FORM 4: BIOLOGY

F4 C2: Cell Biology and Organisation

2.1 Cell Structure and Function

Animal cells

Component Description Function

Mitochondrion ● Rod-shaped or spherical. ● Generates energy through glucose

● Double membrane. oxidation during cellular respiration.
● Enzymes for cellular respiration. ● Releases energy (ATP) for cell activity.

Centriole ● Small and cylindrical, exist in pairs. ● Forms spindle fibre during cell division.
● A complex microtubules arrangement.

Golgi ● A stack of parallel flattened sacs coated ● Processes, modifies, packs, and
apparatus by a single cell membrane. transports chemicals like protein,
● New membrane is added at one end, carbohydrate and glycoprotein.
vesicles bud off from the other.

Plasma ● Outer membrane surrounding cell ● Separates cell content from external
membrane contents, made of proteins and environment.
phospholipids. ● Controls movement of substances into
● Selectively permeable, thin, and elastic. and out of the cell. Allows exchange of
nutrients, respiratory gases, and waste.

Lysosome ● A small spherical sac enclosed in a single ● Hydrolyses complex organic molecules
membrane (protein, nucleic acid, lipid).
● Contains hydrolytic enzymes. ● Breaks down bacteria and components
of damaged cells.
 Component Description Function

Nucleus ● Largest cell component. ● Controls all cell activities.

● Spherical, compressed, enclosed in a ● Chromosomes contain deoxyribonucleic
nuclear membrane. acid (DNA), which determines cell
● Contains chromosomes, nucleolus, and characteristics and metabolic function.
nucleoplasm.

Ribosome ● Small, compact, spherical granules. ● Protein synthesis site.

● Consists of protein and ribonucleic acid
(RNA).
● Present on rough endoplasmic
reticulum’ surface or freely in the
cytoplasm.

Smooth ● A system of interconnected, folded, ● Cell transport system.

endoplasmic flattened sacs. ● A wide surface for enzyme attachment
reticulum ● Membrane continuous with the nuclear and reactions.
membrane. ● Synthesises and transports glycerol and
● No ribosomes. lipids.
● Detoxification of drugs and metabolic
by-products.

Rough ● A system of interconnected, folded, ● Cell transport system.

endoplasmic flattened sacs. ● A wide surface for enzyme attachment
reticulum ● Membrane continuous with the nuclear and reactions.
membrane. ● Transports proteins synthesised by
● Ribosomes attached to the surface. ribosomes.
Plant cells

Component Description Function

Vacuole ● Cell-sap filled sac, surrounded by a tonoplast ● Water is absorbed into the
membrane. vacuole, the cell becomes
● Young cells have many small vacuoles. Mature cells turgid.
have one large vacuole.
● Cell sap: water, organic acids, sugars, amino acids,
enzymes, mineral salts, oxygen, carbon dioxide,
metabolic by-products.

Chloroplast ● Double membrane, oval-shaped. ● Chlorophyll absorbs sunlight

● Contains chlorophyll pigments in the grana (makes to be converted to chemical
plants green). energy by photosynthesis.

Cytoplasm ● Jelly-like medium that contains suspended cell ● A medium for biochemical
components. reactions in cells.
● Contains organic compounds (protein, lipid,
carbohydrate) and inorganic compounds
(potassium ions).

Cell wall ● A strong, rigid outer layer. ● Maintains cell shape.

● Fully permeable, made from cellulose fibre. ● Provides mechanical support
to cells.
Animal-plant cell comparison

Plant cell Animal cell

Fixed shape. No fixed shape.

Cell wall. No cell wall.
Chloroplast. No chloroplast.
Large vacuole. No/small vacuole.
Carbohydrates stored as starch. Carbohydrates stored as glycogen.
No centriole. Centriole.

Cell component density

Abundant cell component Type of cell Function

Sperm cell Requires more energy to swim

towards the uterus and Fallopian
tube for fertilisation.

Mitochondrion Muscle cell Requires more energy to contract

and relax to enable
movement/flight.

Plant meristem cell Requires more energy for active cell

division.

Palisade mesophyll cell To absorb more sunlight for

Chloroplast photosynthesis.
Spongy mesophyll cell

Pancreatic cell To increase synthesis and secretion

of digestive enzymes.
Rough endoplasmic reticulum,
Golgi apparatus Goblet cell To produce mucus.

Liver cell To metabolise carbohydrates, and

detoxify drugs and poisons.
2.2 Living Processes in Unicellular Organisms

Paramecium sp. Amoeba sp.

