Transport

**Away** from the heart (remember: **A**rtery = **A**way).

**Towards** the heart (it returns blood to the heart).

**Thick, muscular and elastic**, with a **narrow lumen** — built to withstand **high pressure**.

**Thin**, with a **wide lumen** and **valves** — it carries blood at **low pressure**.

**One cell thick** — this gives a short diffusion distance for **exchange**.

To **withstand high pressure**: it **stretches** during each surge and **recoils** to push the blood onward.

Blood in veins is at **low pressure**, so it could flow backwards — **valves close to stop backflow**.

Their blood is at **high pressure**, which keeps it flowing forwards, so valves are not needed.

**Wall one cell thick** (short diffusion distance) and a **large surface area** close to every cell.

The **hollow space inside** the vessel through which the blood flows.

The **vein** — thin wall and wide lumen; the artery has a thick wall and narrow lumen.

It has the **thicker wall** and the **narrower lumen** of the two vessels.

Its **elastic wall stretches** during the surge and **recoils** between beats, **smoothing** the pressure.

In the **capillaries** — the only vessels with a wall one cell thick.

Two **atria** (upper, thin-walled, receive blood) and two **ventricles** (lower, thick-walled, pump blood out).

An **atrium** receives blood from the veins and passes it down into a **ventricle**. Atria have thin walls.

A **ventricle** pumps blood out into an artery. Ventricles have thick, muscular walls.

The **left ventricle** — it pumps blood to the **whole body** at high pressure, so it needs the most muscle.

The **right side** — it receives deoxygenated blood from the body and pumps it to the **lungs**.

The **left side** — it receives oxygenated blood from the lungs and pumps it to the **body**.

One complete heartbeat: the repeating sequence of **contraction (systole)** and **relaxation (diastole)** of the heart chambers.

**Atrial systole** (atria contract), **ventricular systole** (ventricles contract) and **diastole** (chambers relax and refill).

Valves shutting: **'lub'** = the AV valves closing, **'dub'** = the semilunar valves closing.

When the pressure **behind** it becomes **higher** than the pressure **in front** of it.

Blood passes through the heart **twice** per body circuit — once for the **lungs** (pulmonary circuit) and once for the **body** (systemic circuit).

The heart **re-pressurises** blood after the lungs, so the body receives **high-pressure** blood, and oxygenated and deoxygenated blood stay **separate**.

Vena cava → **right atrium** → **right ventricle** → **pulmonary artery** → lungs.

Pulmonary vein → **left atrium** → **left ventricle** → **aorta** → body.

The **pulmonary artery** (deoxygenated) and the **pulmonary vein** (oxygenated).

The **force** that flowing blood exerts on the **walls of the arteries**, written as two numbers (e.g. 120/80).

The **higher** number — the pressure when the **ventricles contract** and push blood into the arteries.

The **lower** number — the pressure when the **ventricles relax** between beats and the heart refills.

They carry cholesterol **from the liver to the tissues**; excess is **deposited in artery walls** — the 'bad' carrier.

They carry **excess cholesterol away** from tissues and arteries **back to the liver** for disposal — the 'good' carrier.

**High HDL** (removes cholesterol) and **low LDL** (which deposits cholesterol in arteries).

The build-up of cholesterol **plaque** in artery walls, which **hardens** and **narrows** the artery.

Cholesterol is **deposited in artery walls** → **plaque (atherosclerosis)** → **coronary arteries narrow** → **heart muscle gets less oxygen**.

A **diet high in saturated fat**, **smoking**, **lack of exercise**, **obesity**, or an **inherited (genetic)** tendency.

It raises **blood pressure** (hypertension), which strains the heart and damages arteries.

**Heart rate** (and stroke volume / cardiac output) **rises** to deliver more oxygen to working muscles.

The **heart muscle gets stronger**, so stroke volume rises and the **resting heart rate falls**.

The arteries that supply the **heart muscle itself** with oxygenated blood.

Part of the heart muscle is starved of oxygen and dies — a **heart attack**.

The **loss of water vapour** from the leaves of a plant, mostly through the **stomata**.

Plant tissue made of long, **hollow, dead tubes** that carry **water** (and minerals) **upwards** from roots to leaves.

**Upwards only** — roots → stem → leaves. It never carries water back down.

The continuous, one-way flow of water from the **roots, up the xylem, to the leaves**, driven by transpiration.

Water molecules **stick to one another**, forming one **continuous, unbroken column**.

The **pull** on the water column created when water **evaporates** at the leaf; it is transmitted down the xylem.

Evaporation at the leaf creates **tension**; **cohesion** keeps the column unbroken, so water is **pulled up** the xylem from the roots.

They are **hollow dead tubes with no end walls** (one continuous pipe), and have **lignified walls** that stop them collapsing.

Lignin makes the wall **strong**, so the vessel does **not collapse** under the tension (pull) of the water column.

In the **xylem** — the water-carrying tubes (the central stele), where the strengthened walls show up.

**Hot, dry, windy and bright** conditions — like drying washing on a line.

It **slows it down** — moist surrounding air means a smaller difference, so less water diffuses out.

Light **opens the stomata**, so more water vapour escapes and the rate **increases**.

At the **root hair cells**, which have a large surface area for absorbing water from the soil.

The plant transport tissue that carries **dissolved sugar (sucrose)** around the plant; its conducting cells are living **sieve tubes**.

The movement of **dissolved sugar** through the phloem from a **source** to a **sink**.

Any part that **makes or releases** sugar — usually a photosynthesising **leaf** (but also a store being broken down).

Any part that **uses or stores** sugar — for example a **growing root**, a **fruit**, or a store being built up.

**Either up or down** the plant — it always runs from a source to a sink, wherever those are.

By **active transport** (against its gradient), which uses **ATP**.

The **companion cell** — it is packed with **mitochondria** and keeps the sieve tube alive.

Water **follows by osmosis**, raising the **pressure**, which pushes the sap by **bulk flow** to the sink.

The **mass movement** of the sugary sap along the sieve tubes, driven by the **pressure difference** between source and sink.

**Sieve plates with pores** (sap flows between cells) and **little cytoplasm / no nucleus** at maturity (a clear channel); a **companion cell** sits alongside.

Its sieve tubes are kept alive by **companion cells**, and translocation **needs energy** — it stops if the cells are killed. (Xylem is dead.)

Phloem carries **sugar**, is **living**, and is **two-way**; xylem carries **water**, is **dead**, and is **one-way** (roots to leaves).