AQA GCSE Biology (4401) Unit B1 ANSWERS to Summary pages

Transcription

1 AQA GCSE Biology (4401) Unit B1 ANSWERS to Summary pages Name: Complete each page. Try to only use the key word list when you are stuck. Remember in some cases the same key words may be used more than once. Good luck! Remember to practice and mark past exam questions. They are free to download at

2 B1 Diet and exercise Healthy diet A healthy diet contains the right balance of different foods. Carbohydrates, fats and proteins release energy and are used to build cells. Losing weight People lose weight when: energy in food eaten energy used by body. Exercise increases the energy used by the body, so helps us lose weight. Fruit and vegetables are a good source of vitamins and minerals. Poor diet A person is malnourished if their diet is not balanced. This can mean a person is overweight or underweight. Unbalanced diets can lead to deficiency diseases (eg scurvy lack of vitamin C) or heart disease and type 2 diabetes etc. Metabolic rate This is the rate at which chemical reactions occur inside our cells. Increasing exercise, increases metabolic rate. Muscle cells have a higher metabolic rate than fat cells. So people with a higher proportion of muscle to fat have a higher metabolic rate. Inheritance and health Genes which we inherit from our parents also affect our health eg cholesterol level.

3 B1 Defence against infectious diseases: Part 1 Infectious diseases Infectious diseases can be passed from one person to another eg coughs, sneezes, infected water/food. Pathogens are microorganisms that cause infectious diseases. Bacteria - are single celled microbes that reproduce rapidly inside our body. They make us ill by destroying our cells and making toxins (poisons). Viruses Can only reproduce inside our body cells. They destroy the cells which they invade making us feel ill. Semmelweis was a doctor in the 1850 s. He recognised the importance of hand- washing in preventing the spread of infectious diseases in hospitals. Today hand-washing in hospitals helps to stop the spread of antibiotic resistant bacteria like MRSA. Defence against pathogens White blood cells defend us in 3 ways: 1. Making antitoxins (neutralise toxins). 2. Making antibodies (which bind to antigens on the surface of pathogens, destroying them). 3. Ingesting pathogens.

4 B1 Defence against infectious diseases: Part 2 The immune system: White blood cells produce specific antibodies to kill each type of pathogen. (Each type of antibody can only bind to one specific type of antigen). Sketch a specific antibody against the pathogen Immunisation graph: describe and explain the shape of the curve After 1 st injection antibody levels slowly rise, peaking after 3 weeks. It takes time for the white blood cells to make the specific antibody needed against the pathogen. After 2 nd injection a larger amount of antibody is made more rapidly. White blood (memory) cells quickly make antibody making you immune. Immunisation People can be immunised against some diseases. A vaccine contains small amounts of dead or inactive pathogens. After being vaccinated our white blood cells make antibodies to destroy the pathogen. If you become re-infected with the pathogen white blood cells are stimulated to rapidly make a large quantity of antibody, making you immune to the disease. The MMR vaccine is used to protect children against 3 viruses; measles, mumps and rubella. If most of a population are vaccinated and become immune to a pathogen, its spread is greatly reduced. Painkillers Paracetamol and other painkillers help to relieve the symptoms (eg headache, high temperature) of some infectious diseases. Painkillers do NOT kill pathogens. Antibiotics Antibiotics are drugs that kill infectious bacteria inside the body. Thus, antibiotics like penicillin help to cure bacterial diseases. Antibiotics have NO EFFECT on VIRUSES because viruses live inside body cells and are inaccessible to antibiotics. It is hard to develop drugs that kill viruses without also damaging body cells.

