paper 2

• definition of homeostasis

  the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal or external changes
• automatic control systems

  involve the nervous system of hormones
• receptor cells

  detect changes in the environment aka a stimulus
• coordination centre

  receives and processes information from the receptor
• effector

  a muscle which contracts or a gland which secretes a hormone and carries out the response aka restores the optimum levels
• nervous system

  receptor detects a stimulus and sends electrical impulses down neurons to the central nervous system, which then sends other neurons to the effector which brings about a response
• reflex arc

  a receptor detects a stimulus, electrical impulses pass from the receptor along to the sensory neuron to the CNS, at the end of the sensory neurone there is a junction called a synapse which releases chemicals that diffuse across a relay neurone in the CNS where it triggers an electrical impulse, which then passes along the relay neurone and reaches another synapse where another chemical is released which triggers an impulse in the motor neurone, the impulse now passes down to the effector which contracts and pulls away
• reflex actions

  no decision-making is made by the conscious part of the brain, making reflexes automatic and rapid which protects us from danger
• definition of the endocrine system

  The endocrine system is composed of glands which secrete

  chemicals called hormones directly into the bloodstream, the blood

  carries the hormone to a target organ where it produces an effect, compared to the nervous system the effects are slower but act for

  longer
• the pancreas

  release hormones as well as being involved in controlling the concentration of glucose in the blood
• testes and ovaries

  release hormones involved in puberty and reproduction
• thyroid gland

  produces hormones which are involved in growth and in regulating the body's basal metabolic rate aka how fast the bodies reactions take place
• adrenal glands

  release adrenaline which is produced in times of fear or stress
• pituitary glands

  located in the brain and is also known as the master gland as it releases several different hormones into the blood depending on the conditions, they also act on other glands and cause other hormones to be released, meaning the pituitary gland can trigger a range of different effects in the body
• high glucose concentration

  the pancreas produces insulin that causes glucose to move from the blood into the cells, where in the liver and muscle cells excess glucose is converted to glycogen for storage
• type 1 diabetes

  the pancreas does not produce enough insulin meaning they need to inject themselves with insulin if blood glucose concentration becomes too high
• type 2 diabetes

  the body cells stop responding to insulin produced by the pancreas, this type is often treated by a diet with controlled levels of carbohydrates to prevent the blood glucose from rising too high, they are also advised to exercise, a major risk of type 2 is obesity
• low glucose concentration

  the pancreas releases a hormone called glucagon into the bloodstream, which triggers the liver cells to convert glycogen back into glucose, which is then released into the bloodstream, making the blood glucose concentration return to normal
• testes

  produces the hormone testosterone which stimulates the testes to produce sperm
• ovaries

  produce the hormone oestrogen, when puberty begins eggs in the ovaries start to mature and every 28 days an egg is released aka ovulation
• menstrual cycle

  every 28 days ovulation takes place, in preparation for it the lining of the uterus becomes thick and spongy, and the egg then moves down to the uterus, if sperm is present then the egg can be fertilised so the egg can implant into the uterus wall and develop a baby, if there is no sperm present then the egg and uterus lining are released aka a period
• follicle-stimulating hormone (FSH)

  causes an egg to mature in the ovary
• luteinising hormone (LH)

  causes the egg to be released (ovulation)
• oestrogen and progesterone

  maintain the uterus lining, in case the egg is fertilised
• the menstrual cycle

  FSH is released by the pituitary glands, where it travels through the blood to the ovaries where it causes an egg to mature, at the same time FSH triggers ovaries to make oestrogen which makes the lining thick and stops the pituitary glands from releasing any more FSH, instead, it releases LH, the ovary then releases progesterone which stops the gland from releasing FSH and LH to prevent an egg from being released and keeps the lining thick in case an egg implants
• the pill method of contraception

  contains hormones which prevent the production of FSH aka prevents eggs from maturing

  • highly effective
  • must be taken every day if not there is a risk of pregnancy, side effects such as breast cancer or blood clots
• implant, skin patch and injection methods of contraception

  these contain progesterone which stops an egg from being released and matured

  • convenient as they last longer than the pill
  • neither these or the pill protect against STD's or infections
• condom or diaphragm method of contraception

  prevent the sperm from reaching the egg

  • don't use hormones so they don't have side effects, and also reduce the risk of STD or infections
  • they can break or slip off
• spermicides

  kill and disable sperm and reduce chances of fertilisation
• intrauterine device (IUD)

  aka the coil which prevents an embryo from implanting and some also reduce the chance of fertilisation, they are highly effective and long-lasting and have few side effects but don't protect against diseases or infections
• surgical methods of contraception

  aka sterilisation, prevents the egg from reaching the uterus and prevents the sperm from leaving the penis, both are highly effective but very difficult to reverse and don't protect against STI and STD's
• fertility drug

  FSH and LH are given to the woman which causes her to ovulate more and increases her chances of becoming pregnant
• in-vitro fertilisation aka IVF

  fertilisation takes place outside the body, the mother is treated with FSH and LH which causes several eggs to mature and are then collected, the sperm from the father is also collected to fertilise the eggs in a laboratory, the eggs then develop into embryos which are inserted back into the mother womb where it can then develop normally
• adrenal glands

  located on top of the kidneys which secretes adrenaline during times of fear or stress into the blood, increasing the heart rate meaning more oxygen and glucose are delivered to the brain and the muscles, which are needed for aerobic respiration and prepare the body for fight or flight
• thyroid glands

  located at the base of the neck which releases the hormone thyroxine, which stimulates the body's basal metabolic rate basically making all the reactions in the body occur at a faster rate, and it also plays a part in the growth and development of a person
• negative feedback loop

  levels of thyroxine in the blood are monitored by the brain, meaning when its levels fall the pituitary gland releases the hormone TSH into the bloodstream which triggers the thyroid gland into releasing more thyroxine into the blood, the increased levels are now detected by the brain which prevents the pituitary gland from releasing TSH, as the TSH levels fall the gland releases less thyroxine, this cycle is the same for too much or too little thyroxine in the blood
• gametes

  non-paired sperm and egg cells, contain 23 single chromosomes and are divided by meiosis
• features of sexual reproduction

  fusion of male and female gametes meaning there is a mix of genetic information so the offspring receives information from both parents leading to variation in offspring
• features of asexual reproduction

  only one parent meaning gametes are not involved so there is no missing genetic information and the offspring are all genetically identical, this is a product of mitosis as it produces clones
• meiosis in gamete cells

  only takes place in reproductive organs (testes and ovaries)