Starch is digested to form sugar molecules in the digestive system - AQA - GCSE Biology Combined Science - Question 2 - 2020 - Paper 1

Most food molecules are absorbed in the small intestine.

One advantage of using an electron microscope is that it offers greater magnification, allowing us to see smaller sub-cellular structures or parts.

The blood vessel labelled X is a capillary.

Using the formula: $20 = \frac{\text{size of image}}{\text{size of real object}}$ Given that the real length of one villus is 0.8 mm, we calculate:

the image length is:

$\text{Image length} = 0.8 \times 20 = 16 \text{ mm}$

The process by which sugar moves into cell A is diffusion.

The process by which sugar moves into cell B is active transport.

One use of sugar in the body is to provide energy for cellular respiration.

The villi are adapted for efficient absorption of sugar molecules in several ways:

1. Increased Surface Area: The numerous microvilli on the surface of each villus increase the overall surface area available for absorption, allowing more sugar molecules to be absorbed at once.

2. Thin Wall: The wall of each villus is only one cell thick, facilitating easy and rapid transfer of nutrients across the membrane.

3. Close Capillaries: Capillaries are located close to the surface of the villus, enabling efficient transport of absorbed sugars directly into the bloodstream.

4. Presence of Mitochondria: The cells of the villi contain many mitochondria, which provide the energy necessary for active transport mechanisms to absorb sugar molecules against their concentration gradient.