Science e-Portfolio Post 10

This is my 3rd reflection of my Term 3 e-Portfolio. Please enjoy!

Sexual Reproduction

Sexual reproduction is the biological process of forming a new individual through the fusion of two very specialised cells known as gametes. The fusion process is also known as fertilisation. In sexual reproduction, the two gametes involved are the egg (also known as ovum) and the sperm.

Asexual Reproduction

Asexual reproduction is the biological process of forming a new individual from a single parent without the fusion of gametes.

Feature	Sexual Reproduction	Asexual Reproduction
Requires the fusion of gametes	Yes	No
Number of parents required	Usually involves two parents but may occur within the body of a single hermaphroditic body organism (an organism with both male and female sexual organs)	One
Variation in offspring	Offspring has genetic variations (eg offsprings may have genetic differences between one another	All offspring are genetically identical and are also genetically identical to parent

However, there are many organisms that are capable of reproducing both sexually and asexually.

Male Reproductive System

The function of the male reproductive system is to:

– produce, maintain and transport sperm (the male reproductive cells) and protective fluid (semen)

– discharge sperm within the female reproductive tract

– produce and secrete male sex hormones

These are some organs in the male reproductive system:

– Penis: ejaculates semen, which contains sperm (male reproductive cells), when the man reaches sexual climax (orgasm). When the penis is erect, the flow of urine is blocked from the urethra, allowing only semen to be ejaculated at orgasm.

– Scrotum: Is the loose pouch-like sac of skin that hangs behind and below the penis. Contains the testicles (also called testes), as well as many nerves and blood vessels. Acts as a "climate control system" for the testes. (For normal sperm development, the testes must be at a temperature slightly cooler than body temperature. Special muscles in the wall of the scrotum allow it to contract and relax, moving the testicles closer to the body for warmth or farther away from the body to cool the temperature.)

– Testicles: responsible for making testosterone, the primary male sex hormone, and for generating sperm. Within the testes are coiled masses of tubes called somniferous tubules, which are responsible for producing sperm cells.

– Epididymis: is a long, coiled tube that rests on the backside of each testicle. It functions in the transport and storage of the sperm cells that are produced in the testes. It brings the sperm to maturity, since the sperm that emerge from the testes are immature and incapable of fertilization. During sexual arousal, contractions force the sperm into the vas deferens.

Female Reproductive System

The function of the female reproductive system is to:

– produces the female egg cells necessary for reproduction, called the ova or oocytes.

– produces female sex hormones that maintain the reproductive cycle.

These are some organs in the female reproductive system:

― Vagina: The vagina is a canal that joins the cervix (the lower part of uterus) to the outside of the body. It also is known as the birth canal.

― Uterus (womb): The uterus is a hollow, pear-shaped organ that is the home to a developing fetus. The uterus is divided into two parts: the cervix, which is the lower part that opens into the vagina, and the main body of the uterus, called the corpus. The corpus can easily expand to hold a developing baby. A channel through the cervix allows sperm to enter and menstrual blood to exit.

― Ovaries: The ovaries are small, oval-shaped glands that are located on either side of the uterus. The ovaries produce eggs and hormones.

― Fallopian tubes: These are narrow tubes that are attached to the upper part of the uterus and serve as tunnels for the ova (egg cells) to travel from the ovaries to the uterus. Conception, the fertilization of an egg by a sperm, normally occurs in the fallopian tubes. The fertilized egg then moves to the uterus, where it implants to the uterine wall.

Sexually Transmitted Diseases (STDs)

STDs refers to

– diseases transmitted mainly through sexual intercourse

– caused by bacteria and viruses

– affect the reproductive system

– may not show visible signs or symtoms

– infections can be fatal

Some examples of STDs:

– Syphilis

– Gonorrhea

– AIDS

Prevention of STDs

To reduce the spread of STDs,

– practice monogamy or abstinence

– wear condoms during intercourse

– do not abuse drugs

– do not share instruments that break the skin and may be contaminated with blood

– go to reliable practitioners who use sterilized/disposable instruments

Science e-Portfolio Post 9

This is my 2nd reflection of my Term 3 e-Portfolio. Please enjoy!

Ecology

Ecology is the study of interactions or relationships of organisms with one another and with the biotic and abiotic environment.

Some terms used in Ecology

Habitat - a 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 one another in a particular habitat

Ecosystem - a community and its abiotic environment, where :

· organisms are interdependent

· energy is transferred from one organism to another mainly through feeding

· The Sun is the main source of energy for our Earth

· solar energy from the Sun is absorbed by plants and passed on to other organisms as chemical energy

· most energy is lot as hear

· energy flow is non-cyclical

Abiotic factors

These are some abiotic factors that may influence the livelihood of organisms in a communiity or ecosystem:

Temperature and pH- affects the proper functioning of enzymes. Extreme temperatures and pH disrupts the hydrophobic, hydrophilic and ionic interactions in enzymes, causing them to lose their shape and functionality.

