Life Processes — NCERT Solutions

Correct Option: (a) transport of water.

Justification: Xylem is a vascular tissue in plants responsible for the unidirectional transport of water and dissolved mineral salts from the roots to the aerial parts (stems and leaves). Transport of food (sugars and amino acids) is carried out by phloem.

Correct Option: (d) all of the above.

Justification: Autotrophic nutrition (photosynthesis) requires carbon dioxide and water as raw materials, chlorophyll as the photosynthetic pigment to absorb light energy, and sunlight as the energy source. The overall equation is:
$$6CO_2 + 6H_2O \xrightarrow{\text{sunlight, chlorophyll}} C_6H_{12}O_6 + 6O_2$$
All three conditions are essential, so the answer is all of the above.

Correct Option: (b) mitochondria.

Justification: Pyruvate (3-carbon compound) formed in the cytoplasm during glycolysis is transported into the mitochondria. Inside the mitochondria, it is completely oxidised (aerobic respiration) to give $CO_2$, $H_2O$, and a large amount of energy in the form of ATP. This is why mitochondria are called the powerhouse of the cell.

Given: Fats are complex biomolecules (lipids) that need to be broken down before absorption.

Location: Fat digestion takes place mainly in the small intestine (specifically the duodenum and jejunum).

Process of Fat Digestion:

Step 1 – Emulsification (Physical breakdown):

• Fats enter the small intestine as large fat globules.
• Bile juice (secreted by the liver and stored in the gall bladder) is released into the duodenum.
• Bile salts break large fat globules into smaller droplets — this process is called emulsification of fats.
• Emulsification increases the surface area of fat for enzyme action.

Step 2 – Chemical Digestion (Enzymatic breakdown):

• The pancreas secretes pancreatic lipase into the small intestine.
• Pancreatic lipase acts on the emulsified fat droplets and breaks them down into fatty acids and glycerol.

$$\text{Fats} \xrightarrow{\text{lipase}} \text{Fatty acids} + \text{Glycerol}$$

Step 3 – Absorption:

• The fatty acids and glycerol are absorbed by the villi of the small intestine.
• They are reassembled into fats inside the intestinal cells and transported via the lymphatic system (lacteals) before entering the bloodstream.

Conclusion: Fat digestion occurs in the small intestine through emulsification by bile and enzymatic hydrolysis by lipase.

Given: Saliva is secreted by the salivary glands in the mouth.

Role of Saliva in Digestion:

1. Contains Salivary Amylase (Ptyalin):

• Saliva contains the enzyme salivary amylase which acts on starch (a complex carbohydrate) and breaks it down into maltose (a simpler sugar).

$$\text{Starch} \xrightarrow{\text{salivary amylase}} \text{Maltose}$$

• This is the first step of chemical digestion and it begins in the mouth itself.

2. Moistens and Lubricates Food:

• Saliva moistens the food, making it easier to chew and swallow.
• It helps in forming a soft, slippery mass called a bolus that can be easily swallowed.

3. Maintains pH:

• Saliva keeps the mouth slightly alkaline (pH ~7), which is the optimum pH for salivary amylase to function.

4. Dissolves Food Substances:

• Saliva dissolves soluble components of food, allowing us to taste them (taste buds detect dissolved substances).

5. Cleanses the Mouth:

• Saliva helps clean the mouth and teeth, preventing bacterial growth.

Conclusion: The primary digestive role of saliva is to begin the digestion of carbohydrates (starch) through the enzyme salivary amylase, while also lubricating food for easy swallowing.

Given: Autotrophic nutrition is the mode of nutrition in which organisms prepare their own food from inorganic substances using an external energy source.

Necessary Conditions for Autotrophic Nutrition (Photosynthesis):

All four conditions must be present simultaneously for photosynthesis to occur.

Overall Equation:
$$6CO_2 + 6H_2O \xrightarrow{\text{sunlight + chlorophyll}} C_6H_{12}O_6 + 6O_2$$

By-products of Autotrophic Nutrition:

1. Oxygen ($O_2$): Released as a by-product during the splitting of water molecules (photolysis of water) in the light reaction. This oxygen is released into the atmosphere through stomata.

2. Water ($H_2O$): A small amount of water is also produced as a by-product.

Conclusion: The necessary conditions are $CO_2$, water, sunlight, and chlorophyll. The main by-product is oxygen, which is vital for all aerobic life on Earth.

Given: Respiration is the process of breaking down food to release energy. It can be aerobic or anaerobic.

Differences between Aerobic and Anaerobic Respiration:

Chemical Equations:

Aerobic:
$$C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{Energy (38 ATP)}$$

Anaerobic (in yeast):
$$C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2 + \text{Energy (2 ATP)}$$

Anaerobic (in muscle cells):
$$C_6H_{12}O_6 \rightarrow 2C_3H_6O_3 \text{ (lactic acid)} + \text{Energy (2 ATP)}$$

Organisms using Anaerobic Respiration:

• Yeast (Saccharomyces cerevisiae) — produces ethanol and $CO_2$
• Some bacteria — e.g., Lactobacillus (produces lactic acid)
• Parasitic worms — e.g., tapeworm (Taenia)
• Human muscle cells — during intense/vigorous exercise when oxygen supply is insufficient (produces lactic acid, causing muscle cramps)

Given: Alveoli are tiny air sacs in the lungs where gaseous exchange (between air and blood) takes place.

Design features of alveoli that maximise gas exchange:

1. Extremely large number:

• Each lung contains approximately 300–400 million alveoli, providing an enormous surface area of about 80 square metres — roughly the size of a tennis court.
• This large surface area allows rapid and efficient diffusion of gases.