5 B1 Antibiotic resistance and growing bacteria Mutations (HT only) Mutations (random changes in DNA) produce new strains of pathogens. Antibiotics (against bacteria) and vaccines (against bacteria or viruses) may no longer be effective. As people are no longer immune, new strains can spread rapidly. Antibiotic resistance Some strains of bacteria are no longer killed by antibiotics. They have developed resistance to antibiotics through natural selection. Sort the sequence: 1 Resistant bacteria reproduce 2. Antibiotic used. 3. Mutation causes a new resistant strain of bacteria to appear. 4. Resistant bacteria population increases. 5. Non-resistant bacteria die, resistant bacteria survive Using antibiotics effectively Doctors must: Use specific antibiotics against specific bacteria (choose the most effective antibiotic). Avoid overuse of antibiotics. Avoid non-essential use (eg. non-serious throat infections) Together this will help to slow down the rate of development of resistant bacteria strains. Hopefully in the future new antibiotics can be developed to kill resistant strains of bacteria. Growing microbes uncontaminated cultures of microbes are needed to test antibiotics + disinfectants To avoid contamination: 1. Sterilise petri dishes and culture media to kill unwanted microbes. 2. Sterilise the inoculating loop by heating in a flame, before using it to transfer bacteria to the petri dish. 3. Seal the dish with tape to stop pathogens entering from the air. Incubate microbes at 25 C to reduce the chance of growing harmful pathogens (in industry 40 C allows faster microbe growth).

6 B1: Nervous system Part 1 Label the receptor cell Which stimulus does this receptor detect? light Receptors Special cells called receptors detect changes in the environment called stimuli. membrane Neurones Neurones are nerve cells. They pass electrical signals rapidly from receptors to the CNS and from the CNS to effectors. Organ with receptors Eyes Ears Stimulus detected by receptors Light Sound Ears Balance + position Tongue + nose Skin Chemicals for taste + smell Touch, pain, pressure+ temperature cytoplasm nucleus CNS: Label the two parts of the central nervous system (CNS). brain Spinal cord Synapse (gap between two neurones). Describe how an impulse travels across a synpase. Label the direction of the impulse. Chemical transmitter is released and diffuses across the synapse.

7 B1: Nervous system Part 2 Reflexes Reflexes are rapid automatic (not involving the brain) responses. A person is hit below the knee (P). On the reflex arc diagram identify A, B, C, + label the relay neurone and effector. Remember Effectors are usually muscles (which contract) or glands (that secrete chemicals eg hormones or enzymes). They bring about the response. Complete the pathway for a typical reflex action and when you touch a hot object. Stimulus Hot object C= Spinal cord A = sensory neurone B= Motor neurone Relay neurone Receptor Sensory neurone CNS Motor neurone Effector Pain/temp Sensory neurone CNS Motor neurone arm muscle effector Response Move away

8 B1 Control in the human body Our body must control its internal conditions carefully. This is called homeostasis. I said ions, not irons! Internal condition to control Water Details Lost via lungs (breathing out), skin (in sweat) and kidneys (in urine) Ions Temperature Blood sugar Ions are lost in sweat. Excess ions from our diet are lost via kidneys in urine. Must be kept constant (37 C) so that enzymes work best. Must be kept constant to provide cells with energy source (for respiration).

9 B1 Female sex hormones Hormones Hormones are: 1. Chemical messengers 2. Secreted by glands 3. Transported in the blood 4. Specific and only act on target organs. The menstrual cycle The monthly changes in the lining of the uterus and the development and release of an egg are regulated by several hormones. Hormone Follicle stimulating hormone (FSH) Released by Pituitary gland Effects Stimulates an egg to mature in the ovary. Stimulates oestrogen production. Oestrogen Ovary Stimulates LH release. Luteinising hormone (LH) Pituitary gland (Can inhibit FSH, so used in the pill) Peak triggers ovulation. The pituitary gland This gland is found in the brain. It secretes FSH and LH. Both hormones travel in the blood to their target organ the ovary.

