ch1: kili, fili and pili

Question 1

outline the cell theory (2)

Answer 1

living things are composed of 1+ cells
cells are the basic unit of life
cells come from pre-existing cells

Question 2

outline the therapeutic use of stem cells (5)

Answer 2

stem cells retain their capacity to divide
unspecialised: multi/pluri/totipotent
form a variety of tissues/organs → repair/replace damaged ones
during differentiation: some genes are expressed while some are suppressed
used in medical research: embryonic stem cells can cure Stargardt’s disease

Question 3

outline the use of human embryonic stem cells to treat Stargardt’s disease (2)

Answer 3

eye genetic disorder
stem cells can differentiate into healthy retinal cells
injecting stem cells into the eye can restore vision in animal and human trials

Question 4

discuss the advantages and disadvantages of the use of adult stem cells (3)

Answer 4

advantages:
can differentiate: repair/regenerate tissues/organs
fewer ethical objections than with embryonic stem cells
adults can give informed consent for use of their stem cells
adult source is not killed

disadvantages:
difficult to obtain in adult body bc very few available
some adult tissues contain few to none stem cells
adult stem cells differentiate into fewer cell types than embryonic cells

Question 5

explain the importance of surface area to volume ratio as a factor limiting cell size (7)

Answer 5

V ↑ → ratio of SA to V ↓
rate of substance crossing the membrane depends on SA:
food/oxygen enter
waste leave

larger cell → ↑ metabolic activity
↑ food and oxygen required
↑ waste produced
↑ diffusion time

eventually surface area can no longer serve the requirements of the cell
size of the cell is reduced and kept within size limits
critical ratio stimulates mitosis

Question 6

why are specimens stained? (1)

Answer 6

most cell structures are colourless → clearer observation

Question 7

reasons for using cover slip on specimen (2)

Answer 7

flatten specimen for better focusing
prevent specimen from drying
prevent objective from touching mounting solution

Question 8

distinguish between prokaryotic cells and eukaryotic cells (6)

Answer 8

google docs

Question 9

draw a prokaryotic cell (5)

Answer 9

google docs

Question 10

draw a human eukaryotic cell (5)

Answer 10

google docs

Question 11

draw a plant cell (5)

Answer 11

google docs

Question 12

state the function of a flagella (1)

Answer 12

movement of the bacterial cell

Question 13

state the functions of pili (2)

Answer 13

connect bacterial cells → transfer of genetic material

adhesion to another cell/surface

Question 14

state the functions of the naked DNA in prokaryotic cells (2)

Answer 14

located in the nucleoid region: nucleoid initiates binary fission
controls cell structure and function

Question 15

state the functions of a plasmid (2)

Answer 15

confer luxury functions

e.g. antibiotic resistance

Question 16

state the functions of a capsule (2)

Answer 16

protects cell

promotes adherence

Question 17

state the function of ribosomes (1)

Answer 17

site of synthesis of proteins released to cytoplasm

Question 18

state the functions of a plasma membrane (2)

Answer 18

carries out active transport

controls entry and exit of substances

Question 19

state the function of cytoplasm (1)

Answer 19

contains enzymes that carry out metabolism

Question 20

state the function of lysosomes (1)

Answer 20

digestive enzymes break down food

Question 21

state the function of the Golgi apparatus (1)

Answer 21

collection, packaging, modification and distribution of proteins

Question 22

state the functions of cell walls (3)

Answer 22

protects the cell from damage
prevents the cell from bursting
provide rigidity and support

Question 23

state the function of a rough endoplasmic reticulum (1)

Answer 23

synthesis and transport of proteins

Question 24

state the function of centrosomes (1)

Answer 24

pair of centrioles at right angles → assembly of microtubules → cell division

Question 25

state the functions of a large central vacuole (1)

Answer 25

provide turgidity and support

Question 26

suggest how microscopic images of plasma membranes led to Davson-Danielli model of membrane structure (2)

Answer 26

protein lipid sandwich appears as 2 black lines proteins stained black phospholipids unstained

Question 27

explain how properties of phospholipids help to maintain the structure of cell membranes (8)

Answer 27

phospholipid consisting of head + 2 tails head: glycerol + phosphate hydrophilic: attracted to water tails: fatty acid chains hydrophobic: not attracted to water but each other leads to the formation of double layer in water → stability heads are outer & attracted to water tails in the middle & attracted to each other attraction of non-polar tails to each other → in fluid state allows vesicles to form or fuse with membrane non-polar amino acid side chains attracted to hydrophobic tails

Question 28

why is the structure of the cell membrane fluid and mosaic? (2)

Answer 28

fluid: phospholipid and protein molecules can move laterally mosaic: diff kinds of protein molecules interspersed among phospholipid molecules in mosaic pattern

Question 29

draw a labelled diagram to show the fluid mosaic structure of a plasma membrane (5)

Answer 29

google docs

Question 30

outline how molecules move across a membrane by simple diffusion (2)

