Mitosis and Meiosis

Image shows karyotype of a female. Her somatic cell has a diploid number of 46.

refer to your chapter 5 note.
What is diploid number & haploid number of chromosome?
1. Diploid - organisms or cells that have 2 sets of chromosomes.
2. Haploid - cells that have only one set of chromosomes.

Here are some images which are related to cell division:

1. Image below shows the chromosomes, DNA, histone proteins inside the nucleus of a typical cell.

2. Image below shows chromosomes.

• When the chromosome condense, coil-up and tighten during prophase of mitosis (or prophase I or prohase II of meiosis), the chromosome appear as two identical chromatids called sister chromatids attached together at the contromere.
  
  

3. Prophase I of meiosis I.

• At the chiasma, exchange of genetic material between the non-sister chromatids of bivalent through the process of crossing over.
• Crossing over results in new combination of genetic material and is important source of genetic variation.
  

4. the differences between Meiosis & Mitosis

Plant Hormone

what is coleoptile? it is a tough protective sheath that encloses/protects the tip of a shoot.

• refer to page 22-24, chapter 3.
  
• Plant hormone is a chemical substance produced by plant, which is able to influence the growth & development of the plant.
  
• Plant hormones can be used to produce fruit without seeds, to ripen fruits, to increase the size of fruit, in growing cuttings, controlling weeds, etc.
  
• There are 5 classes of plant hormone:
  1. Auxins (Indole Acetic Acid) - promotes cell elongation at stem tip, roots initiation, fruit development.
  2. Cytokinins - promotes cell division
  3. Gibberellins - promotes cell elongation
  4. Abscisic acid - promotes seed dormancy
  5. Ethylene (ethene) - a gas hormone which is used to ripen fruits, etc
  
• Auxin is a plant hormone that controls tropic response.
• It is produced in the apical meristem of the shoot & root.
• Auxin diffuse from zone of cell division into zone of cell elongation where it stimulates the cell to elongate.
  
• Diagram below shows:
  1. concentration of auxins needed for maximum growth of shoots will inhibit roots growth.
  2. at low concentration of auxin hormone, this promotes roots growth but cannot stimulate shoots growth.
  
  

Below are some experiments related to Auxins hormone:

1. The coleoptile tip is removed (just above the zone of cell elongation). Gelatin/agar block which contains auxin hormone is then placed at one side of the coleoptile.
Results: coleoptile bending towards the side without the agar block.

2. Role of auxins in controlling phototropism: (unilateral light)

3. Shoot placed horizontally. Auxin hormone will accumulate at the lower side.

4. Diagram below showing geotropism on shoot & root of seedling when the seedlings are placed in different positions. The shoot shows negative geotropism while the root shows positive geotropism.

Spinal nerves

This posting about spinal nerve is not covered under spm syllabus. But i hope the diagrams below can give you some understanding about spinal nerve.

We hv 31 pairs of spinal nerves.


1 is spinal cord; 2 is ventral root; 3 is dorsal root; 4 is spinal nerve

Functional types of neurons in spinal nerves (& other nerves):

1. somatic afferent - sensory from general cutaneous receptors (in the skin) & proprioceptors (in skeletal muscles, tendons, & joints)
2. somatic efferent - motor to skeletal muscles
3. visceral afferent - sensory from receptors in the viscera (smooth muscle, cardiac muscle, & glands)
4. visceral efferent - motor to smooth muscle, cardiac muscle, & glands
   
   *viscera =internal organs; singular (viscus)

The skeletal muscle tissue

1. In general, there are 3 types of muscle tissues.

• Skeletal muscle: which is striated and voluntary
• Cardiac muscle: which is striated and involuntary
• Smooth muscle: which is non striated and involuntary

2. Skeletal muscle tissue:

• involuntary muscle (can be made contract or relax by conscious control through the nervous system)
  
• striated or striped muscle because of the presence of alternating dark & light bands on the muscle fibre.
  
  The structure of skeletal muscle:
  1. Is made up of a large number of cylindrical cells called muscle fibres or myofibres.
  (myofibre = a muscle cell)
  2. Each myofibre/muscle fibre is covered by a plasma membrane called sarcolemma, has many nuclei, & contains many protein fibres (called myofibrils) which enable the muscle fibre to contract.
  3. Each skeletal tissue consists of bundles of muscle fibres & these bundles are separated by connective tissue (also called epimysium)
  
  
  
  What is myofibrils?
  1.Myofibrils are composed of individual contractile proteins called myofillaments. These myofilaments are generally divided into thick and thin myofilaments.
  2. The thin myofilaments are composed mainly of a protein known as actin. Actin filaments are anchored into the z-line of a sarcomere.
  3. The thick myofilaments are composed mainly of the protein myosin. It is the orderly overlapping of the actin and myosin filaments that give cardiac and skeletal muscle their striated appearance (light and dark bands).
  
