This page contains the AQA GCSE Biology B2 Cell Divion Kerboodle Answers for revision and understanding of AQA GCSE Biology B2. This page also contains the link to the notes and video for the revision of this topic.
B 2.1 Health and Disease AQA GCSE Biology B2 Health and Disease Kerboodle Answers:Page No. 27
1The word “good health” refers to a state of complete emotional and physical well-being. Healthcare exists to help people maintain this optimal state of health.
2 a The factors that can cause ill health are-
- Diet- if you do not get enough to eat, or the right nutrients, you may suffer from diseases ranging from starvation to Anaemia or Rickets. Too much food, or the wrong type of food, can lead to problems such as obesity, some cancers, or type 2 diabetes.
- Stress – a certain level of stress is inevitable in everyone’s life and is probably needed for our bodies to function properly. However, scientists are increasingly linking too much stress to an increased risk of developing a wide range of health problems. These include heart disease, certain cancers, and mental health problems.
- Life situations – these include: the part of the world where you live your gender your financial status your ethnic group the levels of free health care provided where you live how many children you have local sewage and rubbish disposal.
b An example of ill health that each factor can produce is-
Improper diet leads to diseses like Anaemia, Rickets, Obesity, Type 2 Diabetes
Stress can lead to heart related Diseases.
3 a Health Interaction between a number of Health Problems including HIV status and Drug use in the incidence of Tuberclosis(TB) in Amsterdam.
b Injecting drugs on HIV positive have high chances of getting infected wth Tuberclosis.
c Drug Injecting HIV positive has the greatest chance of getting TB.
4 Interaction between different types of disease can affect the prevalence of a disease around the world in following ways-
- Viruses living in ceils can trigger changes that lead to cancers – for example, the human papilioma virus can cause cervical cancer.
- The immune system of your body helps you destroy pathogens and get better. If there are defects in your immune system, it may not work effectively. This may be a result of your genetic makeup, poor nutrition, or infections such as HIV/AIDS. This means you will be more likely to suffer from other communicable diseases (Figure 2).
- Immune reactions initially caused by a pathogen, even something like the common cold, can trigger allergies to factors in the environment
These allergies may cause skin rashes, hives, or asthma. - Physical and mental health are often closely linked. Severe physical ill health can lead to depression and other mental illness.
• Malnutrition is often linked to health problems including deficiency diseases, a weakened immune system, obesity, cardiovascular diseases, type 2 diabetes, and cancer.
The interaction between different factors, including lifestyle, environment, and pathogens, is an important principle to remember as you look at different types of disease.
B 5.2 B5 Pathogens and Disease AQA GCSE Biology B5 Health and Disease . Kerboodle Answers:Page No. 27
1 a Infectious diseases are caused by pathogenic microorganisms, such as bacteria, viruses, parasites or fungi; the diseases can be spread, directly or indirectly, from one person to another.
b pathogens make us ill as Infection occurs when viruses, bacteria, or other microbes enter your body and begin to multiply. Disease occurs when the cells in your body are damaged as a result of infection and signs and symptoms of an illness appear. The incidence of disease among those infected varies greatly depending on the particular pathogen and individual susceptibility.Thus pathogens make us ill.
2 a Two ways in which disease can spread from one person to another person by different ways are as follows:
Nose, mouth, or eyes to hands to others:
Germs can spread to the hands by sneezing, coughing, or rubbing the eyes and then can be transferred to other family members or friends. Simply washing your hands can help prevent such illnesses as the common cold or eye infections.
Hands to food:
Usually germs are transmitted from unclean hands to food by an infected food preparer who didn’t wash his or her hands after using the toilet. The germs are then passed to those who eat the food. This is easily prevented by always washing your hands after using the toilet and before preparing food items.
b Two ways in which disease spread from one plant to plant through the soil, through tools and direct handling of plants, or through insect vectors.
c Pathogens are passed from one organism to the other in thr following ways-
Nose, mouth, or eyes to hands to others:
Germs can spread to the hands by sneezing, coughing, or rubbing the eyes and then can be transferred to other family members or friends. Simply washing your hands can help prevent such illnesses as the common cold or eye infections.
