Transport in Plants and Animals

🟢 Lite — Quick Review (1h–1d)

Rapid summary for last-minute revision before your NECO exam.

Why Transport is Needed: Single-celled organisms rely on diffusion. Multicellular organisms need a transport system because:

• Volume increases faster than surface area as organisms grow
• Diffusion over large distances is too slow to meet metabolic demands

Animal Transport — The Blood System:

The double circulatory system in mammals:

• Pulmonary circulation: Right ventricle → pulmonary artery → lungs → pulmonary vein → left atrium
• Systemic circulation: Left ventricle → aorta → body → vena cava → right atrium

Heart Structure:

• Right side: Receives deoxygenated blood, pumps to lungs
• Left side: Receives oxygenated blood, pumps to body
• Valves (tricuspid, bicuspid/mitral, pulmonary, aortic) prevent backflow
• Systole: Contraction phase (blood ejected)
• Diastole: Relaxation phase (chambers fill)

Blood Vessels:

• Arteries: Carry blood away from heart, thick muscular walls, high pressure, no valves (except semilunar at heart)
• Veins: Return blood to heart, thin walls, low pressure, have valves, skeletal muscle pumps
• Capillaries: One cell thick, site of exchange between blood and tissues

Plant Transport:

• Xylem: Transports water and mineral salts from roots to aerial parts. Made of dead cells (vessels, tracheids). No energy required (passive).
• Phloem: Transports organic food (sugars) from leaves to other parts. Made of living cells (sieve tubes, companion cells). Energy required.

⚡ NECO Tip: In the transpiration stream, water is pulled up by: (1) root pressure, (2) cohesion-tension theory (water molecules stick together — cohesion — and are pulled up by evaporation from leaves — tension), (3) adhesion of water to xylem walls.

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🟡 Standard — Regular Study (2d–2mo)

Standard content for NECO Biology students with a few days to months.

Blood Composition:

Component	Function
Red blood cells (erythrocytes)	Carry oxygen (haemoglobin)
White blood cells (leucocytes)	Defend against pathogens
Platelets (thrombocytes)	Blood clotting
Plasma	Transport medium: nutrients, wastes, hormones, antibodies

Blood Groups and Transfusion:

Blood Group	Antigens on RBCs	Antibodies in Plasma	Can Donate To	Can Receive From
A	A antigen	Anti-B	A, AB	A, O
B	B antigen	Anti-A	B, AB	B, O
AB	A and B antigens	Neither	AB only	All groups
O	Neither	Anti-A and Anti-B	All groups	O only

Rhesus factor (Rh): Rh+ can receive from Rh+ or Rh−; Rh− can only receive from Rh−. Rh− mother carrying Rh+ baby may produce antibodies against the baby’s blood (haemolytic disease of the newborn).

Transpiration:

Water absorbed by roots → transported through xylem → evaporates from leaves (transpiration) → creates suction force pulling more water up.

Factors affecting transpiration rate:

• Temperature: Higher temp → faster transpiration
• Humidity: Lower humidity → faster transpiration
• Wind: More wind → faster transpiration
• Light: Light stimulates stomatal opening → faster transpiration

Uptake of Water and Mineral Ions by Roots:

• Apoplast pathway: Water moves through cell walls and intercellular spaces (without crossing membranes) — does not require energy
• Symplast pathway: Water moves through the cytoplasm of cells via plasmodesmata — does not require energy
• Endodermis: The Casparian strip (waxy band) forces water through cell membranes, allowing selective uptake of mineral ions via active transport

⚡ NECO Common Mistakes:

• Confusing xylem and phloem function and location
• Thinking transpiration is wasteful — it is essential for cooling, mineral transport, and water movement
• Mixing up systole and diastole phases of the cardiac cycle
• Forgetting that arteries carry oxygenated blood away from the heart except for the pulmonary artery (which carries deoxygenated blood to the lungs)

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🔴 Extended — Deep Study (3mo+)

Comprehensive coverage for NECO and JAMB Biology preparation.

The Cardiac Cycle:

1. Atrial systole: Both atria contract, blood flows into ventricles. AV valves open. Duration: ~0.1 s.
2. Ventricular systole: Both ventricles contract, pressure rises, AV valves close, SL valves open, blood ejected into arteries. Duration: ~0.3 s.
3. Diastole: Both atria and ventricles relax. Blood flows from veins into atria and then into ventricles. Duration: ~0.4 s.

Heart Sounds:

• First sound (lub): AV valves closing
• Second sound (dub): Semilunar valves closing

Blood Pressure:

Systolic pressure (peak during ventricular systole): ~120 mmHg in a healthy adult Diastolic pressure (during diastole): ~80 mmHg Normal: 120/80 mmHg

Hypertension: sustained high blood pressure, increases risk of heart disease, stroke, kidney damage.

The Oxygen Dissociation Curve:

A sigmoid (S-shaped) curve showing how haemoglobin’s affinity for oxygen changes with partial pressure of oxygen ($pO_2$).

At high $pO_2$ (lungs): Haemoglobin loads oxygen (98% saturated). At low $pO_2$ (tissues): Haemoglobin unloads oxygen (70% saturated — leaves 30% for tissues).

Bohr effect: Increased $CO_2$ / decreased pH shifts the curve to the right → haemoglobin releases oxygen more readily (beneficial in metabolically active tissues).

Foetal haemoglobin (HbF): Higher affinity for oxygen than adult haemoglobin — important for getting oxygen from maternal blood in the placenta.

Phloem Transport — Pressure Flow Hypothesis:

Sugars are loaded into sieve tubes (by active transport) → water follows by osmosis → increased pressure at source → pressure pushes sap towards sink (areas of lower pressure) → sugars unloaded at sinks.

Xylem and Phloem Comparison:

Feature	Xylem	Phloem
Function	Water + mineral transport	Organic food transport
Material moved	Inorganic	Organic
Direction of flow	Root → shoot (upward)	Both directions
Living/dead	Dead cells	Living cells
Cells	Vessels, tracheids	Sieve tubes, companion cells
Energy needed?	No	Yes

NECO/JAMB Patterns:

• NECO frequently asks: draw and label the vertical section of a dicotyledonous root, stem, and leaf showing xylem and phloem; explain translocation; describe the double circulatory system; compare xylem and phloem; state adaptations of red blood cells and root hair cells
• Be able to describe an experiment to demonstrate transpiration

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