BIOLOGY

SUMMARIZED NOTES ON THE THEORY SYLLABUS

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CAIE IGCSE BIOLOGY

1. Characteristics and Classification of

Living Organisms
1.1. Characteristics of Living Organisms
The Age-Old Acronym: MRS GREN

 Movement: an action by an organism or part of an organism causing a change of position or place

 Respiration: the chemical reactions in cells that break down nutrient molecules and release energy for
metabolism
 Sensitivity: the ability to detect and respond to changes in the internal or external environment
 Growth: a permanent increase in size and dry mass
 Reproduction: Process which produces offspring genetically identical or different from the parent organism
 Excretion: the removal of the waste products of metabolism and substances in excess of requirements
 Nutrition: the taking in of materials for energy, growth, and development

1.2. Concept and Uses of Classification System

Sequence of Classification
 Organisms are classified into groups by the features they share.
 Species: a group of organisms that can reproduce to produce fertile offspring.
 Sequence of Classification: Kingdom → Phylum → Classes → Orders → Families → Genus → Species.
 Acronym: King Philip, Come Over For Good Soup

The Binomial Nomenclature

 The Binomial System of Naming Species is an internationally agreed system in which an organism's
scientific name is comprised of two parts, namely, the genus and species.
 The format is Genus species. The genus is capitalised, and the species are not.
  The binomial name is typed in italics or written with an ‘underline’
 The classification of organisms helps show the evolutionary relationships between them.
 Scientists also use the DNA base sequence to help classify organisms.
 The similarity in DNA base sequence shows how closely the two organisms are related.

Dichotomous Keys

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 Dichotomous Keys use visible features to classify organisms. They give you a choice of two features, and
you follow the one that applies: each option leads to another option until the organism is narrowed down to

its genus and species.

1.3. Features of Organisms

The Five Kingdoms
  Animals: Multicellular ingestive heterotrophs (eat living organisms). Ex: cat, ladybird, newt, etc.
 Plants: Multicellular photosynthetic autotrophic (make their food) organism with a cellulose cell wall and
chloroplasts. Ex: cactus, oak tree.
 Fungi: Single-celled or multicellular heterotrophic and saprotrophic (feeds on dead and decaying organic
matter) organisms with cell walls not made of cellulose, spread by spreading spores in moist/dark/warm
environments. Most have hyphae and mycelium in structure. Ex: yeast, mushrooms.
 Prokaryotes: Single-celled organisms with no true nucleus and mitochondria. Many also have plasmids
(important for Genetic Engineering). Ex: E.coli, Salmonella.
 Protist or Protoctist: Single-celled organism with a nucleus. Some are multicellular. Ex: Amoeba, seaweed.
 Protoctists, fungi, plants, and animals are all eukaryotes (having a well-defined nucleus), whereas monera
are prokaryotes (No true nucleus).
 Animals are classified as vertebrates (have a backbone) and invertebrates (do not have a backbone).

1.4. Vertebrates

Types of
Features
Vertebrates

Fur or hair on the skin, External ears (pinna), Internal fertilisation, Mammary Glands,
Mammals
give birth to live young of its kind

Reptiles Thick, dry, scaly skin, Usually four legs, Internal fertilisation, Soft Shelled Eggs

Fish Wet scales, Streamlined body shape, External fertilisation, and soft eggs

Smooth, moist skin, External fertilisation, and soft eggs, Gills, & Lungs can live on
Amphibians
land and water. Most have four legs.

Feathers on the body and scales on legs, Constant internal body temperature, Hard
Birds
eggs, Internal fertilisation, birth through eggs

1.5. Arthropods
 Arthropods are the largest group under invertebrates (Organisms that do not have a backbone).
 All arthropods have three standard features:
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1. Exoskeleton
2. Jointed legs
3. Segmented body

Type of
Number of Legs Body parts Wings Antennae
Arthropod

5 pairs (1 modified All body segments tucked

Crustacean None 2 pairs
as claws) under carapace

Myriapods Many Many None 1 pair

2 pairs (1 or both may

Insects 3 pairs 3 (head, thorax, abdomen) 1 pair
be vestigial)

2 (cephalothorax and
Arachnids 4 pairs None None
abdomen)

1.6. Classification of Plants

In IGCSE Biology, the plant kingdom is classified into ferns and flowering plants.

 Ferns:
 Do not produce flowers/seeds
 They are plants with roots, stems, and feathery leaves (fronds)
 Reproduce by spores, produced on the undersides of their fronds
 Flowering plants:
 They are plants with roots, stems and leaves
 Reproduce sexually through flowers and seeds
 Seeds are produced inside the ovary in the flower

Monocotyledons Dicotyledons

One cotyledon/One-seed leaf Two cotyledons/Two-seed leaf

Parallel veins Branching veins

Long Narrow Leaf Broad leaves

The Number of Petals is a Multiple of 3 The Number of Petals is a Multiple of 4 or 5

Scattered Vascular Bundles Ringed Vascular Bundles

Tip: Differentiating monocotyledons and dicotyledons comes up frequently in Multiple Choice Questions

1.7. Viruses
 Viruses are not part of any classification system because they are not considered living things.
 They do not carry out the seven life processes for themselves; instead, they take over a host cell’s metabolic
pathways to make multiple copies of themselves.
 Virus structure contains only a genetic material (RNA or DNA) inside a protein coat.
  Example of virus structure below (No mitochondria or ribosomes)

