Hard questions

Question 1

Describe why facilitated diffusion requires no metabolic energy

Answer 1

1. Particles have their own kinetic energy

2. Move down the concentration gradient

Question 2

Explain why glucose cannot pass through a cell membrane by simple diffusion

Answer 2

1. Phospholipids act as a barrier

2. The molecules are too large

Question 3

Suggest how the leaf of pondweed is supported

Answer 3

1. Air spaces give buoyancy

2. Supported by surrounding water

Question 4

Suggest why antibodies specific to nuclear proteins are not normally made

Answer 4

1. Nuclear proteins normally hidden in the nucleus

Question 5

Suggest how water is being lost from the cut stem when leaves have been treated with petroleum jelly in a potometer experiment

Answer 5

1. Evaporation form upper leaf surfaces

Question 6

Suggest two sources of error in a potometer experiment

Answer 6

1. Not all lower leaf surfaces covered
2. leaks in apparatus
3. Shoot not cut under water
4. Error in reading position of the meniscus

Question 7

Explain why bone is described as a tissue and gills are described as organs

Answer 7

1. Tissue has few types of cells and performs one function
2. Bone has a few types of cells and performs one function
3. Organs consist of several tissues
4. Gills contain blood, bones, epithelial and connective tissue

Question 8

How would the calculated rate differ form the true initial rate of reaction in an enzyme reaction

Answer 8

1. Initial rate is likely to be greater

2. Because higher concentration of substrate at start, so more chance of substrate entering the active site

Question 9

Give ways to refine an experiment so reproducible results would be obtained

Answer 9

1. Specify volumes of reactants added
2. Specify volume that should be removed for testing
3. Stir before taking the sample
4. Test with iodine- for starch, or other chemicals
5. Carry them all out at the same temperature

Question 10

Explain why vaccinations are examples of active immunity

Answer 10

1. Antibodies are produced
2. Activation of lymphocytes
3. Memory cells remain

Question 11

State 3 properties of fibrous proteins that are different to globular proteins

Answer 11

1. Insoluble
2. Strong
3. Unreactive

Question 12

How could haemoglobin be identified in urine

Answer 12

1. Add biurets reagent
2. Colour change from blue to purple
3. Compare with control

Question 13

Outline how the difference in lumen size between arteries and veins is related to their function

Answer 13

1. In arteries small lumen maintains high pressure
2. In veins large lumen- low resistance needed because of low pressure
3. Same flow rate is achieved by having a larger volume

Question 14

Why is movement of molecules from the plasma membrane towards the centre of living cells greater than in an experiment

Answer 14

1. Involvement of vesicles/ cytoskeleton

Question 15

Stem cells can specialise to form a variety of cell types. What other feature is shown by stem cells but not specialised cells

Answer 15

Ability to continue dividing

Question 16

Why do cells need to be stained

Answer 16

1. Provide contrast

2. Identify components

Question 17

State why the structure of enzyme molecules allows them to be detected in solution using the biuret test

Answer 17

1. Enzymes are globular proteins

2. Hydrophilic groups on outside of enzyme

Question 18

Some enzymes work better in the presence of other molecules or ions. Explain how these molecules or ions increase the activity of enzymes

Answer 18

1. Cofactors/ coenzymes
2. Bind to enzyme temporarily
3. They change the shape of the active site and change the charges on the active site
4. They bind to substrate
5. Increased likelihood of substrate binding to active site
6. Carry chemicals between enzymes

Question 19

Explain the benefits to agriculture of maintaining plant biodiversity

Answer 19

1. Maintaining genetic variation- useful source of genes
2. Used for genetic engineering
3. Used for selective breeding
4. Variety might be useful in changing climate
5. Habitat for pollinators
6. Agents for biological control
7. Source of new medicine for livestock

Question 20

Suggest 3 reasons why the three-domain classification system is now used in preference to the five-kingdom system

Answer 20

1. 3 domain system fits phylogeny better- reflects evolutionary history better
2. Number of important differences between bacteria and ekaryotes
3. Eukaryotes all have a nucleus and 80s ribosomes
4. Many fundamental differences between archaea and bacteria
5. They have different cell membrane/ flagella/ enzymes

Question 21

Explain why some foods are stored in a freezer

Answer 21

1. Decay/ food spoilage is slower
2. Molecules have little kinetic energy
3. Fewer collisions between substrate and active site
4. Water availability reduced.

Question 22

What is the name of a limiting level for a population in a particular area

Answer 22

Carrying capacity

Question 23

Why might vegetative propagation be less effective against enabling a tree to survive a disease compared to surviving fire or high wind

Answer 23

1. New sprouts are clones so no genetic variation

2. They are as susceptible as to the disease as the parent plant is

Question 24

What can show the development controlled by homeobox genes in a human embryo

Answer 24

1. Head/tail orientation
2. Position/ development of limbs
3. Segmentation
4. Development of eyes

Question 25

What is the benefit of bacteria being able to transmit plasmids from one cell to another

Answer 25

1. Can take up useful genes 2. Such as antibacterial resistance 3. Faster/ without waiting for mutation

Question 26

Suggest a way other than extracting a gene from one organism or from cDNA libraries to obtain a gene

Answer 26

1. Chemical synthesis/ polynucleotide synthesising.

Question 27

Suggest two ethical arguments for and against genetic manipulating a plant

Answer 27

1. Relief of particular vitamin deficiency 2. Expense of seed for growers and consumers 3. Uncontrolled hybridisation with other species 4. Unknown long-term health effects on consumers' health

Question 28

On a sunny day more pondweed is at the surface of the water but on a cloudy day, less pondweed is at the surface of. Explain this

Answer 28

1. Greater light intensity on sunny day 2. Oxygen produced during photosynthesis 3. Oxygen trapped within the weed created buoyancy.

