Edexcel IAL biology Unit 2

composition and function of chromosome or nucleoid

- chromosomes in bacteria are not bounded by nuclear membrane. it means that bacteria are prokaryotic organisms. in addition to this bacteria don't have other membrane bounded organelles like mitochondria, Golgi apparatus, Endoplasmic reticulum. chromosomes is made up of DNA and histone. - 1. it controls the synthesis of protein. 2. it also contains genes - hereditary material.

Sclerenchyma (note)

- dead - supporting plant - not involved in transporting water and mineral ions

composition and function of mesosome

- it is infolding of cell membrane. it is made of lipid and protein. - aerobic respiration occurs in mesosoma.

composition and function of flagellum

- it is made up of chemical called flagellin. - it is used by bacterium to propel or move through aquatic environment.

composition and function of plasmid

- it is made up of extra nuclear substance and it is used as a vector to carry desired gene used in biotechnology. plasmid also contains mutated gene.

composition and function of cell membrane

- it is made up of lipid and protein. - 1. it acts as a selectively permeable membrane. 2. osmosis, diffusion, facilitated diffusion and active transport occurs through cell membrane. 3. exocytosis, endocytosis and pinocytosis occurs through the cell membrane. 4. it acts as a sac like structure holding cytoplasm and organelle inside it.

composition and function of slime layer

- it is made up of mucopolysaccharide. - 1) it prevents bacterium from being digested by many organisms. 2) it prevents bacterium from being desiccated.

composition and function of cell wall

- it is made up of peptidoglycan. - It provides bacterium a particular shape and prevents bacteria from injury.

composition and function of ribosome

- it is made up of protein and RNA. - it is here protein synthesis occurs.

composition and function of cytoplasm

- it is made up of water and other organic substance such as enzymes, stored glycogen etc and inorganic substance such as mineral ions eg - Na+, K+, Cl- etc - 1. it provides a basis for chemical reaction to occur. 2. it regulates osmotic potential in a cell. 3. organelles such as ribosome chromosome, plasmid etc are suspended in cytoplasm.

parenchyma (note)

- living - packing tissue and stores food

investigating need for mineral salts for plants

- take 5 plants. - the plants must be planted from seedlings of the same parent plant. - they must be of the same age and size at the start . - each plant will have a different concentration of the mineral salt. the concentrations are 1%, 2%, 3%, 4% and 5%. - the temperature and type of soil the plants are exposed must be the same. the concentration of all the other minerals in the soil must be the same. they must be kept in the same area so they are exposed to the same light intensity and temperature - after every week/month, measure the growth of the plants by finding the mass/number of leaves/length of roots/height of plant. - repeat the investigation 5 more times , keeping all the variables the same. - then calculate the mean mass/number/height...

captive breeding and genetic diversity

1. '18 individuals is a small population/small gene pool/low genetic diversity/may have been closely related. 2. captive breeding will increase population. 3. the animals can be taken care of in zoos. 4. they can also be exchanged from different zoos and may mate with other animals of different zoos. 5. this will lead to an increase in their population size as more offspring will be produces. 6. there will also be more genetic diversity. 7. stud books can be kept to select mates. 8. inbreeding must be prevented to avoid genetic drift. 9. IVF (pg 144) can be done to make sure fertilization is successful. the zygote can be implanted into a surrogate mother. 10. genetic diversity can be measured using DNA profiling.

double blind trial

1. a large group of patients are taken. 2. they must be of the same age, gender, non-smokers, etc. 3. the group is divided into two- one group is given the new drug , while the other is given a placebo or an existing drug. 4. a placebo is an inactive substance which is used to compare the effect of the psychological effect and "medical?" effect of the drug. 5. neither the doctor nor the patients know who is in which group.

explain why scientists are breeding the Cavendish banana with different varieties of banana. (4) usually when a lot of information is given, they expect you to use it and also to use your knowledge ofcourse in these "explain" q.s. this answer used the information given.

1. all Cavendish plants are suspectible to the fungus because they are genetically identical/clones. 2. whereas different varieties may have resistance to the fungus or contain an allele for resistance to fungus. 3. therefore breeding could increase genetic diversity. 4. resulting in new banana plants with resistance to the fungus or Panama disease.

explain how the structure of an egg cell is related to its function as a gamete. (4) - jan 16

1. an egg cell has a haploid number of chromosomes so that it can 2. fuse with a sperm cell to produce a diploid zygote. 3. the egg cell also contains lipid droplets to provide energy for the growth of a fetus 4. the egg cell contains cortical granules that release enzymes when a sperm enters an egg. these harden the zona pellucida and destroy the sperm-binding sites on the surface membrane of the egg. these all prevent polyspermy.

cons for seedbank

1. are not of interest to public. 2. cannot spread awareness/raise funds easily.

