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The iris in the human eye is a muscular structure - AQA - A-Level Biology - Question 1 - 2020 - Paper 1
Question 1
The iris in the human eye is a muscular structure. The iris changes the size of the pupil. Figure 1 shows the muscles in the iris. 1. Suggest and explain how the i... show full transcript
Worked Solution & Example Answer:The iris in the human eye is a muscular structure - AQA - A-Level Biology - Question 1 - 2020 - Paper 1
Step 1
Suggest and explain how the interaction between the muscles labelled in Figure 1 could cause the pupil to constrict (narrow).
Answer
The pupil constricts due to the contraction of the circular muscles in the iris while the radial muscles relax. This changes the shape of the iris, reducing the diameter of the pupil and allowing less light to enter the eye. The coordinated interaction between these muscles is crucial for adapting to bright light conditions.
Step 2
Explain how the fovea enables an eagle to see its prey in detail.
Answer
The fovea is densely packed with cones, which are photoreceptor cells responsible for high visual acuity. The concentration of these cones allows for greater sensitivity to fine detail, enabling the eagle to focus sharply on its prey. Each cone is connected to a single neurone, facilitating precise transmission of visual information to the brain, allowing the eagle to discern small movements and details.
Step 3
Calculate the area of the fovea as a percentage of the area of the retina.
Answer
First, we calculate the area of the fovea using the formula for the area of a circle:
A = rac{ ext{π} d^2}{4}
Given the diameter of the fovea is , converting this to mm gives us . Thus, the area of the fovea is:
A_{fovea} = rac{3.14 imes (3)^2}{4} = 7.065 ext{ mm}^2
Next, we convert the area of the retina, to a percentage:
ext{Percentage} = rac{A_{fovea}}{A_{retina}} imes 100 = rac{7.065}{1094} imes 100 o 0.645 ext{ %}.
Step 4
Explain how this enables an owl to hunt its prey at night.
Answer
The high density of rod cells in the retina of an owl enhances its night vision and overall light sensitivity. Rods are highly sensitive to low light levels, allowing owls to detect movements in dim light. This adaptation is crucial for hunting at night as it enables them to perceive their prey in darkness, thus improving their chances of success in low-visibility conditions.