Biology Paper 2 Notes and Flashcards

Definition: Homeostasis is the maintenance of a constant internal environment in the body.
Key Parameters: Blood glucose levels, water levels, and temperature must be controlled to ensure proper body function.
Control Center: The brain acts as the control center, sending signals to various parts of the body like the pancreas.

Components: Composed of the brain, spinal cord (central nervous system, CNS), neurons, receptors, and effectors.
Signal Transmission:
- Stimulus Response: When stimuli are detected, signals travel from the receptors (e.g., fingers) to the CNS and back, sometimes resulting in reflex actions.
- Reflex Action: A quick, involuntary response, such as withdrawing a hand from a hot object.
- Longer Responses: Other actions involve processing signals through the brain, requiring conscious thought before responding.
Nerve Cells: Long nerve cells send fast electrical signals, whereas crossing synapses requires chemical signals, causing delays.

Glands and Hormones:
- Pituitary Gland (brain): Produces FSH and LH.
- Thyroid Gland (neck): Produces thyroxine, regulates metabolism.
- Adrenal Glands (kidneys): Produce adrenaline, manages fight-or-flight response.
- Pancreas: Produces insulin to regulate blood glucose levels.
- Ovaries: Produce estrogen, controls egg maturation and menstrual cycle.
- Testes: Produce testosterone, responsible for male secondary sexual characteristics.

Post-Meal Regulation: After eating, blood glucose rises, detected by the pancreas that releases insulin.
- Insulin Action: Promotes uptake of glucose by body cells, conversion into glycogen in liver/muscle cells, lowering blood glucose levels.
Low Blood Glucose Levels: When glucose levels drop, the pancreas secretes glucagon to convert glycogen back into glucose, raising blood glucose levels.
Types of Diabetes:
- Type 1 Diabetes: Pancreas fails to produce insulin.
- Type 2 Diabetes: Body cells become insensitive to insulin.
Symptoms for Both Types: Weight loss, increased urination, thirst, fatigue, blurry vision, and hunger.
Treatment: Type 1 requires insulin injections; Type 2 is managed through diet and exercise.

Follicle-Stimulating Hormone (FSH): Begins the maturation of the egg.
Luteinizing Hormone (LH): Triggers ovulation.
Steroid Hormones: Estrogen and progesterone lead to menstrual cycle regulation and uterine lining preparation.

Barrier Methods: Condoms prevent pregnancy and STDs.
Hormonal Methods: Birth control pills and IUDs prevent ovulation or implantation of the egg.
Permanent Solutions: Sterilization (vasectomy for men, tubal ligation for women) prevents the release of sperm or eggs.
Infertility Issues: Approximately one in six couples face infertility, often addressed via IVF (In Vitro Fertilization).
- Advantages of IVF: Can provide a baby for those unable to conceive naturally.
- Disadvantages of IVF: Emotionally taxing, requires extensive medication with side effects, high costs, and variable success rates.

Mitosis:
- Results in two identical daughter cells.
- Used for growth and repair.
- Produces diploid cells (normal chromosome number).
Meiosis:
- Produces four genetically different daughter cells (gametes).
- Involves two rounds of division, including crossing over for genetic diversity.
- Produces haploid cells (half the chromosome number, e.g., eggs and sperm).
Asexual Reproduction: Common in bacteria and certain plants, results in genetically identical offspring.