Bio PPQs got wrong topic 3

• vesicles fuse with/protein enters golgi apparatus

• modification of protein inside golgi apparatus

• protein enzyme packaged into secretory vesicles

• vesicles fuse with cell surface membrane

• eukaryotic organisms have membrane - bound organelles

• eukaryotic organisms contain a named membrance - bound organelle

• size of ribosomes larger than in prokaryotes

• eukarotic organisms do not contain plasmids (in cytoplasm)

+ water

Ignore (i)

• presence of a cell wall

• circular DNA/plasmids

• small/70s robosomes

• pili/flagellum

• capsule/mesosome

Explain why the nucleus cannot be observed at the end of prophase in a eukaryotic cell.

• because the nuclear membrane is broken down

• because DNA is coiled/condensed into individual chromosomes

ignore (i)

• phase 1 - to make sure the phospholipase inhibitor is not harmful

• phase 2 to see if it is effective in treating the condition/preventing allergic reactions to wasp venom

• phase 3 to gather much data for statistical tests / to look for rare side effects

Some fish live in very cold parts of the sea where ice can form. Many of these fish produce anti-freeze proteins, which help to stop ice forming inside the fish. Anti-freeze glycoprotein (AFGP) is one type of anti-freeze protein. Messenger RNA coding for AFGP is translated at a ribosome to produce a polypeptide. Describe how this polypeptide is then processed to make AFGP. (4)

• the polypeptide chain moves through the ER then the golgi apparatus

• in the rER the polypeptide is folded

• in the golgi apparatus/ER carbohydrate is added

• the polypeptide/protein is transported around the cell in a vesicle

Some fish live in very cold parts of the sea where ice can form. Many of these fish produce anti-freeze proteins, which help to stop ice forming inside the fish. Anti-freeze glycoprotein (AFGP) is one type of anti-freeze protein. Messenger RNA coding for AFGP is translated at a ribosome to produce a polypeptide. Describe how this polypeptide is then processed to make AFGP. (4)

• the polypeptide chain moves through the endoplasmic reticulum then the golgi apparatus

• in the rER the polypeptide is folded

• in the golgi apparatus/ER carbohydrate is added

• the polypeptide/protein is transported around the cell in a vesicle

Many of the proteins synthesised become extracellular enzymes. Describe what happens to these proteins following the process of translation until they are released from the cell. (3)

• the proteins are folded in the RER

• the proteins are packaged into/ transported in vesicles

• the protein is modified in the golgi apparatus

• exocytosis

Cells in people with these diseases produce incorrectly folded enzyme molecules. Explain why enzymes that are incorrectly folded cannot carry out their function. (3)

• if the protein is not folded correctly the tertiary structure/3D shape would be different

• therefore the active site of the enzyme would not fit/bind with the substrate/it would not be able to form an enzyme substrate complex

• therefore it would not be able to catalyse the reaction

• bacteria fo not possess rER/golgi apparatus

• polypeptide chain is not processed/modified properly

• therefore the protein is incorrectly folded/carbhydrate is not added

• cytoplasmic connection between cells

• which allows transport/communication between cells

• negative correlation between Agil concnetration and number of cell undergoing mitosis/ mitotic index

• no significant difference between 1.0 and 1.5ppm Agil

Devise an investigation to determine the effect of exposure time to Agil on the rate of mitosis in onion root tips.

• controlled concentration of Agil

• one other variable contorlled - e.g. temp. same type onion, source

• roots exposed to agil for a range of time intervals

• details of root tip squash procedure

• an appropiate named stain - toludine blue

• counting number of cells undergoing mitosis (to calculate mitotic index

• fewer stem cells producing sperm (therefore fewer sperm cells produced)

• fewer motile sperm therefore fewer sperm will reach the egg

• poor ability to cross zona pellucida/acrosome reaction inhibited therfore sperm will not reach egg cell membrane

• therefore reducing chance of fertilisation

Deduce the relationship between egg cell diameter and the mass of the adult animal shown by the data (1)

as adult mass increases, egg diameter decreases OR negative correlation between adult mass and egg diameter

Criticise this data set as evidence for a relationship between egg cell diameter and the mass of the adult.(4)

• this data set includes only a few species/animals

• the species in the data are from different taxonomic groups

• there is no evidence of repeats/data for these individuals may not be representative

• the reproductive strategy of the species is likely to influence egg size/ should be controlled

• there are other factors that may affect the egg cell/may affect adult mass/should be controlled

• there is variation about the line/few data points lie exactly on the line therefore the prediction will not be exact

