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Biology

1. Functions of Plant Parts

The Root

  • The root is the part of the plant that takes in water and minerals for the plant.
  • Roots have root hairs that increase the surface area for more water absorption.

The Stem

  • The stem has vessels that transport sap and water throughout the plant.
  • Sap is a nutrient-rich fluid that contains a lot of sugar.

The Leaf

Two Functions of the Leaf

  • Photosynthesis is the process whenleaf cells containing chloropyll take in carbon dioxide and water and using sunlight, make sugar and oxygen.
  • Transpiration is the loss of water from the leaf. This helps to draw water up through the plant from the roots.

Leaf Cross-Section

The Leaf

  • Upper and Lower Epidermis – protective layers on the upper and lower sides of the leaf
  • Cuticle – waxy layer on the upper epidermis to reduce water loss
  • Palisade Cell Layer – layer without chloroplasts beneath the upper epidermis
  • Spongy Mesophyll Layer – layer beneath palisade layer containing chloroplasts which photosynthesise sugars; also contains veins carrying xylem and phloem, and many air spaces for exchange of carbon dioxide and oxygen
  • Stoma (Plural: Stomata) – pores in the lower epidermis that are surrounded by bean-shaped guard cells that contain chloroplasts

The Flower

The Flower

  • The flower is the organ of reproduction in flowering plants.
  • The male part of the flower is the stamen (composed of the anther where pollen is made and the thinfilament).
  • The female part of the flower is the pistil (composed of the stigma, the thin style and the ovary).
  • Pollination occurs when pollen is transferred by insects or wind from the anther to the stigma. Chemicals called enzymes ‘drill’ a channel down through the style to the ovary where the egg is.
  • Fertilisation occurs when the pollen joins with the egg. After this, a seed forms inside a fruit.
  • Germination is the process when a seed grows into a seedling.

How Water and Nutrients are Transported

  • Transpiration is the water loss that occurs through the open stomata. This loss helps to draw water up through the xylem from the root. Factors that affect transpiration are temperature, light intensity and duration, wind speed and relative humidity.
  • Capillary Action – Water moves from the root up to the leaf because of capillary action. This is an adhesive attraction between the water particles and the vessels inside the plant.
  • Diffusion – Almost all chemicals inside a plant move from areas where they are in excess to areas where there are insufficient amounts of the chemicals to maintain a balance. For example, water moves from the root up to the leaf, but sugars produced in the leaf by photosynthesis move downwards to the root.

 

 

 

 

 

Asexual Reproduction

  • Asexual Reproduction is the formation of a new organism where there is the presence of a single parent, and no joining of gametes (e.g. sperm, pollen, egg). The offspring has identical genes and chromosomes to the parent.
  • Advantages of Asexual Reproduction – No energy is expended to find a mate. There is a high chance of survival of the offspring, if the offspring remains near the parent in a stable environment.
  • Disadvantages of Asexual Reproduction – Less genetic diversity gives the offspring a lesser chance of survival if the environment changes.
  • Examples of Asexual Reproduction –
  1. Binary Fission (e.g. of bacteria and Amoeba) occurs when a cell simply grows larger, replicates its DNA in genes and chromosomes, and then forms a cell membrane down the mid-section of the cell to form 2 new ‘daughter’ cells.
  2. Budding (e.g. of yeast and hydras) occurs when a small part of the parent’s body separates from the rest and develops into a new individual, eventually either becoming an independent organism or part of an attached colony.
  3. Spore Formation (e.g. of ferns, malaria-causing protozoan called Plasmodium) occurs where special cells with resistant coverings form. These coverings are resistant to unfavourable environmental conditions such as heat, cold or dryness.
  4. Fragmentation (e.g. of flatworms and starfish) occurs when a parent body is broken into pieces, and each piece may form a new individual.
  5. Regeneration (e.g. of many plants) occurs when part of an organism grows to form other organisms that are often still connected to the original organism. Examples of regeneration in plants are the vegetative propagation of runners of grasses and strawberries, rhizomes in ferns, tubers in potatoes, and growing plants from cuttings.
  6. Parthenogenesis (e.g. of bees, wasps, some cockroaches, and liver flukes inside a host) occurs when a new organism develops from an unfertilised egg. For example, in honeybees, the female or queen honeybee is inseminated just once in her lifetime. The sperm she receives are stored in a little pouch connected to the genital tract, and closed off by a muscular valve. As the queen lays eggs, she can either open this valve permitting sperm to fertilise them (to become female queens or female workers), or she can keep the valve closed so that unfertilised develop into male drones.

Sexual Reproduction

  • Sexual Reproduction is the formation of a new organism from 2 parents usually, and involves the joining of gametes (e.g. sperm, pollen, egg) to form a single cell called a zygote (or fertilised egg). The offspring are similar, but not identical to the parents.
  • Advantages of Sexual Reproduction – There is greater genetic variation of the offspring and therefore, greater chance of survival in changing environments.
  • Disadvantages of Sexual Reproduction – Energy is expended in finding a mate in many organisms. However some organisms have both male and female reproductive organs that are able to produce gametes simultaneously.

