Solution:

1. Alveoli are richly supplied with blood capillaries to facilitate efficient gas exchange. The extensive capillary network maximizes the surface area for oxygen diffusion into the blood and carbon dioxide diffusion out of the blood, enabling rapid gas exchange due to the short diffusion distance.
2. Hemoglobin, the respiratory pigment in human blood, has a higher affinity for oxygen than carbon dioxide. In the lungs, where oxygen partial pressure is high, hemoglobin readily binds oxygen. Its structure is optimized for oxygen transport, although it carries a smaller amount of carbon dioxide.
3. During anaerobic respiration in human muscle cells, pyruvate (a 3-carbon molecule) is converted into lactic acid instead of being oxidized to CO₂. This occurs due to the absence of oxygen, which prevents complete aerobic respiration, leading to energy production through lactic acid fermentation, causing muscle fatigue.

Solution:

1. The movements occurring along the gut are called peristalsis. Peristalsis involves rhythmic contractions and relaxations of the smooth muscles in the digestive tract. These movements:
   • Mix food: The churning action blends food with digestive enzymes for efficient digestion.
   • Propel food: Peristalsis moves food through the gut, ensuring it is processed in each digestive section.
2. Bile juice is stored in the gallbladder. Two roles of bile juice:
   • Emulsification of fats: Bile salts break down large fat globules into smaller droplets, increasing the surface area for lipase action.
   • Fat-soluble vitamin absorption: Bile aids in the absorption of vitamins A, D, E, and K in the small intestine.

Solution:

Events from fertilization to foetus formation:

1. Fertilization: When a sperm reaches the oviduct, it fuses with the ovum (egg) to form a zygote (diploid cell).
2. Cleavage: The zygote undergoes repeated mitotic cell divisions, forming a morula (solid ball of cells).
3. Blastocyst Formation: The morula develops into a blastocyst, a hollow structure with an inner cell mass (future embryo) and an outer trophoblast layer (future placenta).
4. Implantation: The blastocyst attaches to the uterine wall, embedding into the endometrium.
5. Gastrulation: The inner cell mass differentiates into three germ layers (ectoderm, mesoderm, endoderm), which will form the tissues and organs.
6. Organogenesis: The organs and systems begin to develop from the germ layers.
7. Foetal Development: The embryo continues to grow and develop into a foetus, completing organ formation and maturation.

Role of Placenta in Pregnancy:

• Nutrient and Gas Exchange: The placenta facilitates the exchange of nutrients, oxygen, and waste products between the mother's blood and the foetus.
• Protection: It acts as a selective barrier, protecting the foetus from harmful substances.
• Hormone Production: The placenta produces essential hormones like hCG, progesterone, and estrogen, which maintain pregnancy and support foetal development.

Solution:

The power of accommodation is the ability of the eye to adjust its focus on objects at different distances by changing the shape of the lens.

Part of the Eye: The ciliary muscle plays a major role in accommodation.

1. Focusing on Nearby Objects: The ciliary muscles contract, reducing tension on the suspensory ligaments. This makes the lens thicker and more convex, increasing its refractive power.
2. Focusing on Distant Objects: The ciliary muscles relax, increasing tension on the suspensory ligaments. This makes the lens thinner and less convex, reducing its refractive power.

Solution:

The diagram illustrates:

• Point C: Refraction of sunlight as it enters the raindrop.
• Point B: Internal reflection of light within the raindrop.
• Point A: Dispersion of light into different colors as it exits the raindrop.

Two Necessary Conditions:

1. Sunlight: Sunlight must be present to refract and reflect within raindrops.
2. Water Droplets: A sufficient number of water droplets in the atmosphere (e.g., during rain or mist) to create the visible spectrum.

Solution:

The diagram shows:

1. The current in the conductor is marked with an upward arrow.
2. The magnetic field lines form concentric circles around the conductor, with the direction determined by the right-hand thumb rule.

Right-Hand Thumb Rule: If you hold a current-carrying conductor in your right hand with your thumb pointing in the direction of the current, your curled fingers indicate the direction of the magnetic field lines.

Verification: In the given scenario, the current flows vertically upwards, and according to the right-hand thumb rule, the magnetic field lines follow a counterclockwise direction around the conductor. This aligns with the directions marked in the diagram.

Solution:

The phenomenon involved is biomagnification (or biological magnification).