Hands to food:
Usually germs are transmitted from unclean hands to food by an infected food preparer who didn’t wash his or her hands after using the toilet. The germs are then passed to those who eat the food. This is easily prevented by always washing your hands after using the toilet and before preparing food items.
Disease transmission in plant:
Direct transmission: – Disease transmission where the pathogen is carried externally or internally on the seed or planting material like cuttings, sets, tubers, bulbs etc.
Indirect transmission:- The pathogen spreading itself by way of its persistent growth or certain structures of the pathogen carried independently by natural agencies like wind, water, animals, insects, mites, nematodes, birds etc. are the different methods of indirect transmissions.
3 The main differences between bacteria and viruses are-
- Viruses are the smallest and simplest life form known. They are 10 to 100 times smaller than bacteria.
- The biggest difference between viruses and bacteria is that viruses must have a living host – like a plant or animal – to multiply, while most bacteria can grow on non-living surfaces.
- Bacteria are intercellular organisms (i.e. they live in-between cells); whereas viruses are intracellular organisms (they infiltrate the host cell and live inside the cell). They change the host cell’s genetic material from its normal function to producing the virus itself.
- There are some useful bacteria but all viruses are harmful.
- Antibiotics cannot kill viruses, but can kill most bacteria, with the exception of most Gram-negative bacteria.
- An example of a disease caused by bacteria is strep throat and an example of an affliction caused by a virus is the flu.
B 5.3 Growing Bacteria in Lab AQA GCSE Biology B5 Health and Disease . Kerboodle Answers:Page No. 79
1 a Scientist culture microorganisms in the laboratory so that they can be investigated.
b Agar gel is important in setting up bacterial cultures because it is important that the cultures are uncontaminated by other microorganisms, so sterile conditions are needed: the Petri dishes, nutrient agar jelly and other culture media must be sterilised. Therefore agar gel is important in setting up bacteria cultures.
2 a Bacteria are grown at 25oC or below in the school lab when this is not their optimum temperature because we are surrounded by disease causing bacteria all the time. If we culture bacteria at 37oC there would be a high risk of growing some dangerous pathogen. So if we use lower temperature you reduce the likelihood of growing pathogens that might be harmful to people
b Petri dishes are not opened before incubation once they have been inoculated and sealed because these are incubated upside-down to lessen the risk of contamination from airborne particles settling on them and to prevent the accumulation of any water condensation that may otherwise disturb or compromise a culture. Therefore petri dishes are not opened before incubation once they have been inoculated and sealed.
c Bacteria are often cultured at much higher temperatures in industrial plants and hospital laboratories because in industrial condition and hospital lab, bacterial are often cultured at much high temperature to enable the microorganism to grow more rapidly and identified sooner.
3 When we set up a culture of bacteria in a Petri dish you give the bacteria everything they need to grow as fast as possible. However, these ideal conditions do not last forever. Bacteria grow and reproduce more quickly when they are warm than when they are cold. It would be dangerous to incubate (keep and grow) cultures at temperatures close to body temperature (37°C) because doing so might allow the growth of pathogens harmful to health.Therefore despite the optimum conditions the growth of bacteria in a culture on petri dish is limited.
B 5.4 AQA GCSE Biology B5 Preventing Bacterial Growth Kerboodle Answers:Page No. 81
1 a The differences between a disinfectant an antiseptic and an antibiotic is that Antibiotics are medications that stunt the growth or eliminate bacteria, whereas Disinfectants are solutions used on inanimate objects to stop the growth or kill microorganisms. Antiseptics are cleansers used to kill germs on living things.
b A survey shows that disinfectants are most widely used in kitchens and toilets because disinfectant most widely used in kitchen and toilets because it kill all bacteria in the environment
2 Bacteria grow by splitting in two. In ideal conditions bacteria can divide every 20 minutes, so the size of the colony doubles every 20 minutes. This is known as exponential growth. Bacterial growth curve reflects the events in bacterial population when they are grown in a closed system of microbial culture of fixed volume (i.e. batch culture).The typical growth curve for population of cells can be divided into several distinct phases called the lag phase, log phase, stationary phase and death phase.
