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Science B3 Topic 1
GCSE edexcel further additional biology: control systems
| Question | Answer |
|---|---|
| What are circadian rhythms? | Circadian rhythms are daily biological rhythms found in organisms |
| What is a biological clock in humans? | The human brain contains a biological clock which is a timing mechanism that controls many circadian rhythms |
| What is an example of circadian rhythms in humans? | We secrete increased levels of a hormone called melatonin at night as it makes us feel sleepy, and this level drops in the morning |
| What are some examples of circadian rhythms in plants? | Flowers open in the day to allow pollination by insects and close at night to protect the pollen from the cold, flowers only produce nectar during the daytime when insect are likely to visit the flowers |
| What is photoperiodism? | Photoperiodism is the way in which organisms respond to changes in day length, which is over a yearly cycle |
| Why is photoperiodism important in plants? | Plants respond to increased hours of sunlight in a day by: growing more, growing flowers to allow pollination + reproduction, seed germination. Plants grow less in autumn as they concentrate their energy towards surviving the harsh winter conditions. |
| How can plants defend themselves against attack? | Plants defend themselves against attack from pests, herbivores and pathogens by releasing chemicals that kill the organism - for example some chemicals make leaves poisonous |
| How can attack on plants by pathogens affect human food supply? | Potato blight is a pathogen that destroys many varieties of potato plants, and this can reduce human food supply e.g. the famine in Ireland was caused by potato blight |
| What are some human uses of plant poisons? | *Digoxin is found in foxgloves, improves the heartbeat in small quanity & treats heart disorders *Quinine is produced by cinchona trees, treats the disease malaria *Aspirin is produced by willow tree, treats the symptoms of diseases eg. pain &fever |
| What are aseptic techniques? | Aseptic techniques- keeping things free from living microorganisms |
| Pasteur suggested that we should keep microorganisms away from people and food to avoid diseases and preserve food. Pasteurisation is where foods such as milk are heated briefly before being stored to kill bacteria in them | |
| What did Edward Jenner do? | Edward Jenner rubbed pus from a cowpox blister into the skin of a young boy, which resembled a vaccine, and this made him immune to smallpox |
| What is immunisation? | Immunisation is the progress of making someone immune to a disease |
| What are the steps of immunisation? | Harmless version of the pathogen put in body, body recognises antigens, triggers immune response- lymphocyte that fits the antigens divides to produce identical clones, some lymphocytes secrete antibodies, attach to antigens & destroy cells, memory lymph. |
| How is the pathogen 'harmless'? | It is weakened or dead, or contains only part of the pathogen |
| What is an antigen? | the chemicals on the surface of the cells of the pathogen |
| What is a lymphocyte? | A white blood cell- B lymphocytes secrete antibodies, some lymphocytes become memory lymphocytes which remain in the blood for a long time in case of a future infection |
| What is an antibody? | Proteins secreted by lymphocytes that attach to specific antigens on the pathogen and destroy the cells |
| What are some advantages of immunisation? | o A child can become immune to a disease without suffering from it o Reduces risk of long-lasting harm o If enough people are vaccinated against a disease, then it becomes so rare that even unvaccinated people are unlikely to get it |
| What are some disadvantages of immunisation? | o Vaccination commonly causes swelling or redness around the site of the injection o Can cause a mild form of the disease that is being vaccinated against o Can cause allergic reactions |
| What is an infection? | The infection is the entry of a pathogen into the body |
| Why does a bacterial infection grow rapidly? | Bacterial cells reproduce by dividing into two, so the population will show exponential growth, meaning that an infection will rapidly develop |
| What is the body's primary response to an infection? | The primary response is when a pathogen first infects a person and only one or two lymphocytes recognise the antigens on it, so they have to multiply over a period of time and secrete enough antibodies to destroy the pathogen |
| What is the body's secondary response to an infection? | The secondary response is when the pathogen re-enters the body and the memory lymphocytes secrete enough antibodies to destroy the pathogen before it has a chance to increase in number and make the person ill |