the question said EXPLAIN NOT DESCRIBE. FIRST- LOOK AT COMMAND WORD. explain the relationship between the concentration of herbicide and the mean number of species of insects in the three fields. use the information in the graph to support your answer. (4)

1. as the concentration of herbicide increases the mean number of insect species decreases.(1) 2. increase of 100mgdm-3 results in a decrease of 6.2 species. (1) 3. use of herbicides result in fewer plant species. 4. therefore some insects species leave habitat or die from lack of food. 5. fewer plant species results in fewer habitats for insects. (1)

metaphase

1. centrioles reach the poles and form spindles. (plants do not have centrioles but can form spindle fibres) 2. chromatids line up along the metaphase plate (equator) of the spindle. 3. centromeres of each chromatids attach with a separate microtubule of the spindle.

name two structures present in animal cells that are not present in a plant cell. (2)

1. cilia. 2. glycogen granules. 3. flagella

technique used to separate DNA and RNA fragments- gel electrophoresis

1. collect DNA sample from the organisms. 2. put this sample in a test tube and add restriction endonuclease into the test tube to cut the DNA molecules into fragments. 3. the DNA fragments are placed into a well in a slab of agarose of gel and covered in a buffer solution that conducts electricity. 4. an electrical current is passed through the gel. DNA fragments are negatively charged so they move toward the positive electrode at the far end of the gel. 5. short DNA fragements move faster and travel further through the gel so the DNA fragments separate according to length. 6. the DNA fragments appear as bands under UV light. the band can be compared to identify individual or species relateness

describe the methods that would be used to trial a drug containing these compounds. (6)

1. compound needs to be extracted from trees and used to make a drug. 2. compounds tested on Y. pestis (underlined) in vitro. 3. phase I: test the drug on a small number of healthy volunteers. 4. review by independent scientists/medics to see if work can progress to stage 2. 5. phase II: test drug on a small number of patients who have the plague. 6. appropriate concentration or dose of the drug is identified. 7. phase III: drug tested on larger group of patients who have the plague. 8. placed randomly in two groups : one group receives the treatment or drug containing the chemical compounds and the other receives a placebo. 9. reference to double blind test. 10. analyse results with appropriate statistical test/test for significant difference.

drug testing protocols

1. computers used to model effects. 2. tested on human tissue in labs. 3. tested on animals. 4. clinical trial.

after fertilisation, the egg cell divides by mitosis to form a blastocyst. during this process, totipotent cells become pluripotent. describe how a totipotent stem cell becomes a pluripotent cell. (3) take a moment to read, understand and construct a nice structure for your answer. make a little note on the blank page given if required. but ofcourse make sure to finish 3 mark qs within 2-3 minutes. try finish the long qs at the end of the paper first then do the beginning. see if it speeds up your progress.

1. differential gene expression. 2. some genes have been permanently switched off or inactivated. 3. by epigenetic modification. 4. proteins or enzymes made from active genes which permanently modify the cell.

how can variation be brought about in organisms

1. due to mutation caused by ultraviolet rays, gamma rays, xrays or tar in cigarettes. 2. crossing over in meiosis 1. 3. random assortment in metaphase. 4. random fertilisation or fusion of male and female gamete to form a zygote.

need for seedbanks

1. food crop such as wheat, barley, rice and corn (horticulture). 2. medicinal value. 3. materials, such as paper, clothing and building materials. 4. food for wildlife as plants are the base of all food chains. 5. recycling carbon dioxide and producing oxygen. 6. transpiration gives rise to rainfall.

random sampling

1. form a grid using 2 tape measures perpendicular to each other. 2. obtain random coordinates by generating random numbers from a calculator and place the quadrat at these coordinates to reduce bias. 3. repeat in 2 different habitats in order to compare the number of individuals or the different number of species in 2 different habitats.

give two differences between genetic diversity and species richness. (2)

1. genetic diversity considers one species whereas species richness considers different species. 2. genetic diversity considers alleles or genotypes whereas species richness considers whole organisms

discuss the solutions, proposed by these scientists, to overcome the concern of introducing only 11 beavers into Scotland from Norway. Use the information in the map to support your answer.