• the gradient of the line may not remain the same

What does autosomal mean?

not on sex chromosomes

what is a complementary gene?

when two or more genes that

Cell division in a plant such as an onion can be observed using a light microscope. Explain why the following techniques are used when producing a root tip squash to observe cell division. (4) Adding hydrochloric acid to the root tip

Adding a stain to the root tip

adding hydrochloric acid

• breaks down middle lamella

• allowing cells to be separated produce a thin layer of cells

• to allow light

Adding stain

• makes chromosome visible

• so that the stages of mitosis can be identified

Cell division can be affected by various chemicals. The effects of these chemicals can be studied by observing tissues. Chemotherapy is used to treat cancer. Cancer involves uncontrolled cell division. Some chemotherapy treatments have an effect on mitosis. Paclitaxel is a chemical used in chemotherapy to treat various types of cancer. It works by preventing the shortening of spindle fibres. Explain how preventing the shortening of spindle fibres affects mitosis. (2)

• sister chromatid cannot be separated/centromere cannot be split

• mitosis stops at metaphase/anaphase cannot occur/ chromosomes remain at equator

• daughter cells produced with incorrect numbers of chromosomes

Methyl methanesulfonate (MMS) can be used as a cancer treatment. One side effect associated with MMS is teratozoospermia. Three groups of rats were exposed to the following additives to their diet as shown in the table.

Deduce the effects of MMS on the production of sperm cells in rats. (3)

• MMS reduces sperm count/number of sperm cells

• MMS increases percentage of sperm cells with abnormalities

• as the greatest effect is on percentage of sperm swimming normally MMS is likely to affect production of flagella/mitochondria

Give the meaning of the term polygenic (2)

• a characteristic showing continuous variation

• caused by multiple genes at different loci

What is heterochromatin?

tightly packed chromatin

What is euchromatin?

loosely packed chromatin

Fertilisation in humans involves the fusion of a sperm cell with an egg cell. Factors such as the diet of the mother during pregnancy can cause epigenetic changes in the embryo. Explain how epigenetic changes affect the development of tissues in the embryo. (3)

• DNA in a chromosome is wrapped around histones

• acetylation/modification of the histone affects binding of RNA polymerase/chromosome unwinding

• methylation of DNA affects transcription of gene/production of mRNA

• therefore gene expression is altered

• a tissue is made of one type of cell and an organ is made of different tissues

Stem cells can be used to repair damaged organs. Human embryos are another source of stem cells used in medical therapies. Describe the decisions that society has to make about the use of these embryonic stem cells. (3)

• embryonic stem cells are totipotent and can be used in a wider range of therapies

• source of embryonic stem cells has to be considered/regulated

• moral/ethical issues as the use of embryonic stem cells destroys embryos

• need for research establishments to be regulated/licensed

Fertilisation in humans involves the fusion of a sperm cell with an egg cell. Cell division of the fertilised cell produces a ball of totipotent cells. (i) Give the meaning of the term totipotent cell. (2)

a cell that has the ability to differentiate into all cell types

This ball of cells continues to divide to form the embryo. The cells of the embryo become specialised to form tissues and organs. Describe how cells become specialised. (3)

• chemical signals cause some genes to be activated/switched on

• only activated genes are transcribed/produce mRNA

• mRNA leads to synthesis of specific proteins which cause cell modification

Stem cells can be used to repair damaged organs. Part of the eye contains stem cells. These cells can be used to repair damaged corneas in the eye. (i) Explain why stem cells from the heart cannot be used to grow cells to repair the cornea. (3)

• cells are not totipotent

• therefore some genes have already been activated and deactivated

• therefore they will not be able to specialise into cornea cells

Explain why chemicals from the eye are needed to produce corneal cells from a suitable source of stem cells. (4)

• chemicals cause some genes (related to the cornea) to be activated/switched on

• these genes are transcribed producing specific mRNA

• specific mRNA is translated into specific proteins

• these proteins cause the cell to develop into a corneal cell

• time will increase with age

• due to fewer (mesenchymal) stem cells in bone marrow) with age

• (fewer mesenchymal stem cells) to replace cells in bone/muscle/cartilage tissues

• an cell that is undifferentiated

• that can give rise to specialised cells

• that can divide to produce more stem cells

(ii) Compare and contrast the results of mitosis and meiosis in the production of sperm cells from stem cells (4) (ignore i)

similarity

• both increase the number of cells

differences

• mitosis produces cells that are genetically different to each other whereas mitosis produces genetically identical cells