Introduction to Human Reproduction

  • Gametes are the reproductive cells. The male gamete is called the sperm in many animals, and pollen in many complex plants. The female gamete is called the egg or ovum (Plural: ova).
  • Gonads are the reproductive organs that produce gametes and sex hormones. The human male gonad is called the testis (Plural: testes), and the female gonad is the ovary.
  • Puberty is the time during teenage years when males start to produce sperm, and females start to release eggs. Puberty occurs a couple of years earlier for females than males usually.
  • Menopause is the time when females stop releasing eggs. This usually occurs between 45 to 55 years of age. However, males do not undergo menopause and produce sperm all their lives following puberty.

The Human Male Reproductive System

THE PATH THAT SPERM TRAVEL

Testes

Arrow

Epididymis

Arrow

Vas Deferens (or Sperm Duct)

Arrow

Urethra

PARTS OF THE HUMAN MALE REPRODUCTIVE SYSTEM

Male System

Testis

  • There are 2 testes situated in a sac called the scrotum
  • Produces sperm in large numbers in seminiferous tubules
  • Produce male sex hormone called testosterone which regulates sperm production and secondary sexual characteristics (e.g. hair on face chest armpits and pubic area, deep voice, muscle bulk)

Epididymis

  • Stores the large numbers of sperm until they are ejaculated out through the penis

Sperm Duct or Vas Deferens

  • Transports sperm from the testis to urethra

Semen – Producing Glands

  • Semen is the fluid produced to protect the sperm from dehydration and the acidic environment of the female vagina after sexual intercourse. Semen also allows the sperm to swim more easily.
  • Semen – producing glands are Cowper’s Gland, the Seminal Vesicles and the Prostate Gland.

Urethra

  • This is the tube that normally carries urine from the urinary bladder.
  • When semen containing sperm is ejaculated, it also travels out through the urethra, but the prostate gland enlarges to block off any urine from the bladder at that time.

Penis

  • The urethra is the tube inside the penis.
  • During sexual intercourse, the spongy cells that surround the urethra fill with blood, and the penis becomes firm and erect.

2. The Human Female Reproductive System

THE PATH THE EGG TRAVELS

Ovary

Arrow

Oviduct or Fallopian Tube

Arrow

Uterus or Womb

Arrow

Cervix

Arrow

Vagina

PARTS OF THE FEMALE REPRODUCTIVE SYSTEM

Female System

Ovary

  • There are 2 ovaries
  • Produces eggs or ova, female sex hormones (oestrogen and progesterone) that regulate the menstrual cycle, pregnancy, and the secondary sexual characteristics (e.g. pubic and underarm hair, breasts, enlarged hips)
  • At birth, females have all their eggs formed, but in an immature state
  • After puberty and before menopause, one egg is released about every 28 days from each ovary

Oviduct or Fallopian Tube

  • Connects between ovary and uterus
  • Place where conception or fertilisation of an egg by a sperm occurs

Uterus or Womb

  • Strong muscular and elastic organ where an unborn baby develops
  • After an egg is released from the ovary, a blood-filled lining develops on the walls of the uterus in preparation for the nourishment of the unborn baby. If no fertilisation of the egg occurs, then this lining passes out through the vagina over several days as ‘periods’ or menstruation.

Cervix

  • The opening between the uterus and the vagina
  • During pregnancy, a mucous plug forms across the cervix separating the uterus from the outside to prevent infection of the unborn baby. This plug falls out, and the cervix dilates before the birth of a baby.

Vagina

  • Place where the penis is inserted during sexual intercourse
  • An elastic and muscular organ that expands during birth to allow for the passage of the baby

THE FEMALE MENSTRUAL CYCLE

  • The menstrual cycle begins at puberty and ceases at menopause.
  • It takes about 28 days.
  • Menstruation is regulated by the female sex hormones, oestrogen and progesterone.
  • Day 1 is the day when menstruation or ‘periods’ begin
  • Menstruation – Menstruation or ‘periods’ is the release of the blood-filled lining of the uterus if a woman is not pregnant. It lasts about 5 days.
  • Ovulation is the release of the egg from the ovary between about Days 12 to 16.
  • A woman will become pregnant if fertilisation (the joining of the egg and the sperm) occurs several days after ovulation when the egg is in the fallopian tube. During pregnancy, menstruation ceases.

