reproduction Flashcards
(34 cards)
what are the examples of asexual reproduction?
-budding: bacteria, yeast, jellyfish
-binary fission: amoeba, paramecium, euglena
-vegetative propagation: stem runners, root tubers, leaf buds
what are some characteristics of asexual reproduction?
-only parent is needed (no fertilisation=no gametes required)
-offspring inherits all traits (beneficial and disadvantageous) from parents
-no genetic variation in population - more susceptible to changes in the environment (eg. climate, diseases)
-occurs more quickly for populations to colonise large areas easily
-smaller energy and time investment by parent organism
what are some characteristics of sexual reproduction?
-most life on earth reproduce sexually
-usually two parents needed (each parent contributes one gamete for fertilisation to occur)
-offspring may inherit some beneficial and disadvantageous traits from both parents
-variations between individuals may result in some being more resilient or immune to changes in environment
-occurs more slowly due to the need for fertilisation
-parent organisms expend more time and energy in producing gametes and relevant structures
what is a gamete?
sex cell
what is a zygote?
fertilised egg
what is fertilisation?
it describes the fusion of nuclei from two gametes to form a zygote. each gamete only contains one set of chromosomes, ensuring that after fertilisation, the zygote will have two sets of chromosomes. human gametes have 23 chromosome (haploid), while all non-sex cells have 46 chromosomes.
what makes up the stamen and what are their functions?
anther: produces pollen grains which contain male gametes
filament: contains vascular bundle to transport nutrients to the anther
what makes up the carpel and what are their functions?
stigma: secretes a sticky sugary fluid to receive the pollen grains
style: connects the stigma to the ovary
ovary: protects the ovule(s)
ovule: contains a female gamete where fertilisation occurs
what are the non-reproductive organs and their functions?
pedicel: an extension of the stem that connects to and supports the flower
receptacle: the base of the flower where all organs are attached at
sepal: protects the budding flower then supports the petals after blooming
petal: protects reproductive organs within and attract animal pollinators
how can cross-pollination occur?
flowers can be cross-pollinated by animals seeking nectar, or simply by passing a breeze
animal-pollinated vs wind-pollinated?
1) a: usually insects (butterflies and bees), sometimes birds and bats
w: dependent on wind (presence, direction, speed)
2) a: large and brightly-coloured petals (to attract pollinators)
w: small and dull-coloured petals
3) a: petals have obvious nectar guides (to direct pollinators to reproductive organs
w: no nectar guides
4) a: nectar is present (to attract and reward pollinators)
w: no nectar provided
5) a: strongly scented (to attract pollinators)
w: unscented
6) a: stigmas are small and kept within the flower
w: stigmas are large and feathery, and stick outside the flower (greater surface area to catch pollen grains in the wind)
7) a: anthers do not extend outside the flower
w: anthers hang outside the flower due to the long and pendulous filaments (pollen grains can be blown away by the wind more easily)
8) a: pollen grains are sticky or have rough surfaces (to attach onto the bodies of pollinators)
w: pollen grains are small and light (for pollen grains to stay afloat and be carried more easily by the wind)
explain self-pollination
flowers that undergo self-pollination are usually small and dull-coloured as well since they do not need to attract or accommodate any pollinators. these flowers usually have long filaments so that their anthers are located above their stigmas. when the anthers mature, the pollen grains can easily fall downwards directly onto the stigma, completing the pollination process. such flowers also have stamen and carpels that mature at approximately the same time and remain viable for the same duration to increase the chances of pollination occurring.
explain pollen tube growth
when the pollen grain reaches the stigma, the male gamete within needs to be transported to the female gamete in the ovule, which is a relatively long distance to travel. the pollen grain accomplishes this by burrowing through the style to create a pollen tube. the male gamete then follows the path of the pollen tube to enter the ovule and meet the female gamete for fertilisation to occur.
what are the steps to pollen tube growth?
