Year 12 bio notes

Year 12 bio notes 

Reproduction 

Inquiry question: How does reproduction ensure the continuity of a species? 

Students: 

● 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 

External fertilisation: usually occurs in aquatic environments as both eggs and sperm are released into the water - assists in preventing the gametes from drying out and increases mobility 

• Known as SPAWNING which results in a greater mixture of genes for higher genetic diversity and greater chance of survival in hostile environment 

Textbook example: Staghorn coral 

• Example of colony of invertebrate marine animals (polyps) that achieve fertilisation by excreting millions of gametes into the sea 

• When polyps in one coral colony start to spawn, PHEROMONES are released from gametes and stimulate other nearby individuals to spawn too - spreading over a wide area!

– plants: asexual and sexual reproduction 

Parthenogenesis = ‘virgin birth’ - form of asexual reproduction 

• Offspring develop from the female gamete without the prior fertilisation from a male gamete 

• Common in invertebrates (without backbone) such as worms, but rare amongst higher invertebrates (with backbone) > exceptions include the hammerhead shark

– fungi: budding, spores 

– bacteria: binary fission

– protists: binary fission, budding 

– fungi: budding, spores	– bacteria: binary fission	– protists: binary fission, budding
Fungi are eukaryotic and can reproduce asexually  Fungi includes species like mould, mildew, mushrooms, and yeasts  Yeast = unicellular  Mould & mushrooms = multicellular  Small outgrowth forms, DNA replicates, nucleus divides, one copy moves into daughter cell bud, bud detaches itself from parent (chain of buds can form)	Bacteria are unicellular prokaryotic organisms  Binary fission means ‘splitting into two’ Binary fission is the main method of asexual reproduction in unicellular organisms such bacteria (prokaryotes)	Protists are eukaryotic organisms, most are aquatic e.g algae, paramecium, euglena, amoeba  Binary fission is the main method of asexual reproduction in protists (unicellular eukaryotes) Binary fission in Amoeba: During unfavourable environmental conditions, the amoeba may form a cyst and then divide by multiple fissions in the cyst - forms identical cells to be released when favourable conditions return
Spores are unicellular reproductive cells that are produced by fungi  Spores allow fungi to expand their distribution and colonise to new environments  Spores may be transferred by either floating on the wind, or by sticking to an animal		Budding is when adult organism gives rise to a small bud, resulting in the separation of the two individuals

BINARY FISSION = single chromosome in cell copies itself and forms two genetically identical copies of DNA, the cell enlarges, cell then divides into two new daughter cells through PROCESS OF MITOSIS

• Multiple fissions can occur, resulting in the production of more individuals in each reproduction cycle 

Steps of binary fission:

1. The cell elongates and builds more cell wall 

2. The origin of replication in the bacterial chromosome opens and DNA replications begins

3. The duplicate DNA will begin to separate and move towards the poles as the cell elongates further, attaching to the opposite ends of the cell membrane  

4. ‘Cleavage furrows’ begin to develop on each side of the cell, gradually splitting the cell 

5. The cell pinches into two, resulting in two identical daughter cells - such as bacteria!  

Summary of genetic variation in bacteria - 

- analyse the features of fertilisation, implantation and hormonal control of pregnancy and birth in mammals

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Gametogenesis - the production of male and female gametes in ‘gonads’ 

• Haploid gametes are produced by meiosis in the germline tissue within the testes/ovaries

Fertilisation - 

Fertilisation = fusion of the sperm nucleus (haploid) and the ovum nucleus (haploid) > gametes come together to form a ZYGOTE cell (diploid) 

Process of fertilisation: (sperm attaching to egg)

1. Sperm attract to the egg by ‘rheotaxis’ - movement through a fluid

2. Oviducts secrete a fluid that travels down female reproductive tract and sperm will swim upstream (positive rheotaxis)

3. The sperm that reach the oviduct are held in storage and are released in small batches 

4. Sperm become hypermobile and use tails to propel them towards egg (maturation assisted by presence of progesterone and alkaline pH)

5. When sperm cells reach the egg cell, they must cross the three layers > they must physically push through the first membrane which still has follicle cells attached 

