HAPLOID CELL

Another type of cell division is known as meiosis. Meiosis involves the division of a cell into four daughter cells. It takes place only in reproductive organs (eg: in the testes and ovaries of animals and in the anthers and ovules of plants).

The purpose of meiosis is to produce gametes or reproductive cells so that sexual reproduction in organisms can occur.

Unlike those produced through mitosis, these daughter cells are usually not genetically identical to their parent cells. The chromosomes in each daughter cell are half the number found in the parent cell.

While cell division occurs once during mitosis, cell division occurs twice during meiosis. Meiosis I is followed by Meiosis II.

In Meiosis I, the cell divides into two daughter cells, whose number of chromosomes is halved. In Meiosis II, each of the two daughter cells divides into another two daughter cells, resulting in four haploid daughter cells (with the same halved number of the original chromosomes).

Shown in the following diagram are the basic differences between mitosis and meiosis.

SINGLE CELL

A single cell can carry out many function.

A single cell with its numerous components and organelles can be so complete that it is able to function as a complete organism!

Examples of such unicellular organisms (or organisms that are made up of ONE cell only) are protozoa, bacteria, viruses, and certain types of algae and fungi.

In fact, most microorganisms are usually unicellular in nature.

The following table, show how and where the living process are carried out in each of the unicellular organisms;

Living process	Paramecium	Amoeba
a) Respiration	Diffusion through its cell membrane	Diffusion through its cell membrane
b) Excretion of excess water	Contractile vacuole	Contractile vacuole
c) Reproduction	Mitosis (cell division of nucleus) - binary fission	Mitosis (cell division of nucleus) - binary fission
d) Growth	Synthesis of new cytoplasm and organelle	Synthesis of new cytoplasm and organelle
e) Response to environment	Taxis - whole cell moves toward favourable stimuli and away from unfavourable stimuli	Taxis - whole cell moves toward favourable stimuli and away from unfavourable stimuli
f) Locomotion	Pseudopodia	Cilia
g) Nutrition (eating)	Phagocytosis, digestion in food vacuoles and lysozymes	Ingestion through oral groove, digestion in food vacuoles and egestion through its anal pore

ROLES THAT VARY

A number of components or organelles are present within a cell. Each of them has different and specific function within the cell.

The presence or absence of a particular group of organelles tell us what kind of functions the cell can or cannot perform.

For instance, the presence of absence of chloroplasts. The mesophyll cell in the leaves of plants contain chloroplasts. This enables the mesophyll cell to carry out photosynthesis.

Epidermal cells, on the other hand, do not contain chloroplasts. Do you think they can carry out photosynthesis?

The ability of cells to carry out specific function due to the organelles contained in them is known as cellular differentiation.

Different cells carry out different functions because of the varying types of organelles contained in them.

A man's sperm cell, for instance, is packed with organelles known as mitochondria in its neck.

This enables the sperm to produce its own energy for movement.

Thus, a cell's structure determines its function.

PROTEINS

Proteins play an important role in the formation of cellular components, cells and tissues in the human body.

They are also needed for growth and development. Without them, we will not grow or be able to repair damaged tissues in our body.

Among the substances made up of proteins in the human body are haemoglobins, antibodies, enzymes, certain hormones, muscle tissues and part of the cell membrane.

• The basic building block of proteins is the amino acid.
  
• There are 20 types of amino acids.
  
• Of these, the essential amino acids are the ones that cannot be synthesised by the body and must be obtained from the food we eat.
  
• Five example of amino acids are leucine, tryptophan, glutamic acid, valine and serine.
  
• If amino acids are known as monomers, proteins are polymers.
  
• When two amino acids are joined together, a dipeptide is formed.
  
• The bond between two amino acids is called a peptide bond.
  
• The process in which polypeptides are formed from amino acids is known as condensation.
  
• Protein can be broken down to amino acids in a process called hydrolysis.
  
• A molecule that is a protein in nature can be used to speed up the process mentioned above. This molecule is an enzyme.

Resonance structures of the peptide bond that links
individual amino acids to form a protein polymer.

Chemical structure of the peptide bond

A peptide bond between leucine and threonine

CELL DIVISION 2

1. The diagram shows a somatic cell during mitosis.
   
   
   
   • a) State the mitotic phase in the diagram and give your reason.
     
     • Metaphase. Chromosomes are arranged at the equatorial plane.
   • b) After the mitosis is completed,
     
     • i) how many daughter cells are produced?
       
       • 2.
     • ii) how many chromosomes are there in each daughter cell?
       
       • 4.
   • c) Give an example of technology currently used which applies the mitotic process.
     
     • Cloning / tissue culture.
   • d) Name 2 cells which do not undergo mitosis.
     
     • i) Nerve cell.
     • ii) Red blood cell.
2. The figure below shows the different stages of cell division in the mammalian ovary.
   
   
   a) Using the letters in the diagram, arrange the stages of cell division in their correct sequence.
   
   • G → F → A→ C→ E → B→ D
   
   b)
   i) Name the type of cell division illustrated in the figure above.
   
   • Meiosis.
     
   ii) With reference to the figure only, state two evidences to support your answer in [b) i].
   
   • There are 2 cell divisions.
     
