HSC Biology Syllabus Notes
Module 5 – Reproduction
*Your ConquerHSC’s Notes are consistently being revised throughout the 2019 HSC year to ensure quality.
Week 1 Content
Overview of Week 1’s Inquiry Question
Learning Objective #1 – How reproduction ensure continuity of species? Categories of reproduction
Learning Objective #2 – Where reproduction fits in our understanding of Evolution – Darwin’s Theory
Learning Objective #3 – Types of reproductions under the asexual and sexual reproduction categories
Learning Objective #4 – Mammalian reproduction mechanisms – Fertilisation, Implantation and Hormonal Control
Learning Objective #5 – Advancement of scientific knowledge led to the manipulation of plants’ and animals’ genetic material
HSC Biology Syllabus Lecture Video – Reproduction
Week 1 Homework Set (Essential for Band 5)
Curveball Questions (Moving from Band 5 to Band 6!)
Solutions to Week 1 Homework Set
Before we hop on the materialistic train and start digging into the content, please give me a minute to walk you through what you should keep in mind as the ‘major highlights’ for this week’s material.
The inquiry (overarching) question for this week deals with reproduction and its relationship with evolution, aka. the continuity of species.
Under the concept of reproduction, we are specifically concerned about the reproductive mechanisms (how they work) occurring in animals, plants, fungi, bacteria and protists.
We need to classify reproductive processes as sexual or asexual on top of how their mechanisms that allow parent(s) producing and passing genetic materials onto their offsprings.
Out of all types of species, NESA wants us to dive into the land of mammals (e.g. reindeer and human) and explore how their reproduction systems work.
We need to understand the process of fertilisation, implantation and hormonal control during reproduction. These stages of reproduction help pass on genetics materials from parent(s) to their offspring.
I am not sure if you are aware but humanity’s scientific knowledge has advanced a lot over the past century.
So, in the last part of this week’s material, we will turn to some real life application examples of humans applying scientific knowledge in genetics and reproduction to create AWESOME variations in plants and animals!
Learning Objective: 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.
Did you not knowing or writing out a definition for the main keyword can cost you a mark in HSC Questions?
Let’s first define reproduction!
Reproduction is the process of creating a new individual or offspring from their parent(s).
Reproduction means to reproduce = new offspring. They MAY or MAY NOT be clones of the parent.
Reproduction can be done via natural or artificial means. Hence, the terms natural and artificial reproduction.
There are two reproductive pathways: sexual and asexual. Some organisms can do both!
Can you? Let’s find out!
What are sexual and asexual reproduction and how do they work?
Sexual reproduction: The process of forming a new organism from the fusion of the offspring’s parents’ (male + female) gametes. Gametes are sex cells such as sperm and egg cells for humans. The offspring that is formed from sexual reproduction has the genetic material that is derived from its parents. However, in almost* all cases the offspring’s genetic material is NOT IDENTICAL to their parents (it’s mixed). In humans and many other mammals such as cows this process of producing gametes is called meiosis.
- *Note that self pollination involves one plant (parent) and is a type of sexual reproduction. This is because the plant can produce both pollen and ovules (male and female plant gametes). These gametes can combine to produce either a genetically identical offspring or genetically different offspring. Whether the offspring is genetically identical or different, it will depend of whether the single parent plant is homozygous or heterozygous for those genes. We will learn about these two terms when you learn about Punnett Square in Week 4’s notes.
Asexual reproduction: Asexual reproduction is the process of forming an offspring (usually a cell) from just ONE parent through cell division. Depending on the cell division process, there may be many names. For example, in humans and many other mammals, this cell division process is called mitosis. Thus, the offspring has genetic materials that is IDENTICAL to that of its single parent – offspring is a CLONE of the parent.
The most important distinguishing factor between sexual and asexual reproduction is whether or not the fusion of gametes occurred. For sexual reproduction, there must be a fusion of gametes whereas, in asexual reproduction, there is no fusion of gametes.
How sexual and asexual reproduction processes allow parents’ genetic information to be passed on to their offspring, and thus, ensuring the continuity of the species?
During reproduction, the parents’ genetic information (DNA) is copied and passed onto the offspring. The offspring’s genetic material is stored in their cells’ nucleus.
There are two types of cells: somatic and non-somatic (sex) cells. Since humans and many other mammals cannot produce offspring via asexual means, all offsprings produced are from non-somatic cells. Hence, only the parents’ genetic material in non-somatic cells’ (or sex cells’) genetic material is passed onto the offspring.
Genetic information is passed onto the next generation (offspring). Thus, ensuring the continuity of the species.
By week 3’s notes, you will see the importance of creating variation in offspring’s genetic information (new allele combinations, increasing variation in the alleles which gametes can inherit as well as variation in the gametes that are fertilised during fertilisation). Don’t worry if you don’t know what genes and alleles are, we will look into their definitions and role in genetics in Week 2. Essentially, the point is that you will see how the increased variation in the offspring’s genotype will enhance the chances of survival of a species’ population and thus supporting the continuity of the species. In Week 4’s notes, you will see how mutation (apart from sexual and asexual reproduction) can also create genetic variation.
A third point is that reproduction would increase the total number of offsprings in a population, effectively increasing population size. Thus, supporting the continuity of species.
What is evolution?
Evolution is the change in living organism’s genetic information, favourable characteristics and phenotypes (appearance or physical traits) over many generations.
For now, just know that genetic information contributes to an organism’s phenotype. In terms of how this works, this will be comprehensively covered in the upcoming weeks.
But what drives evolution aka. the change in genetic information, for example, how a rainbow unicorn population can slowly turn into a pack of green unicorns, over time?
How and where does reproduction fit in Darwin’s Theory of Evolution by Natural Selection?
Darwin’s Theory of Evolution by Natural Selection is a popular and widely accepted modern theory of evolution.
It explains the drivers and consequences of evolution to a reasonable extent.
It, however, fails to account the origins of life on Earth or any place in our universe from start to finish.
There are other models that deals with the origin of life and such as the RNA world hypothesis but they are not complete.
Please keep in mind that these are all theories! Yes, there are evidence to back them up. However, existing evidence is not complete to transform these theories into universal laws!