| What are monoclonal antibodies, how are they made? | Monoclonal antibodies are many identical antibodies. Made by fusing a B lymphocyte with a cancer cell, producing a hybridoma which divides many times to produce clones, and they all secrete antibodies |
| Why do lymphocytes that produce antibodies not produce clones? | A lymphocyte can divide many times to create clones of itself, however once it has started to make antibodies, it becomes a B lymphocyte which can’t divide |
| What are the uses of monoclonal antibodies? | * pregnancy-testing kits * detecting blood clots and cancer cells * killing cancer cells |
| How are monoclonal antibodies used in pregnancy testing kits? | a dipstick is dipped into some urine, and if it contains a hormone called HGH in then the monoclonal antibodies will bind to it, causing a colour change, indicating that the woman is pregnant |
| How are monoclonal antibodies used in detecting blood clots and cancer cells? | radioactive monoclonal antibodies are injected into patient’s body, they bind to substances found in the membranes of platelets &cancer cells, & radiologists detect where the antibodies are, so cancers/blood clots can be treated |
| How are monoclonal antibodies used in killing cancers? | drugs that are used in chemotherapy can be attached to monoclonal antibodies which ensure that the drug is only delivered to the cells that need to be destroyed, reducing the risk of harming healthy cells and not wasting the drug |
| What is cell metabolism? | Cell metabolism is the chemical reactions that occur inside the body |
| What products does cell metabolism create? | They release waste products such as carbon dioxide and urea which can build up in the blood |
| What is urea produced from, how is it removed? | Urea is produced from the breakdown of excess amino acids in the liver and is removed by the kidneys |
| What is the structure of the urinary system? | *Renal arteries carry blood to kidneys *Kidneys remove substances eg urea from blood & make urine *Renal veins carry cleaned blood to body *Ureters carry urine from kidneys to bladder *Bladder stores urine *Urine flows out of body through urethra |
| What are the functions of the kidneys? | The functions of the kidneys are to remove urea from the blood, make urine, and control the water content of the blood |
| What is a nephron? | A kidney contains thousands of nephrons, which are microscopic tubes |
| What is the structure of a nephron? | The glomerulus is a network of capillaries found inside the Bowman’s capsule, convoluted tubules, the loop of Henlé is the part of the nephron that loops down then sharply upwards, collecting duct is the final part of the kidney where water is reabsorbed |
| How do nephrons form urine? | 1.Blood flows along renal artery & into glomerulus; filtrates blood so water, glucose & urea only enter 2. selective reabsorption of water (osmoregulation) and glucose -> renal vein 3. urine into ureter (urea and excess water) |
| What is osmoregulation? | Osmoregulation is the maintenance of an organism’s water content in the blood |
| What are the kidneys controlled by and how? | The kidneys are controlled by the pituitary gland, which secretes ADH (antidiuretic hormone) to control the water content of the blood and keep it at an optimum level |
| What happens when the water content in the blood is too high? | osmoreceptors in hypothalamus stimulate ADH & release it from pituitary gland, increased ADH levels in blood cause cells lining collecting duct to become more permeable to water so water is reabsorbed into blood, causing urine to be more concentrated |
| What happens when the water content in the blood is too low? | osmoreceptors in hypothalamus aren’t stimulated, so decreased levels of ADH in blood cause cells lining collecting duct to become less permeable to water so less water is reabsorbed into blood, so urine is more dilute, blood water conc drops |
| What type of mechanism is ADH production? | ADH production is controlled by a negative feedback mechanism - a change in a factor leads to an action that reverses the change |
| Why might kidney failure occur? | Infections |
| What are possible solutions for kidney failure? | Kidney transplant is done if kidneys can’t be repaired- donor and patient must have similar antigens on cells else immune system will kill foreign cells. A kidney dialysis machine removes waste products from patient’s blood- waiting for transplant cher |
| What is the menstrual cycle? | The menstrual cycle is a monthly cycle controlled by the hormones oestrogen, progesterone, FSH (follicle-stimulating hormone) and LH (luteinising hormone) |
| Where are the following hormones produced and where do they act: oestrogen, LH, FSH, progesterone? | •Oestrogen and progesterone are produced in the ovary and act in the uterus •FSH and LH are produced in the pituitary gland and act in the ovary |