     • 4 daughter cells are formed.
     • bivalents are formed.
   
   c) What biological term is used to describe the cells in stages D and G with respect to the number of chromosomes in their nucleus?
   
   • D : haploid cell.
   • G : diploid cell.
   
   d) State one difference in appearance between the chromosomes in stage G and F and give your reason.
   
   • Chromosomes in stage G appear as one stand but the chromosomes in stage F appear as two strands.
     
     • Reason: As the chromosomes in G continue to thicken, it is then seen as two sister chromatids in phase F.
3. The cell life cycle of an organism consists of phases X and Y. Phase X comprises of subphases P, Q and R. Phase Y comprises processes U dan V.
   
   
   a)
   i) Name process U.
   
   • Mitosis.
     
   ii) State the role of process U in living organisms.
   
   • For the growth of organism.
   • Replace worn-out tissue // for asexual reproduction.
     
   b) Diagrams I, II, III and IV below show the stages in process U.
   
   
   i) Arrange the stages of process U in the correct sequence below.
   
   • IV → II → III→ I
   
   ii) Name the stages in process U.
   
   • I – Telophase.
     II – Metaphase.
     III – Anaphase.
     IV – Prophase.
   
   c) What is phase X?
   
   • Interphase.

CHEMICAL COMPOSITION OF THE CELL

1. General properties of enzymes.
   
   • i) Enzymes are proteins produced by living cells.
     
   • ii) Enzymes are biological catalysts which speed up the rate of biochemical reactions.
     
   • iii) Enzymes are not destroyed at the end of a reaction.
     
   • iv) Enzyme-controlled reaction is irreversible
     
     • Example : lactose + water , glucose + galactose
       
   • v) Enzymes are sensitive to changes in temperature, and are very active at an optimum temperature of 40°C. Enzymes are denatured at high temperature .
     
   • vi) Enzymes are sensitive to changes in pH of medium.
     
   • vii) Enzyme action is very specific, One type of enzyme can catalyse only one type of substrate.
2. The figure represents the action of an enzyme.
   
   
   • a) State two properties of enzyme illustrated by the above figure.
     
     • Enzymes action is very specific.
     • Enzymes are not destroyed by the reaction they catalysed.
       
   • b) Name two digestive enzymes, their substrate and products.
     
     • Enzyme : Amylase, Substrate : Starch, Products: Maltose.
     • Enzyme : Trypsin, Substrate : Polypeptides, Products: dipeptides.
       
   • c) Figure below shows the relationship between enzyme activity and temperature. Complete the line to show the effect of increasing the temperature from 10°C to 60°C.
     
   • d) Uses of enzymes.
     
     

     Enzymes	Usage types	Effect
     Protease	Leather Industry	Remove hairs from skin
     Papain//Protease	Digestion	Tenderise meat
     Cellulase	Industrial use	Softening vegetables, removing seed coats
     Protease//Lipase	Daily use	Add to washing powder to remove protein stains
     Lipase	Digestion	Convert fat to fatty acids and glycerol
     Amylase	Digestion	Convert starch to maltose

3. The figure shows an experiment set-up to investigate the effect of pH on enzyme activity. Enzyme Q is found inside the mammalian digestive system.
   After 24 hours, the following results were obtained:
   

   pH	Reduction in length of egg white strip (mm)
   1	7
   2	9
   3	6
   4	3
   5	1
   6	0

   
   
   • a) Using the results in the table, plot a graph to show the reduction in length of the egg white strip against pH of the medium.
     
     • P – axis with scales ----1
     • T – points plotted accurately ------ 1
     • B – shape of line – smooth, single curve ------1
   • b) Explain the observed reduction in the length of the egg white strip.
     
     • Increasing the pH value of the medium will decrease the action of enzyme Q on egg white. The optimum pH of enzyme Q is 2. Enzyme Q works at its maximum rate at this pH/ At this pH, the reduction of length of the egg white strip is the greatest.
   • c)
     
     • Name enzyme Q and the products of its action on egg white.
       
       • Enzyme Q : Pepsin,
         Products: Polypeptides / Peptones
     • Which part of the mammalian digestive system produce enzyme Q?
       Stomach.
4. Below shows the structures of four organic compounds which are found in living cells.
   
   
   
   • a)
     
     • i) Name the structures of compounds X and Z.
       
       • X : Protein/ polypeptide.
         Y : triglyceride/ lipid.
     • ii) State the monomer of X and Y.
       
       • X : amino acid.
         Y : glucose.
   • b) What would happen if pancreatic cells unable to synthesis compound X?
     
     • Enzymes / any pancreatic enzyme / hormones /any pancreatic hormone cannot be synthesised.
   • c)
     
     • i) In the space below draw and label the structure of the basic unit of organic compound W.
       
     • ii) Name two types of organic compound W.
       
       • DNA & RNA.
     • iii) State two structural differences between the organic compounds you have named in (c)(ii).
       
       
       • DNA consists of two/double strands polynucleotide but RNA consists of a single / one strand of polynucleotide.
         
       • Strands of polynucleotide in DNA are twisted (around each other) / in a form of double helix but strand of polynucleotide in RNA is linear.
         