Movement ● Rhythmic cilia beats. ● Extends its pseudopodium, followed by

the flow of cytoplasm into it.

Nutrition ● Cilium beats transfer food into the oral ● Extends its pseudopodia to trap food by
groove. phagocytosis.
● The food vacuole combines with ● The food vacuole combines with
lysosome. The enzyme lysozyme in the lysosome. The enzyme lysozyme in the
lysosome hydrolyses the food. lysosome hydrolyses the food.
● Nutrients are absorbed into the ● Nutrients are absorbed into the
cytoplasm. cytoplasm.
● Undigested food is discharged when it ● Undigested food is discharged through
moves. the anus.

Reproduction Suitable conditions: Suitable conditions:

● Asexual reproduction: binary fission ● Asexual reproduction: binary fission
through mitosis. through mitosis.
Unsuitable conditions: Unsuitable conditions:
● Sexual reproduction: conjugation. ● Forms spores that will germinate later.

Excretion ● Wate (carbon dioxide, ammonia) is removed by diffusion.

● Osmoregulation: in freshwater, water diffuses into the contractile vacuole by osmosis. It
expands to its maximum size and contracts. Water is excreted.

Respiration ● Gaseous exchange occurs through the plasma membrane by simple diffusion.

Growth ● Synthesising new cytoplasm.

2.3 Living Processes in Multicellular Organisms

Cell specialisation

Human cells Plant cells

Muscle cell Sieve tube element

● Arranged ass multinuclear striated fibres. ● Long, cylindrical tubes, arranged end-to-end.
● Contract/relax to generate movement. ● Transports organic materials from leaves to
the storage organs.
White blood cell
● Can change shape. Destroys pathogens. Xylem vessel
● Long, continuous hollow tube.
Red blood cell ● Transports water and mineral salts from the
● No nucleus, biconcave-disk shape. roots to the rest of the plant.
● Optimises oxygen transportation.
Palisade mesophyll cell
Nerve cell ● Long, cylindrical, closely arranged vertically.
● Long and thin, sends nerve impulses. ● High chlorophyll density for maximum
photosynthesis rate.
Epithelial cell
● Thin and flat, coats organ surfaces. Spongy mesophyll cell
● Loosely arranged. Large air spaces allow
Sperm cell gaseous exchange from inside the leaves to
● Has a long tail, to swim towards the ovum. the palisade mesophyll cells.
● Head carries male chromosome.
Guard cell
● Modified lower epidermal cells with a thicker
inner cell wall.
● Controls stomatal opening and closing.

Root hair cell

● Long projection adds surface area to absorb
water and mineral salts.
Human cell organisation

● Mouth and oesophagus.

Epithelial ● Surface of lungs, body cavities, and blood vessels.
tissue ● Surface of trachea and bronchus.
● Lines tubules, glands, and kidney ducts.
● Covers the small intestine.

Smooth muscle contracts and relaxes to enable involuntary activities (e.g. peristalsis).
Muscle
tissue Skeletal muscle contracts and relaxes to generate controlled movement in bones and limbs.

Cardiac muscle (builds heart walls) contracts and relaxes to pump blood to the body.

Nerve ● Made of neurons (nerve cells). Consists of a dendrite (body) and axon (fibre).
tissue ● Detects stimuli and sends information as nerve impulses to muscles/glands.
● Regulates and controls body activity.

Connective Loose connective tissue links epithelial tissue to the tissue below. It fixes organs in their
tissue positions.

Fibrous connective tissue form tendons (bone-muscle) and ligaments (bone-bone).

Blood tissue functions in regulation, transportation, and protection.

Bone forms the body frame and protects internal organs.

Adipose tissue keeps fat under skin and the surface of main organs.

Cartilage encloses bone tips and prevents wear-out.

Plant cell organisation

Meristem Apical meristem tissue

tissue
Lateral meristem tissue

Permanent Dermal tissue

tissue
Ground Parenchyma tissue stores starch, protein, and water, and carries out photosynthesis.
tissue
Collenchyma tissue gives support to young, non-woody stems.

Sclerenchyma tissue provides support and mechanical strength to mature plant

parts.

Vascular Xylem tissue transports water and mineral salts from the roots to the rest of the
tissue plant. Ligneous xylem tissue provides support and mechanical strength.
 Phloem tissue transports organic matter (sucrose) from the leaves to the rest of the
plant.
2.4 Levels of Organisation in Multicellular Organisms

Cell -> Tissue -> Organ -> System -> Multicellular organism

Human systems

System Organs Function

Endocrine Endocrine gland Coordinates body activities and the nervous system.