Lag phase
When a microbial population is inoculated into a fresh medium, growth usually does not begin immediately but only after a period of time called the lag phase, which may be brief or extended depending on the history of culture and growth conditions.
Log phase (exponential phase)
When the cell number from such experiment is graphed on arithmetic coordinates as function of elapsed time, one obtains a curve with a constantly increasing slope. The rate of increase in cell number is slow initially but in later stage the cell numbers increases explosively. The rate of exponential growth varies between bacterial genera (i.e. genetic characteristics of bacteria) and is also influenced by cultural conditions.
Stationary phase
In stationary phase there is no net increase or decrease in cell number. The cells functions such as energy metabolism and some biosynthetic processes go on.
Death phase: If incubation continues after a bacterial population reaches the stationary phase, the cells may start dying. Cell death may be due to cell lysis and this is also an exponential process but much slower than that of exponential growth.
Therefore it can be comprehended that in a sealed culture of bacteria, they grow very fast to begin with but the rate of growth eventually slows down and stop.
B 5.5 AQA GCSE Biology B5 Preventing Infections Kerboodle Answers:Page No. 81
1 three examples of things people can do to reduce the spread of pathogens to lower the risk of disease – simple hygiene measures, by isolation of infected individual, vaccination
2 Simple hygiene measures can help to prevent the spread of disease such as stop the spread of germs, focus your efforts on cleaning areas in the house where germs are more likely to spread, such as the kitchen and toilet.
Use either soap or hot water to rinse the germs away, or a disinfectant to kill them.
Make sure you dry surfaces such as worktops and chopping boards thoroughly after cleaning. Dampness helps any remaining germs to survive and, if there’s enough water, multiply.
By isolation of infected person:
If someone has an infectious disease, especially a serious disease such as ebola etc they need to be kept in isolation. The fewer healthy people who come into contact with the infected person, the less likely it is that the pathogens will be passed on.
By vaccination:
During vaccination, doctors introduce a small amount of harmless form of specific pathogens into your body. As result, if you come into contact with the live pathogens you will not become ill as your immune system will be prepared.
3 In 1847 Semmelweis, who was an obstetrician, (a doctor specializing in childbirth) published evidence that when doctors washed their hands before examining or treating patients, the mortality rate for women in his birthing ward in Vienna, Austria, was greatly reduced.
In his hospital doctors were routinely examining diseased corpses in the mortuary, then attending women in childbirth without first washing their hands. In some months, as many as a third of the women in the birthing part of the hospital were dying!
Semmelweis could not explain why hand-washing was effective – he didn’t know about germs – he just saw that it worked and that patients no longer caught fevers and other diseases.
The second tragedy is that although Semmelweis cut death rates in his own hospital, his attempts to spread the word failed. Many people died because hand-washing was not made a routine part of hospital practice.
The third tragic part of the story took place in 1865. Semmelweis had become clinically depressed when his work was rejected and he had started behaving oddly. He was lured by another doctor into an insane asylum in Vienna. Realizing it was a trap, Semmelweis tried to get out, but was held and badly beaten by guards and placed in a straightjacket. He died two weeks later, most likely from injuries he suffered during the beating.
With Semmelweis gone, the fourth tragedy is that his hospital got back to running ‘properly’ again, discarding his ‘crazy’ ideas. Mortality rates increased by a factor of six, but nobody cared. Therefore doctors are so resistant to Semmelweis’ idea.
B 5.6 AQA GCSE Biology B5 Viral Diseases Kerboodle Answers:Page No. 85
1 a Main symptoms of measles include:
- cough
- fever
- red eyes
- light sensitivity
- muscle aches
- runny nose
- sore throat
- white spots inside the mouth
b Measles is now rare in the UK as result of improved living condition and vaccination programme for young children.