       * reject: molecules of DNA is big but molecules of RNA is small

STAGES IN MEIOSIS

1. Anaphase II
   
   • The sister chromatids are pulled apart and head towards opposite ends of the cell.
     
2. Prophase I
   
   • The homologous chromosomes, which are visible under a microscope, appear short, dense and thick. Each chromosome forms its own set of sister chromatids. The homologous chromosomes exist as two tetrads with a total of eight chromatids altogether. Crossing over may occur between non-sister chromatids of the homologous chromosomes.
3. Telophase I
   
   • Spindle fibres disappear. The cell divides into two, each having two chromosomes each. The sister chromatids for each homologous chromosome are still present and attached to a common centromere.
4. Telophase II
   
   • Each end of the cell now has two chromosomes. The nucleoli and nuclear membranes re-form. This stage is followed by cytokinesis.
5. Anaphase I
   
   • The homologous chromosomes separate and move towards opposite ends of the cells.
6. Prophase II
   
   • There are now two chromosomes, each with their sister chromatids present, in each of the two haploid cells. The chromatids thicken and shorten. The nuclear membrane around them disappears again and the chromatids are free to move.
7. Metaphase II
   
   • The sister chromatids align themselves at the imaginary centre of the cell.
8. Metaphase I
   
   • The homologous chromosomes, together with their chromatids, align themselves at an imaginary line along the centre of the cell.

***
English ~ Bahasa Melayu
anaphase ~ anafasa
cell division ~ pembahagian sel
chromosome ~ kromosom
cytokinesis ~ sitokinesis
daughter cell ~ sel anak
interphase ~ interfasa
metaphase ~ metafasa
parent cell ~ sel induk
prophase ~ profasa
telophase ~ telofasa
***

PLASMA MEMBRANE

How do substances enter and leave a cell? They have to permeate the plasma membrane - a layer that separates the cell from its surrounding. To "permeate" means to "pass through".

The plasma membrane (also called the cell membrane or plasmalemma) is the biological membrane separating the interior of a cell from the outside environment.

It is a semipermeable lipid bilayer found in all cells. It contains a wide variety of biological molecules, primarily proteins and lipids, which are involved in a vast array of cellular processes such as cell adhesion, ion channel conductance and cell signaling.

The plasma membrane also serves as the attachment point for both the intracellular cytoskeleton and, if present, the extracellular cell wall.

The plasma membrane is about 7nm-8nm thick. Proteins and a double layer of phospholipid molecules are the main molecules that make up plasma membrane.

A phospholipid is an amphipathic molecule. It has a hydrophobic tail that is not attracted to water and a hydrophilic head that has an affinity for water.

The heads of the phospholipid molecules face an aquatic environment on the outside of the cell, while internally, the tails face the water-rich cytoplasm.

Since the plasma membrane is made up of lipids, only molecules that dissolve in fats/lipids and are non-polar in nature can pass through the phospholipid bi-layer freely. These molecules include steroid hormones eg: estrogen and testosterone and gases (like oxygen and carbon dioxide).

Other substances are allowed in selectively by the cell membrane. This means that the membrane "chooses" the molecules that can pass through it. To do this, the membrane has several types of proteins acting as passageways for the entry of specific molecules. Without these proteins, certain molecules cannot enter a cell at all.

For example, hydrophilic water-soluble polar molecules such as glucose and amino acids can only be taken into a cell if a special carrier protein for them is present in the membrane. These molecules avoid contact with the lipid bi-layer by passing through such transport proteins that span the membrane. Thus, glucose must bind to a carrier protein first before it can be transported across the membrane.

Some carrier proteins are called ion pumps because they hydrolyse ATP and engage in the active transport of ions such as potassium and sodium into and out of the cell.

Other special proteins also include pore proteins, which allow water and certain ions to enter the cell through them.

In short, the plasma membrane acts as an important barrier between the cell and its environment. It is very selective, allowing only certain molecules to pass through. This nature of the membrane is called "semi-permeable".

Illustration of an Eukaryotic cell membrane

Diagram of the arrangement of amphipathic lipid molecules
to form a lipid bilayer. The yellow polar head groups
separate the grey hydrophobic tails
from the aqueous cytosolic and
extracellular environments.

PLANT & GROWTH

1. Name the phase in which the:
   a) centromeres of chromosomes are lined up at an imaginary plane across the middle of the cell
   • Metaphase
   
   b) nucleolus re-forms and the spindle fibres disappear
   • Telophase
   
   c) chromosomes are visible as duplicated, thick and short thread-like structures
   • Prophase
   
   d) cell is about ready to divide by cytokinesis
   • Telophase
   
   e) cell is gathering its energy to begin active mitosis
   • Interphase
   
   f) two sister chromatids of each chromosome separate at the centromere
   • Anaphase
   
   
2. 
   
   
   Based on the diagram, answer the following questions:
   
   a) Name the tissue found at the tip of a plant root.
   • Apical meristem
   
   b) Where else in a plant is this tissue usually found?
   • Shoot tip
   
   c) State the characteristics of the cells found in the tissue named in (a).
   • Very small in size / isodiametric in shape /contain a dense cytoplasm / have a large nucleus
   
   d) When mitosis occurs in these cells, primary growth, which records an increase in length and height, results in the root and shoot.
   
   e) For secondary growth in a plant, mitosis occurs in the vascular cambium, a tissue found between the xylem and phloem tissue in dicotyledons.
   
   f) Mitosis is important for growth because it increases the number of cells in the organism.