| What type of mechanism controls the menstrual cycle? | The menstrual cycle is controlled by a negative feedback mechanism- each hormone inhibits the production of the hormone before it |
| Explain the stages of the menstrual cycle | 1.Menstruation is breakdown of uterus lining 2.An increase in level of FSH stimulates development of a new follicle which matures for around 10 days 3.The maturing follicle causes the oestrogen levels to increase, repairing lining |
| CONTINUATION | 4.Spike in LH level causes ovulation 5.Corpus luteum secretes progesterone, which maintains uterus lining 6.If fertilisation occurs, corpus luteum continues to secrete progesterone so that the embryo can embed in uterus lining. |
| CONTINUATION | If fertilisation doesn't occur, a drop in oestrogen and progesterone levels causes menstruation |
| What is a follicle? | an immature egg |
| What is ovulation? | where the egg cell leaves the ovary and the follicle gets left behind, so it becomes a corpus luteum |
| What are gametes? | Highly specialised sex cells: egg and sperm |
| How is the egg adapted to its function? | *haploid nucleus contains 1 set of genetic material *The cytoplasm contains nutrients, including lipid droplets, to feed the zygote if fertilisation occurs *The cell membrane changes immediately after fertilisation to block the entry of other sperm |
| How is the sperm adapted to its function? | *acrosome is at the front of the sperm and contains enzymes to digest a way into the egg *haploid nucleus contains one set of genetic material *middle section contains mitochondria which release energy by respiring *tail allows it to swim quickly |
| Why do the gametes only have one set of genetic material each? | The haploid nuclei will produce a diploid zygote when they fuse |
| List the types of infertility treatment | * IVF * egg donation * surrogate mothers * hormone treatment |
| How does IVF work? | the woman’s eggs are taken from her ovaries and are fertilised with her partner’s sperm cells in a laboratory, and then the embryo is put into her uterus to develop |
| How does egg donation work? | if the woman’s ovaries aren’t producing eggs, a donor is given hormones to produce eggs, and they are fertilised in a laboratory with the partner’s sperm |
| How does hormone treatment work? | if the woman can’t grow an embryo in her uterus, then her eggs are fertilised with her partner’s eggs, and the embryo is placed in a surrogate mother’s uterus to develop |
| How does surrogacy work? | giving a woman extra hormones may help her produce more eggs |
| What is the advantage of infertility treatment? | allows couples who are infertile to have children |
| What are disadvantages of infertility treatment? | oIVF-babies are often premature, causing more problems in life oEgg donation-donor may react badly to high levels of hormones oSurrogate mothers-surrogate mother may want child oHormone treatment-multiple babies, premature, some women react badly |
| What is the sex of a person controlled by? | The sex of a person is controlled by one pair of chromosomes- women have two X chromosomes, XX, and men have one X and one Y chromosome, XY |
| The sex of offspring is determined by which gamete and why? | Sperm, because egg will always give an X chromosome but the gender is dependent on whether the sperm has an X or a Y |
| What are alleles? | Alleles are different versions of the same gene |
| What is a genotype and a phenotype? | The genotype is the alleles of a particular gene possessed by an organism. The phenotype is the characteristics of an organism |
| How can the possibilities of the sex of offspring be shown? | A punnett square |
| What is haemophilia? | Haemophilia is a sex-linked genetic disorder (a condition caused by an allele on the sex chromosomes) that prevents the normal clotting of blood and is caused by a recessive allele |
| Why do males only have one copy of the haemophilia gene? | Because it is found on the X chromosome |
| Why do the probabilities of women and men inheriting haemophilia differ? | The probability of a man getting haemophilia is higher because although his mother must be a sufferer or a carrier, his father’s genes don’t have an effect. However the father of a female haemophiliac must be a carrier or a sufferer, so it is more rare. |
| What is red-green colour blindness? | Red-green colour blindness is a sex-linked genetic disorder in which sufferers are unable to distinguish red from green, and it is caused by a recessive allele |
| Why do males only have one copy of the red-green colour blindness gene? | Because it is found on the X chromosome |
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