chapter 15 - reproduction Flashcards
asexual reproduction
process that results in the production of genetically identical offspring from one parent by mitosis, without the fusion of nuclei of gametes (sex cells that are produced by the reproductive organ)
mitosis
type of cell division giving rise to genetically identical cells in which the chromosome number is maintained
DNA replication
- each chromosome consist of two identical DNA molecules known as sister chromatids
- the sister chromatids are joined at a point known as the centromere
importance of mitosis
asexual reproduction, growth in multicellular organisms, repair of damaged tissues
examples of asexual reproduction
stem tuber of potato, rhizome in ginger, runner of oxalis
advantages and disadvantages of asexual reproduction
advantages :
- only one parent is required
- fusion of gametes is not required
- all the beneficial qualities are passed on to the offspring
- this method of producing offspring is faster than sexual reproduction
disadvantages :
there is no genetic variation in offspring. species not well-adapted to changes in the environment. eg. if parent does not have resistance to a particular disease, the offspring too would not have resistance either. whole population of plants could be wiped out because of one disease
sexual reproduction
fusion of haploid nucleus of female gamete and the haploid nucleus of male gamete to form a diploid zygote (undergo mitosis to form embryo) which produces genetically dissimilar offsprings. the male and female gametes are produced by meiosis
meiosis
type of cell division that gives rise to genetically dissimilar cells in which the chromosomes number is halved due to separation of homologous chromosomes
homologous chromosomes
a pair of chromosomes where one chromosome is inherited from the male parent and the other from the female parent, which have the same shape, size and sequence of genes
haploid vs diploid
haploid cell = cell with one set of chromosomes
diploid cell = contains homologous chromosomes
importance of meiosis
to produce haploid gametes, which are genetically dissimilar from each other and parent cell (sperm and egg/ovum)
mitosis vs meiosis
mitosis
- parent cell has 23 pairs (46) of homologous chromosomes
- parent cell undergoes DNA replication first
- 2 daughter cells obtained
- each daughter cell has 23 pairs (46) of homologous chromosomes. it is diploid
- daughter cells are genetically identical to each other and to the parent cell
meiosis
- parent cell has 23 pairs (46) of homologous chromosomes
- parent cell undergoes DNA replication first
- 4 daughter cells obtained
- each daughter cell has 23 chromosomes. it is haploid
- daughter cells are genetically dissimilar to one another and to the parent cell
advantages and disadvantages of sexual reproduction
advantages of sexual reproduction :
- offspring may inherit beneficial qualities
- greater genetic variation in the offspring -> leads to species that are better adapted to changes in the environment
disadvantage of sexual reproduction :
- two parents are required, fusion of nuclei of gametes is required (uses more energy)
- method of reproduction is slower
asexual reproduction vs sexual reproduction
asexual :
- does not involve fusion of nuclei of male and female gametes
- only one parent required
- offspring are genetically identical
- relatively quicker method to produce offspring
sexual :
- involves fusion of a haploid nucleus of male gamete with a haploid nucleus of female - - gamete to form a diploid zygote
- requires two parents
- offspring are genetically different
- slower method
sepal
- modified leaf that protects the flower in the bud stage
- all the sepal together make up the calyx
- some flowers have another layer of floral leaves outside the sepal known as the epicalyx
petal
- modified leaf that forms the most obvious (conspicuous) part of a flower
- insect pollinated flowers: petals are brightly coloured to attract insects for pollination and to provide a landing platform for insects
- petals together form the corolla
receptacle
enlarged end of the flower stalk that bears parts of the flower
anther
- produces pollen grains, made up of two lobes, each containing two pollen sacs
- contains a vascular bundles (phloem + xylem)
filament
holds anther in a suitable position to disperse the pollen grains
pollen grains
- have a haploid set of chromosomes
- each pollen grain has two nuclei, the generative nucleus and the pollen tube nucleus/vegetative nucleus
stigma
- swollen structure that receives pollen grains
- mature stigma secretes sugary fluid to stimulate the germination of pollen grains
style
- connects stigma to ovary
- holds stigma in a suitable position to trap pollen grains
ovary
contains one or more ovules
ovule
- contains the ovum and definitive nucleus
- attached to the placenta by a stalk called the funicle
ovum
haploid set of chromosomes
insect pollination
bees collect nectar at flowers with mature anther. pollen grains stick to the body and hairs of the insect. moves the other flower with mature stigmas. pollen grains are deposited onto the stigma.