MITOSIS - PHASES OF CELL CYCLE (Anaphase, Telophase, Cytokinesis)

ANAPHASE

 

When every kinetochore is attached to a cluster of microtubules and the chromosomes have lined up along the metaphase plate, the cell proceeds to anaphase (from the Greek ανα meaning “up,” “against,” “back,” or “re-”).

Two events then occur; First, the proteins that bind sister chromatids together are cleaved, allowing them to separate. These sister chromatids, which have now become distinct sister chromosomes, are pulled apart by shortening kinetochore microtubules and move toward the respective centrosomes to which they are attached.

Next, the nonkinetochore microtubules elongate, pushing the centrosomes (and the set of chromosomes to which they are attached) apart to opposite ends of the cell. The force that causes the centrosomes to move towards the ends of the cell is still unknown, although there is a theory that suggests that the rapid assembly and breakdown of microtubules may cause this movement.

These two stages are sometimes called early and late anaphase. Early anaphase is usually defined as the separation of the sister chromatids, while late anaphase is the elongation of the microtubules and the microtubules being pulled farther apart. At the end of anaphase, the cell has succeeded in separating identical copies of the genetic material into two distinct populations.

Early anaphase: Kinetochore microtubules shorten.

 

TELOPHASE

 

Telophase (from the Greek τελος meaning "end") is a reversal of prophase and prometaphase events. It "cleans up" the after effects of mitosis.

At telophase, the nonkinetochore microtubules continue to lengthen, elongating the cell even more. Corresponding sister chromosomes attach at opposite ends of the cell.

A new nuclear envelope, using fragments of the parent cell's nuclear membrane, forms around each set of separated sister chromosomes.

Both sets of chromosomes, now surrounded by new nuclei, unfold back into chromatin. Mitosis is complete, but cell division is not yet complete.

Telophase: The decondensing chromosomes are surrounded
by nuclear membranes. Note cytokinesis has already begun,
the pinching is known as the cleavage furrow.

 

 

CYTOKINESIS

Cytokinesis is often mistakenly thought to be the final part of telophase; however, cytokinesis is a separate process that begins at the same time as telophase.

Cytokinesis is technically not even a phase of mitosis, but rather a separate process, necessary for completing cell division.

In animal cells, a cleavage furrow (pinch) containing a contractile ring develops where the metaphase plate used to be, pinching off the separated nuclei.

In both animal and plant cells, cell division is also driven by vesicles derived from the Golgi apparatus, which move along microtubules to the middle of the cell.

In plants this structure coalesces into a cell plate at the center of the phragmoplast and develops into a cell wall, separating the two nuclei.

The phragmoplast is a microtubule structure typical for higher plants, whereas some green algae use a phycoplast microtubule array during cytokinesis.

Each daughter cell has a complete copy of the genome of its parent cell. The end of cytokinesis marks the end of the M-phase.

MITOSIS - PHASES OF CELL CYCLE (Metaphase)

PREMETAPHASE

 

The nuclear envelope disassembles and microtubules invade the nuclear space. This is called open mitosis, and it occurs in most multicellular organisms. Fungi and some protists, such as algae or trichomonads, undergo a variation called closed mitosis where the spindle forms inside the nucleus or its microtubules are able to penetrate an intact nuclear envelope.

Each chromosome forms two kinetochores at the centromere, one attached at each chromatid. A kinetochore is a complex protein structure that is analogous to a ring for the microtubule hook; it is the point where microtubules attach themselves to the chromosome. Although the kinetochore structure and function are not fully understood, it is known that it contains some form of molecular motor.

When a microtubule connects with the kinetochore, the motor activates, using energy from ATP to "crawl" up the tube toward the originating centrosome. This motor activity, coupled with polymerisation and depolymerisation of microtubules, provides the pulling force necessary to later separate the chromosome's two chromatids.

When the spindle grows to sufficient length, kinetochore microtubules begin searching for kinetochores to attach to. A number of nonkinetochore microtubules find and interact with corresponding nonkinetochore microtubules from the opposite centrosome to form the mitotic spindle. Prometaphase is sometimes considered part of prophase.

Prometaphase: The nuclear membrane has degraded, and microtubules
have invaded the nuclear space. These microtubules can attach to
kinetochores or they can interact with opposing microtubules.

METAPHASE

 

As microtubules find and attach to kinetochores in prometaphase, the centromeres of the chromosomes convene along the metaphase plate or equatorial plane, an imaginary line that is equidistant from the two centrosome poles.

This even alignment is due to the counterbalance of the pulling powers generated by the opposing kinetochores, analogous to a tug-of-war between people of equal strength.

In certain types of cells, chromosomes do not line up at the metaphase plate and instead move back and forth between the poles randomly, only roughly lining up along the midline. Metaphase comes from the Greek μετα meaning "after."

