Human Reproduction

OCR Human Biology F224

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Describe and explain the changes in the hormone concentrations during pregnancy (7)

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  • HCG (human chorionic gonadotrophin
  • HCG produced by blastocyst
  • Which stimulates corpus luteum
  • So that Oestrogen and Progesterone are continued to secrete
  • Oestrogen proliferates endometrium
  • Progesterone maintains endometrium
  • HCG peaks
  • Progesterone concentration decreases 
  • As placenta takes over
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Explain how multiple pregnancy may occur naturally (3)

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  • More than one egg
  • Fertilised by a different sperm
  • Gives non-identical
  • One egg
  • Splits
  • Each cell grows into seperate embryos
  • Gives identical
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Describe the events occuring inside a cell during prophase 1 of meiosis (4)

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  • Chromosomes coil up
  • Homologous chromosomes pair up
  • Crossing over occurrs
  • Chiasmata formation
  • Nuclear membran begins to break down
  • Spindle begins to form
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State 2 uses of ATP during meiosis (2)

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  • DNA replication
  • Protein synthesis
  • Spindle formation
  • Replication of organelles
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Describe the process taking place in a cell during interphase as it prepares for mitosis (3)

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  • Aerobic respiration
  • DNA replication
  • Proteins synthesised
  • Organelles synthesised
  • Cell growth occurs
  • Energy stores increase
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A population of cells dividing by mitosis remains genetically identical.

Explain the importance of this (2)

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  • Chromosome number maintained
  • Basis of growth
  • Basis of cell replacement
  • Can perform some role as parent cell
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At the start of a new mestrual cycle, the concetration of oestrogen rises.

State what causes the rise in the concentration of oestrogen (1)

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Presence of LH (lutenising hormone) and FSH (follicle stimulation hormone)

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List four differences between mitosis and meiosis (4)

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Mitosis                         Meiosis                                                   

One division per cycle                                 Two divisions per cycle

Two cells produced                                      Four cells produced

Diploid cells produced                                  Haploid cells produced

For growth and repair                                  For reproduction

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Explain why women are asked if they are pregnant before they are given x-ray scans. (2)

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  • X-rays are a form of radiation
  • X-rays may damage DNA of foetus
  • Could affect development leading to abnormalities
  • May lead to cancer
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State the name of the hormone that a pregnancy test is designed to detect (1)

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Human Chorionic Gonadotrophin (hCG)

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Describe how independant assortment during metaphase 1 of meiosis, may lead to different combinations of alleles in a zygote following fertilisation (3)

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  • Random alignment of homologous pairs
  • Any allele of pair can be inherited with any of the other pair
  • On a different homologous pair
  • Fertilisation random process
  • No sperm/ ova genetically identical
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Explain the importance of crossing over in the production of sperm cells? (2)

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  • Genetic variation
  • Idea of conferring survival advantage of sperm
  • Offspring resulting from fertilisation will be genetically varied
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Explain what an allele is? (2)

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A different form of a gene

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Explain the meaning of the term gene (2)

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  • Length of DNA
  • Coding for a polypeptide
  • Single strand
  • Unit of inheritence
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The fluid secreted by the prostate gland and seminal vesicles has the same water potential as the cytoplasm of the sperm cells.

Explain why this is necessary (3)

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  • Prevent movement of water
  • By osmosis
  • Cells may burst
  • Maintains a suitable enviroment for sperm cells
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What is the passage of sperm from the testicles to oviduct? (3)

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  • Epididymis
  • Vas Deferens
  • Urethra
  • Vagina
  • Cervix
  • Uterus
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State the function of the leydig cells (1)

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To produce testosterone

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Explain why sperm need to be kept in an isotonic solution (3)

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  • Prevents movement of water
  • Osmosis
  • Which could cause them to burst
  • Maintains the ionic balance
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Explain why sperm samples in sperm banks are kept for at least six months before being used (2)

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  • Allows time for donor to be tested for infectious diseases
  • May take time to how up e.g HIV
  • Donor tested at srveral times
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State two causes of femal infertility other than endometriosis (2)

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  • Anti sperm anitbodies
  • Ovarian cancer
  • Unterine factors
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Suggest one way in which infertility caused by endomertriosis may be treated (1)

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Surgery to unblock oviducts by removing endometrial tissue

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Outline how endometriosis may cause infertility (2)

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  • Endometrium blocks oviducts
  • Prevens implantation
  • Prevents ova and sperm meeting ( fertilisation)
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Suggest why ovulating more than once in each menstrual cycle may lead to early menopause (2)

