M2 CH2: cells

Question 1

TEM
- how it works
- type of specimen
- details of image produced (2 details)

Answer 1

• electrons pass through specimen, :. must be thin
• non living specimens (due to being placed in a vacuum)
• 2D, black and white images

Question 2

SEM
- how it works
- type of specimen
- details of image produced (2 details)

Answer 2

• electrons bounce off specimen
• non living specimen
• 3D, black and white

Question 3

laser scanning confocal microscope:
- how it works
- type of specimen
- details of image produced (2 details)

Answer 3

• uses laser beams and fluorescent dyes
• can inspect living cells
• 3D, colour

Question 4

state the 4 dyes used in differential staining, and what they stain.

Answer 4

methylene blue & crystal violet:
- stain negatively charged organelles (they are + charged)

Congo red & nigrosin
- act as counter stains, they are - charged so can’t enter cells
- :. they stain the background, highlighting unstained cells

Question 5

state the stain that highlights gram + bacteria. Explain why gram - bacteria does not take up this dye

Answer 5

crystal violet; turns blue/purple
because gram + bacteria have thick peptidoglycan cell walls and so absorb the dye.
gram negative bacteria cell walls are much thinner, so don’t take up the dye

Question 6

state the dye that stains gram - bacteria, and a benefit of gram staining in medicine.

Answer 6

safranin- highlights bacteria in red
helps medics to distinguish gram + and - infections in humans, to prescribe appropriate antibiotics.

Question 7

outline the components of centrioles, and explain what their role is in cells.
(3 points)

Answer 7

1. microtubules in 9 + 2 arrangement
2. forms pairs to form centrosome
3. form part of spindle fibres, which play a role in assembling the chromosomes during mitosis and meiosis

Question 8

distinguish the 2 components that make up the endoplasmic reticulum, referring to each ones structure and function

Answer 8

RER:
- covered in ribosomes
- protein synthesis (in ribosomes) and packaging into vesicles

SER:
- no ribosomes
- synthesises and processes lipids

Question 9

state the 3 components that make up the cytoskeleton, and relate each to a function

Answer 9

1. microfilaments: enable cell movement
2. microtubules: supports cells organelles
3. intermediate fibres: provide mechanical strength

Question 10

state what lysosomes are made of, and state their function
( 2 points )

Answer 10

vesicles containing digestive enzymes
hydrolyse phagocytic cells

Question 11

outline structural features of mitochondria, and state its functions.
(4 points)

Answer 11

• double membrane: cristae, matrix
• 70s ribosomes
• aerobic respiration
• ATP production

Question 12

outline the 4 stages involved in the production and secretion of proteins from cells.

Answer 12

1. polypeptide chains are synthesised in ribosomes on RER
2. packaged into vesicles in RER
3. sent to the golgi apparatus to be further modified
4. vesicles leave GA and fuse with membrane, secreting proteins by exocytosis