Cells and Microscopy

Question 1

What resolution can a light microscope achieve?

Answer 1

200nm

Question 2

What magnification can a light microscope achieve?

Answer 2

x 1400

Question 3

What resolution can a TEM achieve?

Answer 3

0.5nm

Question 4

What magnification can a TEM achieve?

Answer 4

300,000

Question 5

What resolution can an SEM achieve?

Answer 5

0.5nm

Question 6

What magnification can an SEM achieve?

Answer 6

300,000

Question 7

What is the difference between an SEM and a TEM.

Answer 7

An SEM gives a 3D picture and cell surface structures can be seen whereas aTEM gives a 2D picture and allows details of organelles to be seen.

Question 8

Explain the difference between magnification and resolution.

Answer 8

Magnification is the number of times larger the image is compared to the object. Resolution is the ability to distinguish between two objects very close together; it enables the viewer to see detail.

Question 9

Explain the need for stains.

Answer 9

Most biological material within a cell isn’t coloured so it might be difficult to distinguish between different features. Coloured stains are used with light microscopes and heavy metallic stains with electron microscopes.

Question 10

What is the use of methylene blue?

Answer 10

Staining living cells; nucleus goes dark blue, cytoplasm goes light blue and bacteria take up the whole stain.

Question 11

What is the use of iodine solution?

Answer 11

Staining living plant cells; very dark blue starch grains.

Question 12

What is the use of acidified phloroglucinol?

Answer 12

Staining lignin; red.

Question 13

What is the use of eosin?

Answer 13

Staining cytoplasm and dead organelles; pink

Question 14

What is the use of acetic orcein?

Answer 14

Staining nuclei and chromosomes; red.

Question 15

What is the use of light green?

Answer 15

Staining plant cell walls; green.

Question 16

How do electron microscope stains work??

Answer 16

Specimens must be thin and stained with heavy metals e.g lead or osmium.
Ions from these metals are taken up more by some parts of a cell than by others.
These ions are positive so electrons do not pass through these areas so do not hit the screen so these areas stay darker.

Question 17

What is the equation that refers to image size, actual size ad magnification?

Answer 17

image size= actual size X magnification

Question 18

List the features of the nucleus.

Answer 18

Usually the largest organelle.
Takes stains up more readily than the cytoplasm so usually appears as a dark area.
Contains all the cell’s genetic material as DNA which has the instructions for protein synthesis.

Question 19

List the features of a general endoplasmic recticulum, and state the function of each type of endoplasmic recticulum.

Answer 19

A network of membranes; some have ribosomes (RER) and some don’t (SER).
RER transports proteins made by the attached ribosomes
SER is involved with making lipids.

Question 20

List the features of the nucleolus.

Answer 20

Dense, spherical structure inside nucleus, usually the darkest and contains the DNA used to make ribosomes and the nucleolus also makes RNA.

Question 21

What is the nuclear envelope?

Answer 21

A membrane surrounding the nucleus (has nuclear pores which allow the movemen of RNA and ribosomes).

Question 22

List the features of the Golgi apparatus.

Answer 22

A stack of curved membranes enclosing a series of flattened sacs.
Some cells may have several.
Constantly changing structure.
At one side tiny membrane bound vesicles move towards the Golgi apparatus and use together; adding a new layer to the stack.
On the other side the sacs break down forming vesicles that move away from the Golgi apparatus.
Modifies and packages proteins received from the RER and makes lysosomes.

Question 23

List the features of a lysosome,

Answer 23

Sperical sacs (0.1 - 0.5 um diameter).
Surrounded by a single membrane.
Contain hydrolytic enzymes.
Break down unwanted structures; organelles or whole cells e.g destruction of bacteria by white blood cells.
Enzymes can be released outside of the cell e.g when cartilage is replaced with bone during development.

Question 24

List the features of a chloroplast.

Answer 24

Site of photosynthesis.
Surrounded by a double membrane called an envelope, these membranes isolate the reactions that take place in the chloroplast from the rest of the cell.
Inside the chloroplast are grana; which form stacks called thykaloids.
The grana contain chlorophyll; this is where the light dependent reactions take place.
Chloroplasts often contain starch grains.

Question 25

List the features of a mitochondrion.

Answer 25

Surrounded by an envelope. Site of anaerobic respiration. In the mitochondrion oxygen and energy containing molecules (produced from glucose) are used to make ATP (the energy currency of a cell). The inner membrane of a mitochondrion is folded to form cristae, which is where ATP is made. The matrix (background material) of the mitochondrion is the site of the stages of anaerobic respiration called the Krebs cycle.

Question 26

List the features of the plasma membrane.

Answer 26

Every cell (and membrane bound organelle) is surrounded by a plasma membrane. It is a thin layer made up of lipid molecules (phospholipid bilayer). Controls what enters / leaves the cell.

Question 27

List the features of centrioles.

Answer 27

Make and organise tiny structures called microtubules which are made of a protein called tubulin. During cell division microtubules form the spindle and are responsible for moving chromosomes around the cell.

Question 28

List the features of cilia and flagella.

Answer 28

They are long thin extensions from the surface of the cell which can produce movement. Cilia are relatively short and found in groups whereas flagella are longer and are usually only found in ones or twos. Both contain microtubules in a 9 + 2 arrangement (2 in the centre, nine pairs around the outside). Movement is produced by these microtubules sliding against each other.

Question 29

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

Answer 29

1. The gene containing the instructions for the production of the hormones is copied onto a piece of mRNA. 2. mRNA leaves the nucleus through a nuclear pore. 3. mRNA attaches to a ribosome. 4. Ribosome reads the instruction to assemble the protein. 5. Molecules are packaged in vesicles and travel towards the golgi apparatus. 6. Vesicle fuses with golgi apparatus 7. Golgi apparatus processes and packages the molecules, ready for release 8. The molecules are ‘pinched off’ in vesicles from the golgi apparatus and move towards the cell surface membrane 9. Vesicles fuse with the cell surface membrane 10. Cell surface membrane opens to release molecules outside (exocytosis).

Question 30

Explain the importance of the cytoskeleton in providing mechanical strength to cells, aiding transport within cells and enabling cell movement.

Answer 30

Provide strength, stability and support to cells. Determines the shape and changes the shape by moving. the membrane for endo and exocytosis. Move organelles such as mitochondria as well as RNA. proteins, chromosomes and chromatids. Move vesicles along microtubule tracks using ATP. Holds organelles in place. They make up centrioles and spindle fibres. They allow whole cells to move using cilia and flagella.

Question 31

Outline how microtubules function.

Answer 31

Microtubules don't move, but provide an anchor for proteins to move along.

Question 32

Outline how cilia and flagella function.

Answer 32

Flagella and cilia are each made from a cylinder containing 9 microtubules. Flagella move with the aid of the protein, Dynein. When a molecule of dynein ‘swivels’ it pulls one microtubule past the next, causing the cilium to bend. Cilia move out of time with each other to create a ‘wave’

Question 33

Outline the differences prokaryotic cells have from eukaryotic cells.

Answer 33

Prokaryotes: Only one membrane (the cell surface membrane) and do not have any membrane bound organelles such as chloroplasts or mitochondria. They have a cell wall made of peptidoglycan (rather than cellulose). Smaller ribosomes. ATP productions takes place in infolded regions called mesosomes. Circular DNA (nucleoid) which is not surrounded by a membrane. Many smaller loops of DNA called plasmids. Many prokaryotes have flagella.