self pollination
transfer of pollen grains from the anther to the stigma of the same flower or a different flower on the same plant
- flowers are bisexual with anthers and stigmas maturing at the same time
- stigma situated directly below the anther
- certain flowers in bisexual plants never open -> only self-pollination
advantages and disadvantages of self-pollination
advantages :
- only one parent required
- beneficial qualities passed down from parent to offspring
- not dependent on external factors for pollination
- less pollen and energy wasted
- more likely to take place since stigma closer to anthers
disadvantages :
- offspring are genetically similar (not asexual cause not genetically identical) (gene pool is smaller), causing fewer varieties of offspring, less adaptable to changes in environment
- probability of harmful recessive alleles being expressed in offspring higher than cross-pollination
cross pollination
transfer of pollen grains to flower of another plant of the same species
- plants bear either male or female flowers make self-fertilisation
- can happen when anthers and stigmas mature at different times
- or when stigmas are situated at a distance away from anthers
advantages and disadvantages of cross-pollination
advantages :
- offspring inherit beneficial qualities form both parents
- more varieties of offspring produced resulting in greater genetic variation
- increased probability of offspring being heterozygous (alleles are different)
- seeds (sexual reproduction) capable of surviving longer before germination
- probability of harmful alleles being expressed in offspring is lower as compared to self-pollination (gene pool is bigger)
disadvantages :
- two different plants required
- dependent on external factors
- more energy and pollen wasted
- less likely to occur
characteristics of insect-pollinated flowers
petals : large with brightly-coloured petals
nectar : nectar is present
scent : fragrant and sweet-smelling
stigmas : small, compact and do not protrude out of the flowers
stamens : not pendulous and do not protrude out of flowers
pollen : fairly abundant. pollen grains are larger with rough surfaces
nectar guides : present
pollination process
- insects lands on the standard petal
- follows nectar guide into flower
- forces its way in between the two wing petals to collect nectar
- insect back forces the keel petal upwards to expose the anthers and stigma
- pollen grains from the anther stick onto the back of the insect and get transferred to a stigma and is deposited
fertilisation process
- after pollination, pollen grain germinates in response to sugary fluid secreted by mature stigma
- pollen tube grows out from the pollen grain. growth of pollen tube is controlled by pollen tube nucleus
- cytoplasm and two nuclei (generative (male gamete) and pollen tube (growth of pollen tube)) pass into pollen tube
- pollen tube secretes enzymes to digest the surrounding tissue of stigma and style and penetrates through the style to the ovary
- pollen tube enters the ovule through the micropyle (opening)
- generative nucleus divide into two male gametes, while the pollen tube nucleus disintegrates
- when the pollen tube reaches the ovule, its tip absorbs sap and bursts, releasing the two male gametes
- haploid nucleus of male gamete fuses with the haploid nucleus of the ovum to form the diploid zygote (fertilisation). the other haploid nucleus of the male gamete fuses with the definitive nucleus (in the ovule) to form the endosperm nucleus
- zygote divides mitotically and develops into the embryo, and the endosperm nucleus will give rise to an endosperm
- ovule develop into seed, ovary develops into fruit, zygote develops into an embryo
testis
produces sperms and male sex hormones like testosterone
epididymis
stores inactive sperms from the testis before they are released into the sperm ducts
spermatic cord
supplies blood to the testis
scrotum
pouch-like sacs located outside the body cavity to help maintain a lower temperature for the development of sperms
sperm duct
pathway travelled by sperms after they are released from the testis
ovary
produces eggs and female sex hormones like estrogen and progesterone
oviduct
narrow muscular tue with funnel like opening at the ovary
mature eggs are released from the ovary into the oviduct to be fertilised
uterus
location where the fetus develops
has elastic muscular walls that enable contradiction during birth to expel the fetus
uterine lining
soft, smooth inner lining of the uterus rich in blood supply that is important for embryo implantation
vagina
where semen is deposited during sexual intercourse, spans the area from cervix into vulva
ovum
- present in a ovaries of female at birth
- eggs are released into oviducts from the time a female
reaches puberty until menopause (about 45-50 years old) - each ovary releases about 250 mature ova in the lifespan of a female
ovum
- present in a ovaries of female at birth
- eggs are released into oviducts from the time a female
reaches puberty until menopause (about 45-50 years old) - each ovary releases about 250 mature ova in the lifespan of a female
ovum structure
- large nucleus containing one set of haploid chromosomes
- large amount of cytoplasm containing a small amount of yolk
- cell surface membrane that is surrounded by an outer membrane
menstruation
monthly discharge of blood from the uterus via the vagina
menstruation
monthly discharge of blood from the uterus via the vagina
menstruation process
day 1 to 5 : uterine lining and unfertilised egg break down and are shed with some blood
day 6 to 13 : ovary produces oestrogen and the developing follicles secrete oestrogen, which stimulates the uterine lining to repair and thicken. the high oestrogen concentration leads to ovulation.