Respiratory Trachea, nose, lungs, diaphragm Gaseous exchange between body and environment.

Muscular Skeletal muscle, smooth muscle, Contracts and relaxes to generate body movement.
cardiac muscle

Reproductive (M) Testes, prostate gland, penis Produce sperm and male sex hormones.

Reproductive (F) Ovary, uterus, Fallopian tube, Produce ovum and female sex hormones.
vagina, cervix

Lymphatic Spleen, lymph nodes, lymph Maintains bodily fluid balance and prevents
vessels infections.

Nervous Brain, spinal cord, peripheral Detects and sends information, coordinates body
nerves activities.

Circulatory Heart, artery, vein, capillary Transports nutrients, respiratory gases, and waste.

Digestive Mouth, oesophagus, stomach, Digests food into simpler forms for easy absorption.
liver, pancreas, small intestine,
large intestine

Urinary Kidney, ureter, urethra, bladder Eliminates waste (urea, uric acid).

Skeletal Bone, cartilage, ligament, tendon Supports the body, protects internal organs, and is
the base for muscle adhesion.

Integumentary Skin Protects against physical injury, infection, and

dehydration.

Plant systems

Shoot system Root system

● Stems, leaves, shoots, flowers, fruits. ● All roots absorb water and mineral salts.
 ● Stems, twigs: support systems, keep leaves ● Provides support to plants.
vertical for maximum sunlight absorption.
● Flowers: pollination.
F4 C3: Movement of Substances Across a Plasma Membrane

3.1 Structure of a Plasma Membrane

The plasma membrane regulates the movement of substances into and out of the cell to maintain living processes.

Plasma membrane

● Protein molecules float within the phospholipid bilayer, forming a mosaic pattern that changes frequently.
● Each phospholipid consists of a hydrophilic polar head and a hydrophobic nonpolar tail. The heads of the
outer layer face the extracellular fluid, the heads of the inner layer face the cytoplasm. The tails of both
layers face each other.

● Protein molecules are widely dispersed between the phospholipid bilayer.

● Channel proteins have channels/canals. Carrier proteins function as carriers.
● Glycoprotein: proteins with carbohydrate chains attached.
● Glycolipid: lipids with carbohydrate chains attached.
● Glycoproteins and glycolipids act as receptors to hormones (insulin), stabilise the membrane (form
hydrogen bonds with water), and antigens for cell identification.

● Cholesterols make the phospholipid bilayer stronger, more flexible, and less permeable to water-soluble
substances (ions).

The plasma membrane is selectively permeable. It only allows free movement of certain molecules across it, and
prevents/limits the movement of other substances. This property is due to the plasma membrane’s building
structure, determined by the phospholipid bilayer and proteins.
3.2 Concept of Movement of Substances Across a Plasma Membrane

The size, polarity, and ionic charge of a molecule determine whether it can pass through the plasma membrane.

Lipid-soluble substances Lipid-insoluble substances

Type Nonpolar molecules Small molecules, ions Large molecules

Permeates through Phospholipid bilayer Channel proteins Carrier proteins

Examples ● Fatty acid ● Polar molecules (water) ● Glucose

● Glycerol ● Nonpolar molecules ● Amino acid
● Fat soluble vitamins (O2, CO2)
● Steroid compounds ● Ions

Passive transport

Passive transport does not involve the use of energy.

Simple ● The movement of molecules/ions from an area of high concentration to an area of low
diffusion concentration, down the concentration gradient, until dynamic equilibrium is achieved.
● Occurs with/without a plasma membrane.
● e.g. Lipid-soluble molecules diffuse through the phospholipid bilayer.

Osmosis ● The net movement of water molecules from an area of high water potential to an area of low
water potential randomly through a selectively permeable membrane (permeable to water,
impermeable to some solutes).

Facilitated ● Lipid-insoluble molecules (ions, large molecules, amino acids, glucose) are unable to pass
diffusion through the phospholipid bilayer.
● They move across the plasma membrane with the aid of channel or carrier proteins.
● This does not require energy, as it occurs down the concentration gradient, until dynamic
equilibrium is achieved.
● Channel proteins allow small solutes and ions to diffuse across the plasma membrane. Their
channels/canals have specific internal characteristics, only specific ions can pass through.
● Carrier proteins have specific sites, and can only bind to specific molecules.
Active transport

● The movement of substances occurs against the concentration gradient.