1. genetic diversity identified as the variety of alleles in the population. 2. only small numbers of introduced beavers could reduce the genetic diversity. 3. loss of alleles from population. 4. increased homozygosity. 5. introducing more Norwegian beavers could increase genetic diversity. 6. but could have same alleles so no effect on genetic diversity. 7. introducing beavers from different European locations could increase genetic diversity. 8. could be many different alleles in wider populations of European beavers. 9. however the map shows many geographically isolated populations. 10. these small populations could also have low genetic diversity. 11. reproductive isolation could have occurred. 12. preventing introduced beavers mating with Scottish beavers.

genetic variation in a species

1. genetic variation is brought about in two ways in meiosis. 2. in crossing over, sections of chromatids are exchanged. 3. this leads to the formation of recombinants. 4. errors in the progress lead to mutation which also introduces new combinations into the genetic make-up of the species. 5. furthermore, in independent assortment, the maternal and paternal genetic material is distributed completely at random. 6. moreover, a completely random ovum is fertilized by a completely different random sperm.

specialized cells

1. give a stimulus to the cell (e.g. chemical). 2. some genes are activated while others are deactivated. 3. only the active genes are transcribed to produce mRNA at those genes. 4. the mRNA is then translated to make a protein/polypeptide. 5. this protein permanently modifies the cell (and determines the structure and function of the cell).

explain why xylem is described as a tissue. (2)

1. group of cells. 2. with similar structure/function/origin

seedbanks and genetic diversity

1. harvest the seeds from different plants of the same species. 2. collect seeds from plants growing in different locations/countries. 3. this all will increase the variety of alleles in the plants by doin gthis a large gene pool can be obtained.

suggest why it is an advantage for cells with damaged DNA to be prevented from continuing through the cell cycle. (2)

1. idea the DNA will be replicated in the S phase. 2. it prevents formation of daughter cells with damaged DNA (in the S phase). 3. if the DNA is damaged then proteins will not function.

role of the cell cycle

1. in the cell cycle the organism grows as the number of cells increase. 2. asexual reproduction or mitosis leads to the production of clones or genetically identical daughter cells. 3. tissues are also repaired and the cells are replaced. (in phase- ) 4. cell division is also controlled at checkpoints by enzymes called CDKs...

explain the role of mitosis and the cell cycle in the formation of the morula from the zygote. (3)

1. increase in cell number. 2. cells will be genetically identical. 3. there will be an increase in the number of cell organelles during interphase. 4. DNA replication during S-phase

potential risks of stem cell treatment

1. infection from donor/unsterilized equipment. 2. increased suspectibility due to immunosuppressants. 3. risk of cancer/abnormal growth. 4. rejection.

explain how the reintroduction of beavers resulted in a change in the biodiversity in Scotland. (4) use information given and notice how the question said change and not an increase or decrease. this answer seems to be mostly based on the information given.

1. introduction of new beaver species increased the species richness or biodiversity. 2. reduction in plant biodiversity due to trees being cut down. 3. increase in biodiversity due to pond being created. 4. increase in biodiversity due to new food source-fish from pond.

continuous variation

1. it deals with a range of phenotypic expressions. 2. it is controlled by many genes. 3. it shows additive effect. 4. it is affected by the environmental changes. 5. examples - height, skin colour, synthesis of haemoglobin

discontinuous variation

1. it deals with some clear cut phenotypic expression. 2. it is controlled by few genes. 3. genes involved in discontinuous variation shows no additive effect. 4. action of genes is not affected by environmental changes. 5. examples - gender, tongues may roll or may not roll.

explain how seed banks can help to conserve the genetic diversity of plant species. (2)

1. large number of seeds can be collected from many different plants. 2. this ensures variety of alleles or a large gene pool in seeds collected.

suggest how the effects of habitat loss on the biodiversity of a tropical forest could be measured. (2)

1. measure species richness in the forest. 2. compare before and after habitat loss.

meiosis importance

1. meiosis reduces the chromosome number in gametes from diploid to haploid. 2. genetic variation is brought about in two ways :- crossing over and independent assortment. 3. in crossing over, alleles/sections are exchanged between chromatids. 4. this leads to the formation of recombinants. 5. moreover, in independent assortment, the maternal and paternal genetic material is completely randomly distributed into the gametes.

suggest how these undifferentiated cells gave rise to genetically varied egg cells. (4)

1. meiosis results in haploid nuclei. 2. in meiosis, the maternal and paternal genetic material is randomly distributed into the gametes. 3. in crossing over, sections of the chromatids are exchanged. 4. which results in recombinant alleles

explain how a tissue culture technique can be used to grow pitcher plants

1. meristem cells are used in the tissue culture as only these cells can divide by mitosis. 2. grow the explants in agar nutrient mediums. 3. which has a low nitrate concentration. 4. the agar also contains growth hormones. 6. make sure to use sterilized equipment.

key steps in IVF

1. normal mensural cycle steps are blocked temporarily by using hormone-based drugs. 2. synthesis FSH is injected to stimulate ovaries to develop many egg cells. 3. sperms are collected from males in the same or different zoos. sperm stocks can be held frozen in a viable state for later use. 4. several eggs are removed from the ovaries positioned with the help of ultrasound. 5. eggs are mixed with sperms in a shallow dish. fertilization can be checked using microscope. 6. zygote are then incubated at a body temperature for 2-3 days and confirmed that embryos are transferred into the uterus in the expectation that some will implant successfully.