Because proper chromosome separation requires that every kinetochore be attached to a bundle of microtubules (spindle fibres), it is thought that unattached kinetochores generate a signal to prevent premature progression to anaphase without all chromosomes being aligned. The signal creates the mitotic spindle checkpoint.

A cell in late metaphase. All chromosomes (blue) but
one have arrived at the metaphase plate.

Metaphase: The chromosomes have
aligned at the metaphase plate.

MITOSIS - PHASES OF CELL CYCLE (Interphase, Prophase)

 

INTERPHASE

The mitotic phase is a relatively short period of the cell cycle. It alternates with the much longer interphase, where the cell prepares itself for cell division.

Interphase is therefore not part of mitosis. Interphase is divided into three phases, G1 (first gap), S (synthesis), and G2 (second gap). During all three phases, the cell grows by producing proteins and cytoplasmic organelles.

However, chromosomes are replicated only during the S phase. Thus, a cell grows (G1), continues to grow as it duplicates its chromosomes (S), grows more and prepares for mitosis (G2), and finally divides (M) before restarting the cycle.

PREPROPHASE

In plant cells only, prophase is preceded by a pre-prophase stage. In highly vacuolated plant cells, the nucleus has to migrate into the center of the cell before mitosis can begin.

This is achieved through the formation of a phragmosome, a transverse sheet of cytoplasm that bisects the cell along the future plane of cell division.

In addition to phragmosome formation, preprophase is characterized by the formation of a ring of microtubules and actin filaments (called preprophase band) underneath the plasma membrane around the equatorial plane of the future mitotic spindle.

This band marks the position where the cell will eventually divide. The cells of higher plants (such as the flowering plants) lack centrioles: with microtubules forming a spindle on the surface of the nucleus and then being organized into a spindle by the chromosomes themselves, after the nuclear membrane breaks down.

The preprophase band disappears during nuclear envelope disassembly and spindle formation in prometaphase.

PROPHASE

Normally, the genetic material in the nucleus is in a loosely bundled coil called chromatin. At the onset of prophase, chromatin condenses together into a highly ordered structure called a chromosome.

Since the genetic material has already been duplicated earlier in S phase, the replicated chromosomes have two sister chromatids, bound together at the centromere by the cohesion complex. Chromosomes are visible at high magnification through a light microscope.

Close to the nucleus are structures called centrosomes, which are made of a pair of centrioles. The centrosome is the coordinating center for the cell's microtubules.

A cell inherits a single centrosome at cell division, which replicates before a new mitosis begins, giving a pair of centrosomes.

The two centrosomes nucleate microtubules (which may be thought of as cellular ropes or poles) to form the spindle by polymerizing soluble tubulin.

Molecular motor proteins then push the centrosomes along these microtubules to opposite side of the cell.

Although centrosomes help organize microtubule assembly, they are not essential for the formation of the spindle, since they are absent from plants, and centrosomes are not always used in meiosis.

Prophase: The two round objects above the nucleus are
the centrosomes. The chromatin has condensed

    

ORGANELLES AND ITS FUNCTION

RIBOSOME

Function: A site for the synthesis of proteins

 
















Atomic structure of the 50S Subunit from Haloarcula marismortui. Proteins are shown in blue and the two RNA strands in orange and yellow. The small patch of green in the center of the subunit is the active site.

*********************

MITOCHONDRION
Function: A site for cellular respiration and the synthesis of ATP

 

Simplified structure of mitochondrion

*********************

CHLOROPLAST
Function: Enables the plant cell to carry out photosynthesis









Chloroplast ultrastructure:
1. outer membrane
2. intermembrane space
3. inner membrane (1+2+3: envelope)
4. stroma (aqueous fluid)
5. thylakoid lumen (inside of thylakoid)
6. thylakoid membrane
7. granum (stack of thylakoids)
8. thylakoid (lamella)
9. starch
10. ribosome
11. plastidial DNA
12. plastoglobule (drop of lipids)


*********************

CENTRIOLES
Function: Help to form spindle fibres during cell division








 
3-dimensional view of a centriole

*********************

SMOOTH ENDOPLASMIC RETICULUM
Function: A site for synthesis of lipids and steroids

GOLGI BODY
Function: Processes, packages and transport carbohydrates, proteins and phospholipids


Diagram of secretory process from endoplasmic reticulum (orange) to Golgi apparatus (pink). Please click for full labels. Secretory pathway diagram, including nucleus, endoplasmic reticulum and golgi apparatus. 1. Nuclear membrane 2. Nuclear pore 3. Rough endoplasmic reticulum (rER) 4. Smooth endoplasmic reticulum (sER) 5. Ribosome attached to rER 6. Macromolecules 7. Transport vesicles 8. Golgi apparatus 9. Cis face of Golgi apparatus 10. Trans face of Golgi apparatus 11. Cisternae of Golgi apparatus

ORGANELLE 1

1) Chloroplast - This is an organelle made up of a double membrane and several membranous structures.

2) In organelle 1, energy is not created or distroyed. In fact, one form of energy can convert to another.

3) Lense - This is the typical shape of organelle 1.

4) Water - This is one of the requirements for the process in organelle 1 to take place.

5) Oxygen - The name of the gas released during the process that occurs in organelle 1.

6) It is a plant cell that usually contains organelle 1.