day 14 : ovary releases an egg into the oviduct through a process known as ovulation. the two ovaries take turns to release an egg.
day 15 to 28 : ovary produces progesterone to prevent further ovulation and further development of eggs, as well as causes the uterine lining to thicken further, preparing it for implantation and the growth of the embryo. oestrogen production decreases. if no fertilisation of eggs occur, progesterone production decreases, the uterine lining breaks down and the whole cycle repeats.
fertilisation process (humans)
- during sexual interocurse, the penis is inserted into the vagina
- semen containing sperms and nutrients is ejaculated from the penis is deposited into the upper end of the vagina. the sperms will swim into the uterus and enter the oviduct
- if an ovum is present in the oviduct, fertilisation may take place (when the sperm makes the contact with the egg, the sperm’s acrosome releases an enzyme that disperse the follicle cell and breaks down part of the egg’s membrane to allow the sperm to enter. only one sperm nucleus enters the egg, and the haploid nucleus of male gamete fuses with haploid nucleus of female gamete to form a diploid zygote. the zygote divide by mitosis to become a ball of cells of embryo. the embryo is moved towards uterus by peristalsis by the walls of the oviduct and sweeping motion of the cilia, and will be implanted in the uterine lining of the uterus
development of embryo
(implantation) the cilia lining the oviduct sweep the fertilised egg towards the uterus. as the zygote travels along the oviduct, it undergoes mitosis to form an embryo. it takes the embryo about five days to reach the uterus.
(implantation) the embryo may float freely in the uterus for two days before it gets implanted into the uterine lining. implantation refers to the event where the embryo becomes embedded in the uterine lining
(development of the placenta) after implantation, finger-like projections (villi) grow from the embryo into the uterine lining. the embryonic villi and uterine lining make up the placenta. the umbilical cord attaches the embryo to the placenta.
(development of the amniotic sac). the amniotic sac is the membrane that encloses the embryo in a fluid-filled space called the amniotic cavity.
fetal blood system
- fetal blood system is not connected to maternal blood capillaries, but surrounded by the maternal blood spaces
- diffusion of substances occur across maternal blood spaces
why fetal blood system separated from the maternal blood system?
- mothers blood pressure would be too high for foetus
- blood type might be different, might cause agglutination
placenta
site of exchange of nutrients
1. allow oxygen and food substances (glucose and AA) to diffuse from mother’s blood to fetus’s blood
2. allow excretory products like urea to diffuse from fetus’s blood to mother’s blood
3. produces progestrone to maintain and thicken the uterine lining
4. allows antibodies to diffuse from the mother’s blood into the fetus’s blood to protect the fetus agasint diseases
functions of umbilical cord
made up of two umbilical arteries and one umbilical vein
umbilical vein : trasnport oxygenated blood and food substances (glucose and AA) from the placenta to the fetus
umbilical arteries : transport deoxygenated blood and metabolic waste products like urea and carbon dioxide from the fetus to the placenta
amniotic sac
encloses the fetus in the amniotic cavity, containing the amniotic fluid
amniotic fluid
- allows fetus to move freely during growth
- lubricates to reduce friction the vagina during birth
- supports and cushions the fetus, protecting it against physical injury by absorbing shock
sexually trasmitted diseases
- a disease that is spread through sexual intercourse
- caused by bacteria or viruses
- transmitted from an infected person via semen, fluid in the vagina, blood
AIDS
acquired immune deficiency syndrome
- caused by human immunodeficiency virus (HIV)
- HIV destroys the body’s immune system by attacking white blood cells, thus making infected individual prone to many infections
- a person infected with AIDS is not able to produce sufficient antibodies to protect him or herself from other infections
infections that are normally mild may become fatal for a person with AIDS
symptoms and modes of trasnmission of AIDS
symptoms of AIDS : chronic fever, widespread tuberculosis, brain infection, kaposi’s sarcoma, pneumonia
modes of transmission of AIDS : unprotected sexual intercourse with an infected person, blood transfusion with blood from an infected person, sharing of hypodermic needles with an infected person, passed from mother to fetus during pregnancy (not always)
prevention of HIV infection
keep to one sex partner, practice abstinence, use proper protection during sexual intercourse, make sure needles are sterilised, don’t share instruments that can break skin and get contaminated with blood
