What is a pathogen?- definition
-microorganism that causes disease
How when a pathogen enters the body it may be destroyed by phagocytosis
- the phagocyte recognises foreign antigen
- then the pathogen is engulfed
- and enclosed in a vesicle
- the vesicle fuses with a lysosome
- which contains enzymes
- that hydrolyse the pathogen
Antibody specificity
- antibodies are a specific shape
- and antigens on pathogen are complimentary to the antibody and an antibody-antigen complex is formed
Benedicts test for reducing sugars
- Add Benedict’s and
- Heat
- Red/orange/yellow/green shows reducing sugar is present
The type of chemical reaction which produces amino acids from proteins
- hydrolysis
Why the peptides released when gluten is digested cannot be absorbed by facilitated diffusion
- too big
- to fit through
- carrier/channel protein
Factors that should be considered before the drug can be used on patients with the disease
- Dose to be given
- No serious side effects
- How effective
- Cost of drug
How the heart controls and coordinates the regular contraction of the atria and ventricles
- SAN -> AVN -> bundle of His /Purkyne fibres
- impulses over atria
- makes atria contract
- and the non-conducting tissue between the atria and ventricles
- cause a delay at AVN and ensures the atria empty and ventricles fill before they contact
- from apex upwards
How the diet of a person can increase the risk of coronary heart disease
- too much saturated fat/cholesterol in diet
- increases LDL/ cholesterol in blood
- causing atheroma/ fatty deposits in artery walls
- and blocks coronary arteries
- so less oxygen/glucose goes to heart muscle
- it can also cause increased blood pressure#-and increased risk of clot / thrombosis / embolism/ aneurysm
The student prepared a temporary mount of the onion tissue on a glass slide. She covered the tissue with a cover slip. She was then given the following instruction. “Push down hard on the cover slip, but do not push the cover slip sideways. Explain why she was given this instruction.
- Push hard – spread/squash tissue;
- Not push sideways – avoid rolling cells
together/breaking chromosomes;
The student concluded that the cell in Figure was in the anaphase stage of mitosis. Was she correct? Give two reasons for your answer.
- Chromosomes/chromatids are (in two groups) at poles of spindle/at ends of spindle;
- V-shape shows that (sister) chromatids have been pulled apart at their centromeres/that centromeres of (sister) chromatids have been pulled apart;
Breathing out as hard as you can is called forced expiration. Describe and explain the mechanism that causes forced expiration.
- Contraction of internal intercostal muscles;
- Relaxation of diaphragm muscles/of external intercostal muscles;
- Causes decrease in volume of chest/thoracic cavity;
- Air pushed down pressure gradient;
The people in group B were recovering from an asthma attack. Explain how an asthma attack caused the drop in the mean FEV
- Muscle walls of bronchi/bronchioles contract;
- Walls of bronchi/bronchioles secrete more mucus;
- Diameter of airways reduced;
- (Therefore) flow of air reduced;
The scientists used kittens (newborn cats) as model organisms in their laboratory investigation. Other than ethical reasons, suggest two reasons why they chose to use cats as model organisms.
- (Are mammals so) likely to have same
physiology/reactions as humans; - Small enough to keep in laboratory / produce enough milk to extract;
- (Can use a) large number;
Explain why monitoring the pH of the mixture could show whether the cat’s milk contained lipase
- Hydrolysis of lipids produces fatty acids;
2. Which lower pH of mixture;
Suggest how this student would obtain data to give a more precise value for the index of diversity of this habitat.
- Take more samples and find mean;
2. Method for randomised samples described;
One farmer stated that the increase in the use of Bt crop plants had caused a mutation
in one of the insect species and that this mutation had spread to other species of insect. Was he correct? Explain your answer.
(No – no mark)
- Mutations are spontaneous/random;
- Only the rate of mutation is affected by environment;
- Different species do not interbreed/do not produce fertile offspring;
- So mutation/gene/allele cannot be passed from one species to another;
There was a time lag between the introduction of Bt crops and the appearance of the first insect species that was resistant to the Bt toxin.
Explain why there was a time lag.
- Initially one/few insects with favourable mutation/allele;
- Individuals with (favourable) mutation/allele will
have more offspring; - Takes many generations for (favourable)mutation/allele to become the most common allele (of this gene);
One theory of translocation states that organic substances are pushed from a high pressure in the leaves to a lower pressure in the roots. Describe how a high pressure is produced in the leaves.
- Water potential becomes lower/becomes more negative (as sugar enters phloem);
- Water enters phloem by osmosis;
- Increased volume (of water) causes increased pressure;
When a vaccine is given to a person, it leads to the production of antibodies against a disease-causing organism. Describe how.
- Vaccine contains antigen from pathogen;
- Macrophage presents antigen on its surface;
- T cell with complementary receptor protein
binds to antigen; - T cell stimulates B cell;
- (With) complementary antibody on its surface;
- B cell secretes large amounts of antibody;
- B cell divides to form clone all
secreting/producing same antibody;
Describe the difference between active and passive immunity.
- Active involves memory cells, passive does not;
- Active involves production of antibody by plasma cells/memory cells;
- Passive involves antibody introduced into body from outside/named source;
- Active long term, because antibody produced in response to antigen;
- Passive short term, because antibody (given) is broken down;
- Active (can) take time to develop/work, passive fast acting;
Enzyme specificity –explain why maltase only catalyses the hydrolysis of maltose
- the active site of the enzyme has a specific shape caused by the tertiary structure. Thus means the active site is complimentary to the substrate (maltose)
- so only maltose can fit into the active site
- to form an enzyme-substrate complex
Ways in which pathogens can cause disease
- releases toxins
- kills cells
Water potential
- water potential in bacteria cells is higher than in honey
- so water leaves bacteria cells by osmosis
- the loss of water stops metabolic reactions