FERTILISATION OR CONCEPTION

  • After sexual intercourse, the sperm travels up to join with the egg in the fallopian tube
  • The single-celled fertilised egg is called a zygote
  • 23 chromosomes of the sperm and 23 chromosomes of the egg combine in the zygote’s nucleus, so that the developing baby has 46 chromosomes

GESTATION OR PREGNANCY

  • Gestation in humans lasts about 40 weeks or 9 months
  • The first sign that a woman is pregnant is usually absence of menstruation (‘no periods’)
  • After fertilisation in the fallopian tube, the zygote multiplies to form a ball of cells which travels down to the uterus
  • The ball of cells (embryo) implants into the wall of the uterus
  • At the place where implantation occurs, an organ called the placenta develops
  • The umbilical cord grows between the placenta and the unborn baby’s navel
  • Inside the umbilical cord are blood vessels which provide nutrients and oxygen to the baby, and return wastes such as carbon dioxide back to the mother’s bloodstream
  • As the baby grows, it is called a foetus
  • The foetus is protected by amniotic fluid inside an amniotic sac
  • In the ninth month of pregnancy, the foetus turns upside down, and the mother’s breasts enlarge ready for milk production

BIRTH

  • At about 9 months, the ‘plug’ at the cervix releases, the amniotic sac breaks and fluid comes out through the vagina (‘breaking of the waters’)
  • Muscular contractions occur to both dilate the cervix, and ‘push’ out the baby head first from the uterus
  • Further muscular contractions expel the placenta
  • The umbilical cord is cut close to the baby’s navel
  • The mother begins breast milk production
  • The mother begins the menstrual cycle again, after the lining of the uterus from the pregnancy has been expelled over several days
  • Breech Birth occurs when the baby is born legs first
  • Caesarean Birth is the surgical removal of the baby from the mother’s uterus
  • Twins – Identical Twins (i.e. 2 sisters or 2 brothers) form when one egg and one sperm join, but as the zygote multiplies to form a ball of cells, the ball splits and the 2 embryos implant separately into the wall of the uterus.Non-identical or Fraternal Twins are formed when 2 eggs are fertilised by 2 sperm

Plant Reproduction

Plant Reproduction

Parts of a Flower

  • Flower – a modified stem with modified leaves (sepals and petals) and sexual organs (male stamen or femalepistil)
  • Flowers may contain only male reproductive organs (staminate flowers), or only female reproductive organs (pistillate flowers), or both.
  • The development of flowers is often following periods of either long or short nights. However, some angiosperms flower at any time of the year.

Pollination and Fertilisation

  • Pollination is the transfer of the male pollen grain from the anther to the stigma of the female pistil. Pollination may occur by means of the wind or by animals such as bees.
  • Self-pollination – pollination within the same plant
  • Cross-pollination – pollination with another plant
  • Fertilisation – the process when a male pollen grain enzymatically ‘drills’ a pollen tube down the style to the ovary, and then fuses with or fertilises a female ovum to form a single-celled zygote

The Fruit

  • Fruit – the enlarged fleshy ovule (part of the ovary) which contains the seed that developed from the zygote

Germination of the Seed

  • Germination – the growth of the seed into a small plant called a seedling
  • Water is essential for germination
  • Some Australian native plants also require short periods of high temperatures resembling bushfires in order to germinate.
  • Seeds may be dispersed or spread by wind (e.g. pine seed), by water (e.g. coconut) or by animals (e.g. bird).

3. SEL SARAF

Sistem saraf tersusun oleh berjuta-juta sel saraf yang mempunyai bentuk bervariasi. Sistern ini meliputi sistem saraf pusat dan sistem saraf tepi. Dalam kegiatannya, saraf mempunyai hubungan kerja seperti mata rantai (berurutan) antara reseptor dan efektor. Reseptor adalah satu atau sekelompok sel saraf dan sel lainnya yang berfungsi mengenali rangsangan tertentu yang berasal dari luar atau dari dalam tubuh. Efektor adalah sel atau organ yang menghasilkan tanggapan terhadap rangsangan. Contohnya otot dan kelenjar.

Sistem saraf terdiri dari jutaan sel saraf (neuron). Fungsi sel saraf adalah mengirimkan pesan (impuls) yang berupa rangsang atau tanggapan.

Struktur Sel Saraf

 

Setiap neuron terdiri dari satu badan sel yang di dalamnya terdapat sitoplasma dan inti sel. Dari badan sel keluar dua macam serabut saraf, yaitu dendrit dan akson (neurit). Dendrit berfungsi mengirimkan impuls ke badan sel saraf, sedangkan akson berfungsi mengirimkan impuls dari badan sel ke jaringan lain. Akson biasanya sangat panjang. Sebaliknya, dendrit pendek. Setiap neuron hanya mempunyai satu akson dan minimal satu dendrit. Kedua serabut saraf ini berisi plasma sel. Pada bagian luar akson terdapat lapisan lemak disebut mielin yang merupakan kumpulan sel Schwann yang menempel pada akson. Sel Schwann adalah sel glia yang membentuk selubung lemak di seluruh serabut saraf mielin. Membran plasma sel Schwann disebut neurilemma. Fungsi mielin adalah melindungi akson dan memberi nutrisi. Bagian dari akson yang tidak terbungkus mielin disebut nodus Ranvier, yang berfungsi mempercepat penghantaran impuls.

Berdasarkan struktur dan fungsinya, sel saraf dapat dibagi menjadi 3 kelompok, yaitu sel saraf sensori, sel saraf motor, dan sel saraf intermediet (asosiasi).

