Summary of what I learnt (Sexual Reproduction)

Sexual Reproduction is the biological process of forming a new individual through the fusion of two very specialized cells known as gametes. The fusion process is also known as fertilization. The larger gamete is known as the egg or ovum, while the smaller one is known as the sperm.

Asexual reproduction is the biological process of forming a new individual from a single parent without the fusion of gametes (ex. Without fertilization)

Puberty

Puberty is the development process where as child’s body matures into an adult body where he or she is now capable of reproduction.

This process is triggered by:

-release of hormones from the brain to the gonads, which are the organs responsible for the production of sperms and eggs. In males, the gonads are the testes and in females, the gonads are the ovaries.

-in response to the hormonal signals from the brain, the gonads begin secreting sex hormones (such as testosterone and oestrogen)

-the gonads also initiate gametes production. In the testes, sperm are produced, while in the ovaries, eggs begin maturing

-the secondary sexual characteristics also begin to develop

Secondary characteristics:

Male:

-onset at age 11 to 15 years old

-predominant growth of facial, underarm, chest, abdominal and pubic hair

-broadening of chest and shoulders

-enlargement of penis and testes

-Sebaceous (oil) and sweat glands become more active, leading to acne in severe cases

-Deepening of voice as larynx enlarges

-Increased muscle mass and strength; increase in height

Female:

-onset at age 9 to 13 years old

-predominant growth of underarm and pubic hair

-broadening of hips and enlargement of breasts

-sebaceous (oil) and sweat glands become more active, leading to acne in severe cases

Male Reproductive System

Functions of organs in male reproductive system:

Testis:

-production of male gametes (sperm)

-production of male sex hormones

Epididymis:

-temporary storage of sperm

-muscles in epididymis contract to ejaculate sperms

Sperm duct:

-transport sperm from epididymis to the urethra

Glands (seminal vesicles, prostate gland, bulbourethral/ cowper’s glands):

-production of seminal fluid:

-alkaline to neutralize acidity in female reproductive tract

-activates sperms by causing them to swim freely

-nourish sperms with nutrients

Penis:

-insertion into vagina when erected

Physiology of erection and ejaculation:

1) Arterioles bringing blood to the penis and its erectile tissue dilate

2) Blood begin entering the erectile tissues and fills up the blood spaces in the erectile tissue

3) Penis becomes turgid

4) Epididymis contracts

5) Semen is released

Female Reproductive system:

Ovary:

-Production of female gametes (ova) and release of mature ovum

-Production of female sex gametes

Oviduct:

-Deliver mature ovum from ovary to uterus

-Beating of cilia to move ovum along oviduct

-Muscular and had strong contractions

Uterus (or womb):

-muscular and elastic, to push foetus out during birth

-soft and smooth endometrium prepares for implantation of fertilized egg

Endometrium (uttering lining):

-muscular and elastic, to push foetus out during birth

-soft and smooth endometrium prepares for implantation of fertilized egg

Structure of sperm:

Acrosome:

-contains acrosin, a protease enzyme, released by the sperm upon contact with the membrane surrounding the ovum

-acrosin aids in digesting away the membrane, also known as zona pellucida, which surrounds the cell membrane of the ovum. This allows the sperm’s cell membrane to eventually fuse with that of the ovum

Nucleus:

-contains the male genes that will eventually be combined with the female genes in the ovum during fertilization

Minimal cytoplasm:

-the thinner cytoplasm reduces resistance to the motion of the sperm towards the ovum

Middle piece:

-consists of spiral mitochondrion

-the mitochondrion supplies energy for the beating of the tail

Tail (or flagellum):

-beats to propel the sperm towards the ovum

Differences between sperm and the ovum:

Shape:

-The sperm had 3 distinct regions, namely the head, the middle piece, and the tail

-The ovum is spherical

Size:

-The sperm’s size is small

-The ovum’s size is large

Numbers:

-200 to 500 million sperm cells per seminal discharge

-one ova is released on an average of about 28 days

Motility:

-The sperm is motile and move by beating of flagella

-The ovum is non-motile and is swept along oviduct by cilia lining the walls of the oviduct or by contractions of the muscles in the oviduct walls

Lifespan:

-The sperm die rapidly in open air. It dies within a few hours in the vagina and has a lifespan of 2 to 5 days in the oviduct

The ovum can only survives 24 hours if unfertilized

Menstrual Cycle:

Menstrual Cycle refers to a cycle of physiological changes that occur in a fertile woman’s reproductive system. This cycle of events is essential for reproduction to occur. The average period of each cycle is about 28 days. However, it may also range between 14 to 35 days, depending on stress levels and lifestyle. The cycle is under the control of hormones. This cycle can be divided into 3 events that occur sequentially:

Menstruation – Follicular Phase – Day 1 to 14:

-The beginning of each cycle (Day 1) is marked by menstrual bleeding, or menstruation

-This involves the discharge of blood and the breakdown product of the thick uterine lining from the vagina.

-Such discharge could happen up to 7 days.

-During this period, the hormone oestrogen is secreted in increasing concentration

-By Day 7, breakdown of the uterine lining stops and menstrual bleeding ceases as a result of relatively higher oestrogen concentration.

-Thus the uterine lining reaches a minimum thickness by Day 7

-A new ovum begins maturing and continues to mature beyond Day 7 under the influence of a complex interplay of hormones

-Beyond Day 7, the uterine lining begins to thicken again

Ovulation – Day 14:

-By Day 14, oestrogen level reaches a maximum

-A sudden surge in luteinizing hormone level then triggers the release of the mature ovum from one of the ovaries. The ovum then begins its passage through the oviduct towards the uterus.

-Upon release from the ovary, the mature ovum may only survive for 24 hours or less if it is not fertilized

-As the average lifespan of the sperm cell in the oviduct is about 72 hours or about 3 days, any deposition of semen into the female reproductive tract 3 days prior to ovulation may suggest that the woman can still conceive if she ovulates on Day 14.

-A conservative estimate of the fertile period of a woman is hence between Day 11 and Day 16

Luteal Phase – Day 14 to 18:

-After ovulation, the ovaries begin to produce high concentration of progesterone

-This encourages the proliferation (ex. Growth) of the uterine lining (or endometrium), resulting in the growth of more blood capillaries in the endometrial tissues. The uterine lining also becomes thicker, eventually reaching maximum thickness

-The thickness of the uterine lining is maintained mainly by the relatively high concentrations of progesterone

-The proliferation of the uterine is to prepare for the implantation of the fertilized egg

-If implantation does not happen (usually so when the egg is unfertilized) within Day 14 to Day 28, production of progesterone and oestrogen will fall sharply, resulting in the breakdown of the uterine wall.

-The unfertilized egg, together with the fragments of endometrial tissues, blood capillaries and blood, will be removed through menstrual bleeding

-Thus, this marks the beginning of a new cycle

Copulation and fertilization:

Copulation or sexual intercourse refers to the process of placing in the male genitalia into the female reproductive tract. However, fertilization refers to the fusion of the male and female gametes, restoring the diploid number of chromosomes in the zygote. Take note that copulation does not necessarily lead to fertilization.

Post-fertilization:

After the formation of the zygote, several cycles of cell division of the zygote occurs. Eventually, the zygote forms a ball of undifferentiated cells. This ball of cells then begins to form simple tissue layers and is now known as an embryo. In later stages of development, the embryo starts to from distinguishable organs and we term this as foetus. The foetus is nourished and protected by several structures found in womb.

Amniotic Sac and Amniotic Fluid:

The amniotic sac encloses the foetus in the amniotic cavity, which contains the amniotic fluid.

Function of amniotic fluid:

-supports and cushions the foetus while in the uterus

-absorbs shock, for example, if the mother has a fall

-protects the foetus against physical injury as it cannot be compressed

-acts as a lubricant and reduces friction in the birth canal during birth

-allows foetus to move freely during gestation

Placenta:

-the fetal blood system must be separated from the maternal’s system as the 2 systems are functioning at different blood pressure

-the foetus’ blood type may also be different from that of the mother. Mixing of different blood types may result in agglutination and this can be fatal.