6. The protective cells release enzymes to assist penetration by the sperm 

7. When the acrosome (protective cap) of a sperm comes into contact with glycoproteins of the next barrier ‘ZONA PELLUCIDA’ - the acrosome fuses with the cell membrane of the sperm head, allowing the tip of the sperm to release digestive enzymes that assist its penetration 

8. Surface proteins allow only the first sperm to penetrate through the third barrier (PLASMA MEMBRANE) as many sperms may have passed through the first two barriers successfully

9. Once the first sperm passes through the last barriers, this triggers the release of enzymes by the egg that destroy glycoproteins in the ZONA PELLUCIDA and cause electrical charges that prevent the other sperm from entering 

10. First sperm to penetrate the inner barrier causes the ovum to immediately undergo its second meiotic division 

11. The haploid nucleus of the sperm and ovum will form a diploid (zygote)

12. Zygote will divide by mitosis, travelling down the oviduct and to the uterus as it begins developing into an embryo 

Implantation - (day 1-7)

Once the embryo implants into the uterine wall - this marks the beginning of pregnancy 

1. Maturing follicle ruptures (monthly) and is released from ovary, becomes ovum - released into fallopian tube

2. Zygote forms by union of ovum and sperm cell during fertilisation (day 1)

3. Cell division occurs whilst zygote moves through fallopian tube (day 2)

4. Becomes morula - NO cell differentiation/specialisation occurring (day 3-4)

5. Blastocyst enters uterus - development of inner and outer cell mass (day 4-7)

6. Implantation of the blastocyst into uterine wall > eventually becomes embryo (day 7)

After implantation (day 9-25) 

7. Once the blastocyst implants in the endometrium, it must move through that outer uterine epithelium of the endometrium on day 9 (where implantation has occurred)

8. Blastocyst starts to release digestive enzymes which break down the cellular matrix between cells of the epithelium 

9. Complete intrusion/implantation occurs when blastocyst has embedded in the uterine wall > further development will occur such as development into gastrula etc. 

10. Significant embryonic development occurs - with continued differentiation and specialisation occurring, increased maternal blood flow/vascularisation, formation of the umbilical cord 

• the corpus luteum in the ovary continues to grow and secrete hormones for the first three months of pregnancy 

• In the latter six months of pregnancy, the corpus luteum shrinks and degenerates slowly

• Hormones that maintain pregnancy are secreted by the pituitary gland and ovaries of the mother, but once the placenta is established, it will take over the role of producing hormones to maintain pregnancy 

• Levels of oestrogen and progesterone are optimised during the ovulation cycle to create ideal conditions for implantation 

After the joining of the ovum and sperm nucleus into a zygote - 

• once the zygote reaches 12-16 cells (3-4 days post-fertilisation), it will undergo MITOSIS to form a solid ball of cells called a morula  

• Then it will form a blastocyst as the morula continues to divide, undergoing differentiation and cavitation

Blastocyst: cell differentiation of cells has occurred - formation of embryo and placenta  

• Blastocyst will continue down the fallopian tube - three distinct sections: 

Trophoblast = surrounding outer layer > will become placenta

Blastocoele = fluid filled cavity 

Inner cell mass = mass of cells > will become embryo

Implantation of the blastocyst: (6-8 days) 

• The digestive enzymes are released which degrade the endometrial lining 

• Hormones from the blastocyst trigger implantation into the uterine wall 

• Blastocyst becomes embryo as it will gain oxygen and nutrients from the endometrial tissue fluid 

• Following this, the blastula undergoes development into a gastrula - this occurs when a blastula, made up of one layer, folds inward and enlarges to create a gastrula.

• During gastrulation, the blastula folds upon itself to form the three layers of cells. Each of these layers is called a germ layer, which differentiate into different organ systems

• The developing fetus is protected by the placenta, amniotic sac, and umbilical cord 

Amniotic sac = acts as cushion to protect the fetus 

Amniotic fluid = protects fetus from injury and temperature changes as fluid fully surrounds the fetus 

Hormones released by the placenta:

Oestrogen = regulates physiological processes for fetal growth 

Progesterone = supports lining of the uterus (womb)

Exchanging of products between the fetal and maternal blood - 

• It is through the blood vessels in the umbilical cord that the fetus receives the necessary nutrition, oxygen, and life support from the mother via the placenta 

• The waste products and carbon dioxide from the fetus are sent back through the umbilical cord and placenta to the mother’s blood circulation where it is to be eliminated 

