Photo AI
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. Suggest and explain how the inter... 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 interaction between the circular and radial muscles of the iris affects pupil size. When the circular muscles contract, the pupil constricts and becomes smaller, allowing less light to enter the eye. At the same time, the radial muscles relax. This coordinated action is controlled by the autonomic nervous system in response to bright light conditions.
Step 2
Explain how the fovea enables an eagle to see its prey in detail.
Answer
The fovea is a specialized region in the retina that contains a high density of cone cells. This concentration of cones allows for high visual acuity because each cone is connected to a single neurone, which transmits impulses directly to the brain. This separation of impulses ensures that fine details of the eagle's prey are sharply focused and transmitted, providing exceptional visual clarity.
Step 3
Calculate the area of the fovea as a percentage of the area of the retina.
Answer
-
First, calculate the area of the fovea using the formula for the area of a circle:
A = rac{ ext{πd}^2}{4}
The diameter of the fovea is given as μm, which is equal to mm. Therefore, the area of the fovea is:
A_{ ext{fovea}} = rac{3.14 imes (3 imes 10^{-1})^2}{4} = 0.0707 ext{ mm}^2
-
Next, calculate the area of the retina:
-
To find the area of the fovea as a percentage of the area of the retina, use the formula:
ext{Percentage} = rac{A_{ ext{fovea}}}{A_{ ext{retina}}} imes 100
Substituting the values:
ightarrow 0.0064 ext{ %}$$
Step 4
Explain how this enables an owl to hunt its prey at night.
Answer
The retina of an owl has a high density of rod cells, which are highly sensitive to low light levels. This adaptation allows the owl to detect even minimal amounts of light, enhancing its ability to see in dark environments. Furthermore, the convergence of several rod cells onto a single neurone ensures that weak signals are amplified, enabling the owl to perceive its prey in near darkness with high sensitivity.