Topic 7 - Reproduction (part 1)

• Sexual reproduction (features + A/D)


  SEXUAL REPRODUCTION = fertilisation of 2 sex cells (one gamete from each parent 50% of DNA) produced by meiosis to form a zygote which will develop into a genetically unique offspring

  
  

  advantages:

  - increases genetic variation - offspring can adapt to new environment (gives them a survival advantage)

  - less vulnerable to diseases due to variation --> less harmful to the population

  
  

  disadvantages:

  - time-consuming to find mating partner

  - not possible for isolated members
• Asexual reproduction (features + A/D)


  ASEXUAL REPRODUCTION = reproduction by a single parent to produce genetically identical offspring (clones) via mitosis

  
  

  advantages:

  - rapid increase in population

  - thrive in a suitable environment

  - time and energy efficient

  
  

  disadvantages:

  - decreases variation

  - vulnerable to change in environment due to in-adaptability

  - more vulnerable to diseases due to decreases variation (more harmful to population - disease is more likely to affect entire population due to lack of genetic variation)
• Fertilisation definition


  sexual reproduction

  fusion of 2 gamete nuclei to form zygote (fertilised egg cell) = variation in offspring
• Gamete


  Sex cell

  contains half number of chromosomes found in other body cells (23)
• Structure of general flower


  Male = stamen

  ANTHER - produces + releases male gamete (pollen grains)

  FILAMENT - the stalk supporting the anther

  
  

  Female = carpel

  OVARY - produces the female gametes (eggs) inside the OVULES

  STYLE - rod-like section supporting stigma

  STIGMA - top of the female part of flower (where pollen grains attach to)

  
  

  PETAL - brightly coloured in insect-pollinated flowers (attract insects)

  STEM - attaches flower to rest of plant

  SEPAL - protects unopened flower (like the leaf under)
• Insect-pollinated flowers special adaptations (6) + general info


  Pollinating agents = insects (eg. bees, butterflies) --> visit flowers to collect nectar (located at the base of the petals which provide the insects with energy) --> brushes against anther --> visits other flower and brushes against stigma to deposit the pollen = pollination

  
  

  ADAPTATIONS:

  - Brightly coloured petals = attract insects

  - Scented flowers = attract insects

  - Nectaries (glands that produce nectar) = attract insect as nectar used as energy source

  - Sticky + large + sometimes spiky pollen grains = stick to insects easily

  - Firm anthers = insects can brush against (pick up pollen grains --> the male gamete)

  - Sticky stigma = pollen will be more likely to stick when deposited
• Pollination


  transfer of pollen from an anther to a stigma so that the male gametes can fertilise the female gametes in sexual reproduction
• Cross-pollination


  refers to a type of sexual reproduction where one pollen is transferred from the anther of one plant to the stigma of an OTHER plant (OF THE SAME OR SIMILAR SPECIES)

  BRINGS GENETIC VARIATION IN OFFSPRING

  
  

  (rely on insects + wind)
• Wind-pollinated flowers special adaptations (5) + general info


  process of pollination is more random

  when ripe, anthers open + shed pollen into air --> carried by wind --> lands on stigma of plant = pollination

  
  

  ADAPTATIONS:

  - no scent + nectar = no need to attract insects

  - dull + small flowers = no need to attract insects

  - anthers hang out of the flower as filaments are long + swing loosely = release pollen grains easily

  - pollen is light + small = carried by wind easily

  - stigma is FEATHERY + long + outside flower = can catch pollen grains easily
• Self-pollination


  the transfer of pollen grains from an anther to the stigma of the same flower or to the stigma of another flower on the SAME plant

  
  

  REDUCES GENETIC VARIATION OF OFFSPRING (all gametes come from same parents)
• Fertilisation in plants and into fruit/seed growth


  fusion of gametes (pollen grain nucleus + ovum nucleus)

  ovum (egg cell containing female nucleus) --> ovules --> ovary

  
  

  1. pollen grain lands on stigma of flower

  2. POLLEN TUBE grows out of grain + down through style to ovary and into the ovule

  3. nucleus of male gamete moves down tube to join with female gamete in ovule. fertilisation occurs when the new nuclei fuse to form a zygote --> through mitosis into divide into embryo

  
  

  fertilisation leads to fruit + seed growth:

  1. ovule develops into seed after fertilisation

  2. walls of ovule develops into seed coat (TESTA)

  3. parts of flower surrounding ovule (ovary walls) develop into fruit which contains seeds

  4. fruits provide mechanism for SEED DISPERSAL (releasing seeds from parent plant:

  - method 1: fruits eaten by animals which then disperse the seeds via faeces (tough out coat of seeds (TESTA) prevents seed from being digested)

  - method 2: fruits have sticky hooks that get caught in fur of passing animals
• what is the process of removing seeds from parent plant called? give me 2 methods


  seed dispersal

  - method 1: fruits eaten by animals which then disperse the seeds via faeces (tough out coat of seeds (TESTA) prevents seed from being digested)

  - method 2: fruits have sticky hooks that get caught in fur of passing animals
• what is the seed coat called?

  Testa made of ovule walls
• Germination


  - the start of growth and development of a seed

  - require water, oxygen, warm temperature

  - contains COTYLEDONS that surround embryo. contains food reserves for growth UNTIL plant grows leaves for photosynthesis

  - water = testa splits = PLUMULE (first emerging shoot) and RADICLE (first emerging root) produced
• what are the 3 factors required for successful germination?


