Topic 2 - Organisation

 Principles of Organisation

• Cells - Basic building unit of life

• Tissue - Group of cells with a similar function.

• Organs - Similar tissues performing specific functions.

• Organ systems - Organs work together to form an organism.

Mouth

Mechanical digestion by teeth; salivary glands secrete amylase which breaks starch into maltose.

Oesophagus

Food travels to stomach

Stomach

Churns and pummels food.

Pepsin digests proteins (works best in acidic conditions, pH ~2).

Hydrochloric acid kills bacteria.

Small Intestine

• Bile (made in liver, stored in gall bladder):

• Neutralises stomach acid. Emulsifies fats for easier digestion. Produces enzymes

Large Intestine

Absorbs excess water.

Rectum & Anus

Stores faeces → excretion.

Enzymes

Biological catalysts that speeds up a chemical reaction, without being used up itself.  Enzymes help to break down food because they catalyse chemical reactions.

Lock and Key Method

Enzymes have an active site and substrate that binds together. 

• Substrate fits into active site (of enzyme)

• Shape of active site is unique to substrate, 

• Active site and substrate bind together to break the bonds within substrate

Effect of Temperature on Enzymes

• Increased temperature → more kinetic energy → faster reactions (up to the optimum temperature).           

                                                             

• Beyond optimum, bonds break → enzyme loses shape → denaturation. Denatured enzymes → substrate can't bind → reaction stops.

Effect of pH on Enzymes

Too low/high → bonds break → enzyme denatures. Denatured active site → substrate can’t bind → reaction stops.

Amylase

Produced by: Salivary glands, Pancreas, Small intestine;

Substrate: Starch; Product: Maltose.

Protease

Produced by: Stomach, Pancreas, Small intestine;

Substrate: Protein; Product: Amino acids.

Lipase

Produced by: Pancreas, Small intestine;

Substrate: Lipids; Product: Glycerol + fatty acids.

Enzyme Practical

1. Add 2 cm³ of  starch solution and 2 cm³ of amylase solution into separate boiling tubes.                                                                            

2. Place both tubes in a water bath at 20 °C for 5 minutes.                    

3. Mix the starch and amylase solutions together.

4. Every 30 seconds, test the mixture with iodine on a spotting tile until the iodine no longer changes colour.                                                        

5. Repeat the experiment at 25 °C, 35 °C, and 45 °C.                                                               

Key Question: Why did the student leave both tubes in the water bath for 5 minutes in step 2? -  

To get both solutions to the same temperature

Food tests 

1. Grind food with pestle and mortar.

2. Add water, then stir to dissolve the food

3. Filter solution using filter paper.

Benedict's Test

• Tests for: Sugars (e.g., glucose, maltose).

• Steps:

  1. Prepare food sample in a test tube

  2. Add Benedict's solution to test tube using pipette.

  3. Heat in 25°C water bath for 5 mins.

Positive result: From Blue to Green or Yellow or Brick-red (depending on sugar concentration).

Iodine Test

Tests for: Starch in foods like rice, pasta, potatoes.

• Steps:

  1. Prepare food sample.

  2. Add iodine solution directly.

Positive result: Brown/orange → Blue-black.

Biuret Test

• Tests for: Proteins in foods like meat, cheese.

• Steps:

  1. Prepare food sample.

  2. Add Biuret solution (mix of potassium hydroxide + copper(II) sulfate).

Positive result: Blue → Purple.

Sudan III Test

• Tests for: Lipids in foods like olive oil, milk.

• Steps:

  1. Prepare food sample.

  2. Add Sudan III solution.

  3. Shake gently.

Positive result: Red layer on top.

Heart

Organ that pumps blood around the body via a double circulatory system.

Right Ventricle

Pumps deoxygenated blood to lungs for oxygen

Left Ventricle

Pumps deoxygenated blood around the body, where oxygen is used up

Oxygenated blood from lungs to body cells:              

• Blood travels through the pulmonary vein 

• Blood enters left atrium 

• Blood enters the left ventricle 

• Blood leaves the heart through the aorta then to body

 Deoxygenated blood from body cells to lungs:

•  Blood travels through the vena cava

•  Blood enters right atrium

• Blood enters the right ventricle

• Blood leaves the heart through the pulmonary artery then to lungs

Vessels travel

Vessel	Blood Type	From —> To	Mnemonic
Vena Cava	Deoxygenated	Body —> Right Atrium	"Vicious Cats Dance But Run Aggressively."
Pulmonary Artery	Deoxygenated	Right ventricle —> Lungs	"Penguins And Ducks Race Very Loudly."
Pulmonary Vein	Oxygenated	Lungs —> Left atrium	"Purple Vampires Often Love Lemon Apples."
Aorta	Oxygenated	Left Ventricle —> Body	"Always Observe Little Vulnerable Birds."