● Requires energy from adenosine triphosphate (ATP) molecules, generated during cellular respiration.
● Requires specific carrier proteins with specific binding sites for certain molecules/ions.
● Carrier proteins, known as pumps, possess receptors to bind with ATP molecules. The protein changes
shape when a phosphate group attaches.
● Results in the accumulation or excretion of molecules/ions in the cell.

e.g. sodium-potassium pumps

*extracellular fluid: high Na+ concentration*
1. Three sodium ions from the cytoplasm bind to the carrier protein.
2. ATP molecules decompose into ADP and P. The phosphate group (P) binds to the carrier protein.
3. The phosphate bond provides energy to change the shape of the carrier protein. The sodium ions are
transported by the carrier protein out of the cell.
*extracellular fluid: low K+ concentration
4. Two potassium ions from the extracellular fluid bind to the carrier protein. The phosphate group leaves the
carrier protein.
5. The loss of the phosphate group restores the original shape of the carrier protein.
6. Potassium ions are transported by the carrier protein into the cell.

Protein pumps in the epithelial cells of the stomach cavity transports hydrogen ions into the extracellular fluid
through the carrier proteins. The accumulation of hydrogen ions causes acid production in the stomach cavity,
resulting in the acidity of the stomach.

Passive transport Active transport

● Moves a substance across a membrane.

● Occurs through a selectively permeable membrane.

Energy is not required. Energy (ATP) is required.

Occurs down the concentration gradient. Occurs against the concentration gradient.

Occurs until dynamic equilibrium is achieved. Accumulation or excretion of molecules/ions occurs.

3.3 Movement of Substances Across a Plasma Membrane in Living Organisms

Passive transport Active transport

Simple diffusion ● Absorption of glucose and amino

● Gaseous exchange between alveoli and blood capillaries. acids in the villus.
● Reabsorption of glucose through
Osmosis the renal tubule in the kidney.
● Reabsorption of water through the renal tubule in the kidney. ● Transport of sucrose from a leaf to
● Absorption of water by a plant root hair cell. a phloem tissue.
● Absorption of mineral ions by
Facilitated diffusion
plant root hair cells.
● Absorption of fructose molecules in the villus.

Concentration of solutions

Concentration Effect on animal cells Effect on plant cells

Hypotonic solution ● Water diffuses into the cell by ● Water diffuses into vacuoles by
● Low solute osmosis, causing the cell to swell and osmosis, causing them to expand and
concentration burst. push the cytoplasm and plasma
● High water ● The plasma membrane is too thin to membrane against the cell wall.
potential withstand the osmotic pressure. ● Cell becomes turgid.
● The burst of red blood cells is ● Cells do not burst as the cell wall is
haemolysis. rigid and strong.
● The turgor pressure provides plant
support and maintains cell shape.

Isotonic solution ● Water diffuses into and out of the cell ● Water diffuses into and out of the cell
● Equal by osmosis at equal rates. No net by osmosis at equal rates. No net
concentration movement of water. movement of water.
● Normal cell shape is maintained. ● Cell becomes flaccid.

Hypertonic solution ● Water diffuses out of the cell by ● Water diffuses out of vacuoles by
● High solute osmosis, causing the cell to shrink. osmosis, causing them and the
concentration ● The cell undergoes crenation. cytoplasm to shrink.
● Low water ● Plasmolysis occurs. The plasma
potential membrane is pulled away from the
cell wall. Leaves and stems wilt.
● Partially plasmolysed cells can regain
turgidity by deplasmolysis if
immediately returned to a hypotonic
solution.
F4 C4: Chemical Composition in a Cell

4.1 Water

1. Polarity
● Water molecules are polar molecules.
● Polarity produces hydrogen bonds, allowing water to act as a universal solvent.
● Water allows solutes (glucose, electrolytes) to be transported into cells for reactions.

2. Cohesive and adhesive force

● Cohesive force: to each other
● Adhesive force: to other surfaces
● Both forces produce capillary action, allowing water to enter and move along narrow spaces.

3. High specific heat capacity

● 4.2 kJ kg-1 C-1. Absorbs a lot of heat energy, with a small rise in temperature.
● Maintains body temperature of organisms.

4.2 Carbohydrates

● Polymer molecules (composed of monomers) of organic compounds.

● Consist of carbon, hydrogen, and oxygen (1:2:1) as (CH2O)n.