Oxygen content - oxygen is required for aerobic respiration. Lack of oxygen slows down metabolism.

Humidity - high humidity slows down the rate of transpiration in plants but is also critical to the survival of epiphytes and organisms living in arid places.

Amount of water - Affects the number and locations of flora and fauna. Dependent on rain pattern.

Wave action - prevents marine organisms from settling down and feeding.

Wind speed - high wind speed may break the stems of certain plant species and may dissipate humidity.

Light intensity - low light intensity retards plant growth, but high light intensity may bleach chlorophyll and impair the ability of plants to photosynthesise.

Salinity - affects osmotic balance in many aquatic animals and coastal plant species.

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

Interactions

Mutualism - Both organisms benefit

Commensalism - One organism benefits while the other organism remains neutral

Exploitative Relationships - One organism benefit while the other organism is at a disadvantage

Competition - Both organisms are at a disadvantage

Ammensalism - One organism is at a disadvantage while the other remains neutral

*All interactions limit the distribution and abundance of organisms and are crucial elements which shape an ecosystem

Feeding relationship

Food chain - organisms consume one another, and energy is passed on as one organism consume another. A food chain starts with a producer ( usually a green plant which can photosynthesise and make food)

An example of a food chain:

Grass → Grasshopper→ Frog → Snake → Hawk

Food web - When organisms have more than one feeding relationship, food chains may be interconnected, thus forming a food web. A food web comprises interlinked food chains involving organisms from the same ecosystem.

An example of a food web:

Terms used in food web:

Autotrophs - An autotroph is an organism that produces complex organic compounds from simple inorganic molecules using energy from lighy (by photosynthesis) or inorganic chemical reactions (chemosynthesis). They are able to make their own food and do not use organic compounds as an energy source or a carbon source. Aututrophs can reduce carbon dioxide by adding hydrogen to it to make organic compounds.

Primary producers - Autotrophic organisms that supply energy to all other organisms in the food chain / food web.

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

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

Herbivores - Organisms which feed on plants only.

Carnivores - Organisms which feed on other animals only.

Omnivores - Organisms which feed on both plants and animals.

Primary consumers - Organisms which feed on producers.

Secondary consumers - Organisms which feed on primary consumers.

Tertiary consumers - Consumers which feed on secondary consumers.

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

Science e-Portfolio Post 8

This is my 1st reflection of my Term 3 e-Portfolio. Please enjoy!

Lenses

A lens is a piece of transparent material with curved surface. There are two types of lenses : convex lens and concave lens.

All lenses are thinner at the edges and thicker at the centre.

	Case 1	Case 2
Object distance from lens	Long	Short
Image obtained:	Inverted	Upright
	On the opposite side of lens as the object	On the same side of lens as the object
	Diminished	Magnified
	Real	Virtual

Kinds of images:

1) virtual image : it cannot be captured on the screen because no actual light rays meet at an image position.

2) real image: light rays meet at an image point and thus the image can be captured on the screen.

Terms used in ray diagram for lenses:

Optical centre - point at centre of lens

Principal axis - line passing symmetrically through optical centre of lens

Principal focus - point where all rays close to and parallel to the principal axis converge after refraction by lens

Focal length - distance between optical centre and focal point

Focal plane - plane passing through focal length and perpendicular to principal axis

Science e-Portfolio Post 7

This is my 3rd reflection of my Term 2 Science e-Portfolio. Please enjoy!

Science e-Portfolio Post 6

This is my 2nd reflection of my Term 2 Science e-portfolio. Please enjoy!

Reflection on science experiences, laboratory sessions

The science experiments we conducted in the science lab were really interesting and helpful. Hands-on allowed me to understand the topic at hand better. I really enjoyed the experiments and I feel that we should have more of these experiments as we would really be able to understand the concept.

An example would be the testing of reflection and refraction. After conducting the experiment, I was finally able to see it ‘live’. As such, I understood the effect of the change of speed in going through different mediums, which results in refraction. We were also allowed to test for total internal reflection.

Another experiment was the concave and convex mirrors experiment. It allowed us to go closer and further away from both mirrors to see the image appearing in the mirror. As such, we would know the outcome image of ourselves and understand the concept better.

Science e-Portfolio Post 5

This is my 1st reflection of my Term 2 Science e-Portfolio. Please enjoy!

Reflection of learning in Science and personal growth

Acids and bases

Strong and weak acids

A strong acid is a substance which ionizes completely in water to produce many hydrogen ions. There are no molecules remaining and the solution contains a high concentration of ions, thus making it a good electrical conductor.

A weak acid on the other hand is a substance which ionizes partially in water to produce few hydrogen ions. Most of the acid molecules remain as acid molecules and the solution contains a low concentration of ions thus making it a poor electrical conductor.

Importance of water for acidity

The properties of acids are due to the presence of hydrogen ions. Upon mixing with water, ionization of acids occurs and thus hydrogen ions are produced. Therefore, acids only behave as acids when they are dissolved in water.

