reproduction

Question 1

what are the examples of asexual reproduction?

Answer 1

-budding: bacteria, yeast, jellyfish
-binary fission: amoeba, paramecium, euglena
-vegetative propagation: stem runners, root tubers, leaf buds

Question 2

what are some characteristics of asexual reproduction?

Answer 2

-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

Question 3

what are some characteristics of sexual reproduction?

Answer 3

-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

Question 4

what is a gamete?

Answer 4

sex cell

Question 5

what is a zygote?

Answer 5

fertilised egg

Question 6

what is fertilisation?

Answer 6

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.

Question 7

what makes up the stamen and what are their functions?

Answer 7

anther: produces pollen grains which contain male gametes
filament: contains vascular bundle to transport nutrients to the anther

Question 8

what makes up the carpel and what are their functions?

Answer 8

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

Question 9

what are the non-reproductive organs and their functions?

Answer 9

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

Question 10

how can cross-pollination occur?

Answer 10

flowers can be cross-pollinated by animals seeking nectar, or simply by passing a breeze

Question 11

animal-pollinated vs wind-pollinated?

Answer 11

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)

Question 12

explain self-pollination

Answer 12

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.

Question 13

explain pollen tube growth

Answer 13

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.

Question 14

what are the steps to pollen tube growth?

Answer 14

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

Question 15

explain fertilisation (flowers)

Answer 15

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.

Question 16

what are the male reproductive organs and their functions?

Answer 16

-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)

Question 17

what are the female reproductive organs and their functions?

Answer 17

-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

Question 18

gametes
male vs female

Answer 18

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

Question 19

what is puberty?

Answer 19

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.

Question 20

what are the two processes of the menstrual cycle?

Answer 20

menstruation and ovulation

Question 21

explain how the menstrual cycle may change

Answer 21

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

Question 22

explain menstruation

Answer 22

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.

Question 23

explain ovulation

Answer 23

the release of a mature egg from an ovary into the oviduct. ovulation occurs once per menstrual cycle, 14 days after menstruation began.

Question 24

explain oestrogen and progesterone

Answer 24

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

Question 25

explain the days of the menstrual cycle, regarding the hormone levels and its effect

Answer 25

day 0
HL: lowest levels of OE and PG
E: endometrium is no longer maintained, uterine contractions begin, endometrium breaks down and is expelled from the uterus through the cervix and vagina during menstruation
day 0 to 5
HL: OE levels begin to slowly increase, PG levels remain relatively low and constant
E: OE and PG levels still very low, menstruation lasts for 5 to 7 days
day 5 to 14
HL: maturing ovum in the ovary releases more OE, causing OE levels to increase more rapidly, PG levels also increase slightly because of this
E: endometrium grows and thickens, becoming more richly supplied with blood vessels, ovaries restrict maturation of potential ova, ensuring that only one ovum will be released
day 14
HL: peak OE levels trigger ovulation
E: ovary releases mature ovum into the oviduct
day 14 to 28
HL: ovary continues releasing some OE, PG secretion increases drastically
E: endometrium remains thick and vascular to prepare for possible implantation
day 28
HL: OE and PG levels begin to decrease if implantation did not occur
E: endometrium is no longer maintained and is subsequently shed

Question 26

what happens on day 12 to 14 during the menstrual cycle (sperm is deposited)

Answer 26

if semen has been deposited on day 12, sperm cells would have arrived at the oviducts around day 13 and could remain viable for another day or so to await the release of an ovum on day 14 for fertilisation

Question 27

what happens on day 14 to 16 during the menstrual cycle? (sperm is deposited)

Answer 27

once the ovum is released into the oviduct on day 14, it takes about 2 to 3 days for the oviduct to move the ovum into the uterus. the ovum is the most suitable to be fertilised while in the oviduct, and not in the uterus.

Question 28

explain the fertile phase

Answer 28

it is when the woman has the best chance of becoming pregnant should she have sexual intercourse in those few days, but does not guarantee that fertilisation and implantation will occur. likewise, having unprotected sex during her infertile phase may also result in pregnancy.

Question 29

what are the steps of fertilisation/implantation

Answer 29

upon breaking through the layers of protection surrounding the ovum, the cell membrane of the sperm and ovum fuse, releasing the haploid male nucleus into the ovum. there, it fuses with the haploid female nucleus to form a diploid zygote completing the fertilisation process
-ovulation releases a mature ovum into the oviduct
-a single sperm cell fertilises the ovum
-zygote undergoes multiple rounds of cell division to form an embryo
-embryo continues to divide when it reaches the uterus to form a ball of cells
-ball of cells develops into blastocyst which implants itself into the endometrium

Question 30

what are the methods of transmission of hiv

Answer 30

-sexual fluids: sexual intercourse without using a condom
-blood: sharing unsterilised injection needles, unregulated blood transfusions, pregnancy: hiv can pass through the placenta and enter the foetal bloodstream, childbrith: tears along the vaginal walls during labour may expose the baby to the mother’s blood
-breastfeeding: hiv is present in the breast milk of lactating mothers

Question 31

ways hiv cannot be transmitted

Answer 31

-air or water: hiv is not an airborne or waterborne agent
-saliva, sweat, tears: these bodily fluids do not contain hiv, hiv will not be transmitted through shaking hands, hugging, or sharing cutlery with hiv-positive persons
-insects or pets: animals common in our daily lives have little to no chance of transmitting hiv between humans, mosquitoes break down hiv in their bodies, the bloodstream of dogs and cats is inhospitable to hiv

Question 32

what does hiv do?

Answer 32

it specifically targets a type of white blood cell known as CD4 which is responsible for activating the immune system and preparing to fight any infection. the human immune system cannot recognise and attack hiv as it would other pathogens, resulting in a severely weakened immune system that is as good as absent.

Question 33

what are the hiv stages?

Answer 33

stage 1: rapid reproduction of hiv, some people develop flu-like symptoms
stage 2: slow reproduction of hiv and gradual reduction of CD4 cells, no external symptoms
stage 3: low levels of CD4 cells in the body, appearance of opportunistic infections

Question 34

how to prevent hiv?

Answer 34

-being faithful to a sexual partner reduces the risk of unknowingly getting infected
-go for hiv tests to remove any doubt
-practice safe sex by using a condom to prevent sexual fluids from mixing
-use only clean, sterile needles and choosing a reliable service provider when getting a piercing, tattoo, or an injection
-accept only hiv-screened blood for blood transfusions