Monosaccharides Disaccharides Polysaccharides

● Carbohydrate ● Formed when 2 monosaccharides ● Formed through

monomers combine through condensation. 1 water condensation.
(simplest units). molecule is removed. ● Involves hundreds of
● Combine to form ○ Mono. + mono. -(condensation)-> monosaccharides to form
polymers through Di. + H2O long molecular chains.
condensation. ● Broken down through hydrolysis and ● Water insoluble (too large).
● Sweet, form the addition of 1 water molecule. ● Broken down through
crystals, water ○ Di. + H2O -(hydrolysis)-> hydrolysis with dilute acids,
soluble. Mono. + mono. boiling, or enzyme action.
● Has reducing
power.

● e.g. glucose (rice, Condensation ● e.g. cellulose (cell wall),

wheat, grapes), ● Glucose + glucose -> Maltose + water starch (grains, potatoes),
fructose (honey, ● Fructose + glucose -> Sucrose + water glycogen (liver cell).
sweet fruit), ● Galactose + glucose -> Lactose + water
galactose (milk).
Hydrolysis
● Maltose + water -> Glucose + glucose
● Sucrose + water -> Fructose + glucose
● Lactose + water -> Galactose + glucose
Importance of carbohydrates:
● Source of energy (glucose).
● Food reserves (glycogen in animals, starch in plants).
● Support structure (cellulose in cell walls).

4.3 Protein

● Composed of carbon, hydrogen, oxygen, phosphorus, and sulphur.

● Composed of polymers known as polypeptides.
● Polypeptides are made up of monomers known as amino acids.
○ 20 types of amino acids. (9 essential, 11 non-essential)
● Dipeptide: Two amino acids are linked together by a peptide bond through condensation. This
process involves the removal of one water molecule.
● Polypeptide chain: Formed by further condensation to link more amino acids.

Amino acid + amino acid -(condensation)-> Dipeptide + water

Dipeptide + water -(hydrolysis)-> Amino acid + amino acid

Importance of proteins:
● Build new cells.
● Repair damaged tissues.
● For the synthesis of enzymes, hormones, antibodies, and haemoglobin.
● Form keratin in the skin, collagen in bones, and myosin in muscle tissues.
● Breakdown by enzymes provide energy for daily activities.
4.4 Lipids

● Naturally occurring hydrophobic compounds in tissue.

● Composed of carbon, hydrogen, and oxygen.
● Water insoluble. Alcohol/ether/chloroform soluble.

Fats ● Triglycerides, a type of ester.

● Formed from the condensation of one glycerol molecule and three fatty acid molecules.
● Can be hydrolysed through hydrolysis into fatty acids and glycerol.

Saturated fatty acids Unsaturated fatty acids

● Consist of carbon, hydrogen, and oxygen.

● Contain glycerol and fatty acids.
● Contain nonpolar molecules.

● Only single bonds between carbon. ● At least 1 double bond between carbon.
● Do not form chemical bonds with ● Double bonds can receive additional
additional hydrogen atoms. hydrogen atoms.
● Room temp: solid. ● Room temp: liquid.
● More cholesterol (butter, animal fat). ● Less cholesterol (olive/fish oil).

Waxes ● Contains one molecule of alcohol that combines with one molecule of fatty acid.
● Waterproof.
● Found on cuticles of epidermis of leaves, and in sebum from sebaceous gland in skin.

Phospholipids ● Consists of one phosphate group (head) and one molecule of glycerol that combines with
two molecules of fatty acid (tail).
● Main component of plasma membranes.

Steroids ● No fatty acids.

● Cholesterol is important in steroid hormone synthesis.
● e.g. cholesterol, testosterone, oestrogen, progesterone.

Importance of lipids
● Fats as reserved energy for animals.
● Fats line internal organs for physical protection.
● Fats as a heat insulator in animals.
● Glycolipids ensure plasma membrane stability, and help in cell identification.
4.5 Nucleic Acids

● Formed from carbon, hydrogen, oxygen, nitrogen, and phosphorus.

● One or two polymer chains composed of nucleotide monomers, each consisting of:
○ A nitrogenous base (adenine, guanine, cytosine, thymine, uracil)
○ A phosphate group
○ A pentose sugar (ribose, deoxyribose)

DNA: Deoxyribonucleic acid RNA: Ribonucleic acid

● Contains deoxyribose sugar. ● Contains ribose sugar.

