topic 12 - Reproduction Flashcards
what is sexual reproduction?
the process involving the fusion of the nuclei of two gametes to form a zygote (fertilised egg cell) and the production of offspring that are genetically different from each other
what are gametes
sex cells containing 23 chromosomes
3 advantages of sexual reproduction
- increases genetic variation
- the species can adapt to new environments, giving a survival advantage
- disease is less likely to affect population due to variation
2 disadvantages of sexual reproduction
- takes time and energy to find mates
- difficult for isolated members of the species to reproduce
what is asexual reproduction?
The process resulting in genetically identical offspring being produced from one parent
4 advantages of asexual reproduction
- population can be increased rapidly when conditions are right
- can exploit sustainable environments quickly
- more time and energy efficient
- reproduction is completed much faster than sexual reproduction
3 disadvantages of asexual reproduction
- limited genetic variation as offspring are genetically identical to parent
- population is vulnerable to changes in environment, may not be able to adapt
- disease is likely to affect whole population as there’s no genetic variety
4 key differences of sexual and asexual reproduction
- the number of parent organisms
- the level of genetic similarity between offspring
- the possible sources of genetic variation in offspring
- the time taken to produce offspring
what is fertilisation?
Fertilisation is the fusion of a male and female gamete to produce a zygote that undergoes cell division and develops into an embryo
9 features of a plants reproductive system
CARPEL
- style
- stigma
- ovary
STAMEN
- anther
- filament
- petal
- stem
- sepal
- receptacle
what does the sepal do?
protects the unopened flower
what do petals do?
brightly coloured in insect pollenated flowers to attract insects
what does the anther do?
produces and releases the male sex cell (pollen grains)
what does the stigma do?
top of the female part of the flower which collects pollen grains
function of ovary in plants
produces female sex cell (ovum)
function of ovule in plants
contains female sex cells
what are insect-pollinated flowers and how does it work
flowers using insects as the pollenating agent
- insects often visit these flowers to collect nectar
- as an insect enters the flowers in search of nectar, it often brushes against the anthers, which deposit sticky pollen onto the insect’s body
- when the insect visits another flower, it may brush against the stigma of this second flower and in the process, may deposit some of the pollen from the first flower, resulting in pollination
- the structures of an insect-pollinated flower ensure that the flower is well-adapted for pollination by insects
5 features of insect pollenated flowers
- large and brightly coloured petals to attract insects
- strong scent and nectar, enticing insects to pursue flower and push past the stamen to the nectar
- large and sticky pollen grains to attach to insect
- stiff and firmly attached anther for insect to brush against
- sticky stigma so pollen sticks when insects brush against it
what is wind pollination and how does it work?
- when ripe, the anthers open and shed their pollen into the open air
- the pollen is then either blown by the wind or carried by air currents until it (by chance) lands on the stigma of a plant of the same species, resulting in pollination
- the structures of a wind-pollinated flower ensure that the flower is well-adapted for pollination by the wind
6 features of wind pollinated flowers
- small and dull petals
- no scent or nectar as they don’t need to attract insects
- large amount of pollen grains produced to increase chance of pollination
- smooth, small and light pollen grains so they are easily blown in the wind
- anthers outside of the flower release pollen grain easily
- stigma outside of flower to catch pollen grain
what is cross pollination
when the pollen from one plant is transferred to the stigma of another plant of the same species
what is self pollination
self-pollination reduces the genetic variation in the offspring as all the gametes come from the same parent.
