HSCBiology
Animals & Plants 5.1
Inquiry Question 1: How does reproduction ensure the continuity of a species?
Content Descriptor: Explain the mechanisms of reproduction that ensure the continuity of a species, by analysing sexual and asexual methods of reproduction in a variety of organisms, including but not limited to:
Animals: advantages of external and internal fertilisation (5.1.1)
Internal and external
Sexual and asexual
Asexual reproduction:
A technique performed by grasses in which shoots of grass grow outwards away from the main plant. Lobes on this runner grow into the ground. While these are connected to begin with, they can survive as distinct organisms.
Roots which become swollen with food can grow to become distinct organisms. This is used by plants such as potatoes.
Bulbs which asexually form off each other, such as those in onions.
New plants develop as outgrowths from the parent plant. Used by plants such as the spider bush.
Used by plants such as orange trees and dandelions. Embryos in the seed can be produced using the sexual reproduction system of the parent plant. This means that the plant passes on its beneficial traits to its offspring, while still obtaining the range of distribution gained by seed dispersion.
Branches which are touching the ground may grow into roots and begin to produce a new tree.
Method created by humans to produce a high yield of identical clones of a single plant. A hold punch of cells is taken from a plant. These cells are grown in nutrient gel, then separated into individual cells and grown through targeted hormones. Each individual cell can produce identical plants to the original, allowing the cloning of plants that have traits beneficial to humans.
Sexual reproduction:
Aquatic non-vascular plants were some of the first multicellular organisms. Very similar to coral, they have little need to protect their sperm, as they can rely on water to keep the gamete hydrated and currents to move it to another plants reproductive system.
Meaning “naked seed” the seed is not enclosed in an ovule. An example of this is pine cones.
Angiosperms are the only plants which have flowers, which are used to deliberately attract pollinators to the flower, with some even producing nectar to entice pollinators. The male reproductive system of these flowers is called the stamen and the pollen is released from the anthers. The female reproductive system is called the carpel, pollen is received by the stigma. Once the pollen has landed on the stigma, the sperm grows down into the egg, fertilising it. A second sperm nucleus fuses with this zygote producing the endosperm, which nourishes the seed. Fleshy fruit then grows around seeds to protect them and offer a dispersal mechanism.
Sometimes plants deliberately self-fertilise in order to reproduce, however some plants avoid this and terminate the zygote. Note that this is not asexual as it still requires the uniting of gametes.
Note that angiosperms which contain both male and female systems are called perfect flowers.
Pollination:
Bright colours, usually yellow, with a strong scent. May include a landing strip or specific sized cleft for the entry of the insect. The pollen is usually sticky.
Bright colours such as red but usually lacking a scent. Flowers and stems are usually larger and stronger.
Extremely light pollen placed upon extremities high in the air. Nor colours or scents required.
Seed dispersal:
Animals ingesting seeds, which are then deposited in faeces as fertilizer. An example of this is redcurrants. Seeds may also latch onto moving animals to travel large distances. Seeds which use animals for dispersal are characterised by bright colours and easily accessible berries.
Lightweight seeds are carried by the wind. An example of this is dandelions.
Hollow or lightweight structures float on water to travel an incredible distance. Examples include coconuts and mangroves.
Seeds are dropped by the plant and deposited nearby. This is either done through gravity such as pine cones, or some sort of propulsion such as touch-me-not or the exploding cucumber
Methods of fungi reproduction:
Bacteria reproduction:
The genetic information for prokaryotes is found in the nucleoid region. Further DNA can be found in plasmids, which provides additional capabilities such as antibiotic resistance. These traits can be shared through conjugation. Bacteria reproduce via the process of binary fission, where one cell splits in two, which occurs on the origin of replication of the bacterial chromosome. During fission, this section replicates, moves to the other side of the cell. The cell then elongates and then splits.
Protist reproduction:
Due to the genetic diversity of protists as a term, there a variety of techniques employed to reproduce. One asexual method is by binary fission, in which increase their size over a period of growth, before the cell undergoes a nuclear division, splitting the cell in two. Alternatively, budding involves an identical clone of the parent growing as an off-shoot before it detaches and becomes its own organism. Some protists undergo a stage of meiosis, after which two haploid cells meet to form a zygote which then grows to become multicellular.
Content Descriptor: Analyse the features of fertilisation, implantation and
-hormonal control of pregnancy and birth in mammals: (5.1.6)
Gametogenesis:
The production of gametes can be considered the start of the reproductive cycle in mammals. Meiosis results in haploid gametes that can each contain half the chromosomes of the parent.