10 B1 Using hormones Oral contraceptives Oral contraceptives are pills taken to prevent pregnancy. They may contain the hormones oestrogen and progesterone. These inhibit FSH production so that no eggs mature in the ovaries. Pill problems The first type of birth control pills developed had high levels of oestrogen. This resulted in women suffering side effects. Modern pills contain a low dose of oestrogen or contain only progesterone. These have fewer side effects. Fertility drugs Some women are unable to get pregnant because their FSH levels are too low. This stops their eggs from maturing. These women may be given the hormones FSH and LH as a fertility drug. This allows her eggs to mature. Fertility treatment is often used as part of IVF. IVF (in vitro fertilisation) Sort the sequence FSH + LH given to woman Several eggs are stimulated to mature Eggs are collected from ovaries Father s sperm is collected Sperm is used to fertilise eggs in a dish. Fertilised eggs develop into embryos One or two embryos are inserted into mothers uterus Fertility treatment issues Contraceptives help to control human population, reducing poverty. But, some women suffer side effects. Some religions object to contraception as it denies life. Multiple births from IVF can result in premature, unhealthy babies. Ethical issues arise, such as what to do with spare embryos.

11 B1 Control in Plants Moisture Plant roots grow towards moisture. (hydrotropism). Plant hormones Plants are sensitive to light, moisture and gravity. Responses of plants to these stimuli are due to the unequal distribution of the hormone auxin. Light Shoots grow towards light. This response is called phototropism. 1. Auxin is made in the shoot tip. 2. Light makes auxin build up on the shady side of the shoot. 3. Cells on the shady side grow faster. 4. Shoot bends towards light. Gravity Shoots grow against gravity. Roots grow towards gravity. These responses are called gravitropism (or geotropism). 1. Auxin is made in root tip. 2. Gravity makes auxin build up on the lower side of the root. 3. Cells on the lower side grow slower (auxin inhibits). 4. Root bends down towards the force of gravity. Uses of plant hormones Synthetic auxins are used as selective weed killers. They kill broad leaved plants (like dandelions), but not narrow leaved ones (like grass). Auxins are used as rooting hormones. Dipping cuttings in hormone rooting powder stimulates root growth.

12 B1 Drugs Part 1 New drugs Scientists are continually developing new drugs. Each new medical drug must be tested before use. Tissues and animals are often used as models to predict how drugs may affect humans. Complete the steps involved in testing a new drug. What drug is tested on Cells + tissues Aim of test Is drug toxic or effective? Double blind trials Some patients are given a placebo, which does not contain the drug. Neither the doctor or the patients know who has been given the drug or placebo. Animals Healthy humans A few patients Many patients (clinical trial) Find side effects + dose Is drug safe at low dose? Does drug treat disease? Optimum dose Thalidomide This drug was originally developed as a sleeping pill. Without being tested, it was used to prevent morning sickness in pregnant women. Unfortunately, many babies were born with severe limb abnormalities. Thalidomide is now banned for use by pregnant women. Recently thalidomide has been used to treat the bacterial disease, leprosy.

13 B1 Drugs Part 2 Drugs A drug is a chemical that alters the way your body works. Some drugs are addictive. Addiction is when you become physically or mentally dependent on a drug. Addicts suffer from withdrawal symptoms if they stop using drugs. Cannabis Cannabis is an illegal drug. Smoking cannabis may cause mental health problems. There is evidence that using drugs like cannabis can lead to use of hard drugs such as cocaine and heroin which are highly addictive. Other recreational drugs Misuse of ecstasy, cannabis and heroin can have adverse effect s on the heart and circulatory system Alcohol Is a legal drug. Like cannabis, alcohol slows down nerve impulses, increasing your reaction time. Alcohol addiction can lead to liver disease. Drug use by athletes Anabolic steroids are illegally used by some athletes to increase their muscle growth. Stimulants are also banned for use in many sports because they increase heart rates and boost performances. Nicotine Is a legal drug found in cigarettes. Like caffeine and cocaine, nicotine can speed up nerve impulses and act as a stimulant. Addiction to nicotine means that many smokers find it hard to give up and many suffer from lung cancer. Statins These are drugs which can be taken to lower blood cholesterol levels. This helps to lower the risk of heart and circulatory diseases.

