Cells

What is the resolution of a light microscope?

0.2 μm

What is the resolution of an electron microscope?

0.1 nm

What is magnification?

Image size ÷ actual size

What is resolution?

The minimum distance apart that two objects can be distinguished as separate.

What are the two types of electron microscope?

Transmission electron microscope (TEM) and scanning electron microscope (SEM).

How does a TEM work?

A beam of electrons passes through a thin section of a specimen. Areas that absorb electrons appear darker.

How does an SEM work?

A beam of electrons passes across the specimen surface and scatters, producing a 3D image.

Why do electron microscopes require a vacuum?

To prevent air particles deflecting electrons out of beam alignment.

What are the limitations of electron microscopes?

Vacuum prevents viewing living specimens; complex staining can cause artefacts; specimens must be very thin.

Which has greater resolving power: TEM or SEM?

TEM.

What is cell fractionation?

Separating different parts and organelles of a cell so they can be studied.

What is differential centrifugation?

A method of separating cell organelles by spinning homogenate at increasing speeds.

What is homogenate?

The fluid produced when cells are blended in a homogeniser.

What is a pellet?

The sediment formed at the bottom of a centrifuge tube.

What is a supernatant?

The fluid remaining above the sediment.

Which organelle sediments first during centrifugation?

Nuclei.

Which organelle sediments after nuclei?

Mitochondria.

Why is homogenate kept cold?

To inactivate enzymes that could break down organelles.

Why is homogenate kept in a buffered solution?

To prevent fluctuations in pH.

Why is homogenate kept isotonic?

To prevent organelles bursting due to osmotic pressure.

What are the main features of eukaryotic cells?

A nucleus and membrane-bound organelles.

What surrounds the nucleus?

A double membrane called the nuclear envelope.

What are nuclear pores?

Openings in the nuclear envelope that allow molecules to enter and leave.

What is the function of the nucleolus?

Ribosome production.

What is chromatin?

Material found inside the nucleus.

What is the function of rough endoplasmic reticulum?

Folds and processes proteins made on ribosomes.

What is the function of smooth endoplasmic reticulum?

Produces and processes lipids.

What is the function of the Golgi apparatus?

Processes and packages proteins and lipids; produces lysosomes.

What are mitochondria responsible for?

Respiration.

What are cristae?

Folds of the inner mitochondrial membrane.

What is the mitochondrial matrix?

The inside of the mitochondrion containing enzymes needed for respiration.

What is the function of centrioles?

Producing spindle fibres for cell division.

What are ribosomes?

Structures composed of two subunits; site of protein production.

What are lysosomes?

Vesicles containing digestive enzymes surrounded by a single membrane.

What is the bacterial cell wall made of?

Peptidoglycan.

What is the function of a bacterial capsule?

Helps retain moisture and adhere to surfaces.

What are plasmids?

Circular pieces of DNA.

What is the function of a bacterial flagellum?

Rotates to move the cell.

What is the function of bacterial pili?

Attach to other bacterial cells.

What are mesosomes?

Infoldings of the inner membrane containing enzymes required for respiration.

What is the structure of a virus?

Nucleic acid (DNA or RNA) enclosed in a protein capsid, sometimes with a lipid envelope.

How are cells organised in multicellular organisms?

Cells → tissues → organs → systems.

What is the purpose of mitosis?

Produces genetically identical daughter cells for growth and asexual reproduction.

Does mitosis produce genetic variation?

No, daughter cells are genetically identical.

What happens during interphase?

The cell grows and prepares to divide; chromosomes and some organelles replicate.

What happens during mitosis?

The nucleus divides through prophase, metaphase, anaphase and telophase.

What happens during cytokinesis?

The cytoplasm divides, producing two daughter cells.

What are the three reasons mitosis is important?

Growth, repair and reproduction.

How does binary fission begin?

Circular DNA replicates and both copies attach to the cell membrane. Plasmids also replicate.

What happens during the second stage of binary fission?

The cell membrane grows between the DNA molecules and pinches inwards.

What happens during the final stage of binary fission?

A new cell wall forms, dividing the original cell into two daughter cells.

What do daughter cells produced by binary fission contain?

Each has one copy of circular DNA and a variable number of plasmids.