Oogenesis:
Women are born with all of their primary oocytes. Meiosis begins with the development of the primary oocytes in follicles, but halts before birth and only continues after puberty. Polar bodies are created at each phase of telophase, with the last polar body only being created at fertilisation. Since no knew eggs are created, there is a higher chance of infertility in women.
Spermatogenesis:
The production of sperm can occur late into elderly age, however it slows down with the reduction of testosterone in the system. Occurs in the standard processes of spermatogenesis.
Fertilisation:
The fusion of haploid gametes to form a diploid zygote, a single celled egg. The embryo begins dividing and travels down the nucleus, undergoing 5-6 miotic divisions. At this point, the egg must be differentiated enough to implant into the uterine wall.
Human chorionic gonadotropin (hCG) is an embryonic hormone produced by the blastocyst during implantation. hCG maintains the corpus luteum, which during the early months of pregnancy produces progesterone. hCG is needed in high concentrations and as such is secreted in urine; some early pregnancy tests detect hCG.
Progesterone:
Menstrual cycle activity:
Implantation:
Attachment and invasion of the uterus by the blastocyst. In humans this usually occurs 8-10 days after ovulation. If implantation is not sufficiently proceeded, hormonal feedback may not occur leading to the next pregnancy and the loss of the foetus.
Stages of labour:
Lasts for 2-20 hours and includes the time between the onset of labour and the full dilation of the cervix. Amniotic sac may rupture during this time. Oxytocin stimulates contractions, associated with the pain of labour.
Rhythmic contractions push the baby to the end of the vagina. Delivery completes expulsion.
Non-copulative fertilisation in humans:
An extremely cheap method provided there is easy access to sperm. Sperm is implanted into the mother manually through the vagina using a syringe. AI in humans tends to have low success rates, or similar to those of regular sex.
More invasive than artificial insemination but tends to have higher success rates as the sperm is delivered through the cervix into the uterus. Generally, also more expensive than AI.
An expensive method that can only be performed if the mother maintains healthy eggs. Usually performed after exhaustion of other methods. Can also be useful if the mother is unable to carry the child themselves; use of a surrogate.
Content Descriptor: Evaluate the impact of scientific knowledge on the manipulation of plant and animal reproduction in agriculture: (5.1.7)
Selective Breeding:
Selective breeding and the subsequent domestication of animals has been a part of human culture for roughly 11,000 years. While the mechanisms which enabled this selection of specific traits through breeding programs was not specifically known, these methods were used to improve quality of food and agriculture. One example of this was in the cultivation of bananas, which used to once have low yields of fruit and large seeds. The impact of this selective breeding of plants can be seen in. These methods have been epitomised with the widespread use of artificial insemination and artificial pollination in agriculture.
Scientific knowledge and understanding of the natural processes of inheritance has both enabled and encouraged these developments. Another example of selective breeding is the selection of dairy cows which produce A2 protein in their milk, which was found to correlate with a higher yield of milk.
Thus, advanced in both detection mechanisms and close examination of genotypic relations
enabled the increase in efficiency of the dairy industry.
Inquiry Question Review: How does reproduction ensure the continuity of a species? (5.1.8)
You should be able to:
Sample Questions:
Discuss the relative success of external and internal fertilisation in relation to the colonisation of the land:
The very first animals developed in the ocean, using external fertilisation as the watery environment prevented the eggs from desiccating. However, water environments can easily disperse eggs and sperm, leading to a lower chance of fertilisation. Furthermore, since there is only a small sac or fluid around embryos, the survival rate is very low, with many being eaten by predators or dying from disease. As animals moved onto land, they needed to protect the embryo from desiccation. This resulted in the adaptation of internal fertilisation; the gametes uniting inside the mother. Since the sperm is deposited and contained inside the mother, fertilisation rates are relatively high. In contrast to external fertilisation, the mechanisms to protect the embryo during development (pouches, hard eggs shells, internal development) protected the embryos from predators, disease and desiccation, culminating in a far higher success rate.
Analyse the possible ways in which a lemon tree can reproduce:
A lemon tree has a variety of mechanisms which it can use to reproduce. Firstly, it may reproduce sexually, through encouraging bees as its pollinator to transfer pollen from one lemon tree to the stigma on another tree. This causes genetic variation in the offspring which may be useful for new adaptations, and also enables long range seed dispersal. In rare cases, lemon trees may selfpollinate. While this maintains the advantages of seed dispersal, it does not achieve genetic variation.
Similarly, apomixis, an asexual reproduction method in which the seeds are clones of the parents, has the advantage of seed dispersal but lacks genetic variation. Branches which touch the ground may also reproduce sexually through layering, which can be beneficial if the tree has fallen over. Finally, of significant value to humans is the totipotent reproduction, which can be used to directly clone identical plants from a single graft.