In order, here are the Stages of Darwin’s Theory of Evolution by Natural Selection:
1. There is genetic variation in population, which affects it phenotype (physical traits). The genetic variation is derived from a number of factors – from internal biological processes to external environmental factors. These factors will be comprehensively covered in later weeks.
2. The majority of the existing population would have the favourable traits that allow them to survive in the environmental conditions (temperature, food supply, predators, etc) that they are exposed to.
3. There is a SUDDEN change in environmental conditions (e.g. new predator introduced to kill the unicorns, sudden large drop in temperature, a virus, etc)
4. Those organisms with favourable characteristics, derived from favourable genes passed on from parents, will survive and those with less or without favourable characteristics will decline in numbers.
5. Those organisms with favourable characteristics will reproduce more successfully and pass on their favourable genetic information to their offspring. REPRODUCTION FITS IN HERE!
6. Over time, the new population will predominately be made up of organisms with favourable characteristics that allow them to tolerate the new environmental conditions.
The environmental agent is refers to the environmental change. This could be a exotic species introduced into the habitat (e.g. from migration) that is competing for the same food resource as the existing population, a new predator, introduction of chemicals into the environment – e.g. toxic wastes being throw into the river, home to thousands of fish..
It is called Darwin’s Theory of Evolution by Natural Selection because there is a sudden change is due to environmental (nature) change(s).
What are favourable characteristics in Darwin’s Theory of Evolution?
How can organisms acquire these awesome characteristics?
Favourable characteristics that allow organisms to survive in their environment can take three forms:
Physical, Physiological and Behavioural.
‘Favourable’ means that these characteristics allow the organism to specifically or better cope with its ambient environment.
As these characteristics are derived from genetic material INHERITED over generations, they are also referred to as adaptations.
For HSC purposes, an organism CANNOT adapt to its environment during its lifetime.
Adaptations are inherited.
Example: A snake cannot learn to seek shade to prevent itself from overheating during its lifetime if it did not inherit such behavioural characteristics from its parents.
However, you will learn later in Module 6 that a mutation can also give rise to adaptation.
The following characteristics or adaptations are evolved through many generations:
Physical characteristics (PHENOTYPE): Large ears to facilitate cooling. This is favourable for organisms living in hot environments.
Physiological characteristics: Kangaroos licking their paws to encourage evaporation and cooling down. Favourable in hot environments.
Behavioural characteristics: Snakes hiding under rocks to avoid the sun. Favourable in hot environments or during the middle of the day.
In Step 1 of Darwin’s Theory of Evolution by Natural Selection, it was mentioned that there is genetic variation in the population. The main sources of variation are:
- Mutation of DNA as a result of environmental factors
- DNA replication error during meiosis
- Independent assortment and random segregation during meiosis
We will go into details of these sources of variation in the later weeks.
For now, just understand where these factors fit in within the areas of evolution and reproduction that we covered so far.
NOTE: It is important to note that asexual reproduction does not introduce genetic variation in offspring while sexual reproduction does. Despite this, the parent of the offspring has favourable characteristics (adaptations) to allow the parent to tolerate the selective pressures of the ambient environment, asexual reproduction allows the parent to produce offspring with IDENTICAL genetic information (no genetic variation) that codes for the same favourable characteristics (e.g. long or short ears depending on environment temperature). The offspring will now have the same favourable characteristics as parent due to inheriting identical genetic information and thus have the same survival rate of parent if they are exposed to same environment with the same resources.
RECAP on what we covered so far,
- Two categories of reproduction that can take place (sexual & asexual)
- Reproduction allows genetic information to be passed on to offspring via heredity, ensuring continuity of species
- Reproduction increases population size thus supporting the continuity of species
- Genetic variation helps increase the population’s overall survival rate and thus support the continuity of species.
- Sexual and asexual reproduction are both useful in supporting the continuity of species despite asexual reproduction not introducing genetic variation in offspring and, thus, population.
- Reproduction plays an important role during Darwin’s Theory of Evolution via Natural Selection
We will now explore the SPECIFIC TYPES OF REPRODUCTION in the sexual and asexual reproduction categories!
This is very eggciting! Get the joke? Sorry, I needed to do it.
Analyse whether the types of reproduction methods are sexual or asexual?
How do they work?
Internal fertilisation vs External Fertilisation
Internal fertilisation involves the fusion of male and female gametes within a parent’s body. Internal fertilisation tends to occur between terrestrial animals.
External fertilisation involves the fusion of male and female gametes outside a parent’s body. External fertilisation tends to occur between aquatic animals.
Parthenogenesis in animals
Parthenogenesis is the process whereby an unfertilised egg develops into an functional offspring. This is a form of asexual reproduction in animals, e.g. bees. For bees, queen bees can produce egg cells (gametes) via meiosis. These egg cells can undergo parthenogenesis to produce haploid drone (male) bees. Haploid cells are cells that have half the amount of chromosome as parent. Chromosomes contain DNA which you will explore in Week 2 notes. Usually parthenogenesis occurs due to the organism’s hardship in having access to mating partners. This is common for organisms residing in harsh or extreme environments. For the most part, the haploid cell develops as it would it would a diploid cell. So, essentially, the gamete undergoes mitosis to develop into a drone bee which will have a diploid chromosome number.
Plants can also undergo parthenogenesis which is called apomixis.
Mechanisms of Cross-Pollination vs Self-Pollination
Cross pollination involves the transfer of pollen, produced by anther (which is part of the plant’s stamen), to the stigma of another plant. This means that cross pollination involves two plants. The pollen grain essentially contain the male gametes of the plant. Bees, wind and water can be transport methods of pollens grain to stigma of another plant for cross pollination. Pollination is referred to the process where the pollen is successfully transfered to the stigma of another plant.
Once the pollen is on the stigma, it can grow a pollen tube which runs down the style of the plant and eventually into the ovary of the plant which produces the ovules which contains female gametes (ovum or ova) of the plant. Fertilisation occurs inside the ovule where the pollen can fertilise the ovule where male gametes are combined with the ovum inside the ovule forming a zygote. The zygote is diploid, i.e. has double the chromosomes of each of the male and female gametes which are both haploid. We will discuss more of diploid and haploid when we explore Mitosis and Meiosis next week.