2. Organisation of the Organism

2.1. Cell Structure
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 All living things are made of cells.

 New cells are produced by the division of existing cells
 All typical eukaryotic cells (multicellular) have:
 Cell Membrane: controls movement in and out of cells
 Cytoplasm: where chemical/metabolic reactions take place
 Nucleus: contains DNA, stores genetic information and controls the activity of the cell
 Mitochondria: where aerobic respiration happens
 Ribosome: allows protein synthesis in the cytoplasm
 Endoplasmic reticulum: Studded with ribosomes, it looks rough under the microscope.
 A typical animal cell (e.g., the liver cell) has all the above.
 Plant cells especially also have:
 Vacuole: cell sap to keep cell turgid
 Cell Wall: rigid to hold the shape of the cell, strengthens the cell
 Chloroplasts: contain chlorophyll, which absorbs light energy for photosynthesis
 A typical plant cell (e.g., the palisade cell) has everything above.

Prokaryotes
Prokaryotes (Unicellular) DO NOT have mitochondria and a true nucleus.

 One example of a prokaryote is bacteria.

 A bacterial cell only contains a cell wall made of peptidoglycan, cell membrane, cytoplasm, ribosomes, and
plasmids.
 It lacks a nucleus and is represented by a circular chromosome of DNA.
  Plasmids are small, circular rings of DNA in the cytoplasm with extra genes outside the chromosomal DNA.

Syllabus 2.1.3: You must be able to identify the cell structures in diagrams and images of plant, animal and bacterial
cells

2.2. Levels of Organisation

 The division of existing cells produces new cells.

Key Terms

 Cells: Building Blocks of Life

 Tissue: Groups of cells with similar structures working together to perform a shared function
 Organ: Group of tissues working together to perform a specific function
 Organ system: Group of organs with related functions working together to perform body functions.
 Organism: A human

Specialised Cells
 Specialised Cells have Specific Functions.

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Specialised Cells Specific Function Location of Cell

Movement of mucus in the trachea Respiratory Tract, Fallopian

Ciliated cells
and bronchi Tube, Testes

Root Hair cells Absorption Roots

Palisade Mesophyll cell Photosynthesis Leaf Cells

Neurones Conduction of electrical impulses Everywhere in an organism

Red Blood cells Transport of oxygen Everywhere in an organism

Sperm and Egg cells/ovum In their respective gonads

For reproduction
(gametes) (glands)
2.3. Magnification
The general formula is represented in this way:
Magnification=size of drawingsize of specimen=imageactual=IAMagnification=size of specimens
ize of drawing=actualimage=AI
Other Forms in Magnification Formula

 Actual size = image size ÷ magnification

 Image size = magnification x actual size

Unit Conversions (μm - micrometre)

 1cm = 10mm
 1mm = 1000μm
 1μm = 0.001mm

Magnification does NOT have any units (‘x 50’ or ‘x 5000’)

Tip: This comes out frequently in all three papers

3. Movement Into and Out of Cells

3.1. Diffusion
Diffusion: Net movement of particles down the concentration gradient (high → low) as a result of their random

movement.

 At Equilibrium, the concentrations of molecules are equal.

 Energy for diffusion comes from the kinetic energy of the random movement of molecules and ions.
 The diffusion of gases and solutes is important as without it, molecules that are needed for life, (Such as
glucose and oxygen for respiration) would not be able to get to the places they are required.
 Some substances move into and out of cells by diffusion through the cell membrane.

Factors that influence diffusion (Passive Transport)

 Concentration gradient
 Temperature
  Surface area to volume ratio
 Distance

3.2. Osmosis
 The role of water acts as a solvent in organisms to aid with digestion, excretion, and transport.
 Knowing the definition of Diffusion, Osmosis and Active Transport is COMPULSORY!
 The cell membrane is partially permeable, allowing small molecules (like water) through but not larger
molecules.

Osmosis: Net movement of water molecules from a region of higher water potential (dilute solution) to a region of
lower water potential (concentrated solution) through a partially permeable membrane.

Conc. of Solute (In-Cell) Conc. of Solute (Outside-Cell) Condition of the Cell

Low High Cell Shrinks (Flaccid/Hypertonic)

Same Same No Change (Isotonic)

High Low Turgid/Hypotonic

In Animals
 Increasing solute concentration inside a cell can cause it to burst (cell lysis) because it has too much water
and no cell wall.

In Plants

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 Increasing solute concentration inside the cell causes the cell to become turgid, and the vacuole fills up.
The cell wall can withstand the higher turgor pressure.
 Decreasing solute concentration inside the cell causes the cell to become flaccid, losing water, and the
vacuole to get smaller. The cell body shrinks, pulling away from the cell wall.
 Plants are supported by the water pressure inside the cells pressing outwards on the cell wall.
 Plasmolysis: the process in which a plant cell loses water due to osmosis, causing the cell membrane to
shrink away from the cell wall.
Dialysis Tubing Experiment
 Dialysis Tubing (or Visking tubing) is a non-living, partially permeable membrane made from cellulose.
 Pores are small enough to prevent the passage of large molecules (such as sucrose) but allow smaller
molecules (such as glucose and water) to pass through by diffusion and osmosis.