Functions of Placenta:

-allows oxygen and nutrients (glucose, amino acids and mineral salts) to diffuse from the mother’s blood into the foetus’ blood

-allows excretory products (urea and carbon dioxide) to diffuse from the foetus’ blood into the mother’s blood

-allows antibodies (protection against diseases) to diffuse from the mother’s blood into the foetus’ blood

-produces progesterone which maintains the uterine lining during pregnancy

Umbilical Cord:

The umbilical cord attaches the foetus to the placenta and contains 2 umbilical arteries and 1 umbilical vein

Function of umbilical cord:

-umbilical arteries transport deoxygenated blood and metabolic waster products (urea) from foetus to the placenta

-umbilical veins transport oxygenated blood, nutrients (glucose, amino acids) and other useful substances (antibodies, hormones) form the placenta to the foetus

Sexually Transmitted Diseases:

Sexually transmitted diseases (STOs) or sexually transmitted infections (STIs) refer to :

-diseases transmitted mainly through sexual intercourse

-caused by bacteria and viruses

-affect the reproductive system (may also affect other body parts)

-may not show visible signs or symptoms, may pass on the disease unknowingly to their partners

-infections can be fatal

Examples:

-Syphilis

-Gonorrhea

-Acquired Immunodeficiency Syndrome (AIDS)

Symptoms , effect, and treatment for diseases:

Gonorrhea:

Cause:

-spherical bacteria

Transmission:

-sexual intercourse

-from infected mother to baby during birth

-sharing of injection needles with infected person

-transfusion of infected blood

Symptoms:

-painful sensation during urination

-discharge of pus from vagina or penis

Effects:

-infection of urethra

-infection of oviducts which may lead to infertility

-ectopic pregnancy

-infection of newborn’s eyes which may lead to blindness

Treatment:

-antibiotics, but some strains of the bacteria have developed drug-resistance

Syphilis:

Cause:

Spiral bacteria

Transmission:

-sexual intercourse

-from infected mother to baby during birth

-sharing of injection needles with infected person

-transfusion of infected blood

Symptoms:

-painless sores on penis, vagina, cervix or mouth

-non-itchy skin rashes

Effects:

-deformed joints

-paralysis

-insanity

-death

-newborn may be deaf or with abnormal teeth and bone

Treatment:

-antibiotics, only effective at early stage

Acquired Immune Deficiency Syndrome:

Cause:

Human Immunodeficiency Virus (HIV)

Transmission:

-sexual intercourse

-from infected mother to baby during birth

-sharing of injection needles with infected person

-transfusion of infected blood

Symptoms:

-weaken immune system

-loss of appetite and weight

-diarrhoea

-night sweat

-flu-like symptoms

Effects:

-immune system fails

-pneumonia

-tubercolosis

-brain infection

-kaposi sarcoma

Treatment:

-currently, there are no cures. However, cocktail of antiretroviral drugs is used to prolong lifespan and improve quality of lives of patients

Prevention of STDs:

To reduce the risk of contracting AIDs and control its spread:

-practise monogamy or abstinence

-wear a condom during intercourse

-do not abuse drugs

-do no share instruments that break the skin (toothbrush, razors, piercing, needles, tattoo needles) as it may be contaminated

-go to reliable practitioners who use sterilized/ disposable instruments

Birth Control:

Couples practise birth control for various reasons:

-prevent unwanted pregnancy

-family may not be financially ready

-couple may want to pursue career development and do not have time for a child

-family may already have enough children

-couple may want to space out the age-gap of their children

-the woman may be ill and physically unsuitable to go through a pregnancy (eg diabetic/ high blood pressure)

-population control legislation (eg. China’s One child policy)

-reduce risk of being infected with STIs

Options for Birth Control:

There are many options for birth control. Some forms of birth control only prevent pregnancy temporarily. Once the couple stops practising these methods, they are able to get pregnant again. However, it is irreversible once permanent birth control is executed. Below are some examples of birth control:

Natural:

Rhythm Method:

It is temporary. The woman tracks her menstrual cycle and avoids having intercourse during the fertile period. However, it is unreliable, as the menstrual cycle is easily disrupted by hormonal fluctuation in the woman’s body.