Properties of acids

1. Sour taste

2. Change the colour of indicators

3. Contain hydrogen ions and conduct electricity

4. React with metals, carbonate and bases

Reactions of acids and bases

5. Acids react with carbonate to produce carbon dioxide, salt and water

6. Acids react with bases to produce salt and water

7. Acids react with metal to produce salt and hydrogen

8. Bases react with ammonia to produce salt, water and ammonia gas

Bases and Alkalis

What is a base?

-It is the oxides or hydroxides of metal that reacts with an acid to form a salt and water only.

What is an alkali?

-It is the metal hydroxide which is soluble in water and produces hydroxide ions in water.

Note: *All alkalis are bases but not all bases are alkalis.

Strength of an alkali

The strength of an alkali depends on its degree of ionization in water to form hydroxide ions. The properties of alkalis are due to hydroxide ions.

A strong alkali is one that ionizes completely in water to produce hydroxide ions and there will be no molecules left. A weak alkali is one that ionizes partially in water to produce a few hydroxide ions. Most of the alkali molecules remain as molecules.

Properties of bases

1. Alkalis have a soapy feel and a better taste

2. Alkalis can change the colour of indicators

3. Bases can react with acids to form salt and water only - Neutralisation

Colour change of indicators

Indicators	Observation(s)
Litmus paper	Acid turns blue litmus paper red, while alkali turns red litmus paper blue
Methyl Orange	Colour change at pH4 Acid turns methyl orange red Alkali turns methyl orange yellow
Phenolphthalein	Colour change at pH9 Alkali turns phenolphthalein pink Phenolphthalein remains colourless in acid
Universal Indicator	In neutral solutions, universal indicators remain green Strong acids turn universal indicator red Strond alkalis turn universal indicator violet

Reflection and Refraction

1. Light is a form of energy capable of stimulating the light-sensitive cells in the retina of the eye.

2. Light travels in a straight line.

3. The path along which light energy travels is called a ray. It is represented by a straight line with an arrow to show its direction of motion.

4. We are able to see an object only when the light rays coming from it enter our eyes.

Term used in reflection

Incident ray - is a ray of light striking a surface

Reflected ray - is a ray of light reflected (bouncing off) a surface

Normal - imaginary line perpendicular to the surface where reflection or refraction occurs

Angle of incidence (i) - is the angle between the incident ray and the normal

Angle of reflection (r) - is the angle between the reflected ray and the normal

Laws of reflection

• Angle of Incidence = Angle of Reflection

• Incident ray, reflected ray and normal lie on the same plane

Regular and diffused reflection

Regular reflection occurs at smooth surfaces. Diffused reflection occurs at rough surfaces.

Image on a mirror

The characteristics of the image formed in the plane are:

• The image is of the same size as the object.

• It undergoes lateral inversion.

• It is upright.

• It is virtual.

• The distance of the image from the mirror is equal to the distance of the object from the mirror.

Refraction

Normal is the imaginary line perpendicular to the surface where reflection or refraction occurs.

Angle of incidence is the angle between the incident ray and the normal.

Angle of refraction is the angle between the refracted ray and the normal.

What is a refraction?

At the air-glass interface, light is

-partially reflected off the surface and

-partially transmitted through the medium.

The light that is transmitted through the medium bends as it travels from one optical

medium (air) into another (glass).This bending effect of light is known as refraction.

Refraction is the apparent change in direction of light when the ray of light passes from
one transparent medium (optical medium) into another.

What causes refraction?

• Light travels at different speed in different media.

• At the boundary of the two media such as air and glass, there is a sudden change in speed of the light. This change in speed causes the path of the light to change, resulting in refraction.

Amount of refraction

The amount of refraction depends on the optical density of the medium.

Optical density is a measure of the extent to which a substance transmits visible light.

The higher the optical density of a medium, the lower the transmittance, thus the greater is the refraction of light in it.

Why doesn’t refraction occur sometimes?

When a light ray strikes perpendicularly to the surface of an optical medium, its angle of incidence is zero, thus its angle of refraction is also zero. However, even though the light is not bend, its speed still decreases when it enters the optically denser medium.

Rules of refraction

When a light ray travels from an optically less dense medium(eg. air) into an optically denser medium(eg. glass) at an angle, it is always refracted towards the normal as light travels slower in the optically denser medium.

Critical angle

At a point where the refracted ray travels exactly along the glass surface, its angle of refraction is 90^o.

The angle of incidence in glass measured is what is known as the critical angle of glass.

Critical angle is defined as the angle of incidence in the optically denser medium when the angle of refraction in the optically less dense medium is 90^o.

The critical angle is different for different materials as it is dependent on the optical density of a material. A material with a greater optical density will have a smaller critical angle.

All the light is reflected at the interface as if it had hit a mirror – a perfect mirror.

This phenomenon is known as total internal reflection because 100% of the light is reflected within glass itself.

There is no refraction at all.

The light that is reflected follows the law of reflection such that the angle of incidence is equal to the angle of reflection.