3.3. Active Transport

Active Transport: The movement of particles through a cell membrane from a lower concentration region to a higher
concentration region (i.e., against a concentration gradient) using energy from respiration (ATP).

 Carrier Proteins or Protein Carriers are also used during active transport.
  It is embedded in the cell membrane, where it picks up specific molecules and moves them through the
membrane against their concentration gradient.
 Active transport is needed when an organism wants to optimise the nutrients it can take up - ion uptake by
root hair cells.
 Some particles are too large to cross a membrane by diffusion or active transport. A few very specialised
cells have developed a method for taking up these particles; the particles are engulfed by the cell surface
membrane flowing around them which is called Endocytosis. Endocytosis (called phagocytosis) is used by
white blood cells to engulf pathogens.

3.4. Difference between Diffusion, Osmosis, and

Active Transport
Feature Diffusion Osmosis Active Transport

Type of Passive (no energy Active (requires energy-

Passive (no energy required)
movement needed) ATP)

Low → High (against

Direction High → Low concentration High → Low water potential
gradient)

Substance Gases or solutes (e.g.,

Water only glucose, ions, etc.
moved oxygen, CO2CO2)

Membrane A partially permeable Requires membrane and

Not always
needed? membrane is required carrier proteins

4. Biological Molecules
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4.1. Biological Molecules

 Carbohydrates: made from Carbon, Hydrogen and Oxygen (CHO)
 Fats and Oils: made from Carbon, Hydrogen and Oxygen (CHO)
 Proteins: made from Carbon, Hydrogen, Oxygen, Nitrogen and sometimes Sulfur (CHON{S})

Smaller molecules Larger molecules

Simple sugars Starch, glycogen and cellulose

Fatty acids and glycerol Fats and oils

Amino acids Proteins

4.2. Food Tests

Positive Negative
Test for: Solution Process
Result Result

Reducing Benedict Add Benedict solution into a beaker and

Brick Red Blue
Sugars Solution Heat Up to 70-80°C
 Positive Negative
Test for: Solution Process
Result Result

Iodine
Starch Add Iodine solution to the specimen Blue-Black Brown
Solution

Biuret
Protein Add Biuret solution to the sample Purple/Violet Blue
Solution

Fats (Physical Add ethanol to the sample and shake with Cloudy
Ethanol N/A
test) an equal volume of water. Emulsion

Vitamin C DCPIP Add DCPIP solution to the sample Colourless Blue

4.3. Structure of a DNA

 Chromosomes are made of a molecule called DNA
 DNA is also called deoxyribonucleic acid.

 Each chromosome is a very long molecule of tightly coiled DNA

 Two strands coiled together to form a double helix
 Each strand contains chemicals called Bases
 Cross-links between strands are formed by pairs of bases
 The bases always pair up in the same way:
  A and T
 C and G
 You do NOT need to know the names of the DNA bases for this syllabus.

5. Enzymes
5.1. Enzymes
General Characteristics of an Enzyme
 Catalyst: A substance that increases the rate of reaction and is not used up itself.
 Enzymes: Specific proteins involved in all metabolic reactions, functioning as biological catalysts.
 Enzyme lowers the activation energy needed for a reaction to take place.
 It is essential in all living organisms for sustaining life.
 Enzymes are unchanged and can be reused

Lock and Key Model (Hypothesis)

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 Substrate: the molecule(s) before they are made to react, complementary to the active site.
 Product: the molecule(s) that are made in a reaction

Different sequences of amino acids may lead to varying shapes of protein molecules, as these slight differences
(temperature/pH) may be deferred in their function.

5.2. Temperature on Enzymes

 Enzymes have an optimum temperature: the temperature at which they work best. In animals and humans,
the optimum temperature is ≈ 37 °C.
 When temperature increases, molecules move faster, more effectively, and frequently collide.
 Having more kinetic energy makes them more likely to form Enzyme-Substrate complexes.
  If the temperature is too high, enzyme molecules vibrate too vigorously; the enzyme is denatured, It loses
the shape of its active site and no longer forms Enzyme-Substrate complexes.
 When the temperature is too low, there is not enough kinetic energy for the reaction, so fewer E-S complex
forms

5.3. pH on Enzymes
 Enzymes are sensitive to pH.
 Some enzymes work best in an acid, and others in an alkaline.
 Enzymes work best at their optimum pH.
 If the pH changes, the hydrogen bond is broken, denaturing the enzyme, changing the shape of its active
site. Substrate can no longer bind with the enzyme, therefore, no reaction occurs
 Pepsin is used in acidic conditions, Amylase is used in neutral conditions, and trypsin is used in alkaline
conditions.

5.4. Graphs for Changes in Enzyme Activity

Effect of Temperature Effect of pH

6. Plant Nutrition
6.1. Photosynthesis
Photosynthesis: the process by which plants manufacture carbohydrates from raw materials using energy from light.
CarbonDioxide+Water→light+chlorophyllGlucose+OxygenCarbonDioxide+Waterlight+chlorophyll
Glucose+Oxygen
6CO2+6H2O→light+cholorophyllC6H12O6+6O26CO2+6H2Olight+cholorophyllC6H12O6+6O2
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 Only EXTENDED Students must know the Balanced Chemical Equation

 The carbon dioxide diffuses through the open stomata of a plant leaf, and water is taken up through the
roots.
 Chlorophyll is a green pigment that traps light energy and converts it into chemical energy to form
carbohydrates and their subsequent storage.
 Glucose is used for respiration, energy storage, cellulose cell walls, and making proteins and sugars.