14 B1 Adaptations Part 1 Adaptations in animals to survive dry environments eg desert fox Competition Plants compete with each other for light, space, water and mineral ions (from the soil). Animals compete with each other for food, mates and territory. Large ears increase the surface area, increasing heat lost by radiation. Thin coat and body fat reduce insulation and help heat loss by radiation. Camouflage allows this predator to hide from its prey. Adaptations in animals to survive arctic environments eg polar bear. Adaptations by plants to survive dry environments 1. Leaves reduced to spines. The small surface area reduces water loss by evaporation. 2. Water storage tissues. 3. Extensive roots absorb water from the soil. Small ears help to reduce the surface area, reducing heat lost by radiation. Thick coat and body fat layers insulate, reducing heat lost by radiation. Camouflage allows this predator to hide from its prey.

15 B1 Adaptations Part 2 Adaptations to deter herbivores/predators Some plants have sharp thorns to deter herbivores. Extremophiles Some organisms live in extreme environments. These extremophiles may be tolerant to high levels of salt, high temperatures or high pressures. Many extremophiles are microbes. For example bacteria living near deep sea vents have enzymes that do not denature at high temperatures, even up to 80 C. Adaptations to deter predators The coral snake is poisonous. Its colours act as warning and deters its predators. This is exploited by the milk snake which mimics the coral snake. It lives in the same habitat, has similar markings but is not poisonous.

16 B1 Environmental change Changes in the environment affect the distribution of organisms. Global warming has affected the migration and distribution of some birds. Living pollution indicators Some living organisms act as pollution indicators. For example lichen growth and biodiversity is reduced by the presence of sulphur dioxide/acid rain. Loss of habitats and use of pesticides has led to a decline in pollinating insects such as bees. Non-living indicators of environmental change. Scientists can used equipment to measure some changes in the environment. An oxygen probe detects changes in oxygen. A max-min thermometer is used to record the range of daily temperatures. A rainfall gauge helps to record rainfall. Some invertebrates are water pollution indicators, as they need high levels of dissolved oxygen to survive. Polluted water contains less oxygen, so tends to contain fewer invertebrates such as shrimps and mayfly larvae.

17 B1 Energy in biomass Biomass = mass of living material at each stage in a food chain. The Sun The Sun s radiation is the source of energy for most food chains. Plants and algae absorb light energy and transfer it to chemical energy during photosynthesis. This energy is stored in the plants biomass eg starch, sugars and cellulose. The transfer of energy from the Sun to the plant is very inefficient. Most light is the wrong wavelength for plants to absorb and only about 5 % of the Sun s energy is converted to chemical energy in the plants biomass. Pyramids of biomass: show the amount of biomass at each stage in a food chain. Draw a pyramid of biomass for the food chain: Rose aphid robin cat Cat Loss of energy and biomass At each stage in a food chain energy and biomass are lost. Some biomass is lost as waste (eg. faeces) or in parts not eaten. Some energy lost during respiration to provide energy for movement etc. Most of this lost energy is transferred to the surroundings as heat. Robin aphid Rose

18 B1 Decay and the carbon cycle Carbon cycle Decay Decay occurs when organic materials are broken down (digested) by microorganisms (bacteria and fungi). combustion Carbon dioxide photosynthesis Microorganisms are more active when conditions are warm, moist and aerobic (oxygen is present). respiration Carbon in plant biomass as fats, sugars + proteins Carbon in animal as fats, sugars + proteins Decay releases and recycles materials needed for plants to grow including nitrates and the gas carbon dioxide. death Detritus feeders + microbes digest waste and dead organisms, releasing useful nutrients for plants

19 B1 Why organisms are different Inside the nucleus The nucleus of each cell contains the genetic material (DNA) arranged as threads called chromosomes. Each chromosome carries many genes which control characteristics (eg. eye colour). Label the genes. Variation Differences between individuals of the same species are due to the genes they have inherited, the environment or a combination of both. Characteristic Plant height Eye colour Accent Reason for variation (genes, environment or both) G + E G E Body mass G + E Types of reproduction Inheritance Offspring have similar characteristics to their parents due to the genes which they inherit. During sexual reproduction, genes are passed on via the parents sex cells (gametes). Feature Type of reproduction Sexual Asexual Parent number 2 1 Genetic variation in offspring yes None (clones) Sex cells yes no