7) Sun - The source of all energy in an ecosystem ant the source of the energy that can be absorbed by organelle 1.

8) Light - Without this, organelle 1 cannot carry out its funtion.

OCCURRENCE OF MEIOSIS IN EUKARYOTIC LIFE CYCLES

Meiosis occur in eukaryotic life cycles involving sexual reproduction, comprising of the constant cyclical process of meiosis and fertilization. This takes place alongside normal mitotic cell division. In multicellular organisms, there is an intermediary step between the diploid and haploid transition where the organism grows. The organism will then produce the germ cells that continue in the life cycle. The rest of the cells, called somatic cells, function within the organism and will die with it.

Cycling meiosis and fertilization events produces a series of transitions back and forth between alternating haploid and diploid states. The organism phase of the life cycle can occur either during the diploid state (gametic or diploid life cycle), during the haploid state (zygotic or haploid life cycle), or both (sporic or haplodiploid life cycle, in which there two distinct organism phases, one during the haploid state and the other during the diploid state). In this sense, there are three types of life cycles that utilize sexual reproduction, differentiated by the location of the organisms phase(s).

In the gametic life cycle, of which humans are a part, the species is diploid, grown from a diploid cell called the zygote. The organism's diploid germ-line stem cells undergo meiosis to create haploid gametes (the spermatozoa for males and ova for females), which fertilize to form the zygote. The diploid zygote undergoes repeated cellular division by mitosis to grow into the organism. Mitosis is a related process to meiosis that creates two cells that are genetically identical to the parent cell. The general principle is that mitosis creates somatic cells and meiosis creates germ cells.

In the zygotic life cycle the species is haploid instead, spawned by the proliferation and differentiation of a single haploid cell called the gamete. Two organisms of opposing gender contribute their haploid germ cells to form a diploid zygote. The zygote undergoes meiosis immediately, creating four haploid cells. These cells undergo mitosis to create the organism. Many fungi and many protozoa are members of the zygotic life cycle.

Finally, in the sporic life cycle, the living organism alternates between haploid and diploid states. Consequently, this cycle is also known as the alternation of generations. The diploid organism's germ-line cells undergo meiosis to produce gametes. The gametes proliferate by mitosis, growing into a haploid organism. The haploid organism's germ cells then combine with another haploid organism's cells, creating the zygote. The zygote undergoes repeated mitosis and differentiation to become the diploid organism again. The sporic life cycle can be considered a fusion of the gametic and zygotic life cycles.

Gametic life cycle.

Zygotic life cycle.

Sporic life cycle.

NUTRITION

WHAT IS NUTRITION?
The process that organisms obtain energy from food, for growth, maintenance and repair of damage tissue

TYPES OF NUTRITION

1) Autotrophs (self, feed)

• Photosynthesis (Green plants)
• Chemosynthesis (Bacteria synthesis organic compounds by oxidising inorganic compounds - ammonia)

2) Heterotrophs (cannot synthesise their own food)

• Holozoic (Herbivours, Carnivours & Omnivours)
• Saprophytic (Organisms fed on dead / decaying matter
• Parasitic (Organisms obtains nutrient by living on/ in the body of other living organisms

BALANCE DIET

• Balance diet: a diet which contains the right amounts of carbohydrate, proteins, fat, vitamins, mineral, water and fibers.
• Healthy diet: should provide the body with all the substances necessary to maintain growth, to keep good health and repair damage tissue.

WHAT ARE THE FACTORS THAT EFFECTING THE DAILY ENERGY REQUIREMENT?
Climate!
Colder place need more energy to maintain body temp. because of the lost of energy to the surrounding.

FACTORS EFFECTING DAILY ENERGY REQUIREMENT

• Body size - The smaller person have a larger surface per unit volume compare to a larger person, the rate of heat loss is higher, they need more energy.
• Gender - Male need more energy because they are more active & the metabolic rate is higher then female.
• Growing children have higher metabolic rate than older people. They need more energy.
• Occupation - Person does heavy work needs more energy than a person who is only moderately active.

NUTRIENTS IN FOOD

• Carbohydrates: (rice, noodles, potatoes)
  
  • Source of energy for motion and growth
  • Used to form supporting structures in plants (cell wall)
  • Effective methods for food storage (starch/glycogen)
  • Part of nucleus (DNA)
  • Lack of it : become very weak

• Proteins : (meat, fish, cheese, eggs)
  
  • Make new cells for growing
  • Repair & Replace damaged cells/tissues
  • Make enzymes, antibodies & hormones
  • Lack of it: kwashiorkor, very weak, muscle are poorly developed

• Fat : ( oils, butter, milk, nuts)
  
  • Supply energy
  • Part of cell membrane
  • Help absorb certain vitamins (ADEK)
  • Too much: excess fat stored under the skin (obese)
  • Too little: vitamins won’t be absorbed, cell membrane won’t be formed normally

• Vitamins:
  
  • To protect health.
  • Biological catalyst for chemical reaction in the body.
  • 2 categories:
    i) Fat soluble vitamins
    
    • A,D,E,K
    • Stored in the body fat
    • No need to consume everyday (stored in the body)
    ii) Water soluble vitamins
    
    • C and B (8 types)
    • Dissolved easily in water, easily lost
    • Cannot be stored in the body, need to be consumed everyday.
      
