Science 14

Every substance has properties you can observe — state (solid/liquid/gas), colour, smell, whether it burns, whether it is acidic (like vinegar) or basic (like bleach) — and those properties are how you tell substances apart and group them.

A solution forms when a solute dissolves in a solvent — sugar (solute) in water (solvent) makes a sweet drink; the solute is still there, just spread out too small to see.

An element is a pure substance made of one kind of atom (copper, oxygen, gold); a compound is two or more elements chemically joined into something new — table salt is sodium + chlorine, water is $\text{H}_2\text{O}$.

Sorting by properties is a real skill: knowing bleach is a corrosive base and rubbing alcohol is flammable lets you predict how each will behave before you ever use it.

Solubility is how much solute a solvent can hold, and it usually goes up with temperature — which is why sugar dissolves faster in hot tea than in iced tea.

Thermal energy (heat) always flows from the hotter object to the colder one until they even out — a hot coffee cools to room temperature because heat leaves it, not because "cold gets in".

Simple machines — levers, pulleys, ramps (inclined planes), wheels-and-axles, gears — transfer energy from your effort to the load; they make work feel easier by changing the size or direction of the force.

Heating and cooling technology just directs that flow: a furnace adds heat to a cold room, while a fridge or air conditioner pumps heat OUT of a cold space to the warmer outside — that's why the back of a fridge is warm.

Comparing machines shows the same idea in different shapes: a lever pivots, a pulley redirects, a ramp spreads the lift over distance — all moving your effort energy to where the job is.

Insulation works by slowing heat flow — a thermos, a winter coat, attic insulation and a foam cup all trap air or block conduction so heat moves in or out more slowly.

The digestive system breaks food into small nutrients and absorbs them into the blood; the circulatory system (heart, blood, vessels) then delivers those nutrients and oxygen to every cell and carries waste away.

Cells have parts that each do a job: the nucleus (control centre with DNA), the cell membrane (controls what goes in and out), and the cytoplasm inside.

The handoff happens at the small intestine, where absorbed nutrients cross into the bloodstream — that is the exact point where matter moves from one system to the other.

Plant cells add two parts animal cells lack: a stiff cell wall for support and green chloroplasts for making food — otherwise they share most of the same parts.

The two systems depend on each other: digestion is useless without a delivery network, and circulation has nothing to deliver without digestion — together they fuel every cell.

Matter (water, carbon, nitrogen) is not used up — it moves through the biosphere along set cyclical pathways: water evaporates, forms clouds, rains, and returns; carbon moves between air, plants, animals and back.

An ecosystem has biotic (living) parts — plants, animals, insects, microbes — and abiotic (non-living) parts — water, sunlight, soil, temperature, air.

Because the pathways are cyclical, the same atoms get reused again and again — the carbon in your breath may have been in a dinosaur or a tree before.

The living things depend on the non-living conditions to survive: no water or sunlight, no plants; no plants, no animals — so abiotic factors shape which life can live there.

Human activity can overload or break a cycle — burning fuels adds extra carbon to the air, fertilizer runoff floods water with nutrients, and pollution blocks the normal pathway.