Human Reproduction

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

• 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

Explain how multiple pregnancy may occur naturally (3)

• More than one egg
• Fertilised by a different sperm
• Gives non-identical

• One egg
• Splits
• Each cell grows into seperate embryos
• Gives identical

Describe the events occuring inside a cell during prophase 1 of meiosis (4)

• Chromosomes coil up
• Homologous chromosomes pair up
• Crossing over occurrs
• Chiasmata formation
• Nuclear membran begins to break down
• Spindle begins to form

State 2 uses of ATP during meiosis (2)

• DNA replication
• Protein synthesis
• Spindle formation
• Replication of organelles

Describe the process taking place in a cell during interphase as it prepares for mitosis (3)

• Aerobic respiration
• DNA replication
• Proteins synthesised
• Organelles synthesised
• Cell growth occurs
• Energy stores increase

A population of cells dividing by mitosis remains genetically identical.

Explain the importance of this (2)

• Chromosome number maintained
• Basis of growth
• Basis of cell replacement
• Can perform some role as parent cell

At the start of a new mestrual cycle, the concetration of oestrogen rises.

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

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

List four differences between mitosis and meiosis (4)

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

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

• X-rays are a form of radiation
• X-rays may damage DNA of foetus
• Could affect development leading to abnormalities
• May lead to cancer

State the name of the hormone that a pregnancy test is designed to detect (1)

Human Chorionic Gonadotrophin (hCG)

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

• 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

Explain the importance of crossing over in the production of sperm cells? (2)

• Genetic variation
• Idea of conferring survival advantage of sperm
• Offspring resulting from fertilisation will be genetically varied

Explain what an allele is? (2)

A different form of a gene

Explain the meaning of the term gene (2)

• Length of DNA
• Coding for a polypeptide
• Single strand
• Unit of inheritence

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)

• Prevent movement of water
• By osmosis
• Cells may burst
• Maintains a suitable enviroment for sperm cells

What is the passage of sperm from the testicles to oviduct? (3)

• Epididymis
• Vas Deferens
• Urethra
• Vagina
• Cervix
• Uterus

State the function of the leydig cells (1)

To produce testosterone

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

• Prevents movement of water
• Osmosis
• Which could cause them to burst
• Maintains the ionic balance

Explain why sperm samples in sperm banks are kept for at least six months before being used (2)

• Allows time for donor to be tested for infectious diseases
• May take time to how up e.g HIV
• Donor tested at srveral times

State two causes of femal infertility other than endometriosis (2)

• Anti sperm anitbodies
• Ovarian cancer
• Unterine factors

Suggest one way in which infertility caused by endomertriosis may be treated (1)

Surgery to unblock oviducts by removing endometrial tissue

Outline how endometriosis may cause infertility (2)

• Endometrium blocks oviducts
• Prevens implantation
• Prevents ova and sperm meeting ( fertilisation)

Suggest why ovulating more than once in each menstrual cycle may lead to early menopause (2)

• Women have finite number of oocytes
• Present from birth
• Increased ovulations means oocytes are used up more quickly
• Run out ot oocytes

Explain the most likely outcome of ovulation twice during the menstrual cycle (2)

• Increases chances of getting pregnant
• Two oocytes available for fertilisation
• Results in fraternal/dizygotic/non-identical twins

Outline how GIFT and ICSI treatments work (3)

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

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

• 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

What is meant by the term multiple pregnancy? (2)

Two or more embryos in the uterus at one time

Explain what is meant by the genetic code (4)

• Codons
• Triplets of bases
• Code for amino acids
• Each codon codes for only one amino acid (specific)

What are contraceptive devices?

• Birth control pill
• Condoms
• Diaphragms
• Implants and injections
• Steralisation

What are anti-implentation devices?

• IUD or coil
• Morning-after pill

What is sterilisation?

Involves cutting or tying tubes that sperm and oocytes travel down

e.g fallopian tubes and Vas deferens

What is an IUD?

(intra-uterine device)

• Copper device
• Fitted into the uterus
• Stops implantation by an inflammation reaction
• IUD is toxic to sperm and embryo

Outline two risks that are more likely to occur in multiple pregnancies (2)

• Premature baby
• Low birth weight
• Increased risk of a miscarriage
• Anemia in mother
• Pre-eclampsia in mother

Describe the term multiple pregnancy (1)

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

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

• One or more foetuses may be naturally miscarried

• One of a pair of twins my be reabsorbed into the mothers body - twin syndrome

Describe how pre-eclampsia could be detected as part of a routine antinatal care programme (2)

• Blood presuure reading
• Very High blood pressure
• Suddern weight gain
• Presence of protein in urine

Describe on measurement of growth of an unborn foetus using ultrasound scans (1)

• crown - rump length
• Biparietal diameter

Suggest one reason for the overall decrease in the number of triplet pregnancies between the years 2000-2005 (2)

• Triplet pregnancies often due to fertility treatments
• Greater awareness of dangers in multiple pregnancies
• Fewer embryo's are now implanted by IVF

Explain how the male gamete is adapted to its function (5)

• 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

Describe the functions of sertoli cells (3)

• Attached to developing sperm
• Proteins developing sperm
• Nourishes sperm
• Secrete fluid into lumen
• Sensitive to testosterone concentration
• Control of spermatogenesis

Outline how the stages of meiosis during oogenesis differ from the stages of meiosis during spermatogenesis (2)

• 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

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)

Testosterone

Cell membrane contains phospholipids

testosterone dizzolved in phospholipids

ISCH/LH

Molecule too big to go through membrane

Glycoprotein is not lipid soluble

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

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