Key points, AQA AS level biology unit 1

Key points, mark scheme answers

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  • Created by: Aimee
  • Created on: 02-01-13 00:36


Diarrhoea is caused when there is a lower water potential in the lumen than in the epithelial cell, so the water leaves the cell and enters the intestine via osmosis. This causes diarrhoea.  

Oral Rehydration Solution
- Increases the uptake of ions/glucose/sugars/salts
- By co-transport proteins
- Lowers water potential in the cells
- Water moves out of intestine, into cells
- Via osmosis 

ORS contains...
- GLUCOSE/starch/carbohydrate/sugar
- SODIUM/salt

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The Cardiac Cycle

The maximum pressure in the ventricle is higher than the maximum pressure in the atrium because:
- Ventricle has a thicker, more muscular wall
- So contractions are stronger

1. SAN → AVN → bundle of His /Purkyne fibres;
2. SAN sends out wave of electrical activity over artria
3. Atria contract
4. Non-conducting tissue between atria and ventricles
5. Delay at AVN ensures atria empty/ventricles fill before ventricles contract
6. Ventricles contract from apex upwards

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During an asthma attack, less oxygen diffuses into the blood from the alveoli because...
- An asthma attack narrows airways
- Air in alveoli is not replaced as efficiently
- Difference in concentration not as big so lower rate of diffusion

How oxygen in the alveoli enters blood in the capillaries...
- Diffusion
- across alveoli epithelium 

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Antibodies and Antigens

Antibodies will only detect a particular antigen because...
- Antibodies have a specific primary structure
- Shape of binding site is complementary to antigen
- Antibody is complementary to antigen
- Forms an antigen-antibody complex.

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Starch digestion

The role of enzymes in the complete breakdown of starch:
- Amylase converts

- Starch to maltose
- Maltase converts
- Maltose to glucose
- via hydrolysis
- of the glycosidic bond 

Processes involved in the absorption of the products of starch digestion:
- Glucose moves into epithelial cell with sodium
- Via co-transport
- Sodium removed from epithelial cell by Sodium-Potassium pump
- Into blood
- Maintaining low concentration of sodium in the epithelial cell
- Glucose moves into blood; 
- By facilitated diffusion;      


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How diet increases risk of CHD
1. Too much saturated fat/ cholesterol in diet;

2. Increase in LDL/ cholesterol in blood;
3. Atheroma forms in aterial walls
4. Blocks/reduces diamater of coronary arteries
5. Less oxygen/ glucose to heart muscle
6. Increase in blood pressure;
7. Increased risk of thrombosis

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Ventilation helps to maintain a difference in oxygen concentration because...
- Brings in air containing a higher oxygen concentration
- Removes air with a lower oxygen concentration

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How do vaccines protect people from disease?
- Vaccines are dead/weakened pathogens
- Contain antigens
- Memory cells are made
- On second exposure, memory cells recognise pathogens
- Rapidly produce antibodies
- Antibodies destroy pathogens
- Herd effect/fewer people to pass on disease.

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How does emphysema reduce rate of gas efficiency in the lungs? 
- Alveoli break down
- Reduced surface area
- So less diffusion
- Loss of elastin
- Less air expelled
- Reduced diffusion gradient

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Induced fit:
- Active site not complementary
- Active site is flexible
- Change in enzyme allows enzyme-substrate complex to form

Lock and key:
- Active site is rigid/already complementary.

Competitive inhibitor:
- Similar shape to substrate
- Binds to active site
- Less enzyme/substrate complexes formed

Non-competitive inhibitor:
- Different shape to substrate
- Binds to position away from the active site
- Changes shape of active site
- Less enzyme-substrate complexes formed

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Pulmonary Tuberculosis

- Bacteria transmitted in droplets
- Bacteria engulfed by phagocytes
- Bacteria encased in tubercle
- Bacteria dormant
- If immunosuppressed, bacteria activate
- Bacteria destroy alveoli
- Leads to scar tissue
- Leads to lower surface area so less diffusion
- Damage allows bacteria to enter blood/spread to other organs

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Enzymes cannot be taken as a tablet because:
- Enzymes are proteins
- Will be broken down by acid in stomach


- Enzymes are too large
- to be absorbed and enter the bloodstream

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How are lungs adapted to allow rapid exchange of oxygen between the air in the alveoli and the blood in the capillaries around them?
- Alveoli walls folded to provide a large surface area
- Many capillaries provide a large surface area
- So fast diffusion
- Thin alveoli walls
- So short diffusion pathway
- Ventrilation and circulation
- Maintains diffusion gradient

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Revision Mode

These are great, explained very well and easy to understand. Thankyou sooooo much!!

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