Cell Structure

Question 1

What is a dry mount (slide prep)

Answer 1

thin slices or whole specimens are viewed with just the coverslip placed on top
e.g. plant tissue or hair

Question 2

What is a wet mount (slide prep)

Answer 2

water is added to the specimen before lowering the coverslip, a mounted needle prevents air bubbles from forming.
e.g. to view aquatic organisms

Question 3

What is a squash slide (slide prep)

Answer 3

Wet mounts that you push the coverslip down on to squash the sample to ensure a thin enough layer for light to pass through.
e.g. used to create root tip squash sample to view chromosomes in mitosis

Question 4

What are smear slides (slide prep)

Answer 4

created using another slide to smear the sample across the slide to create a smooth, thin, evenly coated specimen. A coverslip is then placed on top.
E.g. blood cells in a blood sample

Question 5

What is differential staining

Answer 5

Technique which involved many chemical stains used to stain different parts of a cell in different colours

Question 6

What stains are used and for what

Answer 6

Crystal violet or methylene blue- stain negatively charged materials
Microsin and congo red- creates a stained background

Question 7

Describe gram staining

Answer 7

Gram positive- crystal violet is added and then iodine, alcohol is used to wash away unbound stain. The bacteria appear blue/purple as the stain is retained due to the thicker peptidoglycan cell wall later absorbing the dye
Gram negative- crystal violet can not be absorbed due to their peptidoglycan cell wall being thin, safranin is used as a counterstain which turns them red.

Question 8

Electron Microscopes

Answer 8

High resolution due to short wavelength of electron beam (small organelles can be visualised)
Image is created using an electromagnet to focus the beam of negatively charged electrons
EM must be in a vacuum because electrons are absorbed by air
Only non living specimens can be examined
Black and white image

Question 9

Transmission Electron Microscopes

Answer 9

Extremely thin specimens are stained and placed into a vacuum
Electron gun produces beam that passes through the specimen
Some parts of the specimen absorb electrons which makes them appear darker
2D image produced

Question 10

Scanning Electron Microscope

Answer 10

Specimen doesn’t need to be thin
Electrons are beamed onto the surface and scattered depending on the contours
Produces a 3D image.

Question 11

Laser Scanning Confocal Microscope

Answer 11

Fluorescent microscope
Image obtained using high light intensity to illuminate specimen using fluorescent dye
High resolution and 3D image

Question 12

Structure of the nucleus

Answer 12

Nuclear envelope- double membrane
Nuclear pores
Nucleoplasm- granular, jelly like material
Chromosomes- protein bound, linear DNA
Nucleolus- smaller sphere inside which is the site of rRNA production and makes ribosomes

Question 13

Function of the nucleus

Answer 13

Site of DNA replication and transcription (making mRNA)
Contains the genetic code for each cell
Site of ribosome synthesis

Question 14

Structure of Flagella

Answer 14

Whip/tail like structure

Question 15

Function of flagella

Answer 15

For mobility and sometimes as a sensory organelle for chemical stimuli

Question 16

Structure of cilia

Answer 16

Hairlike projections out of cells

Question 17

Function of cilia

Answer 17

Can be mobile or stationary
Mobile cilia help move substances in a sweeping motion
Stationary cilia are important in sensory organs such as the nose

Question 18

Structure of centrioles

Answer 18

Made of microtubules
Occur in pairs to form a centrosome

Question 19

Function of centrioles

Answer 19

Involved in the production of spindle fibres and organisation of chromosomes in cell division

Question 20

Structure of cytoskeleton

Answer 20

Network of fibres found within the cytoplasm all over a cell
Consists of microfilaments, microtubules and intermediate fibres.

Question 21

Function of the cytoskeleton

Answer 21

Provides mechanical strength to cells, helps maintain the shape and stability of a cell. Many organelles are bound to the cytoskeleton
Microfilaments are responsible for cell movement
Microtubules are responsible for creating a scaffold like structure
Intermediate fibres provide mechanical strength

Question 22

Structure of the endoplasmic reticulum

Answer 22

Folded membranes called cisternae
Rough ER has ribosomes on the cisternae

Question 23

Function of the Endoplasmic reticulum

Answer 23

Smooth- Synthesis and store lipids and carbohydrates
Rough- Protein synthesis

Question 24

Structure of golgi apparatus (and vescicles)

Answer 24

Folded membranes making cisternae
Secretary vesicles pinch off from the cisternae

Question 25

Function of the golgi apparatus and vesicles

Answer 25

Add carbohydrates to proteins to form glycoproteins
Produce secretory enzymes
Secrete carbohydrates
Transport, modify and store lipids
Form lysosomes
Label molecules with their locations
Finished products are transported to the cell surface in vesicles where they fuse with the membrane and the contents are released

Question 26

Structure of Lysosomes

Answer 26

Bags of digestive enzymes (can contain 50 different)

Question 27

Function of lysosomes

Answer 27

Hydrolyse phagocytic cells
Break down dead cells (autolysis)
Exocytosis (release enzymes to outside of a cell to destroy material)
Digest worn out organelles for the reuse of materials

Question 28

Structure of mitochondria

Answer 28

Double membrane
Inner membrane called the cristae
Fluid centre called the mitochondrial matrix
Loop of mitochondrial DNA

Question 29

Function of mitochondria

Answer 29

Site of aerobic respiration
Site of ATP production
DNA to code for enzymes needed in respiration

Question 30

Structure of ribosomes

Answer 30

Small, made up of two subunits of protein and rRNA
80s- large ribosomes found in eukaryotic cells (25nm)
70s- smaller ribosome found in prokaryotic cells, mitochondria and chloroplasts

Question 31

Function of ribosomes

Answer 31

Site of protein synthesis

Question 32

Structure of chloroplasts

Answer 32

Surrounded by a double membrane
Contains thylakoids (folded membranes embedded with pigment)
Fluid filled stroma contains enzymes for photosynthesis
Found in plants

Question 33

Function of chloroplasts

Answer 33

Site of photosynthesis

Question 34

Structure of a cell wall

Answer 34

(in plants and fungi cells)
Plants- made of microfibrils of the cellulose polymer
Fungi- made of chitin (a nitrogen containing polysaccharide)

Question 35

Function of the cell wall

Answer 35

Provide structural strength to the cell

Question 36

Structure of plasma membrane

Answer 36

Phospholipid bilayer- molecules embedded within and attached in the outside (such as proteins, carbohydrates and cholesterol)

Question 37

Function of plasma membrane

Answer 37

Controls the entrance and exit of molecules

Question 38

Describe the production and secretion of proteins

Answer 38

Polypeptide chains are synthesised by ribosomes on the RER
These chains then travel into the cisternae of the RER where they are packaged into vesicles and sent to the golgi apparatus via the cytoskeleton
They are then modified and packaged into vesicles at the golgi apparatus
The secretory vesicles then carry the proteins to the cell surface membrane where it fuses and releases the proteins via exocytosis

Question 39

Compare prokaryotic and eukaryotic cells

Answer 39

Prokaryotes are much smaller
Prokaryotes have no membrane bound organelles
Prokaryotes have smaller ribosomes
Prokaryotes do not have DNA contained within a nucleus
Prokaryotes have a cell wall made of murein (a glycoprotein)
Prokaryotes may also contain plasmids, a capsule around the cell and flagella