Question 29

ATP is produced in two different ways 1. Produced in Krebs cycle 2. Produced using reduced NAD and FAD on the inner mitochondrial membrane Outline the differences in the two ways by which ATP is produced in respiration

Answer 29

1. By substrate level phosphorylation - By removing phosphate from a compound 2. By chemiosmosis - Hydrogen lost from redNAD / redFAD - electrons pass down electron transport chain - ref to proton gradient / electrochemical gradient - ref to ATP synth(et)ase

Question 30

Suggest why it can be deduced that hormones act on the SAN rather than on individual cardiac muscle cells

Answer 30

1. Stimulation of individual muscle cells would result in uncoordinated response 2. Stimulation of individual muscle cells will not result in a change in heart rate 3. receptors only present on the SAN

Question 31

Describe how the guard cells surrounding leaf pores are adapted to their roles

Answer 31

1. Unevenly thickened walls 2. Able to bend and change shape 3. Transport proteins into plasma membrane 4. Presence of chloroplasts- energy

Question 32

Describe how the structure of cell walls in xylem vessels would differ from undifferentiated plant cells cell walls

Answer 32

1. Thicker 2. Lignified 3. Contains pits

Question 33

Describe how alveoli create a surface for efficient gaseous exchange

Answer 33

1. Wall is one cell thick for shorter diffusion distance 2. Squamous epithelium provide short diffusion distance 3. Elastic so recoil which helps with venitlation 4. Create / maintain, concentration gradient 5. Large number of alveoli provide larger surface area ; 6. Small size of alveoli provide larger surface area to volume ratio 7. Cells secrete surfactant to maintain surface area

Question 34

Describe the effect of high temperature on the structure of yeast cell membrane

Answer 34

1. Phospholipids have more kinetic energy 2. Increases gaps between phospholipids 3. Bilayer becomes more fluid 4. Proteins/glycoproteins denature

Question 35

Define the term parasite

Answer 35

1. Lives in host 2. Gains nutrition from host 3. At the expense of the host

Question 36

Outline significance of low value of Simpson's Index of Diversity

Answer 36

1. Dominated by one/ few species | 2. Ecosystem is unstable

Question 37

Define the term phylogeny and explain how phylogeny is related to classification

Answer 37

1. Phylogeny is the evolutionary relationship between organisms 2. Phylogeny is the basis of classification 3. Base sequence used to classify 4. Species / organisms within the same group have shared phylogeny

Question 38

Explain how selective breeding of wheat could be done

Answer 38

1. Cross-breed high-yielding wheat plants 2. Assess the yield 3. Cross breed high-yielding offspring 4. Over several generations 5. Prevent self-pollination/ unwanted cross-pollination

Question 39

Describe how the structure of antibodies allows them to perform their function

Answer 39

1. 2 light chains and 2 heavy chains / 4 polypeptide chains 2. Variable region allows binding to antigen 3. Two variable regions allow binding of more than one (of the same) antigen 4. Variable region on different antibodies allows specificity to different antigens 5. constant region allows recognition by / attachment to /binding to phagocytes 6. Hinge (region) allows flexibility 7. Disulfide bonds hold polypeptides together

Question 40

Describe how antibodies carry out neutralisation and agglutination

Answer 40

``` Neutralisation 1. Block binding site on pathogen 2. Bind to toxins 3. Prevent entry to host cell Agglutination 1. Clump together many pathogens 2. Too large to cross membranes 3. Increase likelihood of being consumed by phagocyte ```

Question 41

After the initial release of insulin from the beta cell, insulin secretion continues even when there is no further glucose intake. Explain why

Answer 41

1. Continues to be secreted) as long as blood glucose (concentration) remains high than normal 2. ATP is still present and so K+ channels remain closed 3. Exocytosis still being triggered by calcium ions

Question 42

Why does aerobic respiration yield fewer molecules of ATP than the theoretical maximum

Answer 42

1. some ATP used to (actively) transport pyruvate 2. some ATP used to (actively) transport H(+) from (reduced) NAD formed in glycolysis 3. Some energy in electron transport chain is released as heat 4. Not all the H+ movement (back across membrane) is used to generate ATP 5. Not all the, reduced NAD / red NAD / NADH is used to feed into the ETC

Question 43

Why does the dialysis fluid in peritoneal dialysis contain dextrose solution rather than water alone

Answer 43

1. Dialysis is replicating function of kidney and part of kidney’s function is to remove (excess) water from blood 2. Reduces water potential of dialysis fluid 3. Water moves from blood (into dialysis fluid) by osmosis 4. Prevents water moving into the blood from dialysis fluid by osmosis 5. If it was water alone cells would swell / burst

Question 44

Suggest why patients receiving peritoneal dialysis usually need to have the peritoneal dialysis fluid replaced four times a day, but those receiving haemodialysis only need treatment 4 times a week

Answer 44

1. Peritoneal dialysis can remove less waste than haemodialysis 2. In haemodialysis dialysis fluid is constantly refreshed but not in peritoneal dialysis 3. Haemodialysis uses counter-current flow 4. In peritoneal dialysis the concentration gradient reduces / is lower 5. In peritoneal dialysis the fluid reaches equilibrium with the blood