3.2.1.3 Methods of studying cells

What is the main principle behind the functioning of an optical microscope?

• It uses a beam of electrons to create an image.

• It uses visible light to magnify the image of the specimen.

• It uses X-rays to penetrate the specimen.

• It uses sound waves to detect the structure of the specimen.

Answer explanation

The main principle of an optical microscope is that it uses visible light to magnify the image of the specimen, allowing for detailed observation of small structures.

Which of the following is a limitation of transmission electron microscopes (TEM)?

• They can only be used to view living specimens.

• They have a lower resolution compared to optical microscopes.

• They require specimens to be very thin and often dead.

• They cannot achieve high magnification.

Answer explanation

Transmission electron microscopes (TEM) require specimens to be very thin and often dead because the electron beam cannot penetrate thick or living materials, limiting their use to non-living samples.

How does a scanning electron microscope (SEM) differ from a transmission electron microscope (TEM)?

• SEM provides 2D images, while TEM provides 3D images.

• SEM uses light, while TEM uses electrons.

• SEM provides 3D surface images, while TEM provides 2D internal images.

• SEM has a lower magnification than TEM.

Answer explanation

SEM provides 3D surface images by scanning the sample's surface, while TEM provides 2D internal images by transmitting electrons through thin samples, allowing for detailed internal structure visualization.

What is the formula for calculating magnification in microscopy?

• magnification = size of real object / size of image

• magnification = size of image / size of real object

• magnification = size of image + size of real object

• magnification = size of real object - size of image

Answer explanation

The correct formula for calculating magnification in microscopy is magnification = size of image / size of real object. This means that magnification is determined by how much larger the image appears compared to the actual object.

What is the difference between magnification and resolution?

• Magnification refers to the clarity of the image, while resolution refers to the size of the image.

• Magnification is the ability to distinguish two points as separate, while resolution is the enlargement of the image.

• Magnification is the enlargement of the image, while resolution is the ability to distinguish two points as separate.

• Magnification and resolution are the same.

Answer explanation

Magnification is the process of enlarging an image, while resolution refers to the ability to distinguish between two separate points in that image. Thus, the correct choice accurately defines these terms.

Which of the following is a principle of cell fractionation?

• It uses high temperatures to separate cell components.

• It involves breaking cells and separating components based on size and density.

• It uses chemical reactions to dissolve cell components.

• It relies on the magnetic properties of cell components.

Answer explanation

The correct choice states that cell fractionation involves breaking cells and separating components based on size and density. This method allows for the isolation of different organelles, which is essential for studying their functions.

What is ultracentrifugation used for in cell biology?

• To measure the temperature of cell components.

• To separate cell components based on their density.

• To magnify cell components for better viewing.

• To stain cell components for better contrast.

Answer explanation

Ultracentrifugation is a technique used in cell biology to separate cell components based on their density. This allows researchers to isolate specific organelles or proteins for further study.

Why is it important to distinguish between artefacts and cell organelles in microscopy?

• Artefacts are always more important than cell organelles.

• Artefacts can lead to incorrect conclusions about cell structure and function.

• Cell organelles are not visible under a microscope.

• Artefacts are the main focus of cell biology.

Answer explanation

Distinguishing artefacts from cell organelles is crucial because artefacts can mislead researchers, resulting in incorrect interpretations of cell structure and function, which can affect scientific conclusions.

Which of the following is a limitation of optical microscopes?

• They cannot be used to view living specimens.

• They have a lower resolution compared to electron microscopes.

• They require a vacuum to operate.

• They can only be used in complete darkness.

Answer explanation

Optical microscopes have a lower resolution compared to electron microscopes, which limits their ability to resolve fine details. This is a key limitation, as electron microscopes can achieve much higher magnification and resolution.

What is the typical unit of measurement for the size of an object viewed with an optical microscope?

• Miles

• Feet

• Metres

• Micrometres

Answer explanation

The typical unit of measurement for the size of objects viewed with an optical microscope is micrometres, as it allows for precise measurement of small structures, unlike miles, feet, or metres which are too large for microscopic scales.