Answer 30

membranes are permeable allowing diffusion diffusion = passive movement of particles from high to low conc continues until conc are equal across the membrane no use ATP

Question 31

compare simple diffusion with facilitated diffusion as mechanisms to transport solutes across membranes (5)

Answer 31

google docs

Question 32

explain passive transport and active transport across membranes (8)

Answer 32

large and polar molecules cannot cross the hydrophobic membrane freely google docs

Question 33

define osmolarity (1)

Answer 33

measurement of solute concentration of a solution

Question 34

outline the effects of putting plant tissue in a hypertonic solution (4)

Answer 34

hypertonic solution has higher solute concentration than the tissue water moves out of the cells by osmosis from lower solute conc to higher solute conc cell becomes flaccid and plasmolysed

Question 35

describe how the structure of the membrane allows the formation of vesicles (2)

Answer 35

phospholipid bilayer makes membrane fluid → allows change of shape cholesterol affects membrane fluidity: provides firmness and integrity and prevents it from becoming overly fluid phospholipid tails weak bonding kinks prevent close packing

Question 36

explain how vesicles are used to transport materials secreted by a cell (8)

Answer 36

proteins synthesised by ribosomes + rER proteins are bound by vesicles vesicles bud off from rER → transport proteins to Golgi apparatus → fuse with Golgi apparatus membranes Golgi modifies proteins as they move along in vesicles secretory vesicles bud off in trans Golgi → move across the cytoplasm → fuse with plasma membrane exocytosis: release proteins outside the cell rER + vesicle + plasma membrane have phospholipid bilayer structure cells use vesicles to secrete substances e.g. hormones + digestive enzyme can contain cell products other than proteins

Question 37

describe the process of endocytosis (5)

Answer 37

2 phospholipid layers form a pit to enclose a target particle → edges fuse back → make vesicle fluidity of membrane permits movement inner phospholipid layer of original membrane → outer phospholipid layer of vesicle outer phospholipid layer of original membrane → inner phospholipid layer of vesicle vesicle moves into cytoplasm changes in membrane shape require ATP e.g. pinocytosis + phagocytosis

Question 38

outline four different functions of membrane proteins (4)

Answer 38

``` binding site for hormone/neurotransmitter cell-to-cell communication channels for facilitated diffusion pumps for active transport cell adhesion enzymes embedded in the membrane electron transport ```

Question 39

explain the endosymbiotic theory (5)

Answer 39

symbiosis occurs when 2 different species benefit from living and working together endosymbiosis: 1 organism living inside the other ``` there is evidence that mitochondria and chloroplasts were once primitive free-living bacterial cells: DNA loop binary fission double membrane 70s ribosomes ``` a large host cell & the bacteria ingested through endocytosis become dependent on one another for survival → permanent relationship smaller cell was provided food and protection by the larger cell mitochondria would supply energy through aerobic respiration for the larger cell chloroplast would supply food through photosynthesis for the larger cell millions of years of evolution → mitochondria and chloroplasts have become more specialised → cannot live outside the cell

Question 40

describe Pasteur’s experiment of spontaneous generation (4)

Answer 40

he prepared a nutrient broth placed equal amounts of the broth into 2 long-necked flasks: one flask with a straight neck one bent to form an “S” shape boiled the broth in both flasks to kill any living matter → sterile flasks sit at room temperature + exposed to the air broth in the straight-neck flask was discoloured and cloudy: organisms in the air were able to fall unobstructed → contaminate the broth broth in the curved-neck flask had not changed: trapped organisms in its curved neck → prevent them from reaching the broth

Question 41

describe the events that occur during the cell cycle/mitosis (9)

Answer 41

interphase: G1: cell grows + organelles duplicate S: DNA replication G2: chromosomes begin condensing + prep for cell division mitosis: prophase: chromosomes condense by supercoiling → sister chromatids visible nuclear membrane breaks down prophase + metaphase: spindle microtubules grow from poles to equator metaphase: spindle microtubules attach to the centromeres chromosomes line up at equator anaphase: centromeres split sister chromatids separate → dragged to opposite poles by the shortening of spindle microtubules telophase: spindle microtubules disappear nuclear membrane reforms around chromosomes → decondense cytokinesis: cytoplasm divides → 2 daughter cells with identical nuclei plant: cell plate form between nuclei

Question 42

explain how the cell cycle is controlled (5)

Answer 42

cell cycle = G1, S, G2, mitosis levels of cyclins fluctuate during the cell cycle 4 cyclins enter different stages in cell cycle → sequence of stages controlled by cyclins cyclins bind to kinases → activate cyclin-dependent kinases kinases phosphorylate other proteins phosphorylated proteins perform specific functions in the cell cycle conditions inside + outside cell affect regulation

Question 43

list processes that involve mitosis (2)

Answer 43

growth (through increasing cell number) embryonic development tissue production/repair asexual reproduction