Withdrawal Method:

It is temporary. The man withdraws his penis just before ejaculation and sperms are not released into the vagina. However, it is unreliable as sperms may be present in pre-seminal fluids and the man may not be able to withdraw in time.

Chemical:

Spermicide:

It is temporary. A chemical is sprayed in the vagina to kill the sperms upon entry and render them unable to swim up to the oviducts. However, it is only 80% reliable. Some sperms may be resistant to the spermicide and can survive the journey towards the oviduct.

Mechanical:

Condom:

It is temporary. A rubber sheath is worn over the penis during intercourse and sperms are collected in the condom so that they cannot enter the vagina. The success rate is 99.9%, as microscopic tears may be present and sperms may leak through.

Diaphragm:

It is temporary. A rubber cap is fitted over the cervix and act as a barrier between the sperms and the ovum. The success rate is also 99.9%, because if the cap is not fitted properly, sperms can still enter the uterus and swim up to the oviducts.

Hormonal:

Pill:

It is temporary. The pill contains synthetic female hormones that prevent ovulation. The success rate is 99.9%, as women were reported to be impregnated even though they were put on pill.

Injection/Implant:

It is temporary. Synthetic female hormones are regularly injected directly or slowly released from an implanted tube into the blood stream to prevent ovulation. The success rate is 99.9%, as women were reported to be impregnated even they were put on hormonal treatment.

Surgical:

Ligation:

It is permanent. The oviducts are cut and tied up to prevent sperms from meeting the ovum. It is 100% reliable.

Vasectomy:

It is permanent. The sperm ducts are cut and tied to prevent sperms from being released into the urethra and out of the penis. It is 100% reliable.

Facilitated Reproduction:

There are couples who are not able to have children due to various physical conditions:

-the ovaries may be defective

-the oviducts may be blocked

-the uterus/ cervix may be too weak to sustain a pregnancy

-the sperms may be weak

-the man is unable to sustain an erection for penetration

-the woman may be suffering from other medical conditions ( eg. Diabetes / high blood pressure) which makes it difficult for her to conceive

As a result, these couples may turn to facilitated reproduction:

In- vitro Fertilization:

1) The woman is given hormonal treatment to stimulate multiple ovulation and the ova are harvested and screened for vitality

2) The sperms are also collected from the man and screened for vitality

3) A healthy sperm is then used to fertilize one ovum in a petri dish with the help of the microscope

4) The resulting zygote is allowed to divide before it is introduced into the uterus. Usually, up to 3 zygotes are introduced to increase the chances of successful implantations

5) If the zygote is successfully implanted, it can develop into an embryo and after 40 weeks, the foetus is ready for birth.

Summary of what I learnt (Nutrient Cycle)

Carbon Cycle:

Carbon is found in all ecosystems, because all living things on Earth are composed of carbon compounds. The main source of carbon for all ecosystem is the atmosphere. The carbon cycle ensures continuous supply of carbon dioxide for plants to carry out photosynthesis and enables energy to flow through the ecosystem.

Carbon exchanges between the atmosphere and the biosphere occur through the following processes:

Photosynthesis:

Carbon is absorbed in the form of CO2 and converted to glucose which may then be used for respiration and building of protoplasm in plants. Plants are then consumed by primary consumers and the carbon is then transferred into the body tissues of animals. Through successive feeding, carbon compounds move up the trophic levels in the ecosystem.

Respiration:

Plants and animals respire, converting glucose into CO2, which is release back into the atmosphere.

Excretion and egestion:

Microorganisms ferment carbon-rich food in the stomachs of cattle and releases carbon back into the atmosphere in the form of natural gases or methane, CH4. Undigested food removed as faeces contains much of the carbon that was initially ingested as well.