  • Sel saraf sensori

Fungsi sel saraf sensori adalah menghantar impuls dari reseptor ke sistem saraf pusat, yaitu otak (ensefalon) dan sumsum belakang (medula spinalis). Ujung akson dari saraf sensori berhubungan dengan saraf asosiasi (intermediet).

  • Sel saraf motor

Fungsi sel saraf motor adalah mengirim impuls dari sistem saraf pusat ke otot atau kelenjar yang hasilnya berupa tanggapan tubuh terhadap rangsangan. Badan sel saraf motor berada di sistem saraf pusat. Dendritnya sangat pendek berhubungan dengan akson saraf asosiasi, sedangkan aksonnya dapat sangat panjang.

  • Sel saraf intermediet

Sel saraf intermediet disebut juga sel saraf asosiasi. Sel ini dapat ditemukan di dalam sistem saraf pusat dan berfungsi menghubungkan sel saraf motor dengan sel saraf sensori atau berhubungan dengan sel saraf lainnya yang ada di dalam sistem saraf pusat. Sel saraf intermediet menerima impuls dari reseptor sensori atau sel saraf asosiasi lainnya. Kelompok-kelompok serabut saraf, akson dan dendrit bergabung dalam satu selubung dan membentuk urat saraf. Sedangkan badan sel saraf berkumpul membentuk ganglion atau simpul saraf.

Mekanisme Penghantar Impuls

Impuls dapat dihantarkan melalui beberapa cara, di antaranya melalui sel saraf dan sinapsis. Berikut ini akan dibahas secara rinci kedua cara tersebut.

  • Penghantaran Impuls Melalui Sel Saraf

Penghantaran impuls baik yang berupa rangsangan ataupun tanggapan melalui serabut saraf (akson) dapat terjadi karena adanya perbedaan potensial listrik antara bagian luar dan bagian dalam sel. Pada waktu sel saraf beristirahat, kutub positif terdapat di bagian luar dan kutub negatif terdapat di bagian dalam sel saraf. Diperkirakan bahwa rangsangan (stimulus) pada indra menyebabkan terjadinya pembalikan perbedaan potensial listrik sesaat. Perubahan potensial ini (depolarisasi) terjadi berurutan sepanjang serabut saraf. Kecepatan perjalanan gelombang perbedaan potensial bervariasi antara 1 sampai dengart 120 m per detik, tergantung pada diameter akson dan ada atau tidaknya selubung mielin.

Bila impuls telah lewat maka untuk sementara serabut saraf tidak dapat dilalui oleh impuls, karena terjadi perubahan potensial kembali seperti semula (potensial istirahat). Untuk dapat berfungsi kembali diperlukan waktu 1/500 sampai 1/1000 detik.

Energi yang digunakan berasal dari hasil pemapasan sel yang dilakukan oleh mitokondria dalam sel saraf.

Stimulasi yang kurang kuat atau di bawah ambang (threshold) tidak akan menghasilkan impuls yang dapat merubah potensial listrik. Tetapi bila kekuatannya di atas ambang maka impuls akan dihantarkan sampai ke ujung akson. Stimulasi yang kuat dapat menimbulkan jumlah impuls yang lebih besar pada periode waktu tertentu daripada impuls yang lemah.

  • Penghantaran Impuls Melalui Sinapsis

 

Titik temu antara terminal akson salah satu neuron dengan neuron lain dinamakan sinapsis. Setiap terminal akson membengkak membentuk tonjolan sinapsis. Di dalam sitoplasma tonjolan sinapsis terdapat struktur kumpulan membran kecil berisi neurotransmitter; yang disebut vesikula sinapsis. Neuron yang berakhir pada tonjolan sinapsis disebut neuron pra-sinapsis. Membran ujung dendrit dari sel berikutnya yang membentuk sinapsis disebut post-sinapsis. Bila impuls sampai pada ujung neuron, maka vesikula bergerak dan melebur dengan membran pra-sinapsis. Kemudian vesikula akan melepaskan neurotransmitter berupa asetilkolin. Neurontransmitter adalah suatu zat kimia yang dapat menyeberangkan impuls dari neuron pra-sinapsis ke post-sinapsis. Neurontransmitter ada bermacam-macam misalnya asetilkolin yang terdapat di seluruh tubuh, noradrenalin terdapat di sistem saraf simpatik, dan dopamin serta serotonin yang terdapat di otak. Asetilkolin kemudian berdifusi melewati celah sinapsis dan menempel pada reseptor yang terdapat pada membran post-sinapsis. Penempelan asetilkolin pada reseptor menimbulkan impuls pada sel saraf berikutnya. Bila asetilkolin sudah melaksanakan tugasnya maka akan diuraikan oleh enzim asetilkolinesterase yang dihasilkan oleh membran post-sinapsis.