• The contraction of skeletal muscle tissue comes from the collective contractions of each single muscle fibre, whose contraction in turn comes from the contractions of the protein fibres (myofibrils).
  
• The contraction of skeletal muscle requires energy (ATP) produced by mitochondria within the muscle fibres. (sarcosome = the mitochondria of muscle cell).

What is cardiac muscle?

• Cardiac muscle cells are not as long as skeletal muscles cells and often are branched cells.
  
• Cardiac muscle cells may be mononucleated or binucleated. In either case the nuclei are located centrally in the cell.
  
• Cardiac muscle is also striated.
  
• In addition cardiac muscle contains intercalated discs.
  

What is smooth muscle?

• Smooth muscle cells are described as spindle shaped. That is they are wide in the middle and narrow to almost a point at both ends.
  
• Smooth muscle cells have a single centrally located nucleus.
  
• Smooth muscle cells do not have visible striations although they do contain the same contractile proteins as skeletal and cardiac muscle, these proteins are just laid out in a different pattern.

Production of Proteins/Enzymes

This is a useful video to bring you through the production of proteins/enzyme.

For SPM level, your notes (form 4 chapter 2 & 4) regarding the production of Extracellular Enzyme are sufficient. Terms such as transcription, translation are not covered under spm syllabus.

Synapse & transmission of information

What is synapse?
- it is the site where 2 neurones, or a neurone & an effector cell communicate.

Nerve impulses must cross the synapse in order to carry NI/information along to another neurone. Chemicals are used by a neurone to trasmit an impulse across a synapse.

How transmission of chemical signals across the synapse? (refer notes pg7, #6, memorise this!)

Transmission of NI across synapse is an active process/transport which requires energy/ATP. therefore, the synaptic knob contains abundant of mitochondria for generation of energy.

*pls note that action potential, calcium, sodium ion channels, endocytosis are not covered under spm syllabus.

What cloning is? Can we clone human?

What is cloning?

• It is a highly artificial form of asexual reproduction based on mitosis to form new individuals.


• The new individuals are called CLONES, which have the same genetic material as the parent.

How is animal cloning carried out?

• An animal is cloned using a nucleus obtained from an adult tissue.


• The clone is genetically identical to the somatic cell donor.


• In 1996, Scotland , Dolly became the first cloned sheep done through a technique called Somatic Cell Nuclear Transplant (SCNT). She was produced after 270 attempts & has many deformities. She died of lung disease in 2003 at the age of 6, while a normal life span of a sheep is around 10-16 years.

To know more about cloning, watch the video below or click here.

Human embryo cloning – 3 minutes


FIRST HUMAN EMBRYO-CLONE CREATED
Uploaded by neverknwo. - Explore more science and tech videos.

You can watch Dolly, the clone sheep, go to 5-7 minutes of the 2nd video below.
To watch the full documentary, click the video below or click here

Panayiotis Zavos is a controversial fertility doctor. He said to “The Independent” that he had already cloned human embryos and transferred 11 of them into the wombs of four women who had been prepared to give birth to cloned babies.
Since cloning embryos into the human womb is a criminal offense in most countries, Dr. Panayiotis Zavos is said to have worked at a secret laboratory in the Middle East where there is no cloning ban.
Dr. Zavos also revealed that he has produced cloned embryos of three dead people, including a 10-year-old child called Cady, who died in a car crash. He did so after being asked by grieving relatives if he could create biological clones of their loved one.>

Human cloning – 45 minutes






Do you think we should be cloning human?

Nucleic Acid - DNA & RNA

Nucleic Acid are complex macromolecules which store genetic information in the form of a code.


There are 2 types of nucleic acid: DNA (Deoxyribonucleic acid) & RNA (Ribonucleic acid).

• basic units of nucleic acids are nucleotides


• A nucleotide is made up of:
  
  1. a pentose sugar (deoxyribose for DNA, ribose for RNA)
  2. a nitrogenous base


• 3. a phosphate group
  

What is DNA molecule?

