Cell structure

Question 1

What is the structure of the nucleus?

Answer 1

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

Question 2

What is the function of the nucleus?

Answer 2

Site of DNA replication and transcription
Contains the genetic code for each cell

Question 3

What is the structure for the rough and smooth endoplasmic reticulum?

Answer 3

Both have folded membranes - cisternae

Rough has ribosomes on cisternae

Question 4

What is the function of the endoplasmic reticulums?

Answer 4

RER - protein synthesis
SER - synthesis and store lipids and carbohydrates

Question 5

What is the structure of the Golgi apparatus and vesicles?

Answer 5

Folded membranes making cisternae
Secretary vesicles pinch off from the cisternae

Question 6

What is the function of the Golgi apparatus and vesicles?

Answer 6

Add carbohydrates to proteins - glycoproteins
Produce secretory enzymes
Transport, modify and store lipids + proteins
Form lysosomes

Question 7

What is the structure of lysosomes?

Answer 7

Contain powerful hydrolytic enzymes (proteases, lipases, carbohydrase’s and nucleases)

Question 8

What is the function of lysosomes?

Answer 8

Fuses with phagosome (phagolysosome) and release hydrolytic enzymes
Destroy damaged organelles and cells
Exocytosis - release enzymes to outside of cell to destroy material
Completely break down dead cells (autolysis)

Question 9

What is the structure of mitochondria?

Answer 9

Double membrane
Inner membrane - cristae
Fluid centre - matrix
Loop of mitochondria DNA

Question 10

What is the function of mitochondria?

Answer 10

Site of aerobic respiration and ATP production
DNA codes for enzymes needed for respiration

Question 11

What is the structure of ribosomes?

Answer 11

Small, made up of two sub-units of protein and rRNA
80s - large, eukaryotic cells
70s - small, prokaryotic cells, mitochondria and chloroplasts

Question 12

What is the function of ribosomes?

Answer 12

Site of protein synthesis

Question 13

What is the structure of a vacuole?

Answer 13

Filled with fluid surrounded by a single membrane - tonoplast

Question 14

What is the function of a vacuole?

Answer 14

Makes cells turgid - provide support
Temporary store of sugars + amino acids

Question 15

What is the structure of chloroplasts?

Answer 15

Surrounded by double membrane
Thylakoids (folded membranes embedded with pigment)
Fluid filled stroma has enzymes - photosynthesis

Question 16

What is the function of chloroplasts?

Answer 16

Site of Photosynthesis

Question 17

What is the structure of a cell wall?

Answer 17

plants - microfibrils of cellulose
fungi - chitin, nitrogen containing polysaccharide

Question 18

What is the function of a cell wall?

Answer 18

Provide structural strength to the cell

Question 19

What is the structure of the cell membrane?

Answer 19

Selectively permeable
Phospholipid bilayer

Question 20

What is the function of the cell membrane?

Answer 20

Controls the entrance and exit of molecules

Question 21

What do all prokaryotic cells contain?

Answer 21

Cytoplasm, ribosomes, plasma membrane, DNA

Question 22

What is the equation for magnification?

Answer 22

actual size = image/magification

Question 23

What are the features of light microscopes?

Answer 23

magnification = x2000
resolution = 200nm

visible light passes through specimen
cheap, can study living cells
limited magnification and resolution, thin specimen only
2D image

Question 24

What are the features of transmission electron microscopes?

Answer 24

magnification = x500 000
resolution = 0.05-0.2nm

electromagnets focuses a beam of electrons - transmitted through specimen
denser parts absorb more electrons
higher resolution allows internal structure to be seen
no live specimen due to vacuum - removes all water
2D

Question 25

What are the features of a scanning electron microscope?

Answer 25

magnification = x250 000 resolution = 0.5nm scans beam of electrons across specimen thick or 3D specimen used can't observe live specimen, no colour, lower resolution 3D

Question 26

What is cell fractionation?

Answer 26

Used to isolate different organelles to study them 1) homogenisation 2) ultracentrifugation

Question 27

What solution do cells need to be in for cell fractionation?

Answer 27

Cold - reduce enzyme activity, cells break open enzymes released may damage organelles Isotonic - same water potential to prevent osmosis - cells don't shrivel or burst Buffered - pH buffer prevents damage

Question 28

What is homogenisation?

Answer 28

Cells broken up (homogenised) using a blender in cold, isotonic and buffered solution Solution is filtered to remove large cell debris

Question 29

What is ultracentrifugation?

Answer 29

Filtered solution is spun at different speeds in a centrifuge Organelles separate according to densities

Question 30

What is differential centrifugation?

Answer 30

Centrifugal forces causes most dense organelles to from at the bottom Speed increases + each time the super latent (liquid) is removed, leaving a pellet of organelles

Question 31

What is the density order of organelles?

Answer 31

Nuclei Chloroplast Mitochondria Lysosomes Endoplasmic reticulum Ribosomes

Question 32

What are the three stages of cell division?

Answer 32

Interphase Mitosis Cytokinesis

Question 33

What are the stages of mitosis?

Answer 33

prophase, metaphase, anaphase and telophase

Question 34

What happens in prophase?

Answer 34

Chromosomes condense (shorter + thicker) 2 sister chromatids joined by a centromere Nuclear envelope breaks down Centrioles move to opposite poles forming spindle network

Question 35

What happens in metaphase?

Answer 35

Chromosomes align along equator Spindle fibres attach to chromosomes by centromeres

Question 36

What happens in anaphase?

Answer 36

Spindle fibres contract --> pull chromatids to opposite poles Centromere divides

Question 37

What happens in telophase?

Answer 37

Chromosomes uncoil (longer/thinner) Nuclear envelope reforms (2 nuclei) Spindle fibres and centrioles break down

Question 38

What happens in cytokinesis?

Answer 38

Cell divides into two - creates new genetically identical cells

Question 39

What is mitotic index?

Answer 39

percentage/measure of cells undergoing mitosis