20 B1 Cloning Part 1 Clones Clones are genetically identical organisms. All organisms produced by asexual reproduction are clones of their parent. Tissue culture Small groups of cells from part of a plant can be grown on nutrient medium with plant hormones. Whole plants develop. Cuttings Gardeners can produce large numbers of plants quickly and cheaply by taking cuttings. New plants are clones, genetically identical to the parent plant. Embryo transplants Early stage embryo is split Identical embryos develop and are transplanted into the uterus of host mothers Identical clones are born from each host mother

21 B1 Cloning part 2 Adult cell cloning This was like the method used to make Dolly the sheep. Animal A The nucleus is removed from an adult body cell of the animal to be cloned. For Dolly the sheep the body cell was an udder cell. In this example a skin cell is used. Remove nucleus from egg cell Insert skin cell nucleus into empty egg cell. Empty egg Electric shock stimulates cell division and an embryo forms Insert embryo into uterus Foal is a clone of A

22 B1 Genetic engineering Genetic engineering to make herbicide resistant plants Genetic engineering Genes are cut out from chromosomes of one organism and transferred to the nucleus of another organism (eg animal, plant or microbe). Making a GM goat containing a spiders gene! Enzymes are used to cut out a spider gene from its chromosome. The spider gene is inserted into an egg or embryo (from a goat). Apart from having the herbicide-resistance gene, the herbicide-resistant plants are identical to the herbicide-susceptible plants. All their cells have the same DNA as the single parent plant as no sex cells were used. The embryo develops into a GM goat which contains the spider gene in its cells. Genetically modified (GM) crop issues GM crops have been made which are resistant to herbicide (weed killer). Spraying the crop with herbicide kills the weeds, reducing competition for light, minerals etc. So crop yields increase. Some GM crops have genes that make them resistant to insect attack. This also increases crop yields. BUT some people are concerned about the effects of GM food on health. GM crop plants may pass on the inserted gene to wild plants. Using GM resistant crops may encourage the use of herbicides.

23 B1 Evolution part 1 Evolution: The theory of evolution states that all species alive today have evolved from the first simple life forms on Earth over a long period of time. Darwin s theory: Darwin s theory states that evolution occurs by natural selection. Variation exists within all populations. Those individuals which are better adapted, survive and reproduce, increasing in number. Lamarck s theory Lamarck believed that species evolved because changes that occurred in an organism during its lifetime could be inherited. Variation exists in the rat population (due to mutations). Some rats are resistant to poison. Stretching for food led to more neck use Resistant rats survive and breed. More use led to neck getting longer Offspring inherit poison resistance gene (allele). Longer neck characteristic was passed to offspring Numbers of rats resistant to poison increase.

24 B1 Evolution part 2 + classification Darwin s struggle Darwin was the first scientist to state that humans and other primates had common ancestors. Darwin s theory of evolution was only gradually accepted because 1. It challenged the idea that God made all the the animals and plants that live on Earth. 2. there was insufficient evidence. 3. the mechanism of inheritance and variation was not known until 50 years later. Lamarck and Darwin made different theories of evolution. Scientists may produce different hypotheses to explain similar observations. It is only when these hypotheses are investigated that data will refute or support hypotheses. Classification Studying the similarities and differences between organisms allows us to classify living organisms into animals, plants and microorganisms, and helps us to understand evolutionary and ecological relationships. Models such as evolutionary trees allow us to suggest relationships between organisms. Which is the closest relative to fur seals? Sea lions Mutations Where new forms of a gene result from mutation there may be relatively rapid change in a species if the environment changes. eg. Air pollution made tree bark sooty during the Industrial revolution. Mutant black moths evolved and increased in numbers.