Unit 2- Cell Structure

Question 1

What does cell theory state? 3

Answer 1

• all organisms are composed of 1 or more cells, all the processes of life take place within these cells
• Cells are the smallest units that can be alive
• New cells are always formed by division of old cells

Question 2

How do unicellular and multicellular organisms differ, in terms of cells

Answer 2

• unicellular, the cell carries out all the processes of life
• multicellular, the cells are differentiated to carry out different tasks

Question 3

Difference between prokaryotic and eukaryotic cells?

Answer 3

Prokaryotic cells have no nucleus or interior compartments

Eukaryotic cells have a nucleus and various interior compartments

Question 4

Cell membrane:

Answer 4

• thin flexible layer made of phospholipids and proteins
• controls entry and exit of materials
• separates the contents of the cell from the outside

Question 5

Nucleus:

Answer 5

• surrounded by a nuclear envelope, a double membrane with nuclear pores
• interior nucleoplasm, full of chromatin
• in cell division chromatin condenses becoming visible chromosomes
• nucleolus, used in making ribosomes

Question 6

Mitochondria:

Answer 6

• where aerobic respiration occurs, and ATP is synthesised
• double membrane, outer is simple and very permeable while inner is highly folded to give cristae
• cristae, provide large surface area
• mitochondrial matrix, containing small circular strands of DNA
• stalked particles (ATP synthase) on cristae

Question 7

Chloroplasts:

Answer 7

• where photosynthesis takes place
• found in only photosynthetic organisms
• double membrane
• starch grain
• thylakoid membrane folded into disks
• stacks of thylakoid membranes are called grana
• space between membranes is called stroma
• thylakoid membrane contains chlorophyll and carotenoids

Question 8

What is a plastid?

Answer 8

Organelles with a double membrane, which divide by fission

Question 9

Ribosome:

Answer 9

• sites of protein synthesis
• smallest organelle
• found free in the cytoplasm or on RER

Question 10

RER

Answer 10

• studded with ribosomes for protein synthesis
• proteins are processed in the RER, eg modified by adding a carb group)
• exported to the Golgi apparatus after modified

Question 11

SER

Answer 11

• processes/modifies materials, mainly lipids

- modified compounds are sent to Golgi to be transported out the cell

Question 12

Golgi Apparatus:

Answer 12

• series of flattened membranes
• purpose is to transport proteins for extra cellular use from the ER to the cell membrane
• parts of the RER fuse with the Golgi body to form cisternae, pushing a vesicle of proteins off from the cisternae
• vesicles release their contents out the cell by exocytosis

Question 13

Vacuoles:

Answer 13

• Membrane bound sacs containing water or dilute solutions of salts and other solutes
• plant cell vacuoles are surrounded by a membrane called the tonoplast, filled with sap
• they keep cell rigidity and turgidity

Question 14

Lysosomes:

Answer 14

• membrane bound vesicles containing digestive enzymes
• formed from RER
• used to break down toxic chemicals, organelles or cells, where the products are then recycled in the cell
• may fuse with phagosomes

Question 15

Cytoskeleton:

Answer 15

• network of protein fibres throughout all eukaryotic cells
• add support, transport and motility
• attached to the cell membrane providing shape holding organelles in position
• responsible for cell movements such as division, cilia, flagella…

Question 16

Centrioles:

Answer 16

• 2 centrioles found near the nucleus
• part of the cytoskeleton
• used in cell division to make up spindle fibres
• only in animal cells

Question 17

Cilia purpose:

Answer 17

To move the cell or extra cellular fluid

Short and numerous

Question 18

Flagella purpose:

Answer 18

• longer than the cell

- used for motility, eg sperm

Question 19

Microvilli purpose:

Answer 19

• short extensions found in epithelial cells of small intestine and kidney
• increase the surface area for absorption

Question 20

Cytoplasm:

Answer 20

• solution within cell membrane

- contains enzymes, sugars, salts, amino acids, nucleotides and all the resources needed for a cell to function

Question 21

Cell wall:

Answer 21

• thick layer outside the cell membrane
• used to give strength and rigidity to cells
• resists osmotic lysis

Question 22

Give examples of cell walls:

Answer 22

• plant- cellulose
• fungi- chitin
• bacteria- peptidoglycan

Question 23

Plant cell walls composition:

Answer 23

• 3 layers:
  1) outer layer is the middle lamella, thick layer of calcium pectate that glues cells together
  2) middle layer is the primary cell wall, thin layer of cellulose microfibrils and is more flexible
  3) the inner layer is the secondary cell wall, thick, network of of fibres like cellulose, hemicellulose and pectin

Question 24

What makes up the primary cell wall?

Answer 24

Cellulose microfibrils

Question 25

What makes up the outer layer of the cell wall?

Answer 25

• middle lamella

Made of calcium pectate (glue like substance)

Question 26

What is special about xylem cells?

Answer 26

The secondary cell wall contains additional lignin for strength and water proofing, which later form woody tissue

Question 27

What makes up the inner layer of the cell wall?

Answer 27

• secondary cell wall

- network of fibres including cellulose, hemicellulose and pectin

Question 28

What is the plasmodesmata?

Answer 28

Channels between cytoplasm of adjacent cells forming a symplast, allowing solutes to diffuse freely between cells without crossing a membrane

Question 29

What is the difference between prokaryotic and eukaryotic ribosomes?

Answer 29

Prokaryote have 70s ribosomes (made of 30s and a 50s subunit)
Eukaryotes have 80s ribosomes

Question 30

Compare and contrast the eukaryotic and prokaryotic cells

Answer 30

• both have DNA as genetic material
• both have a membrane
• prokaryotes have 70s ribosomes and eukaryotes 80s ribosomes
• prokaryotes do not have membrane bound organelles

Question 31

What are the 9 organelles found in all prokaryotes

Answer 31

• cell membrane
• cytoplasm
• cell wall
• capsule
• DNA
• plasmid
• nucleoid
• flagellum
• 70s ribosomes

Question 32

Describe the capsule, and its function

Answer 32

• thick sticky layer of sugar (polysaccharides)

- used to stick cells together, for a food reserve, protection

Question 33

What are plasmids?

Answer 33

Small circles of DNA, separate from main DNA in prokaryotes used to exchange DNA in bacteria

Question 34

What is the nucleoid?

Answer 34

Region of cytoplasm where main DNA of prokaryote is

Question 35

What is the flagellum?

Answer 35

A rigid helical shaped tail used for propulsion

Question 36

What are the results of the gram stain test?

Answer 36

Gram positive bacteria stain purple

Gram negative bacteria stain red

Question 37

Describe the structure of a gram positive cell wall

Answer 37

• capsule
• very thick peptidoglycan cell wall
• phospholipid bilayer

Question 38

What is a positive and negative feature of gram positive bacteria

Answer 38

+ thick cell wall provides lots of strength against physical conditions
- most antibiotics act on wall formation so these are more vulnerable

Question 39

Describe the structure of the gram negative cell wall

Answer 39

• lipopolysaccharide bilayer
• thin layer of peptidoglycan
• thin layer of cytoplasm (periplasm)
• phospholipid bilayer (cell membrane)

Question 40

Give a positive and negative feature of gram negative bacteria

Answer 40

+ thin cell wall provides less strength so is more easily broken
- outer layer of lipopolysaccharides is resistant against most antibiotics, so these are harder to kill

Question 41

Describe the gram stain test

Answer 41

• add crystal violet stain to slide, (binds to peptidoglycan turning ALL bacteria purple)
• iodine assists the binding process
• add ethanol (dissolves outer lipid layer of gram negative) this washes out purple stain from gram negative but not gram positive
• add safranin (red stain) which binds to remaining peptidoglycan of gram negative