Note that most pollen grains contain two male gametes. One fertilises the ovum inside the ovule and the other male gamete fertilises two polar nuclei (diploid nucleus) inside the ovule which develops into a endosperm which is a tissue that supply nutrients to the zygote (seed) when it grows.
- Fun fact: This means that the endosperm nucleus is a triploid (contains three sets of homologous chromosomes or three copies of each chromosome). Humans are diploids (we contain two sets of chromosomes, i.e. two copies of each chromosome).
- Note that chromosomes in the homologous sets are not necessarily identical copies as the chromosomes may contain different alleles for the same gene. We will explore more about alleles next week.
This fertilised ovule is called a seed which contains the zygote and will develop into an embryo. In some plants, the surrounding space of the ovule will develop into a fruit. Other plants such as sunflowers do not form fruit, what happens is that the seed will drop from the original sunflower which will develop into another sunflower when the seed germinates under the favourable conditions. The seed will germinate (grow) into a plant via mitosis. In some other flora, the ovary will become a fruit. However, this is not for sunflowers as they do not grow fruits XD.
It is important to note that most plants have its own stigma and stamen. Self-pollination is similar to cross pollination. The difference between self-pollination and cross-pollination is that self-pollination does NOT involve a an external agent such as bees, water and wind as mentioned previously. Instead, the stigma can reshape itself to enclose the stamen. This means that the pollen can be easily transferred onto the stigma.
It is important to note that self pollination causes the resulting flower offspring (after seed germination) to have far less genetic variation than their parents in most cases compared to cross pollination. This is because the resulting flower is only produced from only one parent plant rather than two in cross pollination. If the parent in self-pollination is heterozygous for some genes, the resulting flower may have probabilities of being genetically different to their parents for those genes. We will examine why this is the case when we do Punnett Squares in Week 4 where we learn about homozygous and heterozygous alleles for different genes.
Cross pollination will result in a sunflower offspring that genetically different to its parents. It involves the transfer of pollen from one plant to the stigma of a different plant.
You may have heard of vegetative propagation at school. How does vegetative propagation fit in all of this?
Well, vegetative propagation is a type of asexual reproduction that occurs in plants. It results in the parent producing a plant that is genetically identical. Runners, bulbs, fragmentation are some examples of vegetative propagation. Let’s have a look at them now.
Fragmentation is when the original organism separates a small part of itself. This occurs in starfish where a part of its body can be separated from its parent and the separated section can develop into a new starfish that is genetically identical to parent starfish via cell division.
Fragmentation can also occur in mosses when you split one moss into two. The moss will grow via cell division when it becomes into contact with matter such as moisture in the air.
Strawberry plants can develop runners which are stems extending from the plant and along the soil. At certain points along the runners, nodes can develop which extends to the soil, resulting in the formation of new plant roots at another area of the soil whereby a new strawberry plant can grow. The runner joins the new (and genetically identical) strawberry plant to the parent plant.
Bulbs are bud cells that are found underground. These buds can develop into new plants such as onions. When a new plant forms, the underground bulb provide nutrients to the plant for its survival.
Budding in Fungi
Budding in fungi such as yeast involves the parent cell developing a bud cell, a daughter nucleus. This usually occur when the environmental conditions are favourable for the fungi. Over time, this bud undergoes cell division while still being attached to the parent which may result in a chain of bud cells due to cell division. During cell division, but prior to separation of the protruding bud from the parent yeast (fungi), the parent’s nucleus replicates and divides. One copy of the DNA moves into the bud cell which results in the successful transfer of the parent’s DNA into the daughter (bud) cell. The bud separates from its parent fungus when it grows to a sufficient size to be able support itself independently. This now-separated bud undergoes further cell division to produce more bud cells. The result is yeast that is genetically identical to parent.
Budding is also found in another type of organism called Hydras and the budding process is similar to that of fungi.
Asexual spore production in Fungi
Spores are microscopic reproductive units (cells) that can be formed as a result of mitosis or meiosis.
Spores different to gametes as they do NOT need to combine or be fertilised by another spore to form an offspring.
Mycelium is part of a fungi that branches out into a network structure of fine ‘threads’ called hyphae (plural for hypha). Each hypha have ends of that are capable of producing spores called sporangia (plural for sporangium). These sporangia (and thus spores) are produced when environment conditions are favourable for the fungi’s survival. Mushroom is a type of fungi where the mushroom cap is above the hyphae spread along the stem and to the mushroom cap. The mushroom cap therefore has basida, which are examples of sporangia, that produces spores.
These asexual spores are usually produced when ambient environment conditions are favourable via mitosis. These spores are usually carried by the wind as they are light-weight. These spores then germinates to form genetically identical fungus when environmental conditions are favourable. This typically involves the spores absorbing moisture and decaying organic matter from its environment, allowing the cytoplasm to expand and the fungus developing into a mycelium whereas new spores can be produced.
Sexual spore production in Fungi
Sexual spores are developed when opposite gender hyphae are combined together to develop a sporing-producing structure known as zygospore. The zygospore is diploid as each of the hypha are haploid. Under favourable conditions, the diploid zygospore undergoes meiosis to produce haploid sexual spores which are dispersed into the environment. These spores that are genetically different from their parents.
Under favourable conditions, these spores will germinate and a genetically different fungus to its parents will be formed. These fungi are haploid as most fungi spend their lives as haploid organisms until time of sexual reproduction where hyphae combine to form a diploid zygospore to produce haploid sexual spores.
In some fungus, the mycelium contains hyphae of two genders (male and female). This means that these fungus can produce spores via meiosis and disperse them into the environment.
The term ‘plasmogamy’ refers event where the nucleus of the one hyphae enters the cytoplasm of another hyphae.
The term ‘karyogamy’ refers to the event where the two nucleus are combined into one.