Bagaimanakah penghantaran impuls dari saraf motor ke otot? Antara saraf motor dan otot terdapat sinapsis berbentuk cawan dengan membran pra-sinapsis dan membran post-sinapsis yang terbentuk dari sarkolema yang mengelilingi sel otot. Prinsip kerjanya sama dengan sinapsis saraf-saraf lainnya.

Terjadinya Gerak Biasa Dan Gerak Refleks

Gerak merupakan pola koordinasi yang sangat sederhana untuk menjelaskan penghantaran impuls oleh saraf. Gerak pada umumnya terjadi secara sadar, namun, ada pula gerak yang terjadi tanpa disadari yaitu gerak refleks. Impuls pada gerakan sadar melalui jalan panjang, yaitu dari reseptor, ke saraf sensori, dibawa ke otak untuk selanjutnya diolah oleh otak, kemudian hasil olahan oleh otak, berupa tanggapan, dibawa oleh saraf motor sebagai perintah yang harus dilaksanakan oleh efektor. Gerak refleks berjalan sangat cepat dan tanggapan terjadi secara otomatis terhadap rangsangan, tanpa memerlukan kontrol dari otak. Jadi dapat dikatakan gerakan terjadi tanpa dipengaruhi kehendak atau tanpa disadari terlebih dahulu. Contoh gerak refleks misalnya berkedip, bersin, atau batuk.

Pada gerak refleks, impuls melalui jalan pendek atau jalan pintas, yaitu dimulai dari reseptor penerima rangsang, kemudian diteruskan oleh saraf sensori ke pusat saraf, diterima oleh set saraf penghubung (asosiasi) tanpa diolah di dalam otak langsung dikirim tanggapan ke saraf motor untuk disampaikan ke efektor, yaitu otot atau kelenjar. Jalan pintas ini disebut lengkung refleks. Gerak refleks dapat dibedakan atas refleks otak bila saraf penghubung (asosiasi) berada di dalam otak, misalnya, gerak mengedip atau mempersempit pupil bila ada sinar dan refleks sumsum tulang belakang bila set saraf penghubung berada di dalam sumsum tulang belakang misalnya refleks pada lutut.

Sistem Saraf Pusat

Sistem saraf pusat meliputi otak (ensefalon) dan sumsum tulang belakang (Medula spinalis). Keduanya merupakan organ yang sangat lunak, dengan fungsi yang sangat penting maka perlu perlindungan. Selain tengkorak dan ruas-ruas tulang belakang, otak juga dilindungi 3 lapisan selaput meninges. Bila membran ini terkena infeksi maka akan terjadi radang yang disebut meningitis.

Ketiga lapisan membran meninges dari luar ke dalam adalah sebagai berikut.

  1. Durameter; merupakan selaput yang kuat dan bersatu dengan tengkorak.
  2. Araknoid; disebut demikian karena bentuknya seperti sarang labah-labah. Di dalamnya terdapat cairan serebrospinalis; semacam cairan limfa yang mengisi sela sela membran araknoid. Fungsi selaput araknoid adalah sebagai bantalan untuk melindungi otak dari bahaya kerusakan mekanik.
  3. Piameter. Lapisan ini penuh dengan pembuluh darah dan sangat dekat dengan permukaan otak. Agaknya lapisan ini berfungsi untuk memberi oksigen dan nutrisi serta mengangkut bahan sisa metabolisme.

Otak dan sumsum tulang belakang mempunyai 3 materi esensial yaitu:

  1. Badan sel yang membentuk bagian materi kelabu (substansi grissea)
  2. Serabut saraf yang membentuk bagian materi putih (substansi alba)
  3. Sel-sel neuroglia, yaitu jaringan ikat yang terletak di antara sel-sel saraf di dalam sistem saraf pusat

Walaupun otak dan sumsum tulang belakang mempunyai materi sama tetapi susunannya berbeda. Pada otak, materi kelabu terletak di bagian luar atau kulitnya (korteks) dan bagian putih terletak di tengah. Pada sumsum tulang belakang bagian tengah berupa materi kelabu berbentuk kupu-kupu, sedangkan bagian korteks berupa materi putih.

Otak

 

Otak mempunyai lima bagian utama, yaitu: otak besar (serebrum), otak tengah (mesensefalon), otak kecil (serebelum), sumsum sambung (medulla oblongata), dan jembatan varol.

  • Otak besar (serebrum)

Otak besar mempunyai fungsi dalam pengaturan semua aktifitas mental, yaitu yang berkaitan dengan kepandaian (intelegensi), ingatan (memori), kesadaran, dan pertimbangan. Otak besar merupakan sumber dari semua kegiatan/gerakan sadar atau sesuai dengan kehendak, walaupun ada juga beberapa gerakan refleks otak. Pada bagian korteks serebrum yang berwarna kelabu terdapat bagian penerima rangsang (area sensor) yang terletak di sebelah belakang area motor yang berfungsi mengatur gerakan sadar atau merespon rangsangan. Selain itu terdapat area asosiasi yang menghubungkan area motor dan sensorik. Area ini berperan dalam proses belajar, menyimpan ingatan, membuat kesimpulan, dan belajar berbagai bahasa. Di sekitar kedua area tersebut dalah bagian yang mengatur kegiatan psikologi yang lebih tinggi. Misalnya bagian depan merupakan pusat proses berfikir (yaitu mengingat, analisis, berbicara, kreativitas) dan emosi. Pusat penglihatan terdapat di bagian belakang.

