Life Processes — NCERT Solutions, AI Tutor & Practice

Understanding the term:

Life processes are the basic functions performed by living organisms that are necessary to maintain and sustain life.

The essential life processes are:

1. Nutrition – obtaining and utilising food for energy and growth.
2. Respiration – breaking down food to release energy.
3. Transportation – carrying materials (food, oxygen, wastes) within the body.
4. Excretion – removal of harmful metabolic wastes.

Additional processes such as control and coordination, growth, and reproduction also occur, but the four listed above are directly involved in maintenance of life.

Conclusion: These processes keep body structures functioning and repair molecular wear-and-tear, which is why molecular movements (a sign of these processes) are used to decide whether something is alive.

Understanding diffusion:

Diffusion is the movement of molecules from a region of higher concentration to lower concentration. It is effective only over very short distances.

Analysis:

• In small organisms (e.g. Amoeba), the surface area is large relative to volume, and every cell is close to the surrounding environment, so oxygen can diffuse directly into cells.
• In large multicellular organisms, most cells lie deep inside the body, far from the outer surface.
• Diffusion over such long distances would be extremely slow — it would take an impractically long time for oxygen to reach the innermost cells.

Conclusion: Because diffusion cannot supply oxygen fast enough over large distances, higher organisms need specialised respiratory and circulatory (transport) systems to deliver oxygen efficiently to all cells.

Understanding: Amoeba shows holozoic nutrition — it takes in solid food and digests it inside its body.

Steps of nutrition in Amoeba:

1. Ingestion: Amoeba pushes out finger-like extensions called pseudopodia around the food particle and engulfs it, forming a food vacuole.
2. Digestion: Digestive enzymes are secreted into the food vacuole; complex food is broken down into simpler soluble substances.
3. Absorption: The digested food diffuses from the food vacuole into the surrounding cytoplasm.
4. Assimilation: The absorbed food is used to obtain energy, for growth and repair.
5. Egestion: Undigested material is thrown out when the vacuole fuses with the cell membrane and the residue is expelled.

Conclusion: Amoeba carries out all steps of nutrition within a single cell using pseudopodia and food vacuoles.

1. Aerobic respiration (in presence of oxygen):

$C_6H_{12}O_6 \xrightarrow{\text{in presence of } O_2} 6CO_2 + 6H_2O + \text{Energy (large amount)}$

Glucose is completely broken down in the mitochondria into carbon dioxide and water.

2. Anaerobic respiration in yeast (fermentation):

$C_6H_{12}O_6 \xrightarrow{\text{absence of } O_2} 2C_2H_5OH + 2CO_2 + \text{Energy (small amount)}$

Glucose is converted to ethanol and carbon dioxide in the cytoplasm of yeast.

3. Anaerobic respiration in muscles:

$C_6H_{12}O_6 \xrightarrow{\text{lack of } O_2} 2C_3H_6O_3 \;(\text{lactic acid}) + \text{Energy (small amount)}$

Glucose is converted to lactic acid during vigorous exercise, causing muscle cramps.

Conclusion: Aerobic respiration releases much more energy than anaerobic respiration because glucose is completely oxidised.

Understanding double circulation:

Double circulation means that in one complete cycle, blood passes through the heart twice.

The two circuits:

1. Pulmonary circulation: Right side of heart → lungs → left side of heart. Deoxygenated blood is sent to the lungs to be oxygenated.
2. Systemic circulation: Left side of heart → body tissues → right side of heart. Oxygenated blood is delivered to the body.

Analysis — why it is important:

• The heart has four chambers, keeping oxygenated and deoxygenated blood completely separate.
• This prevents mixing of the two types of blood.
• It ensures an efficient supply of oxygen to tissues.

Conclusion: Double circulation is essential in warm-blooded animals like humans, which need high energy to maintain body temperature.

Definition: Photosynthesis is the process by which green plants make their own food (glucose) using carbon dioxide and water in the presence of sunlight and chlorophyll.

Raw materials: Carbon dioxide ($CO_2$) and water ($H_2O$).

Products: Glucose ($C_6H_{12}O_6$) and oxygen ($O_2$).

Balanced equation:

$6CO_2 + 6H_2O \xrightarrow[\text{Chlorophyll}]{\text{Sunlight}} C_6H_{12}O_6 + 6O_2$

Necessary conditions:

1. Sunlight – provides energy.
2. Chlorophyll – green pigment that absorbs light energy.
3. Carbon dioxide – taken in through stomata.
4. Water – absorbed by roots.

Key events:

• Absorption of light energy by chlorophyll.
• Conversion of light energy to chemical energy and splitting of water into hydrogen and oxygen.
• Reduction of carbon dioxide to carbohydrates.

Conclusion: Photosynthesis stores solar energy as chemical energy in glucose.

Understanding the need: Efficient gas exchange requires a large surface area and close contact between air and blood.