Binary fission in Bacteria
Binary fission is a form of mitosis that is commonly performed by unicellular organisms such as bacteria. The process starts with the copying the genetic material (in the form of bacterial chromosomes) of the parent cell. Each chromosome moves to each side of the cell. This is followed by the elongation of the cell and cytokinesis which is the splitting of the cell membrane and cytoplasm of the cell into two daughter cells. As there is no cell nucleus in bacteria, there will not be the splitting of cell nucleus. It is important to note that the parent cell won’t exist at the end because it is now part of the two daughter cells. The two daughter cells are genetically identical to each other as well as identical to the parent which they obtained their genetic information came from.
NOTE: There are multicellular organism that reproduce asexually via binary fission. However, they are uncommon. Some example of this is the organism named Trichoplax.
Budding in Protists
Budding in protists is a type of fission (cell division) called multiple fission. In short, budding in protists starts off by the parent protozoan producing a bud which is a daughter nucleus that is created based on the separation of the parent protozoan’s cytoplasm (one fission). Over time, this daughter nucleus undergoes further fission (internal cell division – mitosis) to grow and mature, resulting in a protists that is genetically ideal to parent.
Binary fission in Protists
The mechanism of binary fission in protist is similar to that of bacteria’s binary fission process. However, as DNA is stored in the nucleus (whereas no nucleus in bacteria), the chromosome will move to each side of the nucleus before the splitting of the nucleus and eventually splitting of the cell membrane and cytoplasm into two daughter cells. The splitting of the parent cell into two daughter cells is called cytokinesis.
NOTE: Binary fission in protist vs bacteria and budding in protist vs fungi are similar. So, it is important to determine the unique characteristics fungi and protist.
- Protists are mostly unicellular whereas fungi are mostly multicellular.
- Fungi also have hypha.
- Protists are microscopic whereas fungi are macroscopic.
- Protists are eukaryotes whereas bacteria are prokaryotes.
Advantages and disadvantages of internal and external fertilisation
• Internal fertilisation occurs inside the female’s body which means that the zygote is protected from the external environment of the parent. This means there are less environmental factors that affect the zygote in internal fertilisation compared to external fertilisation. This increases the survival of the zygote.
• Internal fertilisation is NOT restricted to terrestrial environments unlike external fertilisation which is restricted to aquatic environments only.
• Internal fertilisation has higher fertilisation success rate on a per gamete basis compared to external fertilisation. This is because the sperm does not need to travel by chance to fertilise an egg. Internal fertilisation provides the sperm a direct route towards to egg cell inside the female’s body. During such journey, the sperm cell is subjected to less variable and/or violet environment factors such as strong current or predators.
• Internal fertilisation typically have less mating partner options than external fertilisation. This can lead to a lower genetic variation in species population as the mating process is more selective than external fertilisation
• Internal fertilisation generally required more energy in search for a mating partner and perform the mating process which are unnecessary in external fertilisation.
• Less gametes are produced via internal fertilisation compared to external fertilisation. This leads to a lower overall amount of offsprings produced. Arguably, this means that internal fertilisation may low the chance of the continuity of a species (if we assume that genetic variation is controlled for both internal and external fertilisation, i.e. genetic variation is the same for both external and internal fertilisation).
• Greater quantity of gametes are produced via external fertilisation compared to internal fertilisation. This leads to a greater overall amount of offsprings produced. Arguably, this could supports the continuity of species more than internal fertilisation.
• External fertilisation can give raise to more mating partner options than internal fertilisation. This can lead to greater genetic variation in species population as the mating process is less selective than internal fertilisation.
• Upon fertilisation, the zygote is exposed to the environment rather than protected inside the mother’s body for internal fertilisation. Due to the limited defence capabilities of the zygote (e.g. against predators), it is more susceptible to death than zygotes found via internal fertilisation. Most of the gametes are being attacked by predators or fail to be fertilised. The zygote therefore has a lower chance of survival via external fertilisation.
External fertilisation is restricted to aquatic environments. The flagellum component of the sperm cell allows it to move through water that otherwise would not be possible on land. If performed on land, the egg will dry out.
External fertilisation has a lower fertilisation success rate than internal fertilisation. This is because the sperm and egg cells are subjected to greater amount of factors in external fertilisation than internal fertilisation. For example, the more environmental factors such as predators (Sea life) and harsh aquatic environment conditions (e.g. harsh currents).
Example of a case of external fertilisation (Sea urchin):
Male and female sea urchins produce gametes which are dispersed in the ocean.
Male salmon produce gametes (Sperm) to fertilise a nest of eggs that is produced by female salmon somewhere in the ocean.
Extra Notes on sexual and asexual reproduction
Now that we have explored asexual and sexual reproduction with examples, let’s see what they involve beyond differences between number of parents involved and genetic variation in offspring that we have mentioned at the beginning of this notes.
Here are some extra notes between sexual and asexual reproduction:
Sexual reproduction requires more energy than asexual reproduction.
However, asexual reproduction tends to occur at a faster rate than sexual reproduction.
Genetic variation is created in sexual reproduction and NOT in asexual reproduction.
Genetic variation increases the likelihood of the continuity and evolution of the species – relating back to inquiry question.
Asexual reproduction would also be a concern if the parent genes code an unfavourable trait because there is no other source of genes from another parent to override it.
This problem is reduced in sexual reproduction as the offspring’s genome is a mix of both parents (rather than single parent) and unfavourable trait could be overridden.
More details about overriding genes in later weeks. It is based on concepts of dominant and recessive genes.
Asexual reproduction generally ONLY take place because the ambient environment conditions are favourable as asexual reproduction does not increase variability in genetic materials.
An asexual offspring is a clone of its parent. If one clone is affected, the whole cloned population have equally as great of a danger for extinction.
Well done! we have broadly covered reproduction processes for a range of organisms. We will now examine reproduction for mammals specifically!
Learning Objective: Analyse the features of fertilisation, implantation and hormonal control of pregnancy and birth in mammals
- Requires gametes (sperm and egg) meet and combine to form a zygote
- Gametogenesis is the name of the gamete formation process.
- Gametogenesis can be divided into spermatogenesis (producing sperm) and oogenesis (formation of matured egg cells)
- The hormone testosterone is produced in cells’ in the testes organ of male as part of spermatogenesis as it plays a role in producing sperm cells.
