2.1 Cell Structure

Question 1

Describe how a light microscope works.

Answer 1

•Lenses focus rays of light and magnify the view of a thin slice of a specimen
•Different cellular structures absorb different amounts of wavelengths of light
•Reflected light is transmitted to the observer via the objective lens and the eyepiece

Question 2

Describe how a transmission electron microscope (TEM) works.

Answer 2

•A high energy bean of electrons is passed through a thin slice of specimen
•The more dense of the cellular structures appear darker as they absorb more electrons

Question 3

Describe how a scanning electron microscope (SEM) works.

Answer 3

•A beam of electrons is focused onto a specimen’s surface using electromagnetic lenses
•Electrons are then reflected off of the specimen and into a collecting device, which generates an image

Question 4

Describe how a laser scanning confocal microscope works.

Answer 4

•A laser beam is focused onto a small area on a sample’s surface using objective lenses
•A fluorescent stain is added to the sample, which reflects the laser
•A detector then generates an image of the sample pixel by pixel.

Question 5

How should field of view in microscopy be recorded?

Answer 5

•Draw diagram of image
•Include scale bar
•Annotate visible structures

Question 6

State an equation to calculate the actual size of a structure from microscopy.

Answer 6

•Image size = Actual size x Magnification

Question 7

Define magnification and resolution

Answer 7

•Magnification: the factor by which the image is larger than the actual specimen
•Resolution: the smallest separation distance at which 2 separate structures can be distinguished from one another

Question 8

Why do samples need to be stained for light microscopes ?

Answer 8

•Coloured dyes bind to the structures
•Allows for the absorption of some wavelengths of light to produce an image with contrast.

Question 9

What is differential staining ?

Answer 9

•Contrast between heavily and lightly stained areas, allows for distinguishing structures.

Question 10

State the magnification and resolution of a optical light microscope.

Answer 10

•Magnification : x2000
•Resolution : 200nm

Question 11

State the magnification and resolution of a TEM.

Answer 11

•Magnification : x500,000
•Resolution : 0.5nm

Question 12

State the magnification and resolution of a SEM.

Answer 12

•Magnification : x500,000
•Resolution : 3-10nm

Question 13

Explain how to use the eyepiece graticule and stage micrometre to measure the size of a sample’s structures.

Answer 13

•Place micrometre on stage to calibrate eyepiece graticule
•Line up scales on graticule and micrometre. Count how many graticule divisions are in 100µm on mictometre
•Length of 1 eyepiece division = 100µm / number of divisions
•Use calibrated values to calculate actual length of structures

Question 14

Describe the structure of the nucleus.

Answer 14

•It is surrounded by a semipermeable double membrane called the nuclear envelope
•Nuclear pores allow substances to enter/exit
•Dense nucleolus made of RNA and proteins, assembles ribosomes.

Question 15

Describe the function of the nucleus

Answer 15

•Contains DNA coiled around chromatin into chromasones
•Controls cellular processes: gene expression (specialisation and site of mRNA transcription), mitosis, semiconservative replication

Question 16

Describe the structure and function of the endoplasmic reticulum (ER)

Answer 16

•Rough ER: many ribosomes attached for protein synthesis and transport
•Smooth ER: lipid synthesis

Question 17

What is the cisternae?

Answer 17

•The network of tubules and flattened sacs that extends from cell membrane and connects to nuclear envelope
•What makes up the golgi and ERs

Question 18

Describe the structure and function of the golgi apparatus

Answer 18

•A stack of membrane bound flattened sacs.
•It Modifies and packages proteins/lipids for export

Question 19

Describe the structure and function of ribosomes

Answer 19

•It is formed of protein and rRNA
•They have a large subunit which joins to amino acids and a small subunit with an mRNA binding site

Question 20

Describe the relationship between the organelles involved in the production and secretion of proteins.

Answer 20

•The ribosomes that synthesise proteins are attached to the rER
•The golgi apparatus which modifies proteins for secretion aligns with the rER.

Question 21

Describe the structure of a mitochondrion

Answer 21

It is surrounded by a double membrane
It has a folded inner membrane called the cristae

Question 22

Describe the structure of a chloroplast

Answer 22

Contains flattened discs called thylakoids, which contain chlorophyll
Thylakoids are organised into grana
Intergranal lamellae are tubes that attach thylakoids within grana

Question 23

State the function of mitochondria and chloroplasts

Answer 23

Mitochondria: the site if aerobic respiration to produce ATP
Chloroplasts: the site of photosynthesis to convert solar energy into chemical energy

Question 24

Describe the structure and function of a lysosome

Answer 24

A single membrane sac that contains digestive hydrolase enzymes.

Question 25

Describe the structure and function of a plant cell wall

Answer 25

Made of cellulose microfibrils
Plasmodesmata between adjacent cells forms apoplast pathway

Question 26

What are bacterial and fungal cell walls made of ?

Answer 26

Bacteria: peptidoglycan
Fungi: Chitin

Question 27

Describe the structure and function of centrioles.

Answer 27

A group of microtubules
Centrioles migrate to opposite poles of the cell during prophase and spindle fibres form between them

Question 28

Describe the structure and function of the cell surface membrane

Answer 28

Structure:
‘Fluid mosaic’ phospholipid bilayer
Extrinsic proteins (exterior) and intrinsic proteins (through) embedded

Function: Separates cytoplasm for extracellular environment
Selectively permeable to regulate the transport of substances
Involved in cell signalling and recognition

Question 29

Explain the role of cholesterol, glycoproteins and glycolipids in the cell-surface membrane.

Answer 29

Cholesterol: connects phospholipids, increasing packing. Increases fluidity at low temps decreases at higher temps
Glycoproteins: cell signalling, cell recognition (antigens) and binding cells together
Glycolipids: cell signalling and recognition

Question 30

Describe the structure and function of flagella

Answer 30

Hollow tube made of the protein flegellin
Rotates to propel cell

Question 31

Describe the structure and function of cilia

Answer 31

Hairlike protrusions on eukaryotic cells
They move back and forth to sweep foreign substances (eg dust/pathogens) and to enable some movement

Question 32

Why is the cytoskeleton important?

Answer 32

Provides mechanical strength
Aids transport within cells
Enables cell movement

Question 33

What are the differences between prokaryotic and eukaryotic cells

Answer 33

Eukaryotic are larger
Prokaryotic lack membrane bound organelles + nucleus
Eukaryotic have linear chromosomes with histones
Prokaryotic have smaller ribosomes
Prokaryotic divide by binary fission not mitosis/meiosis
Prokaryotic cell wall is made of peptidoglycan not cellulose/chitin
Prokaryotic always have capsule and sometimes cytoskeleton
Eukaryotic have no capsule and always cytoskeleton