Answers to Last Issue’s Do You Know?
1. Why is photosynthesis important for life on Earth?
Ans: Most living organisms, including humans, need energy and nutrients to live, but where do these nutrients and energy come from? The answer is photosynthesis. Photosynthesis is the ultimate source of nearly all energy used in all living organisms. This process is carried out by plants, algae, and bacteria to transform the energy of sunlight into chemical energy that can be stored and used by them and other organisms. Also, as a byproduct of photosynthesis, oxygen is released into the air for us to take when breathing.
Because of this, without photosynthesis, life on Earth as we know it would not be possible!

What is photosynthesis?
Photosynthesis is the biological process by which plants use sunlight, water, and carbon dioxide to create oxygen and energy in the form of simple sugars such as glucose and sucrose. During photosynthesis, plants take in carbon dioxide (CO2) and water (H2O) from the air and soil. Inside the plant, the water is converted into oxygen and CO2 into glucose by a chemical process. The plant then releases the oxygen into the air, and stores energy in glucose molecules. Later, this simple sugar is converted into more complex molecules like cellulose, lipids, or amino acids, needed for plants to develop and grow.
As plants can make their own food through photosynthesis, they are called autotrophs or primary producers. They are the basis of ecosystems since other organisms (herbivores) obtain energy by eating them. That includes us as well! Sadly, we cannot use light energy directly to supply our needs. Thus, we depend on plants for oxygen production and food.
So, practically, you and the global population owe your life to photosynthesis!
Photosynthesis is vital for life as it produces the oxygen we breathe, creates the food that forms the base of all food chains (making energy available for all life), and regulates Earth's climate by absorbing carbon dioxide, making the planet habitable. Without it, the atmosphere would lack oxygen, food webs would collapse, and greenhouse gases would rise, making complex life impossible.

Key Roles of Photosynthesis:
Oxygen Production: It's the primary source of atmospheric oxygen, essential for the respiration of most living things (humans, animals, etc.).
Food Source: Plants convert sunlight into chemical energy (sugars), forming the foundation of nearly all food webs; animals eat plants, and other animals eat them, transferring energy up the chain.
Energy Conversion: It's the unique process that captures solar energy and converts it into chemical energy, fueling ecosystems.
Climate Regulation: By consuming carbon dioxide (a greenhouse gas) from the atmosphere, photosynthesis helps control Earth's temperature and mitigate climate change.
Carbon Cycle: It drives the carbon cycle, storing carbon in plant biomass and soils, which is crucial for planetary balance.
Habitat Creation: Plants themselves provide shelter, food, and resources for countless other organisms.
In essence, photosynthesis sustains virtually all life by providing oxygen, food, and energy, and by shaping the Earth's atmosphere and climate.

2. Why is there a differential in a car (or lorry)?
Ans: The function of a differential is to transmit power from the engine to the axle that moves the wheels and allow the wheels to move at different speeds from each other.
You may have seen a bunch of children performing march-past on sports day or even rows of soldiers marching on Republic day. As they turn, the person on the outside of the row must march faster than the person on the inside, who is nearly stationary. Then, when the turn is complete, they will all again be in a straight line. This is because the persons on the inner side travel a smaller circle than those on the outside. The same thing is needed when a car turns: if the wheels on both sides keep turning at the same speed, the car will simply move forward and cannot turn.
A car's differential is a crucial gearbox that splits engine power to the wheels, allowing them to rotate at different speeds, essential for smooth turning. This prevents the tyres from slipping and skidding. It does this by sending more torque (rotatory power) to the outside wheel (which travels farther) and less to the inside wheel (traveling shorter distance). (It also has other functions like changing the direction of power flow by 90 degrees in rear-wheel drive vehicles, acting as a final gear reduction for torque multiplication, enhancing traction, stability, and overall performance.)

Key Roles of the Differential:
Allows Different Wheel Speeds: When turning, the outer wheel covers more ground than the inner wheel, so it needs to spin faster. The differential's gears (spider gears, side gears) accommodate this difference.
Distributes Torque: It sends power (torque) to both wheels, ensuring they both receive it, but allows for speed variations, preventing slippage.
Enhances Traction & Stability: By managing wheel speed, it improves grip and control, especially during cornering.

To understand how it works, first see the picture for a definition of various gears that transmit rotatory forces.

Differential operation while driving in a straight line:
Input torque (rotatory force) is applied to the ring gear (purple), which rotates the carrier (purple) at the same speed. When the resistance from both wheels is the same, the planet gear (green) doesn't rotate on its axis (although the gear and its pin are orbiting due to being attached to the carrier). This causes the sun gears (red and yellow) to rotate at the same speed, resulting in the car's wheels also rotating at the same speed.

