unit test Flashcards
B2
135 Define the term antigen
a molecule that triggers an immune response
usually a protein found on the cell surface membranes or cell walls
B2
137 Why do phagocytes move towards pathogens
chemical products of pathogens or dead, damaged abnormal cells act as attractants
B2
138 What is a phagosome
vesicle containing the pathogen
B2
144 When a pathogen enters the body it may be destroyed by phagocytosis
describe how
- phagocyte recognises antigen
- pathogen engulfed
- enclosed in phagosome
- phagosome fuses with lysosome
- lysosome contain enzymes
- pathogen digested
B2
149 Why does the secondary immune response secrete more antibodies at a faster rate?
- After the primary immune response memory cells remain
- When memory cells encounter the same antigen they divide rapidly into plasma cells
- plasma cells produce large amounts of antibodies quickly
B2
159 Describe the role of antibodies in producing a positive result in an ELISA test
- first antibody binds to complementary antigen
- second antibody with enzyme attached is added
- second antibody attaches to first antibody
- solution containing substrate added and colour changes
B3
4 Describe and explain the main features of a specialised exchange surface
- Large SA:VOL = increases rate of exchange
- very thin = short diffusion pathway
- selectively permeable to regulate movement of substances
- movement of environmental medium to maintain diffusion gradient
- movement of internal medium to maintain diffusion gradient
B3
9 The tracheoles extend throughout the body tissue - why is this an advantage?
air rich in oxygen is brought directly to the respiring tissues
so short diffusion pathway from tracheole to any body cell
B3
12 How does an insect limit water loss?
can close spiracles
waterproof covering over body surface
B3
18 Explain how the mesophyll layer makes gas exchange more efficient in leaves
irregular in shape
therefore air spaces
so large SA
B3
26 What causes thoracic cavity to increase?
external intercostal muscles contract
ribs move up and out of
diaphragm contracts and moves down
B3
41 Why are there mineral salts in the saliva?
help maintain pH around neutral
B3
43 Describe the role of enzymes of the digestive system in the complete breakdown of starch
- amylase
- starch to maltose
- maltase
- maltose to glucose
- hydrolysis of glycosidic bond
B3
48 What is a micelle?
monoglycerides and fatty acids associated with bile salts and phospholipids
B3
49 What is the role of bile
neutralises stomach acid
so enzymes in ileum do not denature
emulsifies lipids into smaller droplets
so increases SA for lipases enzymes
B3
55 Why can monoglycerides and fatty acids cross the membranes of the epithelial cells
small and non polar
B3
66 In respiring tissue what is the pp of O2 like
relatively low
B3
68 What effect does the binding of one oxygen molecule have on the affinity of Hb for oxygen
increases affinity as it changes the shape of oxygen molecule
so 2nd and 3rd oxygen molecules can bind more readily
B3
68 Describe and explain the effect of increasing carbon dioxide concentration on the dissociation of oxyhaemoglobin
- more oxygen dissociation/unloading
- decreases haemoglobin’s affinity for O2
- by decreases pH
B3
78 What is a double circulatory system
blood passes through the heart twice for one complete circuit of the body
B4
7 What term is given to the fixed position of a gene
locus
B4
8 What are the different versions of a gene called
allele
B4
10 The genetic code is universal.
What does this mean
the same triplet codes for the same amino acids in all organism
B4
14 Within a gene only some of the bases code for amino acids
What are these parts called
exons
B4
20 Where would you find the following
triplet, codon, anticodon
triplet = DNA
codon = mRNA
anticodon = tRNA
B4
26 Describe how mRNA is produced in a plant cell
- helicase breaks hydrogen bonds between 2 strands
- only one of the strands is used as s template
- complementary base pairing so A➡️U and C➡️G
- RNA nucleotides joined by RNA polymerase
- pre-mRNA formed
- splicing removes introns to form mRNA