prophase

1. nuclear membrane is disintegrated. 2. nucleolus is disintegrated. 3. chromosomes become shortened and thickened and more visible. 4. each chromosome now has two chromatids joined to a centromere. 5. centrioles start moving to the pole at late prophase.

describe the process of double-fertilisation in flowering plants (3)

1. one haploid male gamete fuses with haploid egg cell. 2. to produce a diploid zygote. 3. one haploid male gamete fuses with two polar nuclei. 4. to produce a triploid endosperm nucleus

give two differences between an organ and a tissue. (2)

1. organ has many functions whereas a tissue has one or fewer. 2. organ has many or several cell types whereas a tissue has one cell type or similar cells

taxonomic classification

1. organisms with common features are placed in a group. 2. the characteristics are assessed by observing the characteristics, (e.g. behavioural, physiological and but mainly, anatomical adaptations similarities in DNA, molecular phylogeny.)

zoos

1. prevent extinction. 2. maintains breeding populations when habitats are lost. 3. breeding programmes increase numbers so endangered animals can be introduced back into the wild. 4. zoos are used for research to gain a better understanding for conservation. 5.zoos raise awareness to educate the public on endangered species.

critical evaluation of this paper by the scientific community did not fully support the conclusions. there were calls for the paper to be withdrawn. suggest how the process of critical evaluation failed to support the conclusions of this paper. (3)

1. reference to peer review - many peer scientists individually repeated the investigation? 2. the other scientists repeated the experiment. 3. the results they achieved was not the same

critical evaluation of scientific ideas

1. scientific findings can be published in a journal or newspaper. 2. they can also be presented in a scientific conference. 3. peer review can be done, in which other scientists can repeat the experiments to confirm or validate the findings (test reliability of data)

explain how secondary thickening in the cell wall contributes to the physical properties of xylem vessels. (3)

1. secondary thickening provides greater tensile strength. 2. secondary thickening provides extra rigidity. 3. lignin provides waterproofing. 4. pits present for movement of water into or out of xylem.

seedbank collection

1. seeds are collected from a large number of individual plants to ensure a high genetic diversity. 2. seeds are x-rayed to check for fully formed embryos so that only viable seeds are stored. 3. seeds are dried to prolong viability/survival and stored at -20dC to stop enzyme activity and prevent germination and decomposition. 4. seeds are periodically germinated to make new seeds, replace dead and decaying seeds and check for viability.

pros for seedbank

1. since seeds are small, they take up less space when storing. 2. if large numbers of seed are stored there is greater genetic diversity. 3. seeds can also be stored for along time. because they can stay dormant for a long time. 4. many different species of plants seeds can be stored easily and in similar conditions. 5. growing plants require more regular maintenance. 6. they are less expensive to keep than growing plants.

preparing root tip squash. for example : describe how to prepare a root tip squash so that the chromosomes can be seen. (4)- june 15

1. soak the roots in hydrochloric acid at 55dc for 5 minutes. then rinse it with tap water. cut root tips of 5-10mm in length. let them fall in a vial of acetic orcein standing on a white tile. place a lid over the vial. place the vial containing the root tips in acetic orcein in the 55dc water bath for 5 minutes to intensify the staining. after 5 minutes, use forceps to remove the tips from the vial and place them on a microscope slide. use the blunt edge of a knife to gently press on a coverslip on to the slide. gently clean slide with a paper towel. use an electron microscope to observe.

suggest why the Chinese hamster sperm cell has such a long flagellum. (3)

1. sperm with longer flagellum swim fast to the egg cell. 2. sperm have increased chance of fertilizing the egg cell. 3. competition with sperm from other (male Chinese) hamsters.

telophase

1. spindle fibres break down. 2. nuclear membrane and nucleolus reforms. 3. centrioles reform and chromosomes unravel.

you did not read the question and understand properly and thus you got the whole answer wrong! explain why chemicals from a whole heart are needed to produce mature heart cells from immature heart cells. (4) (take 2-3 minutes here only)

1. the chemicals switch on some genes and switch off some genes. 2. the genes coding for heart cells are switched on. 3. mRNA is produced at these active genes. 5. mRNA is translated to produce proteins. 6. these proteins determine the structure and function of the mature heart cells and they also permanently modify the cells as heart cells.

testing drugs on whole animals (instead of just tissues)

1. the drug may have an effect on other tissues. 2. the effect on organs and systems by the drug must also be found. 3. drug metabolism... 4. whether the drug is toxic must also be found.

explain why this organelle cannot be seen using a light microscope. (2)

1. the magnification/resolution of a light microscope is not high enough to see this organelle. 2. because it is very small.

anaphase

1. the overlapping microtubules (spindle fibres) contract - this uses energy, pulling chromatids from each pair to opposite poles. 2. pairs of chromatids have been separated to opposite ends.