2 a AIDS is a condition. HIV is a virus that may cause an infection, but AIDS is a condition or a syndrome. Being infected with HIV can lead to the development of AIDS, which stands for acquired immunodeficiency syndrome. AIDS develops when HIV has caused serious damage to the immune system
b Untreated HIV is usually fatal because during this phase, a person may have no symptoms at all, only mild symptoms or severe symptoms. Untreated HIV is usually fatal because the infection eventually progresses until the immune system is too weak to defend against life-threatening infections and cancers. This stage is called AIDS.
3 a i The number of cases of measles globally between 1980 and 1985 is 20000000
ii The number of cases of measles globally between 2000 and 2005 is 5000000.
4 Similarities and differences between tobacco mosaic virus in plants and measles in people are as follows. Tobacco mosaic virus (TMV) is a positive-sense single stranded RNA virus. The infection causes characteristic patterns, such as “mosaic”-like mottling and discoloration on the leaves (hence the name). TMV enters plants through wounds. Damage to the plant cell membrane permits entry of infectious particles into the cytoplasm. TMV ‘hijacks’ the hosts protein synthesis machinery to make viral proteins and TMV makes many copies of its RNA. TMV spreads into neighbouring cells using its movement protein which modifies tiny channels, called plasmodesmata, Symptoms include mosaic patterns on leaves, mottling, necrosis, stunting and leaf curling. TMV is transmitted very easily making control difficult. For example, infected leaves rubbing against healthy plants, or contaminated tools or workers hands (which can become contaminated with virus from cigarettes) can all spread TMV.
Measles: Measles is a viral disease that can spread rapidly. Also known as rubeola or morbilli, measles is an endemic disease, meaning it is continually present in a community, and many people develop resistance.It is an unpleasant condition but one that normally passes without treatment within 7 to 10 days. Measles is caused by the measles virus, a single-stranded, negative-sense, enveloped RNA virus of the genus Morbillivirus within the family Paramyxoviridae.
Humans are the only natural hosts of the virus, and no other animal reservoirs are known to exist. This highly contagious virus is spread by coughing and sneezing via close personal contact or direct contact with secretions. Risk factors for measles virus infection include immunodeficiency caused by HIV or AIDS.
Clinical diagnosis of measles requires a history of fever of at least three days, with at least one of the three C’s (cough, coryza, conjunctivitis). Observation of Koplik’s spots is also diagnostic of measles. People who have already had measles are normally immune and they are unlikely to get it again.People who are not immune should consider the measles vaccine.
Measles vaccination: In the United States, the measles, mumps, and rubella (MMR) vaccine is routinely given at 12 to 15 months of age, followed by a booster shot before entering school at the age of 4 to 6 years.Newborns carry their mother’s immunity for a few months after birth if their mothers are immune, but sometimes the vaccine is recommended before the age of 12 months, and as early as 6 months.This may happen if they are, or are likely to be, in an area where there is a serious outbreak.
The above exaplains the difference and similarities between tobacco virus in plant and measles in people.
B 5. 7 AQA GCSE Biology B5 Bacterial Diseases Kerboodle Answers:Page No. 87
1 Antibiotics work to cure bacterial infection by affecting things that bacterial cells have but human cells don’t. For example, human cells do not have cell walls, while many types of bacteria do. The antibiotic penicillin works by keeping a bacterium from building a cell wall.
2 Salmonella is spread through undercooked food and poor hygiene.
Salmonella are bacteria that live in the guts of many different animals. They can found in raw meat, poultry eggs, and eggs products such as mayonnaise. If these bacteria get into our bodies, they disrupt the balance of natural gut and people become infected with food poisoning caused by Salmonella.
b Doctors in the UK rarely treat SolmoneSta food poisoning with antibiotics, insteas poultry are vaccinated against salmonella to control the spread of the disease. Campylobacter, another bacterium found in chickens, cause food poisoning. To prevent food poisoining , keep raw chicken away from food that is eaten uncooked, avoid washing raw chicken, wash hand etc.