Use and Storage of the Carbohydrates Made in Photosynthesis

 starch as an energy store

 cellulose to build cell walls
 glucose used in respiration to provide energy
 sucrose for transport in the phloem

6.2. Mineral Requirements

Nitrate ions Magnesium ions

Making amino acids Making chlorophyll

Deficiency: small plant due to slow/stunted Deficiency: The plant lacks chlorophyll, leaves turn
growth yellow.

Tip! You need to know the purpose of these required nutrients.

6.3. Investigation of Chlorophyll

 Take a potted plant with variegated (green and white) leaves.
 De-starch the plant by keeping it in complete darkness for about 48 hours.
 Expose the plant to sunlight for a few days.
 Leaf boiled in water for 2 minutes to break down cell walls, denature enzymes and allow for easier
penetration by ethanol.
 Warmed in ethanol until the leaf is colourless to extract chlorophyll, which would mask the observation
  Dipped into the water briefly: to help soften the leaf
 The leaf is placed on a white tile, and iodine is added. If starch is present, the colour will be blue-black; if
absent, it will remain brown.

6.4. Investigation of Light Intensity

NOTE: This type of question is frequently asked in Paper 2.

 De-starch the plant by keeping it in the dark for 48 hours

 Place a stencil over part of a leaf
 Place the leaf in sunlight for 4-6 hours
 Remove the stencil and test for starch
 +ve result = parts which received light turn blue-black
 -ve result = parts that didn’t receive light remain brown
6.5. Investigation of Carbon Dioxide Concentration
 Take two de-starched potted plants.
 Cover both the plants with bell jars and label them A and B.
 Inside A, keep NaHCO3NaHCO3 (Sodium Bicarbonate). It produces CO2CO2.
 Inside B, keep NaOHNaOH (Sodium Hydroxide). It absorbs CO2CO2.
 Keep both set-ups and do the starch test in the sunlight for at least 6 hours

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 The leaves of Plant A will turn black after the starch test
 The leaves of Plant B will remain brown after the starch test

Hydrogencarbonate indicator: measures the carbon dioxide concentration

Key: PMROY, purple being the lowest

carbon dioxide concentration, and yellow the highest.
6.6. Limiting Factors
Limiting Factors: Conditions where something present in the environment (Temperature, Carbon Dioxide
Concentration and Light Intensity) is in such short supply that it restricts life processes.

Light intensity

 As the amount of light increases, the rate of photosynthesis increases (A-B)

 The limiting factor is light
 Increasing the amount of light after a certain point does not affect the rate (C)
 The limiting factor is now carbon dioxide or temperature.

6.7. Leaf Structure

Most dicotyledonous plant leaves have a large surface area and are thin.
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Structure Function

Waxy Cuticle A waterproof waxy layer that prevents water loss from the top of the leaf

Upper & Lower

Thin and transparent to allow light to enter the palisade mesophyll cells
Epidermis

Palisade Mesophyll Found at the top of the cell and contains the MOST chloroplasts that absorb
Cells sunlight for photosynthesis.

Spongy Mesophyll Irregularly shaped cells create air spaces to allow the gaseous exchange to take
Cells place; do not contain many chloroplasts

Vascular Bundle Made up of xylem and phloem

Xylem A tissue vessel that transports water and mineral ions

Phloem A tissue vessel that transports sucrose and amino acids

Stomata/Stoma Tiny gaps that open and close to allow the gaseous exchange to occur

Guard Cells Control the opening and closing of stomata

Opening and closing of Stomata:

 Stomata open when guard cells absorb water by osmosis, become turgid, and curve outward, creating a
gap.
 They close when guard cells lose water, become flaccid, and collapse, sealing the pore to reduce water
loss.
Syllabus 6.2.3: You must be able to explain how the structures above adapt leaves for photosynthesis

6.8. Adaptations of Leaf Structure for Photosynthesis

 Here is a table of different adaptations of the specific leaf structure helping towards photosynthesis.

Adaptation Functions

Large Surface Area of Increase surface area for diffusion of carbon dioxide and absorption of light for
Leaf photosynthesis.

Thin Allow carbon dioxide to diffuse quickly into the palisade mesophyll cells

Chlorophyll Absorb light energy so photosynthesis can take place.

Network of Veins Allow efficient transport of water and mineral ions throughout the plant

Epidermis is thin Allow more light to reach the palisade mesophyll cells

Stomata/Stoma Allow oxygen and carbon dioxide to continuously diffuse in and out of the leaf

7. Human Nutrition
7.1. Diet
Balanced Diet: A diet that includes the appropriate amounts of carbohydrates, fats, proteins, vitamins, minerals,
fiber, and water needed to support the body's growth, energy needs, and overall health.