  • Otak tengah (mesensefalon)

Otak tengah terletak di depan otak kecil dan jembatan varol. Di depan otak tengah terdapat talamus dan kelenjar hipofisis yang mengatur kerja kelenjar-kelenjar endokrin. Bagian atas (dorsal) otak tengah merupakan lobus optikus yang mengatur refleks mata seperti penyempitan pupil mata, dan juga merupakan pusat pendengaran.

  • Otak kecil (serebelum)

Serebelum mempunyai fungsi utama dalam koordinasi gerakan otot yang terjadi secara sadar, keseimbangan, dan posisi tubuh. Bila ada rangsangan yang merugikan atau berbahaya maka gerakan sadar yang normal tidak mungkin dilaksanakan.

Jembatan varol (pons varoli)

Jembatan varol berisi serabut saraf yang menghubungkan otak kecil bagian kiri dan kanan, juga menghubungkan otak besar dan sumsum
tulang belakang.

Sumsum sambung (medulla oblongata)

Sumsum sambung berfungsi menghantar impuls yang datang dari medula spinalis menuju ke otak. Sumsum sambung juga mempengaruhi jembatan, refleks fisiologi seperti detak jantung, tekanan darah, volume dan kecepatan respirasi, gerak alat pencernaan, dan sekresi kelenjar pencernaan. Selain itu, sumsum sambung juga mengatur gerak refleks yang lain seperti bersin, batuk, dan berkedip.

Sumsum tulang belakang (medulla spinalis)

Pada penampang melintang sumsum tulang belakang tampak bagian luar berwarna putih, sedangkan bagian dalam berbentuk kupu-kupu dan berwarna kelabu. Pada penampang melintang sumsum tulang belakang ada bagian seperti sayap yang terbagi atas sayap atas disebut tanduk dorsal dan sayap bawah disebut tanduk ventral. Impuls sensori dari reseptor dihantar masuk ke sumsum tulang belakang melalui tanduk dorsal dan impuls motor keluar dari sumsum tulang belakang melalui tanduk ventral menuju efektor. Pada tanduk dorsal terdapat badan sel saraf penghubung (asosiasi konektor) yang akan menerima impuls dari sel saraf sensori dan akan menghantarkannya ke saraf motor. Pada bagian putih terdapat serabut saraf asosiasi. Kumpulan serabut saraf membentuk saraf (urat saraf). Urat saraf yang membawa impuls ke otak merupakan saluran asenden dan yang membawa impuls yang berupa perintah dari otak merupakan saluran desenden.

Human Nervous System

Main Parts of the Nervous System

  1. Brain
  2. Spinal Cord
  3. Nerves – Sensory and Motor Nerves

 

 

The Neurone

  • Nerve cells are called neurones.
  • A neurone consists of a cell body (with a nucleus and cytoplasm),dendrites which carry electrical impulses to the cell, and a long axon which carries the impulses away from the cell.
  • The axon of one neurone and the dendrites of the next neurone do not actually touch. The gap between neurones is called the synapse.

 

 

The Central Nervous System

  • The Central Nervous System comprises the Brain and the Spinal Cord – the parts enclosed and protected by bone.
  • Parts of The Brain
  1. Cerebrum (Forebrain) – the largest section of the brain, which lets us think, interpret sensory messages, carry out voluntary muscle movements, remember and have consciousness
  2. Cerebellum (Midbrain) – helps us to keep our balance, and have repetitive muscle control
  3. Medulla Oblongata (Hindbrain) – control the vital functions of heartbeat, breathing and blood pressure

 

 

 

The Peripheral Nervous System

  • This is the part of the nervous system that does not include the brain and the spinal cord.
  • There are 2 types of nerves – sensory and motor nerves.
  • Sensory Nerves carry information about the surroundings from the sense receptors in the skin, eyes, ears, nose and tongue, along the spinal cord to the brain to be interpreted.
  • Motor Nerves carry messages from the brain through the spinal cord to the muscles and other organs to produce an action.
  • Some of the nerves of the peripheral nervous system are under voluntary control (e.g. controlling motor nerves and muscles when writing). Other nerves are involuntary or uncontrolled (e.g. regulating heartbeat).

 

 

A Reflex Arc

  • A reflex arc involves transmission of a nervous impulse or message from sensory receptors to the spinal cord and back to muscles. Later, the message also reaches the brain for interpretation.
  • Example: touching your hand on a hot stove

 

 

Senses

  • The main senses are:
  1. Touch
  2. Smell
  3. Taste
  4. Sight
  5. Hearing
  • The sense of touch includes touch, pressure, heat, cold and pain.
  • A stimulus is a factor in the surroundings that causes the sense receptors to function.

