A-Level Biology AQA Notes

Google rating

4.8

Trustpilot rating

4.7

View All Resources

Communication Systems

The neuronal system uses neurones to carry signals very rapidly through the body to produce short-term responses
The hormonal system uses blood to carry hormones from endocrine glands to target cell with the specific receptors. This usually produces long-term responses.
- Peptide hormones are made of amino acids and must bind to receptors on the cell surface, activating second messengers which control transcription.
- Steroid hormones are formed from lipids and soluble in the plasma membrane, therefore entering cells and binding to proteins to enter the nucleus and have an effect on the DNA.

Homeostasis

Homeostasis is the maintenance of a constant internal environment despite internal or external changes.
Temperature & pH are important to regulate to allow optimum enzyme activity and rate of metabolic reactions.
Water potential is important to regulate to prevent cells bursting or shrinking.
Glucose concentration is important to regulate to allow cells to have access to the substrate for respiration, whilst preventing cell damage by dehydration caused by high concentrations.
Negative feedback is the body’s mechanism for reversing a change so that it returns back to the optimum. The stages involve

Positive feedback is a deviation from the optimum which causes changes resulting in an even greater deviation from the norm. This is usually harmful due to the large, unstable change in the body.

Google rating

4.8

Trustpilot rating

4.7