Topic 3 Voice of the genome

Question 1

Describe how DNA is organised in a bacterial cell. (3)

Answer 1

-DNA is circular.
-DNA not associated with histone proteins.
-Several plasmids.
-Located in cytoplasm/no nucleus.

Question 2

What’s the differences between eukaryotic and prokaryotic cells? (4)

Answer 2

-Eukaryotic cells have membrane bound organelles.
-Eukaryotic cells contains RER.
-Eukaryotic cells have 80s ribosomes whereas prokaryotic cells have 70s ribosomes.
-Eukaryotic cells have linear DNA.
-Eukaryotes don’t have plasmids.

Question 3

Describe features that could be used to identify prokaryotic cells in blood sample. (4)

Answer 3

-Presence of cell wall.
-Circular DNA/plasmids.
-70s ribosomes.
-Pilli/flagellum.
-Capsule/mesosome.

Question 4

Explain why the nucleus cant be seen at the end of prophase. (2)

Answer 4

-As nuclear membrane is broken down.
-As DNA is condensed into individual chromosomes.

Question 5

Describe how a polypeptide is processed to produce a protein. (4)

Answer 5

-The polypeptide chain moves through the endoplasmic reticulum then the Golgi apparatus.
-In the RER the polypeptide is folded.
-In the Golgi apparatus a carbohydrate is added.
-The protein is then transported around cell in vesicle.

Question 6

Explain why interferon made by genetically modified bacteria is different from interferon made by animal cells. (3)

Answer 6

-Bacteria doesn’t have an RER.
-Meaning polypeptide chain isn’t modified properly.
-Therefore protein is incorrectly folded.

Question 7

Describe what happens in an acrosome reaction. (1)

Answer 7

-Sperm cell releases digestive enzymes that digest zona pellucida.

Question 8

Devise an investigation to determine the effect of exposure time to Agil on the rate of mitosis in onion root tips. (6)

Answer 8

-Controlled concentration of agil used.
-Temp/age of onion kept same.
-Roots exposed to agil for a range of time intervals.
-HCl used to make cells more visible, macerate.
-Toluidine blue stain used to make chromosomes more visible then squash down with a cover slip.
-Observe under microscope and count no. cells undergoing mitosis and total no. cells and calculate mitotic index.

Question 9

Explain why HCl is added to root tip in mitosis CPAC. (2)

Answer 9

-Breaks down middle lamella.
-Allowing cells to be separated.
-So light can pass through more easily.

Question 10

Explain why a stain is added to root tip in mitosis CPAC. (2)

Answer 10

-Makes chromosomes more visible.
-So stages of mitosis can be identified.

Question 11

Explain how preventing shortening of spindle fibres affects mitosis. (2)

Answer 11

-Sister chromatids can’t be separated.
-Mitosis stops at metaphase.
-Daughter cells produced with incorrect no. chromosomes.

Question 12

Describe the events of fertilisations that occurs after the acrosome reaction. (3)

Answer 12

-Sperm cell fuses with egg cell membrane.
-Cortical granules release contents into zona pellucida.
-Contents of cortical granules cause zona pellucida to harden once they react with one another.
-Sperm and egg cells haploid nuclei fuse.

Question 13

Explain why twins may be genetically different although they have the same parents. (2)

Answer 13

-Each zygote is formed from different gametes.
-Each gamete contains different combinations of alleles.
-Different combinations of alleles due to independent assortment and crossing over during meiosis.

Question 14

Once a egg cell has been fertilised by a sperm cell explain why a second sperm cell can’t fertilise the same egg cell. (3)

Answer 14

-Cortical reaction occurs meaning cortical granules fuse with egg cell membrane.
-Causing the zona pellucida to harden.
-Therefore other sperm cells can’t reach egg cells membrane.

Question 15

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

Answer 15

-It is a disorder caused by a mutated allele.
-Located on sex chromosomes (X/Y).
-So disorder is more likely linked in one gender than the other.

Question 16

Explain why a sperm cell with 2 flagella may reduce fertility. (3)

Answer 16

-Presence of 2 flagella affects ability of sperm to propel itself.
-May prevent sperm from reaching egg.
-Preventing fertilisation.

Question 17

Describe how meiosis leads to genetic variation in gametes produced. (2)

Answer 17

-Non identical gametes produced due to independent assortment of chromosomes.
-Crossing over between non sister chromatids of homologous chromosomes.

Question 18

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

Answer 18

-There are more genes than there are chromosomes.
-Linkage relates to genes for different characteristics located in same non sex chromosomes.
-Sex linkage relates to genes on sex (X/Y) chromosomes.

Question 19

Explain how crossing over may differ in sex chromosomes. (2)

Answer 19

-Crossovers can’t form between some sections of X and Y chromosomes.
-As they aren’t homologous chromosomes.

Question 20

What is a homologous pair?

Answer 20

2 Chromosomes with exactly the same genes but different alleles, maternal and paternal.

Question 21

Explain why is DNA replicated before mitosis begins. (2)

Answer 21

-To ensure there’s one copy of each chromosome in each daughter cell.
-To ensure daughter cells are genetically identical.