SENSE

SENSE ORGANS

STIMULUS

Touch, pressure, heat, cold, pain Skin, joints, internal organs Internal or external force or temperature
Smell Nose Airborne chemicals
Taste Taste buds on tongue Ingested chemicals
Sight Eyes Light
Hearing Ears Sound

 

 

The Eye

The Path of Light through the Eye

Cornea

Aqueous Humour

Pupil

Lens

Vitreous Humour

Retina

Functions of the Parts of the Eye

  • Cornea – thin transparent layer at the front of the eye
  • Aqueous Humour – watery substance that fills the cavity between cornea and lens
  • Pupil – a hole to allow to pass to the lens
  • Iris – a coloured circular muscle that contracts or relaxes to dilate or constrict the pupil
  • Lens – a transparent elastic ball that focuses light rays onto the retina
  • Ciliary Ligament – attached to lens, and contracts or relaxes to adjust the lens
  • Ciliary Body – attaches the ciliary ligament to the eyeball, and produces both aqueous and vitreous humours
  • Vitreous Humour – a more viscous fluid that fills the cavity behind the lens
  • Retina – a hemispherical layer of light-sensitive cells (rods and cones) at the back of the eye
  • Fovea – a small area of the retina which is directly in line with the centre of the cornea and the lens, and is concentrated with the colour-sensitive cones
  • Optic Nerve – the nerve which connects the retina with the vision area of the brain
  • ‘Blind Spot’ – the place on the retina where the optic nerve attaches; has no light-sensitive cones and rods
  • Choroid Coat – sheet of cells next to the retina with a black pigment to absorb extra light, and blood vessels to nourish the retina
  • Sclera – tough outer coat of the eyeball

Light-Sensitive Sense Receptors – Rods and Cones

  • Rods are the more numerous cells that detect shades of black, grey and white light. They are more prevalent in the periphery of the eye.
  • Cones are cells that detect coloured light. They are more prevalent in the centre of the retina, particularly the fovea.
  • There are no rods nor cones in the ‘Blind Spot’ where the optic nerve meets the retina.

Vision

  • Focus of the Lens – When looking at distant objects, the lens is long and thin in shape. When looking at close objects, the lens is short and wide.
  • Binocular Vision – Two eyes are important in judging distance and depth.
  • Pupil Size – In bright light, the iris muscle relaxes and the pupil decreases in size so that less light enters the eye. In dim light, the iris muscle contracts and the pupil increase in size to allow more light to enter.
  • Short-sightedness (Myopia) – This is a condition where the person can see close objects well, but not distant objects. Light focuses in front of the retina. It is corrected with concave lenses in spectacles.
  • Long-sightedness (Hyperopia) – This is a condition where the person can see distant objects well, but not close objects. Light focuses behind the retina. It is corrected with convex lenses in spectacles.
  • Astigmatism – This is a condition where the cornea is curved unevenly, so that different light rays focus in different places. It is corrected with spectacles.

 

 

The Ear

Path of Sound through the Ear

OUTER EAR
Pinna

Auditory Canal

Eardrum

MIDDLE EAR
3 Earbones or Ossicles

Oval Window

INNER EAR
Cochlea

Functions of the Parts of the Ear

OUTER EAR

  • Pinna – funnel-shaped visible flap that directs sound waves into the auditory canal
  • Auditory Canal – canal that carries the sound waves to the eardrum
  • Eardrum – a thin membrane which is vibrated by sound waves

MIDDLE EAR

  • 3 Earbones or Ossicles (Hammer, Anvil and Stirrup) – These are the smallest bones in the body. The eardrum vibrates, and this vibrates the hammer, the anvil and the stirrup one after another. The stirrup then vibrates the Oval Window.

INNER EAR

  • Cochlea – This is a spirally coiled tube containing fluid and the actual organ of hearing, the Organ of Corti. Each organ of Corti contains thousands of hairs that are vibrated by the sound waves. The hairs then initiate nervous impulses in the Auditory Nerve which is connected to the auditory areas on the sides of the brain.

Pitch and Amplitude of Sound

  • High-pitched sounds causes intese stimulation of the hairs in the cochlea, whereas low-pitched sounds cause less stimulation.
  • Loud sounds stimulate a greater number of hairs in the cochlea, than do quiet sounds.

Other Features of the Ear

  • Semi-Circular Canals – These are 3 fluid-filled canals that detect the position of the head in 3 dimensions. Impulses are sent through via the auditory nerve to the brain.
  • Eustachian Tube – There is a tube that connects each middle ear to the pharynx to equalise air pressure within the middle ear.