(make sure to see how many marks the graph q is worth and the command word. generally, 2/3 m q that are worded exactly like this one MUST be answered like this. you must clearly mention the increase or decrease of the variable when describing the graph and also giving the data manipulation!) (take 1-2 mins only for these q and make sure to look at the graph as revise the correction) using the information in the graph, describe the changes in the growth of this pollen tube. (3)

1. the rate of growth of the pollen tube is variable or inconsistent or fluctuating. 2. as the time passes after germination, the pollen tube length increases. 3. the length of the pollen tube increases by 42 um from 5 minutes to 45 minutes.

embryos can also be frozen for future use. this process has the following disadvantages

1. there is not enough space or sufficient resources in zoos and parks for the endangered species. 2. animals can have problems breeding outside their natural habitat which can be hard to recreate in a zoo. for ex - stress in cage menstrual cycle in animals. 3. reintroduction to the wild will be unsuccessful unless the original reason for the species being pushed to the edge of extinction is removed. reintroduced organisms can bring new diseases to habtiats, harming other organisms living there. 4. animals breed in captivity may have great problems in adjusting to unsupported life in the wild. for ex - problems with finding food or communicating with wild members of their species. 5. this program is very expensive and time consuming and it may fail.

the mature heart cells produced can be used to test drugs developed for treating heart disease. suggest the advantages of using mature heart cells to test these drugs. (2)

1. these cells will function like heart cells. 2. the use of animals is reduced. 3. the clinical trials will not be carried out unless drugs target heart cells. 4. clinical trials will not be carried out unless the drugs are shown to be safe.

explain the importance of water to plants (3)

1. to dissolve mineral ions 2. and transport the mineral ions to parts of the plant. 3. to act as a medium for chemical reactions. 4. it keeps plant cells turgid and provides the plant support and keeps them upright. 5. to bring about hydrolysis of bonds in reactions. 6. as a reactant. 7. to regulate temperature by transpiration.

suggest two applications of the use of stem cell therapy

1. to treat Parkinson's disease. 2. produce transplant organs. 3. replace/repair damaged tissue.

ultraviolet light has been shown to increase the risk of skin cancer. suggest how skin cancer is the result of an interaction between genotype and the environment (3)

1. ultraviolet light is an environmental factor that causes skin cancer. 2. ultraviolet light causes mutations in the genetic makeup, 4. affecting DNA replication in the cell cycle. 5. this results in the formation of an oncogene and tumours. 6. the control of the cell cycle is then lost.

investigating antimicrobial properties. for example : describe an investigation to determine the effect of the concentration of garlic extract on other species of bacteria.

1. use a mortar to grind a garlic into a paste and then mix the paste with alcohol. make several mixtures like this of different garlic concentrations. the concentrations are 1%, 2%, 3%, 4% and 5%. soak a disk in each of the beakers of garlic extract. then soak one disc in only ethanol. 2. use a marker to mark 6 places on the agar plate that has been seeded with bacteria (or take 2 agar plates and label 3 places in both of them..); label five according to the concentrations of the garlic extracts and one control. 3. then using forceps place the discs according to their labels in the agar plate. use clean forceps for each disc. 4. place one piece of tape on each side of the petri dish to hold it down. 5. invert the plate and incubate at a temperature of 25dc for 48 hours. 6. finally, use a ruler to measure the diameter of the clear zones around each disc. record your results in a suitable table. clear away all the equipment. petri dishes should be returned for sterilization. 7. do the whole procedure, keeping everything the same, but using different species of bacteria. make sure to use garlic of the same size and parent plant. do this with atleast 4 more different species of bacteria. then repeat each of the experiments 5 more times to find the mean diameter of each of the discs.

acrosome reaction

1. when the sperm touches the ovum, acrosome releases acrosin. 2. the acrosome fuses with cell surface membrane of sperm. 3. the acrosin will be released by exocytosis and will digest the zona pellucida and allow the sperm to penetrate through the barrier.

adaptations of xylem to carry its function

1. xylem starts of as living tissue and the first xylem produced is protoxylem which can be stretched and grown with the growth of plants. thus, it provides flexibility.

investigating tensile strength. for example : suggest how a valid investigation could be carried out to produce reliable data to compare the tensile strength of white fibres and brown fibres (4) -june 14

1.take 9 white fibre and 9 brown fibre strings of the same length of 10cm and of same diameter. 2. clamp one of the strings between two retort stands. ensure it is held securely. 3. place the cushioning underneath the string. ensure the tray is kept beneath the masses, so they do not strike the bench when the string breaks. 4. hang masses 10g at a time to the string until the string breaks. record the mass required to break the string in the results table. 5. repeat the procedure with each of the other strings and calculate the mean mass required to break a white fibre string and a brown fibre string.

