Reproduction

what is a gamete?

a sex cell eg sperm and ovum, pollen nucleus and ovum

how do gametes differ from normal cells?

contain half the number of chromosomes than in other body cells = haploid nucleus

only contain one copy of each chromosome

what happens when male and female gametes fuse?

they become a zygote with 46 chromosomes = diploid nucleus

advantages of sexual reproduction

• increases genetic variation

• species can adapt to new environments due to variation = survival advantage

• disease less likely to affect population

disadvantages of sexual reproduction?

• takes time and energy to find mates

• difficult for isolated members of the species to reproduce

what is asexual reproduction?

• does not involve gametes or fertilisation, only one parent required

• offspring genetically identical to parent and each other

advantages of asexual reproduction

• population can be increased rapidly when conditions are right

• can exploit suitable environments quickly

• more time and energy efficient

• reproduction is completed much faster than sexual reproduction

disadvantages of asexual reproduction

• limited genetic variation in population

• population vulnerable to changes in conditions and may only be suited to one habitat

• disease likely to affect the whole population

features of asexual reproduction

• one parent organism

• offspring produced by mitosis

• offspring genetically identical to each other and the parent

• genetic variation only from mutation

• usually large numbers of offspring produced

• offspring usually produced quickly

features of sexual reproduction

• two parent organisms

• offspring produced from the fusion of two haploid gametes, which are produced by meiosis

• offspring genetially unique and genetically different from both parents

• three sources of variation (50% of dna from each parent, production of gametes by meiosis, random distribution of chromosomes into gametes during meiosis)

• usually limited numbers of offspring produced

• offspring usually produced relatively slowly

what types of cells does meiosis produce?

haploid from diploid, produces gametes used in sexual reproduction

how many divisions of meiosis are there?

two → meiosis I and II

what mechanisms in meiosis lead to genetic variation?

• crossing over → the process by which non-sister chromatids exhange alleles in meiosis I

• independent assortment → production of different combinations of alleles in daughter cells due to the random alignment of homologous pairs of chromosomes during meiosis I

• random fertilisation → there are millions of combinations of sperm and egg cells

where does meiosis occur?

• in the testes of male animals and the ovaries of female animals

• in the anthers and ovaries of flowering plants

features of sperm cells

• very small

• many structural adaptations

  • acrosome on head contains digestive enzymes to break down the zona pellucida

  • flagellum for movement

• capable of locomotion

• produced every day in huge numbers

features of egg cells

• large

• round cell with few structural adaptations

  • covered in a jelly coating

• not capable of locomotion

• thousands of immature eggs in each ovary but only one released each month

label the female reproductive system

label the male reproductive system

what is the function of the oviduct?

connects the ovary to the uterus and is lined with ciliated cells to push the ovum down

fertilisation occurs here

what is the function of the ovary?

contains ova (female gametes) which will mature and develop when hormones are released

what is the function of the uterus?

muscular bag with a soft lining where the fertilised egg will be implanted to develop into a foetus

what is the function of the cervix?

ring of muscle at the lower end of the uterus to keep the developing foetus in place during pregnancy

what is the function of the vulva?

a collection of structures (including pubic mound, labia, clit & hymen), one function of which is to protect the more internal parts of the female reproductive system

what is the function of the prostate gland and seminal vesicle?

produces semen which gives nutrients to sperm cells

what is the function of the sperm duct?

sperm passes through it to be mixed with fluids produced in the glands before being passed into the urethra for ejaculation

what is the function of the urethra?

tube running down the centre of the penis that can carry urine or semen, a ring of muscle in the urethra prevents the urine and semen mixing

what is the function of the testis?

contained in the scrotum and produces sperm and testosterone

what is the function of the scrotum?

protects the testes outside the body to ensure sperm are kept at a temperature slightly lower than body temperature

what is the function of the epididymis?

coiled tubes that store sperm until ejaculation

what generally happens in the menstrual cycle?

• days 1-7ish → menstruation (period)

• days 7-28 → uterus lining thickens in preparation of receiving a fertilised egg

• day 14 → ovulation (egg release), travels down the oviduct to the uterus

• failure for the egg to be fertilised leads to menstruation, breakdown of endometrium

which hormones are involved in the menstrual cycle?

• FSH & LH (pituitary gland)

• oestrogen & progesterone (corpus luteum)

what is the role of FSH?

• secreted by pituitary gland and stimulates development of immature egg cells in follicles in the ovary

• also stimulates the secretion of oestrogen by follicle wall

what is the role of LH?

• pituitary gland stimulated to release LH when oestrogen levels reach their peak

• LH causes ovulation to occur, mature egg shedded from follicle and released into ovary

• this leaves behind an empty egg follicle called the corpus luteum

• LH also stimulates the production of progesterone from the corpus luteum

what is the role of oestrogen?

• levels rise from day 1 to peak just before day 14

• causes the endometrium to start thickening and the egg cell to mature

• peak in oestrogen occurs just before the egg is released

what is the role of progesterone?

• stays low from day 1-14 and starts to rise once ovulation has occured

• produced by the corpus luteum

• increasing levels of progesterone causes the endometrium to continue to thicken

• a fall in progesterone levels as the corpus luteum deteriorates causes the endometrium to break down = period

what is the relationship between FSH and oestrogen?

• FSH stimulates the production of oestrogen

  • FSH stimulates the development of a follicle, follicle wall produces oestrogen

• oestrogen also causes an increase in FSH receptors, making follicles more receptive to FSH which in turn stimulates more oestrogen production

• this is positive feedback

• when oestrogen levels are high enough it inhibits the secretion of FSH → negative feedback

what is the relationship between LH and oestrogen?

• when oestrogen rises to a high enough level it stimulates the release of LH from the pituitary gland causing ovulation around day 14

• after ovulation, LH causes the wall of the follicle to develop into the corpus luteum, which secretes more oestrogen

• positive feedback

what is the relationship between LH and progesterone?

• LH stimulates the wall of the follice to develop into the corpus luteum, which secretes progesterone

• progesterone thickens and maintains the endometrium but also inhibits the secretion of FSH and LH from the pituitary gland

• negative feedback