● Consists of two polynucleotide chains, ● Consists of a single polynucleotide chain
intertwined in opposite directions, forming the (shorter than DNA).
double helix. ● Uracil (U) replaces thymine (T).
● Nitrogenous bases bound by hydrogen bonds. ● Types of RNA in the protein synthesis process:
○ Adenine (A) = Thymine (T) ○ Messenger RNA (mRNA)
○ Guanine (G) ≡ Cytosine (C) ○ Ribosomal RNA (rRNA)
● In the nucleus, chloroplast, mitochondrion. ○ Transfer RNA (tRNA)

Protein synthesis from DNA

1. DNA polynucleotides unwind to expose genetic codes.

2. Transcription occurs to synthesise mRNA.

3. mRNA diffuses out of the nucleus, and attaches to the ribosomes in cytoplasm (known as rRNA).

4. tRNA at the ribosome translates genetic code into amino acids. Every 3 genetic codes form 1 amino acid.

5. Translation occurs at the ribosome.

6. Amino acid links to another by peptide bond, forming a long linear polypeptide chain (primary structure of
protein).

Importance of nucleic acids

● Carrier of hereditary information.
● Determinant of characteristics in living organisms.

Formation of chromosomes
● Chromosomes are formed from DNA polynucleotide chains wound around a histone protein.
● Histones do not carry genetic information.
● DNA molecules combine with histone proteins, forming nucleosomes.
● Nucleosomes intertwine to form the chromosome structure.
F4 C5: Metabolism and Enzymes

5.1 Metabolism

Catabolism Anabolism

● Breaks down complex substances into simple ● Synthesis of complex molecules from simple
substances. molecules.
● Releases energy. ● Absorbs energy.
● A (substrate) → B + C (products) ● A+B (substrate) → C (product)
● Eg. Cellular respiration ● Eg. Photosynthesis
- Glucose + O2 → CO2 + H2O + - CO2 + H2O → Glucose + O2
Energy

5.2 Enzyme
● Organic catalysts, made up of proteins.
● Substrate + Enzyme active site → Enzyme-substrate complex

CHARACTERISTICS
● Act rapidly.
● Small quantities required, reusable.
● Structure remains unchanged after reaction.
● Specific reactions. (Must fit active site)
● Reversible for most reactions.
● Slowed down/stopped by inhibitors. (Eg. lead, mercury)
● Some need cofactors for efficiency. (Eg, vitamin B, magnesium ion)
● Speed up biochemical reactions.

Intracellular Enzymes Extracellular Enzymes

● Synthesised in a cell for its own use. ● Secreted outside cell.

● Eg. Hexokinase (Glycolysis during cellular ● Eg. Trypsin
respiration) - Produced by pancreatic cells
- Secreted into duodenum to break down
polypeptides

MECHANISM OF ENZYME ACTION

‘Lock/Enzyme and Key/Substrate’ hypothesis
1. Specific substrate approaches enzyme.
2.Substrate combines with active site to form enzyme-substrate complex.
3.A reaction occurs and a product is created. Product leaves active site when reaction is complete.
FACTORS
(a) Temperature
● Temperature ↓, Rate of reaction ↓
● Temperature ↑
- Kinetic energy of molecules ↑
- Frequency of effective collision ↑
- Rate of reaction ↑
- Rate of reaction doubles per 10°C ↑ until optimal temperature.
● At optimal temperature (~37°C), the reaction is at maximum.
● After reaching optimal temperature, the rate of reaction stops and enzyme activity reduces rapidly
until it stops at 60°C.
● Enzymes are denatured as extreme temperatures break chemical bonds in enzyme molecules.

(b) pH
● Range for optimal pH: ph 6 - 8
- Eg. Salivary amylase (pH 6.8)
- Pepsin (pH 1.5 - 2.5)
- Trypsin (pH 8.5)
● Changes charge (ion H+) on the active site of enzymes and substrate surfaces. Therefore, enzyme-
substrate complexes cannot be formed.
● When pH returns to optimal level, charge is restored. Enzymes will function as normal.
● Extreme change in pH breaks structural chemical bonds and denature active sites.

(c) Substrate concentration

● Concentration ↑
- Effective collision ↑, Rate of reaction ↑ until maximum level.
- At maximum level, concentration becomes a limiting factor.
- Rate of reaction ↑ if enzyme concentration ↑
- All active sites are saturated with substrate.