- The hormone oestrogen in males help with the maturing of the sperm cells in males.
- The fertilisation process and fusion of gametes occurs in the fallopian tube of female’s body
- The zygote will develop into a living organism that has mixed genetic information from the parents.
- Zygote is the continuity of a species (relating back to inquiry question)
- Fertilisation involved multiple stages that MUST be fulfilled for successful fertilisation and zygote formation and thus producing a new offspring.
- Three necessary stages for successful fertilisation are:
- Formation and maturation of gametes
- Spermatozoa must journey into the oviduct
- Spermatozoa must make contact and fuse with the egg cells.
- The gametes fuse with one purpose – to form a zygote, single cell with 46 chromosomes
- During fusion, the head of the sperm cell detaches from its tail (flagellum) and the sperm-egg species journeys down the female’s uterus.
- Also, during fusion, the sperm cell activates the egg cell resulting in cell division of the egg cell growth/development. The resulting product is called a blastocyst.
- Once the sperm fused with the egg, other sperms will no longer be able to fuse with the same egg
- Fertilisation takes approximately 90 days when performed outside the female’s body (external fertilisation). This is our estimation of internal fertilisation.
- Most of our contemporary knowledge of fertilisation in mammals comes from laboratory testing with mice gametes.
- The gametes must be from the same species in other for successful fertilisation.
- Implantation is the process of adhering the fertilised egg to stick to the walls of the reproductive tract, providing the most suitable environment for zygote development.
- It is a crucial phase for successful pregnancy.
- The blastocyst is implanted on the walls of the reproductive tract (uterine wall).
- Successfully implantation means pregnancy.
- This implantation process onto the walls establishes blastocyst’s access to nutrients to develop into an embryo (blood vessels surrounding the blastocyst carries blood which has dissolved nutrients)
- Embyro develops into a fetus (approx 5-11 weeks)
- Embryro becomes a new organism upon release from female’s body.
Below is a diagram showcasing the steps of fertilisation and implantation:
The idea of the diagram is just to allow you have a rough idea of where fertilisation and implantation occurs in the female’s body. The steps in the diagram not as important.
Note, at ovulation stage, the matured egg cell is released from the follicle and travels up and along the fallopian tube (the C-shaped tube as shown in diagram below) that connects the ovary to the uterus. It at the uterus where the embryo is implanted on the uterus wall (endometrium) during implantation phase.
Successful implantation of the embryo means successful pregnancy.
Note that: When the sperm enters the vagina, up to the uterus, along and down the fallopian tube where it can combine and fertilise the mature egg. This means that the mature egg and sperm encounter each other head-on as the egg is moving in the direction from ovary to uterus and sperm is moving in the direction of uterus to ovary.
This means that they are likely to meet at the fallopian tube, which is where fertilisation of the mature egg cell most commonly takes place in reality.
In the diagram below, we see that the zygote (fertilised egg) is formed in the fallopian tube where the sperm meets and fertilises the egg.
Diagram for the delivery of offspring
Fetus moves from uterus (womb) and then through cervix and then out through vagina.
(Download hormonal control diagram as PDF below)
Extra notes on hormonal control during pregnancy and birth
Other roles of progesterone during pregnancy.
- Encourage the growth of blood vessels, allowing greater volumes of blood and thus nutrients surrounding the embryo.
- Help develop and maintain the lining of the placenta.
- Strengthening muscles of pelvic floor which support the delivery of offspring via the uterus then cervix and then through the vagina.
- Oxytocin hormones are released stimulate uterine muscles to increase the strength and frequency of dilation and contraction of the cervix. This allows the parent to deliver the offspring by pushing out placenta. The hypothalamus produces oxytocin and stores it in the pituitary gland, situated below the hypothalamus. Upon stimulation of hypothalamus’s neurone cells, the pituitary gland will secrete oxytocin into the bloodstream.
- Endorphin hormones are released to increase concentration and relief pain to focus on the delivery of offspring. The levels of endorphin peaks as the strength and frequency of cervix dilations and contractions increase to combat pain.
- Adrenaline hormones are released during giving birth. This is due to the body’s response to fear and pain. Adrenaline provides energy for the parent to continue delivering the offspring by producing stronger dilation and contractions of the cervix. However, adrenaline may also cause the opposite response which is decreasing cervix contractions due to fear.
Learning Objective: Evaluate the impact of scientific knowledge on the manipulation of plant and animal reproduction in agriculture
Advancement in scientific knowledge provided humanity the knowledge that genes play an important role in the process of protein-synthesis.
The protein that is formed during protein-synthesis will determine an organism’s characteristics. Not just structural characteristics (phenotype) but also physiological and behavioural characteristics!
With this knowledge, scientists uses various technologies and methodologies to alter an organism’s gene sequence.
As a result, the modified organism’s offspring would have the favourable traits that was manipulated by the scientists.
The following methodologies are used to manipulate the reproduction processes of plants and animals in the agriculture industry:
- Artificial insemination
- Artificial pollination
- In-vitro Fertilisation
It involves a male sperm cell being inserted into a female’s reproductive tract.
The fusion of the sperm and egg cell results in fertilisation of the egg cell, producing of zygote.
Hence, artificial insemination is a form of sexual reproduction (involves gametes).
Artificial insemination is primarily used to produce offsprings with favourable characteristics, mix of both male and female parents.
Artificial insemination is a form of selective breeding because it allows the sperm cell of a selected male to fertilise the egg cell of a selected female. Usually, both the male and female parents have favourable characteristics that an offspring would combine.
Other benefits of artificial insemination involves minimising the costs of transporting animals from one country to another in order to be crossed over.
This is because the sperm cell of a selected male can be frozen and transported to another country, ready to be fused with a selected female’s egg cell.
Mass artificial insemination will reduce genetic variation.
This is because one selected male’s sperm cells can be used to inseminate many female egg cells. OR
A selected female’s egg cell fusing with a selected male’s sperm cell.
Imagine producing offsprings from the same selected male and female over and over again.
The majority of the population’s would be genetically identical – having same mixed genes of the selected male and female parent.