Decomposition:

As dead organisms decay and become decomposed, they release carbon dioxide into the atmosphere.

Destruction of vegetation:

Bush fires or slash-and-burn agriculture may burn away large areas of forests which release large quantity of carbon dioxide from plant material

Sedimentation and mineralization:

When organisms die and are very quickly buried, they do not undergo decomposition, but may be compacted by layers of mud and rock. Overtime these dead organisms may become fossil fuels. Much of the carbon in the tissues of these organisms thus becomes stored in the formed of fossil fuels.

Carbon dioxide from the atmosphere dissolves in the sea in the form of bicarbonate ions or carbonate ions. Marine organisms use carbonate ions to produce hard shells and support structures. When these organisms die, their hard shells will settle down to the bottom of the ocean (sedimentation) and become compacted. This becomes limestone (calcium carbonate) over a long period of time, storing the carbon in limestone.

Dissolution:

Precipitation may dissolve limestone structures, thus releasing the carbonate ions back into rivers and streams.

Burning of Fossil Fuels (combustion):

When fossil fuels is removed from deep underground, and burnt for energy, the carbon in the fossil fuel is released as large quantities of carbon dioxide.

Nitrogen Cycle:

It helps to keeps the nitrogen level in the atmosphere constant and ensures a continuous supply of nitrates for green plants to make proteins and protoplasm. It also enables proteins to be supplied to other organisms in the food chains.

Nitrogen is removed from the air:

-By nitrogen-fixing bacteria to produce nitrates in the soil

-By lightning that combines nitrogen with oxygen in the air to form oxides of nitrogen. The oxides of nitrogen dissolve in water to from nitric acid. The nitric acid reacts with other substances to form nitrates.

Nitrogen is returned to the air:

-By the action of denitrifying bacteria on the nitrates found in the soil, decomposing the nitrates into oxygen for the bacteria’s use and nitrogen for release into the air.

Nitrogen compounds are removed from the soil:

-Through the absorption by green plants for their growth

-By leaching; in which nitrates dissolve in rain water or drainage water and are washed away beyond the reach of plant roots.

Nitrogen compounds are returned to the soil:

-By the action of decomposers on dead animals and plants

Summary of what I learnt (Ecology)

Ecology is the study of interaction and relationships between the organisms and the biotic as well as abiotic environment. Every organism is interdependent. Energy is transferred form one organism to another mainly through feeding. The sun is the main source of energy for Planet Earth, as the solar energy is absorbed by the sun and passed on to other organisms as chemical energy. However, most of this energy is eventually lost as heat and the energy is non-cyclical too.

Terms used for ecology:

Habitat: the place where an organism lives

Population: a group of organisms of the same species living in a particular habitat

Community: All populations of organisms living and interacting with each other in a particular habitat.

Ecosystem: A community and its abiotic environment

Abiotic Factors that will affect the livelihood of organisms living in a community or ecosystem:

Temperature and pH: Extreme temperatures and pH disrupts the hydrophobic, hydrophilic, ionic interactions and proper functioning of enzymes, and will cause them to lose their shape and functionality.

Oxygen Content: Oxygen is required for aerobic respiration, thus a lack of oxygen will slows down metabolism.

Humidity: High humidity slows down the rate of transpiration in plants but is crucial and critical to the survival of epiphytes and organisms living in arid places.

Amount of water: Affects number and location of flora and fauna. However, it is affected by rain pattern

Wave action: Prevents marine organisms form settling down and feeding

Wind Speed: High wind speed may break the stems of certain plant species but will dissipate humidity

Light Intensity: Low light intensity retards plant growth, but high light intensity may bleach chlorophyll and impairs the ability of plants to photosynthesize

Salinity: Affects osmotic balance in many aquatic animals and coastal plant species

Type of substratum: Clayey, sandy or rocky substratum will influences ability of plants and sessile organisms to anchor themselves

Biotic Environment

Mutualism:

Both organisms benefit. For example, Lichen is made up of algae and fungus. The algae make food for the fungus while the fungus takes in water for the algae.