ecological isolation

2 populations inhabit the same region, but develop preferences for different parts of the habitat.

name the three domains

Bacteria, Archaea, Eukaryota

speciation

Formation of new species

one type of ironwood tree, Tabebuia avellanedae (underlined), is native to south America. state the genus to which this plant belongs. (1)

Tabebuia

state what is meant by the term species. (1)

a group of organisms that are capable of interbreeding and producing fertile offspring.

log phase

bacteria used to be adapted to the condition and becomes suitable by obtaining nutrients for multiplication.

what are the structures formed as a result of double fertilisation

diploid zygote and triploid endosperm nucleus

allopatric speciation

geographical isolation followed by mutations can result in the formation of a new species. this can be illustrated with the finches of the Gala pagos islands. there are many different species in the Gala Pagos islands ultimately from a common ancestral species.

make sure to go through ..

hardy weinberg, the last few math q and any other maths q

woese suggested that bacteria and archaea were two separate groups of prokaryotic organisms. describe the evidence woese used to make this suggestion. (2)

he used molecular phylogeny and DNA profiling. woese looked at DNA.

to soften or marcerate the tissue before staining the cells, the root tips may be placed in

hydrochloric acid

suggest why calcium ions affect the tensile strength of plant fibres. (2)

if there are more calcium ions, more calcium pectate will strongly bind adjacent cellulose microfibrils in the middle lamella and so the fibres will be stronger and harder to break.

explain how a decrease in population size can result in a reduced genetic diversity. (2)

inbreeding or mating with closely related individuals such as siblings reduces the gene pool in a population

data obtained due to continuous variation

is plotted in the graph then a bell shaped curve is achieved. it is due to normal distribution of the variable. in this case a difference between highest and lowest value in the variation is called standard deviation. if the standard deviation is larger then the reliability of the data distributed is less due to overlapping. if the standard deviation is less then the probability for overlapping of the data will be less and its reliability will increase.

geographical isolation

it happens when a physical barrier such as a river, mountain range, flood, volcanic eruptions, earthquakes separate individuals from an original population.

pit

it is a depression in the cell wall where cell wall becomes very thin. it exists in pairs. it helps to exchange material.

chloroplast

it is a double membrane bounded organelle. some inner membrane stack to grana in which fluid is filled. thylakoid is present. in thylakoid chlorophyll is present which traps light energy and converts into chemical energy for photosynthesis. stroma contains enzymes which catalyzes chemical reactions to reduce CO2 into glucose. stroma also contains loop of DNA controls the synthesis of protein needed for chemical reactions in photosynthesis

amyloplast

it is also double membrane bounded organelle. produced by leucoplast and present in some plant cells such as potato. it stores amylopectin a form of starch

placebo

it is an inactive drug that is used as a control. it is compared with the actual drug and used to find the psychological effect of taking the drug or placebo.

variation

it is caused due to mutation in the gene in a cell.

middle lamella

it is outer layer of a cell it acts as a glue holding two adjacent cells together. it strengthens the cell.

sap vacuole

it is surrounded by a membrane called tonoplast which is partially permeable. this vacuole contains sap in which water, enzymes, glucose or starch, mineral ions are present. it also contains different pigments such as betalain in beetroot, toxin such as digitalin in fox cloves. cell sap regulates osmosis in the cell.

population bottleneck

it is the effect of an event or series of events that dramatically reduces the size of a population and causes a severe decrease in the gene pool of the population resulting in large changes in allele frequency and a reduction in genetic diversity.

species richness

it is the number of different species in an area

suggest why it is better to store seeds from several individual plants of one species rather than seeds from one individual plant. (2)

it maintains genetic diversity. it will reduce chance of inbreeding. so, it will reduce chance of storing seeds with low viability.

describe the role of the sperm tail (2)

it makes whip-like movements and allows the sperm to move and swim to transfer the male genetic material from the cervix to the ovum

sympatric speciation

it occurs between populations of a species living in the same place that become reproductively isolated by mechanical, behavioural or seasonal changes. due to selective pressure, mutations may result in reproductive incompatibility. a new gene producing for example hormone may lead an animal to be rejected from the mainstream group but breeding may be possible within its own group of variants.

adaptive speciation

it occurs when one species develops rapidly to form several different species which occupy different ecological niches. it occurs after allopatric speciation

name two substances found in the secondary cell wall that provide support. (2)

lignin and hemicellulose

seedbank conditions

low temperatures and dry atmosphere- 1. reduces the enzyme activity and respiration in seeds. 2. the seed will thus be less likely to germinate/seed kept dormant. 3. this also reduces the enzyme activity and growth of bacteria/fungi/microorganisms. 4. this also decreases the rate of decomposition.