Differential operation while turning left:
Input torque is applied to the ring gear (purple), which rotates the carrier (purple) at the same speed. The left sun gear (red) provides more resistance than the right sun gear (yellow), which causes the planet gear (green) to rotate anti-clockwise. This produces slower rotation in the left sun gear and faster rotation in the right sun gear, resulting in the car's right wheel turning faster (and thus travelling farther) than the left wheel.

3. You have heard of temperature of +50oC or -50oC. Is there an absolute zero of temperature?
Ans: For an ideal gas, you may have learned that the pressure at constant volume decreases linearly with temperature (Gay-Lussac's law). Also, the volume at constant pressure also decreases linearly with temperature (Charles' law). If you draw a graph (see figure) of the pressure as a function of temperature for different gas samples (all the time keeping the volume constant), and extrapolate the lines down to zero pressure, you will see that this occurs at a temperature approximately −273.15 °C.
The same is true if we were to plot the volume as a function of temperature. There is no meaning to negative pressure or negative volume; these are unphysical results. So this implies the existence of a lower bound on temperature, an absolute minimum of temperature below which you cannot go.
This led to the concept of absolute temperature, with 0 kelvins defined as the point at which pressure or volume would vanish in an ideal gas. This temperature corresponds to −273.15 °C, and is referred to as absolute zero. The ideal gas law is therefore formulated in terms of absolute temperature to remain consistent with observed gas behavior and physical limits.
There is a catch, though. Entropy is a fundamental concept in science, most simply described as a measure of randomness or disorder in a system. The Second Law of Thermodynamics states that the total entropy of an isolated system tends to increase over time, meaning things naturally move from ordered to more disordered states (like ice melting).
The Third Law of Thermodynamics concerns the behavior of entropy as temperature approaches absolute zero. It states that the entropy of a system approaches a constant minimum at 0 K. However, Nernst heat theorem states that the change in entropy for any constant-temperature process tends to zero as the temperature approaches zero. A key consequence is that absolute zero cannot be reached, since removing heat becomes increasingly inefficient as the system cools, and entropy changes vanish. This unattainability principle means no physical process can cool a system to absolute zero in a finite number of steps or finite time.

4. Sometimes when you have a cold, you can lose balance or feel wobbly. Why?
Ans: In vertebrates, the inner ear is mainly responsible for sound detection and balance. The ear labyrinth is the complex, fluid-filled inner ear structure responsible for hearing and balance. The vestibular system of the inner ear is responsible for the sensations of balance and motion. It uses fluids and detection cells (hair cells) to send information to the brain about the attitude, rotation, and linear motion of the head. The type of motion or attitude detected by a hair cell depends on its associated mechanical structures, such as the curved tube of a semicircular canal or the calcium carbonate crystals (otolith) of the saccule and utricle (see figure).
The vestibular system works with the visual system to keep objects in view when the head is moved. Joint and muscle receptors are also important in maintaining balance. The brain receives, interprets, and processes the information from all these systems to create the sensation of balance.
Losing balance with a cold is common due to inner ear inflammation (labyrinthitis or vestibular neuritis) from the virus, which disrupts balance signals; sinus pressure affecting the ears; dehydration from fever; fatigue; or even cold weather affecting circulation and inner ear fluid. This dizziness (vertigo) often subsides as the illness clears, but staying hydrated, resting, and avoiding sudden head movements helps manage symptoms
Vertigo is most often caused by inner ear conditions affecting balance. Following a cold or ear infection, inflammation in the inner ear or vestibular nerve can disrupt the signals between your ear and brain, leading to vertigo.
Here are the most common conditions:
1. Labyrinthitis: It is an inner ear infection that inflames the labyrinth, a coiled part of the inner ear responsible for balance and hearing. It’s usually caused by a viral infection that develops during or after a cold. Symptoms include vertigo, hearing loss, and ringing in the ears.
2. Vestibular Neuronitis: It occurs when the vestibular nerve, which helps control balance, becomes inflamed. Like labyrinthitis, it’s typically caused by a viral infection. While hearing usually remains unaffected, the vertigo can be intense, lasting days or even weeks.
3. Benign Paroxysmal Positional Vertigo (BPPV): This occurs when tiny calcium particles in the inner ear become dislodged and interfere with balance signals. Though often triggered by changes in head position, BPPV can sometimes follow an ear infection. The Epley manoeuvre, performed by specialists, is a common treatment to resolve this issue.
Sources:
https://labassociates.com/photosynthesis-the-basis-of-life-on-earth; Wikipedia