Question 1

1. In a resting neuron, the $Na^+/K^+$ pump actively transports ions across the membrane to maintain the electrochemical gradient. If the pump moves 300 $Na^+$ ions out of the cell, how many $K^+$ ions are simultaneously moved into the cell?

A) 150 ionsB) 200 ionsC) 450 ionsD) 600 ions

Answer

✓ Correct Answer: Option B

Explanation: Explanation: The $Na^+/K^+$ ATPase pump operates in a fixed ratio of $3 Na^+$ out for every $2 K^+$ in. Given: $Na^+_{out} = 300$. Let $K^+_{in} = x$. Setting up the ratio: $$\frac{3}{2} = \frac{300}{x}$$ $3x = 600 ⇒ x = 200 ions.$

Question 2

2. A graph of an Action Potential shows the membrane potential (y-axis) in mV vs Time (x-axis) in ms. If the resting potential is -70 mV and the threshold potential is -55 mV, what is the minimum voltage change (\Delta V) required to trigger an "all-or-none" response?

-15 mV

Question 3

3. Consider a myelinated axon of length L = 1.8 meters. If the nerve impulse travels via saltatory conduction at a velocity of v = 120m/s, calculate the time t taken for the signal to reach the axon terminal.

A) 15 msB) 1.5 msC) 0.15 sD) 150 ms

Answer

✓ Correct Answer: Option A

Explanation: Explanation: Velocity $v = \frac{L}{t} ⇒ t = \frac{L}{v}$. $$t = \frac{1.8m}{120m/s} = 0.015 seconds.$$ To convert to milliseconds: $0.015 \times 1000 = 15 ms$.

Question 4

4. In a chemical synapse, a delay occurs due to neurotransmitter release and diffusion. If a reflex arc involves 3 synapses with a delay of 0.5 ms each, and the total conduction time through the neurons is 12 ms, what is the total reflex latency?

A) 12.5 msB) 15 msC) 36 msD) 13.5 ms

Answer

✓ Correct Answer: Option D

Explanation: Explanation: Total Latency = Conduction Time + (Number of Synapses $\times$ Synaptic Delay). $$T = 12 ms + (3 \times 0.5 ms) = 12 + 1.5 = 13.5 ms.$$

Question 5

5. Visual acuity is highest at the Fovea Centralis. If the density of cones in the fovea is $150,000 per mm^2$ and the density of rods in the peripheral retina is $160,000 per mm^2$, but the fovea contains ZERO rods, what is the ratio of Rods to Cones in a $1 mm^2$ sample taken exactly from the foveal center?

A) 16:15B) 1:1C) 0:1D) 15:16

Answer

✓ Correct Answer: Option C

Explanation: Explanation: In the fovea centralis, only cones are present. Rods are entirely absent. $$Ratio = \frac{Rods}{Cones} = \frac{0}{150,000} = 0.$This is cleanly expressed as a0:1$ ratio.

Question 6

6. The human ear can distinguish frequencies from 20 Hz to 20,000 Hz. If a specific sound wave has a wavelength of \lambda = 1.7cm in air (where speed of sound v = 340m/s), determine if this frequency falls within the human audible range.

A) No, it is 2,000 Hz (Infra-sonic)B) Yes, it is 20,000 Hz (Upper limit)C) Yes, it is 200 HzD) No, it is 200,000 Hz (Ultra-sonic)

Answer

✓ Correct Answer: Option B

Explanation: Explanation: Frequency $f = \frac{v}{\lambda}$. Convert \lambda to meters: 1.7cm = 0.017m. $$f = \frac{340}{0.017} = \frac{340000}{17} = 20,000 Hz.$$ This value marks the exact upper limit of standard human hearing capabilities.

Question 7

7. A patient has a defect in the refractive power of the eye. If the focal length of the eye lens is 2 cm, what is its power P in Dioptres (D)? (Use P = 1/f where f is in meters).

