paper 2 biology

• there are 23 pairs of chromosomes in human DNA
• homeostasis is maintaining a stable internal environment by regulating the conditions inside your body
• receptor detects a stimulus level is too high/low, the coordination centre recieves and processes the information and organises a response. effector produces a response which counteracts the change and restores the optimum level. this is negative feedback.
• the central nervous system (CNS) consists of the brain and spinal cord. the CNS is connected to the body by sensory neurons and motor neurons.
• sensory neurons carry information as electrical impulses from the receptors to the CNS.
• motor neurons carry electrical impulses from the CNS to effectors.
• effectors are muscles and glands that respond to nervous impulses.
• stimulus -> receptor -> sensory neuron -> CNS -> motor neuron -> effector -> response
• the connection between two neurons is called a synapse
• reflex is an action that is performed without conscious thought as a response to a stimulus (e.g releasing the hormone adrenaline when shocked)
• cerebral cortex controls conciousness, intelligence, memory, and language
• the hypothalamus controls temperature
• pituitary gland releases hormones
• cerebellum coordinates and regulates muscular activity
• medulla controls breathing, heart rate, digestion
• myopia is short-sightedness because the light hits the retina too soon. concave lens glasses are worn to help this
• hyeropia is long sightedness where light hits the retina too late. convex lens glasses are worn to help this
• endocrine system = hormonal system. endocrine glands include pituitary gland, ovaries, thyroid, testes, adrenal gland, and pancreas.
• the pancreas monitors the level of glucose in the blood using the hormones insulin and glucagon in a negative feedback cycle.
• blood glucose level too high -> insulin added
• blood glucose level too low -> glucagon added
• type 1 diabetes is where the pancreas produces little or no insulin, so the blood glucose level can become dangerously high. insulin is injected throughout the day to prevent this.
• type 2 diabetes is where a person's body becomes resistant to their own insulin and the cells don't respond properly to the hormone. this is usually caused by obesity.
• ions are removed from the body in urine by the kidneys when there is an excess, the right number are reabsorbed back into the blood.
• kidneys balance the amount of water by removing some in the form of urine
• if kidneys don't work properly, waste substances build up in the blood and the number of ions and water in your body cannot be controlled
• dialysis and kidney transplants are ways to treat someone with kidney failure.
• the menstrual cycle: day 1 = lining of the uterus breaks down (menstruation occurs), day 4 = lining of the uterus builds up, day 14 = egg released (ovulation occurs), day 19 = lining of uterus is maintained until the cycle starts again.
• FSH (follicle-stimulating hormone) is produced in the pituitary gland. it causes an egg to mature and stimulates the ovaries to produce oestrogen.
• oestrogen is produced in the ovaries. it causes the lining of the uterus to grow and stimulates the release of LH, which causes the release of an egg.
• LH is produced by the pituitary gland. it stimulates the release of an egg on day 14 (ovulation)
• progesterone is produced by the ovaries by the remains of a follicle after ovulation. it maintains the lining of the uterus, when the progesterone level falls, the uterus lining breaks down. it inhibits the release of LH and FSH.
• the menstrual cycle is monitored by FSH, LH, oestrogen, and progesterone
• urea is transported to the kidneys, where it is absorbed out of the blood and excreted from the body in urine.
• gametes contain half the genetic information than a normal cell, so they are called haploid cells
• chromosomes from the mother: maternal chromosomes
• chromosomes from the father: paternal chromosomes
• the 4 types of bases in DNA are adenine, thymine, cytosine and guanine
• a single nucleotide contains a base, phosphate and sugar
• hormones are proteins that carry messages around the body