• The blood of the mother and the baby do not mix due to ‘rhesus factor’ (as if incompatible blood types were to mix during pregnancy, the mother’s immune system would make antibodies that would attack the baby's blood cells)

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Hormonal control - menstrual cycle, pregnancy, birth (in mammals) 

Menstrual cycle - (cycle of changes in the ovaries and the uterus)

• Average menstrual cycle repeats every 28 days 

Follicular phase:

Menses = day 1 - 4 

Pre-Ovulation = day 5 - 13

Ovulation: day 14

Luteal phase:

Secretion = day 15 - 20

Pre-menstruation = day 21 - 28

PHASES:

1. Menses = (menstrual period) - endometrium lining breaks down and tears away through menstruation 

2. Pre-ovulation = new endometrial lining forms in the uterus 

3. Ovulation = Ovary releases an ovum (egg) where it travels down fallopian tube where it waits to be fertilised by a sperm cell  

• If the egg is not fertilised, the corpus luteum will begin to degenerate 8-10 days after ovulation forming the mass of fibrous tissue known as the ‘corpus albicans’ 

• After ovulation, the corpus luteum enlarges in the ovary and secretes progesterone and some oestrogen into the bloodstream 

4. Secretion = endometrium becomes highly vascularised, reaching a peak after 8 or 9 days after ovulation (around the expected time of ovulation)

• Glands in the endometrium secrete watery mucus in this phase

5. Pre-menstruation = end of the cycle right before menstruation as body prepares for menstrual cycle, oestrogen and progesterone levels drop, causing increase in FSH and GnRH levels  

• if the egg is left unfertilised, it was degenerate during this phase 

• Pregnancy = If fertilised ovum implants itself in the uterus, pregnancy will result and the uterine wall is maintained by the secretion of progesterone and oestrogen, placenta will form and attach the developing embryo to the uterine wall 

• Placenta secretes hormones including progesterone, oestrogen, and human chorionic gonadotropin (hCG) to maintain the pregnancy, once the placenta is able to secrete these hormones, the corpus luteum in the ovary begins to degenerate   

1st trimester = high levels of hCG

2nd trimester = low levels of hCG, increasing progesterone and oestrogen 

3rd trimester = low levels of hCG, high levels of oestrogen, higher levels of progesterone

SEX HORMONES - pituitary glands secretes number of hormones that regulate other endocrine glands such as the ovaries in females 

• Regulate the ovarian and menstrual cycle 

• Hormones of the pituitary and gonads are key players in regulating reproductive cycles of mammals 

• Balance of sex hormones in the body at any point in time determines the fertility of a female and whether she can conceive a child 

The hormones of the pituitary controls oestrogen and progesterone, and the ovaries produce them - (found in both males and females)

The pituitary secretes two gonadotropic hormones, the Follicle Stimulating Hormone and Luteinising Hormone - (only found in females)

Birth (Parturition) - 

Positive feedback = response that reinforces the change 

~ The process of childbirth occurs via positive feedback under hormonal control 

Positive Feedback Loop: (continuous chain reaction until birth results) 

Repeated cycle of contracting of uterine muscles stimulated by oxytocin > fetus responds to instability of environment in uterus by releasing prostaglandins, triggering more powerful muscle contractions - leads to the final birth of the baby as it leaves the uterus 

Childbirth triggers the release of the hormone OXYTOCIN that induces uterine muscles to contract 

• After 9 months: the baby stretches the walls of the uterus which induces the release of chemicals to trigger a rise in the levels of oestrogen 

• Prepares smooth muscle of the uterus for hormonal stimulation by increasing its sensitivity to OXYTOCIN 

• Oestrogen inhibits progesterone - prevents uterine contractions while fetus develops 

Positive feedback: childbirth

1. Brain stimulates the pituitary gland to secrete OXYTOCIN

2. OXYTOCIN was carried in the bloodstream to the uterus 

3. OXYTOCIN stimulates uterine contractions and pushes the baby towards the cervix

4. Head of the baby pushes against the cervix

5. Nerve impulses from the cervix would transmit to the brain 

• The posterior pituitary gland would release OXYTOCIN during labour 

- evaluate the impact of scientific knowledge on the manipulation of plant and animal reproduction in agriculture 