      
      • Vitamin A
      Source: Milk, green leaf, butter, tomatoes, cod liver, egg.
      Function: Normal growth, healthy eyes & skin.
      Deficiency disease: Night blindness.
      
      
      • Vitamin B1
      Source: Milk, peas, cereals, green leaf.
      Function: Growth & development.
      Deficiency disease: Beriberi (disease affects the nervous system).
      
      
      • Vitamin B2
      Source: Peas, yeast, egg, meat.
      Function: Healthy skin growth.
      Deficiency disease: Skin disease, retarded growth.
      
      
      • Vitamin B4
      Source: Whole cereals, potatoes, tomatoes, meat, fish.
      Function: Healthy skin, digestive & nervous system.
      Deficiency disease: Pellagra (disease affect the skin, alimentary canal & nervous system).
      
      
      • Vitamin C
      Source: Tomatoes, green leaf, vegetables, fruits.
      Function: Healthy growth, strong blood vessels.
      Deficiency disease: Scurvy (gums easily bleed).
      
      
      • Vitamin D
      Source: Sunlight, milk, butter.
      Function: Strong bones & teeth.
      Deficiency disease: Rickets ( Soft bones & deformed on children).
      
      
      • Vitamin E
      Source: Vegetables, oils, milk, butter.
      Function: Protect the cell membrane.
      Deficiency disease: Affect fertility.
      
      
      • Vitamin K
      Source: Green vegetables, Soya bean oils.
      Function: Help in clotting the blood.
      Deficiency disease: Excessive bleeding from wound.

• Mineral salts:
  
  • Major trace mineral- required in large amount
  • Minor trace mineral- required in small amount
• Iron - Formation of heamoglobin
• Calcium - Strong bones & teeth, muscle contractions, clotting blood
• Phosphorus - Strong bones
• Potassium - Growth & osmotic balance
• Sodium - Osmotic balance, proper functioning of nervous system
• Iodine - Body metabolism, development of brain
• Roughage/ fiber
  
  • Higher water holding capacity
  • Help peristalsis / bowel movement
  • Prevent from constipation
  • Lower the cholesterol
  • Reduce the risk of heart disease

• Water:
  
  • Medium for biochemical reactions
  • Medium for transportation of respiratory gases
  • Regulates body temp.
  • Removes excretory waste
  • Maintain osmotic pressure
  • Aids peristaltic movement
  • Hydrolyse some food substances
  • Dissolve most chemical substances

SPECIAL DIET

• Pregnant lady
  Need more nutrient to provide more energy to meet the need of my growing fetus
  
  • Folate – brain development
  • Iron – prevent from anemic
  • Calcium - growth of baby’s bone & teeth

• Baby
  Need mother’s milk to provide me with energy & nutrient.

• Children
  They are active & love to play. They need carbohydrates to give us energy and protein to develop new tissue.

• Vegetarian
  They need supplement in order to complete their need.

• Diabetic
  Low sugar.

• Teenagers
  
  • Carbohydrates – provides energy (they’re active)
  • Protein – still growing
  • Iron – menstruation (girl)

• Athletes
  Carbohydrates – they need more energy.

MALNUTRITION

• Starvation – insufficient amount of food
• Eating disorder:
  
  • Anorexia Nervosa – Girls believe themselves to be fat (they’re extremlely thin), don’t want to eat.
  • Bulimia – Overconcern with body weight, eat a lot and then force themselves to vomit.

• Overweight/ Obesity - high risk of diabetes,hypertension, heart attack
• Over consumption of cholesterol & saturated fat:
  
  • Can cause arthrosclerosis (build up fatty deposits in the coronary arteries/ blood vessels.

• Constipation: lack of dietary fiber.

Class Of Chemicals

Cells need various types of organic and inorganic compounds to enable them to carry out their functions, as well as build their cellular components. While organic compounds contain the element carbon, inorganic compounds do not.

Below is the classified descriptions of chemical compound.

Carbohydrate

• Starch made up of long chain of glucose
• The ratio of C:H:O in it is 1:2:1
• Cellulose that strengthens the cell walls of plants
• Maltose can be converted into glucose by hydrolysis
• Its glucose molecules can be converted into glycogen

Lipid

• Cholesterol is an example of it
• Fats have the triglyceride molecules in them
• Fatty acids can be saturated and unsaturated
• The hormone testosterone is an example of it

Nucleic Acid

• An example is the DNA found in the nucleus of a cell
• Genetic material that directs protein synthesis
• Contain pentose sugars and phosphate groups

Protein

• Amino acids are its building blocks
• Nearly all enzymes are examples of it
• The haemoglobin molecules in the red blood cells
• Builds muscles and aids growth

Water

• An inorganic compound with no carbon in it
• A polar molecule with two H atoms and one O atom
• A universal solvent
• Acts as a medium for reactions in one's body

Proteins

Proteins play an important role in the formation of cellular components, cells and tissues in the human body.

They are also needed for growth and development. Without them, we will not grow or be able to repair damaged tissues in our body.