 Diet-related to age/gender/lifestyle:
 Children Below 12: Require more calcium
 Teenagers: Highest calorie intake
 Adults: Balanced meal with fewer calories
 Pregnant Women: more iron, calcium
 Males: Generally require more energy
7.2. Nutrition
Nutrients Uses

Carbohydrates Energy

Source of energy, building materials, energy store, insulation, buoyancy, making

Fats and oils
hormones

Energy, building materials, enzymes, haemoglobin, structural material (muscle),

Proteins
hormones, antibodies

Vitamin C Collagen, resistance to diseases

Vitamin D Absorption of calcium

Calcium Development and maintenance of strong bones and teeth

Iron Making haemoglobin

Fibre
Provides bulk for faeces, helps peristalsis
(Roughage)

Water Chemical reactions, solvent for transport

7.3. Deficiencies
 Vitamin C: Scurvy; loss of teeth, pale skin & sunken eyes
 Calcium/Vitamin D: Rickets, Osteoporosis; weak bones and teeth

7.4. Digestive System

Process of Digestion

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 Ingestion: taking substances (e.g. food, drink) into the body through the mouth.
 Physical/Mechanical Digestion: breakdown of food into smaller pieces without chemical change.
 It increases the surface area of food for the action of enzymes in chemical digestion.
 Chemical Digestion: breakdown of large, insoluble food molecules into small, soluble molecules.
 Absorption: the movement of nutrients from the intestines into the blood
 Assimilation: uptake and use of nutrients by cells
 Egestion: the removal of undigested food from the body as faeces

Main Organs in the Alimentary Canal

 Mouth: contains teeth used for mechanical Digestion, an area where food is mixed with salivary amylase &
where ingestion takes place
 Salivary glands: produce saliva, which contains amylase and helps food slide down the oesophagus
 Oesophagus: tube-shaped organ that uses peristalsis (circular muscle contract and relax) to transport food
from mouth to stomach
 Stomach: has pepsin (a protease that works best in acidic conditions) to break down proteins into amino
acids and kills bacteria with hydrochloric acid. They also have elastic walls.
 Mechanical digestion in the stomach occurs via peristaltic contractions of the smooth muscle.
 Small intestine: tube-shaped organ composed of three parts:
 Duodenum: fats are emulsified by bile and digested by pancreatic lipase to form fatty acids and
glycerol. Pancreatic amylase and trypsin (a protease) break down starch.
 Jejunum (not in syllabus)
 Ileum: Maltase breaks down maltose to glucose. This is where absorption also takes place.
 Pancreas: produces amylase, trypsin (a protease that works best in alkaline conditions), and lipase.
 Liver: produces bile (emulsifies fats, neutralises acidic fat molecules), deamination, and makes urea to be
sent to the kidney. Also, it is the site of the breakdown of alcohol and other toxins.
 Gall bladder: stores bile from the liver
 Large intestine: tube-shaped organ composed of two parts:
 Colon: organ for absorption of minerals and vitamins and reabsorbing water from waste to
maintain the body’s water levels
 Rectum: where faeces are temporarily stored
 Anus: a ring of muscle that controls when faeces is released.

7.5. Teeth
Our teeth play a key role in mechanical digestion to help increase the surface area of food.
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Incisors Canines Premolars Molars

Rectangular shape, Blunt for chewing and Blunt chewing and grinding.
Sharp-pointed for
sharp for cutting and grinding, one or two roots, Two or three roots, ridges at
piercing and tearing
biting cusps/bumps at the end the end
Structure of Tooth
Our teeth are embedded in bone, and the gums

 Enamel: the strongest tissue in the body made from calcium salts
 Cement: helps to anchor tooth
 Pulp: contains tooth-producing cells, blood vessels, and nerve endings that detect pain.
 Dentine: calcium salts deposited on a framework of collagen fibers
 Nerves: Detect sensation
 Blood vessels: Provide nutrition

7.6. The Stomach

The stomach lining contains many smooth muscles that contract to squeeze physically and mix the food with the
strong digestive juices present, a process also known as "stomach-churning."

 The food will be digested within the stomach for several hours
 First stop for protein digestion
7.7. Chemical Digestion
 Chemical Digestion: the breakdown of large insoluble molecules into small soluble molecules
 The role of chemical digestion in producing small soluble molecules that can be absorbed

7.8. Enzymes in Digestion

 Amylase: breaks down starch into maltose; it is produced in the pancreas (secreted into the duodenum) and
salivary glands.

 Maltase: breaks down maltose into glucose in the membrane of the epithelium lining in small intestines.
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 Protease: breaks down proteins into peptides and amino acids. Pepsin comes from the stomach (acidic),
and trypsin comes from the pancreas (alkali).

 Lipase: breaks down lipids into fatty acids and glycerol, produced by the pancreas.

7.9. Hydrochloric Acid and Bile

 Functions of Hydrochloric acid in gastric juice:
 Denaturing enzymes in harmful microorganisms
 Giving the optimum pH for pepsin activity
 Kills pathogens
 Bile:
 Produced by the liver
 Stored in the gall bladder, transported by the bile duct
 an alkaline mixture that neutralises the acid mixture of food and gastric juices entering the
duodenum from the stomach to provide a suitable pH for enzyme action.
 Bile helps with the digestion of fats by breaking them down from large molecules to smaller
molecules, making a larger surface area.
7.10. Absorption and Villus
Absorption: the movement of nutrients from the intestines into the blood

 The small intestine is the region for absorption of digested food through diffusion, osmosis, and active
transport.
 The small intestine is folded into many villi, increasing the surface area for absorption. One villus will have
tiny folds on the cells on its outside called microvilli.
 The epithelium is one cell thick, allowing efficient diffusion of nutrients.
 A large surface area means more absorption of nutrients can happen.
 Lacteals: absorbs fatty acid and glycerol
 Capillaries: provide a good blood supply and a steep concentration gradient.
 Most water is absorbed from the small intestine, and some from the colon (large intestine).