Design features of the lungs:

1. Alveoli: The lungs contain millions of tiny balloon-like sacs called alveoli. They provide a very large surface area (estimated around $80\,m^2$) for gas exchange.
2. Thin walls: Alveolar walls are extremely thin (one cell thick), allowing easy diffusion of gases.
3. Rich blood supply: Alveoli are surrounded by a dense network of blood capillaries, so gases exchange directly with the blood.
4. Moist surface: The inner surface is moist, which helps gases dissolve and diffuse.

Mechanism: Oxygen diffuses from alveolar air into blood; carbon dioxide diffuses from blood into alveolar air to be breathed out.

Conclusion: The alveolar structure maximises surface area and minimises diffusion distance, ensuring efficient gas exchange.

Structure of a nephron:

Each kidney contains many filtering units called nephrons. A nephron consists of:

1. Glomerulus – a cluster of capillaries where filtration occurs.
2. Bowman's capsule – a cup-shaped structure that surrounds the glomerulus.
3. Tubular part – a long, coiled tubule that leads to a collecting duct.

Working of a nephron:

1. Filtration: Blood enters the glomerulus at high pressure. Water, glucose, salts, urea and other small molecules are filtered into Bowman's capsule. Blood cells and proteins are too large and stay in the blood.
2. Selective reabsorption: As the filtrate flows through the tubule, useful substances such as glucose, amino acids, salts and most water are reabsorbed into the surrounding blood capillaries.
3. Urine formation: The remaining liquid, containing urea and excess salts and water, becomes urine.

Collection: Urine from many nephrons is collected in the collecting duct and passes to the ureter → urinary bladder.

Conclusion: The nephron filters blood and reabsorbs useful materials, producing urine to remove nitrogenous wastes.

Understanding: Both arteries and veins are blood vessels but differ in structure and function.

| Feature | Arteries | Veins | |---------|----------|-------| | Direction of flow | Carry blood away from the heart | Carry blood towards the heart | | Type of blood | Usually carry oxygenated blood (except pulmonary artery) | Usually carry deoxygenated blood (except pulmonary vein) | | Wall thickness | Thick, elastic and muscular walls (to withstand high pressure) | Thin walls, less elastic | | Valves | Absent | Present (to prevent backflow of blood) | | Pressure of blood | Blood flows at high pressure | Blood flows at low pressure |

Conclusion: Arteries are built for high-pressure outward flow; veins are built for low-pressure return flow and need valves.

Definition: Translocation is the transport of soluble products of photosynthesis (mainly sucrose) and other substances from the leaves to the rest of the plant through the phloem.

Tissue involved: Phloem, made up of sieve tubes and companion cells.

Mechanism of transport:

1. Food (sucrose) is loaded into the sieve tubes of the phloem using energy from ATP.
2. This increases the concentration of solutes in the phloem, so water moves in from the surrounding tissues by osmosis.
3. This raises the pressure inside the phloem tissue.
4. The pressure moves the material to tissues that have lower pressure (e.g. growing parts or storage organs).

Direction: Translocation can occur in both directions — food can move upward (to growing tips) and downward (to roots) as needed.

Conclusion: Unlike the passive movement of water in xylem, translocation in phloem is an active, energy-requiring process that distributes food throughout the plant.

Understanding: The small intestine is the main site of absorption of digested food.

Structure of villi: The inner wall of the small intestine has many tiny finger-like projections called villi.

Adaptations and role:

1. Large surface area: The villi greatly increase the surface area of the intestinal wall, allowing more digested food to be absorbed.
2. Rich blood supply: Each villus contains a network of blood capillaries that carry absorbed food (glucose, amino acids) into the bloodstream.
3. Thin walls: The walls of villi are thin (one cell thick), enabling easy and quick absorption of digested nutrients.
4. Lymph vessel (lacteal): Each villus also contains a lymph vessel that absorbs digested fats.

Fate of absorbed food: It is carried by blood to all cells for energy, growth and repair (assimilation).

Conclusion: The villi increase surface area and provide a rich blood supply, making the small intestine highly efficient at absorbing nutrients.

Autotrophic nutrition:

• Organisms make (synthesise) their own food from simple inorganic substances such as $CO_2$ and $H_2O$ using sunlight.
• These organisms are called autotrophs.
• Example: Green plants, some bacteria (they carry out photosynthesis).

Heterotrophic nutrition:

• Organisms cannot make their own food and depend on other organisms (plants or animals) for their food.
• These organisms are called heterotrophs.
• Example: Animals such as humans, and fungi.

Differences:

| Autotrophic | Heterotrophic | |-------------|---------------| | Prepares own food | Depends on others for food | | Contains chlorophyll | Generally no chlorophyll | | Uses $CO_2$, water and sunlight | Uses ready-made complex organic food |

Conclusion: Autotrophs are the producers that support heterotrophs, which are consumers in the food chain.