Among the substances made up of proteins in the human body are haemoglobins, antibodies, enzymes, certain hormones, muscle tissues and part of the cell membrane.

• The basic building block of proteins is the amino acid.
  
• There are 20 types of amino acids.
  
• Of these, the essential amino acids are the ones that cannot be synthesised by the body and must be obtained from the food we eat.
  
• Five example of amino acids are leucine, tryptophan, glutamic acid, valine and serine.
  
• If amino acids are known as monomers, proteins are polymers.
  
• When two amino acids are joined together, a dipeptide is formed.
  
• The bond between two amino acids is called a peptide bond.
  
• The process in which polypeptides are formed from amino acids is known as condensation.
  
• Protein can be broken down to amino acids in a process called hydrolysis.
  
• A molecule that is a protein in nature can be used to speed up the process mentioned above. This molecule is an enzyme.

Battery Biohazard

Throwing your batteries in the dustbin can harm the environment.

You've probably got a dozen things that are powered by batteries. Just check your mobile phone, calculator, television remote control, camera and torchlight.

Batteries are incredibly useful but they run on poisonous chemicals and metals like mercury, lead, cadmium and nickel. That is why you mustn't throw old and damaged batteries in the dustbin.

When batteries are thrown into a rubbish heap or a landfill, the chemicals they run on leak into the soil and groundwater. Nobody wants that in their food or water!

If you throw a battery into incinerator, heavy metals like mercury can vapourise and be released into the air. When it rains, they fall back to the earth, poisoning soil, rivers and oceans.

Burning batteries leave ashes with concentrated cadmium and lead. When these are dumped, the poison leaks into the environment.

You can reduce the amount of batteries you use by buying rechargeable products. They cost a little more, but you can use them many times.

You can also buy batteries with fewer dangerous chemicals. Modern alkaline batteries have up to 90% less mercury than those used 20 years ago. Some are completely mercury free. Just read the label!

When your batteries dies, take it to a recycle centre. The recycle centre disposes of any leftover chemicals in such a way that they can't harm the environment.

Animal Cell & Plant Cell

The cell is the basic unit of all organism. It is made up of a cell membrane that encloses the cytoplasm.
Contained within the cytoplasm are not only the nucleus but also organelles, whose specific functions help the cell perform a range of activities.

While plant and animal cells are similar, the plant cell has, in addition to the cell membrane, another boundary that separates it from its external environment. This is called the cell wall.

As most plant cells carry out photosynthesis - the synthesis of organic substances - they contain chloroplasts.

In plant cells, vacuoles also tend to be larger in size and smaller in number than those found in animal cells.
In the laboratory, you have learned how to prepare a microscope slide of human cheek cells as well as the epidermal cells of onions.

a) The differences you can observe between the two types of cells in term of the following:

• Shape
  Onion cells have a regular shape while cheek cells have an irregular shape.
  
• Presence or absence of cell wall
  Onion cells have a cell wall while cheek cells do not.
  
• Presence or absence of vacuoles
  Onion cells have a large vacuole while vacuoles in cheek cells, if present, are small.

b) Can you observe chloroplasts in the epidermal cells of onions? Explain your answer.
No chloroplasts can be observed in the epidermal cells of onions because epidermal cells do not carry out photosynthesis.

Diffusion

Various substances pass through the plasma membrane of a cell. The simplest mode of transport for these substances is by diffusion.
Diffusion is defined as the movement of substances from an area of high concentration to an area of low concentration. When substances move in this manner, we say that they are moving along the concentration gradient.

This movement process is simple and passive, which means that the substances move easily from the region of high concentration to the one whose concentration is lower without requiring any energy.

When water moves from an area of high concentration to an area of low concentration across a semi-permeable membrane, its movement called osmosis.

Therefore, when a cell absorbs water by diffusion through its semi-permeable cell membrane, we say that water has entered the cell through osmosis.

Eg: Roots absorb water through osmosis because the soil solution around the roots has a higher water concentration than the root cells.

Certain substances need help in the diffusion process. These substances move into a cell by diffusion through the membrane but they are brought in by special carrier proteins. Such a diffusion process is known as facilitated diffusion.

An active diffusion takes place when a substance moves from an area of low concentration to an area of high concentration, with the use of energy. This movement goes against the concentration gradient.

An active diffusion process usually involves transporting important ions into and out of a cell, whose plasma membrane may have special protein pumps to engage in it.

Onion Skin Cell & Cheek Squamous Epithelial Cells

Roles That Vary

A number of components or organelles are present within a cell. Each of them has different and specific function within the cell.

The presence or absence of a particular group of organelles tell us what kind of functions the cell can or cannot perform.

For instance, the presence of absence of chloroplasts. The mesophyll cell in the leaves of plants contain chloroplasts. This enables the mesophyll cell to carry out photosynthesis.

Epidermal cells, on the other hand, do not contain chloroplasts. Do you think they can carry out photosynthesis?

The ability of cells to carry out specific function due to the organelles contained in them is known as cellular differentiation.

Different cells carry out different functions because of the varying types of organelles contained in them.

A man's sperm cell, for instance, is packed with organelles known as mitochondria in its neck.

This enables the sperm to produce its own energy for movement.

Thus, a cell's structure determines its function.