Pacemaker (Natural)

Group of cells in right atrium that controls heartbeat.

Pacemaker (Artificial)

Electrical device fitted to control irregular heartbeat.

Artery

Thick walls, narrow lumen

Artery Function

Carries high-pressure oxygenated blood around body’s organ

Vein

Thin walls, large lumen(hole), 

valves(prevents backflow of blood).

Vein Function

Return low pressure deoxygenated blood from the body to the heart

Capillary

One cell thick; allows exchange of substances with tissues.

Lungs

• Trachea → Bronchi → Bronchioles → Alveoli ➔ Air Pathway: "The Best Battles Are Amazing."

• Air enters through the trachea (big tube), splits into two bronchi (one to each lung), branches into smaller bronchioles, and finally reaches the alveoli (tiny air sacs for gas exchange).

Alveoli adaptations

Adaptation	Explanation
Large surface area	More space for oxygen and carbon dioxide to diffuse quickly.
Thin walls	Short diffusion distance, making gas exchange faster and more efficient.
Moist	Gases dissolve easily, helping diffusion across alveolar walls.
Good blood supply	Maintains a steep concentration gradient for faster diffusion of gases.

Red Blood Cells

 Transport oxygen around the body.

 Biconcave shape for large surface area; no nucleus to maximise space.

White Blood Cells

Defend body against pathogens; have a nucleus.

Platelets

Forms  blood clot at wound. - Prevent excessive bleeding and entry of pathogens.

Plasma

Carries blood cells, nutrients, CO₂, urea, hormones, heat around body

Coronary Heart Disease

• Build-up of fatty material in coronary arteries → reduced oxygen → heart attacks.

Statins

Drugs that lower LDL ('bad') cholesterol by:

• Inhibiting its production in the liver

• Reducing fatty build-up in arteries

• Lowering the risk of coronary heart disease.

Statins advantages

• Lower risk of heart attacks, strokes, and CHD.

• May prevent other diseases.

• Increase HDL cholesterol levels

Statins disadvantages

• Must be taken regularly over a long period.

• Takes time to become effective.

• Possible side effects: muscle and joint pain, kidney problems

Stents

Small tubes inserted into arteries to widen them and allow blood flow.

Stents advantages

• Quickly restore blood flow to the heart muscle.

• Effective at reducing the risk of heart attacks.

• Long-lasting solution.

• Procedure is relatively simple and minimally invasive

Stents disadvantages

• Risk of blood clots (thrombosis) forming around the stent.

• Risk of infection during the procedure.

• Potential damage to the blood vessel during insertion

Weak Immune System

Higher risk of infection and illness.

Cancer

Uncontrolled cell division forming tumours.

Benign Tumour

Non-cancerous; grows in one place and doesn’t invade other tissues.

Malignant Tumour

• Cells divide uncontrollably, invade nearby tissues, and spread  via the bloodstream to form secondary tumours.

Cancer Risk Factors

• Lifestyle: Smoking (lung cancer), obesity (bowel, kidney), alcohol.

• Environment: UV radiation (skin cancer).

• Infections: HPV (linked to cervical cancer).

Genetic: Inherited faulty genes (e.g. BRCA in breast cancer).

Epidermal Tissue (Plant)

Covers plant surfaces; protects; secretes waxy cuticle to reduce water loss.

Palisade Mesophyll

Packed with chloroplasts → main site of photosynthesis

Spongy Mesophyll

Loosely packed cells for gas exchange; air spaces increase diffusion.

Xylem

Transports water and minerals from roots to leaves (one-way).

Phloem

Transports sugars from leaves to rest of the plant (two-way, translocation).

Meristem

Found in root/shoot tips; cells divide by mitosis for growth.

Leaf Adaptation

• Flat shape: Increases surface area for light absorption.

• Thin: Short diffusion path for gases.

• Large surface area: Maximises light capture.

Root Hair Cells

• Long projections: Increase surface area.

• Thin cell walls: Short diffusion path.

• Many mitochondria: Provide energy for active transport of mineral ions.

• Absorb water by osmosis and minerals by active transport.

Xylem

• Made of dead cells forming hollow tubes.

• Strengthened with lignin for support.

• Carries water and minerals upwards from roots to leaves.

• Movement is one-way.

Transpiration

Evaporation of water from leaf surfaces, mainly through stomata.
Creates a pull (transpiration stream) that draws water up through xylem.

Factors Increasing Transpiration

High light, temperature, wind; low humidity.

work

Stomata

• Stomata: Allow CO₂ in for photosynthesis and O₂ out; water vapour also escapes.

Guard Cells

pen in light (absorb water, become turgid) and close in dark or drought (flaccid), helping to reduce water loss

Phloem

Living cells with sieve plates; transports sugars; uses energy (active transport).

Translocation

Movement of sugars from leaves to other parts of plant.