3 a Gonorrhea is a sexually transmitted disease (STD) that can infect both men and women. It can cause infections in the genitals, rectum, and throat. It is a very common infection, especially among young people ages 15-24 years.
b Until recently gonorrhoea was relatively easy to treat because Modern antibiotics can cure most gonorrhea infections. Most states also provide free diagnosis and treatment at state-sponsored health clinics.
c Three different ways to prevent spreading of gonorrhea:
- Use safe sexual practices. Abstaining from sex is the only surefire way to prevent gonorrhea, but it’s not the most practical solution. Using condoms every time you have any sexual contact can reduce your risk of getting gonorrhea
- Limit sexual partners. Your significantly increase your risk of getting gonorrhea by having sex with multiple partners.[5] Limit the number of people with whom you have sex to minimize your risk of getting the disease.
- Avoid touching your eyes. If you have or suspect you have gonorrhea, don’t touch your eyes after touching genitalia or your rectum. This can spread the disease to your eyes and cause an infection.
B 5.8 AQA GCSE Biology B5 Diseases Caused by Fungi and Protists Kerboodle Answers:Page No. 89
1 a
Three ways in which fungal diseases such as black spot or stem rust can spread from plant to plant are-
The black spot fungus produces spores which are released under wet conditions and usually spread by rain-splash.
The disease can also be passed from plant to plant on hands, clothing or tools.
Spores overwinter mostly on the shoots, but can survive on fallen leaves and within the soil.
b roses affected by black spot produce fewer, smaller flowers than healthy plants because black spot is the most serious disease of roses. It is caused by a fungus, Diplocarpon rosae, which infects the leaves and greatly reduces plant vigour. Unfortunately, this means that the resistance bred into new varieties usually fails to last because new strains of the fungus arise to overcome it.Therefore roses affected by black spot produce fewer and smaller flowers than healthy plants.
2 a People get malaria by being bitten by an infective female Anopheles mosquito. Because the malaria parasite is found in red blood cells of an infected person, malaria can also be transmitted through blood transfusion, organ transplant, or the shared use of needles or syringes contaminated with blood. Above mentioned are few ways in which malaria is passed from one person to another.
b Insecticide-treated mosquito nets help prevent the spread of malaria in two ways.First as a mechanical barrier against the bites of malaria-carrying mosquitoes and second as a means of killing mosquitoes on contact with the insecticide. Insecticide coated nets are so important because they kill mosquitoes that land on them, drawn to the nets by the odour of the person sleeping beneath it.
3 For travellers from the UK going to an area with malaria, doctors suggest the ABCD approach. This stands for Awareness, Bite prevention, Chemoprophylaxis (antimalarial medicines), and Diagnosis. Each of points of ABCD approach reduce the chance of becoming seriously ill with maleria in the following way.
AWARENESS OF RISK
- Seasonal rainfall can increase mosquito breeding and as a result, in some areas the risk of Malaria can be highly seasonal. So make sure you think about the time of year you are travelling too.
- For a full breakdown of what injections or medication you will need check out our handy Malaria Risk Map.
- Alternatively, you can talk to your Pharmacist, GP or any other trained health professional.
B – BITE PREVENTION
- Whether you are headed to a high or low risk area, it is important that you try to avoid being bitten by mosquitos. In short, the fewer bites you get, the safer you are.
- There are many repellents on the market but the UK Government Guidelines for Malaria Prevention recommends the use of repellents containing DEET at a concentration of 20% or over for maximum protection. The higher the strength of DEET the less frequently you will need to apply the repellent. DEET up to a concentration of 50% is considered suitable for infants over 2 months, breast feeding mothers and pregnant ladies although the product packaging may differ.
C – CHEMOPROPHYLAXIS
- In some areas where there is a risk of Malaria, it is advised that you use antimalarial medication to reduce your risk of contracting malaria should you get bitten.
- medication you need will vary dependent upon:
- Where you are travelling
- Your medical status
- Personal preference
Not all antimalarials are suitable for all areas. This is because the malaria parasite has developed resistance to some of the drugs used in some areas of the world. Be sure you obtain the right medication for the area you are travelling.
D – DIAGNOSIS
- Nothing is absolute. Even if you follow all these measures there is still a small chance of you contracting malaria.
- After you return from your trip, it is essential that you report any fever, diarrhoea, vomiting or shivering occurring within a year of your return.
- Prompt diagnosis of malaria ensures you get the right treatment when you need it and ultimately, improves your chances.