Thus, mass artificial insemination reduces the number of offsprings produced by random breeding (speaking from a total population’s genetic variation perspective).
Artificial Pollination involves the manual transfer of pollens into stigma of another plant to combine with the egg cell (ovule) of the plant. This type of reproductive technology was used by the well-known scientist and monk, Gregor Mendel in his pea plants experiments – which helped create modern laws of genetic inheritance.
We will talk more about Gregor Mendel in later weeks.
Anyways, successful transfer results in pollination and fertilisation of the egg cell, producing a seed.
Each of these seeds will develop into an offspring, a new plant.
Artificial pollination is used to produce offsprings with favourable characteristics, that are the mix of the two plants. Since these two parent plants were selected and made to breed with each other, artificial pollination is therefore a form of selective breeding.
Example: Producing plant offsprings that have both purple and red flower colours – combined characteristics of the two plants
Artificial pollination is cost effective way of producing new plant variations with relative ease. This is because artificial pollination can be performed manually. No fancy technology required.
Artificial pollination is a form of sexual reproduction.
Mass artificial pollination would reduce genetic diversity. This is because if artificial pollination is used to produce a million plants, the majority of the plant population will be genetically identical. Similar concept to artificial insemination.
Cloning is a type of asexual reproduction used to create offsprings that are genetically identical to the parent.
Some farmers may want their crops to be genetically identical because they have the favourable traits.
Example: Maybe a flower with a really pretty yellow colour. Many genetically identical flowers can be produced via cloning. Remember earlier, genes determine phenotype (physical traits e.g. colour)
For plant cloning, it involves cutting a section of the mother plant’s which contains at least one stem cell. The cutting is then planted in the same environment as the mother plant to allow the cutting to develop the same characteristics as the mother plant, producing the same yield with the same harvest time.
Since clones are genetically identical, mass cloning activities would make the entire cloned population susceptible to an entire wipeout.
Example: a deadly virus (environmental agent) that the cloned population has no resistance to.
Please note that, although artificial insemination and artificial pollination are forms of sexual reproduction, if the majority of offsprings are genetically identical, they are equally susceptible for a major wipeout.
Hence, all forms of mass selective breeding is equally risky if consequences are not evaluated.
The cloning of plants have been used for tens of centuries but the cloning animals is more complex and less understood.
Dolly the Sheep (cute sheep clone example)
In 1988, Dolly the Sheep is an offspring that was a clone offspring. Dolly was successfully cloned using a sheep’s (sheep A) mammary gland (a group of somatic/body cells).
The scientists then removed the nucleus (therefore DNA) of another sheep’s (sheep B) egg cell and inserted the nucleus of the somatic cell from the mother sheep into the egg cell.
The egg cell undergoes cell growth and development inside a foster mother sheep (sheep C) to produce Dolly the Sheep.
Dolly the Sheep has the same genetic information as Sheep A (inherited Sheep A’s genetic information) and thus is a clone of Sheep A.
However, Dolly the Sheep died earlier than scientists’ expectation. :'(
This led to questions relating to health and ethical problems of cloning.
Also, should we clone humans? Is it a smart thing to do?
We will explore ethics on artificial reproductive methods with greater details in the later weeks.
In Vitro Fertilisation
In vitro fertilisation (IVF) is a reproductive technique used for increasing the likelihood of developing offspring when couples have fertility problems but wishes to have their children.
As females are born with a lifetime limited supply of oocytes, their age may be a cause of infertility.
For males, abnormalities in their sperm cells’ ability to fertilise mature eggs may be their cause in infertility. Some males not be able to produce sufficient quantities of sperm cells required to fertilise egg cells which means the rate of fertilisation (and thus zygote formation) is low.
Firstly, IVF processes involves a stage known as a ovulation hyperstimulation where multiple matured egg cells or oocytes are produced. If you recall from the natural female menstrual cycle, only one mature oocyte is produced. Hyperstimulation is possible when the female takes the supplied fertility drugs such as those containing FSH (Follicle-stimulating hormone) or GnRH hormones as mentioned in the hormonal cycle.
Following ovaulation hyperovulation, IVF involves removing good quality, mature these oocytes from the female’s ovaries. These egg cells are then placed in a petri dish to be fertilised with sperm cells. The petri dish is then placed inside a incubator for cultivation where conditions are optimised for the enhance the probability of the zygote developing into an embryo and eventually blastocyst. About three days later, those zygote that successfully developed into a blastocyst are transferred into the women’s uterus (womb).
The female is later tested for successfully pregnancy which depends on the number of embryo that is transferred to the woman’s uterus (womb). Of course, there is a limit. Left out good quality embryos can be frozen and stored. The female’s age is also another factor in determining the success rate of successful pregnancy.
Notice that by using IVF, more egg cells are fertilised with sperm cells than without IVF. This will increase the chance of couples with fertility problems in producing their children. IVF can bypass the fertility issues of many couples rendering them having a low probability in producing an offspring.
There are many ethical issues surrounding in vitro fertilisation. The mother of the offspring can be of an old age (over the age of 70) when her children is born. In these cases, the mother may not be able to support their children and their children may lose their mother before they hit their teenage years. For such reasons, many governments have banned the use of in vitro fertilisation techniques for women over a certain age.
Week 1 – HSC Biology Syllabus Lecture Video – Reproduction
[Video will be uploaded HERE SOON!]
Week 1 Homework Set (Essential for Band 5)
Question 1: Distinguish between sexual reproduction and asexual reproduction [4 marks]
Question 2: Describe how reproduction fits into Darwin’s Theory of Evolution by Natural Selection [6 marks]
Question 3: Explain the process of hormonal control before and during pregnancy of mammals [6 marks]
Question 4: Explain how the continuity of a species is achieved and maintained [4 marks]
Question 5: Define the term ‘environmental agent’ and provide an example [2 marks]
Question 6: Define the term ‘adaptation’ [1 mark]
Question 7: Explain how an organism derives its favourable characteristics [3 marks]
Question 8: Describe the difference between structural, physiological and behavioural adaptations [6 marks]
Question 9: Describe how fungi asexually and sexually reproduce [6 marks]
Question 10: Outline the process of binary fission [3 marks]
True or False:
Artificial reproduction belongs to the sexual reproduction category. (T/F)
Genetic variation tends to increase the probability of the continuity of a species. (T/F)
Curveball Questions (Moving from Band 5 to Band 6!)