suggest how these programmes can help conserve the lion-tailed macaque. (5)

macaques can be exchanged between zoos. a stud book can be used for the selection of mated and the macaques can mate with other macaques from different zoos and outbreeding can also be encouraged. this will result in an increase in their population size and increase their genetic diversity. the macaques can be prepared to be re-introduced into the wild by reducing their food intake. this will reinforce their wild behavior. they can then be released into a national park or reserve and can be protected from predators and poachers.

gametic isolation

male and female gametes from 2 populations are simply incompatible with each other.

cellulose microfibrils

many beta-glucose units are held together by 1,4-glycosidic bonds to form cellulose in a condensation reaction. every alternative monomer unit has to be turned round/inverted so the bonding can take place. the cellulose molecules formed are unbranched chains and these chains are held together by hydrogen bonds. this is called cross-linking (holding neighbouring bonds together)

suggest how scientists could find out if biodiversity within the town of Pripyat has increased or decreased since the Chernobyl disaster in 1986. (2)

measure the species richness in Pripyat and compare it with the species richness of Pripyat in 1986 and over time (compare over time)

the technique Woese used to classify organisms

molecular phylogeny

polygenic inheritance

more than one gene affects a single trait or at many different loci

explain the importance of nitrate ions to plants. (2)

nitrate ions are required to make amino acids and proteins. the amino acids are used for the synthesis of proteins such as enzymes, bases for synthesis of DNA, nucleic acids, for cell division, ATP as an energy source.

stationary phase

number of organisms die. this is due to unfavourable environment such as waste produced by microbes or nutrients, temperature, pH may not be optimum.

clinical trials/contemporary drug testing protocols

phase 1 : tested on small group of healthy volunteers. phase 2 : larger group of patients with the disease. must be split into two groups. one group will be given the placebo. (neither the doctor or patient will know who got the new drug) - mine phase 3 : compared to existing treatments on thousands of patients (double blind trials)

state the function of pili

pili allows bacteria to adhere to surfaces.

the cytoplasm of the pollen tube contains organelles, including the pollen tube nucleus, rough endoplasmic reticulum and Golgi apparatus. explain the importance of these organelles in the production of extracellular enzymes needed for the growth of the pollen tube. (6)

pollen tube nucleus: 1. it contains the DNA coding for the enzymes. 2. DNA is transcribed or mRNA is produced in the nucleus. rough endoplasmic reticulum: 3. the ribosomes in the RER are involved in translation/polypeptide synthesis. 4. the polypeptide chain becomes folded in the RER. 5. then the polypeptide is packaged into vesicles to be transported to the Golgi apparatus. Golgi apparatus: 6. polypeptide is modified in the Golgi apparatus. 7. the proteins are packaged into secretory vesicles. 8. these fuse with the cell membrane to release the enzymes out of the cell by exocytosis. 9. the enzymes are needed to digest the style.

the fur of koalas is not affected by their environment. koalas that live in habitats between the north and south of Australia have a range of fur colouration from grey to brown. suggest one reason for this range of fur colour. (1)

polygenic inheritance or more than one gene codes for fur colour.

Behavioural isolation

populations don't respond to each others reproductive displays.

exponential growth phase

rapid multiplication of bacteria occurs. hence, multiplication occurs by binary fission to increase the number.

using the information in the table, describe the niches of the clownfish and the sea anemone. (3) - june 18. I did not read, underline and understand quick and proper enough.

sea anemone: 1. provides food/shelter/protection for the clownfish. 2. feeds on fish. clownfish : 3. brings food/fish to the sea anemone. 4. feeds on tentacles of sea anemone.

state the function of slime capsule

slime capsule prevents dehydration of cell.

temporal isolation

species in the same area but are active for reproduction at different times

give the structure and role of the ribosome

structure: 1. consists of two subunits. 2. made of protein and RNA. role: translation

give the structure and role of the mitochondrion

structure: 1. inner membrane folded to form cristae. 2. contains circular DNA. role: aerobic respiration.

give the structure and role of the Golgi apparatus

structure: 1. stacks of cisternae. 2. cisternae have curved shape. 3. vesicles. role: protein modification

give the structure and role of the lysosome

structure: 1. surrounded by a single membrane. 2. contains hydrolytic enzymes. role: destruction of bacteria

give the structure and role of centrioles

structure: 1. pair of cylinders/tubes/hollow rods. 2. at right angles. 3. 9 triplets of microtubules. role: formation of spindle fibres.