B 5.9 AQA GCSE Biology B5 Human Defence Response Kerboodle Answers:Page No. 91
1 a. Washing your hands before preparing a salad is the single most effective way to prevent the spread of infections. You can spread certain “germs” (a general term for microbes like viruses and bacteria) casually by touching another person. You can also catch germs when you touch contaminated objects or surfaces and then you touch your face (mouth, eyes, and nose).Therefore washing hands before salad preparation prevents the spread of disease.
b Throwing away a tissue after you have blown your nose prevent the spread of bacteria because when you throw it in the garbage can then people don’t pick it up, therefore preventing the spread of bacteria.
c Making sure sewage does not get into your drinking water prevent bacteria and viruses being spread because it stops people from catching disease that are body have got rid of. Also when we drink sewage water the pathogens get into our body and give people diseases.
2 a Hemophilia is a rare bleeding disorder in which the blood doesn’t clot properly . If you have hemophilia, you may bleed for a longer time than others after an injury. This bleeding can damage your organs and tissues and may be life threatening.
b A low white blood cell (WBC) count is a decreased number of white blood cells (leukocytes) in the blood. A low WBC count is referred to medically as leucopenia. When a low white blood cell count than person may be immunosuppressed, which means that they are more vulnerable to potentially serious infections that do not go away or are hard to treat.
3 white blood cells help to prevent you from suffering from communicable diseases. White blood cells are really important in the immune response. They circulate in the blood along with red blood cells and other components.
There are different types of white blood cells – some are able to engulf and digest microorganisms so that they are completely destroyed. This kills microorganisms very quickly and happens they first invade the immune system.
Other white blood cells are able to generate and release special chemicals called antibodies. These are attracted to special markers on the surface of microorganisms called ANTIGENS. Each white blood cell is specific to only one type of antigen. Antibodies are released, they attach to their specific antigen on the surface of microorganisms – microorganisms can then be bunched up into clumps, making it easier for white blood cells to engulf and digest them.
Antibodies take time to generate but once they are, the body is able to recognise specific microorganisms and can react quickly to release antibodies in future attacks – this is called natural immunity.
B 5.10 AQA GCSE Biology B5 More about Plant Diseases Kerboodle Answers:Page No. 93
1 a lack of nitrate ions in the soil affects the plants in following way:
Nitrate provides the nitrogen for the construction of vital molecule. Such as amino acids. Nitrogen is a constituent of amino acids, proteins, coenzymes, nucleic acids and chlorophyll. Nitrogen has a great affect on plant growth and a deficiency or excess markedly affects plant growth and fruit yield. Nitrogen is a mobile element in the plant and deficiency symptoms will develop first on lower leaves as the nitrogen is removed for use in new developing leaves. The older leaves become chlorotic (turn yellow) and eventually die. Nitrogen deficiencies can have a considerable effect on final yield if it occurs for prolonged periods during critical stages of growth. A lack of nitrate ions in the soil therefore decreases the growth of plants.
b Magnesium is an essential constituent of chlorophyll and is required for activation of many enzymes involved in the energy transfer processes. A lack of magnesium ions in the soil will seriously affect plant growth and development as photosynthesis is directly affected.
Deficiency of magnesium frequently occurs due to an imbalance with potassium or ammonium ions, appearing as interveinal chlorosis developing first on older leaves.
B 5.11 AQA GCSE Biology B5 Plant Defence Responses Kerboodle Answers:Page No. 95
1 a The plants defend themselves against pathogens by a combination of weapons from two arsenals : ( 1 ) structural characteristics act as physical barriers and inhibit the pathogen from gaining entrance and spreading through the plant , and ( 2 ) biochemical reactions that take place in the cells and tissues of the plant and produce substances that either are toxic to the pathogen or create conditions that inhibit growth of the pathogen in the plant .
b Three ways a plant might defend itself against attack by a herbivore are-
The first line of defense in plants is an intact and impenetrable barrier composed of bark and a waxy cuticle. Both protect plants against herbivores.
Other adaptations against herbivores include hard shells, thorns (modified branches), and spines (modified leaves).