• meiosis produces cells that are genetically different to each other whereas mitosis produces genetically identical cells

• mitosis results in 8 spermatocytes from each stem cell whereas meiosis results in 4 sperm cells from each spermatocyte

Duchenne muscular dystrophy (DMD) is a sex-linked disorder. (i) Explain what is meant by the term sex-linked disorder. (2)

• a disorder caused by a mutated faulty gene

• located on the X/Y chromosome

• therefore the disorder is more likely in one gender than another

Dystrophin is a protein needed to maintain the structure of muscle cells. In DMD the affected allele prevents the production of this protein, leading to symptoms that include a progressive effect on muscle tissue. Stem cells are a potential treatment for DMD. Explain why stem cells from a healthy donor may provide a treatment for this disorder. (3)

• stem cells can differentiate into muscle cells

• these cells will not have the affected allele

• the protein/dystrophin will be produced

Epigenetic changes can cause monozygotic twins to have different body masses. Explain how epigenetic changes can cause differences in a characteristic. (3)

• histone modification/DNA methylation

• affects activation of/ activates/deactivates genes

• affecting enzyme production/metabolism

As pluripotent stem cells divide, epigenetic changes are passed on. Explain how epigenetic changes affect the activation of genes in daughter cells. (3)

• genes are activated/deactivated in stem cells

• because of methylation of DNA/ histone binding

• therefore the same genes will be activated in the daughter cells

Explain why an individual may have a greater adult height than their biological parents. (4)

• height is affected by the environment as well as teh genotype

• height is an example of polygenic inheritance

• therefore offspring can inherit a mixture of alleles from both parents that increase height

• description of a names environmental factor that increases height e/g higher protein diet

• monozygotic twins show higher correlation than dizygotic twins at all ages

• therefore genetic factors have a greater effect

• because monozygotic twins have identical alleles for body mass

• monozygotic twins show less than 100% correlation

• therefore environmental factors affect body mass

What is meant by the term molecular phylogeny?

• the idea of molecular differences/ similarities

• in DNA /RNA

• in proteins / proteonmics

• Idea of evolutionary relationships between organisms

(3)

• appropriate calculation e.g:4% of plants, 3.6% of vertebrates or 4% of combined total, 80.9 plants 78.1% of vertebrates endemic, 3.2% of plants, 2.8% of vertebrates or 3.2% of combined total, density of plants/ vertebrates/ total on Madagascar/ earth

• the species density of animals / plants in Madagascar is higher than for the earth

• many of the species are found in Madagascar are not found anywhere else

Species number may increase due to

• Fragmentation of habitat / geographical isolation

• Different selection pressures on populations of C. hoffmanni

• Different allele frequencies within separate populations

• Evolution leading to formation of new species

Species number may decrease due to

• B. pygmaeus is currently critically endangered

• Only one population

• Therefore could be vunerable to inbreeding depression

• At risk of natural disaster, disease, predation etc

• Therefore may become extinct

• biodiversity measured / compared using a diversity index

• species richness assessed

• genetic diversity of populations / species

• presence of any endemic / rare species

Explain how the primary structure of typsin molecules can be used to produce a phylogenetic tree (3)

• determine the sequence of amino acids (for trypsin)

• determine the number of differences / similarities in sequences (of amino acids) between species

• the greater the number of differences the less closely related the species are

H

• Mutation leads to variation within a population

• natural selection leads to organisms which were better suited for survival

• therefore giving rise to 2 populations with differing allele frequency

• as a result of natural selection the 2 populations became reproductively isolated

• sympatric speciation

Why might organisms be classed as different species? (2)

• they are no longer able to interbreed to produce fertile offspring

• because populations have become reproductively isolated

Name the process that leads to new species (1)

Natural selection

True or false archaea has prokaryotic cells

True

Describe how the Hardy-Weinberg equation can be used to provide evidence for changes in the elephant population in Mozambique (2)

• calculate the allele frequencies / number of dominant and recessive alleles in the population in Mozambique

• regular sampling over a period of time

Explain how molecular phylogeny can be used to show that two populations are reproductively isolated (3)

• Comparing similarities and differences in DNA/proteins

• Comparison of nucleotide sequences / amino acid sequences

• the greater the number of differences the more likely they are to be reproductively isolated

Describe how mutations may lead to this population becoming separate species (4)

• Mutations result in the production of new alleles

• Selection pressures cause the alleles / mutations to be advantageous

• more individuals with the advantageous alleles survive and reproduce

• after time the population would not be able to reproduce with other badger species to produce fertile offspring

