GCSE BIOLOGY • SPECIFICATION 1.2

Organisation

Aligned to AQA GCSE Biology (8461/8464). Wording consistent with AQA mark schemes.

Mastering the hierarchy of life and the human transport system.

1. Levels of Organisation

Exam Definition (Tissue):

"A tissue is a group of cells with a similar structure and function."

Level	Definition / Example
Cell	The basic building block/unit of all living organisms.
Tissue	A group of cells with similar structure and function (e.g. Muscle).
Organ	Aggregations of tissues performing specific functions (e.g. Stomach).
Organ System	Organs working together to perform a function (e.g. Digestive System).

2. The Digestive System & Enzymes

The digestive system is an organ system in which several organs work together to digest and absorb food.

[Image of the human digestive system]

Enzyme Theory: Enzymes are biological catalysts. High temperatures or extreme pH change the shape of the active site, meaning the substrate no longer fits. The enzyme is denatured.

[Image of the enzyme lock and key model]

Enzyme	Site of Production	Action (Substrate → Product)
Amylase (Carbohydrase)	Salivary glands, Pancreas	Starch → Maltose
Protease	Stomach, Pancreas	Proteins → Amino Acids
Lipase	Pancreas, Small Intestine	Lipids → Glycerol & Fatty Acids

Practical Connection

In the required practical, we use Iodine to test for the disappearance of starch. If the solution remains orange/brown, starch has been broken down into sugars.

3. Heart and Blood Vessels

Double Circulatory System:

"The right ventricle pumps blood to the lungs; the left ventricle pumps blood to the rest of the body. Blood passes through the heart twice in one complete circuit of the body."

[Image of the heart diagram]

Blood Vessel Comparison

Artery	Vein	Capillary
Thick muscular/elastic walls	Thin walls	Wall is one cell thick
Small lumen	Large lumen + Valves	Provides short diffusion distance
High pressure	Low pressure	Allows exchange of substances

Q: Why does the Left Ventricle have a thicker muscle wall than the Right Ventricle?

It must pump blood at a higher pressure to the entire body (greater distance), whereas the right ventricle only pumps to the lungs.

4. Blood Composition

Blood is a tissue consisting of plasma, in which red blood cells, white blood cells and platelets are suspended.

Red Blood Cells: Biconcave shape and no nucleus for max haemoglobin. The biconcave shape increases the surface area to volume ratio for faster oxygen diffusion.
White Blood Cells: Part of the immune system; produce antibodies or antitoxins and perform phagocytosis.
Platelets: Small fragments of cells that help blood clotting at wound sites.
Plasma: Transports CO₂, urea, soluble products of digestion, and hormones.

5. Plant Tissues and Transport

Note: Transpiration is assessed here as a function of specialised plant tissues.

[Image of a leaf cross-section]

Feature	Xylem	Phloem
Transport	Water and mineral ions	Dissolved sugars (Translocation)
Direction	One way (up)	Two ways (up and down)
Cell State	Dead cells strengthened by lignin	Living cells with sieve plates

Explain the effect of high humidity on the rate of transpiration (3 Marks).

High humidity means a high concentration of water vapour outside the leaf.
This reduces the concentration gradient between the leaf and air.
Water evaporates/diffuses out slower; rate of transpiration decreases.

Final Exam Guardrail

• Coronary arteries supply the heart muscle itself with oxygenated blood.
• Bile is alkaline to neutralise stomach acid and emulsifies fat to increase surface area for lipase.
• Statins reduce blood cholesterol (preventative); Stents keep coronary arteries open (mechanical).
• Always specify "shape of the active site" when explaining denaturation.

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