Cell structure and division

Question 1

Name some structural features of a prokaryotic cell

Answer 1

Plasma membrane (made of lipids and proteins, controls the movement of substances in and out)
Cell wall (provides support made of murein)
Capsule (protect from cell)
Plasmids (small loop of DNA)
Free floating DNA (not attached to histone)
Flagellum (helps to move)
Cytoplasm

Question 2

Name some structural features of a eukaryotic cell

Answer 2

Cell surface membrane (movement of substances)
Nucleus (transcription of DNA)
Mitochondrion (site of respiration)
Chloroplast (photosynthesis takes place)
Golgi apparatus (processes and packages lipids/proteins)
Golgi vesicle (stores lipids/ proteins) 
Lysosome (digestive enzymes, lysozymes)
Ribosome (site of protein synthesis)
RER (folds and processes proteins)
SER (synthesises and processes lipids)
Cell wall (supports cells)
Cell vacuole (maintain pressure)

Question 3

Name some structural features of a virus

Answer 3

No plasma membrane 
No cytoplasm 
No ribosomes 
A core of genetic material, RNA or DNA 
Protein coat called capsid
Attachment proteins

Question 4

Describe the process of binary fission

Answer 4

Circular DNA and plasmids replicate
Cell gets bigger
DNA loops move to opposite poles
Cytoplasm begins to divide
Cytoplasm divides into two daughter cells
(Each daughter cell with one copy of loop but a variable number of plasmids)

Question 5

How do viruses replicate?

Answer 5

Use attachment proteins to bind to receptors on host
They inject DNA or RNA into host
The hosts organelles replicate the viral particles

Question 6

What is the equation for magnification?

Answer 6

Magnification= size of image / size of real object

Question 7

What are the two types of microscopes?

Answer 7

Optical and electron

Question 8

What are the characteristics of a light microscope?

Answer 8

Use light to form an image
Resolution of 0.2 micrometres
Max magnification is X1500

Question 9

What are the characteristics of an electron microscope?

Answer 9

Use electrons to form an image
Resolution of 0.0002 micrometres
Magnification of X1500000

Question 10

Scanning microscope characteristics

Answer 10

Scan electrons across specimen, knocks off electrons which are gathered in cathode ray tube
Shows a 3D image
Thick specimen
Lower resolution

Question 11

Transmission microscope characteristics

Answer 11

Use electromagnets to focus a beam of electrons through the specimen
Denser parts absorb more (making them darker)
High resolution
Can see internal organelles
Thin specimens

Question 12

How is a temporary mount prepared?

Answer 12

Small drop of water on slide
Use tweezers to place thin specimen on top
Add a stain to highlight objects
Add a cover slip

Question 13

What are the three stages of Cell fractionation?

Answer 13

Homogenisation
Filtration
Ultracentrifugation

Question 14

What does homogenisation refer to?

Answer 14

Breaking up the plasma membrane of cells to release organelles into a solution
The solution must be kept ice cold
Keep isotonic (same chemicals as the cells prevent osmosis)
Ensure solutions pH is maintained
eg.
Grind cells in blender, place in beaker of ice, add buffer solution

Question 15

What does filtration refer to?

Answer 15

Getting rid of the big bits
Solution is filtered through a gauze
Removing any large debris
Organelles can pass through

Question 16

What does ultracentrifugation refer to?

Answer 16

Cell fragments poured into a tube
Spun at a low speed, heaviest organelles to bottom
The supernatant is poured into another tube
Spun at a faster speed
Repeated until the lightest organelles are left

Question 17

What are the four stages of mitosis?

Answer 17

(Interphase)
Prophase
Metaphase
Anaphase
Telophase

Question 18

What happens in prophase?

Answer 18

Chromosomes condense
Centrioles move to opposite poles
Spindle fibres form
Nuclear envelope breaks down

Question 19

What happens in metaphase?

Answer 19

Chromosomes line up along the equator and become attached to spindle fibres by centromeres

Question 20

What happens in anaphase?

Answer 20

Centromeres divide
Separating sister chromatids
Spindles contract
Pulling chromatids to opposite poles

Question 21

What happens in telophase?

Answer 21

Chromatids reach opposite poles
Uncoil and become long and thin
Nuclear envelope begins to form
Now two daughter cells

Question 22

How do you work out how long each phases of mitosis lasts?

Answer 22

10/100 X 900= 90mins

10 of 100 cells are in metaphase, the whole cycle lasts 900 mins

Question 23

What does uncontrolled cell division cause?

Answer 23

Cancer
Usually cells stop dividing after they’ve made enough cells, a mutation can occur when this doesn’t happen, causing a tumour. A cancerous tumour invades surrounding tissue.

Question 24

Describe how some cancer treatments can target the cell cycle.

Answer 24

Chemotherapy can prevent the synthesis of enzymes used in DNA replication, the cell kills itself.
Radiation therapy and some other drugs can damage DNA, when the cell is checked it will kill itself preventing more growth.
These drugs don’t distinguish between cancer and body cells.