Question 22

Name the part of a chromosome that is occupied by a gene. (1)

Answer 22

-Locus.

Question 23

Describe what happens during prophase in an animal cell. (3)

Answer 23

-Nucleus/nuclear envelope breaks down.
-Spindle fibres formed.
-Chromosomes condense.
-Centrioles migrate to opposite poles/ends of the cell.

Question 24

Why is there a high density of mitochondria in the midpiece of a sperm cell? (1)

Answer 24

-Provides energy for movement of the flagellum.

Question 25

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

Answer 25

-X chromosome carries genes that aren't present on Y chromosome. -Males have only one copy of some genes. -If only one allele inherited it will be expressed.

Question 26

Describe the appearance of chromosomes in cells undergoing metaphase. (2)

Answer 26

-Chromosomes are condensed. -They are joined to spindle fibres. -The chromosomes are aligned on the equator of the cell.

Question 27

What does polygenic mean? (2)

Answer 27

-A characteristic showing continuous variation. -Caused by multiple genes at different loci.

Question 28

What is continuous variation?

Answer 28

Variation within a range, includes mass and height.

Question 29

What is discontinuous variation?

Answer 29

Can only take particular values such as gender or shoe size.

Question 30

Explain how epigenetic changes affect development of tissues in embryos. (3)

Answer 30

-DNA is wrapped around histones. -Acetylation/modification of histone affects binding of RNA polymerase. -Methylation of DNA affects transcription of genes. -Therefore gene expression is altered. -

Question 31

Give a difference between a tissue and an organ. (1)

Answer 31

-A tissue is made of one type of cell and an organ is made of different tissues.

Question 32

Describe the decisions society has to make about the use of embryonic stem cells. (3)

Answer 32

-Embryonic stem cells are totipotent and can be used in a wider range of therapies than other stem cells. -Source of embryonic stem cells has to be regulated. -Ethical issues surrounding the embryos being destroyed by using embryonic stem cells. -Need for research establishments to be regulated/licensed.

Question 33

Give the meaning of the term totipotent cell. (2)

Answer 33

-A cell that has the ability to differentiate. -Into all types of cells.

Question 34

Describe how embryonic stem cells can be specialised to form tissues and organs. (3)

Answer 34

-Chemical signals/activators and repressors cause some genes to be switched on or off. -The genes that are activated/switched on are transcribed and produce mRNA. -mRNA leads to synthesis of specific proteins which cause cell modification.

Question 35

Explain why stem cells from the heart can't be used to grow cells to repair the cornea. (3)

Answer 35

-Stem cells from the heart are not totipotent. -Therefore some genes have already been activated and deactivated. -Therefore will not be able to specialise into cornea cells.

Question 36

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

Answer 36

-Chemicals cause some genes to be switched on or off. -The genes that are switched on are transcribed producing specific mRNA. -Specific mRNA is translated into specific protein. -These proteins cause the cell to develop into a corneal cell.

Question 37

Deduce why age affects time taken to recover from injuries. (3)

Answer 37

-As age increases, time taken to recover from injury increases. -Due to fewer stem cells in bone marrow with age. -Fewer stem cells to replace cells in bone/muscle/cartilage tissues.

Question 38

What is a stem cell? (2)

Answer 38

-A cell that is undifferentiated. -That can give rise to specialised cells. -That can divide to produce more stem cells.

Question 39

Compare and contrast the results of mitosis and meiosis in production of sperm and stem cells. (4)

Answer 39

-They both increase the number of cells. -Mitosis produces diploid cells and meiosis produces haploid cells. -Mitosis produces cells that are genetically identical , whereas meiosis produces cells that are genetically different. -Mitosis results in 2 daughter cells whereas meiosis results in 4 daughter cells.

Question 40

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

Answer 40

-DNA methylation/histone modification. -Causes genes to be switched on or off/activated or deactivated. -Affecting enzyme production.

Question 41

Explain how epigenetic changes affect activation of genes in daughter cells. (3)

Answer 41

-Genes switched on or off in stem cells. -Due to DNA methylation. -Therefore same genes will be activated in daughter cells.

Question 42

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

Answer 42

-Height is affected by environment as well as genotype. -Height is an example of polygenic inheritance. -Therefore offspring can inherit a mixture of alleles from both parents. -Diet can also influence height, high calcium or protein diet can increase height.

Question 43

Describe how stem cells can give rise to different types of cells. (4)

Answer 43

-Different stimuli activate/switch on different genes. -The activated genes are transcribed to produce mRNA. -mRNA then translated to produce a protein. -Protein determines function of cell. -Different proteins produced from different activated genes produce different types cells.

Question 44

Describe what is meant by the term operon. (2)

Answer 44

-A section of DNA. -Controlled by a single operator/promotor.

Question 45

Describe the effect of lactose on the lac operon. (3)

Answer 45

-When lactose is present it binds to the repressor. -This changes the repressors shape, now it can't bind to the operator site. -This allows RNA polymerase to now carry out transcription.