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  • Women have finite number of oocytes
  • Present from birth
  • Increased ovulations means oocytes are used up more quickly
  • Run out ot oocytes
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Explain the most likely outcome of ovulation twice during the menstrual cycle (2)

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  • Increases chances of getting pregnant
  • Two oocytes available for fertilisation
  • Results in fraternal/dizygotic/non-identical twins
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Outline how GIFT and ICSI treatments work (3)

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GIFT

Sperm and oocytes planed in oviduct, so natural fertilisation can occurr

ICSI

Sperm is injected directly into the oocyte in a petri dish the embryo is then inserted into the uterus directly

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Outline how the monoclonal antibodies in a pregnancy test are used to detect pregnancy (6)

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  • Dipstick dipped into urine
  • Antibodies on end of dipstick
  • Specific for hCG
  • Antbodies have a coloured die attached
  • hCG in urine binds to antibody
  • Antibodies move up the stick
  • Another antibody binds to antibody complex
  • hCG-antibody-gold complexes hold in place
  • Colour line develops
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What is meant by the term multiple pregnancy? (2)

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Two or more embryos in the uterus at one time

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Explain what is meant by the genetic code (4)

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  • Codons
  • Triplets of bases
  • Code for amino acids
  • Each codon codes for only one amino acid (specific)
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What are contraceptive devices?

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  • Birth control pill
  • Condoms
  • Diaphragms
  • Implants and injections
  • Steralisation
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What are anti-implentation devices?

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  • IUD or coil
  • Morning-after pill
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What is sterilisation?

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Involves cutting or tying tubes that sperm and oocytes travel down

e.g fallopian tubes and Vas deferens

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What is an IUD?

(intra-uterine device)

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  • Copper device
  • Fitted into the uterus
  • Stops implantation by an inflammation reaction
  • IUD is toxic to sperm and embryo
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Outline two risks that are more likely to occur in multiple pregnancies (2)

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  • Premature baby
  • Low birth weight
  • Increased risk of a miscarriage
  • Anemia in mother
  • Pre-eclampsia in mother
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Describe the term multiple pregnancy (1)

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Two or more embryo's growing in the uterus at the same time

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Suggest why note every multiple pregnancy will result in a multiple birth (2)

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  • One or more foetuses may be naturally miscarried
  • One of a pair of twins my be reabsorbed into the mothers body - twin syndrome
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Describe how pre-eclampsia could be detected as part of a routine antinatal care programme (2)

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  • Blood presuure reading
  • Very High blood pressure
  • Suddern weight gain
  • Presence of protein in urine
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Describe on measurement of growth of an unborn foetus using ultrasound scans (1)

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  • crown - rump length
  • Biparietal diameter
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Suggest one reason for the overall decrease in the number of triplet pregnancies between the years 2000-2005 (2)

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  • Triplet pregnancies often due to fertility treatments
  • Greater awareness of dangers in multiple pregnancies
  • Fewer embryo's are now implanted by IVF
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Explain how the male gamete is adapted to its function (5)

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  • Haploid
  • Acrosomal head- contains enzyme's which digest their way ino oocyte
  • Middle piece- contains many mitrochondria which are needed for aerobic respiration to allow the gamete to travel
  • Axial filament- in tal for movement
  • Streamline shape
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Describe the functions of sertoli cells (3)

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  • Attached to developing sperm
  • Proteins developing sperm
  • Nourishes sperm
  • Secrete fluid into lumen
  • Sensitive to testosterone concentration
  • Control of spermatogenesis
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Outline how the stages of meiosis during oogenesis differ from the stages of meiosis during spermatogenesis (2)

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  • Oogenesis begins in embryo
  • Oogenesis is not a continuous process
  • Meiosis in oogenesis does not complete until fertilisation
  • Two polar bodies provided
  • Only one secondary oocyte produced
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Explain why testosterone is able to pass through the cell membrane of its target cells, wereas ICSH/LH cannot pass through the cell membran of it's target cells (3)

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Testosterone

Cell membrane contains phospholipids

testosterone dizzolved in phospholipids

ISCH/LH

Molecule too big to go through membrane

Glycoprotein is not lipid soluble

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Discuss two possible disadvantages of using the 'morning after pill' (2)

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  • Can inly be used within 72 hours
  • Abbdominal cramps
  • Sickness
  • Ethical reasons
  • Does not protect against STI's
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