• DNA molecules can be found inside the nucleus, the mitochondria & chloroplast organelles.


• The sequence of nitrogenous base in a DNA molecule is called gene.
  
• A DNA molecule contains thousand of genes which code for the synthesis of specific proteins. (eg: enzyme)
  
• A DNA molecule consists of two polynucleotide strands coiled together/twisted around each other to form a DOUBLE HELIX. (above diagram)
  
  
  
  
  
  How are the nucleotides linked?
  Each nucleotide is joined to the next nucleotide through the phosphate group to form a long polynucleotide strand.
  Diagram shows 2 polynucleotide strands arranged in anti-parallel.
  
  
  




• 
  
  
  
  
  
  
  In 1953 James D. Watson and Francis Crick suggested what is now accepted as the first correct double-helix model of DNA structure.
  
  
  
  
  
  

What is RNA?

• can be found in the nucleus, ribosomes & cytoplasm.


• there are 3 types of RNA (mRNA, rRNA, tRNA) - this is not covered under spm syllabus.


• messenger RNA (mRNA) carries DNA's genetic code into the cytoplasm & direct the synthesis of proteins.

What are the differences between DNA & RNA?

1. DNA consists of 2 strands of polynucleotide (that coiled together to form a double helix) while RNA consists of only one strand of polynucleotide.

2. The pentose sugar in DNA is deoxyribose while in RNA it is ribose.

3. types of nitrogenous bases - you will learn in form 5.

Spinal Cord & Neurones

Human Nervous System is made up of the Central Nervous System (CNS) & the Peripheral Nervous System (PNS).

• PNS consists of the cranial nerves (12 pairs) & the spinal nerves (31 pairs).
• CNS is the control centre of the body.
  
• Spinal Cord (SC) link between the brain & the PNS.

*note: in the above diagram, an Interneurone should be drawn to connect the Sensory neurone to motor neurone via synapse.


• In a cross section, SC consists of :
  1) grey//gray matter which consists mainly of cell bodies of neurones (nerve cells).
  2) white matter (surrounding the grey matter), which consists of myelin-coated axons of neurones.
  
• Spinal nerves arise from the SC & has a dorsal root & a ventral root.
  
• Dorsal root ganglion - contains cell bodies of afferent neurone.
  
  
  

• Neurones (nerve cells):
  1) a typical neurone has a cell body, dendrites & usually one axon.
  2) neurones transmit nerve impulses (NI)/electrical signal to other nerve cells, glands or muscles.
  
  
• There are 3 types of neurones.
  1) Afferent neurone (AN) / sensory neurone
  2) Interneurone (IN) / (relay neurone, association neurone)
  3) Efferent neurone (EN) / motor neurone

*note: EN (neurone P), IN (neurone Q), AN (neurone R).
** unipolar, bipolar, multipolar neurones are not part of spm syllabus.

• State the differences between neurones:
  1) AN has cell body located at one side, EN has cell body located at one end while IN has cell body located at the centre.
  2) AN transmits/sends NI from the sensory receptor to the CNS, EN transmits NI from the CNS to the effectors while IN transmits NI from the AN to the EN.
  3)
• State the function of dendrite, axon, myelin sheath, node of Ranvier. (refer yr notes.)
• draw a labelled diagram of EN. (refer yr notes for drawing)

Osteoporosis - A Silent Disease

Bone to the left is normal bone, bone to the right is osteoporotic bone.





Osteoporosis is a disease that results in reduction in bone mass, the bones become thinner, lighter, more porous and more brittle.

It is a disease which is common among old people. In everyone, progressive loss of bone density starts after mid-30s.



















Women during menopause/postmenopausal (due to hormonal change, in particular a drop in oestrogen level) tend to loose their bone density faster than men. After reaching 65-70 years of age, this rapid rate of bone density loss decreases, reaching the same level as men.

Osteoporosis affect the whole body, but the most affected areas are the part which support most of the body's weight: the vertebrae, pelvic-leg system (hip, femur).

Risks:

1. fracture of the vertebrae & bones (hip, wrist, etc)

2. reduction in height over time

3. stooped posture.







Prevention:




1. taking diet rich in calcium, phosphate, vitamin D.

2. carry out physical exercise (weight-bearing exercise) that stress the bone

3. stop smoking

4. stop alcohol abuse

5. maintain healthy body weight

Remember: Osteoporosis has NO symptoms until a bone is fractured!