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8. Transport in Plants
8.1. Xylem and Phloem
Functions of Xylem

 transport water and mineral ions, and support the plant’s overall structure.

Functions of Phloem

 transport sucrose and amino acids from the source to the sink.
Adaptations of Xylem

1. thick walls with lignin (dead cell)

2. No cell contents
3. cells joined end to end with no cross walls to form a long, continuous tube

Syllabus 8.1.2: You must be able to

identify in diagrams and images the position of the xylem and phloem as seen in sections of roots, stems, and leaves
of non-woody dicotyledonous plants

8.2. Water Uptake

Root Hair Cells

 Function: to absorb water and minerals from the soil

 They have an elongated shape for a larger surface area, which increases the water absorption rate by
osmosis and ions by active transport.

The large surface area of root hairs is crucial as it increases the uptake of water and mineral ions.

 Water enters root hair cells from moist soil via osmosis because water potential is higher in soil than in the
cytoplasm.
 Then, it enters the root cortex cells, xylem, and mesophyll cells.

Investigate the Pathway of Water through the Above-Ground Parts of a

Plant
 Water uptake can be investigated by placing a plant (like celery) into a beaker of water with a stain (dye,
food colouring) added.
  A few hours later, the celery leaves turn the same colour as the dyed water.
 When the cross-section of the celery is cut, only certain areas are stained by the colour of the water,
showing that it is being carried in specific vessels through the stem - a.k.a xylem vessels.

8.3. Transpiration
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Transpiration: loss of water vapour from leaves, which evaporates from the surface of the mesophyll cells into the
air spaces and diffuses out of the leaves through the stomata.

 Water leaves mesophyll cells into air spaces created by an irregular shape of spongy mesophyll cells, then
diffuses out of the stomata.
 Water vapour loss is due to the large internal surface area provided by the interconnecting air spaces
between mesophyll cells and the size and number of stomata.
 Water moves upwards in the xylem in terms of a transpiration pull that draws up a column of water
molecules held together by cohesive and adhesive forces of attraction between water molecules.

Wilting
Wilting occurs if water loss exceeds water uptake. Cells become flaccid, and tissues become limp.

 This is when all the cells of the plant are not full of water, so the strength of the cell walls cannot support the
plant, and it starts to collapse

Factors affecting the Rate of Transpiration

 Temperature: The kinetic energy of the water molecules increases, so they evaporate and diffuse faster
from the mesophyll cells, increasing the transpiration rate
 Humidity: Low humidity increases the concentration gradient between the leaf and the atmosphere, hence
increasing the transpiration rate, while high humidity decreases the gradient, reducing the transpiration rate.
 Wind Speed: Removing water molecules to maintain a steep concentration gradient

8.4. Translocation
Translocation: Movement of sucrose and amino acids in the phloem from regions of production (sources) to regions
of storage or regions of utilisation in respiration or growth (sinks).

 Translocation in different seasons:

 Spring: sucrose transported from stores in roots to leaves
 Summer & early autumn: sucrose goes from photosynthesizing leaves to root stores,
 Below is a picture of a girdle in a tree trunk.

9. Transport in Animals
9.1. Circulatory Systems
Circulatory System: a system of tubes (veins, capillaries, arteries) with a pump (heart) and valves (in heart and
veins) to ensure a one-way flow of blood.
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 Single Circulation System (fish):

 Blood flows through the heart once every complete circuit (No Septum)
 Two heart chambers (Atrium and Ventricle)
 Blood absorbs oxygen in the gills in lower-pressure
 Released in body cells, then back to the heart
 Double Circulation System:
 Four heart chambers
 Blood passes through the heart twice every complete circuit
 Oxygenated in the lungs, to the heart, to the body, and back to the heart
 Advantages:
 Delivers a greater blood flow rate to tissues around the body as the heart pumps the rich
oxygenated blood to it from the lungs,
 Prevents the mixing of oxygenated and deoxygenated blood.
 Lowers pressure to lungs - protects lung tissues from damage
 More efficient - supports high metablic rates in warm-blooded animals like mammals and birds.

