Transport

Anatomy & Physiology of Animals — Biology (Age 15, Kenyan context)

This note covers the importance of transport in animals and the main types of transport systems. Examples use animals you may meet in Kenya (e.g., mosquitoes, tilapia, frogs, lizards, crocodiles, humans) to help you understand differences and why each system suits the animal's environment and activity.

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A. Why transport is important (Learning outcome a)

• Distribution of nutrients (glucose, amino acids) from digestion to cells for energy and growth.
• Transport of respiratory gases: oxygen to cells and carbon dioxide away from cells.
• Removal of metabolic wastes (e.g., urea) to excretory organs (kidneys).
• Transport of hormones and chemical signals to coordinate body functions.
• Heat distribution to maintain body temperature (important in warm climates like Kenya).
• Immune defence: moving immune cells to sites of infection or injury.

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B. Structure of transport systems in selected animals (Learning outcome b)

1. Insects (open circulatory system)

- Main features: a dorsal tubular heart pumps haemolymph into body cavities (hemocoel). Haemolymph bathes organs directly; no separate blood vessels for exchange.

2. Fish (single circulation — two-chambered heart)

- Heart has one atrium and one ventricle. Blood goes: heart → gills (oxygenation) → body → back to heart. Common example: Nile tilapia found in Kenyan lakes.

3. Amphibians (double circulation, three-chambered heart)

- Heart has two atria and one ventricle. Blood from lungs and skin enters left atrium; body blood enters right atrium. Some mixing in ventricle but double circulation allows higher blood pressure to tissues than single circulation. Example: common Kenyan frogs.

4. Reptiles (mostly three-chambered; crocodiles have four-chambered)

- Most reptiles (lizards, snakes) have two atria and a partly divided ventricle reducing mixing. Crocodiles and birds have fully divided ventricles (4 chambers) giving complete separation of oxygenated and deoxygenated blood. Example: Nile crocodile (4-chambered heart).

5. Mammals (closed circulation, four-chambered heart)

- Complete separation of pulmonary (lungs) and systemic (body) circulation. Heart has 2 atria + 2 ventricles. Blood pressure can be high so oxygen delivery is efficient—important for active animals and warm-blooded mammals (humans, cattle, goats, etc.).

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C. Pumping mechanism of the mammalian heart (Learning outcome c)

Structure: 4 chambers (left/right atria, left/right ventricles), valves ensure one-way flow — tricuspid (right AV), mitral/bicuspid (left AV), pulmonary and aortic semilunar valves.

Conduction system (controls heartbeat):

• SA node (sinoatrial node) in right atrium: natural pacemaker — starts electrical impulse.
• Atrial muscle contracts → impulse reaches AV node (atrioventricular node).
• AV node delays slightly → impulse down bundle of His → Purkinje fibres → ventricular muscle contracts.

Cardiac cycle (one heartbeat):

1. Diastole: ventricles relax and fill with blood from atria.
2. Atrial systole: atria contract to push extra blood into ventricles.
3. Ventricular systole: ventricles contract, AV valves close (LUB), semilunar valves open, blood is pumped to lungs (right ventricle) and body (left ventricle). When semilunar valves close (DUB) cycle ends.

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D. Human lymphatic and immune systems, and blood clotting (Learning outcome d)

Lymphatic system — main points

• Network of lymph vessels, lymph nodes, spleen, tonsils and thymus.
• Collects tissue fluid (lymph) that leaks from capillaries and returns it to the blood — prevents swelling (edema).
• Absorbs fats from the small intestine (lacteals) into lymph vessels.
• Lymph nodes filter lymph and contain immune cells (lymphocytes) that respond to pathogens.

Immune system — basic components

• Innate (non-specific): skin, mucus, phagocytes (macrophages, neutrophils), inflammation, fever.
• Adaptive (specific): B-lymphocytes (produce antibodies), T-lymphocytes (help or kill infected cells). Memory cells give long-term protection.
• Spleen stores and filters blood, removes old red blood cells, and mounts immune responses.