2. Very thin walls (one cell thick):

• The walls of alveoli are made of a single layer of squamous epithelial cells, making them extremely thin.
• This reduces the distance over which diffusion must occur, speeding up gas exchange.

3. Rich blood supply (dense capillary network):

• Each alveolus is surrounded by a dense network of blood capillaries.
• This ensures a continuous supply of deoxygenated blood and rapid removal of oxygenated blood, maintaining the concentration gradient for diffusion.

4. Moist surface:

• The inner surface of alveoli is moist, which allows gases ($O_2$ and $CO_2$) to dissolve and diffuse easily across the membrane.

5. Balloon-like (spherical) shape:

• The spherical shape maximises the surface area to volume ratio, allowing more gas exchange per unit volume.

Mechanism:

• $O_2$ diffuses from alveolar air (high concentration) → into blood capillaries (low concentration).
• $CO_2$ diffuses from blood capillaries (high concentration) → into alveolar air (low concentration).

Conclusion: The large number, thin walls, moist surface, and rich capillary network of alveoli collectively maximise the efficiency of gaseous exchange.

Given: Haemoglobin (Hb) is the iron-containing red pigment present in red blood cells (RBCs) that transports oxygen.

Role of Haemoglobin:

• Haemoglobin binds with oxygen in the lungs to form oxyhaemoglobin and releases it to body tissues.
• It also carries a small amount of $CO_2$ from tissues back to the lungs.

Consequences of Haemoglobin Deficiency:

1. Reduced oxygen supply to cells:

• Less haemoglobin means less oxygen is transported to body cells and tissues.
• Cells receive insufficient oxygen for aerobic respiration, leading to reduced energy (ATP) production.

2. Anaemia:

• Deficiency of haemoglobin leads to a condition called anaemia, characterised by fatigue, weakness, and pale skin.

3. Breathlessness and fatigue:

• The body tries to compensate by increasing the breathing rate and heart rate, causing a person to feel breathless even during mild activity.

4. Reduced cellular respiration:

• Cells may be forced to switch to anaerobic respiration, producing lactic acid and causing muscle cramps.

5. Impaired organ function:

• Vital organs like the brain, heart, and muscles receive less oxygen, impairing their function. This can lead to dizziness, headaches, and poor concentration.

6. Reduced $CO_2$ transport:

• Removal of $CO_2$ from tissues becomes less efficient, leading to a build-up of waste gases.

Conclusion: A deficiency of haemoglobin severely impairs oxygen transport, leading to anaemia, fatigue, breathlessness, and reduced efficiency of all body functions.

Given: In human beings, the heart is a four-chambered organ that pumps blood through two separate circuits.

Double Circulation:

Double circulation means that blood passes through the heart twice in one complete circuit of the body. It consists of two circuits:

1. Pulmonary Circulation (Heart → Lungs → Heart):

• Deoxygenated blood from the body collects in the right atrium.
• It passes to the right ventricle, which pumps it to the lungs via the pulmonary artery.
• In the lungs, blood releases $CO_2$ and picks up $O_2$ (becomes oxygenated).
• Oxygenated blood returns to the left atrium via the pulmonary veins.

2. Systemic Circulation (Heart → Body → Heart):

• Oxygenated blood from the left atrium passes to the left ventricle.
• The left ventricle pumps it to the entire body (all organs and tissues) via the aorta.
• Oxygen and nutrients are delivered to body cells; $CO_2$ and wastes are collected.
• Deoxygenated blood returns to the right atrium via the vena cava.

Diagram summary:
$$\text{Body} \rightarrow \text{Right Atrium} \rightarrow \text{Right Ventricle} \rightarrow \text{Lungs} \rightarrow \text{Left Atrium} \rightarrow \text{Left Ventricle} \rightarrow \text{Body}$$

Why is Double Circulation Necessary?

1. Separation of oxygenated and deoxygenated blood:

• The four-chambered heart ensures that oxygenated and deoxygenated blood never mix, so tissues always receive pure, oxygen-rich blood.

2. Efficient oxygen supply:

• Blood is re-pressurised by the left ventricle after returning from the lungs, ensuring it reaches all parts of the body with sufficient pressure.

3. Supports high metabolic rate:

• Warm-blooded animals (like humans) have a high metabolic rate and need a constant, efficient supply of oxygen — double circulation fulfils this need.

Conclusion: Double circulation ensures complete separation of oxygenated and deoxygenated blood, providing efficient oxygen delivery to all body tissues.

Given: Xylem and phloem are the two types of vascular tissue in plants responsible for transport.

Differences between Transport in Xylem and Phloem:

Additional points:

• In xylem, water moves due to the transpiration pull created when water evaporates from leaves, pulling water up from the roots.
• In phloem, food prepared in leaves (source) is transported to storage organs, roots, and growing parts (sink) using energy.

Conclusion: Xylem transports water and minerals upward passively, while phloem transports food in both directions using metabolic energy.

Given: Alveoli are the functional units of the lungs; nephrons are the functional units of the kidneys. Both are highly specialised structures for exchange/filtration.

Comparison of Alveoli and Nephrons:

Similarities:

1. Both alveoli and nephrons have thin walls to facilitate easy exchange/filtration.
2. Both are surrounded by a rich network of blood capillaries.
3. Both have a large surface area to maximise efficiency.
4. Both help in removing waste from the body (alveoli remove $CO_2$; nephrons remove urea and other wastes).
5. Both are present in very large numbers to increase efficiency.

Conclusion: Both alveoli and nephrons are structurally adapted (thin walls, large surface area, rich blood supply) to perform their respective functions of gas exchange and blood filtration efficiently. While alveoli work by simple diffusion, nephrons use a more complex process of filtration, reabsorption, and secretion.