as 2020 1 and 2

Question 1

why does convergent evolution occur

Answer 1

due to continuous variation of these species

Question 2

why is the type of nuclear division in a zygote mitosis and not meiosis

Answer 2

mitosis is for growth; which needs genetically identical cells

Question 3

explain the role of embryonic stem cells in the development of an embryo

Answer 3

-undifferentiated/ not specialised
-are a renewing source of cells/ can differentiate into any cell type

Question 4

explain why cells of an inner cell mass of a blastula are not totipotent

Answer 4

-they are pluripotent
-not totipotent as cannot form a whole organism
-cannot give rise to extra embryonic tissue
-placenta not formed

Question 5

why is collagen a fibrous protein

Answer 5

-only has two different amino acids
-has a structural function/ provides strength
-long chain of amino acids
-little/ no tertiary structure
-insoluble/ many non-polar amino acids

Question 6

why is collagen so strong

Answer 6

-cross linking between adjacent molecules
-hydrogen bonds between polypeptides
-have staggered ends

Question 7

describe the structure of the rough endoplasmic reticulum

Answer 7

-phospholipid molecules form a bilayer
-forming cisternae/ network of membranes/ flattened sacs
-covered on outside with ribosomes
-membrane continuous with nuclear envelope

Question 8

explain the role of the membrane in the rough endoplasmic reticulum

Answer 8

-hold ribosomes/ enzymes in place
-compartmentalisation
-

Question 9

when error bars are large, what does this mean

Answer 9

means that the standard deviation is spread out

Question 10

describe the apoplast pathway

Answer 10

moves between/ along cell wall

Question 11

explain how a specific molecule is used to show that two different species have evolved from a recent common ancestor

Answer 11

-sequence of amino aicds/ DNA bases/ RNA bases
-the smaller the number of differences between the molceule, the more closely related they are

Question 12

what is a res of an SEM

Answer 12

5-50nm

Question 13

how are erythrocytes specialised for their function

Answer 13

-space for o2 maximised
-flexible
-haemoglobin
-flexible shape
-transport O2/ CO2
-move/ squeeze through blood vessels
-large sa to volume ratio

Question 14

how are neutrophils specialised for their function

Answer 14

-multilobed nucleus
-hydrolytic enzymes
-can change shape
-immune response
-destroy pathogens
-move to site of infection/ wound
-engulf pathogens

Question 15

how are squamous epithelial cells specialised for their function

Answer 15

-flatterened shape
-thin
-fit together tightly
-for rapid diffusion
-at alveoli/ blood vessels

Question 16

how are ciliated epithelial cells specialised for their function

Answer 16

-have cillia; hair like structures
-move/ beat in rhythm
-to move mucus/ trapped pathogens from lungs

Question 17

why can members of the same family get a disease

Answer 17

it can be passed down in genes

Question 18

what pathogen causes potato blight

Answer 18

prorocista

Question 19

outline the action of agglutinins

Answer 19

-clump/join pathogens
-stop pathogens moving/ reproducing
-helps phagocytes then engulf multiple/ clumped pathogens
-phagocytosis of clumped pathogens

Question 20

outline the process of vaccination to give an individual immunity

Answer 20

-a vaccine is produced that is a safe form of an antigen
-a small amount of vaccine is injected into the blood of the individual to be vaccinated
-antigen presentation occurs/ antigen bind to specific B/T lymphocyte/ cell
-clonal selection/ clonal expansion/ plasma cells produced/ produce antibodies- primary immune response
-memory cells/ secondary immune response

Question 21

explain why vaccinating most of the pop reduces spread of an infection

Answer 21

herd immunity occurs
fewer people can catch/ spread virus/ measles or fewer vaccinated.
most people cannot catch or spread the virus

Question 22

how are more precise results obtained

Answer 22

-repeats and calc mean
-use a biosensor to measure glucose conc
-more smaller temp intervals
-more regular time intervals

Question 23

what is the role of cartilage in gas exchange

Answer 23

cartilage stops trachea/ bronchus from collapsing

Question 24

what is the role of elastic fibres in gas exchange

Answer 24

elastic fibres allow for recoil of alveoli

Question 25

how does ventillation occur in bony fish

Answer 25

-water enters mouth
-pressure/ volume change in buccal cavity
-water flows/ pushed over gills
-water leaves via operculum
-throughflow system/ one direction flow

Question 26

how does bony fish gas exchange occur

Answer 26

-gill fillaments/ lamellae
-large surface area
-thin
-short diffusion distance
-good blood supply/ blood vessels
-steep conc grad
-counter current system
-tips of gill filaments overlap to slow down water transfer

Question 27

how does ventillation occur in insects

Answer 27

-muscular movements
-abdominal pumping
-volume/ pressure change in abdomen
-thorac change in flight
-air drawn in or forced out
-size of spiracles changes
-large surface area to volume ratio= diffusion may be sufficient

Question 28

how does gas exchange occur in insects

Answer 28

-gas/o2/co2 diffuses out of trachea
-oxygen dissolves in water at tracheoles
-diffuses into surrounding cells
-many tracheoles so large surface area
-spirals of chittin hold trachea open