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penis
- Passes urine out of the body from the bladder
- Allows semen to enter into the vagina of a woman during sexual intercourse
Testis
- Contained in the scrotum
- Produces sperm and testosterone
Sperm Duct
Sperm passes through the sperm duct where it mixes with fluids produced by the sex gland
Sex gland
Produces semen - provides sperm cells with nutrients
Urethra
Exports urine or semen from the body
Ring of muscle in the urethra prevents mixing of urine and semen
Where is testosterone made and what is its function?
Testes
Stimulates secondary sexual characteristics like voice deepening, sperm production, pubic hair
Oviduct
Connects the ovary with the uterus
Lined with cilated cells to push the ovum towards the uterus for fertilisation
Ovary
Contains female gametes (ova) which mature and develop when FSH is released
uterus
muscular structure with a soft lining
fertilised egg cell implanted there to develop into a foetus
Cervix
Ring of muscle at lower end of uterus
Keeps foetus in place during pregnancy
Urethra
Tube that passes urine out of the body
Vagina
Muscular tube that the male’s penis enters during sexual intercourse
How long does the menstrual cycle last
Approximately 28 days
On which day is the egg usually released
14
What is menstruation
Breakdown of the thickened uterus lining
Occurs when the egg has not been fertilised
How long does menstruation last
5-7 days
Where is oestrogen made and what is its function?
Ovaries
Stimulates secondary sexual characteristics - hips widening, breast growth, pubic hair
Causes thickening of uterus lining
Inhibits FSH and stimulates LH
Where is progesterone made and what is its function?
Initially corpus luteum, later in pregnancy the placenta
Maintains uterus lining
Inhibits release of LH and FSH
Describe the changes that take place in the uterus during the menstrual cycle
Uterus lining thickens
Progesterone maintains lining
If fertilisation has not occured, lining breaks down and is shed
If egg is fertilised, lining not broken down
Describe the passage of sperm in the female human
Semen (contains sperm and fluid from seminal vescicles) is ejaculated into the vagina
Sperm swims through uterus to oviduct
Where does fertilisation take place?
Oviduct
What is the function of the acrosome in the head of a sperm cell?
Contains digestive enzymes that break through the egg membrane
Why does sperm cell require mitochondria?
Respiration
Provides energy for tail
What is the function of the sperm cell’s tail?
Allows sperm cell to move
Explain why avoiding sexual intercourse at certain times of the menstrual cycle may not be a reliable method of birth control
Ovulation may vary within a woman
Sperm can survive for a number of days
Give the different stages of development during human reproduction
Gametes
Zygote
Embryo
Foetus
Baby
Explain how an 8 cell embryo is formed
Sperm and egg made by meiosis
Fertilisation in oviduct
Zygote implants in uterus wall
Divides by mitosis
What is the role of the placenta
Provides embryo with oxygen and nutrients from the mother’s blood
Removes urea and CO2 from embryo
Releases progesterone in late pregnancy
Describe how a developing foetus is supplied with nutrients
Nutrients (glucose, oxygen, amino acids) from mother’s blood
Diffuse through placenta
Placenta has a large surface area and thin walls
Umbilical cord join foetus blood supply to placenta
How is the placenta adapted for efficient exchange of substances
Villi - large surface area
Good blood supply from capillaries - steep concentration gradient
Thin walls- short diffusion distance
What is the role of amniotic fluid?
Protects foetus from physical impact
Acts as shock absorber
Where does the amniotic sac develop?
Uterus
What is a genome
The entire DNA of an organism
What is a gene
Section of DNA which codes for a protein
Where are genes found
In chromosomes within the nucleus
What is the role of genes
Control the activities of the cell
Determine which proteins are made
What is an allele
Different form of the same gene which gives rise to different characteristics
Define homozygous
Having two copies of the same allele
Define heterozygous
Having two different copies of the same allele
Define genotype
The alleles an organism has
Define phenotype
The physical appearance of an individual
Define recessive
Allele only expressed if the dominant allele is not present
Define dominant
Allele expressed even if only one is present
Define monohybrid interitance
Single gene responsible for phenotype
Define polygenic inheritance
Many genes combine to give a phenotype
Most phenotypic features are a result of polygenic inheritance
What is a carrier?
Someone who has a gene for a disease but doesnt suffer from any symptoms
What is a pedigree diagram
Shows how a genetic condition is passed from generation to generation
Possible to work out which is the dominant allele
Can then work out genotype of each person or animal in the diagram
What are the genotypes for males and females?
Males XY
Females XX
How is sex inherited
X chromosome from mother
All eggs contain one X chromosome
X or Y chromosome from father
50% of sperm cells contain one X chromosome, 50% contain one Y chromosome
Define haploid (n)
Contains 1 set of chromosomes, eg 23 in humans
Gametes are haploid
Define diploid (2n)
Contains 2 sets of chromosomes eg 46 in humans
Define clone
Genetically identical cell or organism
Give examples of when mitosis occurs
Growth , repair
Cloning
Asexual reproduction
Main steps of mitosis
Prophase
Metaphase
Anaphase
Telophase
What is the product of one round of mitosis
2 genetically identical cells
Cells are diploid
Where does meiosis occur
Sex organs
Meiosis produces gametes
What is the product of one round of meiosis
4 genetically varied cells
Haploid
Compare the features of mitosis and meiosis
Number of cell divisions : 1 for mitosis, 2 for meiosis
Number of daughter cells formed: 2 for mitosis, 4 for meiosis
Number of chromosomes in cells formed: DIploid in mitosis, haploid in meiosis
Type of cells formed: Body cells in mitosis, Sex cells in meiosis
Genetic variation in cells formed: None in mitosis, Variation in meiosis
How is variation within a species bought about
Genetics eg hair colour
Environmental conditions (eg. reduced growth due to poor diet when young)
Or a combination of both
How does genetic variation occur
Random fertilisation of gametes
Mixing of alleles from both parents
Meiosis
What is a mutation?
A rare, random change in the genetic material that can be inherited
Define evolution
All organisms alive today, and many more which are now extinct, evolved from simple life forms which first developed more than 3.2 billion years ago
Define the mechanism of Natural Selection
Variation within a species due to mutation
Individuals better adapted more likely to survive and reproduce
Alleles passed onto offspring
Repeats over many generations
Selected for alleles to become more prominent in population
How may bacteria become resistant to antibiotics?
Some bacteria have mutations that make them more likely to survive
The bacteria reproduce and pass on these favourable alleles to future bacteria
Soon the whole population of bacteria is resistant to the antibiotic.
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