Organisation

Cell: The basic building block of all living organisms. Examples: red blood cell, nerve cell, sperm cell.
Tissue: A group of similar cells working together to perform a specific function. Examples: muscular tissue, glandular tissue, epithelial tissue.
Organ: A group of different tissues working together to perform a specific function. Examples: stomach (contains muscular, glandular, and epithelial tissue), heart, lung, leaf.
Organ System: A group of organs working together to perform a major function. Examples: digestive system, circulatory system, respiratory system.
Organism: A complete living thing, made up of many organ systems working together.

Epithelial tissue: Covers some parts of the body and lines internal organs.
Muscular tissue: Contracts to produce movement.
- Higher Tier: Types include skeletal (voluntary movement), smooth (involuntary movement in internal organs), and cardiac (involuntary movement of the heart).
Glandular tissue: Produces and secretes chemical substances such as enzymes and hormones.
Nervous tissue: Carries electrical impulses.
Connective tissue: Supports and binds other tissues. Examples include blood, bone, and cartilage.

Examples of Animal Organs: Stomach, small intestine, heart, lungs, brain, kidney.
Examples of Animal Organ Systems:
- Digestive system: Breaks down and absorbs food.
- Circulatory system: Transports substances around the body.
- Respiratory system: Facilitates gas exchange.
- Nervous system: Controls and coordinates body activities.
- Skeletal system: Provides support, protection, and enables movement.

Epidermal tissue: Covers the surfaces of the plant, protecting it. Some epidermal cells have adaptations like root hairs (for increased absorption) or guard cells (controlling stomata).
Palisade mesophyll tissue: Located beneath the upper epidermis in leaves, contains many chloroplasts and is the main site of photosynthesis.
Spongy mesophyll tissue: Located below the palisade layer, contains large air spaces to facilitate the diffusion of gases for photosynthesis and respiration.
Xylem tissue: Transports water and dissolved mineral ions from the roots to the rest of the plant. Composed of dead cells with lignified walls for strength and support.
Phloem tissue: Transports dissolved sugars (sucrose) produced during photosynthesis from the leaves to other parts of the plant, including growing regions and storage organs. Composed of living sieve tubes and companion cells.
Meristematic tissue: Found at the growing tips of roots and shoots. Contains actively dividing cells (undifferentiated) that lead to plant growth.

Examples of Plant Organs: Leaf (for photosynthesis), stem (for support and transport), root (for anchorage and absorption of water and minerals).
Plant Organ System: Plants generally have a root system and a shoot system.

Mouth: Ingestion of food; mechanical digestion (chewing) and chemical digestion (salivary amylase breaks down starch).
Oesophagus: A muscular tube that transports food from the mouth to the stomach via peristalsis (wave-like muscular contractions).
Stomach: Muscular sac that churns food with digestive juices.
- Produces hydrochloric acid (kills bacteria, provides optimum acidic pH for protease enzymes).
- Produces protease enzymes (e.g., pepsin) to begin protein digestion.
Small Intestine: The primary site of chemical digestion and absorption of nutrients.
- Duodenum: Receives bile from the liver/gallbladder and pancreatic juice (containing amylase, protease, lipase) from the pancreas.
- Ileum: Main area for absorption of digested food.
  - Adaptations for absorption: Long length, folded inner surface, presence of villi and microvilli (collectively increasing surface area), thin walls (one-cell thick), good blood supply via a capillary network.
  - Digested nutrients (glucose, amino acids, fatty acids, glycerol) pass into the bloodstream or lymphatic system.
Large Intestine: Primarily absorbs water from undigested food material, forming faeces.
- Colon: Main site of water absorption.
- Rectum: Stores faeces before egestion.
Anus: Muscular opening through which faeces are egested from the body.

Salivary glands: Produce saliva containing amylase.
Pancreas: Produces digestive enzymes (amylase, protease, lipase) and alkaline fluid to neutralise stomach acid.
Liver: Produces bile.
Gallbladder: Stores and concentrates bile.
Bile:
- Higher Tier: Emulsifies fats (breaks large fat globules into smaller droplets), increasing the surface area for lipase action.
- Higher Tier: Is alkaline, neutralising the acidic chyme from the stomach to provide an optimum pH for enzymes in the small intestine.

Biological Catalysts: Substances (proteins) that speed up the rate of chemical reactions in living organisms without being used up in the reaction itself.
Specific Shape: Each enzyme has a specific three-dimensional shape, crucial for its function.
Active Site: A specific region on the enzyme where the substrate binds.
Substrate: The molecule(s) upon which the enzyme acts.
Lock and Key Model: Explains enzyme specificity; only a substrate with a complementary shape can fit into the enzyme's active site, like a key fitting into a lock.
Products: The molecules formed after the enzyme-catalysed reaction.

Temperature:
- As temperature increases, so does the kinetic energy of enzyme and substrate molecules, leading to more frequent collisions and a faster reaction rate.
- Optimum Temperature: The temperature at which an enzyme is most active (e.g., around 37^ ext{o}C for most human enzymes).
- Denaturation (Higher Tier): At temperatures significantly above the optimum, the enzyme's specific three-dimensional shape, including the active site, is permanently altered. This means the substrate can no longer bind effectively, and the enzyme loses its function.
pH:
- Each enzyme has an optimum pH at which it functions most efficiently (e.g., amylase in saliva works best at neutral pH, pepsin in the stomach works best at acidic pH).
- Higher Tier: Extreme pH values (too acidic or too alkaline) can cause the enzyme to denature, changing the shape of the active site and reducing