  Water - needed to burst testa (coating of seed) so that embryo plant can exit seed. water allows enzymes in embryo to start working so that growth can occur (metabolic activity)

  Oxygen - needed to break glucose down for energy (respiration) for growth

  Temperature - optimum temps for enzyme
• practical: investigate the conditions needed for seed germination


  METHOD:

  1. cotton wool is placed at the bottom of four boiling tubes, each containing five seeds

  2. test tube A: moist cotton wool and placed in warm temperature (hot water bath set at appropriate temperature)test tube B: dry cotton wool and placed in warm environment (hot water bath set at appropriate temperature)test tube C: moist cotton wool and is placed in cold environment (bucket of ice) test tube D: cotton wool soaked in boiled water (doesn't contain any dissolved oxygen) that is cooled off, and layered with Oil on top (prevent oxygen from dissolving into water)

  3. the germinating seeds in each test tube are allowed to adjust to new environment for a few days (leave for a few days)

  4. after a few days, compare number of seeds that have germinated and the height of the germinated seed.

  
  

  RESULTS:

  - test tube A = yes, seeds germinated

  - test tube B, C, D = no seeds germinated

  - this is because test tube A had all conditions for germination present whilst test tubes B, C and D did not.
• Where do germinating seeds get energy from?


  food stores

  -developed seeds contain embryo and store of food reserves wrapped a hard seed coat, which it gets its glucose for respiration from until the plant has grown enough to produce green leaves and start to photosynthesise
• Why use boiled water in germinating practical?


  doesn't contain any dissolved oxygen (tube wants absence of oxygen to show that germination won't occur as oxygen is needed to break glucose molecules into energy for growth)
• COTYLEDONS


  Surround embryo. Contains food reserves for growth in germination UNTIL plant grows leaves for photosynthesis
• what is the name of the first emerging shoot?

  plumule
• what is the name of the first emerging root?


  radicle
• Asexual reproduction in plants (natural + artificial)


  - one parent, all offspring genetically identical to parent + each other

  
  

  NATURAL:

  - plants grow side branches (RUNNERS) that have PLANTLETS at their ends

  - once they reach the soil, plantlets will grow roots + will become independent from parent plant

  
  

  ARTIFICIAL:

  - CUTTINGS

  - take cuttings from good parent plants (healthiest, best looking)

  - place cuttings into soil

  - rooting powder (rooting hormones) may be used to encourage new root growth

  - CHEAP + QUICK
• Male reproductive system structure


  GLANDS - produces fluid called semen that provide sperm cells with NUTRIENTS

  PENIS - passes urine out of body from bladder + allows semen to pass into vagina of woman during sexual intercourse

  ERECTILE TISSUES - swells when filled with blood to make sperm erect

  URETHRA - tube carrying sperm through penis during ejaculation. Urine passes through to exit body. RING OF MUSCLE in urethra prevents urine and semen from mixing

  FORESKIN - under penis head

  SPERM DUCT - muscular tube that carries sperm from testis to urethra

  TESTIS - produces sperm + testosterone

  SCROTUM - sac holds testes + ensures sperm kept at temp slightly lower than body temp
• what prevents urine and semen from mixing in the urethra?

  muscular ring
• Female reproductive system structure


  VAGINA - muscular tube leads to inside of woman's body. where penis enters during sexual intercourse + sperm is deposited

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

  UTERUS - muscular bag with soft lining where fertilised egg (ZYGOTE) will be implanted to develop into a foetus

  OVIDUCT - (fallopian tube) a muscular tube carrying the ovum (egg) from the ovary to the uterus

  OVARY - produces female gamete (ova) and sex hormones

  UTERUS LINING - has good blood supply for implantation of embryo
• OVA AND OVUM ARE THE SAME (ova is plural)


  female gametes
• Fertilisation in humans


  ejaculation = sperm duct carries sperm from testes to urethra + glands release semen --> urethra carries sperm to penis where during sexual intercourse, sperm is ejaculated into vagina of female --> sperm follow chemical trail + travel to uterus --> sperm travel to oviduct where the sperm cell meets the egg cell.

  
  

  fertilisation can occur (fusion of nuclei from male + female gamete) --> head of sperm releases enzyme that digest a path through protective outer layer of egg cell. when they fuse = zygote (fertilised egg cell) --> zygote divided by mitosis into embryo is formed. Embryo implanted in uterus
• where do the sperm and egg cell meet?

  Oviduct
• Role of oestrogen in the menstrual cycle


  - levels rise from day 1 and peak before day 14 (ovulation)

  - causes uterine wall to start thickening + egg to mature

  - stimulates release of LH (release of egg)
• Menstrual cycle


  28 days

  ovulation occurs halfway (release of egg)

  failure to fertilise = menstruation = breakdown of thickened lining of uterus
• Ovulation


  release of egg
• Role of progesterone in menstrual cycle


  - rises once ovulation has occurred (release egg day 14)

  - increase levels = uterine lining thickens further

  - fall in progesterone levels = uterine lining breaks down (menstruation)

  - inhibits release of LH and FSH
• Placenta


  Facilitates the growth of the foetus during gestation by providing nutrients (glucose, amino acids, water, oxygen) from the mother's blood
• Role of placenta during gestation period


  1. Foetus grows by gaining nutrients from mother's blood

  2. Waste products (CO2 + urea) removed from foetus blood via diffusion / active transport

  3. Minerals diffuse
• Placenta


  • Large surface area = efficient diffusion
  • Thin wall = short distance for efficient diffusion
  • Acts as barrier to prevent toxins + pathogens getting into foetus blood (HOWEVER DEPENDS ON SIZE OF MOLECULE)
• After birth, the placenta detaches from the uterus wall
• Embryo is surrounded by what fluid?

  Amniotic fluid (made of mother's blood plasma) held in amniotic sac

  • protects embryo during development by cushioning it from bumps