(d) Enzyme concentration

● Concentration ↑, Rate of reaction ↑
- Due to presence of more active sites ready for catalytic action
● If concentration is doubled, amount of substrate converted to products is also doubled
- Under condition; there is excess supply of substrate
● At maximum rate, substrate concentration becomes a limiting factor.
Rate of reaction ↑ if substrate concentration ↑

5.3 Application of Enzymes in Daily Life

Immobilized enzyme technology
● Pectinase/Cellulase → Juice production
● Digestive enzymes → Medical sector
● Lactose → Lactose-free milk
● Amylase/Lipase/Protease/Cellulase → Bio detergent
● Protease → Separate fish skin
● Trypsin → Fur extraction for leather products
F4 C6: Cell Division

6.1 Cell Division

● Involves karyokinesis (nucleus division) and cytokinesis (cytoplasm division).

● Organism cells are divided into:
Somatic cells Reproductive cells / Gametes
● Produced through mitosis. ● Produced through meiosis.
● Contains a diploid number of chromosomes. ● Contains a haploid number of
● Chromatin is a long thread chromosome. chromosomes.
● A pair of chromosomes is called a homologous chromosome.

6.2 Cell Cycle and Mitosis

G1 PHASE
● Cells grow.
● Mitochondria and endoplasmic reticulum are produced.
● Proteins used in the cell cycle are synthesised.
● The nucleus looks big.
● Chromosomes are in the form of chromatin.

S PHASE
● DNA synthesis occurs.
● DNA in the nucleus is replicated.
● Each chromosome multiplies into two sister chromatids, joined at
the centromeres.

G2 PHASE
● Cells continue to grow, and remain metabollically active.
● Cells gather energy to enter the next stage.
MITOSIS
● The division of the nucleus of a parent cell into two nuclei.
● Embryo development: mitosis enables rapid cell growth. Injuries: mitosis produces new cells.

1. Prophase 2. Metaphase

● Chromatin shortens and thickens to form ● Centrioles are at opposite poles.

chromosomes, made up of sister chromatids. ● Spindle fibres maintain chromosomes at the
● The nucleus membrane disintegrates, and the equatorial plane, aligning them in a single row.
nucleolus disappears. ● Ends when the centromeres divide.
● Centrioles move to opposite poles, and spindle
fibre starts to form.
3. Anaphase 4. Telophase

● Centromeres divide into two, and the sister ● Chromatids at opposite poles are daughter
chromatids separate. chromosomes.
● Spindle fibres shorten and contract. ● Each pole has one set of complete, identical
● Sister chromatids are attracted to opposite poles. chromosomes, shaped as fine chromatid threads.
When they arrive, anaphase ends. ● Nucleoli form, spindle fibres disappear.
● Nucleus membrane is formed.

CYTOKINESIS
● The division of cytoplasm that happens immediately after the nucleus is formed.
Animal cells Plant cells
● Occurs when the plasma membrane constricts in ● Vesicles combine to form cell plates at the centre of
the middle of the cell between two nuclei. the cell.
● Microfilaments contract, causing the cell to split ● Cell plates are surrounded by new plasma
into two daughter cells. membranes, and expand outwards to combine
with the plasma membranes.
6.3 Meiosis

● The process of cell division that occurs in reproductive organs to produce gametes, that contains a haploid
number of chromosomes.

1. Prophase I 2. Metaphase I
● ●
3. Anaphase I 4. Telophase I
● ●
5. Prophase II 6. Metaphase II
● ●
7. Anaphase II 8. Telophase II
● ●

6.4 Issues of Cell Division on Human Health

(a) Uncontrolled mitosis

● Formation of tumours
Benign tumour Malignant tumour

● Remains at original site. ● Known as cancer.

● Not dangerous and can be removed ● Caused by radiation, chemical substances,
surgically. carcinogens, genetic factors,
bacteria/viruses.
● Cancer cells spread to other parts of the
body, competing with normal cells for
nutrients to destroy them.

(b) Abnormal meiosis

● Occurs due to spindle fibres failing to function during anaphase I/anaphase II.
Effects:
● Chromosomes fail to separate (nondisjunction).
● Gametes have an abnormal number of chromosomes (22/24).
- Fertilisation of normal gamete + abnormal gamete = zygote with abnormal number of chromosomes
- Down syndrome, Klinefelter syndrome: 47 chromosomes
- Turner’s syndrome: 45 chromosomes
● Effects of Down syndrome: Mental retardation, slanted eyes, slightly protruding tongue, stunted body
growth
● Gene mutation
- Errors in DNA replication due to change in nucleotide sequence of DNA molecules
- Sickle cell anemia
- Albinism
F4 C7: Cellular Respiration