Commensalism:

One party benefits while the other remains neutral. For example, Remora fish help to clean and eat parasites from sharks’ gills.

Exploitative relationships (Predation, Parasitism, Herbivory):

One party benefits while the other had a fitness disadvantage. For example, the snake had a fitness advantage when it feed on the rabbit, but the rabbit had a fitness disadvantage.

Competition:

Both party had a fitness disadvantage. For example, both snake and eagle have similar feeding habits, thus both had a fitness disadvantage.

Ammensalism:

One party had a fitness disadvantage while the other is neutral. For example, a smaller plant had a fitness disadvantage when it is shaded out by a tall tree, as it could not receive sufficient amount of sunlight, but the tall tree was neutral as it did not affect the tree.

Feeding Relationship:

Feeding relationship is shown through a food chain, which is a sequence of organisms, starting with a photosynthesizing organism, through which energy is passed as one organism is eaten by the next in the sequence.

Examples of food chain:

grass -> rabbit -> fox

grass -> zebra -> lion

grass -> grasshopper ->bird -> snake

Food chains can be then interconnected to form a more complex food web, which comprises interlinked food chains involving organisms from the same ecosystem.

Terms used in food web:

Autotrophs: Organisms that are capable of synthesizing organic molecules, such as glucose, using inorganic molecules, such as carbon dioxide, and energy derived from sunlight.

Primary Producers: Autotrophic organisms that supply energy to all other organisms in the food chain/ food web. Note that all primary producers are autotrophic but not all autotrophs are primary producers.

Heterotrophs: Organisms which use organic molecules both as a source of carbon and as a source of energy, and acquire these molecules by feeding on other organisms.

Consumers: Heterotrophic organisms that depend ultimately on the producers as energy sources.

Primary Consumers: Organisms that feed directly on producers

Secondary Consumers: Consumers which feed on the primary consumer

Tertiary Consumers: Consumers that feed on the secondary consumers

Herbivores: Organisms that only feed on plant matter

Carnivores: Organisms that only feed on other animals

Omnivores: Organisms that feed on both plant matter and other animals

Decomposers: Organisms which release enzymes to break down large molecules in dead organic matter into smaller ones which then can be recycled.

Conservation

Man has greatly altered natural habitats when they exploit the natural environment for fossil fuel, wood and other natural sources. This may result in increased rates of species extinction as organisms are unable to adapt fast enough to the rapid changes. When a species go extinct, food webs become destabilized and an entire ecosystem may collapse. Thus, this will eventually affect mankind as we obtain our food sources from the natural environment.

Thus, conservation is important for the following reasons:

-prevent extinction of plant and animal species

-maintain a stable and balanced ecosystem, prevent disruption of natural cycles such as carbon and water cycle, prevent global warming

-maintain large gene pool so as to preserve favourable genes; helps to improve agricultural produce or crops with better resistance to diseases

-conserve marine life as a food source

-scientific value – study of evolution

-nature appreciation – recreational purposes such as hiking, fishing, skiing

-maintain biodiversity – economical (rice, pineapple and banana are food plants developed from rainforest plants), medical (Quinine, an anti-malarial drug is found from the bark of Cinchona), industrial (latex is tapped from rubber trees and used to make tyres) purposes

Effects of selective addition/removal of species

The dynamic flow of energy, nutrients and intricate interactions between organisms and their environment establishes a state of delicate balance in the ecosystem, which changes only gradually over time. This state of balance gives stability and self-sustainability to an ecosystem.

Such stability and self-sustainability requires:

-A constant input of energy

-Presence of producers which are able to harness this source of energy, converting it into chemical energy required to power the rest of the food chain

-Continuous circulation of matter between the biotic and abiotic components of an ecosystem

By altering any of the above requirements, the stability of an ecosystem may be disrupted. An example is the addition or removal of species from an habitat, such as the use of biological pest control.

Natural predators of the pest may be introduced to effectively control the pest population. However, care must be taken when selecting the natural predator so that they may not offset the local ecological balance. This may happen if the natural predator target unintended prey, and compete with the indigenous species.