1) pollen grain lands on stigma and is stimulated by the sticky sugary fluid
2 ) pollen tube grows through the style by releasing digestive enzymes that break down the plant tissues
3) tip of the pollen tube arrives at the opening of the ovary and absorbs cell sap to burst open and release the male gamete
4) male gamete enters the ovule for fertilisation to occur
explain fertilisation (flowers)
the fusion of nuclei from two gametes is a critical juncture that contributes to genetic variation in the population. after the male gamete enters the ovule, it fuses with the female gamete within to form a zygote. the zygote undergoes multiple rounds of cell division to form the embryo that grows in the seed. the ovule develops into the seed while the ovary develops into the fruit. the anthers, filament, stigma, style, petals, sepals all wither and fall off the plant.
what are the male reproductive organs and their functions?
-testis: male gonads (produce gametes) on either side of the penis (produce sperm cells and male sex hormones:testosterone, sperm production occurs best 2d.c. below core body temperature
-scrotum: thin layer of skin (suspends testes outside of main body cavity for optimal sperm production
-sperm ducts: a narrow tube that transports mature sperm cells from the testes to the urethra
-prostate gland: an accessory gland that secretes anticoagulant enzymes and sperm nutrients into the urethra (thin semen for sperm to move through more easily, provide sperm with a source of nutrients for respiration)
-urethra: runs the length of the penis (conducts semen from the sperm ducts to outside the body , is also connected to the bladder for urine to be excreted) the urethra will only allow either semen or urine to pass through at any one time
-penis: contains spongy erectile tissue (fills with blood from the arteries during an erection, deposits semen into the vagina during sexual intercourse)
what are the female reproductive organs and their functions?
-ovary: female gonads on each side of the uterus (release mature ova and female sex hormones:oestrogen and progesterone, each ovary alternates to release only one mature ovum per menstrual cycle
-oviduct: a narrow tube extending from the uterus to each ovary (site of fertilisation, cilia on the inner lining of the oviducts propel the ova (or zygote) towards the uterus, peristaltic contractions also help with this movement)
-uterus: thick and muscular organ capable of expanding 4 times its normal size (where the foetus develops during pregnancy
-endometrium: innermost lining of the uterus (thickness changes throughout the menstrual cycle, thickens and becomes more vascular to prepare for implantation, thins and is shed during menstruation if implantation did not occur)
-cervix: a ring of muscles between the uterus and vagina (remains closed to maintain pregnancy, dilates during labour to allow foetus to be pushed out)
-vagina: muscular and elastic chamber, also known as the birth canal (site of insertion of the penis to deposit semen, where the baby passes through during birth, epithelial cells secret acids to kill foreign particles and maintain a sterile environment
gametes
male vs female
1) relative size
f: largest human cell, up to 1.2cm
m: smallest human cell, 50 micrometer
2) quantity
f: only one released per menstrual cycle
m: up to 300 million released per ejaculation
3) number of chromosomes
f: 23 chromosomes (one set - haploid)
m: 23 chromosomes (one set - haploid)
4) mitochondria concentration
f: up to 200000
m: up to 100 (packed in the midpiece)
5) special features
f: protective layer of cells and jelly-like matrix protect the ovum and ensure that only one sperm can fertilise the ovum
M: flagellum allows the sperm to propel itself-is motile, acrosome contains digestive enzymes to break down the protective layers surrounding the ovum
what is puberty?
it is the maturation of reproductive organs where the testes begin producing sperm cells and releasing testosterone into the bloodstream, and the ovaries start to release oestrogen and progesterone that regulate the menstrual cycle.
what are the two processes of the menstrual cycle?
menstruation and ovulation
explain how the menstrual cycle may change
a typical menstrual cycle lasts 28 days but is easily affected by a woman’s diet, stress levels, and health condition. not having proper nutrition, feeling extreme emotions, and falling ill will change the concentration of hormones coursing through the body. the ovarian hormones are no different and when their levels in the body change, the duration of the menstrual cycle and the days which menstruation and ovulation occur will also change
explain menstruation
the break down and shedding of the endometrium which is then expelled from the uterus through the cervix and vagina. menstruation marks the first day of the menstrual cycle.
explain ovulation
the release of a mature egg from an ovary into the oviduct. ovulation occurs once per menstrual cycle, 14 days after menstruation began.
explain oestrogen and progesterone
oestrogen stimulates the maturation and release of an ovum from the ovary
oestrogen repairs and stimulates the growth of the endometrium
progesterone maintains the thickness of the endometrium
progesterone inhibits uterine contractions and keeps the endometrium well-vascularised