Curveball Question 1: Explain in what scenarios will artificial reproduction methods increase and decrease genetic variation in a population of rainbow unicorns (4 marks)
Curveball Question 2: Explain the implications of how adaptations can only be passed down via heredity on evolution (4 marks)
Curveball Question 3: Suppose there is a large population of white and brown rabbits living on a heavy snowy mountain. A hungry rabbit hunter wandered into this juicy hunting environment O_O’. Explain what will happen to the size of the brown and white rabbit population over time? (8 marks)
Solutions to Week 1 Homework Set
Solution to Question 1:
Sexual reproduction, such as meiosis, is the process of forming a new organism from the fusion of the offspring’s parents’ gametes. Comparatively, asexual reproduction, such as mitosis, is the process of producing an offspring from just one parent through cell division or mitosis.
The offspring as a result of sexual reproduction does not have genetic material that is identical to its parents. The offspring from asexual reproduction is a clone of its parent, meaning it has the same allele combinations as its parent.
- 1 mark = Define sexual reproduction
- 1 mark = Define asexual reproduction
- 1 marks = A factor that distinguish between asexual and sexual reproduction (genetic variation, number of parents, mitosis vs meiosis, performed using germ cell verses somatic cell, etc)
- 1 mark = Provide an example of sexual and asexual reproduction.
Solution to Question 2:
Darwin’s Theory of Evolution by Natural Selection states that new selective pressures introduced in an environment will alter a species’ population based on the species’s favourable characteristics which is derived from their genetic information. Those species with favourable characteristics to tolerate the the new conditions will survive and reproduce more successfully than those without.
Part of Darwin’s Theory of Evolution states that genetic variation is present in a population. Reproduction processes such as meiosis can be used to explain the origin of such variation. More specifically, during meiosis, the processes of independent assortment, crossing over, random segregation, mismatch of nitrogenous bases during DNA replication as well as the random fusion of gametes contribute towards the genetic variation in a species’s population.
Secondly, the mechanisms of meiosis allows parents’ DNA, coding for favourable characteristics, to be passed on to their offsprings. Those species with favourable characteristics for the new environment will survive and reproduce more successfully than those without. This is critical in Darwin’s Theory to explain the shift in a population’s dominant characteristics over time due to selective pressures.
- 1 mark = Definition of Darwin’s Theory of Evolution
- 1 mark = Relating reproduction variation in Darwin’s Theory
- 1 mark = Explaining how variation occurs during reproduction (crossing over, independent assortment, etc)
- 1 mark = Relating reproduction to allow genetic materials to be passed onto offspring
- 1 mark = Relating to how an offspring’s favourable characteristics will allow it to survive and reproduce more successfully.
- 1 mark = Relating how the passion on of genetic material from parents to offspring permits the change in a population’s adaptations outlook over time.
Solution to Question 3:
Prior to fertilisation, as per normal menstrual cycle to prepare for pregnancy, Gondadotrophin-releasing hormone (GnRH) is secreted in response to low levels of progesterone and oestrogen from the hypothalamus to stimulate the pituitary gland. This results in the pituitary gland to release follicle stimulating hormones (FSH) and luteinising hormones (LH) to encourage follicle (and its containing oocytes) to develop inside the ovaries. As follicles mature, they secrete oestrogen into the blood stream which releases in a spike in LH level. This spike in LH level will result in ovulation where the matured egg is released from the developed follicle. The empty follicle will collapse to form the corpus lute which further secretes oestrogen and progesterone, preventing any further production of FSH of LH.
The mature egg will migrate to the ovary’s surface and eventually into the fallopian tube where it will be moved by cilia along the tube and into the uterus. It is in the fallopian tube whereby the sperm may encounter, interact and fertilise the matured egg. Once the cilia moves the matured egg cell into the uterus, it will be implanted onto the uterus walls (endometrium).
Upon successful implantation, it will encourage the corpus luteum to secrete more oestrogen and progesterone. LH will also be produced by the pituitary gland which will encourage further progesterone production from the corpus luteum resulting in a spike progesterone level. The oestrogen will help develop the placenta. The embryo will also produce HCG to sustain the corpus luteum which is the reason why human chorionic gonadotropin (HCG) levels are high when tested for pregnancy.
The progesterone will stimulate the glands in the endometrium which secretes mucus to thicken the uterus lining until placenta forms. Other nourishing substances secreted by the glands will help sustain the embryo by supplying it with oxygen and nutrients.
About three months in, the placenta takes over the hormone secretion role of the corpus luteum where the secretion of progesterone and oestrogen will decreases towards birth of offspring. Progesterone suppresses urinal activities to reduce disturbance that may otherwise affect the development of embryo into foetus.
However, during this time, the placenta will provide the pathway in which carbon dioxide and urea can be eliminated from the foetus into the endometrium via diffusion and secreted out of the mother’s body. The placenta also supplies the blood (oxygen and nutrient) required by the foetus to sustain pregnancy.
- 6 mark = Role of GnRH, FSH, oestrogen, progesterone, luteinising hormone, placenta, corpus luteum before and during pregnancy.
- 2 marks = Explain how these hormone are secreted and changes in their levels before and during pregnancy.
Solution to Question 4:
The continuity of a species refer to how a species can reproduce offsprings that are favourable to the ambient environment and avoid extinction in general. This can be explained by how the processes of crossing over, random segregation, independent assortment increases the genetic variation of offsprings in a population whenever meiosis occurs. This increase in genetic variation means that there are more allele combinations and, thus, more unique adaptations. A population of species with more unique adaptations would mean greater chance of a characteristics that would be favourable in tolerating changes in environmental conditions. Thus, the increase in genetic variation would reduce the probability of mass extinction and ‘ensures’ (supports) the continuity of a species.
- 1 mark = Define continuity of species
- 1 mark = Describe how genetic variation may occur
- 2 marks = Explain how genetic variation supports continuity of species
Solution to Question 5:
An environmental agent is a selective pressure in the ambient environment for a population of species. This environment agent determine the favourable characteristics in a population.
