細胞結構與特化細胞：练习题

A student carries out standard chemical food tests on a liquid sample. When Biuret reagent is added to the sample, the colour changes from blue to purple.
Which type of biological molecule is present in the sample?

Which statement correctly explains how sperm cells are adapted for their function through their sub-cellular structures?

An enzyme-controlled reaction is occurring at its optimum pH. If the pH is significantly increased, the rate of reaction drops to zero. Which of the following best explains this at a molecular level?

A student uses a microscope to observe a cell. The diagram shows a typical plant cell. Which of the following sub-cellular structures is only found in plant cells and not in animal cells?

A student uses an electron microscope to observe a mitochondrion. The image length of the mitochondrion is \(35\text{ mm}\). If the actual length of the mitochondrion is \(2.5\,\mu\text{m}\), what is the magnification of the image?

Explain how the structure of mitochondria within an animal cell is related to its primary function.

A student observes a bacterial cell under a microscope. Explain how the functions of plasmid DNA and chromosomal DNA differ within this cell.

Explain how the high number of mitochondria in a sperm cell is related to its specific function during reproduction.

A student carried out a practical investigation to test samples of food for the presence of different biological molecules.

(a) State the chemical reagent used to test a food sample for the presence of starch and describe the positive colour change observed.

(b) Describe how the student should safely test a liquid food sample for the presence of reducing sugars using Benedict's solution.

(c) State the reagent used to test for protein and give the colour that indicates a positive result.

A group of students investigated the effect of pH on the activity of the enzyme amylase. Amylase breaks down starch into maltose. In their experiment, they mixed amylase and starch solutions at different pH levels and recorded the time taken for the starch to be completely broken down.

a) Explain the mechanism of enzyme action, including the importance of the active site and why enzymes are described as having specificity.
b) At pH 7, the starch was broken down in 120 seconds. Calculate the rate of reaction in \(\text{s}^{-1}\). Give your answer in standard form.
c) Explain why the rate of reaction would decrease significantly if the students repeated the experiment at pH 12.