unit test

Question 1

B2
135 Define the term antigen

Answer 1

a molecule that triggers an immune response
- usually a protein found on the cell surface membranes / cell walls

Question 2

B2
137 Why do phagocytes move towards pathogens

Answer 2

chemical products of pathogens or dead, damaged abnormal cells act as attractants

Question 3

B2
138 What is a phagosome

Answer 3

vesicle containing the pathogen

Question 4

B2
144 When a pathogen enters the body it may be destroyed by phagocytosis
describe how

Answer 4

1. phagocyte recognises antigen
2. pathogen engulfed
3. enclosed in phagosome
4. phagosome fuses with lysosome
5. lysosome contain enzymes
6. pathogen digested

Question 5

B2
149 Why does the secondary immune response secrete more antibodies at a faster rate?

Answer 5

• After primary immune response, memory cells remain
• When memory cells encounter same antigen, they divide rapidly into plasma cells
• plasma cells produce large amounts of antibodies quickly

Question 6

B2
159 Describe the role of antibodies in producing a positive result in an ELISA test

Answer 6

1. first antibody binds to complementary antigen
2. second antibody with enzyme attached is added
3. second antibody attaches to first antibody
4. solution containing substrate added and colour changes

Question 7

B3
4 Describe and explain the main features of a specialised exchange surface

Answer 7

• 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

Question 8

B3
9 The tracheoles extend throughout the body tissue - why is this an advantage?

Answer 8

air rich in oxygen is brought directly to the respiring tissues
so short diffusion pathway from tracheole to any body cell

Question 9

B3
12 How does an insect limit water loss?

Answer 9

• can close spiracles
• waterproof covering over body surface

Question 10

B3
18 Explain how the mesophyll layer makes gas exchange more efficient in leaves

Answer 10

irregular in shape
therefore air spaces
so large SA

Question 11

B3
26 What causes thoracic cavity to increase?

Answer 11

external intercostal muscles contract
ribs move up and out of
diaphragm contracts and moves down

Question 12

B3
41 Why are there mineral salts in the saliva?

Answer 12

help maintain pH around neutral

Question 13

B3
43 Describe the role of enzymes of the digestive system in the complete breakdown of starch

Answer 13

1. amylase
2. starch to maltose
3. maltase
4. maltose to glucose
5. hydrolysis of glycosidic bond

Question 14

B3
48 What is a micelle?

Answer 14

monoglycerides and fatty acids associated with bile salts and phospholipids

Question 15

B3
49 What is the role of bile

Answer 15

neutralises stomach acid
- so enzymes in ileum do not denature

emulsifies lipids into smaller droplets
- so increases SA for lipases enzymes

Question 16

B3
55 Why can monoglycerides and fatty acids cross the membranes of the epithelial cells

Answer 16

small and non polar

Question 17

B3
66 In respiring tissue what is the pp of O2 like

Answer 17

relatively low

Question 18

B3
68 What effect does the binding of one oxygen molecule have on the affinity of Hb for oxygen

Answer 18

increases affinity
as it changes shape of oxygen molecule
2nd and 3rd oxygen molecules bind more readily

Question 19

B3
68 Describe and explain the effect of increasing carbon dioxide concentration on the dissociation of oxyhaemoglobin

Answer 19

1. more oxygen dissociation/unloading
2. decreases haemoglobin’s affinity for O2
3. by decreasing pH

Question 20

B3
78 What is a double circulatory system

Answer 20

blood passes through the heart twice for one complete circuit of the body

Question 21

B4
7 What term is given to the fixed position of a gene

Answer 21

locus

Question 22

B4
8 What are the different versions of a gene called

Answer 22

allele

Question 23

B4
10 The genetic code is universal.
What does this mean

Answer 23

the same triplet codes for the same amino acids in all organism

Question 24

B4
14 Within a gene only some of the bases code for amino acids
What are these parts called

Answer 24

exons

Question 25

B4 20 Where would you find the following triplet, codon, anticodon

Answer 25

triplet = DNA codon = mRNA anticodon = tRNA

Question 26

B4 26 Describe how mRNA is produced in a plant cell

Answer 26

1. helicase breaks hydrogen bonds between 2 strands 2. one of the strands is used as template 3. complementary base pairing A➡️U and C➡️G 4. RNA nucleotides joined by RNA polymerase 5. pre-mRNA formed 6. splicing removes introns to form mRNA

Question 27

B3 31 Describe and explain how the lungs are adapted to allow rapid exchange of oxygen between air in the alveoli and blood in the capillaries around them

Answer 27

1. many alveoli with folded walls = large SA 2. many capillaries = large SA 3. so fast diffusion 4. thin alveoli and capillary walls = short distance between alveoli and blood 5. flattened epithelium - so short diffusion distance = fast diffusion rate 6. ventilation - maintains a diffusion gradient = faster diffusionl

Question 28

B4 145 Describe how antibodies are produced in the body following a viral infection.

Answer 28

1. virus contains antigen; 2. virus engulfed by phagocyte; 3. presents antigen to B-cell; 4. B cells activated by cytokines; 5. B cells divides to form clones; 6. by mitosis; 7. plasma cells produce antibodies; 8. antibodies specific to antigen:

Question 29

describe how HIV is replicated

Answer 29

1. attachment proteins attach to receptors on helper T cell 2. RNA enters cell 3. reverse transcriptase converts RNA to DNA 4. enzymes produced 5. virus assembled snd released

Question 30

describe how HIV is replicated once inside helper T cells

Answer 30

1. reverse transcriptase converts RNA to DNA 2. DNA inserted into nucleus 3. DNA transcribed into RNA 4. HIV mRNA translated into new HIV proteins

Question 31

describe how mRNA is produced from an exposed template strand of DNA

Answer 31

1. nucleotides form complementary base pairs 2. phosphodiester bonds form 3. by RNA polymerase

Question 32

describe the role of a ribosome in the production of a polypeptide

Answer 32

1. mRNA binds to ribosome 2. ribosome has two codons 3. allows tRNA with anticodons to bind 4. peptide bond forms between amino acids 5. moves along mRNA

Question 33

explain the differences between the mean concentration of antibodies in blood samples 1,2,3

Question 34

describe the pathway taken by an oxygen molecule from an alveolus to the blood

Answer 34

1. alveolar epithelium 2. endothelium of capillary

Question 35

explain one feature of an alveolus allows efficient gas exchange to occur

Answer 35

1. one cell thick 2. creates short diffusion pathway

Question 36

explain how an arteriole can reduce the blood flow back into capillaries

Answer 36

1. muscle contracts 2. narrows arteriole/lumen