Explain why the frequency of an allele may change from one generation to the next (3)

• because the allele may undergo mutation

• because gene flow may cause alleles to be lost or gained from the population

• due to natural selection / changed selection pressure

• because people with the condition may not have children

Explain how the Hardy - Weinberg equation can be used to show that natural selection is occurring in a population (2)

• Hardy - Weinberg equation shows the allele frequency in the population

• if natural selection is occurring there would be a change in allele frequency over time

Explain how molecular phylogeny could be used to determine the relationship between the Scottish wildcat and other subspecies of European wildcat (2)

• compare sequence of bases in DNA / amino acids in proteins

• the more similarities in common the more closely relation the subspecies

What is a stem cell? (2)

• an undifferentiated cell

• that can give rise to specialised cells

• that can divide to produce more stem cells

Describe how pluripotent stem cells become specilaised cells (4)

• idea of stimulus e.g. chemical

• idea that some genes are active / switched on / expressed

• idea of transcription / mRNA produced at active genes

• mRNA is translated / used to produce protein

• idea that this protein modifies cell OR idea that this protein determines cell structure / function

Explain what is meant by the term sex linked disorder (2)

• a disorder caused by a mutated / faulty gene

• located on the X / Y chromosome

• therefore the disorder is more likely in one gender than another

Explain why the genotype frequency for males with a sex linked ddisorder cannot be calculated using the Hardy - Weinberg equation (2)

• males only have 1 allele for this gene

• males cannot be heterozygous

• the Hardy-Weinberg equation assumes all individuals have 2 alleles for the gene

Dystrophin is a protein needed to maintain the structure of muscle cells. In DMD the affected allele prevents the production of this protein, leading to symptoms that include a progressive effect on muscle tissue. Stem cells are a potential treatment for DMD. Explain why stem cells from a healthy donor may provide a treatment for this disorder. (3)

• stem cells can differentiate into muscle cells

• these cells will not have the affected allele

• the protein / dystrophin will be produced

Explain how vesicles are involved in the successful fertilisation of an egg cell by only one sperm (2)

• cortical granules fuse with the egg cell surface membrane (exocytosis)

• releasing contents / enzyme that harden / thicken zona pellucida

Explain why some genes show linkage and others show sex linage (3)

• there are more genes than there are chromosomes

• linkage relates to genes for different characteristics located on the same (non-sex) chromosome

• sex linkage relates to genes on the sex / X / Y chromosome

Explain how crossing over and independent assortment can produce gametes with new combinations of the alleles shown in the diagram of the two pairs of chromosomes (4)

Crossing over

• chromatids are produced with different combinations of alleles

• for example (Ab/aB)

Independent assorment

• different combinations of chromosomes (1 and 2) are produced

• therefore alleles for A and B could be in the same gamete as C or c

Explain why DNA is replicated before mitosis begins (2)

• to ensure that diploid chromosomes / one copy of each chromosome in each daughter cell

• to ensure daughter cells are genetically identical

Expain how large number of cells with the same phenotype can be produced in a tissue (2)

• phenotype is determined by genotype and effect of environment

• mitosis produces cells with the same genotype

Explain why the nucleus cannot be observed at the end of prophase in a eukaryotic cell (2)

• because the nuclear membrane is broken down

• because DNA is coiled / condensed into individual chromosomes

Describe how each gamete only receives one allele of each gene (2)

• in meiosis homologous chromosomes carrying alleles for the same genes are separated from one another

• sister chromatids containing copies of the same alleles are also separated form one another

• spindle fibres pull the chromosomes / chromatids to opposite poles of the cell

Describe how the acrosome is involved in the digestion of the zona pellucida (2)

• the membrane of the acrosome fused with the plasma membrane of the sperm cell

• releasing enzymes from the acrosome

• by exocytosis

Describe the events that occur during prophase (3)

• nuclear envelope breaks down

• spindle fibres formed

• chromosomes / chromatids condense

• centrioles migrate to opposite poles of cell

Explain why genes found on the sex chromosome pair have a pattern of inheritance that is different from genes found on other chromosomes pairs (2)

• X chromosome carries genes / loci not present on the Y chromosome

• males have only one copy / allele of some genes

• if only one allele is inherited it will be expressed

Describe the appearance of the chromosomes in the cells undergoing metaphase (3)

• condensed / visible

• seen as pairs of chromatids held together by a centromere

• joined to the spindle fibres

• aligned on the equation of the cell