An example of an environment agent can be a predator (e.g. Leopard) for a rabbit population.
- 1 mark = Define environmental agent
- 1 mark = Appropriate example of an environmental agent
Solution to Question 6:
Adaptation are the inherited favourable characteristics of an offspring from its parent(s). These characteristics may be physical (Structural), physiological or behavioural.
- 1 mark = correctly definition of adaptation
Solution to Question 7:
Favourable characteristics are adaptations that allow an organism to effectively tolerate the selective pressures in its ambient environment. an organism’s adaptations are inherited from its parent(s) via asexual or sexual reproduction. During reproduction, the parents’ genetic materials, coding for adaptations, are passed onto the offspring.
- 1 mark = Define favourable characteristics (adaptation)
- 1 mark = Show understanding that adaptations can only be inherited
- 1 mark = Describe how adaptation and genetic information are related
Solution to Question 8:
Structural adaptations refer to physical characteristics of an offspring. An example of this may include the long ears of Red Kangaroos that aid cooling. (You will learn more about this in later modules)
Physiological adaptations refer to the biochemical processes that an organism is able to perform to allow it to tolerate its ambient environment’s selective pressures. An example of this is how echidna can decrease its heart rate to reduce the oxygen it consumes per minute when they are swimming to escape floods.
Behavioural adaptations refer to how an organism moves to respond to a threat, need or any other event to ensure the continuity of the species. An example of a behavioural adaptation is how snakes seek shade (e.g. under rocks) during a hot summer day to prevent overheating so enzymes do not denature.
- 2 marks = Define structural adaptation and provide example
- 2 marks = Define physiological adaptatation and provide example
- 2 marks = Define behavioural adaptation and provide example
Solution to Question 9:
Fungi can give reproduce offspring by creating asexual spores. A spore is a microscopic reproductive unit that can give rise to an offspring (fungus), provided that the ambient environmental conditions are favourable.
Moreover, a fungi can give reproduce sexually via sexual spores. In this reproductive pathway, the fungi produces genetically different fungi cells called hyphas which fuse together to give rise to sexual spores. Each of these sexual spores can develop into a fungus by itself.
- 1 mark = Recognise that fungi can produce sexual and asexual spores
- 1 mark = Recognise how both sexual and asexual spores can develop into a fungus offspring
- 1 mark = Explain what is mention by sexual and asexual spores
- 1 mark = Describe how sexual spores are formed.
Solution to Question 10:
Binary fission is an example of an asexual reproduction process. First, the somatic cell’s genetic material is duplicated which is then followed by the separation of the somatic cell into two daughter cells. The two daughter cells are clones of the parent somatic cell, that is, they both have identical genetic information as their parent.
- 1 mark = Define Binary Fission
- 2 mark = Genetic material replicates followed by cell division to produce two daughter cells that are clones of parent.
Answer to True/False Question #2: True.
Solution to Curveball Questions
Solution to Curveball Question 1:
Artificial insemination involves the fertilisation of an egg with a sperm cell. This is performed to reproduce an offspring with favourable characteristics of both parents. While artificial insemination can be used to create new allele combinations (and thus variation) by crossing over animals of the same species that are geographically separated, it can also lead to a decrease in genetic variation. Mass artificial insemination activities will lead to the same favourable offspring by crossing over the same male and female over and over again. Over time, the genetic variation in the species’s population will decrease as most of the species have the same adaptations.
Cloning is another artificial reproduction method that involves the production of genetically identical species. This will always decrease genetic variation as the offspring are genetically identical to its parent. This is because no new allele combinations are created.
- 2 marks = Describe how artificial insemination can increase and decrease a population’s genetic variation
- 2 marks = Describe how cloning decreases a population’s genetic variation.
Solution to Curveball Question 2:
As an offspring’s adaptations can only be inherited from its parent(s), this would mean that an organism cannot adapt to its environment’s selective pressures during its lifetime. For example, a fully-grown giraffe with a short neck cannot grow its neck over time to reach the leaves that it so want to have on taller trees. According to Darwin’s Theory of Evolution by Natural Selection, this would mean that organisms that inherit favourable characteristics will reproduce more successfully and predominate the population over time. The organisms without such favourable characteristics will decrease in quantity or may face the risk of extinction.
- 1 mark = Recognise that organism cannot develop adaptations during its lifetime
- 2 marks = Implications of heredity of genetic information
- 1 mark = Relating implications to Darwin’s Theory
Solution to Curveball Question 3:
The change in the population of white and brown rabbits over time can be predicted using Darwin’s Theory of Evolution by Natural Selection.
Darwin’s Theory of Evolution states the following:
1. In a population, there is genetic variation.
2. There is a sudden change in ambient environmental condition.
3. The organisms with the favourable characteristics to tolerate such change will reproduce more successfully and pass on their favourable characteristics to their offsprings.
4. Over many generations of reproduction, the population will predominately made up of the offsprings with favourable characteristics.
Applying the four steps of Darwin’s Theory to this case of brown and white rabbits, the two different coloured rabbits indicate that there is genetic variation in the population due to different allele combination. The sudden change in ambient environment is the introduction of the rabbit hunter who is hunting the rabbits. The white rabbits have greater survival chances compared to the brown rabbits due to its favourable white appearance. This is because the snowy mountain’s white background provides camouflage benefits for the white rabbit and not for the brown rabbits. According to Darwin’s Theory, this would mean that the white rabbits will survive and reproduce more successfully than the brown rabbits population. Over time, the white rabbits pass on its favourable characteristic (white colour) to its offspring and dominate the rabbit population.
- 4 marks = One mark for each of Darwin’s Theory of Evolution
- 4 marks = Apply each step of Darwin’s Theory of Evolution to the rabbit population.
Week 1 Extension Questions
*Extension Questions will be constantly uploaded throughout the 2019 HSC. The upload frequency for extensin questions will increase when the notes for all four modules are complete before the end of term 1.
Extension Question #1: Discuss the ethical issues that may arise when using employing reproductive technologies in supporting the continuity of species?