7.1 Energy production through cellular respiration

Respiration:
(a) External respiration
● Breathing
- Mechanical process by which O2 is transferred from surrounding air/water into body cells, and CO2 is
transferred from body cells to surrounding air/water.
→ Inhalation
→ Exhalation
(b) Internal respiration
● Cellular respiration
- Biochemical process by which oxidation of organic molecules (glucose) results in release of energy, CO2,
and H2O in living cells.
→ Aerobic respiration
→ Anaerobic respiration (Fermentation)

Metabolism:
(a) Anabolism
● Process of synthesising simple molecules to complex ones.
● Absorbs energy.
● Eg. Protein formation.
(b) Catabolism
● Process of breaking down complex molecules to simple ones.
● Releases energy.
● Eg. Glucose breakdown in cellular respiration.

7.2 Aerobic Respiration

● Breakdown of glucose involving O2 to produce chemical energy.

(a) Glycolysis (Glucose → Pyruvate)

● Breakdown of glucose by enzymes in the cytoplasm.
● 1 glucose molecule → 2 pyruvate molecules

(b) Oxidation of Pyruvate (CO2 + H2O + Energy)

● Oxidised in the mitochondrion.

Aerobic respiration:
Glucose → Pyruvate ⟶ CO2 + H2O + Energy
● Group of non-organic phosphate is added to adenosine diphosphate (ADP) to produce ATP molecules.
● ATP molecules have weak phosphate links.
● When phosphate links are broken, energy released is supplied to cells to help carry out daily activities.

Glucose oxidation:
Glucose + O2 → CO2 + H2O + Energy (2898 kJ)
7.3 Fermentation
● Incomplete breakdown of glucose in limited/no oxygen conditions.
● Differs from aerobic respiration after glycolysis
● Pyruvate undergoes either:
(a) Alcohol Fermentation
Glucose → Ethanol + CO2 + Energy (210 kJ)
(i) Yeast
● Ethanol used to make beer and wine.
● CO2 makes bread dough rise.
(ii) Plants
● Paddy plants in waterlogged areas with less O2.
● Ethanol produced is toxic to most plants, but paddy plants have higher tolerance.
● Paddy plants produce alcohol dehydrogenase enzymes which break down ethanol
molecules → CO2

(b) Lactic acid Fermentation

Glucose → Lactic acid + energy (150 kJ)
(i) Lactobacillus
● Carries out milk fermentation to produce yoghurt.
● Acts on lactose and turns it to lactic acid.
● Lactic acid coagulates casein (milk protein) to produce yoghurt
● Source of sour taste
(ii) Human muscle cells
● During vigorous training, rate of O2 used exceeds O2 supplied by blood circulatory system,
● In an O2-deficiency state and undergoes oxygen debt.
● During oxygen debt, glucose cannot break down completely. Accumulation of lactic acid occurs until a
level of concentration that can cause fatigue and muscle cramps.
● Once vigorous activity stops, excess O2 oxidises lactic acid into CO2, H2O and Energy. When all lactic
acid is expelled, O2 debt is repaid.

Comparison:
● Occurs in yeast, bacteria, animals, plants.
● Process begins with glycolysis when glucose → pyruvate.
● Produces chemical energy in the form of ATP.
● Breakdown of glucose and its conversion to chemical energy.

Aerobic respiration Fermentation

● Breakdown process of glucose is ● Breakdown process of glucose is incomplete

completed in the presence of O2. without O2 or in limited O2 conditions.
● Occurs in cytoplasm and mitochondrion. ● Occurs in cytoplasm.
● Produces H2O. ● X produces H2O.
● Glucose is oxidised completely into CO2 ● Glucose is not oxidised completely into ethanol
and H2O. and CO2 or lactic acid.
● 1 molecule glucose generates 2898 kJ of ● 1 molecule of glucose generates 210 kJ (alcohol)
energy. or 150 kJ (lactic acid) of energy.
F4 C8: Respiratory Systems in Humans and Animals

8.1 Types of Respiratory system

Unicellular organisms Multicellular organisms

● Shorter distance of O2 diffusion. ● Longer distance of O2 diffusion.

● Simple diffusion through plasma ● Low TSA:V.
membrane. ● Special respiratory structure.
● High TSA:V.
● No complex respiratory structure.

Insects Fish Amphibians Humans

Respiratory Tracheole Filament and Skin and lungs Alveolus

structure Lamellae

Large TSA ↑ No. of ↑ No. of Folded surface

adaptation tracheoles filaments
and
lamellae

Structure that
helps breathing

Oxygen passage

Breathing
mechanism