reproduction sl Flashcards
Differences between sexual and asexual reproduction
- Include these relative advantages: asexual reproduction to produce genetically identical offspring by individuals that are adapted to an existing environment, sexual reproduction to produce offspring with new gene combinations and thus variation needed for adaptation to a changed environment.
- In asexual reproduction there are no gametes formed - the offspring is essentially a clone. In sexual reproduction haploid gametes are formed, which during sexual intercourse and fertilisation form again a diploid zygote.
- see chart on table 8!
Role of meiosis and fusion of gametes in the sexual life cycle
- Students should appreciate that meiosis breaks up parental combinations of alleles, and fusion of gametes produces new combinations. Fusion of gametes is also known as fertilization.
Differences between male and female sexes in sexual reproduction
- Include the prime difference that the male gamete travels to the female gamete, so it is smaller, with less food reserves than the egg. From this follow differences in the numbers of gametes and the reproductive strategies of males and females.
- see slide 12!
- MSFAR
Anatomy of the human male and female reproductive systems
- Students should be able to draw diagrams of the male-typical and female-typical systems and annotate them with names of structures and functions.
Changes during the ovarian and uterine cycles and their hormonal regulation
- Include the roles of oestradiol, progesterone, luteinizing hormone (LH), follicle-stimulating hormone (FSH) and both positive and negative feedback. The ovarian and uterine cycles together constitute the menstrual cycle.
Follicular phase
Luteal phase
Ovulation = the generation of a female gamete once a month
The ovum moves down the fallopian tube, driven along by peristalsis (rhythmic contractions of muscles in the wall of the oviduct) and cilia (fine hair-like structures).
The Menstrual Cycle (w/ feedback mechanisms)
Fertilization in humans
- Include the fusion of a sperm’s cell membrane with an egg cell membrane, entry to the egg of the sperm nucleus but destruction of the tail and mitochondria.
- Also include dissolution of nuclear membranes of sperm and egg nuclei and participation of all the condensed chromosomes in a joint mitosis to produce two diploid nuclei.
Fertilization is the fusion of a sperm with an egg to form a zygote.
Receptors in the plasma membrane of sperm allow the detection of chemicals released by the egg, and therefore directional swimming.
When the sperm and egg membranes fuse, the sperm nucleus enters the egg but the tail and mitochondria (mid piece) are destroyed
The nuclear membranes of both the egg and sperm dissolve, allowing the two sets of condensed chromosomes to undergo a joint mitosis
The resulting cell (zygote) has a diploid nucleus, allowing it to undergo further mitotic divisions to form a new multicellular organism (embryo)
fertilization
During fertilization, the ovum membranes alters to form a barrier to the entry of other sperm. The head of the sperm (the male nucleus) then moves towards the nucleus of the ovum and the two fuse together.
Use of hormones in in vitro fertilization (IVF) treatment
- The normal secretion of hormones is suspended, and artificial doses of hormones induce superovulation.
note: Natural methods of fertilization in humans are called “in vivo”, while fertilization outside the body is called in vitro.
see slide 22!
Sexual reproduction in flowering plants
- Include production of gametes inside ovules and pollen grains, pollination, pollen development and fertilization to produce an embryo.
- Students should understand that reproduction in flowering plants is sexual, even if a plant species is hermaphroditic.
- A zygote is produced and retained inside the ovaries of the female parent, and supplied with food as it grows and develops into an embryo inside a seed.
- pollination
- fertilization
- seed dispersal
The tube nucleus grows into a tube
The generative nucleus divides into two haploid sperm cells. One fertilizes the haploid egg cell, the other one fertilizes the diploid polar (endosperm) cells.
Features of an insect-pollinated flower
- Students should draw diagrams annotated with names of structures and their functions.
Methods of promoting cross-pollination
- Include different maturation times for pollen and stigma, separate male and female flowers or male and female plants.
- Also include the role of animals or wind in transferring pollen between plants.
- slides 40-45
- Cross-pollination is the transfer of pollen from an anther in a flower on one plant to a stigma of another plant. This brings about genetic variation, diversity and evolution.
- Self-pollination is when pollen from the same plant is transferred to the stigma of that plant. Many plants are hermaphrodites – they produce both pollen and ovules with female gametes.
Self-incompatibility mechanisms to increase genetic variation within a species
- Students should understand that self-pollination leads to inbreeding, which decreases genetic diversity and vigour.
- They should also understand that genetic mechanisms in many plant species ensure male and female gametes fusing during fertilization are from different plants.
- Sometimes a hermaphrodite plant receives pollen from its own stamens. In most plants self-incompatibility prevents the pollen to germinate or growing. This prevents inbreeding. Plants with the same self-incompatibility alleles cannot successully fertilize each other.