A) 50 DB) 2 DC) 0.5 DD) 20 D

Answer

✓ Correct Answer: Option A

Explanation: Explanation: First, convert the focal length to meters: $f = 2cm = 0.02m.$ Now solve for power: $$P = \frac{1}{f} = \frac{1}{0.02} = \frac{100}{2} = 50 Dioptres.$$

Question 8

8. During the Repolarization phase of an action potential, the permeability of the membrane to $K^+$ increases significantly. If the efflux of $K^+$ ions results in the potential dropping from +30 mV to -70 mV in 1 ms, what is the rate of voltage change?

A) 40 mV/msB) -40 mV/msC) 100 mV/msD) -100 mV/ms

Answer

✓ Correct Answer: Option D

Explanation: Explanation: Rate of change = $\frac{V_{final} - V_{initial}}{\Delta t}$. $$Rate = \frac{-70 mV - (+30 mV)}{1 ms} = \frac{-100 mV}{1 ms} = -100 mV/ms.$$

Question 9

9. The human brain contains approximately 100 billion neurons. If each neuron has an average of 1,000 synapses, estimate the total number of synaptic connections in the brain using scientific notation.

A) $10^{11}$B) $10^{14}$C) $10^{12}$D) $10^{15}$

Answer

✓ Correct Answer: Option B

Explanation: Explanation: Total synapses = Neurons $\times$ Synapses per neuron. $$100 billion = 100 \times 10^9 = 10^{11} neurons.$$ $$Total = 10^{11} \times 1,000 = 10^{11} \times 10^3 = 10^{14} connections.$$

Question 10

10. Imagine a cross-section of the spinal cord. If there are 31 pairs of spinal nerves, how many total individual roots (dorsal and ventral) exit the spinal cord in total?

A) 31B) 62C) 124D) 93

Answer

✓ Correct Answer: Option C

Explanation: Explanation: There are 31 pairs of nerves (62 individual nerves total). Each singular spinal nerve splits into or is formed by the union of exactly one dorsal root and one ventral root. $$Total roots = 31 pairs \times 2 nerves/pair \times 2 roots/nerve = 124 roots.$$

Accepted Answer

✓ Correct Answer: Option C

Explanation: Explanation: The threshold stimulus is the minimum depolarization required. $$\Delta V = V_{threshold} - V_{resting}$$ $\Delta V = -55 mV - (-70 mV) = -55 + 70 = +15 mV.$

Grade 11 Biology: Neural Quiz

1. In a resting neuron, the $Na^+/K^+$ pump actively transports ions across the membrane to maintain the electrochemical gradient. If the pump moves 300 $Na^+$ ions out of the cell, how many $K^+$ ions are simultaneously moved into the cell?

2. A graph of an Action Potential shows the membrane potential (y-axis) in mV vs Time (x-axis) in ms. If the resting potential is -70 mV and the threshold potential is -55 mV, what is the minimum voltage change (\Delta V) required to trigger an "all-or-none" response?

3. Consider a myelinated axon of length L = 1.8 meters. If the nerve impulse travels via saltatory conduction at a velocity of v = 120m/s, calculate the time t taken for the signal to reach the axon terminal.

4. In a chemical synapse, a delay occurs due to neurotransmitter release and diffusion. If a reflex arc involves 3 synapses with a delay of 0.5 ms each, and the total conduction time through the neurons is 12 ms, what is the total reflex latency?

6. The human ear can distinguish frequencies from 20 Hz to 20,000 Hz. If a specific sound wave has a wavelength of \lambda = 1.7cm in air (where speed of sound v = 340m/s), determine if this frequency falls within the human audible range.

7. A patient has a defect in the refractive power of the eye. If the focal length of the eye lens is 2 cm, what is its power P in Dioptres (D)? (Use P = 1/f where f is in meters).

8. During the Repolarization phase of an action potential, the permeability of the membrane to $K^+$ increases significantly. If the efflux of $K^+$ ions results in the potential dropping from +30 mV to -70 mV in 1 ms, what is the rate of voltage change?

9. The human brain contains approximately 100 billion neurons. If each neuron has an average of 1,000 synapses, estimate the total number of synaptic connections in the brain using scientific notation.

10. Imagine a cross-section of the spinal cord. If there are 31 pairs of spinal nerves, how many total individual roots (dorsal and ventral) exit the spinal cord in total?