Blood clotting — simplified mechanism

When a blood vessel is damaged:

1. Blood vessel constricts to reduce flow.
2. Platelets stick to the damaged site and form a temporary plug.
3. Clotting factors (proteins in plasma) activate a cascade → convert fibrinogen to fibrin.
4. Fibrin threads form a stable mesh trapping blood cells → clot (scab forms above vessel).

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E. ABO and Rhesus (Rh) blood group systems (Learning outcome e)

ABO system: Red blood cells (RBCs) have antigens A, B, both (AB), or neither (O). Plasma contains antibodies opposite to your antigens:

• Type A: A antigen on RBCs; anti-B antibody in plasma.
• Type B: B antigen; anti-A antibody.
• Type AB: Both antigens; no anti-A/B antibodies — universal plasma recipient.
• Type O: No A/B antigens; both anti-A and anti-B antibodies — universal red cell donor (but not universal plasma donor).

Rhesus (Rh) factor: Either Rh-positive (has D antigen) or Rh-negative (no D).

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F. Appreciating diversity of transport systems (Learning outcome f)

Transport systems vary because of:

• Size — small animals (insects) can use open systems because diffusion distances are short for exchange with cells.
• Metabolic rate and activity — active or warm‑blooded animals (mammals, birds) need efficient closed systems with high-pressure circulation.
• Environment — aquatic animals often use gills and single circulatory loops; terrestrial animals use lungs and double circulation.
• Evolutionary history — structures evolved to suit an animal’s niche (e.g., crocodile’s efficient heart for diving and high activity).

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Suggested learning experiences (classroom & field activities — age 15, Kenyan schools)

1. Practical: Measure pulse and breathing rate before and after light exercise (walking, jogging or climbing stairs). Record results and discuss why rates change.
2. Model building: Use balloons and straws to make a simple model of the heart (two balloons for ventricles, one for atrium) to demonstrate valves and flow direction. (Non-harmful craft activity.)
3. Microscope work: Observe prepared blood smears to identify red blood cells, white blood cells and platelets. Compare stained slides and draw observations.
4. Class activity: Role-play circulation — students act as blood cells moving between 'heart', 'lungs', and 'body' to show single vs double circulation.
5. Investigation: Compare respiratory surfaces — examine gill structure in illustrations or preserved specimens (where ethical and legally allowed) and compare with lung tissues. Discuss how gills suit fish in Kenyan lakes.
6. Field study: Visit a local river, pond or school farm to observe animals (tilapia, frogs, small mammals) and discuss how their transport systems help them survive in that habitat.
7. Group research & presentation: Each group studies one animal (insect, fish, amphibian, reptile, mammal) and presents its transport system, with diagrams and reasons for its design.
8. Demonstration: Show blood clotting with safe classroom models (e.g., gelatin and threads to mimic fibrin) — focus on concept rather than working with real blood.
9. Health link: Discuss blood groups and transfusion safety using case studies (e.g., emergency transfusion, Rh sensitisation in pregnancy). Emphasise importance of blood typing in clinics and blood donation awareness.

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Assessment ideas

• Draw and label diagrams of at least two transport systems (e.g., insect vs mammal) and explain advantages of each.
• Describe the cardiac cycle and how electrical signals control heartbeats.
• Short report on the pulse/breathing practical with data table and conclusion.
• Multiple choice / short answer questions on ABO/Rh compatibility and a short scenario on pregnancy risk.

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Useful reminder: Always follow school safety rules during practicals. For dissections or use of preserved specimens, obtain permission and use protective equipment. When discussing medical topics (transfusions, pregnancy risks) encourage students to seek reliable advice from healthcare professionals.

Prepared for Kenyan secondary school learners (Form 3 / Age 15). Teacher may adapt depth and activities to class level and available resources.