Biology IGCSE

• Vaccination causes artificial active immunity
• An autoimmune disease is a disease caused by a persons immune system is attacking their own body cells
• Antibiotics are used to treat bacterial infections only
• Bacteria can randomly mutate and develop resistance to antibiotics that previously killed them.
• A nerve impulse is an electrical signal that passes along the neurones
• A reflex action is an automatic, involuntary response which is inbuilt for protection. They do not require conscience control.
• A reflex arc is a pathway that the nerve impulse travels along during a reflex action
• A synapse is a junction or gap between two neurones
• A sense organ is a group of receptor cells which respond to a specific stimuli
• The pupil will constrict in bright light and will dilate in low light intensity. Both changes in the pupil diameter are brought about by the antagonistic action of muscles in the iris.
• To cause pupil constrictions: The circular muscles contract whilst the radial muscles relax.
• To cause pupil dilation: The radial muscles contract while the circular muscles relax
• The rod cells allow us to see when light intensity is low
• The cone cells allow us to see colour in bright light
• Accommodation (Near Objects)- The cilary muscles contract, causing the attached suspensory ligaments to become less tense and this allows the lens to become thicker
• Accommodation (Distant Objects)- The cilary muscles relax, causing the attached suspensory ligaments to become less tense and this allows the lens to become long and thin
• A hormone is a chemical which is produced by an endocrine gland and transported in the blood
• A hormone can alter the activity of one or more specific organs in the body
• Homeostasis is the maintenance of a constant internal environment
• Vasodilation: The pre-capillary sphincters relax to allow increased blood flow to the skins surface through arterioles. More heat energy will be lost to the persons surroundings by radiation
• Vasoconstriction: The pre-capillary sphincters contract preventing blood flow to the skin's surface through arterioles. Less heat energy will be lost from the person's body by radiation.
• Blood glucose must be kept at a fairly consistent level. If it is too high, it will draw water out of the body cells by osmosis, causing dehydration. If it falls too low, this will reduce respiration of cells leading to the person having less energy
• Cause of Type 1 Diabetes: Not enough insulin produced by pancreas
• Symptoms of Type 1 Diabetes: Thirst, weight loss, fatigue and excessive urination
• Treatment for Type 1 Diabetes: Insulin injections when blood sugar goes too high, managing diet and avoiding too much carbs
• Phototropism: shoots grow towards light
• Gravitropism: roots grow towards gravitational pull (downwards)
• Phototropism in a shoot:

  1. Auxin is made in the shoot tip
  2. Auxin diffuses down the shoot
  3. Auxin will distribute itself to the more shaded side
  4. Auxin stimulates cell elongation
  5. The dark side of the shoot grows more and bends towards the light.
• Excretion is the removal of waste products of metabolism, toxic materials, and substances in excess.
• The liver has an important role in processing chemicals such as hormones, drugs, and excess amino acids in the body
• Some of the amino acids in the liver are converted to protein in the process of assimilation
• Deamination is the removal of the nitrogen containing part of amino acids to form urea
• Fertilisation: The fusion of the nuclei of the male and female gamete
• After fertilisation, a zygote (diploid cell) is formed.

  The zygote starts to divide and move towards the uterus.

  The ball of cells, now an embryo, implants into the nucleus.

  The placenta forms between the mother and the embryo.

  After 6 weeks of development the embryo is known as a fetus
• Secondary Sexual Characteristics: features that develop during puberty in humans and differentiate between males and females
• Male secondary sexual characteristics:

  • Growth of pubic, body, and facial hair
  • Production of sperm
  • Broadening of chest and shoulders
• Female secondary sexual characteristics:

  • Growth of pubic hair
  • Breasts develop
  • Broadening of hips
  • Menstrual cycle starts
• What happens if a pregnancy doesn't occur?

  • Corpus luteum degenerates
  • Progesterone levels fall and FSH levels start to rise again
  • The lining of the uterus breaks down
• What happens if a pregnancy does occur?

  • Progesterone levels stay high
  • FSH and LH are inhibited
  • No more ova mature so ovulation can't occur
• Sexually transmitted infections: An infection that is transported by sexual contact (usually bacterial or viral)