Biological Physics Lecture Summary

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Questions and Answers

What is the approximate fraction of second-hand air in a room when measuring CO2 levels?

$rac{400}{40,000}$ (correct)

$rac{300}{40,000}$

$rac{500}{40,000}$

$rac{200}{40,000}$

What is the approximate speed of mucus particles falling under gravity?

$3 ext{ cm s}^{-1}$ for droplets of radius 10 µm

$1 ext{ cm s}^{-1}$ for droplets of radius 10 µm

$2 ext{ cm s}^{-1}$ for droplets of radius 10 µm (correct)

$2 ext{ cm s}^{-1}$ for droplets of radius 5 µm

How is the mortality rate for a particular cancer defined?

The likelihood of developing cancer in that year

The probability that a person of age t dies from that cancer at that age (correct)

The cumulative risk of dying from that cancer over a lifetime

The expectation of dying from any cause at age t

What does the variable 'K' represent in the model for cancer mortality?

The number of independent random mutations required for cancer Signup and view all the answers

Which factor influences the keeping of aerosol droplets suspended in the air?

Air currents in the room Signup and view all the answers

What does a high Péclet number indicate about flow and diffusion?

Flow dominates diffusion. Signup and view all the answers

In the context of a nanomotor, which of the following is the correct formula for work done?

Work done = force × distance. Signup and view all the answers

What is the approximate information storage capacity of the human genome?

6 billion bits. Signup and view all the answers

What is required for a biochemical switch to operate effectively?

Input must affect output. Signup and view all the answers

Which of the following forces is typical for a nanomotor during its operation?

10 nN. Signup and view all the answers

In terms of cell signaling, what does 'cooperative binding' refer to?

Multiple molecules binding together to affect output. Signup and view all the answers

What type of diseases are transmitted via aerosols?

Airborne infectious diseases. Signup and view all the answers

What happens when the Péclet number is much less than 1?

Diffusion dominates over flow. Signup and view all the answers

What is the relationship between the mass of an animal and its ability to walk on land?

Mass scales with the cube of the height. Signup and view all the answers

Why can water striders walk on water while humans cannot?

Surface tension only increases with contact length, not mass. Signup and view all the answers

In which scenario do gravity forces dominate over surface tension for droplets?

When the Bond number is much greater than 1. Signup and view all the answers

How does the time to diffuse a distance scale with that distance according to the diffusion equation?

It increases as the square of the distance. Signup and view all the answers

What characterizes the time taken to move via flow across a distance?

It increases linearly with the distance. Signup and view all the answers

Which of the following correctly describes the change in droplet shape as its size increases?

Smaller droplets are almost spherical, while larger droplets are flattened. Signup and view all the answers

What does the inequality regarding surface tension and gravity indicate for water striders?

The surface tension force is sufficient to hold them up. Signup and view all the answers

Which factor limits the size of animals that can walk on land?

The cross-sectional area of their femurs. Signup and view all the answers

Study Notes

Biological Physics Revision Lecture Summary

Lecture 1: Fermi Estimation and King Kong
- Stress on femur is limited by bone strength (≤10⁹ Pa)
- Animal leg size is constrained by this.
- Mass scales with size cubed (h³), while load-bearing area of femurs scales with size squared (h²).
Lecture 2: Walking on Water
- Surface tension force must exceed gravity force.
- Surface tension scales with size linearly (h¹), while gravity scales with size cubed (h³).
- This explains why some creatures can walk on water but humans cannot.
Lecture 3: Dimensionless Numbers
- Dimensionless numbers (like the Bond number) compare competing forces.
- The Bond (Bo) number compares gravitational and surface tension forces.
- Little droplets are spherical because surface tension dominates.
- Larger droplets are flattened due to gravity.
Lecture 4: Diffusion, Flow, and Heart Attacks
- Diffusion time is proportional to the square of the distance.
- Diffusion is fast for short distances, slow for long distances.
- Flow is much faster than diffusion over large distances.
Lecture 5: Tiny Motors in Muscles
- Motors are very small, even at nanometer level.
- Maximum force in nanomotors is ~10⁻¹¹N.
- Energy is released from reactions to overcome distance.
Lecture 6: DNA Information and Gene Switches
- DNA storage capacity is enormous.
- Human genome store lots of information.
- Cellular signals trigger switches regulating proteins or genes.
Lecture 7: Airborne Infectious Diseases
- COVID-19 and other diseases spread via aerosols.
- Second-hand air has a higher concentration of relevant gases than the room air itself (e.g., CO₂).
Lecture 8: A Simple Model for Cancer Mortality
- Cancer mortality rate is related to age.
- A power law describes the age and cancer rate (cancer mortality increases with age).
- Cancer is a multi-step process (e.g., mutations).
Lecture 9: Evolution of Milk Drinking
- Evolution is related through common ancestry.
- The proportion of an allele in a population grows exponentially through the generations.
Lecture 10: Aerosol Particles
- Stokes drag affects how fast objects fall.

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Description

This quiz covers essential concepts from biological physics, including Fermi estimation, walking on water, and the importance of dimensionless numbers. Each lecture highlights significant physical principles that govern biological systems and structures. Test your understanding of these fascinating topics and their implications in nature.