Manipulation of plant and animal reproduction in agriculture - 

Selective breeding = used to produce animals and useful/attractive/favourable characteristics for thousands of years 

• Reproduction in agriculture has expanded as biological processes, skills and technology have developed 

• The Contributions of scientists have influenced this: Mendel, Watson, Crick

Production of agricultural crops and animals via SELECTIVE BREEDING:

• Artificial pollination 

> Pollen from the anthers is transferred onto the stigma of another plant

• Important in horticulture as it contributes to producing offspring with favourable characteristics 

E.g - plant hybrids for flower colour or disease resistant fruit 

• Can increase genetic diversity by creating new varieties but overuse may lead to crops being susceptible to disease/pests if plants are too similar 

Examples of agricultural plants

CLONING - 

• Produces genetically identical organisms through non-sexual means 

• Recent, not yet used in large scale commercial agriculture 

• Cloned animals in agriculture is confined to the meat and dairy industries 

• In the pig industry, shooter-term cloning technology remains restricted to generating high value animals for medical use 

GENE TECHNOLOGY - 

• Transgenic animals/plants (transferring of gene from one organism into another) 

• Can produce genetically modified organisms (GMOs)

• Techniques are being increasingly applied to treatment of diseases and in agriculture for food production 

Example - Transgenic sheep developed by injection of the gene responsible for producing a blood clotting factor 

• factor is then obtained from sheep’s milk and can be used to treat haemophilia in humans 

• Food crops like soy and corn have been genetically modified for pest and herbicide resistance and BT (Bacillus Thuringiensis) cotton - grown in Australia commercially

RECOMBINANT DNA TECHNOLOGY - 

• Using enzymes and various laboratory techniques to manipulate and isolate DNA segments of interest 

• Used to produce GMOs > new gene is inserted into another species using bacteria or viruses 

• Used to combine or splice DNA from different species or to create genes with new functions 

GENETICALLY MODIFIED ORGANISMS - 

Example - Golden Rice 

• Genetically modified rice that produces beta-carotene > the precursor to vitamin A 

Cell Replication 

Inquiry question: How important is it for genetic material to be replicated exactly? 

Students: 

● model the processes involved in cell replication, including but not limited to: 

– mitosis and meiosis (ACSBL075) 

– DNA replication using the Watson and Crick DNA model, including nucleotide composition, pairing and bonding (ACSBL076, ACSBL077) 

● assess the effect of the cell replication processes on the continuity of species (ACSBL084) 

DNA and Polypeptide Synthesis 

Inquiry question: Why is polypeptide synthesis important? 

Students: 

● construct appropriate representations to model and compare the forms in which DNA exists in eukaryotes and prokaryotes (ACSBL076) 

● model the process of polypeptide synthesis, including: (ACSBL079) 

– transcription and translation 

– assessing the importance of mRNA and tRNA in transcription and translation (ACSBL079) – analysing the function and importance of polypeptide synthesis (ACSBL080)

 – assessing how genes and environment affect phenotypic expression (ACSBL081) 

● investigate the structure and function of proteins in living things 

Genetic Variation 

Inquiry question: How can the genetic similarities and differences within and between species be compared? 

Students: 

● conduct practical investigations to predict variations in the genotype of offspring by modelling meiosis, including the crossing over of homologous chromosomes, fertilisation and mutations (ACSBL084) 

● model the formation of new combinations of genotypes produced during meiosis, including but not limited to: 

– interpreting examples of autosomal, sex-linkage, co-dominance, incomplete dominance and multiple alleles (ACSBL085) 

– constructing and interpreting information and data from pedigrees and Punnett squares 

● collect, record and present data to represent frequencies of characteristics in a population, in order to identify trends, patterns, relationships and limitations in data, for example: 

– examining frequency data 

– analysing single nucleotide polymorphism (SNP)

Inheritance Patterns in a Population 

Inquiry question: Can population genetic patterns be predicted with any accuracy? 

Students: 

● investigate the use of technologies to determine inheritance patterns in a population using, for example: (ACSBL064, ACSBL085)  DNA sequencing and profiling (ACSBL086) 

● investigate the use of data analysis from a large-scale collaborative project to identify trends, patterns and relationships, for example: (ACSBL064, ACSBL073)  the use of population genetics data in conservation management  population genetics studies used to determine the inheritance of a disease or disorder  population genetics relating to human evolution