2.1.1 Cell Structure

Question 1

(c) The use of staining in light microscopy
To include the use of differential staining to identify different cellular components and cell types

Answer 1

Allows specimens to be seen (increases colour and contrast) as biological samples are transparent

• Methylene blue: +vely charged attracted to -vely charged materials in cytoplasm, staining cell components

Differential staining technique: Distinguish between two organelles by binding to specific cell structures, for easy identification

• Acetic orcein binds to DNA –> stains chromosomes dark red
• Eosin –> stains cytoplasm
• Sudan red –> stains lipid
• Iodine (from KI solution) –> stains cellulose in plant cell wall yellow + starch granules blue/black

Question 2

(e) The use and manipulation of the magnification formula

Answer 2

Magnification = (Image size)/(Actual size)

Question 3

(f) The difference between magnification and resolution
To include an appreciation of the differences in resolution and magnification that can be achieved by a light microscope, a transmission electron microscope and a scanning electron microscope

Answer 3

Magnification: How many times larger the image is than the actual size of the object being viewed.
Resolution: The degree of detail. The ability to distinguish between two separate objects.

RESOLUTION & MAGNIFICATIONS:

• Light microscope: 200nm & x1,500
• Transmission Electron microscope: 0.1nm & x500,000
• Scanning Electron mocroscope: 0.1nm & x100,000

Question 4

(i) The interrelationship between the organelles involved in the production and secretion of proteins
No detail of protein synthesis is required

Answer 4

• The gene for the protein copied onto mRNA by transcription
• mRNA leaves nucleus through nuclear pore and attaches onto ribosome (ribosome may be attached to rough endoplasmic reticulum)
• Ribosome reads instructions to assemble protein
• Transported by vesicle to Golgi apparatus
• Protein is processed and packaged in Golgi apparatus
• ‘Pinched off’ in vesicles which move to the cell surface membrane
• Vesicles fuse with cell surface membrane and protein released via exocytosis

Question 5

(j) The importance of the cytoskeleton
To include providing mechanical strength to cells, aiding transport within cells and enabling cell movement

Answer 5

Structure of cytoskeleton - Made of two kinds of protein fibres: ​

• Microfilaments
• Microtubules

Function:

• move organelles around in cell by contracting
• strengethening cell + maintaining cells stable shape by providing internal framework
• Microtubules:
  
  • transportation - form spindle fibres to move chromosomes during mitosis
  • make up cilia and flagella (for cells to move)
• Cytoskeleton motor proteins –> use ATP

Question 6

(k) The similarities and differences in the structure and ultrastructure of prokaryotic and eukaryotic cells

Answer 6

Question 7

(g) the ultrastructure of eukaryotic cells and the functions of the different cellular components
To include the following cellular components and an outline of their functions: nucleus, nucleolus, nuclear envelope, rough and smooth endoplasmic reticulum (ER), Golgi apparatus, ribosomes, mitochondria, lysosomes, chloroplasts, plasma membrane, centrioles, cell wall, flagella and cilia

Answer 7

Question 8

(d) the representation of cell structure as seen under the light microscope using drawings and annotated diagrams of whole cells or cells in sections of tissue

Answer 8

• Clear continuous lines
• No shading
• Use most-all of space given
• Include total magnification
• Label all relevant structures