In cancer cells, mechanisms 1, 2 and 3 (of the cell cycle) do not occur. A student suggested that in a sample of cancer cells there will be greater proportion of cells in mitosis than in a sample of healthy cells. describe an investigation that could be carried out to test this suggestion. (5)

take a tissue sample of cancer cells and a tissue sample of healthy cells. both samples must have the same type of tissue. using only sterilized equipment such as sterile petri dishes, put the tissues in two different dishes of the same agar nutrient medium. label one "cancer cells" and the other "healthy cells". use the same growth hormone on both of them. use acetocarmine stain on both of the tissue samples. using an electron microscope, find the total number of cells and the number of cells in mitosis in both tissues. calculate the mitotic index for both tissue samples. repeat the experiment five more times and calculate the mean mitotic index.

suggest how damage to the acrosome membrane could affect the fertilisation of an egg. (4)

the acrosome cannot fuse with cell surface membrane of sperm. no acrosin will be released from the acrosome by exocytosis and so the zona pellucida will not be digested by the acrosin .

explain how the structure of the cell walls in this tissue enables it to be strong and flexible. (2) - jan 15

the cell walls consist of many cellulose microfibrils which lay parallel to one another in layers for flexibity. there is also a mesh of microfibrils in secondary cell wall for strength. the cellulose microfibrils are also bound together by calcium pectate bonds which make the fibre very strong. - look at book and rewrite

suggest why it is difficult for a specialized cell to be reprogrammed to become a stem cell. (1)

the cells are permanently modified and so it is hard to reprogram the genes.

describe a process that would not occur with the ICSI technique.

the cortical reaction would not occur as the sperm head will not touch the surface of the egg cell. cortical granules are released in this reaction which destroy the sperm binding sites on the secondary oocyte membrane(recheck) and that harden the zona pellucida. (the ion channels on the ovum also open and close to make the ovum positively charged like the outside. this all prevents polyspermy.

explain how endemic lemurs evolved in Madagascar (3)

the group of early monkeys from Africa, after arrived to Madagascar, had a mutation in their genes as they continued to in live in Madagascar. the alleles from these genes helped the lemurs better adapt to and survive in the climate with the type and amount of food they get in Madagascar. as a result these new species called lemurs were naturally selected for and reproduced to make more lemurs which also had the mutated gene. this increased the allele frequency of the mutated gene. these lemurs also survived and they never left Madagascar and so are only found there.

explain how damage to the mitochondria could affect the ability of sperm to fertilize an egg. (3)

the mitochondria provides energy by respiration to enable the sperm to swim to the ovum. so without the mitochondria the sperm cannot move and reach the ovum to fertilize it

suggest how molecular phylogeny can be used to determine the evolutionary relationships between the different species of penguin. (3) - jan 15

the more sequences of bases two different species have in common, the more closely related they are. DNA profiling is used to study the sequence of the bases - recheck with book

explain what is meant by the term genetic diversity

the number of alleles within a gene pool or species or population.

state what is meant by the term biodiversity (2)

the number or variety of species

mechanical isolation

the reproductive organs no longer fit together.

protein synthesis

the ribosomes in the rough endoplasmic reticulum make the proteins. the RER has a large surface area for the synthesis of the proteins. the polypeptide chain is folded into a 3-D shape and then packaged into vesicles to be transported to the Golgi apparatus. the proteins are modified in the Golgi apparatus/enzyme is activated in the Golgi apparatus. carbohydrate is added to some proteins to form glycoproteins. the proteins/enzymes are then enclosed in vesicles to form lysosomes. the lysosomes fuse with the cell membrane and release the enzymes out of the cell by exocytosis.

niche

the role of an organism within the habitat in which it lives

describe the structure of the plasmodesmata

these are cytoplasmic bridges and are pores in the cell wall between adjacent cells. there is cytoplasm running through the plasmodesmata.

explain the meaning of the term totipotent stem cells. (2)

these are undifferentiated cells which can be given a stimulus to become any type of specialized cell and divide continuously by mitosis.

explain what is meant by the term tissue. (2)

this is a group of cells with a similar structure or function or origin

explain why scientists tool samples of tissue from very specific parts of the S. chirata plant (to investigate...)

this is because only certain parts of the plant can grow by mitotic division. this is usually the meristem of the root of a plant.

describe what is meant by the tensile strength of fibres

this is measured by force required to break the fibres

genetic diversity

variety of alleles within a gene pool

cortical reaction

when the sperm cell fuses with the egg cell membrane, cortical granules in the cytoplasm of the ovum release enzymes into the zona pellucida. these enzymes destroy the sperm-binding sites and also thicken and harden the jelly of the zona pellucida to form a tough fertilisation membrane. the ion channels in the cell membrane of the ovum open and close inside the cell, instead of being electrically negative with respect to the outside, becomes positive. these all prevent polyspermy.

in a beaver population, the frequency of a recessive homozygous genotype is 0.09. calculate the percentage of beavers in this population that are homozygous for the dominant allele, using the equation : p2 +2pq + q2. (3)

√0.09 / 0.3 (1 − 0.3) / 0.7 p2 = 49%