9.2. Heart
The mammalian heart contains a systemic and pulmonary circuit.
  Right Atrium: collect deoxygenated blood & pump it to the right ventricle
 Right Ventricle: pumps deoxygenated blood to lungs
 Pulmonary Artery: carries deoxygenated blood from the right ventricle to the lungs
 Septum: separates the left and right sides of the heart and keeps deoxygenated and oxygenated blood
separate.
 Pulmonary Vein: carries oxygenated blood from the lungs to the left atrium
 Left Atrium: collect oxygenated blood and pump it to the left ventricle
 Left Ventricle: pumps oxygenated blood to the body via the aorta
 Aorta: carries oxygenated blood from the left ventricle to the rest of the body
 Atrioventricular and Semi-lunar Valves: prevent backflow of blood

IMPORTANT! Relative Muscle Wall Thickness: Atria < Right Ventricle < Left Ventricle

9.3. Functioning of the Heart

 The deoxygenated blood incoming from the body flows into the right atrium via the vena cava.
 Once the right atrium has filled with blood, the blood is pushed through the atrioventricular valve into
the right ventricle.
 The ventricle contracts and the blood is pushed into the pulmonary artery through the semilunar
valve, which prevents blood from flowing back into the heart.
 The blood travels to the lungs and moves through the capillaries, passing the alveoli.
 Oxygenated blood returns to the left atrium via the pulmonary vein
 It passes through the atrioventricular valve into the left ventricle
 The thicker muscle walls of the ventricle contract to push the blood forcefully into the aorta and around the
body
 The semilunar valve in the aorta prevents the blood from flowing back down into the heart

Example Past Year Question

Explain the reasons for changes in pressure seen in arteries (0610/42/F/M/23)
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 caused by contraction of muscles (of the heart/ventricle)

 pressure increases when the heart / ventricles contract/pump
 pressure decreases when the heart/ventricles relax

9.4. Exercise on Heart Rate

 The heart's electrical activity can be monitored by the electrocardiogram (ECG), pulse rate, stethoscope and
listening to the sounds of the valves closing.
 Physical activity makes the heart beat more quickly and deeply for increased blood circulation so that more
oxygen and glucose can get to the muscle.

9.5. Coronary Heart Disease

 The coronary arteries are the heart’s blood supply.
 They supply oxygenated blood and nutrients, allowing it to continue contracting and pumping blood.
 The coronary artery becomes blocked, interrupting blood supply to the heart muscle.
 Part of the heart muscle stops contracting, causing a heart attack
 Risk factors are diet, lack of exercise, stress, smoking, genetic predisposition, age and sex
 This can be prevented by not smoking, avoiding fatty food (a good diet) and exercising regularly
9.6. Blood Vessels
Vessel Function Structure

Elastic tissue walls stretch and relax as blood is forced out;

causes pulse

Transport high-pressure blood

Arteries
away from heart Thick walls to withstand high pressure

Small lumen maintains (high) blood pressure.

Valves prevent backflow of blood.

Blood is at low pressure, but nearby muscles squeeze

Transport low pressure blood to
Veins veins and help push blood to the heart
the heart

Large and wide lumen to reduce resistance to the flow of

blood

One cell thick wall for easy diffusion

Allow substances to diffuse into Highly branched; large surface area

Capillaries
cells

Capillary beds constantly supplied with fresh blood, so

diffusion occurs

Major Blood Vessels

Heart: Vena Cava, Aorta, Pulmonary Arteries & Vein
Lungs: Pulmonary Arteries and veins
Kidney: Renal Arteries and veins
Liver: Hepatic Artery, Hepatic Veins and Hepatic Portal Vein

 The hepatic artery brings oxygenated blood from the heart to the liver
 The hepatic vein brings deoxygenated blood from the liver back to the heart
 The hepatic portal vein carries blood from the gastrointestinal tract, gallbladder, pancreas and spleen to
the liver. This blood contains nutrients and toxins extracted from digested contents.
Arterioles and Venules
 The vessels that connect arteries to capillaries are called arterioles
 The vessels that connect capillaries to veins are called venules

9.7. Blood
 Red blood cells: biconcave shape, haemoglobin and oxygen transport (oxy-haemoglobin)
 White blood cells: phagocytosis and antibody production
 Platelets: allows/promotes blood clotting
 Plasma: transport of blood cells, ions, nutrients, urea, hormones and carbon dioxide (mostly water and
dissolved substances)

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Syllabus 9.4.2: You must be able to identify red and white blood cells in photomicrographs and diagrams

White Blood Cells

Phagocyte Lymphocyte

Phagocytes have lobed/irregular C-shaped nuclei Lymphocytes have a circular nucleus and are
and vesicles containing digestive enzymes. found in blood

Phagocytosis: engulfs pathogen, vesicles fuse with Large nucleus/small cytoplasm, and they produce
the vacuole, enzymes digest bacteria. antibodies,

Antibodies: Y-shaped proteins bind to label

Antigens: protein/carbohydrate on the surface of
pathogens, marking them for destruction by the
the pathogen which provokes the immune system
phagocytes.
Blood Clotting
 Reduces blood loss and keeps pathogens out
 Fibrinogen (inactive) turns to fibrin (activated), forms a mesh to trap red blood cells, and eventually dries to
form a scab.

10. Diseases and Immunity

10.1. Pathogens
 Pathogen: a disease-causing organism.
 Transmissible Disease: a disease in which the pathogen can be passed from one host to another.
 The pathogen for a transmissible disease may be transmitted either:
 Direct Contact: the pathogen is passed directly from one host to another through blood, body
fluids, semen, etc.
 Indirect Contact: the pathogen leaves the host and is carried in some way to another e.g.,
contaminated surfaces/food, from animals, from air

10.2. Body Defences

The human body has many natural defences against pathogens.

