Cell structure and division

Question 1

How do algal cells differ from plant cells?

Answer 1

Algae can be either unicellular or multicellular

Chloroplasts are a different shape and size to plant cell chloroplast

Question 2

plant cell vs animal cell

Answer 2

plant cells have a vacuole, cell wall (with channels) , chloroplast

Question 3

How do fungal cells differ from plant cells?

Answer 3

Fungi can be either unicellular or multicellular
They don’t have chloroplasts
Their cell walls are made of chitin, not cellulose

Question 4

describe the structure and function of the nucleus

Answer 4

Structure: organelle surrounded by nuclear envelope which has nuclear pored on its surface. Function: contains chromosomes which contain instructions to make proteins and a nucleolus which makes ribosomes

Question 5

Describe the structure and function of mitochondria in Eukaryotic cells.

Answer 5

Oval shaped organelle surrounded by a double membrane, the inner of which is highly folded to form cristae. The matrix within contains enzymes involved in respiration.

Question 6

Describe the structure and function of chloroplasts in Eukaryotic cells.

Answer 6

Oval shaped organelle surrounded by a double membrane and also has membranes within called thylakoids which stack to form grana where some of the reactions of photosynthesis occur. Other reactions occur in the stroma within the chloroplast.

Question 7

Describe the structure and function of Golgi apparatus in Eukaryotic cells.

Answer 7

Fluid filled membrane-bound flattened sacs, from which vesicles can bud off. It processes and packages new lipids and proteins and also makes lysosomes

Question 8

Describe the structure and function of lysosomes in Eukaryotic cells.

Answer 8

A lysosome is a type of Golgi vesicle containing digestive enzymes used to digest invading cells or to break down worn out cell components.

Question 9

Describe the structure and function of ribosomes in Eukaryotic cells.

Answer 9

Made up of protein and rRNA, it can either be free in the cytoplasm or attached to membranes of the RER. Ribosomes are the site of protein synthesis

Question 10

Describe the structure and function of the Rough endoplasmic reticulum (RER).

Answer 10

System of fluid filled membranes with many ribosomes attached, which folds and processes proteins made at the ribosome.

Question 11

Describe the structure and function of the Smooth endoplasmic reticulum (SER).

Answer 11

System of fluid filled membranes. Synthesises and processes lipids.

Question 12

structure and function of cell wall

Answer 12

rigid structure that surrounds cells. Supports cell and stops it from changing shape

Question 13

How do Prokaryotic cells differ from Eukaryotic cells?

Answer 13

Prokaryotic cells:
do not have membrane bound organelles
Have free floating circular DNA as opposed to linear DNA in the nucleus
Murein cell was instead of cellulose
Smaller ribosomes

Question 14

prokaryotic cell division

Answer 14

Circular DNA and plasmids replicate, then the cell divides to produce two daughter cells, each with a single copy of the circular DNA and a variable number of copies of plasmids.

Question 15

How do viruses replicate?

Answer 15

Viruses invade host cells and their DNA is inserted into the DNA of the host cell and use the host cell organelles within the host cell to replicate themselves.

Question 16

What is the formula for calculating magnification?

Answer 16

Magnification = image size ÷ actual size

Question 17

What is the difference between magnification and resolution?

Answer 17

Magnification is how much bigger the image is than the specimen, whereas Resolution is how well a microscope distinguishes between two points that are close together.

Question 18

Describe the structure of a typical virus.

Answer 18

Viruses consist of genetic material (either DNA or RNA), surrounded by a protein coat (capsid) with attachment proteins sticking out.

Question 19

What are the limitations of an optical microscope?

Answer 19

Optical microscopes have a maximum resolution of 0.2µm and the maximum useful magnification is about x1500

Question 20

What are the advantages and disadvantages of a Transmission Electron Microscope (TEM)?

Answer 20

A = Can show very small objects due to the high resolution.
D = Can only be used on thin, non-living specimens.

Question 21

What are the advantages and disadvantages of a Scanning Electron Microscope (SEM)?

Answer 21

What are the advantages and disadvantages of a Scanning Electron Microscope (SEM)?
A = Can be used on thick specimens to show 3D structure.
D = Gives lower resolution images than TEM and can only be used on non-living specimens.

Question 22

How might you be able to distinguish between an artefact and an organelle?

Answer 22

Artefacts usually occur during preparation of the slide, so by repeating specimen preparation in different ways would enable you to identify artefacts.

Question 23

How would you homogenise a sample of cells during cell fractionation?

Answer 23

Use a blender to break open cells, so that organelles are released. The solution must be ice-cold to prevent enzyme activity and isotonic to prevent damage to organelles through osmosis and a buffer should be added to maintain the pH.

Question 24

How does ultracentrifugation allow the separation of organelles?

Answer 24

Spinning at low speed causes the heaviest organelles such as nuclei to sediment into a pellet.
The supernatant can be removed and re-spun at increasingly higher speeds, removing the sediment each time containing lighter organelles each time.

Question 25

Starting at the end of mitosis, describe what happens to a stem cell during the cell cycle.

Answer 25

The new cell grows and new organelles are made (G1)
DNA replicates (S)
The cell continues to grow and proteins needed for cell division are made (G2)

Question 26

interphase

Answer 26

DNA is unravelled to allow transcription and replication

Question 27

prophase

1st stage of mitosis

Answer 27

chromosomes condense, centrioles move to opposite ends of the cell forming spindle fibres and the nuclear envelope breaks down.

Question 28

metaphase (2nd stage of mitosis)

Answer 28

chromosomes line up along the middle of the cell and attach to spindle fibres by their centromere.

Question 29

anaphase (3rd stage of mitosis)

Answer 29

Spindles shorten causing centromeres to split and pulling chromatids towards the poles.

Question 30

telophase (4th stage of mitosis)

Answer 30

At the poles, chromatids (now chromosomes) uncoil and a new nuclear envelope forms around each set.

Question 31

What causes tumours to form?

Answer 31

If there is a mutation in a gene which normally controls cell division, cells can divide to frequently forming a tumour.

Question 32

Why are normal cells often affected by cancer treatments as well as tumour cells?

Answer 32

Treatment disrupts the cell cycle, killing dividing cells including normal dividing cells.

Question 33

List the steps you would take in order to view a sample using an optical microscope

Answer 33

Clip the slide onto the stage
Select lowest power objective lens
Use coarse adjustment to lower lens as close to specimen as possible
Look down the eyepiece and use fine adjustment until the image is focussed
Increase to a higher objective lens as required

Question 34

How would you use a stage micrometer and an eyepiece graticule to estimate the size of cells?

Answer 34

Line up the two scales and work out what each division on the eyepiece graticule represents e.g. each division on the stage micrometer = 0.1mm, count how many divisions on the eyepiece graticule fit into one of these divisions e.g 4.5 then divide to give the size = 0.1 ÷ 4.5 = 0.022mm
Replace the stage micrometer with your specimen slide and count how many eye piece divisions each cell occupies. Multiply by 0.022 or whatever your previous calculated value was to give the actual length.