Biology Paper 2

• Homeostasis is regulation of the internal environments or conditions that just means keeping things constant
• Homeostasis


  Keeping conditions inside cells and whole organisms constant so that enzymes work effectively
• Conditions that need to be kept constant in humans

  • Blood glucose concentration
  • Water levels
  • Body temperature (around 37 degrees Celsius)
• Stimulus


  A trigger for the homeostatic processes in the body, a change in the environment
• Receptor cells


  Detect changes in the environment
• Coordination Centre


  Receives and processes information from receptor cells (e.g. brain, pancreas)
• Effectors


  Carry out the response to restore conditions to the optimal level (e.g. muscles, glands)
• Main sense organs in the body

  • Eye (detects light)
  • Nose (detects chemicals/smell)
  • Tongue (detects chemicals/taste)
  • Ears (detect sound and balance)
  • Skin (detects pressure and temperature)
• Neuron


  Individual nerve cell
• Path of the nervous system

  1. Receptor cell detects stimulus

  2. Sensory neuron passes impulse

  3. Relay neuron passes impulse

  4. Motor neuron triggers effector

  5. Effector carries out response
• Nervous system impulses are very fast
• Synapse


  Small gap between neurons where chemical messengers (neurotransmitters) diffuse to pass on the impulse
• Reflex action


  1. Receptor cells detect stimulus

  2. Sensory neuron passes impulse

  3. Relay neuron passes impulse

  4. Motor neuron triggers effector

  5. Effector (muscle) carries out rapid response
• Reflex actions help protect organisms from harm and involve automatic, rapid responses
• Endocrine system


  System of glands that secrete hormones into the bloodstream
• Main glands in the human body

  • Pituitary
  • Thyroid
  • Pancreas
  • Adrenal
  • Testes
  • Ovaries
• Pituitary gland


  Master gland that releases hormones to control other glands
• Thyroid gland


  • Produces thyroxine to control metabolic rate, growth and development
  • Adrenal glands produce adrenaline to prepare the body for fight-or-flight response
• Negative feedback


  Mechanism that controls hormone levels by reducing production when levels are too high
• Control of blood glucose

  1. Glucose from food enters bloodstream

  2. Pancreas detects high glucose and releases insulin

  3. Insulin allows glucose to enter cells or be stored as glycogen

  4. Pancreas detects low glucose and releases glucagon

  5. Glucagon converts stored glycogen to glucose to raise blood glucose levels
• Glucose is essential for cell respiration to release energy
• Type 1 diabetes


  Pancreas does not produce insulin, treated with insulin injections
• Type 2 diabetes


  Body cells do not respond to insulin, treated with exercise, diet and sometimes drugs or insulin
• Secondary sex characteristics in males during puberty

  • Sperm production
  • Growth spurt
  • Development of underarm, facial and pubic hair
  • Voice breaking (deepening)
• Secondary sex characteristics in females during puberty

  • Growth spurt
  • Development of underarm and pubic hair
  • Breast development
  • Menstrual cycle begins
• Hormones controlling the menstrual cycle

  • FSH (follicle stimulating hormone)
  • LH (luteinizing hormone)
  • Oestrogen
  • Progesterone
• Stages of the menstrual cycle

  1. Egg matures in ovary

  2. Ovulation (egg released)

  3. Uterus lining thickens

  4. Uterus lining breaks down (period)
• Contraception methods


  • Hormonal (e.g. oral contraceptive pill)
  • Non-hormonal (e.g. condoms, IUD)
• Ovaries


  Cause the lining of the uterus to develop ready for a fertilized egg
• Progesterone


  • Produced by the empty follicle in the ovary after ovulation
  • Inhibits LH so more than one egg is not released
  • Maintains the lining of the uterus for around ten days keeping it thick and ready for a fertilized egg
• Methods of contraception


  • Hormonal
  • Non-hormonal
• Oral contraceptive pill


  • Contains hormones that stop the eggs from maturing
  • Inhibits FSH
• Oral contraceptive pill


  • Easy to use
  • Highly effective if used properly
  • Can have side effects like increased blood pressure
• Patch, injection, implant


  • Use the hormone progesterone
  • Inhibit eggs in the ovary from maturing or being released
  • Last progressively longer
  • Require a nurse or doctor to receive
• Spermicides


  • Chemical method that can kill or stop sperm from working
  • Readily available
  • Not very effective
• Barrier methods (condoms, diaphragms)


  • No side effects
  • Can prevent against some STDs
  • Need to be fitted correctly
  • Can easily let sperm through if damaged
• IUD


  • Inserted into the uterus
  • Prevents early embryos from implanting
  • Some also release progesterone
  • Very effective and long-lasting
  • Can be uncomfortable and cause period pains in early days
• Surgical methods (vasectomy, tubal ligation)

  • Permanent
  • For people who know they don't want to conceive
  • Requires general anaesthetic for women which carries a risk
• Abstinence


  • No side effects
  • High risk of pregnancy
• NHS states that as many as one in seven couples have difficulty conceiving or getting pregnant