Explanation:

1. Pesticides in the Environment: Pesticides sprayed on crops enter the environment through water runoff, soil infiltration, or direct consumption by lower trophic level organisms.
2. Bioaccumulation: Primary consumers (e.g., herbivores) ingest the pesticides present in plants or water. These chemicals accumulate in their bodies because they are non-biodegradable.
3. Trophic Level Amplification: Predators consume multiple organisms from lower trophic levels, leading to a higher concentration of pesticides in their bodies. This process repeats at each trophic level.
4. Human Impact: Humans, being at the top of many food chains, accumulate the highest pesticide concentrations. This can lead to severe health effects, including hormonal imbalances, nervous system disorders, and cancers.

Solution:

(i) Carbon has four valence electrons. To achieve a stable octet, carbon would need to:

• Lose four electrons to form C⁴⁺, which is highly unfavorable due to the enormous energy required.
• Gain four electrons to form C⁴⁻, which is unstable due to strong electron-electron repulsion.

Instead, carbon forms covalent bonds by sharing electrons, achieving a stable configuration without forming ions.

(ii) A homologous series is a group of organic compounds with the same functional group, similar chemical properties, and a uniform difference of CH₂ between successive members. Two consecutive aldehydes are:

• Methanal (HCHO)
• Ethanal (CH₃CHO)

(iii) Structure of cyclohexane:

Solution:

(i) A commercially important compound is ethanol (C₂H₅OH).

(ii) Reactions:

• With Sodium: 2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂
  Product: Sodium ethoxide
• With Concentrated Sulfuric Acid: C₂H₅OH → C₂H₄ + H₂O (dehydration)
  Product: Ethene
• With Ethanoic Acid (Esterification): C₂H₅OH + CH₃COOH → CH₃COOC₂H₅ + H₂O
  Product: Ethyl ethanoate
• With Acidified Potassium Dichromate: 3C₂H₅OH + K₂Cr₂O₇ + 4H₂SO₄ → 3CH₃COOH + Cr₂(SO₄)₃ + H₂O
  Product: Ethanoic acid

Solution:

(i) Hormonal Co-ordination: Plants vs. Animals

• Transport: Plant hormones are transported through xylem and phloem; animal hormones use the bloodstream.
• Response: Plant responses are slower; animal responses are faster.
• Specificity: Animal hormones target specific organs; plant hormones influence multiple processes.

(ii) Brain Regions and Functions:

• Intelligence: Controlled by the cerebrum (cerebral cortex).
• Riding a bicycle: Coordinated by the cerebellum for motor control and balance.
• Vomiting: Regulated by the medulla oblongata.
• Controlling hunger: Managed by the hypothalamus.

(iii) Protection of Brain and Spinal Cord:

• Bony Protection: The brain is encased in the skull, and the spinal cord is surrounded by the vertebral column.
• Meninges: Three protective layers (dura mater, arachnoid mater, pia mater) cushion the brain and spinal cord.
• Cerebrospinal Fluid (CSF): CSF acts as a shock absorber, reducing the impact of mechanical forces.

Solution:

(i) Tropic Movements: Directional growth movements in plants in response to a unidirectional stimulus, such as:

• Examples:
  • (1) Inhibits growth: Abscisic acid (ABA).
  • (2) Promotes cell division: Cytokinins.

(ii) Directional Movement in Tendrils (Thigmotropism): When a tendril touches a support, the cells on the side of contact stop growing, while the cells on the opposite side elongate, causing the tendril to bend toward and wrap around the support. Auxin is the hormone responsible for this movement.

Solution:

Image Characteristics (Half-Covered Lens):

• Position: At 2F on the right side of the lens (same as the uncovered lens).
• Nature: Real, inverted, and of the same size as the object.
• The image will be dimmer compared to the uncovered lens because only half of the lens contributes to image formation, reducing brightness.

Difference with Uncovered Lens: An uncovered lens forms a brighter and sharper image since all parts of the lens contribute to refracting light. When part of the lens is covered, fewer light rays contribute, resulting in a dimmer image, but the position and size remain unchanged.

Reason: Even when half of the lens is obscured, sufficient rays from the object refract through the remaining part of the lens to form a complete image. The image intensity is reduced because fewer light rays are utilized in image formation.

Solution:

The lens formula is:

\( \frac{1}{v} - \frac{1}{u} = \frac{1}{f} \)

Where:

• \( u = -30 \, \text{cm} \) (negative because the object is on the left side)
• \( f = -15 \, \text{cm} \) (negative for concave lens)
• \( v \) (image distance, to be determined)

Substitute the values:

\( \frac{1}{v} - \frac{1}{-30} = \frac{1}{-15} \)

\( \frac{1}{v} = -\frac{1}{15} - \frac{1}{30} = -\frac{3}{30} = -\frac{1}{10} \)

\( v = -10 \, \text{cm} \)

Result: The image distance is -10 cm. The negative sign indicates that the image is virtual and on the same side as the object.