They discourage animals by causing physical damage or by inducing rashes and allergic reactions.
2 the combinations of structural characteristics and biochemical re actions employed in the defense of plants are different in different host – pathogen systems. In addition, even within the same host and pathogen, the combinations very with the age of the plant. The kind of plant organ and tissue attacked the nutritional condition of the plant, and with the weather conditions . The way each of the plant defences are explained below-
Structural Defense :
Preexisting Defense Structures :A plant’s first line of defense against pathogens is uts surface , which the pathogen must penetrate if it is to cause infection . Some structural defenses are present in the plant even before the pathogen comes in contact with the plant . Such structures include the amount and quality of wax and cuticle that cover the epidermal cells , the structure of the epidermal cell walls , the size , location , and shapes of stomata and lenticels , and the presence on the plant of tissues made of thick-walled cells that hinder the advance of the pathogen .
Waxes on leaf and fruit surfaces form a water-repellent surface and thereby prevent the formation of a film of water on which pathogens might be deposited and germinate (fungi) or multiply (bacteria) . A thick mat of hairs on a plant surface may also exert a similar water-repelling effect and may reduce infection. A thick cuticle may increase resistance to infection in diseases in which the pathogen enters its host only through direct penetration . Cuticle thickness , however , is not always correlated with resistance , and many plant varieties with cuticle of considerable thickness are easily invaded by directly penetrating pathogens .
The thickness and toughness of the outer wall of epidermal cells are apparently important factors in the resistance of some plants to certain pathogens thick , tough walls of epidermal cells make direct penetration by fungal pathogens difficult or impossible . plants with such walls are often resistant , although if the pathogen is introduced beyond the epidermis of the same plants by means of a wound , the inner tissues of the plant are easily invaded by the pathogen .
Many pathogenic fungi and bacteria enter plants only through stomata . Although the majority of pathogens can force their way through closed stomata , some , like the stem rust of wheat , can enter only when stomata are open . Thus , some wheat varieties in which the stomata open late in the day , are resistant because the germ tubes of spores germinating in the night dew desiccate owing to evaporation of the before the stomata begin to open . the structure of the stomata – for example , a very narrow entrance and broad , elevated guard cell – may also confer resistance to some varieties against certain of their pathogens .
The cell walls of the tissues being invaded very in thickness and toughness and may sometime inhibit the advance of the pathogen . the presence , in particular , of bundles or extended areas of sclerenchyma cells , such as are found in the stems of many cereal crops , may stop the further spread 0f pathogens like the stem rust fungi . Also , the xylem , bundle sheath , and sclerenchyma cell of the leaf veins effectively block the spread of some fungal, bacterial , and nematode pathogens that cause the various angular leaf stops because of their spread only into areas between , but not across veins .
Defense Structures formed in Response to Infection by the pathogen :
In spite of the preformed superficial or internal defense structures of host plants , most pathogens manage to penetrate their hosts and to produce various degrees of infection . Even after the pathogen has penetrated the preformed defense structures , however , plants usually respond by forming one or more types of structures that are more or less successful in defending the plant from further pathogen invasion . Some of the defense structures formed involve tissues ahead of the pathogen (deeper into the plant) and are called histological defense structures ; others involve the walls of invaded cells and are called cellular defense structures ; still others involve the cytoplasm of the cells under attack , and the process is called cytoplasmic defense reaction . Finally , the death of the invaded cell may protect the plant from further invasion , and this is called necrotic or hypersensitive defense reaction .
B5 Plant Defence Responses Summary questions:and Kerboodle Answer Page No. 96
1 As a result of budget cuts, your school has decided to buy a cheaper disinfectant to use for washing the floors, and to tell cleaners to dilute the disinfectant more when they use it so that it lasts longer. The biology department decides to check if this risks the spread of more communicable diseases in the school. The efficacy of the two disinfectants and effect of diluting the disinfectant which is used to wash school floors can be associated with the following method:
- Firstly we have to grow soil bacteria.
