cells and microscopes

Question 1

describe the structure and function of the nucleus

Answer 1

Structure
double membrane and pores
Chromatin (DNA associated with histones)
Function
Stores genetic information for polypeptide production.
Site of DNA replication.
Site of production of mRNA (transcription) and tRNA.
Site of production of rRNA/ribosomes (Nucleolus)

Question 2

describe the structure and function of mitochondria

Answer 2

structure
Double membrane
Inner membrane highly folded to form cristae (increase surface area)
Matrix (liquid part) containing mitochondrial DNA, 70s ribosomes, proteins and lipids.
Function
Site of ATP production by AEROBIC respiration

Question 3

describe the structure and function of a rough endoplasmic reticulum

Answer 3

Structure
Highly folded membranes with 80s ribosomes embedded.
The membrane is folded into flattened sacks called cisternae.
Joined to the nucleus.
Function
Synthesises and transport of proteins throughout the cell

Question 4

describe the structure and function of cytoplasmic ribosomes

Answer 4

Structure
Made up of 2 subunits that are made of long strands of rRNA AND ribosomal proteins.
Function
Site of protein synthesis from amino acids

Question 5

describe the structure and structure of a smooth endoplasmic reticulum

Answer 5

Structure
Highly folded membranes flattened into sacks called cisternae
Function
Recombines glycerol and fatty acids to make triglycerides.
Packages triglycerides into vesicles and transports them to the Golgi apparatus

Question 6

describe the structure and function of a golgi body

Answer 6

Structure
Flattened sacs made of membrane filled with fluid.
Golgi vesicles pinch off from the main membrane.
Function
Sorts, modifies, and packages proteins and triglycerides into vesicles.
Golgi vesicles used to form lysosomes

Question 7

describe the function of lysosomes

Answer 7

Contains and releases hydrolytic enzymes that hydrolyse pathogens/damaged organelles once released into vesicles.

Question 8

describe the structure and function of centrioles

Answer 8

Structure
Microtubules
Not in plant cells
Function
Form a network of spindle fibres which attach to the centromere of chromosomes.
Pull sister chromatids apart during mitosis.

Question 9

Compare and contrast structures found in a plant and animal cell.

Answer 9

Both have rough and smooth endoplasmic reticulum
Both have golgi body
Both have mitochondria
Both have nucleus

plant cells have a cellulose cell wall whereas animal cells have no cell wall
plant cells have chloroplasts whereas animal cells do not
plant cells have a large central vacuole whereas animal cells do not
plant cells have carbohydrates stored as starch whereas animal cells have carbohydrates stored as glycogen
plant cells have no centrioles whereas animal cells have centrioles

Question 10

describe the structure and function of chloroplasts

Answer 10

Structure
Thylakoid membranes contain chlorophyll that absorbs light (needed for photosynthesis).
Function
Site of photosynthesis

Question 11

Describe and explain how cell fractionation and ultracentrifugation can be used to isolate named organelle From a suspension of cells.

Answer 11

1. Cell homogenisation to break open cells and filter to remove whole cells/debris
2. Solution must be:
   Isotonic – keep water potential the same to stop organelles bursting.
   Ice cold – prevent enzyme activity
   Buffered – pH kept constant preventing enzyme denaturation
3. Centrifuge at high speed to separate nuclei.
4. Remove pellet containing nuclei.
5. Re-spin supernatant at higher speeds to get mitochondria/chloroplasts in second pellet
   (Repeat steps 3-5 for smaller organelles

Question 12

Describe the principles of an electron microscope

Answer 12

Principles:
1. Electrons pass through / enter (very thin) specimen;
2. Denser parts absorb more electrons;
3. (So) denser parts appear darker;
4. Electrons have short wavelength so give high resolution;

Question 13

Describe the advantages/disadvantages of TEM over a light microscope

Answer 13

Advantages:
1. Small objects can be seen (ultrastructure’s/smaller organelles);
2. TEM has higher resolution;
3. Wavelength of electrons shorter;

Limitations:
4. Cannot look at living cells;
5. Must be in a vacuum;
6. Must cut section / thin specimen;
7. Preparation may create artefacts (false image);

Question 14

give one advantage of TEM over SEM

Answer 14

Higher resolution
Can see internal structures

Question 15

Give one advantage of SEM over TEM

Answer 15

Produce 3D image
See surface of specimen

Question 16

state advantages of light microscopes and explain the disadvantages compared to TEM

Answer 16

Advantages = can observe living specimens as stains are non-toxic. can stain specific organelles with colour
Disadvantage = lower resolution as wavelength of light is longer so you cannot see smaller organelles/ultrastructure’s.