Section 2: Cell structure

Question 1

What is the structure and function of the cell-surface membrane?

Answer 1

• Phospholipid bilayer with embedded proteins
• Selectively permeable - controls passage of substances
• Barrier between internal and external environments

Question 2

What is the structure and function of the nucleus?

Answer 2

• Nuclear envelope, nuclear pores, nucleolus, DNA/ chromatin
• Controls cell activities through transcription of mRNA
• Nuclear pores allows substances to move
• Nucleolus makes ribosomes which are made of proteins and ribosomal RNA

Question 3

What is the structure and function of the mitochondria?

Answer 3

• Double membrane - inner membrane folded to form cristae
• Matrix containing 70S ribosomes, small circular DNA and enzymes
• Aerobic respiration producing ATP

Question 4

What is the structure and function of the Golgi Apparatus?

Answer 4

• Fluid filled membrane bound sacs with vesicles at the edge
• Receives proteins from RER
• Modifies/ processes proteins e.g add carbohydrates
• Packages into vesicles
• Makes lysosomes

Question 5

What is the structure and function of lysosomes?

Answer 5

• Type of golgi vesicle containing lysozymes
• Breaks down/ hydrolyse pathogens and worn out cell components

Question 6

What is the structure and function of ribosomes?

Answer 6

• Float free in cytoplasm or bound to RER - not membrane bound
• Made from 1 large and 1 small subunit
• Site of protein synthesis - translation

Question 7

What is the structure and function of the RER?

Answer 7

• Ribosomes bound by membranes
• Folds polypeptides to secondary/ tertiary structure
• Packages to vesicles, transport to the Golgi

Question 8

What is the structure and function of SER?

Answer 8

• Similar to RER but without ribosomes
• Synthesises and processes lipids

Question 9

What is the structure and function of chloroplasts?

Answer 9

• Thylakoid membranes are stacked up to form grana which are linked by lamellae
• These sit in the stroma and are surrounded by a double membrane
  
  • Also contains starch granules and circular DNA
• Chlorophyll absorbs light for photosynthesis

Question 10

What is the structure and function of the cell walls?

Answer 10

• Made of cellulose in plants and algae and chitin in fungi
• Rigid structure surrounding plant and fungi.
• Prevents the cell changing shape and bursting lysis

Question 11

What is the structure and function of the cell vacuole?

Answer 11

• Contains cell sap - weak solution of sugars and salts
• Surrounding membrane is called the tonoplast
• Maintains pressure in the cell
• Stores/ isolates unwanted chemicals in the cell

Question 12

What is a tissue?

Answer 12

• Group of organised cells, joined together to perform a particular function

Question 13

What is an organ and organ system?

Answer 13

• Group of organised tissues, working together to perform a particular function
• Group of organised organs, working together to perform a particular function

Question 14

What are the differences between prokaryotic and eukaryotic cells?

Answer 14

• Prokaryotic = no membrane bound organelles
• Prokaryotic = no nucleus/ contains free floating DNA
• Prokaryotic DNA = circular and not associated with proteins. Eukaryotic is
• Prokaryotic cell walls = murein and peptidoglycan. Eukaryotic = cellulose
• Prokaryotic = smaller 70s ribosomes, Eukaryotic = 80S
• Prokaryotic = plasmid, capsule, flagella

Question 14

What are the differences between prokaryotic and eukaryotic cells?

Answer 14

• Prokaryotic = no membrane bound organelles
• Prokaryotic = no nucleus/ contains free floating DNA
• Prokaryotic DNA = circular and not associated with proteins. Eukaryotic is
• Prokaryotic cell walls = murein and peptidoglycan. Eukaryotic = cellulose
• Prokaryotic = smaller 70s ribosomes, Eukaryotic = 80S
• Prokaryotic = plasmid, capsule, flagella

Question 15

What are the different structures in a virus?

Answer 15

• Attachment proteins
• Capsid
• RNA
• Reverse Transcriptase
• Lipid envelope

Question 16

How do you use an optical microscope and what is its resolution and magnification?

Answer 16

• Use light to form 2D image
• Visible light longer wavelength
• Magnification = x1500
• Resolution = 0.2 micrometres

Question 17

Advantages of using an optical microscope:

Answer 17

• Can see living organisms
• Staining process less complicated and cheaper

Question 18

Disadvantages of using an optical microscope?

Answer 18

• 2D image
• Only on thin specimens
• Low resolution - can’t see internal structures
• Low magnification

Question 19

How to use a scanning electron microscope and what is its magnification and resolution:

Answer 19

• Forms 3D image
• Beam of electrons scan surface, knocking off electrons from the specimen and are gathered in a cathode ray tube to form an image
• Electrons have a shorter wavelength = 0.2nm
• High mag x1500000

Question 20

Advantages of using TEM or SEM:

Answer 20

• SEM = 3D image
• High resolution
• High magnification
• SEM = on thick specimens

Question 21

What are the disadvantages of using SEM:

Answer 21

• Vacuum, can’t see living organisms
• Lower resolution than TEM

Question 22

How to use a TEM and what is its magnification and resolution?

Answer 22

• Electromagnets to focus a beam of electrons onto a specimen
• More dense areas = more absorbed
• Electrons have shorter wavelength, resolution = 0.2nm
• High mag = x1500000

Question 22

How to use a TEM and what is its magnification and resolution?

Answer 22

• Electromagnets to focus a beam of electrons onto a specimen
• More dense areas = more absorbed
• Electrons have shorter wavelength, resolution = 0.2nm
• High mag = x1500000

Question 23

What is magnification?

Answer 23

Magnification - how much bigger the image of a sample is compared to the real size, measured by Magnification = Size of image / Size of real object

Question 24

What is resolution?

Answer 24

Resolution - how well distinguished an image is between 2 points; shows amount of detail; limited by wavelength of radiation used

Question 25

How do you measure the size of an object viewed with an optical microscope?

Answer 25

* Line up eyepiece graticule with stage micrometer * Use stage micrometer to calculate the size of divisions on eyepiece graticule at a particular magnification * Take the micrometer away and use the graticule to measure how many divisions make up the object * Calculate the size of the object by multiplying the number of divisions by the size of division * Recalibrate eyepiece graticule at different magnifications

Question 26

How do you prepare a temporary mount?

Answer 26

- Use tweezers to place a thin section of specimen e.g. tissue on a water drop on a microscope slide - Add a drop of a stain e.g. iodine in potassium iodide solution used to stain starch grains in plant cells - Add a cover slip by carefully tilting and lowering it, trying not to get any air bubbles

Question 27

What are the main stages in cell centrifugation?

Answer 27

* Homogenise * Filter * Ultracentrifuge