- Then by adding circles of filter paper by taking different concentrations of disinfectant
- Now seal and flip
- We have to determine the total area of light circles
2 a The fridge temperature is lower than room temperature so that the activity of bacteria is slowed down which inhibit the growth of bacteria and room temperature favours the growth of bacteria.
b i Division occurs every hour, so 24 times in 24 hours at room temperature
1 × 224 = 16 777 216
ii division occurs every 6 hours, so 4 times in 24 hours in the fridge.= 32
c The percentage difference in the numbers of rot-causing bacteria between fruit stored in the fridge and the fruit stored at room is-
16777216
16777184 × 100 = 99.9% more bacteria formed at room temperature
d Someone suggested heating the strawberries to 100 °C for a few minutes to prevent them going bad. The pros is that heating would kill bacteria and cons that heating will cause denaturation of enzymes.
3 a Human Immunodeficiency Virus (HIV) is a virus. AIDS is a disease caused by virus.
b i The approximate numbers of people living with HIV and dying of AIDS in sub- saharan africa in 2013. 70% of total AIDS population are living in sub-Saharan Africa. There are 1.5 million AIDS-related deaths internationally and 70% in sub-Saharan Africa calculated out to be 1,050,000 deaths from AIDS in sub-Saharan Africa
ii Our answer is only approximate because we do not know the exact number of people affected by HIV. Most of the cases are not diagnosed as well as deaths due to this are not counted precisely.
c i The percentage of the people suitable for treatment with antiretroviral therapy actually get treatment is 52%
ii The health infrastructure is not so good as to diagnose the disease in earlier phase. Most of the suffered people live in poor countries which cannot afford the expensive treatment.
d i By using protection while intimating, do not reuse the needles, use of disposable syringe, by having sex with limited partners we can prevent AIDS.
ii Protection that is condoms prevent the mixup of body fluids which also bars the virus from passing. By using disposable needles the risk of infection from blood can be prevented. By limiting partners we can reduce the chance of taking virus.
4 a Display these results graphically or in a chart. [5 marks]
b Cotton is the crop which benefitted most from the protective measures.
The crop loss reduced by 53.2%
c Wheat was the least affected by crop protection measures.
crop loss reduced by = 21.6%
e By maintaining a good field hygiene , using pest control methods and by planting the plants on proper gap can help to protect their crops from plant disease.
f As a food security measure, crop yields can be protected from disease. Good crop productivity can make the nation economically stable. It can reduce the risk of famines.
B5 Plant Defence Responses Practice questions: Kerboodle Answer Page No. 97
01.1 AIDS is a virus, Malaria is a protest, Salmonella food poisoning caused by bacterium
01.2 In year 1997 was the highest number of confirmed cases of Salmonella.
01.3 There were 2320 confirmed cases in that year.
01.4 one reason why this value may not be the total number of Salmonella cases in Wales that year. This value may not be the total number of Salmonella cases in Wales that year because–
- not all people would visit the doctor
- not all people would give a sample for analysis
01.5 The high number of cases that year was due to people eating eggs from infected chickens.
The number of cases of So/mone//<3 has rapidly decreased since then. Two reasons for the decrease in the number of cases are-
- chickens / poultry are now vaccinated against
Salmonella
- food cooked thoroughly
- food stored in fridges / freezers
- raw and cooked foods stored separately
- people wash hands / surfaces before preparing food
02.1 The rose black spot disease might affect the growth of a rose bush in following ways-
less chlorophyll / leaves
(so) less light absorbed
or
(so) less photosynthesis
(so) less sugar / glucose / food
made
02.2 Two things a agardener could do to kill the fungus and reduce the chance of another rose black spot infection are-
use a fungicide
(remove and) destroy / burn the
infected leaves
03 Two precautions the student should take so that only bacteria from the milk grow on the nutrient agar are-
sterilise Petri dish / agar / loop
to kill / prevent transfer of
bacteria / microorganisms
tape the Petri dish lid
or
do not open the lid too far / too
long
(so) less chance of bacteria /
microorganisms getting in
or
less contamination from air
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References:
BBC Bitesize
AQA GCSE Science Kerboodle textbook
Wikipedia
Wikimedia Commons
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