 Mechanical barriers:
 Nostrils contain hairs that help trap dust
 The skin has a thick outer layer of dead cells
 Chemical barriers:
 Sticky mucus which can trap pathogens
 In the stomach, hydrochloric acid is secreted, which kills many of the bacteria in food
 Cells: Pathogens that manage to get through all these defences are destroyed by white blood cells:
 Some of these cells take in and digest the pathogens by phagocytosis
 Others produce antibodies that incapacitate or kill the pathogen and vaccination against disease
helps antibodies to be made very quickly

Ways of Controlling the Spread of Diseases

 a clean water supply
 hygienic food preparation
 good personal hygiene
 waste disposal
 sewage treatment

10.3. Active and Passive Immunity

Antibody: proteins that bind to antigens, directly destroying or marking pathogens for destruction by phagocytes.

 The surface of the pathogen contains antigens, and they have specific shapes.
 Specific antibodies have complementary shapes which fit specific antigens.
 To destroy a pathogen, antibody molecules must be made that are exactly the right shape to fit into antigens
outside the pathogen.
 Antibodies lock onto antigens, leading to the destruction of pathogens/marking of pathogens for phagocytes
to engulf.
  If a pathogen enters the body, it meets many lymphocytes. One of these will recognise the pathogen and
divide rapidly by mitosis.
 These lymphocytes then secrete antibodies, creating active immunity.

Active Immunity
Active Immunity: defence against a pathogen by antibody production in the body.
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 Active Immunity is gained after infection by a pathogen or by vaccination.

 Vaccines immunise children against diseases caused by pathogens.
 Having a population vaccinated against a particular disease helps to achieve herd immunity.
 Process of Vaccination:
 weakened pathogens or their antigens are put into the body
 the antigens stimulate an immune response by lymphocytes, which produce antibodies
 The body responds to the pathogen and makes its own antibodies. Some of the lymphocytes
become memory cells, which provide long-term immunity

Passive Immunity
Passive Immunity: short-term defences against a pathogen by antibodies acquired from another individual.

 Memory cells are NOT made in passive Immunity

 Babies get passive immunity by breastfeeding.
 Breast milk contains antibodies from the mother, which are passed on to her baby.
 Useful because a young baby’s immune system is not well developed; the mother’s antibodies can
protect it against any diseases.
 Some diseases are caused by the immune system mistakenly targeting and destroying the body’s own cells,
thinking they are harmful. These are called autoimmune diseases.

10.4. Cholera
 Diarrhoea: loss of water from watery faeces
 Oral rehydration therapy and antibiotics are used to cure this.
 The bacterium, “Vibrio cholerae”, causes Cholera.
 The bacterium is transmitted through contaminated water.
 The cholera bacterium produces a toxin that causes the secretion of chloride ions into the small
intestine, decreasing water potential in the gut, water moves into the gut down the water potential
gradient, causing diarrhoea, dehydration, and loss of salts and water from the blood.

11. Gas Exchange in Humans

11.1. Gas Exchange Surfaces
Properties Reasons

Thin surface Short distance to diffuse (one cell thick)

Large surface
Many molecules can diffuse at once/More alveoli
area
 Properties Reasons

Regular fresh air supplies keep up concentration gradients for oxygen and carbon
Good ventilation
dioxide.

Good blood
Gases can be carried to/from the cells that need/produce them
supply

Moist Allow gases to dissolve, ready for diffusion

11.2. Structure of the Lungs

The lung contains a diaphragm, ribs, intercostal muscles, larynx, trachea, bronchi, bronchioles, alveoli and associated
capillaries

 Cartilage (in the trachea): prevents the trachea from collapsing during the absence of air and protects it by
keeping it open.
 Ribs: to protect vital organs and blood vessels and expand and contract (and efficient breathing).
 Intercostal (internal & external) muscles: situated between the ribs that create and move the chest wall.
 Diaphragm: produces volume and pressure changes in the thorax, leading to the ventilation of the lungs.
Composition of Breathing Dry Air
Inspired Air Expired Air

Oxygen 21% 16%

Carbon Dioxide 0.04% 4%

Nitrogen 78% 78%

Water Vapour Lower Higher

 Test for CO2: Add CO2 through limewater. +ve result = turns cloudy

11.3. Physical Activity on Breathing

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 Physical activity increases the breathing rate – more respiration - and higher CO 2 concentration in the blood.
 This is measured with a spirometer to produce a spirogram.
 During exercise, tissues respire at a higher rate; the change in breathing volume and rate helps keep
CO2 concentration and pH safe.

11.4. Breathing
Inspiration Expiration

External intercostal muscles contract – pulls ribcage External intercostal muscles relax – ribcage falls
upwards and outwards downwards and inwards

Diaphragm muscles contract – the diaphragm moves Diaphragm muscles relax – return to a dome
downwards, and the volume of the thorax increases shape, and the volume of the thorax decreases

Atmospheric Pressure > Pressure in Thorax Atmospheric Pressure < Pressure in Thorax

Air moves into the lungs Air moves out of the lungs
  Internal intercostal muscles are used in coughing and sneezing.
 Mucus & cilia: goblet cells produce sticky mucus to trap and eliminate particulate matter and
microorganisms.
 Ciliated cells have cilia, little hairs which sweep/beat back and forward in a coordinated way to brush
mucus up the lungs into the mouth.

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CAIE IGCSE
Biology
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