molecules into simpler ones that can be absorbed by the body. Digestive enzymes are biological catalysts that speed up these chemical reactions.


The function of digestive enzymes is to break down large, complex food molecules into smaller, simpler molecules that the body can absorb and utilize. These enzymes act as biological catalysts, meaning they speed up the chemical reactions of digestion without being consumed in the process. For example, carbohydrates are broken down into simple sugars, proteins into amino acids, and fats into fatty acids and glycerol. This process is essential for obtaining nutrients from the food we eat.

Question:

Autotrophic nutrition is the process where organisms produce their own food, primarily through photosynthesis. Photosynthesis involves converting light energy into chemical energy in the form of glucose. Key inputs are carbon dioxide and water, and the main output is glucose.


The primary by-product of autotrophic nutrition, specifically photosynthesis in plants and algae, is oxygen. While the main goal is to produce glucose (food) for the organism, oxygen is released as a waste product into the atmosphere. Other by-products can include water vapor released through transpiration.