B- Form and Function

1- Molecules: Carbohydrates and Lipids, and Proteins

• Carbon atoms can form four single bonds or a mix of single and double bonds with other non-metal elements.

• Scientific terms like 'kilo', 'centi', 'milli', 'micro', and 'nano' follow international standards.

• Large molecules (macromolecules) are made by joining small units (monomers) in condensation reactions. They can be broken down into monomers by hydrolysis, which uses water.

• Glucose is a stable, water-soluble sugar that can be used for energy in cells.

• Polysaccharides like starch and glycogen store energy. They are compact and don’t dissolve in water.

• Cellulose is a tough plant fiber made of straight chains linked by hydrogen bonds.

• Glycoproteins help cells recognize each other, like in blood types.

• Lipids (fats, oils, waxes, and steroids) dissolve in non-polar liquids.

• Triglycerides in fat tissue store energy and keep the body warm.

• Phospholipids form membranes with water-loving and water-fearing parts. This allows certain hormones like testosterone and oestradiol to pass through.

• Each of the 20 amino acids has a central carbon (alpha carbon) attached to an amine group, a carboxyl group, a hydrogen atom, and a unique R-group.

• The R-group gives each amino acid its special properties.

• Amino acids link together in condensation reactions to form proteins, creating peptide bonds.

• Essential amino acids must come from food because the body can't make them.

• Non-essential amino acids can be made by the body.

• The genetic code uses 20 amino acids and gives instructions to build proteins. This code is the same in all living things.

• High temperatures or extreme pH can break bonds in a protein, causing it to unfold or denature and lose its shape.

2- Cells: Membranes and transport, Organelles and compartmentalization, and Cell Speciation

• Cell membranes are made of lipids, proteins, and a little cholesterol.

• Proteins in the membrane are either integral (inside the membrane) or peripheral (on the surface).

• Phospholipids have water-loving and water-fearing parts, so they form a bilayer in water. The inside part blocks many substances.

• Molecules move across the membrane by:

  • Simple diffusion (no energy, small non-polar molecules),

  • Facilitated diffusion (no energy, uses channel proteins like aquaporins for water),

  • Active transport (needs energy/ATP to move substances).

• The membrane only lets certain substances through – it's selectively permeable.

• Glycoproteins and glycolipids help cells stick together and recognize each other.

• The fluid mosaic model shows the membrane as a flexible layer with moving proteins.

• Organelles are specialised structures in cells with specific functions.

• Compartmentalisation allows for the development of specialised cell structures.

• Ribosomes are organelles, but the cytoskeleton, cell wall and cytoplasm are not c

  onsidered organelles.

• After fertilisation, the first cells are unspecialised.

• Morphogen gradients in the early embryo control which genes are turned on or off, guiding development.

• There are different types of stem cells, each with the ability to become specific kinds of cells.

• A stem cell niche is the special environment that gives stem cells signals about what to do.

• Human cells come in many sizes and do many different jobs.

• A cell's size and surface area affect how fast materials can move in and out of it.

3- Organisms: Gas Exchange, and Transport

• As organisms get bigger, their surface area-to-volume ratio gets smaller, so they need special gas-exchange surfaces (like lungs, gills, or leaves) to get enough oxygen.

• Good gas-exchange surfaces have:

  • Large surface area

  • Thin walls (short diffusion distance)

  • Moist surfaces

  • Steep concentration gradients, helped by blood flow and breathing (in animals).

• In mammals, lungs are used for gas exchange. They have tiny sacs called alveoli where oxygen and carbon dioxide are exchanged.

• Ventilation (breathing) moves air in and out using the diaphragm and intercostal muscles. Abdominal muscles help in forced breathing out.

• A spirometer measures lung volumes and can check lung health.

• In plants, leaves are the gas exchange organs. They have small pores (mostly underneath) for gas exchange.

• Transpiration is the loss of water from leaves. It’s affected by temperature, wind, humidity, and light.

• Stomatal density is how many stomata are in a given area. It’s calculated by dividing the number of stomata seen by the area viewed.

• The body has three types of blood vessels:

  • Arteries carry blood away from the heart under high pressure. They have thick, strong walls.

  • Capillaries are tiny vessels where substances are exchanged between blood and tissues. They have thin, leaky walls and a large surface area.

  • Veins carry blood back to the heart. They have thin walls, large openings (lumens), and valves to stop blood from flowing backward.

• Pulse rate (or heart rate) is how many times the heart beats in a minute—normally 60–100 bpm—and can be measured by hand or with a device.

• Coronary arteries bring blood to the heart muscle. If they get blocked by fatty plaque, it can cause coronary heart disease by reducing blood flow.

• In plants, xylem carries water. It's a hollow tube strengthened with lignin.

• Water is pulled up through the xylem by transpiration from the leaves, using capillary action.

4- Ecosystems: Adaptation to environment, and ecological niches

• A habitat is the place where an organism, population, or community lives.

• Organisms adapt to their non-living (abiotic) environment through genetic, physiological, or behavioural changes.

• Plant adaptations in sand dunes: deep roots, water storage, and ways to reduce water loss.

• Animal adaptations in mangroves: removing salt, breathing air, and crabs feeding on dead leaves.

• Abiotic factors like temperature, rainfall, soil, and light affect where species live.

• A species' tolerance range for a limiting factor sets its survival boundaries.

• Coral reefs need warm (20–30 °C), clear, alkaline, nutrient-rich water with lots of light.

• Temperature and rainfall control where different biomes (like deserts and rainforests) are found.

• A biome is a group of ecosystems with similar environments and living things.

• Plants and animals are highly adapted to survive in both hot deserts and tropical rainforests.

• A species' ecological niche is its role in the ecosystem, shaped by living (biotic) and non-living (abiotic) factors. These affect how it survives, grows, reproduces, and gets food.

• Organisms have different oxygen needs:

  • Obligate anaerobes – survive without oxygen

  • Facultative anaerobes – can live with or without oxygen

  • Obligate aerobes – need oxygen to live

• Photosynthetic organisms (like plants, algae, and some bacteria) make their own food using sunlight.

• Animals are heterotrophs, meaning they eat other organisms. They use holozoic nutrition: food is eaten, digested, absorbed, and used.

• Mixotrophs (like plankton and Euglena) can get energy from both sunlight and eating. Some must do both, others can choose.

• Decomposers like fungi and bacteria use saprotrophic nutrition – they release enzymes to break down food outside their bodies, then absorb it.

• Life is divided into three domains:

  • Eukarya (organisms with complex cells)

  • Bacteria

  • Archaea (very diverse, can get energy from light, inorganic chemicals, or carbon)

• Humans are holozoic and need teeth to chew. Fossils show how tooth shape relates to diet (e.g., plant-eaters vs. meat-eaters).

• All organisms have adaptations to survive:

  • Herbivores are built to eat plants.

  • Predators and prey use tricks like camouflage, speed, or poison.

  • Plants have features to capture as much light as possible.

• Every organism has a niche—its role in the environment:

  • Fundamental niche – what it could do based on its traits

  • Realised niche – what it actually does due to competition

  • If two species compete for the same niche, one may be pushed out or both will have smaller niches (competitive exclusion).