4. Food Chains & Food Webs


  • Food Chain – A food chain is the series of organisms showing feeding relationships. A food chain almost always begins with a green plant (producer) which is eaten by an animal (consumer). The arrow means ‘is eaten by’, and shows the flow of matter and energy along the food chain. There are no decomposers in a food chain.
  • Example of a Food Chain:
  • Grass(Producer) Arrow Grasshopper(1st order Consumer) ArrowKookaburra(2nd order Consumer)
  • Producer – usually a green plant that produces its own food by photosynthesis
  • First-order Consumer – the organism that eats the producer
  • Second-order Consumer – the organism that eats or derives nutrients from the first-order consumer
  • Herbivore – a plant eater
  • Carnivore – an organism that obtains nutrients from the blood or flesh of an animal
  • Omnivore – an organism which eats both plant and animal matter
  • Scavenger – an consumer that eats dead animals (e.g. crab)
  • Detritivore – a consumer that obtains its nutrients from detritus
  • Decomposer – an organism such as bacteria and fungi that breaks down dead organisms and their wastes
  • Trophic Level – A trophic level is each level in a food chain. Matter is always ‘lost’ as heat energy at each trophic level.
  • Basal Energy Requirement (B.E.R.) – the amount of energy used by an organism’s body just to keep alive, when no food is being digested and no muscular work is being done
  • Food Web – a network of interrelated food chains in a given area

Food Web


Biomass Pyramids

  • Loss of Matter and Energy – At each trophic level along a food chain, there is always a ‘loss’ of matter and energy in the forms of waste (e.g. carbon dioxide, faeces), and heat and kinetic energy (e.g. constant body temperature of mammals, the energy used to move). Up to 90% of matter and energy can be ‘lost’ at each level.
  • Biomass – the total dry weight of the organisms in a trophic level
  • Biomass Pyramid – a diagram showing the biomass at each trophic level of a food chain

Biomass Pyramid


Biological Magnification

  • Some chemicals that are taken in from the environment by plants, or consumed by animals, cannot be excreted by organisms. They accumulate in the body by the organisms, sometimes up to toxic levels. The more organisms there are in a food chain, the greater is the accumulation in the higher order consumers. Such chemicals include the pesticide DDT, and heavy metals such as mercury.


Biological Control

  • Pests – Pests may be plant or animal. They usually are introduced from overseas. Because of both their ability to survive and reproduce successfully in the Australian habitat, and their lack of predators or parasites, they reach pest population numbers, competing with the native flora and fauna.
  • Biological Control of the populations of pest plants and animals is accomplished by non- chemical means involving predation, parasitism, or interruption to reproduction. Biological control is usually specific to a particular pest organism.
  • Successful Biological Control Experiment Examples
  1. Prickly Pear Cactus – This introduced species was a pest throughout cattle farms in Queensland. The introduction of the Cactoblastis Moth reduced its numbers through consumption.
  2. European Rabbit – Rabbits arrived in Australia in 1788 and reproduced rapidly. The Myxoma Virus was developed in the 1900’s to spread by direct contact and cause death.
  • Unsuccessful Biological Control Experiment Examples
  • Cane Toad – Cane toads were originally introduced to sugar cane fields to reduce the numbers of cane beetles destroying sugar cane. However, cane toads did not eat cane beetles, instead reproducing rapidly themselves and causing death to native wildlife which ate them. No successful predators exist in Australia.


Cycles in Nature

  • Law of Conservation of Matter

Matter cannot be created nor destroyed in any chemical reaction. It can only be transformed from one form to another.

  • Cycle – A cycle shows the reusing of certain elements and compounds (e.g. water, carbon, oxygen, nitrogen, phosphorus) in different forms in ecosystems.

WATER CYCLE

  • The sun provides the heat energy required for the cycle to continue.
  • The oceans and rivers are the main reservoirs of water.
  • Evaporation – Water evaporates into the atmosphere.
  • Condensation – Water condenses into droplets in the clouds.
  • Precipitation – As the water droplets in clouds enlarge, water falls to earth in the form of rain, snow or hail.
  • Transpiration – Water is lost through the leaves of plants (‘trees perspiring’).

CARBON AND OXYGEN CYCLES

  • Carbon occurs in all living organisms in the forms of carbon dioxide, carbohydrates (sugars and starches), proteins and fats.
  • Oxygen occurs in all living organisms in the forms of oxygen gas, water, carbon dioxide, carbohydrates, proteins and fats.
  • Photosynthesis – Photosynthesis is the process used by plants containing chlorophyll to utilise sunlight, carbon dioxide and water to form sugar (as glucose) and oxygen.
  • Carbon Dioxide + Water Cells Arrow Glucose Sugar + Oxygen
  • CO2 + H2Cells Arrow C6H12O6 + O2
  • Respiration – Respiration is the process that most living organisms (including animals, plants, fungi and micro-organisms) use to obtain energy from glucose sugar and oxygen. The wastes formed are carbon dioxide and water.
  • Glucose + Oxygen Arrow Carbon Dioxide + Water + Energy
  • C6H12O6 + O2Arrow CO2 + H2O + Energy
 

One response to “Biology

  1. thenewlittlegirl

    December 4, 2011 at 12:43 pm

    Increase your knowledge in here

     

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