3 factors required for successful germination
- water
- oxygen
- warmth
germination conditions practical method
- set up 4 test tubes, with each containing 10 cress seeds on cotton wool
- label the test tubes A, B, C and D
- for test tube A, leave the cotton wool dry
- for test tube B, add enough water to the cotton wool so that it becomes moist
- for test tube C, add enough water to cover the cotton wool and seeds, then carefully add a layer of oil on top of the water
- for test tube D, add enough water to the cotton wool so that it becomes moist
- leave tubes A, B and C at room temperature or incubated at a specific temperature (e.g. 20°C)
- place tube D in a fridge (approximately 4°C)
- leave all tubes for a set period of time (e.g. 3 - 5 days)
- ensure the cotton wool in tubes B and D remains moist throughout this time by adding more drops of water if required
- compare the results and see which tube has the greatest number of germinated seeds, only tube B will have germinated
how do germinating seeds utilise food reserves until the seedling can carry out photosynthesis
- when the seed germinates, this embryo begins to grow into the young seedling
- structures known as cotyledons surround the embryo
- the cotyledons contain food reserves that supply the young seedling with food (and, therefore, energy for growth) when the seed starts to germinate
- the cotyledons fulfil this role until the young plant grows its own leaves and becomes capable of making its own food via photosynthesis
how does natural asexual reproduction in plants - runners work
- some plants grow side branches, known as runners, that have small plantlets at their ends
- runners are horizontal stems that grow sideways out of the parent plant
- once they touch the soil, these plantlets will grow roots and the new plantlets will grow and become independent from the parent plant
how does artificial asexual reproduction in plants – cuttings work
- gardeners take cuttings from good parent plants (i.e. those that are healthiest and best-looking)
- a section of the parent plant with a new bud is cut off
This cutting can either be placed into water until new roots grow or can sometimes be placed directly into soil - sometimes, the stem of the cutting may first be dipped into ‘rooting powder’, which contains plant growth regulators (rooting hormones) that encourage new root growth
- these cuttings are then planted and eventually grow into adult plants that are genetically identical to the original plant
- plants cloned by taking cuttings can be produced cheaply and quickly
7 features of the male reproductive system
- bladder
- glands
- sperm duct
- urethra
- penis
- testes
- scrotum
function of the prostate gland
produces semen that provide sperm cells with nutrients
function of sperm duct
sperm passes through the sperm duct to be mixed with fluids produced by the glands before being passed into the urethra for ejaculation
function of urethra
tube running down the centre of the penis that can carry out urine or semen. a ring of muscle in the urethra prevents the semen and urine from mixing
function of the testes
contained in the scrotum and produce sperm and testosterone
function of the scrotum
sac supporting testes outside the body to ensure sperm are kept at a temperatures slightly lower than body temperature
function of the penis
passes urine out the body from the bladder and allows semen to pass into the vagina of a woman during sexual intercourse.
7 features of the female reproductive system
- oviduct
- ovaries
- uterus
- cervix
- bladder
- urethra
- vagina
function of oviduct
connects ovary to uterus and is lined with ciliated cells to push the released ovum down it. fertilisation occurs here
function of ovaries
contains eggs which will mature and develop when hormones are released
function of uterus
muscular bag with soft lining where fertilised egg will be implanted to develop into a fetus
function of cervix
ring of muscle at the lower end of the uterus to keep the developing fetus in place during pregnancy
function of vagina
muscular tube leading into the woman’s body. where male penis enters and where sperm is deposited
3 adaptations of sperm
- has a flagellum (tail) so it can swim to the egg
- contains enzymes in the head to digest through the jelly coat and membrane of an egg cell when it meets one
- contains many mitochondria to provide energy for respiration so that the flagellum can move.
2 adaptations of eggs
- cytoplasm containing energy for dividing zygote after fertilisation
- jelly like coating that changes after fertilisation by forming an impenetrable barrier to prevent other sperm from reaching the egg cell.
role of estrogen in the menstrual cycle
- stimulates the uterus to develop a lining to replace lining lost during menstruation
- post-ovulation, inhibits FSH and LH production in the pituitary gland
role of progesterone in the menstrual cycle
- maintains and thickens uterus lining
- inhibits FSH and LH production
- if fertilisation doesn’t occur, levels drop and menstruation occurs
adaptations of the placenta
large surface area and a thin wall for efficient diffusion
role of the placenta
- the placenta passes oxygen, nutrients and antibodies from your blood to your baby
- it also carries waste products from your baby back to your blood, so your body can get rid of them.
what does FSH do?
stimulates follicles on the ovary to grow and prepare the eggs for ovulation
what does LH do?
spurs ovulation and helps with the hormone production needed to support pregnancy
role of amniotic fluid
the amniotic fluid protects the embryo during development by cushioning it from bumps to the mother’s abdomen
development process of fetus
- after fertilisation in the oviduct, the zygote travels towards the uterus
- this usually takes about 3 days, during which time the zygote will divide several times to form a ball of cells known as an embryo
- once it reaches the uterus, the embryo embeds itself in the thick lining of the uterus (implantation) and continues to grow and develop
- a placenta forms where the embryo is attached
- the placenta is an organ that ensures materials can be exchanged between the blood of the mother and the blood of the growing embryo
- the umbilical cord joins the embryo’s blood supply to the placenta for exchange of nutrients and removal of waste products
- For the next 9 months, the embryo grows in the uterus. this is known as the gestation period
- major development of organs takes place within the first 12 weeks, during which time the embryo gets nutrients from the mother by diffusion through the uterus lining
- after this point, the organs are all in place, the placenta has fully formed and the embryo is now called a foetus (sometimes spelt fetus)
- the remaining gestation time is used by the foetus to grow bigger in size
effects of estrogen
- breasts develop
- hair growth
- hips get wider
- menstruation starts
effects of testosterone
- voice gets deeper
- growth of penis and testes
- growth of facial and body hair
- muscles develop
- testes start producing sperm
