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